Tumor Control and Toxicity for Common Stereotactic Body Radiation Therapy Dose-Fractionation Regimens in Stage I Non-Small Cell Lung Cancer

International Patterns of Practice for Stereotactic Ablative Radiotherapy for Early-Stage Non-Small Cell Lung Cancer: Are We All in Sync?: Global patterns of practice for SABR for early-stage NSCLC

PURPOSE

To generate an understanding of the similarities and variations in international practice patterns for stereotactic ablative radiotherapy (SABR) in early-stage non-small cell lung cancer (NSCLC).

METHODS

An online survey was conducted from October to December 2023, addressing general clinical and technical considerations for lung SABR, and for 5 specific anatomical NSCLC locations (peripheral, abutting chest wall, near brachial plexus, central, and ultra-central). Invitations to participate were extended through email and were distributed on social media.

RESULTS

The survey was completed by 255 radiation oncologists, each representing a single institution across 51 countries. Respondents reported treating a median of 20 cases annually. A total of 38% of participants reported using single-fraction SABR, and 54% applied an upper limit on the maximum dose (Dmax). Among those who applied a Dmax limit, 58% reported a Dmax threshold at ≥130% of the prescription, though this limit varied by region and national economy status. Respondents from low- and middle-income countries were less likely to set a Dmax limit at ≥130% (30% vs. 66%, p < 0.01) and less likely to use single-fraction SABR (14% vs. 44%, p < 0.01). Higher annual SABR patient volumes were associated with higher Dmax adoption (г = 0.23, p < 0.01). Across the 5 clinical scenarios presented; 57 distinct dose regimens were recommended. The most common regimen in each scenario was: 54 Gy in 3 fractions for peripheral tumors, 50 Gy in 5 fractions for apical, central, and abutment of chest wall, and 60 Gy in 8 fractions for ultra-central tumors. Approximately two-thirds of practices recommend a biologically effective dose (BED10) <100 Gy for one or more anatomical sites.

CONCLUSION

The findings reveal considerable variation in global SABR practice. These differences highlight the need for further data to guide prescription practices, and an international experts' consensus may be beneficial to standardize practice.

Assessing proton plans with 3 different beam lines vs photon plans for early-stage lung cancer

To compare proton plans (IMPT) to VMAT plans and intercompare proton plans using 3 different spot sizes with robustness: cyclotron-generated proton beams (CPB) (σ: 2.7-7.0 mm), linear accelerator proton beams (LPB) (σ: 2.9-5.5 mm), and linear accelerator proton mini beams (LPMB) (σ: 0.9-3.9 mm) for the treatment of early-stage lung cancer. Twenty-two lesions from a total of twenty patients with early-stage lung cancer, originally treated with SBRT, were replanned using CPBs, LPBs, LPMBs, and VMAT using the same treatment planning system and dose calculation algorithm. The average intensity projected CTs (AIP-CT) were used for planning and 3D robust optimization was used for all proton plans. Conformity index (CI), homogeneity index (HI), R50, lung V20 Gy, and mean lung dose were compared among all proton plan types and with VMAT plans. Set-up uncertainties of ±5 mm and ±3.5% range uncertainty were included in the IMPT robust optimization and evaluation, using V100%Rx > 98% of the ITV. The Wilcoxon signed-rank test was used to evaluate statistical differences between VMAT plans and all proton plan types. When compared to VMAT plans, all proton plans generally show improvement in CI, HI, Lung V20 Gy, Mean lung dose, and R50. The LPMB plans showed the most improvement from VMAT plans. Comparison between CPB and linear accelerator proton plans showed statistical significance (p < 0.05). R50 and mean lung dose for the CPB, LPB and LPMB plans were 3.6 ± 0.9, 3.1 ± 0.8 and 2.6 ± 0.6; 2.2 ± 1.1 Gy, 1.9 ± 1 Gy and 1.6 ± 0.9 Gy, respectively (p < 0.05). The mean R50 and mean lung dose from the VMAT plans were 4.1 ± 0.4 and 3.8 ± 2 Gy, respectively. The V20 Gy (%) of lung and mean lung dose were improved across all proton plans when compared with those of VMAT plans. When evaluated for robustness in the worst-case scenario at V100%Rx of the ITV > 98%, average ITV coverage of 98.6 ± 0.3%, 98.6 ± 0.6%, and 98.9 ± 0.6% were achieved for CPB plans, LPB plans, and LPMB plans, respectively. With decreased spot size, the LPB and LPMB plans are excellent alternatives to VMAT and cyclotron-generated proton plans with reduced dose to normal tissue and improved plan quality for early-stage lung cancer treatments.

Stereotactic Lung Re-Irradiation After a First Course of Stereotactic Radiotherapy with In-Field Relapse: A Valuable Option to Be Considered

BACKGROUND/OBJECTIVES

Stereotactic body radiation therapy (SBRT) has demonstrated high local control rates for inoperable early-stage lung cancers. However, 5-15% of patients experience local relapse within the irradiated volume after treatment, with limited curative salvage options. The aim of this review is to clarify the modalities and outcomes after a second course of SBRT in patients with local relapse after a previous lung SBRT.

METHODS

An exhaustive literature review was conducted to identify, analyse and summarise the results of 21 main studies.

RESULTS

Local repeat lung SBRT after a first course of SBRT showed a favourable local control at 1 and 2 years, ranging from 70 to 90% and 45 to 80%, respectively. Good overall survival rates were also observed at 1 and 2 years reaching up to 95% and 85%, respectively. Toxicity was rare but could be severe, with cases of Grade 4 and 5 toxicities (≈5%). An important dose relationship was observed between re-irradiation dose levels and local control, highlighting the importance of precise dosing. The cumulative doses impacting organs at risk were similarly associated with increased radiation-induced toxicity. Central lung lesions presented a higher risk for severe side effects compared to peripheral ones.

CONCLUSIONS

In conclusion, repeat lung SBRT after a first course of SBRT represents a feasible treatment option in cases of local recurrence. In order to limit severe toxicity, patients must be carefully selected, and particular attention should be given to cumulative doses to organs at risk, as well as tumour location. Thus, further investigations are still needed to refine the optimal parameters for SBRT lung re-irradiation.

The effect of increasing the prescribed dose in stereotactic body radiotherapy for primary lung cancer without lymph node metastasis

BACKGROUND

This study aimed to identify the efficacy of increasing the dose of stereotactic body radiotherapy (SBRT) for lung cancer.

METHOD AND MATERIALS

Patients who received SBRT for primary lung cancer between 2002 and 2021 were evaluated retrospectively. The patients were categorized into the 48, 50, and 55 Gy groups according to the prescribed dose. Analyses were performed for all matched patients.

RESULT

A total of 323 patients underwent SBRT for lung lesions at doses of 48, 50, and 55 Gy in four fractions. The median follow-up period in the 55 Gy group (32.3 months; Interquartile range (IQR), 15.1-54.1 months, P = 0.01) was significantly shorter than in the 48 Gy (47.0 months; IQR, 16,2-107.7 months) and 50 Gy (78.9 months; IQR 47.2-104.2 months) groups. The 3-year local progression-free survival (LPFS) was 90% in the 55 Gy group (95% confidence interval (CI), 62.4%-94.0%), 75.7% in the 48 Gy group (62.1%-85.0%), and 79.1% in the 50 Gy group (62.2%-89.1%). LPFS in the 55 Gy group was significantly higher than that in the 48 Gy group (hazard ratio (HR), 0.40; 95% CI, 0.20-0.79; P = 0.025). There is no significant difference in the local control rate between the 55 Gy group and the 50 Gy group (HR 0.60, CI 0.27-1.39). After propensity score matching, the 3-year LPFS in the 55 Gy group was 88.3% (CI, 71.2-95.5%). LPFS in the 55 Gy group did not significantly differ from that of the 48 Gy group (HR, 0.47; CI, 0.17-1.35) and the 50 Gy group (HR, 0.83; CI, 0.28-2.51).

CONCLUSION

We conducted the analysis using propensity score matching. It was not apparent whether there was a significant difference in the effect of increasing the dose, owing to a lack of power caused by the small number of cases after propensity score matching. A prospective study is in progress, and the results are awaited.

Deep Learning-Guided Dosimetry for Mitigating Local Failure of Patients With Non-Small Cell Lung Cancer Receiving Stereotactic Body Radiation Therapy

PURPOSE

Non-small cell lung cancer (NSCLC) stereotactic body radiation therapy with 50 Gy/5 fractions is sometimes considered controversial, as the nominal biologically effective dose (BED) of 100 Gy is felt by some to be insufficient for long-term local control of some lesions. In this study, we analyzed such patients using explainable deep learning techniques and consequently proposed appropriate treatment planning criteria. These novel criteria could help planners achieve optimized treatment plans for maximal local control.

