Stereotactic body radiation therapy: the report of AAPM Task Group 101

Consensus recommendations regarding local and metastasis-directed therapies in the management of relapsed/recurrent Ewing sarcoma

Limited randomized or prospective data are available to guide local/metastasis directed therapy (LMDT) in relapsed/recurrent Ewing sarcoma (RR-ES), resulting in uncertainty regarding best clinical practice for these patients. This report reviews the available literature on LMDT approaches and provides consensus recommendations regarding therapeutic decision making, timing, and indications for the use of LMDT in the management of RR-ES. LMDT should be considered on a case-by-case basis to assess appropriateness, optimal timing/modality, palliative versus curative intent, and its role in relation to chemotherapy. One commonly used LMDT is radiotherapy (RT), which can be delivered through standard, hypofractionated, or stereotactic techniques based on factors including prior RT, tumor size, and/or location. Chemotherapy can be combined with RT, although prospective data are limited in the relapse setting. Surgery for LMDT not only addresses the tumor but also provides tissue for analysis, though the potential surgical morbidity based on location, extent of resection, and recovery complications should be considered. Interventional radiology approaches also can procure tumor tissue while delivering LMDT; there are several different procedures available based on the location, size, and extent of disease. Finally, a combination of LMDT approaches can be used for patients with RR-ES. Decisions regarding the management of RR-ES should involve a multidisciplinary team and factor in the burden of disease, progression-free interval, life expectancy, toxicity profiles of LMDT, and quality of life. In such patients, informed and shared decision making with patients and their families is paramount.

Dosimetric comparison of utilizing saline or air-filled endorectal balloons in MR linac-based prostate SBRT

In prostate cancer Stereotactic Body Radiation Therapy (SBRT), endorectal balloons are commonly used to reduce rectal exposure to excessive radiation. This study investigates the magnetic field-induced dose effects associated with air-filled endorectal balloons in MR-linac treatments and compares the dosimetric metrics and radiobiological outcomes between air-filled and saline-filled balloons. A retrospective analysis was conducted on 20 prostate cancer patients treated with a 1.5-Tesla MR-linac using a saline-filled rectal balloon. Each patient received a total prescription dose of 36.25 Gy to the Planning Target Volume (PTV) over 5 fractions. The simulation scans and treatments were performed with an 80 mL saline-filled balloon in place. To simulate the use of air-filled balloons, Intensity-Modulated Radiation Therapy (IMRT) plans were generated, adjusting the balloon density to represent air, followed by re-optimization to preserve the target dose. Dosimetric and radiobiological metrics for targets and organs at risk (OARs) were compared between the 2 scenarios. Rectal wall toxicity was assessed using the Lyman-Kutcher-Burman (LKB) normal tissue complication probability (NTCP) model. The introduction of air-filled endorectal balloons during MR-linac treatments intensifies material heterogeneity, leading to dose perturbations within the treatment field. Specifically, the V40 Gy hot spot on the rectal wall increased from 0.55% to 1.51% due to the electron return effect (ERE). A more pronounced impact was observed in patients receiving prostate-only irradiation compared to those with pelvic lymph node involvement, likely due to the reduced number of beam angles. Additionally, undesired dose deposition on the rectal wall outside the treatment field was noted, attributed to increased scatter and the electron streaming effect (ESE), where secondary electrons deflected by the transverse magnetic field deposited energy on the surfaces they encountered. The mean maximal out-of-field rectal wall dose was 4 Gy, ranging from 2 to 7.4 Gy. Consequently, the cohort's rectal wall NTCP increased with the use of air-filled balloons. This study highlights that the use of air-filled endorectal balloons can introduce hot spots to the rectal wall and cause unwanted ESE-related dose depositions outside the treatment field. In contrast, saline-filled balloons provide superior dosimetric performance and better protect the rectum from radiobiological damage in prostate SBRT delivered with MR-linac. These findings suggest that saline-filled balloons may be preferable for this type of therapy to minimize potential adverse effects on the rectum.

Oncological Outcomes in Patients with Prostate-specific Membrane Antigen Positron Emission Tomography/Computed Tomography-detected Oligometastatic Prostate Cancer Treated with Metastasis-directed Radiotherapy as the Single Treatment Modality

BACKGROUND AND OBJECTIVE

In patients with biochemical recurrence (BCR), prostate-specific membrane antigen (PSMA) positron emission tomography/computed tomography (PET/CT) can detect oligometastatic prostate cancer (PCa). However, the optimal treatment approach for oligometastatic disease remains unclear. This study aims to assess the oncological outcomes of metachronous oligometastatic PCa patients treated with metastasis-directed radiotherapy (MDRT).

METHODS

We retrospectively evaluated patients with hormone-sensitive, metachronous oligometastatic PCa who underwent MDRT for BCR (from July 2012 to September 2022). Patients had one to four lymph nodes and/or bone metastases on PSMA PET/CT and were irradiated with 5 × 7 or 3 × 10 Gy. The biochemical response to MDRT was assessed as undetectable prostate-specific antigen (PSA) at follow-up, PSA response (PSA ≤ pretreatment level), or biochemical progression (PSA > pretreatment level). Biochemical progression-free survival (bPFS) and local remission of disease (absence of disease at the MDRT site on follow-up PSMA PET/CT or undetectable PSA) were evaluated.

KEY FINDINGS AND LIMITATIONS

Eighty patients underwent MDRT for 105 PSMA PET/CT-confirmed lesions. The median time from curative treatment to MDRT was 55 mo (interquartile range [IQR] 31-103). At a median follow-up of 32 mo after MDRT (IQR 21-64), 10% of the patients were PSA free, 10% had a PSA response, and 80% experienced biochemical progression. The bPFS rates at 1 and 2 yr were 54% and 38%, respectively. A total of 87% of patients had local control of disease after MDRT, whereas 72% had new metastatic lesions on repeated PSMA PET/CT. Limitations include the retrospective design and a small cohort.

CONCLUSIONS AND CLINICAL IMPLICATIONS

MDRT for oligometastatic disease shows high local efficacy. However, disease progression is observed in a substantial proportion of patients.

Enhancing outcomes in metastatic renal cell carcinoma: Integrating precision radiotherapy with targeted therapy and anti-PD-1 immunotherapy

PURPOSE

This study assesses the safety and disease control outcomes in metastatic renal cell carcinoma (mRCC) patients undergoing concurrent tyrosine kinase inhibitors (TKI), immune checkpoint inhibitors (ICIs), and high-dose stereotactic ablative body radiotherapy (SABR) .

PATIENTS AND METHODS

Between February 2020 to May 2023, 54 mRCC patients receiving vascular endothelial growth factor (VEGF) targeted therapy and ICIs with high-dose radiotherapy (RT) were included. Genetic testing was performed on 25 pathology samples using the Acornmed 70™ panel. Endpoints included progression-free survival (PFS) 1, PFS2 (time to progression to change systemic therapy), LRFS, OS, disease control rate (DCR) and safety. Kaplan‒Meier analysis was used for time-to-event endpoints. HRs and 95% CIs were calculated. R version 4.3.1 was used for statistical analysis RESULTS: In this study involving 54 patients, SABR was employed in 81% of cases, achieving a 98% DCR. Median PFS1 was 16.9 months, with 2-year PFS2 and OS rates of 53% and 81%, respectively. Subgroup analysis revealed that early RT significantly improved PFS1 (P = 0.023). VHL-driven mRCC demonstrated a trend toward improved PFS1, statistical significance was not reached due to the limited sample size (P = 0.3). Safety analysis indicated grade 3 or 4 treatment-related adverse events in 50% of patients, with no grade 5 events.

CONCLUSIONS

The investigated trimodality treatment strategy is both safe and effective, resulting in prolonged PFS without requiring a change in systemic treatment. Overall, early RT intervention may offer additional benefits. Future research should provide molecular-level insights into treatment response.

Efficacy and Safety of Donut-Shaped Circumferential Spine CyberKnife Stereotactic Body Radiotherapy for Metastatic Spine Disease

BACKGROUND AND OBJECTIVES

Spinal metastases (SM) with epidural spinal cord compression (ESCC) present a significant challenge because of the high risk of radiation-induced injury to critical structures such as the spinal cord and nerve roots. Traditional treatment approaches often avoid circumferential stereotactic body radiotherapy (SBRT) to reduce these risks. The efficacy and safety of donut-shaped circumferential SBRT, designed to target the spinal column while sparing the spinal cord, remains underexplored. The aim of this study was to evaluate the safety and efficacy of donut-shaped circumferential CyberKnife SBRT for SM, particularly in preventing radiation-induced myelopathy and achieving local tumor control (LTC).

METHODS

We retrospectively analyzed data from patients treated with donut-shaped circumferential SBRT between 2014 and 2023. Key parameters examined included patient demographics, ESCC grade (Bilsky), prior treatments, clinical symptoms, and treatment parameters. We focused on SBRT dosimetric data, radiation exposure to the spinal cord and cauda equina, adherence to dose-volume constraints, and post-SBRT outcomes, including myelopathy and LTC.

RESULTS

Forty-eight lesions in 43 patients (median age: 65; range: 20-78) were reviewed. One patient required separation surgery for severe ESCC (Bilsky grade 3). The median clinical target volume was 63.77 cm3, and the median margin dose was 24 Gy. Over a median follow-up of 8 months, LTC was 91.1% at 6 months, 87.1% at 1 year, 82.8% at 3 years, and 62.1% at 5 years. The median overall survival was 17 months. Of the 21 lesions exceeding dose constraints, only one patient exhibited clinical myelopathy, which correlated with local tumor recurrence. No radiographic myelopathy or other radiation-induced complications were observed.

CONCLUSION

Donut-shaped circumferential CyberKnife SBRT is a safe and effective treatment of SM, achieving high LTC with minimal radiation-induced complications, including myelopathy.

Immune Modulation Through Stereotactic Radiotherapy: The Role of TBX21, GATA-3, FoxP3, and RORɣt

Background and Objectives: Stereotactic radiotherapy enhances local tumor control by delivering high doses directly to the tumor. It is thought to activate the immune system via T-cells, possibly creating a systemic response. This study aims to evaluate stereotactic body radiotherapy's (SBRT) impact on the immune system by measuring T-cell transcription factors, such as TBX21, GATA-3, FoxP3, and RORɣt. Materials and Methods: Peripheral blood samples were collected from 103 patients before SBRT and from 66 patients two months post-treatment. We measured transcription factors TBX21, GATA-3, FOXP3, and RORγt using ELISA, and performed a complete blood count and C-reactive protein analysis to rule out infections. Statistical analyses included paired t-tests and correlation analyses to assess changes before and after treatment. Results: Post-treatment, significant reductions were observed in TBX21 (Th1), GATA-3 (Th2), and FOXP3 (Treg), while RORɣt (Th17) remained stable but trended higher in lung cancer patients. No correlations were found with demographic factors. However, TBX21 levels were significantly related to the planning target volume (PTV) and biologically effective dose (BED10) in the lung region. Larger PTVs (≥16.5 cc) and higher BED10 doses (≥100 Gy) were linked to smaller reductions in TBX21 (p = 0.008, p = 0.04) and increased RORɣt levels (p = 0.01). Conclusions: Stereotactic radiotherapy reduces immunosuppressive markers like FOXP3 and GATA-3, indicating its potential to boost immune activation by suppressing Treg and Th2 cells. Larger target volumes and higher BED10 values may enhance Th1 responses through TBX21. These findings suggest that SBRT activates the immune system, and its combination with immunotherapy could be promising.

An investigation into the feasibility and efficacy of stereotactic radiosurgery for 1-3 cm single brain lesions on the ring-mounted Halcyon LINAC

PURPOSE

An evaluation of the accuracy, safety, and efficiency of the Halcyon ring delivery system (RDS) for stereotactic radiosurgery (SRS) treatment to relatively small (1-3 cm) brain lesions.

METHODS

After completing the extensive in-house quality assurance checks including Winston-Lutz test and independent dose verification via MD Anderson IROC SRS head phantom irradiation on Halcyon, fifteen brain SRS patients previously treated with a single dose of 20 Gy on TrueBeam (6MV-FFF) with HyperArc geometry were retrospectively replanned on Halcyon (6MV-FFF). Plan quality metrics including conformity index (CI), gradient index (GI), gradient distance (GD), PTV coverage, gross tumor volume (GTV) dose, heterogeneity index (HI), and doses to organs-at-risk (OAR) including normal brain dose were evaluated. Patient-specific quality assurance (PSQA) and independent dose verification via in-house Monte Carlo (MC) 2nd checks were performed.

RESULTS

The Halcyon was able to provide highly conformal brain SRS plans. When compared to TrueBeam, CI, planning target volume (PTV) coverage, GTV dose (mean and minimum), HI, and doses to brainstem, optic pathway, and cochlea were statistically insignificant. Statistically significant increases in GI (3.76 vs. 3.25, p < 0.001), GD (0.56 cm vs. 0.48 cm, p = 0.001), and V12Gy (5.5 cc vs. 4.6 cc, p = 0.014), on average using Halcyon versus TrueBeam was found, albeit clinically acceptable values for the majority of brain SRS cases. Halcyon plans provided statistically insignificant maximum dose to most adjacent OARs, though there was a statistically significant decrease in the maximum dose to the spinal cord (0.1 Gy vs. 0.4 Gy, p = 0.009). Halcyon beam-on time increases by a factor of ∼2 (p < 0.001). However, the faster patient setup on Halcyon results in a comparable estimated overall treatment time for both platforms. Plan deliverability and accuracy was ensured with PSQA (> 95% pass rate for 2%/2 mm clinical gamma criteria) results and MC 2nd check agreement within ± 5.0%.

CONCLUSIONS

Halcyon brain SRS plans provided a similar plan quality compared to HyperArc plans, although it demonstrated an inferior intermediate dose fall off thus slightly higher V12Gy. This study suggests that Halcyon provides acceptable treatment for solitary relatively small brain lesions of 1-3 cm in diameter. Treatment of select patients on Halcyon will be started at our clinic and it is recommended that other clinics complete an end-to-end test, validate, and implement Halcyon SRS treatments at their practices, especially community cancer centers to provide high-quality service to an underserved patient cohort.

Rapid dose prediction for lung CyberKnife radiotherapy plans utilizing a deep learning approach by incorporating dosimetric features delivered by noncoplanar beams

Purpose. The dose distribution of lung cancer patients treated with the CyberKnife (CK) system is influenced by various factors, including tumor location and the direction of CK beams. The objective of this study is to present a deep learning approach that integrates CK beam dose characteristics into CK planning dose calculations.Methods. The inputs utilized for the geometry and dosimetry method (GDM) include the patient's CT, the PTV structure, and multiple CK noncoplanar beam dose deposition features. The dose distributions were calculated using the Monte Carlo (MC) algorithm provided with the CK system and served as the ground truth dose label. Additionally, dose prediction was conducted through the geometry method (GM) for comparative analysis. The gamma pass rateγ(1 mm,1%),γ(2 mm,2%) andγ(3 mm,3%) were calculated between the predicted model and the MC method.Results. Compared to the GDM, the GM shows a significant dose difference from the MC approach in the low-dose region (<5 Gy) outside the target created by the various CK noncoplanar beams. The GDM increased theγ(1 mm, 1%) from 49.55% to 81.69%,γ(2 mm, 2%) from 73.24% to 98.11% and theγ(3 mm, 3%) from 81.69% to 99.37% when compared with the GM's results.Conclusions. This work proposed a deep learning dose calculation method by using patient geometry and dosimetry features in CK plans. The proposed method extends the geometric and dosimetric feature-driven deep learning dose calculation method to CK application scenarios, which has a great potential to accelerate the CK planning dose calculation and improve the planning efficiency.

Development and clinical implementation of a comprehensive multifractionation scheme HyperArc-based RapidPlan model for single and multiple brain metastases

Propose a solution to help mitigate the 1 to 2-week delay from simulation to treatment time for single-isocenter single- and multi-lesion brain stereotactic radiosurgery/radiotherapy (SRS/SRT) plans. Utilizing new machine learning techniques to automate and standardize the treatment planning process. 89 previously treated high-quality, highly conformal HyperArc SRS/SRT plans delivered on a TrueBeam LINAC (6MV-FFF), were used to develop a HyperArc-based RapidPlan (HARP) model. The training set consisted of 69 plans (8 single-fraction, 15 to 22 Gy; 33 three-fraction, 24 to 27 Gy; 28 five-fraction, 25 to 40 Gy) with a total of 133 metastases. The testing set consisted of 20 plans (3 single-fraction, 9 three-fraction, 8 five-fraction) with a total of 45 metastases. The model was trained then the testing plans were replanned using the HARP model. The HARP model was then used clinically to treat our first patient. Across all 3 fractionation schemes, the HARP model produced clinically acceptable plans in under 20 minutes. For target coverage, the HARP plans achieved a comparable PTV D95% with a median of 101.48% compared to the manual plan's 101.33%. The GTV D100% received a median of 108.24% and 105.39% for the HARP plan and original plan, respectively (p < 0.01). Maximum doses to organs-at-risk (OARs) were well within standard SRS/SRT criteria. All plans received clinically acceptable EPID-based portal dosimetry gamma pass rates and Monte Carlo 2nd check rates. The clinical 2-lesion HARP plan was generated in 15 minutes and used for patient treatment. The comprehensive HARP model can handle 3 different fractionation schemes, adequately sparing OARs, including normal brain toxicity, delivering a therapeutic dose to the brain lesions, generating plans in under 20 minutes. The utilization of HARP models can significantly decrease the treatment planning time, allowing institutions to standardize patient care, optimize the clinical workflow, and increase the accessibility of high-quality radiation therapy treatments.

AAPM-RSS Medical Physics Practice Guideline 9.b: SRS-SBRT

The purpose of this Medical Physics Practice Guideline (MPPG) is to describe the minimum level of medical physics support deemed prudent for the practice of linear-accelerator, photon-based (linac) stereotactic radiosurgery (SRS), and stereotactic body radiation therapy (SBRT) services. This report is an update of MPPG 9.a1 published in 2017. As SRS and SBRT services are rapidly adopted into the community-practice setting, this guideline has been developed to build on the work presented in MPPG 9.a and provide current appropriate minimum practice guidelines for such services.

Five-year evaluation of linear accelerator-based SRS platform isocentricity

Linear accelerator (LINAC)-based stereotactic radiosurgery (SRS) has become a mainstay in the management of intracranial tumors. However, the high fractional doses and sharp gradients used in SRS place heavy demands on geometric accuracy. Image guidance systems such as ExacTrac (ETX, Brainlab AG, Munich, Germany) have been developed to facilitate position verification at nonzero table angles. Though convenient, potential loss of mechanical rigidity between the imaging and treatment systems can be cause for concern, as the ETX system is not mounted to the rotating gantry. In this retrospective study, we analyzed 518 Winston-Lutz (WL) tests performed in the last 5 years with ETX alignment on our Elekta Versa HD (Elekta AB, Stockholm, Sweden) linear accelerator to determine the achievable limits of precision and stability over time for our LINAC-based SRS platform. Results demonstrated remarkable stability over time. 3D and directional misalignments never exceeded 1.0 mm over the study period; however, table rotation was shown to be the most significant source of positional uncertainty. Gantry sag, as measured by gun-to-target misalignments at the gantry-0 and gantry-180-degree positions, was consistent, measuring 1.23 ± 0.18 mm over the study period. Measured accuracy was well within acceptable tolerances for cranial SRS treatment delivery. Notably, the use of the ETX system for intrafraction repositioning effectively eliminates couch walkout, the most significant source of uncertainty identified in this study. Our results thus corroborate safe SRS treatment delivery on our Versa HD with ExacTrac image guidance.

Clair W, Pokhrel D. A knowledge-based planning model to identify fraction-reduction opportunities in brain stereotactic radiotherapy

OBJECTIVE

To develop and validate a HyperArc-based RapidPlan (HARP) model for three-fraction brain stereotactic radiotherapy (SRT) plans to then use to replan previously treated five-fraction SRT plans. Demonstrating the possibility of reducing the number of fractions while achieving acceptable organs-at-risk (OAR) doses with improved target biological effective dose (BED) to brain lesions.

METHODS

Thirty-nine high-quality clinical three-fraction HyperArc brain SRT plans (24-27 Gy) were used to train the HARP model, with a separate 10 plans used to validate its effectiveness. Fifty-eight five-fraction HyperArc brain SRT plans (30-40 Gy) attempted to be retrospectively replanned for three fractions scheme using the HARP model. All planning was done within the Eclipse treatment planning system for a TrueBeam LINAC with a 6 MV-FFF beam and Millenium 120 MLCs and dosimetric parameters were analyzed per brain SRT protocol.

RESULTS

The HyperArc RapidPlan model was successfully trained and tested, with the validation set demonstrating a statistically significant (p = 0.01) increase in GTV D100% from 28.5 ± 0.7 Gy to 29.4 ± 0.6 Gy from the original to RapidPlan plans. No statistically significant differences were found for the OAR metrics (p > 0.05). The five-fraction replans were successful for 20 of the 58 five-fraction brain SRT plans. For those 20 successful brain SRT plans, the maximum doses to OAR were clinically acceptable with a three-fraction scheme including an average V18Gy to Brain-PTV of 9.9 ± 5.9 cc. Additionally, the replanned five-fraction brain SRT plans achieved a higher BED to the tumors, increasing from a GTV D100% of 52.9 ± 4.5 Gy for the original five-fraction plans to 57.3 ± 3.1 Gy for the three-fraction RapidPlan plans. All RapidPlan plans were generated automatically, without manual input, in under 20 min.

CONCLUSIONS

The HARP model developed in this research was used to successfully identify select five-fraction plans that were able to be reduced to three-fraction SRT treatments while achieving clinically acceptable OAR doses and improved target BED. This tool encourages a fast and standardized way to provide physicians with more options when choosing the necessary fractionation scheme(s) for HyperArc SRT to single- and multiple brain lesions.

Photon mini-GRID therapy for preoperative breast cancer tumor treatment: A treatment plan study

BACKGROUND

Breast cancer is the leading cause of female cancer mortality worldwide, accounting for 1 in 6 cancer deaths. Surgery, radiation, and systemic therapy are the three pillars of breast cancer treatment, with several strategies developed to combine them. The association of preoperative radiotherapy with immunotherapy may improve breast cancer tumor control by exploiting the tumor radio-induced immune priming. However, this requires the use of hypofractionated radiotherapy (3 × 8 Gy), increasing the risk of toxicity. Mini-GRID therapy (mini-GRT) is an innovative form of spatially fractionated radiation therapy (SFRT) characterized by narrow beam widths between 1 to 2 mm that promises a significant increase in normal tissue dose tolerances and could thereby represent a new alternative for preoperative breast cancer treatment. Mini-GRT has been successfully implemented at the Hospital de Santiago de Compostela (Spain) with a flattening filter-free LINAC (megavoltage x-rays).