METHODS AND MATERIALS

A total of 535 patients treated with 50 Gy/5 fractions were used to develop a novel deep learning local response model. A multimodality approach, incorporating computed tomography images, 3-dimensional dose distribution, and patient demographics, combined with a discrete-time survival model, was applied to predict time to failure and the probability of local control. Subsequently, an integrated gradient-weighted class activation mapping method was used to identify the most significant dose-volume metrics predictive of local failure and their optimal cut-points.

RESULTS

The model was cross-validated, showing an acceptable performance (c-index: 0.72, 95% CI, 0.68-0.75); the testing c-index was 0.69. The model's spatial attention was concentrated mostly in the tumors' periphery (planning target volume [PTV] - internal gross target volume [IGTV]) region. Statistically significant dose-volume metrics in improved local control were BED Dnear-min ≥ 103.8 Gy in IGTV (hazard ratio [HR], 0.31; 95% CI, 015-0.63), V104 ≥ 98% in IGTV (HR, 0.30; 95% CI, 0.15-0.60), gEUD ≥ 103.8 Gy in PTV-IGTV (HR, 0.25; 95% CI, 0.12-0.50), and Dmean ≥ 104.5 Gy in PTV-IGTV (HR, 0.25; 95% CI, 0.12-0.51).

CONCLUSIONS

Deep learning-identified dose-volume metrics have shown significant prognostic power (log-rank, P = .003) and could be used as additional actionable criteria for treatment planning in NSCLC stereotactic body radiation therapy patients receiving 50 Gy in 5 fractions. Although our data do not confirm or refute that a significantly higher BED for the prescription dose is necessary for tumor control in NSCLC, it might be clinically effective to escalate the nominal prescribed dose from BED 100 to 105 Gy.

Factors associated with cavity formation after stereotactic body radiation therapy for peripheral early-stage lung cancer

PURPOSE

This retrospective study aimed to identify the factors associated with cavity formation after SBRT in peripheral early-stage lung cancer patients. We analyzed the occurrence of cavity changes after SBRT.

MATERIALS AND METHODS

We examined 99 cases with T1-T2aN0 peripheral non-small cell lung cancer treated with SBRT from 2004 to 2021. Patients underwent respiratory function tests, including diffusing capacity for carbon monoxide (DLco), before treatment. The median observation period was 35 months (IQR 18-47.5 months). Treatment involved fixed multi-portal irradiation in 67% of cases and VMAT in 33%. The total radiation doses ranged from 42 to 55 Gy, delivered over 4 to 5 fractions.

RESULTS

Cavity formation occurred in 14 cases (14.1%), appearing a median of 8 months after SBRT. The cavity disappeared in a median of 4 months after formation. High DLco and total radiation dose were identified as factors significantly associated with cavity formation. There have been no confirmed recurrences to date, but one patient developed a lung abscess.

CONCLUSION

Although cavity formation after SBRT for peripheral early-stage lung cancer is infrequent, it can occur. This study showed high DLco and total radiation dose to be factors significantly associated with cavity formation. These findings can be applied to optimizing radiation therapy (RT) and improving patient outcomes. Further research is needed to determine the optimal radiation dose for patients with near-normal DLco for whom surgery is an option. This study provides valuable insights into image changes after RT.

Treatment outcomes of stereotactic body radiation therapy for pulmonary metastasis from sarcoma: a multicenter, retrospective study

PURPOSE

The aim of this study was to evaluate the treatment outcomes and potential dose-response relationship of stereotactic body radiation therapy (SBRT) for pulmonary metastasis of sarcoma.

MATERIALS AND METHODS

A retrospective review of 39 patients and 71 lesions treated with SBRT from two institutions was performed. The patients had oligometastatic or oligoprogressive disease, or were receiving palliation. Doses of 20-60 Gy were delivered in 1-5 fractions. The local control per tumor (LCpT) was evaluated according to the biologically effective dose with an α/β ratio of 10 (BED₁₀) of the prescribed dose (BED₁₀ ≥ 100 Gy vs. BED₁₀ < 100 Gy). Clinical outcomes per patient, including local control per patient (LCpP), pulmonary progression-free rate (PPFR), any progression-free rate (APFR), and overall survival (OS) were investigated.

RESULTS

The median follow-up period was 27.2 months. The 1-, 2-, and 3-year LCpT rates for the entire cohort were 100.0%, 88.3%, and 73.6%, respectively. There was no observed difference in LCpT between the two BED₁₀ groups (p = 0.180). The 3-year LCpP, PPFR, APFR, and OS rates were 78.1%, 22.7%, 12.9%, and 83.7%, respectively. Five (12.8%) patients with oligometastasis had long-term disease-free intervals, with a median survival period of 40.7 months. Factors that were associated with a worse prognosis were oligoprogression (vs. oligometastasis), multiple pulmonary metastases, and simultaneous extrathoracic metastasis.

CONCLUSION

SBRT for pulmonary metastasis of sarcoma is effective. Some selected patients may achieve durable response. Considerations of SBRT indication and disease extent may be needed as they may influence the prognosis.

Accelerated hypofractionated radiotherapy with 3 Gy per fraction for central/ultra-central lung tumors: toxicity to mediastinal organs

BACKGROUND

Accelerated hypofractionated radiotherapy with 3 Gy per fraction is routinely performed for central lung tumors in Japan. However, the tolerable doses to mediastinal organs at risk during this procedure are unclear. This study aimed to clarify the rate of toxicities and tolerable doses to mediastinal organs.

METHODS

Patients treated with accelerated hypofractionated radiotherapy using a total dose of 60-75 Gy, with 3 Gy per fraction, for central lung tumors (July 2009-April 2021) were retrospectively reviewed. We extracted patients who received ≥30 Gy irradiation to each mediastinal organ and analyzed dosimetric factors, including doses to 0.03, 0.5, 1, 4 and 10 mL of each organ, in relation to grade 3-5 toxicities, except for radiation pneumonitis.

RESULTS

In total, 251 organs in 91 (ultra-central, 24) lesions were analyzed, with a median follow-up duration of 26 months (range, 4-94). The prescribed doses were 75/72/69/66/63/60 Gy for 52/14/16/3/2/4 lesions, respectively. Grade 3 bronchopulmonary hemorrhage was confirmed in two (2.2%) patients, whose tumors were located ultra-centrally. The two patients with toxicity received up to 74.5 and 71.6 Gy to the bronchus. Among patients who received 70 Gy or more to the bronchus, the incidence rate was 7% (2/28 patients).

CONCLUSION

The rate of severe toxicities was low (2.2%). Although we did not identify the dose tolerance of the organs, because of the low incidence rate, we did note that doses of >70 Gy to the bronchus were likely to cause bronchopulmonary hemorrhage.

Stereotactic Body Radiation Therapy for Pulmonary Metastasis from Colorectal Adenocarcinoma: Biologically Effective Dose 150 Gy is Preferred for Tumour Control

AIMS

To compare the local control rate of pulmonary metastatic lesions in colorectal adenocarcinoma treated with stereotactic body radiation therapy (SBRT) using a biologically effective dose with an α/β ratio of 10 (BED₁₀) of 150 Gy.

MATERIALS AND METHODS

We analysed 231 pulmonary metastatic lesions from colorectal adenocarcinoma treated with SBRT in 135 patients. The patients were referred for the control of oligometastatic or oligoprogressive disease in the lungs. A dose of 40-60 Gy in three to eight fractions was delivered. The local control per tumour (LCpT) by BED₁₀ was evaluated. The local control per patient (LCpP), pulmonary progression-free survival (PPFS), any progression-free survival (APFS) and overall survival were also reported as clinical outcomes.

RESULTS

A significant difference was observed in the LCpT between the BED₁₀ groups (P < 0.001). The 1-, 2- and 3-year LCpT were 38.9%, 25.9% and 25.9% in BED₁₀ < 100 group; 84.1%, 62.6% and 60.4% in 100 ≤ BED₁₀ < 150 Gy group; and 97.3%, 94.9% and 85.2% in BED₁₀ ≥ 150 Gy group, respectively. BED₁₀ ≥ 150 Gy remained significant in the multivariate analysis of LCpT. The 3-year LCpP, PPFS, APFS and overall survival rates were 62.7%, 26.5%, 24.8% and 67.7%, respectively. Oligoprogression (versus oligometastasis), multiple pulmonary nodules and extrapulmonary metastasis were associated with a poor prognosis.