PURPOSE

In this dosimetry proof-of-concept study, we evaluate the feasibility of photon mini-GRT for preoperative breast cancer treatment. We also assess the clinical potential of mini-GRT and compare it with the current treatment standard of intensity-modulated radiotherapy (IMRT).

METHODS

Seven unbiased breast cancer dosimetries of patients treated with stereotactic body radiotherapy (SBRT) (3 × 8 Gy, IMRT) were selected for the study. Photon mini-GRT was compared with SBRT using three main criteria: (i) the dose to organs at risk (OARs), (ii) the dose constraints dictated by normal tissue tolerance, and (iii) the lateral penumbra in OARs. Tumor coverage was evaluated in terms of normalized total dose at 8 Gy-fractions. The optimized SBRT by IMRT was realized at the Institut Curie, Paris, France. The dose in mini-GRT was calculated by means of Monte Carlo simulations based on the mini-GRT implementation realized at the University Hospital in Santiago de Compostela.

RESULTS

Compared to SBRT plans, mini-GRT resulted in a reduction of the mean dose to the lungs, heart, chest wall, and lymph nodes in the studied cases by a factor ranging from 50% to 100%. Additionally, valley, mean, and peak doses to normal tissues meet the dose tolerance limits for the considered OARs, the most challenging of all being the skin. The mean dose to the skin was reduced (20%-60% less) for most of the studied cases. Mini-GRT also yielded sharper lateral penumbras in the skin and lungs (size reduced by at least 50%). Similar tumor integral doses were obtained for the two treatment modalities.

CONCLUSION

Mini-GRT with megavoltage x-rays is an innovative treatment approach already implemented in a clinical context. In this proof-of-concept study, we evaluated mini-GRT for partial breast cancer irradiation, demonstrating its potential for preoperative treatment thanks to the high skin and normal tissue-sparing capabilities. These initial results represent a first step towards clinical use and encourage further prospective clinical studies.

Patient setup variation on Elekta Unity and its impact on adaptive planning

PURPOSE

The unique design of the MR-linac may restrict the use of effective immobilization devices, resulting in significant patient setup variations (PSVs). The purpose of this study is to analyze the PSVs on the Elekta Unity system and investigate their impact on adaptive planning.

METHODS

The PSVs for 10 brain, 10 pancreas, five prostate, and five rectum patients previously treated on Elekta Unity were analyzed. The five prostate and five pancreas plans were selected to investigate the impact of PSVs on adaptive planning. The reference scans were shifted by 1, 2, and 3 cm in the left-right (LR) and superior-inferior (SI) directions to simulate PSVs. Both the adaptive-to-position (ATP) and adaptive-to-shape (ATS) workflows were executed. The adaptive planning time, number of monitor units (MUs), and dosimetric metrics quantifying target coverage and organ-at-risks (OARs) sparing were compared.

RESULTS

For brain treatments, the average/maximum PSVs were -0.2 ± 0.3 cm/0.8 cm (LR), 0.3 ± 0.7 cm/1.8 cm (SI), and 0.8 ± 0.7 cm/1.8 cm in the anterior-posterior (AP) direction. For pancreas treatments, the PSVs are -0.1 ± 1.0 cm/3.8 cm (LR), -0.1 ± 0.8 cm/3.5 cm (SI), and 0.3 ± 0.3 cm/1.3 cm (AP). Pelvis treatments had similar PSVs as pancreas treatments. The ATS workflow took two to three times longer than the ATP workflow. The only trend observed was that the plan MUs increased slightly (< 10%) with PSVs in the ATP workflow for prostate patients. Both workflows effectively reproduced target coverage and OAR sparing, regardless of the magnitude of the PSVs.

CONCLUSIONS

Significant PSVs were observed on Elekta Unity due to suboptimal patient immobilization. Using prostate and pancreas treatments as examples, we demonstrated that adaptive planning can effectively accommodate such PSVs. Nevertheless, efforts should be made to minimize PSVs-particularly rotations-to mitigate intra-fraction motion and reduce treatment time.

Survival Without Quality of Life Deterioration in the GORTEC 2014-04 "OMET" Randomized Phase 2 Trial in Patients with Head and Neck Cancer with Oligometastases using Stereotactic Ablative Radiation Therapy (SABR) alone or Chemotherapy and SABR

PURPOSE

Patients with oligometastasis may have prolonged survival with multisite stereotactic ablative radiation therapy (SABR). Evidence to support this paradigm is scarce in squamous cell carcinoma of the head and neck (HNSCC). The multicenter open-label randomized GORTEC 2014-04 (NCT03070366) phase 2 study assesses survival without definitive quality of life (QoL) deterioration of omitting upfront chemotherapy in oligometastatic patients with HNSCC using SABR alone, in the French Head and Neck Intergroup.

METHODS AND MATERIALS

Eligible participants (≥18 years old with 1-3 oligometastases, the Eastern Cooperative Oncology Group score 0-2) were randomly assigned (1:1) to receive chemo-SABR or SABR alone. Salvage treatments were left to the physician's appreciation. The standard therapy was considered to be systemic therapy and SABR (chemo-SABR; EXTREME regimen [5 fluorouracil/platinum/cetuximab]). The primary endpoint was 1-year (±3 months) overall survival rate without definitive deterioration (ie, without subsequent better QoL score) of the global European Organisation for Research and Treatment of Cancer QoL Questionnaire-Core30 score.

RESULTS

Between September 2015 and October 2022, 69 participants were assigned to receive chemo-SABR (N = 35) or SABR alone (N = 34); 57 had lung-only metastases (82.6%), and 40 had isolated metastasis (58.0%). The median baseline QoL score was 66.7 (IQR, [50.0-83.3]). The median follow-up was 55.3 months (95% CI, 45.0-69.7). Of participants (N = 59) evaluable for the primary endpoint, 16 of 29 (55.2%, 90% CI, 0.38-0.71) and 16 of 30 (53.3%, 90% CI, 0.37-0.69) were alive and free of QoL deterioration at 1 year in the SABR-alone and chemo-SABR arms. However, QoL deterioration was deeper with chemo-SABR (50.0; IQR, [41.7-66.7]) than with SABR alone (16.7; IQR, [16.7-41.7]). In intent-to-treat analysis (N = 69), median survival was 42.3 months (95% CI, 26.5-not reached) with chemo-SABR and 41.1 months (95% CI, 32.1-66.9) with SABR alone; median progression-free survival was 12.9 (95% CI, 7.5-17.3) and 7.4 months (95% CI, 4.2-15.6) in the chemo-SABR and SABR alone arms, respectively. Rates of severe treatment-related toxicities were 21 of 35 (60.0%) with chemo-SABR and 3 of 34 (8.8%, no grade 5) with SABR alone.

CONCLUSIONS

Using SABR alone, the omission of upfront EXTREME-based chemotherapy and maintenance cetuximab in oligometastatic patients with HNSCC resulted in similar survival but much less severe QoL deterioration and fewer toxicity rates. SABR alone could be a reasonable alternative in oligometastatic patients with HNSCC.

A systematic review of tumour position reproducibility and stability in breath-hold for radiation therapy of the upper abdomen

Background and purpose

Upper abdominal malignancies are relatively rare, and although surgery is considered the primary treatment option, radiation therapy has an emerging role in the management of liver, pancreas, kidney and adrenal gland tumours. Furthermore, stereotactic radiation therapy for the management of upper abdominal metastases is an expanding clinical indication. Breath-hold is one respiratory motion management strategy used in upper abdominal radiation therapy, and the reproducibility, and stability of breath-hold is critical for overall treatment accuracy.

Materials and methods

A systematic review of the literature was conducted in Medline, Embase and Cochrane databases with keyword and vocabulary terms related to radiation therapy, breath-hold and upper abdominal tumours.

Results

Following screening against the selection criteria, 41 studies were included. Breath-hold reproducibility was the most commonly reported outcome and exhale breath-hold was the most common type. Studies were either prospective or retrospective cohort studies, and the mean sample size was 19 participants. The risk of bias of each included study was assessed, and the mean quality assessment score for included studies was 90 % (77-100 %). Median exhale breath-hold cranio-caudal inter-fraction reproducibility was 0.6 mm, (IQR 0.3-1.6 mm), compared to inspiratory breath-hold 0.0 mm (IQR -0.6-2.97 mm). Stability measurements were ≤3 mm in 71 % of studies, irrespective of breath-hold type.

Discussion

Formulating institutional protocols for best clinical practice regarding breath-hold for upper abdominal tumours is challenging, given the significant variation in practices, interventions and definitions observed in the literature. Further investigation to individualise breath-hold strategies and safety margins is warranted.

Development and Validation of Monte Carlo Methods for Converay: A Proof-of-Concept Study

BACKGROUND

Radiotherapy technology has undergone significant advancements, driven by the pursuit of improved tumor control probabilities and reduced normal tissue complication probabilities. This has been achieved primarily through innovative approaches that prioritize high dose conformity on complex treatment targets. The CONVERAY project introduces a groundbreaking teletherapy system featuring a convergent X-ray beam, which enables highly conformal dose distributions by converging photons to a focal spot, thereby achieving exceptionally high fluence rates.

METHODS

Customized Monte Carlo subroutines have been developed to simulate particle fluence and associated dosimetry effects for the CONVERAY device. This simulation approach facilitated a detailed, step-by-step characterization of radiation fluence and interaction processes, enabling seamless integration with a conventional clinical linear accelerator head. Key physical properties of the radiation beam have been comprehensively characterized for various CONVERAY configurations, providing a solid foundation for evaluating the corresponding dosimetry performance.

RESULTS

Monte Carlo simulations successfully tracked the phase state of the CONVERAY device, characterizing the influence of individual components on convergent photon beam production. Simulations evaluated dosimetry performance, confirming the device's capability to achieve high dose concentrations around the focal spot. Preliminary tests on realistic scenarios (intracranial and pulmonary irradiations) demonstrated promising spatial dose concentration within tumor volumes, while gantry rotation significantly improved dose conformation.

CONCLUSIONS

This proof-of-concept Monte Carlo study of the CONVERAY prototype provided critical insights into the generation of convergent X-ray beams, validating the device's ability to achieve its primary objective. Notably, simulation results reveal the potential for exceptionally high dose concentrations within complex treatment volumes, demonstrating promising dosimetry performance.

Patient selection, ventricular tachycardia substrate delineation, and data transfer for stereotactic arrhythmia radioablation: a clinical consensus statement of the European Heart Rhythm Association of the European Society of Cardiology and the Heart Rhythm Society

Stereotactic arrhythmia radioablation (STAR) is a novel, non-invasive, and promising treatment option for ventricular arrhythmias (VAs). It has been applied in highly selected patients mainly as bailout procedure, when (multiple) catheter ablations, together with anti-arrhythmic drugs, were unable to control the VAs. Despite the increasing clinical use, there is still limited knowledge of the acute and long-term response of normal and diseased myocardium to STAR. Acute toxicity appeared to be reasonably low, but potential late adverse effects may be underreported. Among published studies, the provided methodological information is often limited, and patient selection, target volume definition, methods for determination and transfer of target volume, and techniques for treatment planning and execution differ across studies, hampering the pooling of data and comparison across studies. In addition, STAR requires close and new collaboration between clinical electrophysiologists and radiation oncologists, which is facilitated by shared knowledge in each collaborator's area of expertise and a common language. This clinical consensus statement provides uniform definition of cardiac target volumes. It aims to provide advice in patient selection for STAR including aetiology-specific aspects and advice in optimal cardiac target volume identification based on available evidence. Safety concerns and the advice for acute and long-term monitoring including the importance of standardized reporting and follow-up are covered by this document. Areas of uncertainty are listed, which require high-quality, reliable pre-clinical and clinical evidence before the expansion of STAR beyond clinical scenarios in which proven therapies are ineffective or unavailable.