CONCLUSION

A BED₁₀ ≥ 150 Gy may be required to achieve sufficient local control. The indications for SBRT and the extent of metastatic disease should be assessed for proper estimation of the clinical outcomes.

Role of Stereotactic Radiation Therapy in Operable and Inoperable Early-Stage Non-small Cell Lung Cancer

OPINION STATEMENT

Radiation therapy is becoming an increasingly important part of non-small cell lung cancer (NSCLC) management. Approximately 60% of all cancer patients require radiation therapy (RT) as part of their treatment. For lung cancer, this number is even higher, reaching approximately 77% of all patients, from radical to palliative modalities of RT. This percentage may even be underestimated, as it may not account for the more recent use of RT in oligometastatic lung cancer patients. Thus, we can estimate that each year there will be approximately 21,890 new lung cancer patients in the USA requiring RT. These numbers are expected to continue to rise, as lung cancer radiation techniques continue to improve. There is growing interest in determining the best treatment options for early-stage NSCLC patients. There is well-established data showing the benefit of RT for inoperable patients, and more recent encouraging data even in operable patients.

High-dose stereotactic body radiotherapy using CyberKnife® for stage I peripheral lung cancer: a single-center retrospective study

Background

This retrospective study was performed to evaluate the efficacy and toxicity of high-dose stereotactic body radiotherapy (SBRT) using a CyberKnife® for patients with stage I peripheral non-small cell lung cancer (NSCLC).

Methods

Ninety-six patients with stage I peripheral NSCLC who were treated with SBRT using a CyberKnife® from August 2010 to June 2019 were identified and included in this study. Local control (LC), local progression-free survival (LPFS), progression-free survival (PFS), overall survival (OS), and late toxicity were evaluated. Potential risk factors associated with LC, LPFS, PFS, or OS were investigated by univariate analyses.

Results

Data of 96 patients were examined. The prescribed dose to the tumor was 54 Gy in 3 fractions in 91 patients and 60 Gy in 3 fractions in 5 patients. The median follow-up duration was 27 months. The 2-year LC, LPFS, PFS, and OS rates were 97%, 88%, 84%, and 90%, respectively. The T factor was significantly correlated with LC, LPFS, and PFS. The 2-year LC rate for patients with T1a/T1b and T1c/T2a disease was 100% and 90%, respectively (p < 0.05), and the 2-year PFS rate for the corresponding patients was 95% and 65%, respectively (p < 0.001). One patient (1%) developed grade 3 radiation pneumonitis.

Conclusions

High-dose SBRT using a CyberKnife® for stage I peripheral NSCLC produced favorable treatment outcomes with acceptable late toxicity. Further studies are needed to improve the treatment outcomes for patients with T1c/T2a disease.

Single-fraction 34 Gy Lung Stereotactic Body Radiation Therapy Using Proton Transmission Beams: FLASH-dose Calculations and the Influence of Different Dose-rate Methods and Dose/Dose-rate Thresholds

Purpose

Research suggests that in addition to the dose-rate, a dose threshold is also important for the reduction in normal tissue toxicity with similar tumor control after ultrahigh dose-rate radiation therapy (UHDR-RT). In this analysis we aimed to identify factors that might limit the ability to achieve this "FLASH"-effect in a scenario attractive for UHDR-RT (high fractional beam dose, small target, few organs-at-risk): single-fraction 34 Gy lung stereotactic body radiation therapy.

Methods and Materials

Clinical volumetric-modulated arc therapy (VMAT) plans, intensity modulated proton therapy (IMPT) plans and transmission beam (TB) plans were compared for 6 small and 1 large lung lesion. The TB-plan dose-rate was calculated using 4 methods and the FLASH-percentage (percentage of dose delivered at dose-rates ≥40/100 Gy/s and ≥4/8 Gy) was determined for various variables: a minimum spot time (minST) of 0.5/2 ms, maximum nozzle current (maxN) of 200/40 0nA, and 2 gantry current (GC) techniques (energy-layer based, spot-based [SB]).

Results

Based on absolute doses 5-beam TB and VMAT-plans are similar, but TB-plans have higher rib, skin, and ipsilateral lung dose than IMPT. Dose-rate calculation methods not considering scanning achieve FLASH-percentages between ∼30% to 80%, while methods considering scanning often achieve <30%. FLASH-percentages increase for lower minST/higher maxN and when using SB GC instead of energy-layer based GC, often approaching the percentage of dose exceeding the dose-threshold. For the small lesions average beam irradiation times (including scanning) varied between 0.06 to 0.31 seconds and total irradiation times between 0.28 to 1.57 seconds, for the large lesion beam times were between 0.16 to 1.47 seconds with total irradiation times of 1.09 to 5.89 seconds.

Conclusions

In a theoretically advantageous scenario for FLASH we found that TB-plan dosimetry was similar to that of VMAT, but inferior to that of IMPT, and that decreasing minST or using SB GC increase the estimated amount of FLASH. For the appropriate machine/delivery parameters high enough dose-rates can be achieved regardless of calculation method, meaning that a possible FLASH dose-threshold will likely be the primary limiting factor.

A guide for managing patients with stage I NSCLC: deciding between lobectomy, segmentectomy, wedge, SBRT and ablation-part 4: systematic review of evidence involving SBRT and ablation

Background

Clinical decision-making for patients with stage I lung cancer is complex. It involves multiple options [lobectomy, segmentectomy, wedge, stereotactic body radiotherapy (SBRT), thermal ablation], weighing multiple outcomes (e.g., short-, intermediate-, long-term) and multiple aspects of each (e.g., magnitude of a difference, the degree of confidence in the evidence, and the applicability to the patient and setting at hand). A structure is needed to summarize the relevant evidence for an individual patient and to identify which outcomes have the greatest impact on the decision-making.

Methods

A PubMed systematic review from 2000-2021 of outcomes after SBRT or thermal ablation vs. resection is the focus of this paper. Evidence was abstracted from randomized trials and non-randomized comparisons with at least some adjustment for confounders. The analysis involved careful assessment, including characteristics of patients, settings, residual confounding etc. to expose degrees of uncertainty and applicability to individual patients. Evidence is summarized that provides an at-a-glance overall impression as well as the ability to delve into layers of details of the patients, settings and treatments involved.

Results

Short-term outcomes are meaningfully better after SBRT than resection. SBRT doesn't affect quality-of-life (QOL), on average pulmonary function is not altered, but a minority of patients may experience gradual late toxicity. Adjusted non-randomized comparisons demonstrate a clinically relevant detriment in long-term outcomes after SBRT vs. surgery. The short-term benefits of SBRT over surgery are accentuated with increasing age and compromised patients, but the long-term detriment remains. Ablation is associated with a higher rate of complications than SBRT, but there is little intermediate-term impact on quality-of-life or pulmonary function tests. Adjusted comparisons show a meaningful detriment in long-term outcomes after ablation vs. surgery; there is less difference between ablation and SBRT.

Conclusions

A systematic, comprehensive summary of evidence regarding Stereotactic Body Radiotherapy or thermal ablation vs. resection with attention to aspects of applicability, uncertainty and effect modifiers provides a foundation for a framework for individualized decision-making.

An Analysis of Clinical Toxic Effects and Quality of Life as a Function of Radiation Dose and Volume After Lung Stereotactic Body Radiation Therapy

Purpose

To analyze clinical toxicity and quality-of-life (QOL) outcomes among patients with stage I non-small cell lung cancer (NSCLC) after stereotactic body radiation therapy (SBRT) as a function of radiation dose and volume parameters.

Methods and Materials

In this institutional review board-approved study, 55 patients with stage I NSCLC who received SBRT (12 Gy × 4) and completed QOL forms were analyzed. Clinical symptoms and QOL outcomes were measured at baseline and at 3, 6, 12, 18, 24, and 36 months after SBRT. Clinical toxicity was graded using the Common Terminology Criteria for Adverse Events, version 4.0. Quality of life was followed using the validated Functional Assessment of Cancer Therapy-Lung-Trial Outcome Index (FACT-L-TOI) instrument. Dosimetric parameters including the mean lung radiation dose and the volume of normal lung receiving greater than 5, 10, 13, or 20 Gy (V₅, V₁₀, V₁₃, and V₂₀) were measured from the radiation treatment plan. Student t tests and Pearson correlation analyses were used to examine the relationships between radiation lung metrics and clinically meaningful changes in QOL and/or clinical toxic effects. The Kaplan-Meier method was used to estimate rates of local control (LC), disease-free survival (DFS), and overall survival (OS).