Proton stereotactic centralized ablative radiation therapy for treating bulky tumor: a treatment plan study

Objective

Stereotactic centralized/core ablative radiation therapy (SCART) is a novel radiotherapy approach. This study investigates the potential benefits of proton-based SCART (pSCART) by leveraging the dosimetric advantages of protons and integrating them with the SCART technique.

Methods

Five clinical cases previously treated with conventional proton therapy were selected for this study. The pSCART plans utilized a relative biological effectiveness (RBE) prescription dose of 24 Gy (RBE) × 3 fractions, with each plan consisting of three to five fields. The prescribed dose for the CyberKnife SCART was the highest value meeting the organs-at-risk (OARs) dose limits and the tumor edge dose limits. The dose distributions of the CyberKnife-based SCART and pSCART plans were compared using five criteria: i) prescription dose; ii) 80% prescription dose volume, targets coverage at 80% and 20% dose levels, and the 80%/20% ratio; iii) volume receiving >5 Gy outside the tumor edge; iv) dose tolerance limits to OARs; and v) mean dose to OARs.

Results

pSCART can deliver a higher prescription dose of 24 Gy × 3 fractions versus SCART's 15 Gy × 2-3 fractions or 18 Gy × 2 fractions. Specifically, pSCART outperforms SCART in terms of the 80% prescription dose volume and 80% dose level coverage of stereotactic centralized/core target volumes (SCTV) achieving 69.77%-100.00% versus SCART's 43.6%-99.5%. The 20% dose level coverage for gross target volume (GTV) is slightly lower for pSCART, achieving 88.96%-98.64% versus SCART's 90.1%-99.9%. The maximum point dose outside the target volume is lower for pSCART at 4.58-6.19 Gy versus SCART's 4.78-6.67 Gy; additionally, the V5Gy at the tumor edge is significantly smaller for pSCART at 5.93-23.72 cm3 versus SCART's 6.85-151.66 cm3. The average dose to most OARs in the pSCART plan is lower than in the SCART plan.

Conclusions

This work provides initial insights into evaluating treatment plans for bulky tumors using pSCART. Compared to the CyberKnife SCART, pSCART generates significantly higher prescription doses and larger high-dose regions within the GTV while delivering lower doses at the tumor edge, enhancing normal tissue sparing.

Evaluation of dosimetric and spatial accuracy of a virtual cone technique for radiosurgery using linac-integrated CBCT-based polymer gel dosimetry

PURPOSE

This study evaluates the dosimetric and geometric precision of a virtual cone technique using CBCT-based polymer gel dosimetry, enabling radiation delivery, and imaging readout within an identical spatial coordinate system.

METHODS

We created a C# script for a virtual cone technique that generates a treatment plan with 10 gantry arcs at 0°, 36°, 72°, 288°, and 324° couch angles, with 2 arcs per couch angle using 45° and 135° collimator angles. Two verification plans using Eclipse v15.6 (AcurosXB) were created with 20 Gy at the maximum dose for: (1) a cylindrical gel, with an additional calibration region; (2) a 3D printed anthropomorphic skull phantom with a gel insert. The 50% isodose (10 Gy) width through the central axis of the axial and sagittal planes (SPs) were measured for the gel experiment. The distance between the centers-of-masses of the 10 Gy isodose region of the plan and the gel (skull phantom) were calculated for an end-to-end spatial accuracy test.

RESULTS

The maximum point dose measured with gel was within 1% of the plan, though the gel measured 50% isodose widths of 5.56± $\; \pm \;$ 0.02 mm, 5.65 ± $ \pm \;$ 0.04 mm, 4.23 ± $ \pm \;$ 0.01 mm for axial (anterior-posterior), axial (left-right), sagittal (superior-inferior) respectively, which were slightly narrower than Eclipse (1.29 mm maximum difference in the SP due to CBCT slice thickness). The center-of-mass distance was 0.66 mm for the gel experiment, and 0.94 mm for complete end-to-end testing with the anthropomorphic phantom, including CBCT setup (kV-MV isocenter uncertainty).

CONCLUSION

The 50% isodose width of the gel measurement was 5.15 mm (mean), which was tighter than our Eclipse v15.6 beam model. The end-to-end spatial accuracy test, only achievable with gel dosimetry using CBCT readout, resulted in sub-millimeter accuracy. This study demonstrates the value of gel dosimetry in verifying the dosimetric and spatial accuracy of this high precision, stereotactic technique.

A Randomized, Multicenter, Phase 2 Trial of Camrelizumab With or Without Metastasis-directed Stereotactic Body Radiation Therapy in Recurrent or Metastatic Nasopharyngeal Carcinoma

PURPOSE

To investigate the efficacy of metastasis-directed therapy (MDT) when added to camrelizumab (Cam) in patients with recurrent or metastatic nasopharyngeal carcinoma (R/M-NPC).

METHODS AND MATERIALS

We conducted a randomized, controlled, multicenter, phase 2 trial in 3 centers from China (NCT04830267). Patients with R/M-NPC, without prior exposure to immunotherapy, who presented with ≥2 lesions, and at least 1 measurable lesion were randomized 1:1 to either Cam alone or Cam plus MDT (Cam+MDT). Patients randomized to the MDT group must have 1 lesion that is amendable to stereotactic body radiation therapy (SBRT) prescribed to 27 Gy in 3 fractions every other day. The primary endpoint was objective response rate (ORR) of unirradiated lesions using Response Evaluation Criteria in Solid Tumors v1.1.

RESULTS

Between April 2021 and August 2023, 39 patients were randomly assigned to receive either Cam (n = 20) or Cam+MDT (n = 19). In total, 17 out of 39 (43.6%) patients had oligometastatic disease (≤3 lesions), 18 out of 39 (46.2%) had liver involvement, and 3 out of 39 (7.7%) had locoregional recurrent disease. ORR of unirradiated lesions did not differ between the treatment groups (26.3% [Cam+MDT] vs 30.0% [Cam], P = 1.0). The disease control rate of unirradiated lesions was 73.7% in the Cam+MDT group compared with 60.0% in the Cam group (P = .571). After a median follow-up of 25.8 months, median progression-free survival was 9.3 (95% CI, 6.2-not reached [NR]) months in the Cam+MDT group and 8.8 (95% CI, 3.3-NR) months in the Cam group (P = .750). Exploratory analyses suggested a longer overall survival (OS) with Cam+MDT for patients with >3 lesions (HR, 0.23; 95% CI, 0.07-0.77; P = .009). G3 and above adverse events were comparable between the treatment groups (15.8% [Cam+MDT] vs 20.0% [Cam]). The overall rate of capillary proliferation was 17.9% (7/39) for the trial.

CONCLUSIONS

Our study did not meet its primary endpoint of superior ORR of unirradiated lesions with the addition of MDT to Cam in patients with R/M-NPC.

Clinical practice in stereotactic radiotherapy delivery at treatment unit: a practitioner survey and consensus-based recommendations for multidisciplinary professional development

PURPOSE

Stereotactic radiation therapy (SRT) is on the rise around the world. We aimed to provide recommendations to streamline and assess medical practices in SRT delivery at treatment unit, while complying with legal obligations concerning safety.

MATERIALS AND METHODS

We conducted an online closed practice survey for heads of radiotherapy departments both nationally in comprehensive cancer centers and university hospitals throughout France, and internationally. The aim was to obtain a better understanding of how the delivery of SRT at treatment unit was managed across different centers according to experience, and to the machines and repositioning techniques used. Radiation oncologists (ROs) were also asked to assess the difficulties of technical implementation in the department, and whether residents were involved in the validation and delivery of SRT. Differences among countries regarding legislation governing the validation of SRT sessions at treatment unit were also collected. A videoconference was then held to draw up proposals for regulatory changes based on the results obtained. Finally, recommendations were drawn up by the steering committee and approved by heads of radiotherapy departments in comprehensive cancer centers and university hospitals throughout France.

RESULTS

Thirty-five French centers and 15 centers from 14 foreign countries responded to the questionnaire. The most common stereotactic machines were Varian Truebeam STX® (45%) and Cyberknife® (39.2%). The departments had been performing SRT for more than 10 years in 60.5% of cases, and for less than 5 years in 10.1% of cases. A RO validated the SRT fractions at each session in 62.9% of French departments, while in countries outside France RO validation concerned the first fraction only for 35.3% or was performed only in the event of an issue for 23.5%. RO patient positioning validation of SRT fractions were considered as: time-consuming / task-interrupting (80%); having no added value with regards its systematic use (41.8%); and leading to a loss of machine time (33.1%). Most heads of departments would like to see an evolution towards systematic RO validation for the first session, then validation by a radiation therapist (RTT) for all subsequent sessions, leaving open the possibility of RO intervention when required in case of difficulty. We drew up a task delegation procedure to meet these requirements.

CONCLUSION

Comparing the French practice to international ones confirmed the need to develop and harmonize recommendations in terms of patient positioning validation at treatment unit. Regulatory changes incorporating a competence transfer to RTTs, particularly after the empowerment process, is key. However, these changes need to be adapted to the experience of each Center and to that of each RTT, as assessed with clearly established criteria and learning curve.

Convergent-Diffusion Denoising Model for multi-scenario CT Image Reconstruction

A generic and versatile CT Image Reconstruction (CTIR) scheme can efficiently mitigate imaging noise resulting from inherent physical limitations, substantially bolstering the dependability of CT imaging diagnostics across a wider spectrum of patient cases. Current CTIR techniques often concentrate on distinct areas such as Low-Dose CT denoising (LDCTD), Sparse-View CT reconstruction (SVCTR), and Metal Artifact Reduction (MAR). Nevertheless, due to the intricate nature of multi-scenario CTIR, these techniques frequently narrow their focus to specific tasks, resulting in limited generalization capabilities for diverse scenarios. We propose a novel Convergent-Diffusion Denoising Model (CDDM) for multi-scenario CTIR, which utilizes a stepwise denoising process to converge toward an imaging-noise-free image with high generalization. CDDM uses a diffusion-based process based on a priori decay distribution to steadily correct imaging noise, thus avoiding the overfitting of individual samples. Within CDDM, a domain-correlated sampling network (DS-Net) provides an innovative sinogram-guided noise prediction scheme to leverage both image and sinogram (i.e., dual-domain) information. DS-Net analyzes the correlation of the dual-domain representations for sampling the noise distribution, introducing sinogram semantics to avoid secondary artifacts. Experimental results validate the practical applicability of our scheme across various CTIR scenarios, including LDCTD, MAR, and SVCTR, with the support of sinogram knowledge.

Phase II Evaluation of Ultra-Hypofractionated Postoperative Radiation Therapy for Breast Cancer: Toxicity and Efficacy in a Single-Center Nonrandomized Prospective Study

PURPOSE

To evaluate the toxicity profile and efficacy of postoperative ultra-hypofractionated radiation therapy in elderly patients with breast cancer.

MATERIALS AND METHODS

This is a nonrandomized, single-center, prospective Phase II trial. Patients with breast cancer older than 65 years were treated with ultra-hypofractionated radiation therapy in 5 fractions of 5.7 Gy on alternate days in the breast or chest wall, or regional lymph nodes. The primary end point was acute toxicity.