Results

With a median follow-up of 24 months, the 3-year LC, DFS, and OS were 93%, 65%, and 84%, respectively, with a 5.5% rate of grade-3 toxic effects and no grade 4 or 5 toxic effects. Clinically meaningful declines in patient-reported QOL (FACT-L-TOI, lung cancer subscale, physical well-being, and/or functional well-being) posttreatment significantly correlated with increased dosimetric parameters such as V₁₀, V₁₃, and V₂₀.

Conclusion

Although lung SBRT was associated with excellent LC and minimal clinical toxic effects for early-stage NSCLC, clinically meaningful declines in QOL were significantly correlated with increasing lung dose and volume parameters.

Impact of local recurrence on cause-specific death after stereotactic body radiotherapy for early-stage non-small cell lung cancer: dynamic prediction using landmark model

PURPOSE

The purpose of this study was to assess the impact of local recurrence (LR) on cause-specific death (CSD) in patients with non-small cell lung cancer (NSCLC) treated with stereotactic body radiotherapy (SBRT). A dynamic prediction model that incorporated LR as a time-dependent covariate was used.

METHODS AND MATERIALS

This study included 535 stage I (cT1-T2aN0M0) NSCLC patients treated with SBRT from two institutions. We developed a landmark dynamic prediction model to estimate the probability of a CSD. This model determined the probability of surviving for an additional 3 years at different prediction time points during follow-up, given the history of recurrence status. The baseline covariates included in the model were age, sex, T stage, and histology, while the time-dependent covariates were LR and regional and/or distant recurrence (RDR) status.

RESULTS

Overall, 137 patients (25.6%) died of lung cancer within a median follow-up of 4.1 years. Of the 195 patients who developed recurrence, 28, 125, and 42 patients had LR only, RDR only, and both, respectively. The landmark model showed that older age, advanced T stage, LR, and RDR were significantly associated with an increased risk of subsequent CSD. Among these covariates, LR (odds ratio [OR], 8.5; 95% confidence interval [CI], 6.0-12.0; P < .001) and RDR (OR, 11.6; 95% CI, 9.1-14.9; P < .001) demonstrated strong effects on CSD within 3 years after the prediction time points. The dynamic prediction provided information on the probability of future CSD according to individual recurrence status during follow-up.

CONCLUSIONS

Dynamic prediction using the landmark model showed that LR had a substantial impact on subsequent CSD, which was comparable to that of RDR. This result supports the notion that strategies to improve local control are reasonable.

Safety and efficacy of 10-fraction hypofractionated radiation therapy for non-small cell lung cancer

Purpose

To investigate the safety and efficacy of hypofractionated radiation therapy (HFRT) in patients with non-small cell lung cancer who are unfit for surgery or stereotactic body radiation therapy (SBRT) at our institution.

Materials and Methods

From May 2007 to December 2018, HFRT was used to treat 68 lesions in 64 patients who were unsuitable for SBRT because of central tumor location, large tumor size, or contiguity with the chest wall. The HFRT schedule included a dose of 50–70 Gy delivered in 10 fractions over 2 weeks. The primary outcome was freedom from local progression (FFLP), and the secondary endpoints included overall survival (OS), disease-free survival, and toxicities.

Results

The median follow-up period was 25.5 months (range, 5.3 to 119.9 months). The FFLP rates were 79.8% and 67.8% at 1 and 2 years, respectively. The OS rates were 82.8% and 64.1% at 1 and 2 years, respectively. A larger planning target volume was associated with lower FFLP (p = 0.023). Dose escalation was not associated with FFLP (p = 0.964). Four patients (6.3%) experienced grade 3–5 pulmonary toxicities. Tumor location, central or peripheral, was not associated with either grade 3 or higher toxicity.

Conclusion

HFRT with 50–70 Gy in 10 fractions demonstrated acceptable toxicity; however, the local control rate can be improved compared with the results of SBRT. More studies are required in patients who are unfit for SBRT to investigate the optimal fractionation scheme.

A 54 Gy in three fractions of stereotactic body radiotherapy using CyberKnife for T1b-2aN0M0 pathologically confirmed non-small cell lung cancer

OBJECTIVE

Optimal dose-fractionation regimen of stereotactic body radiotherapy for peripheral early-stage non-small cell lung cancer remains unclear. We retrospectively investigated outcomes of stereotactic body radiotherapy using CyberKnife at 54 Gy in three fractions in 26 patients (median age: 76 years) with pathologically confirmed T1b-T2aN0M0 non-small cell lung cancer.

METHODS

A 54 Gy in three fractions was prescribed to cover the 99% of gross tumor volume. We estimated cumulative local control, progression-free survival and overall survival rates (Kaplan-Meier method), and toxicity (Common Toxicity Criteria for Adverse Events, version 5.0).

RESULTS

All the tumors were located at peripheral area of lung. Mean distance from chest wall to tumor was 6.5 mm (range: 0-32 mm). The patients' pathological diagnoses were: adenocarcinoma: n = 18, squamous cell carcinoma: n = 7 and non-small cell carcinoma: n = 1. Their stages were T1b: n = 9, T1c: n = 14 and T2a: n = 3. Median follow-up was 24 months (range: 6-54). Cumulative 2-year effect rates were local control: 100%, progression-free survival 70% and overall survival: 92%. Twenty patients developed grade one radiation pneumonitis, but grade 2 or greater radiation pneumonitis was not observed.

CONCLUSIONS

We found CyberKnife-stereotactic body radiotherapy for pathologically confirmed T1b-T2aN0M0 non-small cell lung cancer to be effective and safe. However, these results should be validated with a larger patient cohort and prospective follow-up monitoring.

Multiblock Discriminant Analysis of Integrative 18F-FDG-PET/CT Radiomics for Predicting Circulating Tumor Cells in Early-Stage Non-small Cell Lung Cancer Treated With Stereotactic Body Radiation Therapy

PURPOSE

The main objective of the present study was to integrate 18F-FDG-PET/CT radiomics with multiblock discriminant analysis for predicting circulating tumor cells (CTCs) in early-stage non-small cell lung cancer (ES-NSCLC) treated with stereotactic body radiation therapy (SBRT).

METHODS

Fifty-six patients with stage I NSCLC treated with SBRT underwent 18F-FDG-PET/CT imaging pre-SBRT and post-SBRT (median, 5 months; range, 3-10 months). CTCs were assessed via a telomerase-based assay before and within 3 months after SBRT and dichotomized at 5 and 1.3 CTCs/mL. Pre-SBRT, post-SBRT, and delta PET/CT radiomics features (n = 1548 × 3/1562 × 3) were extracted from gross tumor volume. Seven feature blocks were constructed including clinical parameters (n = 12). Multiblock data integration was performed using block sparse partial least squares-discriminant analysis (sPLS-DA) referred to as Data Integration Analysis for Biomarker Discovery Using Latent Components (DIABLO) for identifying key signatures by maximizing common information between different feature blocks while discriminating CTC levels. Optimal input blocks were identified using a pairwise combination method. DIABLO performance for predicting pre-SBRT and post-SBRT CTCs was evaluated using combined AUC (area under the curve, averaged across different blocks) analysis with 20 × 5-fold cross-validation (CV) and compared with that of concatenation-based sPLS-DA that consisted of combining all features into 1 block. CV prediction scores between 1 class versus the other were compared using the Wilcoxon rank sum test.

RESULTS

For predicting pre-SBRT CTCs, DIABLO achieved the best performance with combined pre-SBRT PET radiomics and clinical feature blocks, showing CV AUC of 0.875 (P = .009). For predicting post-SBRT CTCs, DIABLO achieved the best performance with combined post-SBRT CT and delta CT radiomics feature blocks, showing CV AUCs of 0.883 (P = .001). In contrast, all single-block sPLS-DA models could not attain CV AUCs higher than 0.7.

CONCLUSIONS

Multiblock integration with discriminant analysis of 18F-FDG-PET/CT radiomics has the potential for predicting pre-SBRT and post-SBRT CTCs. Radiomics and CTC analysis may complement and together help guide the subsequent management of patients with ES-NSCLC.

Improving geometric sparing and therapeutic effectiveness of lung SBRT for central and ultra-central tumors

The use of stereotactic body radiotherapy (SBRT) for central- and ultra-central lung tumors is a major therapeutic challenge since there are trade-offs between delivering adequate dose to the tumor and minimizing toxicity to critical mediastinal organs. This work investigates improving the therapeutic effectiveness of such SBRT treatments by enhancing the geometric sparing of normal tissue and systematically applying a planning target volume (PTV) margin smaller than the conventional values. Using plans from 10 previously SBRT-treated patients, we retrospectively created highly conformal plans with a reduced PTV margin of 2 mm and compared them to the clinical plans with a standard 5 mm PTV margin. We compared various dosimetric and biological parameters. We calculated the geometrical sparing factor (GSF) (ratio of biological dose between normal tissue and targets) for the mediastinal organs and the uncomplicated tumor control probability (UTCP) for the esophagus. We tracked tumor fraction doses using cone-beam computed tomography (CBCT) images. With geometric sparing, the median dose for critical mediastinal organs (proximal bronchial tree, great vessels, esophagus, and heart) dropped by 10 Gy (p ≤ 0.006). Dose sparing for the spinal cord and chest wall was 5 Gy and 8 Gy, respectively (p = 0.002). The geometrical sparing factor (GSF) dropped by 50% for the esophagus and the proximal bronchial tree (PBT) and 40% for the great vessels (p < 0.05). The CBCT fractional tumor dose varied by 2.7% (0.2 Gy) for the initially intended treatment volume and 4% (0.3 Gy) when accounting for daily volume changes. The expected delivered dose was above the prescribed value. Systematically reducing the PTV margin to 2 mm in lung SBRT of central and ultra-central tumors is feasible and ensures consistency in contouring and dose prescribing. It allows safe delivery of highly conformal treatments with significantly higher therapeutic effectiveness, potentially reducing treatment-related complications. Consequently, it may enable safer dose escalation, more effective fractionations, and safer management of retreatments and treatments of multiple synchronous lung tumors.

Late Toxicity and Long-Term Local Control in Patients With Ultra-Central Lung Tumours Treated by Intensity-Modulated Radiotherapy-Based Stereotactic Ablative Body Radiotherapy With Homogenous Dose Prescription

AIMS

To report late toxicity and long-term outcomes of intensity-modulated radiotherapy (IMRT)-based stereotactic ablative body radiotherapy (SABR) in patients with ultra-central lung tumours.

MATERIALS AND METHODS

This is a single-institution retrospective analysis of patients treated with SABR for ultra-central tumours between May 2008 and April 2016. Ultra-central location was defined as tumour (GTV) abutting or involving trachea, main or lobar bronchi. Respiratory motion management and static-field dynamic-IMRT were used, with dose prescribed homogeneously (maximum <120%). Descriptive analysis, Kaplan-Meier method, log-rank test and Cox regression were used to assess outcomes.

RESULTS

Sixty-five per cent of patients had inoperable primary non-small cell lung cancer and 35% had lung oligometastases. The median age was 72 (range 34-85) years. The median gross tumour volume and planning target volume (PTV) were 19.6 (range 1.7-203.3) cm³ and 57.4 (range 7.7-426.6) cm³, respectively. The most commonly used dose fractionation was 60 Gy in eight fractions (n = 51, 87.8%). Median BED₁₀ for D98%PTV and D2%PTV were 102.6 Gy and 115.06 Gy, respectively. With a median follow-up of 26.5 (range 3.2-100.5) months, fatal haemoptysis occurred in five patients (8.7%), of which two were directly attributable to SABR. A statistically significant difference was identified between median BED₃ for 4 cm³ of airway, for patients who developed haemoptysis versus those who did not (147.4 versus 47.2 Gy, P = 0.005). At the last known follow-up, 50 patients (87.7%) were without local recurrence. Freedom from local progression at 2 and 4 years was 92 and 79.8%, respectively. The median overall survival was 34.3 (95% confidence interval 6.1-61.6) months. Overall survival at 2 and 4 years was 55.1 and 41.2%, respectively.

CONCLUSION

In patients with high-risk ultra-central lung tumours, IMRT-based SABR with homogenous dose prescription achieves high local control, similar to that reported for peripheral tumours. Although fatal haemoptysis occurred in 8.7% of patients, a direct causality with SABR was evident in only 3%. Larger studies are warranted to ascertain factors associated with outcomes, especially toxicity, and identify patients who would probably benefit from this treatment.

IR-Surviving NSCLC Cells Exhibit Different Patterns of Molecular and Cellular Reactions Relating to the Multifraction Irradiation Regimen and p53-Family Proteins Expression

Simple Summary

For the first time, we demonstrated that the significant decrease in p63/p73 expression together with the absence of functional p53 could underlie an increase in the fraction of polyploid cells, transformation rates, and the glycolytic NAD(P)H production in multifraction X-ray radiation exposure (MFR)-surviving cancer cells, providing conditions for radioresistance associated with epithelial–mesenchymal transition (EMT)-like process activation. During radiation therapy (RT), the treatment dose, fractionation, and dose limits for organs at risk (OARs) do not change between patients and are still prescribed mainly based on the Tumor, Node, Metastasis (TNM) stage, performance status, and comorbidities, taking no account of the tumor biology. Our data once again emphasize that non-small cell lung cancer (NSCLC) therapy approaches should become more personalized according to RT regimen, tumor histology, and molecular status of critical proteins.

Abstract

Radiotherapy is a primary treatment modality for patients with unresectable non-small cell lung cancer (NSCLC). Tumor heterogeneity still poses the central question of cancer radioresistance, whether the presence of a particular cell population inside a tumor undergoing a selective outgrowth during radio- and chemotherapy give rise to metastasis and tumor recurrence. In this study, we examined the impact of two different multifraction X-ray radiation exposure (MFR) regimens, fraction dose escalation (FDE) in the split course and the conventional hypofractionation (HF), on the phenotypic and molecular signatures of four MFR-surviving NSCLC cell sublines derived from parental A549 (p53 wild-type) and H1299 (p53-null) cells, namely A549FR/A549HR, H1299FR/H1299HR cells. We demonstrate that sublines surviving different MFR regimens in a total dose of 60 Gy significantly diverge in their molecular traits related to irradiation regimen and p53 status. The observed changes regarding radiosensitivity, transformation, proliferation, metabolic activity, partial epithelial-to-mesenchymal transition (EMT) program activation and 1D confined migratory behavior (wound healing). For the first time, we demonstrated that MFR exposure led to the significant decrease in the expression of p63 and p73, the p53-family members, in p53null cells, which correlated with the increase in cell polyploidy. We could not find significant differences in FRA1 expression between parental cells and their sublines that survived after any MFR regimen regardless of p53 status. In our study, the FDE regimen probably causes partial EMT program activation in MFR-survived NSCLC cells through either Vimentin upregulation in p53null or an aberrant N-cadherin upregulation in p53wt cells. The HF regimen likely less influences the EMT activation irrespectively of the p53 status of MFR-survived NSCLC cells. Our data highlight that both MFR regimens caused overall higher cell transformation of p53null H1299FR and H1299HR cells than their parental H1299 cells. Moreover, our results indicate that the FDE regimen raised the radioresistance and transformation of MFR-surviving NSCLC cells irrespectively of their p53 status, though the HF regimen demonstrated a similar effect on p53null NSCLC cells only. Our data once again emphasize that NSCLC therapy approaches should become more personalized according to radiation therapy (RT) regimen, tumor histology, and molecular status of critical proteins.

Analysis of the efficacy and safety of iodine-125 seeds implantation in the treatment of patients with inoperable early-stage non-small cell lung cancer

Purpose

To evaluate the efficacy and safety of iodine-125 (¹²⁵I) seeds implantation for inoperable early-stage non-small cell lung cancer (NSCLC).

Material and methods

PubMed, Cochrane Library, Embase, China Biology Medicine disc (CBM), China National Knowledge Infrastructure (CNKI), and Wanfang Data were searched from inception until April 2020. Data were collected concerning overall survival, short-term efficacy, and complications. Meta-analysis was performed using R software (version 3.6.3).

Results

Nine studies involving 308 patients were included. Meta-analysis showed that the 1-, 2-, and 3-year survival rates were 0.98% (95% CI: 0.95-0.99%), 0.83% (95% CI: 0.77-0.89%), and 0.65% (95% CI: 0.55-0.75%), respectively; short-term local control rate (LCR) and effective rates were 0.99% (95% CI: 0.98-1.00%) and 0.92% (95% CI: 0.83-0.98%), respectively; 1-, 2-, and 3-year LCRs were 0.96% (95% CI: 0.83-1.00%), 0.94% (95% CI: 0.85-0.99%), and 0.95% (95% CI: 0.76-1.00%), respectively. Sub-group analysis of the prescribed dose found that when the prescribed dose was > 120 Gy, short-term efficacy and 1-year LCR were increased significantly (p < 0.01). The incidence of bleeding, pneumothorax, and radiation lung injury was 0.14% (95% CI: 0.07-0.21%), 0.19% (95% CI: 0.11-0.28%), and 0.00% (95% CI: 0.00-0.03%), respectively. Two studies involving 106 patients compared ¹²⁵I seeds combined with chemotherapy versus chemotherapy alone for NSCLC. Results showed that compared with chemotherapy alone, ¹²⁵I seeds combined with chemotherapy could improve short-term LCR (RR = 1.34, 95% CI: 1.09-1.65%, p = 0.005) and short-term effective rate (RR = 1.49, 95% CI: 1.14-1.96%, p = 0.004).