RESULTS

A total of 60 patients were analyzed, with a median follow-up of 42.5 months (range, 13.8-66.2). Most patients presented pathologic stage I (56.6%, n = 34) or stage II (33.3%, n = 20) disease. Regional lymph node irradiation was performed in 22% (n = 13) of patients. During treatment, 51% (n = 31) of patients experienced grade 1 or 2 acute toxicity, with no cases of grade 3 acute toxicity reported. Late toxicity included 1.7% (n = 1) of patients developing grade 3 fibrosis and 1.7% (n = 1) developing grade 3 pneumonitis. Regional lymph node irradiation was not associated with a statistically significant increase in toxicity risk (P = .194). Cosmesis evaluations revealed no significant changes when comparing pretreatment assessments with evaluations at 10 weeks (P = .223) and 26 weeks (P = .615) post-treatment. Quality of life was not adversely affected, regardless of whether regional lymph nodes were irradiated. Recurrence rates included two patients with both locoregional and distant recurrence and five patients with distant recurrence. The 3-year disease-free survival probability was 81.7%, and the 3-year overall survival probability was 86.7%.

CONCLUSION

This study demonstrates the safety of ultra-hypofractionated radiation therapy in terms of toxicity in patients with breast cancer. The findings for side effects, cosmesis, quality of life, and survival outcomes are consistent with those observed in moderately hypofractionated radiation therapy regimens, suggesting its use as a viable treatment option in this demographic.

Feasibility and safety study of ultra-hypofractionated neoadjuvant radiotherapy to margins-at-risk in retroperitoneal sarcoma

PURPOSE

Retroperitoneal sarcomas (RPS) are rare tumors that present unique challenges, often due to late presentation, and the proximity of critical organs makes complete surgical resection challenging. This study aimed to assess the feasibility of neoadjuvant short-course radiotherapy (SCRT) targeting margins-at-risk and to assess its potential impact on outcomes.

MATERIALS AND METHODS

This is a single-center, prospective, non-randomized feasibility study. SCRT was administered via image-guided volumetric modulated arc therapy, consisting of 5 fractions of daily radiotherapy followed by immediate surgery. As a starting dose, patients were prescribed 25 Gy in 5 fractions. For the escalation stage, patients were prescribed 30 Gy in 5 fractions. Only the presumed threatened surgical margins were delineated for large tumors.

RESULTS

Patients with either primary or recurrent RPS were recruited. Eight patients underwent SCRT but one patient did not have a resection as planned. Seven patients underwent surgical resection, of whom one passed away 3 months postoperative from a cardiac event. After a median follow-up of 20.5 months for the six postoperative survivors, there were no overt long-term toxicities and one patient relapsed out-of-radiotherapy-field.

CONCLUSION

SCRT to RPS with a margin boost followed by immediate surgery is worth investigating. A starting dose of 30 Gy in 5 fractions is recommended for further studies. Longer-term follow-up is necessary.

Comparing the Robustness of Intensity-modulated Proton Therapy and Proton-arc Therapy Against Interplay Effects of 4D Robust-optimised Plans for Lung Stereotactic Body Radiotherapy

AIMS

To assess the robustness of 4D-optimised IMPT and PAT plans against interplay effects in non-small cell lung cancer (NSCLC) patients with respiratory motion over 10 mm, and to provide insights into the use of proton-based stereotactic body radiotherapy (SBRT) for lung cancer with significant tumour movement.

MATERIALS AND METHODS

Fourteen patients with early-stage NSCLC and tumour motion >10 mm were selected. Three hypofraction regimens were generated using 4D robust optimisation with the IMPT and PAT techniques. The nominal plan qualities for both techniques were compared, and their robustness against setup and range uncertainties was evaluated. 4D dynamic dose and the 4D static dose were generated to calculate ΔIMR(%) for interplay effects.

RESULTS

PAT plans demonstrated superior target metrics such as D95 and D2, and offered enhanced protection for organs at risk (OARs), particularly in lung metrics, across multiple fractionation schemes (p < 0.05). The robustness of target coverage against setup and range uncertainties was better in PAT plans than IMPT, with average pass rates of 97.8% and 95.4%, respectively (p < 0.01). The interplay effect significantly affected target metrics in single-fraction plans, decreasing with more fractions, while its effect on OAR metrics was minimal. Median values for single-fraction plans were: ΔID98GTV was -3% for IMPT and -0.7% for PAT (p < 0.01); ΔID95GTV was -2.4% for IMPT and -0.6% for PAT (p < 0.01); ΔID2GTV was 3.2% for IMPT and 0.9% for PAT (p < 0.05). The interplay effects resulted in median homogeneity index deviations of 9.1% and 2% for the IMPT and PAT plans, respectively (p < 0.01). Different starting phases affected IMPT more significantly than PAT.

CONCLUSION

PAT demonstrated greater robustness to interplay effects than IMPT for hypofractionated treatments of early-stage NSCLC, particularly in single-fraction schemes. Additionally, PAT showed good resilience to variations in different starting phases.

Single Fraction Radiosurgical Tolerance of Brainstem, Trigeminal Nerve, and Meckel's Cave for Facial Numbness

PURPOSE

This article reviews toxicity outcomes for a series of patients treated with stereotactic radiosurgery for trigeminal neuralgia, focusing on dose to the brainstem, trigeminal nerve, and Meckel's cave as possible explanatory variables for the development of the most common posttreatment neuropathy, facial numbness.

METHODS AND MATERIALS

A retrospective review of 136 cases treated with CyberKnife radiosurgery for trigeminal neuralgia was performed. Dose was initially (cohort 1) prescribed to 57 to 64 Gy covering a 6-mm cylindrical shaped target volume ≥2 mm from the dorsal root entry zone. Subsequently, a deliberate change to isocentric treatment planning occurred, resulting in delivery of 85 Gy to a spherical target (cohort 2). Brainstem, trigeminal nerve, and Meckel's cave were contoured, and a variety of dosimetric and clinical factors were analyzed for association with development of treatment-related facial numbness.

RESULTS

Treatment-related numbness occurred in 59 of 136 (43%) patients and did not differ between the treatment cohorts. Fifty-two patients experienced Barrow Neurological Institute (BNI) grade II toxicity, and 7 patients experienced BNI grade III toxicity. Time to numbness was 16.0 months for cohort 1 and 10.4 months for cohort 2 (P = .184). The median brainstem maximum dose was 26.1 Gy, ranging from 4.2 Gy to 57.3 Gy. Maximum dose to the trigeminal nerve was 85 Gy. Mean trigeminal nerve dose was 47.3 Gy. The median Meckel's cave maximum and mean doses were 26.0 Gy and 6.8 Gy, respectively. No definitive upper limit dose threshold was detected for the structures analyzed, but trends were noted for maximum trigeminal nerve dose of 85 Gy (P = .083) and for prescription dose (P = .057) and trigeminal nerve V40 (P = .077) in the type I subset.

CONCLUSIONS

Brainstem, trigeminal nerve, and Meckel's cave tolerated doses within the range delivered. Discussion of the literature is provided to guide treatment planning and management.

Experience and uncertainty analysis of CT-based adaptive radiotherapy for abdominal treatments

BACKGROUND

Online adaptive radiotherapy (ART) allows for daily replanning of treatment plans with adjustments according to current day anatomy. The purpose of this work is to present our methodology for using CT-based ART applied to abdominal cases along with our experience with this treatment. We additionally aim to estimate some of the uncertainties associated with the adaptive process.

METHODS AND MATERIALS

Analysis was performed on patients with abdominal targets (N = 41, 205 fractions), treated on a CT-based adaptive treatment unit; treatment sites were divided into 3 categories: pancreas, liver, and other (e.g., lymph nodes). Statistics regarding contouring time, planning target volume (PTV) coverage, and organ-at-risk (OAR) sparing are presented. Contouring uncertainty was estimated by expanding critical OARs and recalculating dose, and auto-registration uncertainty was estimated by adjusting the registration between the cone beam computed tomography scan and the dose cloud and recalculating dose.

RESULTS

Coverage for the planning optimization PTV (PTV_Opt) for adaptive plans was on average 94.7 ± 0.4 %, while for scheduled plans it was on average 92.0 ± 0.6 %. The average decrease in OAR maximum dose by using the adaptive plans was 11.6 ± 1.0 %. Contouring time was on average 23 ± 0 min. Uncertainty estimates for PTV V100% were on average 0.6 ± 0.4 %; combined uncertainties for maximum OAR dose were on average 4.6 ± 0.4 %.

CONCLUSION

Adaptive therapy on average led to plans with improved PTV coverage or OAR sparing, and our workflow allowed for treatment to be completed within a reasonable timeframe. The benefit of adaptive therapy largely outweighed estimates of uncertainty.

Quality assessment of automatically planned o-ring linac SBRT plans for pelvic lymph node and lung metastases, evaluating the optimal minimum target size

The purpose of this study is to assess the influence of Planning Target Volume (PTV) on the quality of automatic planned O-Ring Halcyon linac stereotactic body radiation therapy (SBRT) plans of pelvic lymph nodes (LN) and lung metastases and to evaluate an absolute PTV volume threshold as a plan quality prediction criterion. A total of 21 pelvic LN and 18 lung clinical treatment plans were replanned for Halcyon with unattended autoplanning. The prescription dose range was 26-40 Gy for LN and between 39-54 Gy for the lung in the mean 3 fractions. The mean/median PTV was 4.0/ 3.6 cm3 for LN and 4.9/ 4.3 cm3 for the lung. The criteria for the plan quality evaluation consisted of using dose metrics for conformity, spillage, and coverage and dose limits on healthy tissue assessment. A statistical study was performed based on systematic Mann-Whitney U test and cluster analysis to evaluate a PTV volume predictor threshold of plan quality. 95% (n = 20) LN and 100% (n = 18) lung plans met all tolerance criteria. For both cohorts of plans, a PTV threshold was determined, indicating a reduction of particular dose indices when below this threshold. Low risk of toxicity in healthy tissues was predicted. A PTV threshold of 4.0 cm3 was estimated as quality criteria in both cohorts of plans. The results of our study demonstrated the promising performance of Halcyon for pelvic and lung SBRT for small tumors, although plan-specific QA is required to verify machine performance during plan delivery.

Hypofractionated stereotactic radiotherapy using coplanar VMAT for single small brain metastasis: dosimetric analysis and clinical outcomes

Purpose

To evaluate the dosimetric parameters and clinical outcomes of hypofractionated stereotactic radiotherapy (HSRT) for small brain metastases [BMs; planning target volume (PTV) ≤ 4 cm3) via coplanar volumetric modulated arc therapy (C-VMAT).

Methods

Between March 2019 and February 2023, 68 patients with a single BM treated with Linac-based HSRT (24-39 Gy in three fractions) via C-VMAT and a 3-mm PTV margin were enrolled in this retrospective analysis. A frameless head-neck-shoulder thermoplastic mask, whose immobilization accuracy is inferior to that of specialized mask fixation systems, was used to immobilize patients. Dosimetric parameters and clinical outcomes were evaluated.