Conclusions

¹²⁵I seeds implantation is safe and effective approach for the treatment of inoperable early-stage NSCLC, but high-quality clinical research is still needed to further confirm the findings.

Stereotactic lung reirradiation for local relapse: A case series

Introduction

Local recurrence after lung SBRT for early stage NSCLC is rare but its treatment remains a challenge due to limited surgical options. We report a case series of 5 patients treated by stereotactic lung salvage reirradiation for local relapse after a previous lung SBRT.

Material and methods

Included patients presented an isolated primary lung relapse within at least the 50% isodose of the previous SBRT treatment. Typical reirradiation schedule was 60 Gy in 8 fractions at isodose 80% and was delivered by Cyberknife® using Synchrony® fiducial tracking system. Dose summations were performed to evaluate the safety of the reirradiation.

Results

We identified 5 patients presenting peripheral lesions. All reirradiated lesions were locally controlled after a median follow-up of 11.1 months (6,7-12,2), while PFS at 6 months was 60% (n = 3). We did not notice any Grade 3 or more acute or late adverse event.

Conclusion

We observed encouraging short-term outcome of lung SBRT reirradiation in patients presenting isolated local relapse of an early-stage NSCLC. Further studies are necessary to confirm the safety and efficiency of this salvage treatment approach.

Stereotactic Radiation for Lung Cancer: A Practical Approach to Challenging Scenarios

Stereotactic body radiation therapy (SBRT) is an effective and well-tolerated treatment for medically inoperable patients with early stage NSCLC. SBRT is a noninvasive treatment involving the delivery of ablative radiation doses with high precision in the course of a few treatments. Relative to conventionally fractionated radiation, SBRT achieves superior local control and survival. SBRT use has increased dramatically in the past 15 years and is currently considered the standard of care in cases of inoperable early stage NSCLC. It is being increasingly applied to more complex patient populations at higher risk of treatment-related toxicity. In these more complex patients, there is an increasing need to balance patient and treatment factors in selecting the optimal patients for SBRT. Here, we review several challenging clinical scenarios often encountered in thoracic multidisciplinary tumor boards.

Hypofractionation in Early Stage Non-Small Cell Lung Cancer

Radiation treatment of early stage nonsmall cell lung cancer has evolved over the past 2 decades to progressively more hypofractionated treatment courses. Results comparable to surgical resection are seen with stereotactic body radiotherapy, which is now the standard of care for medically inoperable patients, and a treatment option for operable patients as well. Understanding of the optimal radiation dose and fractionation are evolving, especially for central tumors which have higher treatment toxicity than peripheral tumors.

Dose and fractionation schedules in radiotherapy for non-small cell lung cancer

In the field of radiotherapy (RT), the issues of total dose, fractionation, and overall treatment time for non-small cell lung cancer (NSCLC) have been extensively investigated. There is some evidence to suggest that higher treatment intensity of RT, when given alone or sequentially with chemotherapy (CHT), is associated with improved survival. However, there is no evidence that the outcome is improved by RT at a higher dose and/or higher intensity when it is used concurrently with CHT. Moreover, some reports on the combination of full dose CHT with a higher biological dose of RT warn of the significant risk posed by such intensification. Stereotactic body radiotherapy (SBRT) provides a high rate of local control in the management of early-stage NSCLC through the use of high ablative doses. However, in centrally located tumors the use of SBRT may carry a risk of serious damage to the great vessels, bronchi, and esophagus, owing to the high ablative doses needed for optimal tumor control. There is a similar problem with moderate hypofractionation in radical RT for locally advanced NSCLC, and more evidence needs to be gathered regarding the safety of such schedules, especially when used in combination with CHT. In this article, we review the current evidence and questions related to RT dose/fractionation in NSCLC.

The development and external validation of an overall survival nomogram in medically inoperable centrally located early-stage non-small cell lung carcinoma

BACKGROUND AND PURPOSE

Current nomograms predicting survival prognosis after stereotactic body radiation therapy (SBRT) in non-small cell lung cancer (NSCLC) are based on peripherally located tumors. However, patients with a central lung tumor tend to be older, the tumor is often larger and fraction-schedules are risk-adapted. Therefore, we developed and externally validated a nomogram to predict overall survival (OS) in patients having centrally located early-stage NSCLC treated with SBRT.

MATERIALS AND METHODS

Patients who underwent SBRT for centrally located NSCLC were identified and baseline characteristics were obtained. A nomogram was built to predict 6-month, 1-, 2- and 3-year OS using Cox proportional hazards model. The model building procedure was validated using bootstrap sampling. To determine generalizability, external validation was performed on a cohort of patients with central NSCLC treated with SBRT from another center. Discriminatory ability was measured with the concordance index (C-index) and calibration plots were used to compare Kaplan-Meier-estimated and nomogram-predicted OS.

RESULTS

The nomogram was built on data of 220 patients and consisted of the following variables: PTV, age, WHO performance status, tumor lobe location and ultracentral location. The C-index of the nomogram (corrected for optimism) was moderate at 0.64 (95% confidence interval (CI) 0.59-0.69). Calibration plots showed favorable predictive accuracy. The external validation showed acceptable validity with a C-index of 0.62 (95% CI 0.61-0.64).

DISCUSSION

We developed and externally validated the first nomogram to estimate the OS-probability in patients with centrally located NSCLC treated with SBRT. This nomogram is based on 5 patient and tumor characteristics and gives an individualized survival prediction.

Stereotactic body radiation therapy using CyberKnife for T1N0M0 lung cancer patients with severe pulmonary dysfunction

We retrospectively investigated the efficacy and safety of stereotactic body radiotherapy (SBRT) for T1N0M0 lung cancer using CyberKnife (CK) among 13 patients with severe pulmonary dysfunction which was defined as forced expiratory volume in 1 s (FEV1.0) of <1 L. The prescribed dose was 54 Gy in 3 fractions but adjusted for some patients if their tumors were in close proximity to the organs at risk (54 Gy/3 fractions: n = 11; 50 Gy/5 fractions: n = 1; 60 Gy/8 fractions: n = 1). During follow up (median follow-up: 27 months), we evaluated local control, overall survival and toxicity, using diagnostic imaging and laboratory tests. The patients' median FEV1.0 was 0.84 L. Of the 13 patients, 3 were diagnosed as having lung cancer histologically and 10 diagnosed clinically. Their 2-year rates for overall survival and local control were 89 and 100%, respectively. So far, we have seen no adverse effects of grade 2 or higher. We concluded that CK-SBRT is effective and well tolerated for T1N0M0 lung cancer, even in patients with severe pulmonary dysfunction, but should be further evaluated with a larger cohort and longer follow-up periods.

Nodal recurrences after stereotactic body radiotherapy for early stage non-small-cell lung cancer

Lobectomy is considered the standard of care for early stage non-small-cell lung cancer. However, for those patients who remain unfit to undergo surgery due to advanced age, poor performance status, comorbidities, poor pulmonary reserve or a combination of these are now treated with stereotactic body radiation therapy (SBRT). Due to its noninvasive nature, lower cost, lower toxicity, reduced recovery time and equivalent efficacy, even medically operable patients are attracted to the option of SBRT despite the lack of level I evidence. Thus, studying the incidence and patterns of recurrence after SBRT help in understanding the magnitude of the problem, risk factors associated with the different patterns of recurrence, and aid in devising strategies to prevent them in future. Nodal recurrences are not uncommon after SBRT and can potentially lead to further seeding for distant metastases and ultimately poor survival. This review is aimed at reviewing the published data on the incidence of nodal recurrences after SBRT and compare it to surgery, identify potential risk factors for recurrence, salvage treatment options and prevention strategies.

Five- Versus Ten-Fraction Regimens of Stereotactic Body Radiation Therapy for Primary and Metastatic NSCLC

INTRODUCTION

At our institution, stereotactic body radiotherapy (SBRT) has commonly been prescribed with 50 Gy in 5 fractions and in select cases, 50 Gy in 10 fractions. We sought to evaluate the impact of these 2 fractionation schedules on local control and survival outcomes.

METHODS

We reviewed patients treated with SBRT with 50 Gy/5 fraction or 50 Gy/10 fraction for early-stage non-small cell lung cancer (NSCLC) and metastatic NSCLC. Cumulative incidence of local failure (LF) was estimated using competing risk methodology. Progression-free survival (PFS) and overall survival (OS) were estimated using the Kaplan-Meier method only for patients with stage I disease.

RESULTS

Of the 353 lesions, 300 (85%) were treated with 50 Gy in 5 fractions and 53 (15%) with 10 fractions. LFs at 3 years were 6.5% and 23.9% and Kaplan-Meier estimate of median time to LF was 17.5 months and 26.2 months, respectively. Multivariable analysis revealed increasing planning target volume (hazard ratio 1.01, P = .04) as an independent predictor of increased LF, but tumor size, ultracentral location, and 10 fractions were not. Among patients with stage I NSCLC (n = 298), overall median PFS was 35.6 months and median OS was 42.4 months. There was no difference in PFS or OS between the 2 treatment regimens for patients with stage I NSCLC. Low rates of grade 3+ toxicity were observed, with 1 patient experiencing grade 3 pneumonitis after a 5-fraction regimen of SBRT.

CONCLUSION

Dose-fractionation schemes with BED₁₀ ≥ 100 Gy provide superior local control and should be offered when meeting commonly accepted constraints. If those regimens appear unsafe, 50 Gy in 10 fractions may provide acceptable compromise between tumor control and safety with relatively durable control, and minimal negative impact on long-term survival.

[Stereotaxic radiotherapy of primary extracranial tumors]

Stereotactic radiotherapy is a fundamental change from the conventional fractionated radiotherapy and represents a new therapeutic indication. Stereotactic radiotherapy is now a standard of care for inoperable patients or patients who refuse surgery. The results are encouraging with local control and survival rates very high in selected populations. The rate of late toxicity remains acceptable. Good tolerability makes it appropriate even for elderly and frail patients. In these fragile patients or in certain specific clinical situations, different surgical, radiotherapy or interventional radiology attitudes can be discussed on a case-by-case basis. These situations are considered in this article for the pulmonary, hepatic and prostatic localizations.

SBRT combined with PD-1/PD-L1 inhibitors in NSCLC treatment: a focus on the mechanisms, advances, and future challenges

Immune checkpoint inhibitors targeting programmed cell death 1 (PD-1), programmed cell death ligand-1 (PD-L1), and others have shown potent clinical efficacy and have revolutionized the treatment protocols of a broad spectrum of tumor types, especially non–small-cell lung cancer (NSCLC). Despite the substantial optimism of treatment with PD-1/PD-L1 inhibitors, there is still a large proportion of patients with advanced NSCLC who are resistant to the inhibitors. Preclinical and clinical trials have demonstrated that radiotherapy can induce a systemic antitumor immune response and have a great potential to sensitize refractory “cold” tumors to immunotherapy. Stereotactic body radiation therapy (SBRT), as a novel radiotherapy modality that delivers higher doses to smaller target lesions, has shown favorable antitumor effects with significantly improved local and distant control as well as better survival benefits in various solid tumors. Notably, research has revealed that SBRT is superior to conventional radiotherapy, possibly because of its more powerful immune activation effects. Thus, PD-1/PD-L1 inhibitors combined with SBRT instead of conventional radiotherapy might be more promising to fight against NSCLC, further achieving more favorable survival outcomes. In this review, we focus on the underlying mechanisms and recent advances of SBRT combined with PD-1/PD-L1 inhibitors with an emphasis on some future challenges and directions that warrant further investigation.

Prognostic factors of local control and disease free survival in centrally located non-small cell lung cancer treated with stereotactic body radiation therapy

Background: Stereotactic body radiation therapy (SBRT) results in high local control (LC) rates in patients with non-small cell lung cancer (NSCLC). For central lung tumors, risk-adapted fractionation schedules are used and underdosage to the Planned Target Volume (PTV) is often accepted to respect the dose constraints of the organs at risk in order to avoid high rates of toxicity. The purpose of this study was to analyze the effect of PTV underdosage and other possible prognostic factors on local- and disease control after SBRT in patients with central lung tumors.Material and Methods: Patients with centrally located NSCLC treated with SBRT were included. The doses were converted into biologically equivalent dose using α/β-value of 10 Gy (BED₁₀). Underdosage to the PTV was defined as the (percentage of) PTV receiving less than 100 Gy BED₁₀; (%)PTV < 100 BED₁₀. Potential prognostic factors for LC and Disease Free Survival (DFS) were evaluated using Cox regression analysis.Results: Two hundred and twenty patients received ≤12 fractions of SBRT. LC-rates were 88% at 2 years and 81% at 3 years. Twenty-seven patients developed a local recurrence. Both the PTV < 100 BED₁₀ and %PTV < 100 BED₁₀ were not prognostic for LC. Tumor size and forced expiratory volume in 1 second (FEV₁) were independently prognostic for LC. Disease progression was reported in 75 patients with DFS-rates of 66% at 2 years and 56% at 3 years. Disease recurrence was independent significantly associated with larger tumor diameter, lower lobe tumor location and decreased FEV₁. Grade 4-5 toxicity was reported in 10 patients (8 with ultra-central tumors) and was fatal in at least 3 patients.Conclusion: Decrease in tumor coverage was not correlated with the local recurrence probability. The LC and DFS were promising after SBRT of centrally located NSCLC with tumor size, FEV₁ and tumor location (for DFS only) as prognostic factors.

Pulmonary function in stereotactic body radiotherapy with helical tomotherapy for primary and metastatic lung lesions

AIMS

This retrospective study reports outcomes after stereotactic body radiation therapy (SBRT) as delivered by helical tomotherapy (HT) for lung lesions. It promotes a dose escalation program.

METHODS

Histological and/or radiological findings and/or case histories identified 41 primary and 15 metastatic lesions. Thirty patients received 40 Gy in 5 fractions (BED 72 Gy_10Gy) and 26 50 Gy in 5 fractions (BED 100Gy_10Gy). Primary end point was lung toxicity. Secondary end points were respiratory function, local control and local progression-free survival.

RESULTS

Acute toxicity developed in 18/56 patients and late toxicity in 8/54. Median FEV-1 variations versus baseline were - 0.5% (range - 16 to + 43%) at 6 months and - 4.00% (range - 42 to + 18%) at 24 months. Median DLCO variations versus baseline were - 1% (range - 38 to + 36%) at 6 months and - 12.2% (range - 48 to + 11%) at 24 months. At 6 months, a significant positive correlation emerged between FEV-1 change and KPS (p = 0.047). At 24 months, a significant negative correlation emerged between FEV-1 change and the ipsilateral lung V5 (p = 0.006). A low baseline DLCO correlated with more marked DLCO worsening at 6 months (p = 0.012). At 24 months, DLCO worsening correlated significantly with the median contralateral lung dose (p = 0.003). At the last checkup, 23 patients were in complete remission, 16 were in partial remission, 5 had stable disease, and 7 were in relapse. Median follow-up was 12 months (range 5-56).

CONCLUSIONS

In patients with lung disease, SBRT, as delivered by HT, was well tolerated and provided good local control.

Recurrence After Stereotactic Body Radiation Therapy Versus Lobectomy for Non-Small Cell Lung Cancer

BACKGROUND

Although lobectomy remains the standard of care for early-stage non-small cell lung cancer, several studies suggest equipoise between lobectomy and stereotactic body radiation therapy (SBRT). However randomized evidence is lacking. We compared outcomes of early-stage non-small cell lung cancer patients treated with lobectomy or SBRT.

METHODS

We included clinical T1-2N0 non-small cell lung cancer treated with lobectomy or SBRT to a biologically effective dose of ≥100 Gy₁₀. We used Cox proportional hazards and nearest-neighbor propensity score (2:1) matching to adjust for confounders. Kaplan-Meier curves were used to assess survival and recurrence.

RESULTS

We identified 554 patients treated with lobectomy (n = 389) or SBRT (n = 165) at our institution between 2008 and 2018. After propensity score matching, there were 132 SBRT patients and 85 lobectomy patients. SBRT was associated with increased local recurrence (hazard ratio [HR], 6.80; 95% confidence interval [CI], 1.92-24.10; P = .003) and regional nodal recurrence (HR, 2.58; 95% CI, 1.17-5.68; P = .018), and with worse overall survival (HR, 2.00; 95% CI, 1.21-3.32; P = .007) and progression-free survival (HR, 2.34; 95% CI, 1.50-3.67; P < .001). There was no difference in distant recurrence (HR, 1.19; 95% CI, 0.57-2.52; P = .64).