Results

C-VMAT provided clinically satisfactory treatment plans, with median gradient index, conformity index, homogeneity index, and PTV coverage values of 4.30, 1.05, 1.28, and 98%, respectively. The median volumes of normal brain tissue receiving 18 Gy, 21 Gy, and 23 Gy were 7.29 cm3, 5.33 cm3, and 4.40 cm3, respectively. High delivery accuracy was observed, with a gamma passing rate ≥90% for all plans. As of June 2023, the median follow-up time was 9.1 months. The intracranial objective response rate and disease control rate were 64% and 96%, respectively. The median intracranial progression-free survival was 26.9 (95% CI, 12.7-41.1) months. The 1- and 2-year local control (LC) rates were 91.5% (95% CI, 80.1%-100%) and 83.2% (95% CI, 64.6%-100%), respectively. The 1- and 2-year intracranial control rates were 70.9% (95% CI, 55.2%-86.6%) and 51.2% (95% CI, 32.6%-69.8%), respectively. Only four irradiated lesions progressed at the end of follow-up. The cerebral radiation necrosis rate of all patients was 7.4%.

Conclusion

C-VMAT HSRT combined with a 3-mm PTV margin is an effective and safe treatment modality for small BMs.

Patterns of failure after stereotactic body radiotherapy to non-spine bone metastases

BACKGROUND AND PURPOSE

Stereotactic body radiotherapy (SBRT) has proven useful for non-spine bone metastases (NSBM). We analyzed local relapse rates and patterns of failure after NSBM-SBRT, contrasting our results with existing contouring guidelines.

MATERIALS AND METHODS

We conducted a retrospective analysis of NSBM-SBRT treatments performed between 2013 and 2024 in a single institution. Clinical, pathologic, and treatment-related data were collected. Failure patterns were assessed based on imaging tests and categorized as in-field, marginal/out-of-field.

RESULTS

Among 119 NSBM-SBRT treatments in 85 patients, the most common primary tumors were prostate (36.1%) and breast cancer (24.4%). The coxal bone was the predominant metastatic site (52.9%). The median follow-up was 32.8 months. OS rates at 1, 2, and 3 years were 90.1%, 83.5%, and 75.8%, respectively. Twenty seven relapses were observed in the treated bone with a median recurrent tumor volume of 9.9 cm3 and a median time to recurrence of 15.1 months. Relapse-free survival in the treated bone was 89.4%, 78.5%, and 74.2% at 1, 2, and 3 years, respectively. Median recurrent tumor volume within the CTV was 50.6% and the median distance from the relapse center to the initial tumor was 11.4 mm.

CONCLUSION

NSBM-SBRT provides effective local control with relapses often occurring near the initial tumor lesion. While adherence to existing contouring guidelines captures most scenarios, consideration of larger CTV expansions may be warranted in cases with poorer prognosis. Further studies are needed to identify risk factors for relapses outside the margins and optimize volume delineation in these scenarios.

The effect of kV imaging dose on PTV and OAR planning constraints in lung SBRT using stereoscopic/monoscopic real-time tumor-monitoring system

PURPOSE

Quantify the impact of additional imaging doses on clinical dose constraints during lung stereotactic body radiotherapy (SBRT) treatment utilizing stereoscopic/monoscopic real-time tumor monitoring.

MATERIALS AND METHODS

Thirty lung SBRT patients treated with the volumetric arc therapy technique were randomly selected from the institutional clinical database. Contours of patients' and computed tomography data were extracted from the Eclipse treatment planning system, along with information regarding the treatment dose. Subsequently, patient-specific three-dimensional real-time imaging dose distributions were computed using a validated Monte Carlo simulation of the ExacTrac imaging. The 3D imaging dose was added to the treatment dose, and the influence of the imaging dose on clinical dose constraints was analyzed for planning target volume (PTV) and various organs at risk (OARs).

RESULTS

Among the 30 patients, 14 patients exhibited one or more failed OAR constraints based solely on the treatment dose, resulting in a total of 24 constraint failures. The addition of the real-time imaging dose altered the pass/fail criteria for one OAR constraint and two PTV constraints. The change in constraint due to additional imaging dose relative to the prescription dose was less than 1% for all patients, except for one case, where it reached 1.9%, which had remained below the threshold of 5% recommended by AAPM TG-180 guidelines. Furthermore, the additional imaging dose relative to the treatment dose resulted in an increase in OAR constraints ranging from 0 to 27% (mean of 0.8%), with nine cases exceeding 5%.

CONCLUSION

The current study represents the first attempt to investigate the impact of additional imaging doses on clinical planning constraints in real-time tumor monitoring during lung SBRT utilizing ExacTrac imaging system. The addition of an imaging dose will likely have minimal clinical impact.

Biological dose-based fractional dose optimization of Bragg peak FLASH-RT for lung cancer treatment

BACKGROUND

The FLASH effect is dose-dependent, and fractional dose optimization may enhance it, improving normal tissue sparing.

PURPOSE

This study investigates the performance of fractional dose optimization in enhancing normal tissue sparing for Bragg peak FLASH radiotherapy (FLASH-RT).

METHODS

15 lung cancer patients, including eight with peripherally located tumors and seven with centrally located tumors, were retrospectively analyzed. A uniform fractionation prescription of 50 Gy in five fractions was utilized, corresponding to a biological equivalent dose (BED) of 100 Gy, calculated using an α/β value of 10 Gy. For each patient, uniform (UFD) and nonuniform fractional dose (non-UFD) plans were designed. In UFD FLASH plans, five multi-energy Bragg peak beams were optimized using single-field optimization, each delivering 10 Gy to the target. In non-UFD FLASH plans, fractional doses were optimized to enhance sparing effects while ensuring the target received a BED comparable to UFD plans. A dose-dependent FLASH enhancement ratio (FER) was integrated with the BED to form the FER-BED metric to compare the UFD and non-UFD plans. An α/β value of 3 Gy was applied for normal tissues in the calculations.

RESULTS

Bragg peak FLASH plans showed high dose conformality for both peripheral and central tumors, with all plans achieving a conformality index (the ratio of the volume receiving the prescribed dose to the CTV volume) below 1.2. In non-UFD plans, fractional doses ranged from 5.0 Gy to 20.0 Gy. Compared to UFD plans, non-UFD plans achieved similar BED coverage (BED98%: 96.6 Gy vs. 97.1 Gy, p = 0.256), while offering improved organ-at-risk sparing. Specifically, the FER-BED15cc for the heart reduced by 10.5% (9.4 Gy vs. 10.5 Gy, p = 0.017) and the V6.7GyFER-BED for the ipsilateral lung decreased by 4.3% (29 .1% vs. 30.4%, p = 0.008). No significant difference was observed in FER-BED0.25cc of spinal cord (UFD: 7.1 Gy, non-UFD: 6.9 Gy, p = 0.626) and FER-BED5cc in esophagus (UFD: 0.4 Gy, non-UFD: 0.4 Gy, p = 0.831).

CONCLUSIONS

Bragg peak FLASH-RT achieved high dose conformality for both peripheral and central tumors. Fractional dose optimization, using a single beam per fraction delivery mode, enhanced normal tissue sparing by leveraging both fractionation and FLASH effects.

Surgery Versus Stereotactic Radiotherapy in Patients over 75 Years Treated for Stage IA-IIA NSCLC

INTRODUCTION

Lobectomy with lymph node dissection is the gold standard treatment for stage IA-IIA Non-Small Cell Lung Cancer (NSCLC). Surgery is responsible for higher early mortality but offers better overall long-term survival. The patient population concerned is often elderly and combines the comorbidities of smoking and age. Several trials have shown good results of stereotactic radiotherapy (SABR) in terms of local control and tolerance in elderly subjects. Our objective is to study the survival and regional control of patients over 75 years treated by surgery or SABR for localized NSCLC.

MATERIALS AND METHOD

We conducted a single-center retrospective study between January 2012 and December 2022 including elderly patients who received surgery or SABR for NSCLC less than 5 cm in size, N0, M0. A cumulative comorbidity index was calculated for each patient, considering severity and impact of treatment. We performed subgroup analyses using CART method to identify factors impacting survival and early death.

RESULTS

After propensity score matching, 127 operated patients were matched to 85 patients treated with SABR. Overall survival at 1 and 5 years for the operated patients was 83.87% and 47.30% compared with 88.8% and 31.5% in the radiotherapy group (p = 0.068). We have identified four factors influencing the incidence of early mortality: gender, World Health Organization Performance status (WHO status), Forced Expiratory Volume in 1 s (FEV1), and treatment group.

CONCLUSIONS

Surgery seems to remain the standard of treatment in terms of overall survival and locoregional recurrence, in a context where SABR nevertheless provides excellent local control and tolerance in the short and long term. In order to improve patient selection, we are proposing for the first time a tool to aid therapeutic decision-making.

A Retrospective Analysis of the First Clinical 5DCT Workflow

BACKGROUND/OBJECTIVES

5DCT was first proposed in 2005 as a motion-compensated CT simulation approach for radiotherapy treatment planning to avoid sorting artifacts that arise in 4DCT when patients breathe irregularly. Since March 2019, 5DCT has been clinically implemented for routine use at our institution to leverage this technological advantage. The clinical workflow includes a quality assurance report that describes the output of primary workflow steps. This study reports on the challenges and quality of the clinical 5DCT workflow using these quality assurance reports.

METHODS

We evaluated all thoracic 5DCT simulation datasets consecutively acquired at our institution between March 2019 and December 2022 for thoracic radiotherapy treatment planning. The 5DCT datasets utilized motion models constructed from 25 fast-helical free-breathing computed tomography (FHFBCTs) with simultaneous respiratory bellows signal monitoring to reconstruct individual, user-specified breathing-phase images (termed 5DCT phase images) for internal target volume contouring. Each 5DCT dataset was accompanied by a structured quality assurance report composed of qualitative and quantitative measures of the breathing pattern, image quality, DIR quality, model fitting accuracy, and a validation process by which the original FHFBCT scans were regenerated with the 5DCT model. Measures of breathing irregularity, image quality, and DIR quality were retrospectively categorized on a grading scale from 1 (regular breathing and accurate registration/modeling) to 4 (irregular breathing and inaccurate registration/modeling). The validation process was graded according to the same scale, and this grade was termed the suitability-for-treatment-planning (STP) grade. We correlated the graded variables to the STP grade. In addition to the quality assurance reports, we reviewed the contour sessions to determine how often 5DCT phase images were used for treatment planning and delivery.

RESULTS

There were 169 5DCT simulation datasets available from 156 patients for analysis. The STP was moderately correlated with breathing irregularity, image quality, and DIR quality (Spearman coefficients: 0.26, 0.30, and 0.50, respectively). Multiple linear regression analysis demonstrated that STP was correlated with regular breathing patterns (p = 0.008), image quality (p < 0.001), and better DIR quality (p < 0.001). 5DCT datasets were used for treatment planning in 82% of cases, while in 12% of cases, a backup image process was used. In total, 6% of image datasets were not used for treatment planning due to factors unrelated to the 5DCT workflow quality.

CONCLUSIONS

The strongest association with STP was with DIR quality grades, as indicated by both Spearman and multiple linear regression analysis, implying that improvements to DIR accuracy and evaluation may be the best route for further improvement to 5DCT. The high rate of 5DCT phase image use for treatment planning showed that the workflow was reliable, and this has encouraged us to continue to develop and improve the workflow steps.

Modeling the Acute Mucosal Toxicity of Fractionated Radiotherapy Combined with the ATM Inhibitor WSD0628

Ataxia Telangiectasia-mutated (ATM) inhibitors are being developed as radiosensitizers to improve the antitumor effects of radiotherapy, but ATM inhibition can also radiosensitize normal tissues. Therefore, understanding the elevated risk of normal tissue toxicities is critical for radiosensitizer development. This study focused on modeling the relationship between acute mucosal toxicity, radiation dose, fractionation schedule, and radiosensitizer exposure. The ATM inhibitor WSD0628 was combined with single or fractionated doses of radiation delivered to the oral cavity or esophagus of Friend Leukemia virus B (FVB) mice. The potentiation by WSD0628 was quantified by a sensitizer enhancement ratio (SER), which describes the changes in radiation tolerance for radiation combined with WSD0628 relative to radiation-only regimens. WSD0628 profoundly enhanced radiation-induced acute oral and esophageal toxicities. For oral mucosal toxicity, the enhancement by WSD0628 with 3 fractions of radiation resulted in an SER ranging from 1.3 (0.25 mg/kg) to 3.1 (7.5 mg/kg). For the 7.5 mg/kg combination, the SER increased with increasing number of fractions from 2.2 (1 fraction) to 4.3 (7 fractions) for oral toxicity and from 2.2 (1 fraction) to 3.6 (3 fractions) for esophageal toxicity, which reflects a loss of the normal tissue sparing benefit of fractionated radiation. These findings were used to develop a modified biologically effective dose model to determine alternative radiation schedules with or without WSD0628 that result in similar levels of toxicity. Successful radiosensitizer dose escalation to a maximally effective therapeutic dose will require careful deliberation of tumor site and reduction of radiation dose volume limits for organs at risk.

Randomized phase III study comparing re-irradiation stereotactic body radiotherapy and conventional radiotherapy for painful spinal metastases: Japan Clinical Oncology Group study JCOG2211 (RESCORE study)

Bone metastases are often associated with pain and can occur in various types of cancer, significantly affecting patients' quality of life. Despite the high response rates to initial conventional radiotherapy in patients with painful spinal metastases, recurrence and inadequate response still occur. Thus, the development of a highly effective strategy for pain recurrence is crucial to improving the quality of life in patients with advanced metastatic cancer. This randomized phase III trial aims to confirm the superiority of re-irradiation with stereotactic body radiotherapy (24 Gy in 2 fractions) over conventional radiotherapy (8 Gy in a single fraction) in achieving a complete pain response at 12 weeks in patients with previously irradiated painful spinal metastases. A total of 158 patients from 33 hospitals will be enrolled in Japan over 3.5 years. This trial has been registered in the Japan Registry of Clinical Trials as jRCTs1030240172 (https://jrct.niph.go.jp/latest-detail/jRCT1030240172).

Stereotactic Radiosurgery for Vestibular Schwannoma - A Case-Based Practice Guide From the Radiosurgery Society

PURPOSE

Vestibular schwannomas (VS) are the most common benign intracranial nerve sheath tumors. Surgery and radiation therapy - particularly stereotactic radiosurgery (SRS) - are the primary treatment options. SRS is the dominant treatment for small- and medium-sized VS and selected larger tumors due to its excellent local control rates and favorable safety profile compared with surgery. However, careful treatment planning is essential, taking into account patient preferences, tumor location and size, symptoms, and anticipated treatment-related toxicity.

METHODS AND MATERIALS

Four clinical VS scenarios have been selected to illustrate the use of SRS, including a unilateral small intracanalicular VS, a large VS with cystic components, reirradiation with SRS after local tumor recurrence, and bilateral VS in the setting of neurofibromatosis type 2-related schwannomatosis.

RESULTS

SRS is an effective and safe treatment modality for the majority of VS cases, requiring careful treatment planning and a thorough understanding of potential limitations and challenges.

CONCLUSIONS

This case-based practice guide aims to provide a concise overview of the treatment of VS with SRS. We present and discuss 4 different clinical scenarios of VS to highlight the pitfalls and best practice recommendations.

Implementing stereotactic arrhythmia radioablation with STOPSTORM.eu consortium support: intermediate results of a prospective Israeli single-institutional trial

BACKGROUND

Ventricular tachycardia (VT) is a life-threatening arrhythmia originating from the heart's ventricles. Traditional treatments include antiarrhythmic medications, implantable cardioverter-defibrillators (ICDs), and catheter ablation. Stereotactic body radiation therapy (SBRT) targeting the arrhythmogenic focus in the left ventricle-stereotactic arrhythmia radioablation (STAR)-is an emerging treatment and may offer a potential solution for patients with refractory VT.

OBJECTIVE

We designed an interventional prospective clinical trial in Israel aligned with the STOPSTORM.eu consortium's benchmarks, recommendations, and directives to assess the safety and efficacy of STAR in patients with refractory VT.

METHODS

Our phase I/II single-institutional trial was approved by the Ministry of Health of Israel for 10 patients, initially assessing safety in the first 3 patients. We included patients with ICDs experiencing symptomatic monomorphic VT after an inadequate response to previous therapies. The primary endpoints were treatment-related serious adverse events and a reduction in VT burden as assessed by ICD interrogation. Secondary outcomes included a reduction in antiarrhythmic medications and changes in quality of life.

RESULTS

From August 2023 to August 2024, 3 patients underwent STAR treatment. The prescription dose was a single fraction of 25 Gy. Planning target volumes were 47.8, 49.7, and 91.8 cc, and treatment was successfully delivered with no grade 3 or higher adverse events reported. Over a follow-up period of 12 months for the first patient and 8 months for the second one, no VT events were recorded after treatment. The third patient died from progressive heart failure 3 months after treatment. Left ventricular ejection fraction remained stable, and no significant radiation-induced inflammatory changes were noted.

CONCLUSION

The initial results of this trial suggest that STAR can reduce VT episodes in patients with refractory VT without severe adverse effects. The study highlights the importance of international collaboration and standardization in pioneering new treatments. Further follow-up and additional patient data will be necessary to confirm these findings and evaluate long-term outcomes, including potential adjustments to antiarrhythmic medication regimens.

Radiation Myelitis Risk After Hypofractionated Spine Stereotactic Body Radiation Therapy

Importance

Stereotactic body radiation therapy (SBRT) for spinal metastases improves symptomatic outcomes and local control compared to conventional radiotherapy. Treatment failure most often occurs within the epidural space, where dose is constrained by the risk of radiation myelitis (RM). Current constraints designed to prevent RM after spine SBRT are derived from limited data.

Objective

To characterize the risk of RM after spine SBRT and to update the dosimetric constraints for preventing it.

Design, Setting, and Participants

This cohort study was conducted in a single tertiary cancer care center with patients treated for spinal metastases from 2014 to 2023. All included participants had undergone spine SBRT, had a minimum of 1-month follow-up with magnetic resonance imaging (MRI), a maximal cord dose to a voxel (Dmax) greater than 0 Gy, and no overlapping prior radiotherapy. In all, 2051 patients received SBRT to 2835 spinal metastases (levels C1-L2) during the study period.

Exposures

Three-fraction spine SBRT to a prescription dose of 27 to 36 Gy.

Main Outcomes and Measures

RM defined as radiographic evidence of spinal cord injury in the treatment field, classified as grade (G) 1 to G4 or G3 to G4 per the Common Terminology Criteria for Adverse Events, version 5.0. Multiple dosimetric parameters of the true spinal cord structure were assessed for an association with risk of RM to determine the important covariates associated with this toxicity.

Results

The analysis included 1423 patients (mean [SD] age, 61.6 [12.9] years; 695 [48.8%] females and 728 [51.1%] males) who received SBRT for 1904 spinal metastases. Among them, 30 cases of RM were identified, 19 of which were classified as G3 to G4. Two years after SBRT, the rate of G1 to G4 RM was 1.8% (95% CI, 1.2%-2.5%) and the rate of G3 to G4 RM was 1.1% (95% CI, 0.7%-1.7%). The minimum dose to the 0.1 cm3 of spinal cord receiving the greatest dose (D0.1cc) was the most important covariate on univariable cause-specific hazards regression for RM (for G3 to G4: hazard ratio, 2.14; 95% CI, 1.68-2.72; P < .001). A true cord D0.1cc of 19.1 Gy and Dmax of 20.8 Gy estimated a 1.0% risk (95% CI, 0.3%-1.6% and 0.4%-1.6%, respectively) of G3 to G4 RM 2 years after SBRT.

Conclusions and Relevance

The findings of this cohort study indicate that a cord (myelogram or MRI-derived) D0.1cc constraint of 19.1 Gy and a Dmax constraint of 20.8 Gy correspond with a 1.0% risk of G3 to G4 RM at 2 years.

Refining Treatment Planning in STereotactic Arrhythmia Radioablation: Benchmark Results and Consensus Statement From the STOPSTORM.eu Consortium

PURPOSE

STereotactic Arrhythmia Radioablation (STAR) showed promising results in patients with refractory ventricular tachycardia. However, clinical data are scarce and heterogeneous. The STOPSTORM.eu consortium was established to investigate and harmonize STAR in Europe. The primary goal of this benchmark study was to investigate current treatment planning practice within the STOPSTORM project as a baseline for future harmonization.

METHODS AND MATERIALS

Planning target volumes (PTVs) overlapping extracardiac organs-at-risk and/or cardiac substructures were generated for 3 STAR cases. Participating centers were asked to create single-fraction treatment plans with 25 Gy dose prescriptions based on in-house clinical practice. All treatment plans were reviewed by an expert panel and quantitative crowd knowledge-based analysis was performed with independent software using descriptive statistics for International Commission on Radiation Units and Measurements report 91 relevant parameters and crowd dose-volume histograms. Thereafter, treatment planning consensus statements were established using a dual-stage voting process.

RESULTS

Twenty centers submitted 67 treatment plans for this study. In most plans (75%) intensity modulated arc therapy with 6 MV flattening filter free beams was used. Dose prescription was mainly based on PTV D95% (49%) or D96%-100% (19%). Many participants preferred to spare close extracardiac organs-at-risk (75%) and cardiac substructures (50%) by PTV coverage reduction. PTV D0.035cm3 ranged from 25.5 to 34.6 Gy, demonstrating a large variety of dose inhomogeneity. Estimated treatment times without motion compensation or setup ranged from 2 to 80 minutes. For the consensus statements, a strong agreement was reached for beam technique planning, dose calculation, prescription methods, and trade-offs between target and extracardiac critical structures. No agreement was reached on cardiac substructure dose limitations and on desired dose inhomogeneity in the target.

CONCLUSIONS

This STOPSTORM multicenter treatment planning benchmark study not only showed strong agreement on several aspects of STAR treatment planning, but also revealed disagreement on others. To standardize and harmonize STAR in the future, consensus statements were established; however, clinical data are urgently needed for actionable guidelines for treatment planning.

Partial Stereotactic Ablative Radiotherapy Boost Before Conventional Radiotherapy (P-SABR) for Large (> 5 cm) Unresectable Stage III Nonsmall Cell Lung Cancer

OBJECTIVE

Stereotactic ablative radiotherapy (SABR) is renowned for its high local control (LC) rates. Nonetheless, for tumors that are either large in volume or in close proximity to critical organs at risk, the application of SABR to the entire tumor becomes impractical. This study aims to evaluate the efficacy and safety of partial SABR boost before conventional radiotherapy (P-SABR) for the treatment of large (> 5 cm) unresectable stage III nonsmall cell lung cancer (NSCLC).

METHODS

From April 2014 to January 2024, 44 patients with > 5 cm unresectable T3-4N0-3M0 stage III NSCLC were analyzed. The median diameter was 9 cm (5.2-22.7 cm). The P-SABR plan is combined with a partial SABR boost part and a conventional fractionated radiotherapy (CFRT) part. In the partial SABR boost plan, the prescription dose for planning target volume (PTV) was 1.8-3 Gy per fraction over 3-4 fractions, and the artificially delineated gross tumor boost volume (GTVb) within GTV received a simultaneously integrated SABR dose (6 or 8 Gy per fraction). In the following CFRT plan, the median dose for the entire PTV was 54 Gy in 22 fractions. For the synthetic P-SABR plan, the median cumulative dose delivered to the PTV was 62.1 Gy, while the median cumulative dose to the GTVb was escalated to 78 Gy.

RESULTS

The median follow-up time was 36 months (95% CI, 14.6-57.4 months). The LC rates at 1 and 2 years were 90.2% and 76.8%, respectively. The median OS was 47.0 months (95% CI, 16.8-77.2 months) and 15.0 months (95% CI, 6.0-24.0 months) for the chemoradiotherapy and radiotherapy groups, respectively. Univariate analysis showed that P-SABR combined with immunotherapy was associated with significantly longer OS (HR, 0.163; 95% CI, 0.038-0.704). Only one (2.3%) patient experienced grade 3 acute pneumonitis.

CONCLUSIONS

The P-SABR treatment has shown a high rate of LC and tolerable toxicity in patients with large unresectable stage III NSCLC.

Impact of diaphragm motion on dosimetry in lower thoracic spine stereotactic body radiotherapy

BACKGROUND AND PURPOSE

Free-breathing computed tomography (FBCT) used in treatment planning for lower thoracic (Th8-Th12) spine stereotactic body radiotherapy (SBRT) can cause deviations between planned and irradiated doses due to diaphragm movement (DM). This study analyzed the dosimetric impact of DM on lower thoracic spine SBRT.

MATERIALS AND METHODS

Data were collected from 19 patients who underwent FBCT and four-dimensional CT (4DCT) during the same session. The 4DCT data were divided into ten respiratory phases (0-90%), and an average CT (AveCT) was reconstructed from them. Using FBCT, target and normal tissues near the diaphragm were contoured and spine SBRT plans with 24-Gy doses in two fractions were created. These plans were applied to each phase of CT and AveCT, with doses recalculated using the same parameters. Actual treatment doses (Deformed AveCT) were estimated by accumulating doses across each 4DCT phase using deformable image registration on the AveCT. Dose-volume histogram (DVH) indices were compared between the FBCT, AveCT, 0% phase, 50% phase, and Deformed AveCT plans.

RESULTS

The mean differences in DVH indices for target and normal tissues were within 2.4 and 2.1%, respectively, when the diaphragm displacement was between -1.6 cm and 2.0 cm, as compared with FBCT. DM displacement showed moderate to strong correlations with DVH differences.

CONCLUSION

Our results indicate that DM has a minor impact on DVH indices if the diaphragm remains within 1.5 cm of the FBCT position.

Treatment Outcome of Brain Metastases from Breast Cancer Following Gamma Knife Radiosurgery: A Retrospective Study in Vietnam

BackgroundGamma Knife radiosurgery has proven to be highly effective for small brain lesions and those with a limited number of metastases. This study aimed to evaluate the treatment outcome of Gamma Knife radiosurgery in Vietnamese breast cancer patients with brain metastasis.MethodsThis retrospective descriptive study included 75 patients treated between January 2019 and December 2023. Eligible patients had 1 to 5 brain lesions ≤ 3 cm, a Karnofsky Performance Status (KPS) score of ≥ 60, and no prior whole-brain radiotherapy or brain tumor resection. Clinical characteristics were documented, and imaging responses were evaluated using RECIST criteria. Overall survival (OS), brain-specific progression-free survival (BSPFS), and overall response rates were analyzed using Kaplan-Meier survival curves and Cox regression.ResultsSeventy-five patients were included in the study, with a median follow-up time of 15.9 months. The median age was 53.0 years (range: 29-73 years), and 39 patients (52%) were HER2-positive. The median total tumor volume per patient was 3.78 cm3. A total of 152 brain tumors were identified, of which 131 (86.2%) were <2 cm in diameter, 36 patients (48.0%) had a single lesion. The intracranial tumor control rates were 96% at 3 months and 92.5% at 6 months. The median overall survival (OS) was 17.2 months (range: 13.7-20.7 months). Multivariate analysis revealed that the total volume of metastatic lesions ≤7.0 cm3, hormone receptor negativity, ≤ 3 lines of systemic treatment before brain metastasis and controlled extracranial metastases were correlated with both BSPFS and OS.ConclusionGamma Knife radiosurgery is an effective treatment for limited brain metastases, demonstrating a high rate of local control over brain lesions, which contributed to the promising survival outcome in Vietnamese breast cancer patients.

Advanced Radiotherapy Technologies in Spine Tumors: What the Surgeon Needs to Know

STUDY DESIGN

Narrative review of existing literature.

OBJECTIVES

Significant technological advancements in radiotherapy planning and delivery have enabled new radiotherapy techniques for the management of spine tumors. The objective of this study was to provide a comprehensive summary of these treatment techniques for practicing spine surgeons.

METHODS

A narrative review of the existing literature on stereotactic body radiation therapy (SBRT) and particle beam therapy (PBT) for the treatment of spine tumors was performed. The characteristics, implementation and evidence supporting these strategies in the management of primary spinal neoplasms were summarized.

RESULTS

The clinical effectiveness of SBRT for the control and symptom palliation of metastatic spinal tumors are well demonstrated in multiple clinical trials. Risks such as fracture, radiculopathy and plexopathy exist after spine SBRT, necessitating an individualized approach in a well experienced multidisciplinary setting. SBRT should be considered a key component of a well-rounded treatment plan for metastatic spine tumors in combination with surgery, vertebral augmentation, and drug therapy, where indicated, to achieve optimal patient outcomes. Additionally, PBT and SBRT are also leading to promising results for primary spine tumors, though comparative effectiveness studies and prospective clinical trials are required to establish these modalities more formally as alternatives to conventionally fractionated photon radiotherapy.

CONCLUSIONS

SBRT and PBT are emerging as effective and well tolerated treatment options for primary and metastatic spine tumors. Additional investigation is needed to personalize these treatment options and further strengthen these approaches as key components in a multidisciplinary approach to the management of spinal neoplasms.

Centralized Quality Assurance of Stereotactic Body Radiation Therapy for the Veterans Affairs Cooperative Studies Program Study Number 2005: A Phase 3 Randomized Trial of Lung Cancer Surgery or Stereotactic Radiotherapy for Operable Early-Stage Non-Small Cell Lung Cancer (VALOR)

PURPOSE

The phase 3 Veterans Affairs Lung Cancer Surgery Or Stereotactic Radiotherapy study implemented centralized quality assurance (QA) to mitigate risks of protocol deviations. This report summarizes the quality and compliance of the first 100 participants treated with stereotactic body radiation therapy (SBRT) in this study.

METHODS AND MATERIALS

A centralized QA program was developed to credential and monitor study sites to ensure standard-of-care lung SBRT treatments are delivered to participants. Requirements were adapted from protocols established by the National Cancer Institute's Image and Radiation Oncology Core, which provides oversight for clinical trials sponsored by the National Cancer Institute's National Clinical Trials Network.

RESULTS

The first 100 lung SBRT treatment plans were reviewed from April 2017 to October 2022. Tumor contours were appropriate in all submissions. Planning target volume (PTV) expansions were less than the minimum 5 mm requirement in 2% of cases. Critical organ-at-risk structures were contoured accurately for the proximal bronchial tree, trachea, esophagus, spinal cord, and brachial plexus in 75%, 92%, 100%, 100%, and 95% of cases, respectively. Prescriptions were appropriate in 98% of cases; 2 central tumors were treated using a peripheral tumor dose prescription while meeting organ-at-risk constraints. PTV V100% (the percentage of target volume that receives 100% or more of the prescription) values were above the protocol-defined minimum of 94% in all but 1 submission. The median dose maximum (Dmax) within the PTV was 125.4% (105.8%-149.0%; SD ± 8.7%), where values reference the percentage of the prescription dose. High-dose conformality (ratio of the volume of the prescription isodose to the volume of the PTV) and intermediate-dose compactness [R50% (ratio of the volume of the half prescription isodose to the volume of the PTV) and D2cm (the maximum dose beyond a 2 cm expansion of the PTV expressed as a percentage of the prescription dose)] were acceptable or deviation acceptable in 100% and 94% of cases, respectively.

CONCLUSIONS

The first 100 participants randomized to SBRT in this study were appropriately treated without safety concerns. A response to the incorrect prescriptions led to preventative measures without further recurrences. The program was developed in a health care system without prior experience with a centralized radiation therapy QA program and may serve as a reference for other institutions.

AAPM task group report 135.B: Quality assurance for robotic radiosurgery

AAPM Task Group Report 135.B covers new technology components that have been added to an established radiosurgery platform and updates the components that were not well covered in the previous report. Considering the current state of the platform, this task group (TG) is a combination of a foundational task group to establish the basis for new processes/technology and an educational task group updating guidelines on the established components of the platform. Because the technology discussed in this document has a relatively small user base compared to C-arm isocentric linacs, the authors chose to emphasize the educational components to assist medical physicists who are new to the technology and have not had the opportunity to receive in-depth vendor training at the time of reading this report. The TG has developed codes of practice, introduced QA, and developed guidelines which are generally expected to become enduring practice. This report makes prescriptive recommendations as there has not been enough longitudinal experience with some of the new technical components to develop a data-based risk analysis.

FCB-CHOPS: An Evolution of a Commonly Used Acronym for Evaluating Radiation Treatment Plans

Checklists have been used across many fields as a systematic framework to reduce human error and improve safety. In radiation oncology, the CB-CHOP acronym was previously developed as a tool to aid physicians in assessing the quality of radiation treatment plans for approval. This manuscript updates the acronym for the modern era with the addition of F and S to create FCB-CHOPS: fusion, contours, beams, coverage, heterogeneity, organs at risk, prescription, and dose summation. These 2 additions reflect the evolution and importance of image fusion to aid in the delineation of targets and organs at risk and dose summation to reflect the increased incidence of reirradiation and the need to consider prior treatment courses in the final plan evaluation. Utilization of this and similar checklists is critical in maintaining high-quality and safe radiation oncology treatments.

Radiation Therapy for Brain Tumors in Dogs and Cats

External beam radiation therapy (RT) has become the standard of care for non-resectable or post-operative incompletely excised brain tumors in dogs and cats due to its relatively low side effect profile and increasing availability. This article reviews the indications for, expected outcomes of and possible toxicities associated with RT, follow-up care recommendations after RT, and publications about specific tumor types in dogs and cats with brain tumors.

Ensuring High Quality Treatment Plans with a Plan Quality Review Checklist

Treatment plan quality is a crucial component for a successful outcome of radiation therapy treatments. As the complexity of radiation therapy planning and delivery techniques increases, the role of the medical physicist in assessing treatment plan quality becomes more critical. Integrating plan quality review throughout the treatment planning process allows improvements without delaying treatment or rushing to produce changes at the last minute. In this work, we aim to provide practical check items for physicists to reference when assessing treatment plan quality with a critical eye, asking questions such as "is this the best dose distribution feasible for this patient?," "could we change any planning parameters to improve plan quality?," and "could we change the planning strategy for this particular patient or for future patients?"; and to work with planners and physicians to create a multidisciplinary collaborative culture that achieves the best plan feasible for every patient. We tabulate the features that affect plan quality in each process step and check details for individual items. This report is aimed at medical physicists, planners, radiation oncologists, and other professionals who are involved in treatment planning.