CONCLUSIONS

We found superior outcomes in patients with early-stage non-small cell lung cancer treated with lobectomy compared with SBRT, including locoregional control. These findings should be interpreted with caution because of selection bias but underscore the importance of robust randomized prospective data to clarify the relative efficacy of these modalities.

Effects of the recurrence pattern on patient survival following SABR for stage I lung cancer

Background: Information on the effect of the recurrence pattern on survival for stage I lung cancer following stereotactic ablative radiotherapy (SABR) is limited.Materials and Methods: The recurrence pattern was analyzed for 100 consecutive stage I non-small-cell lung cancer patients treated with SABR using predominantly 12 Gy × 4. Recurrences were classified as local, regional lymph nodes and distant. Distant recurrences included recurrences in the lung and outside the chest. Single lung recurrences were named solitary, if no other location was involved. Kaplan-Meier survival estimates were calculated for different locations of recurrence. Clinical and dosimetrical factors affecting survival were also analyzed.Results: Median follow-up was 32 months (3-123), median age 70 years (49-95). In total, 31 patients had recurrences after a median 21 months (4-60): 5 local; 10 regional; 8 distant outside the chest; 25 non-local lung recurrences, of which 15 were single - 10 of which solitary - and 10 multiple lung nodules. Patients with a solitary lung recurrence had longer survival compared to local or distant recurrences (p = .04 each), and compared to multiple lung nodules (p = .09). 3-year local recurrence-free survival was 92%, disease-free survival 69% and overall survival 59%. On multivariate analysis, disease-free survival was associated with statin use (p = .038) and tumor location (p = .035). Smoking history predicted overall survival (p < .0006).Conclusions: A total of 81% of recurrences involved the lungs. Patients with solitary lung recurrences/second primary lung cancers had the longest overall survival suggesting definitive treatment should be considered. The effects of statin use need to be explored further.

[Minimally Invasive Therapies for Early Stage Non-small Cell Lung Cancer]

肺癌是目前全球最常见的癌症和癌症死亡的主要原因，其中非小细胞肺癌（non-small-cell lung cancer, NSCLC）约占肺癌总数的85%。随着计算机断层扫描（computed tomography, CT）等影像学筛查手段得到不断普及，肺癌的病理类型从以往以晚期中央型肺鳞癌为主，转变为现在的以早期周围型磨玻璃样结节等为表现的肺腺癌为主。肺癌的早诊早治有着重要意义，而微创介入技术的不断发展完善，使得肺癌治疗有了更多的选择，例如立体定向放射、经皮穿刺消融、支气管介入等。本文将就目前临床常见的这些微创介入治疗的作用原理、优势、不足及展望做一评述。

Validation of RTOG 0813 Proximal Bronchial Tree Constraints for Pulmonary Toxicity With Stereotactic Body Radiation Therapy for Central Non-small Cell Lung Cancer

PURPOSE

Clinical validation of protocol-specified dosimetric constraints for the proximal bronchial tree (PBT) is limited for central non-small cell lung cancer treated with stereotactic body radiation therapy. We sought to validate Radiation Therapy Oncology Group (RTOG) PBT constraints with a large institutional data set.

METHODS AND MATERIALS

Lesions ≤2 cm from the PBT treated with definitive stereotactic body radiation therapy from 2009 to 2016 were identified from a prospective registry of 1462 patients. Every PBT dose and volume combination, ranging from 0 cGy to 8000 cGy in increments of 10 cGy and volumes ranging from 0.03 cm³ to 50 cm³ in increments of 0.03 cm³, was analyzed. The sensitivity and specificity of these endpoints for identifying pulmonary toxicity were calculated. Pulmonary toxicity was classified as pneumonitis or nonpneumonitis toxicity (NPT) (fistula, stenosis, necrosis, hemoptysis, clinically significant pleural effusion). The optimal dosimetric predictor was chosen by calculation of F-score (highest sensitivity and specificity).

RESULTS

The study included 132 patients, with 26.0-month median follow-up. Eight grade ≥2 NPT (2 grade 5) and 8 grade 2 pneumonitis toxicities were observed. The PBT dosimetric endpoint with the highest F-score for identification of grade 2 to 5 NPT was D0.03cc ≤5000 cGy and that for grade 3 to 5 NPT was D0.33cc ≤4710 cGy, with sensitivity and specificity of 87.5% and 76.6% and 100.0% and 85.7%, respectively. Applying the RTOG 0813 PBT constraints to our data set achieved a sensitivity and specificity of 33.3% and 92.1% for D4cc ≤1800 cGy and 37.5% and 92.7% for D0.03cc ≤5250 cGy for identification of grade 2 to 5 NPT. A PBT dosimetric correlation for pneumonitis toxicity could not be identified.

CONCLUSIONS

This novel dosimetric analysis validates current RTOG constraints and emphasizes high-dose, small-volume constraints as better predictors for NPT. We demonstrated that a slightly lower maximum point dose PBT constraint may be optimal for identification of NPT. Validation of these findings in a larger cohort of patients with longer follow-up is necessary.

Repeat stereotactic body radiation therapy (SBRT) for salvage of isolated local recurrence after definitive lung SBRT

PURPOSE

Optimal management of isolated local recurrences after stereotactic body radiation therapy (SBRT) for early non-small cell lung cancer (NSCLC) is unknown and literature describing repeat SBRT for in-field recurrences after initial SBRT are sparse. We investigate the safety and efficacy of salvage SBRT for isolated local failures after initial SBRT for NSCLC.

METHODS/MATERIALS

Patients receiving SBRT for isolated local recurrence after initial SBRT for early NSCLC were identified using a prospective registry. Both courses were 3-5 fractions with a biologically effective dose (BED10) of ≥100 Gy. Local failure was defined as within 1 cm of the initial planning target volume (PTV) or an overlap of the ≥25% isodose lines of the first and second treatments. Failures >1 cm beyond the PTV and without ≥25% overlap, or with additional recurrence sites were excluded. Kaplan-Meier analysis was used to estimate survival.

RESULTS

A total 21 patients receiving salvage SBRT from 2008 to 2017 were identified. Median interval from initial SBRT to salvage SBRT was 23 months (7-52). Six patients (29%) had central tumors. Median follow-up time from salvage SBRT was 24 months (3-60). Median overall survival after salvage was 39 months. After reirradiation, two-year primary tumor control was 81%, regional nodal control was 89%, distant control was 75% and overall survival was 68%. Grade 2 pneumonitis occurred in 2 patients (10%) and grade 2 chest wall toxicity in 4 patients (19%). No grade 3+ toxicity was observed.

CONCLUSIONS

Salvage SBRT for isolated local failures after initial SBRT appears safe, with low treatment-related toxicity and encouraging rates of tumor control.

Radiotherapy in Lung Cancer: Current and Future Role

Lung cancer is divided into two subgroups concerning its natural course and treatment strategies as follows: non-small cell lung cancer (NSCLC) and small cell lung cancer (SCLC). In this review, for NSCLC, the role of stereotactic body radiation therapy (SBRT) in early-stage, chemoradiation in the locally advanced stage, post-operative radiotherapy for patients with high risk after surgery and radiotherapy for metastatic disease will be discussed. Also, for SCLC, the role and timing of thoracic irradiation and prophylactic cranial irradiation (PCI) for the limited and extensive stages will be discussed.

Pre-treatment serum bicarbonate predicts for primary tumor control after stereotactic body radiation therapy in patients with localized non-small cell lung cancer

BACKGROUND

Tumor aggressiveness and hypoxia are linked to acidosis in the tumor microenvironment (TME). We hypothesized that low pre-treatment serum bicarbonate, potentially correlating with an acidic and hypoxic TME, predicts for poor outcomes after stereotactic body radiation therapy (SBRT) for non-small cell lung cancer (NSCLC).

METHODS

We included patients with localized NSCLC treated to a biologically effective dose (BED) ≥ 100 Gy, with available pre-treatment bicarbonate values within 3 months of treatment. We used receiver operating characteristic analysis to determine the bicarbonate concentration optimally predicting for primary tumor recurrence, and evaluated its association with recurrence and survival. We validated our findings in an independent cohort of patients from three collaborating institutions.

RESULTS

A total of 110 patients and 114 tumors were included in the training cohort, with median follow-up of 15.0 months. Bicarbonate < 26 mEq/L was associated with primary tumor recurrence on univariate (HR = 5.92; 95% CI 1.69-24.88; p = 0.005) and multivariate analysis (HR = 5.48; 95% CI 1.37-25.19; p = 0.020). The validation cohort consisted of 195 patients and 208 tumors with median follow-up of 27.5 months. In the validation cohort, bicarbonate < 26 mEq/L was again associated with primary tumor recurrence on univariate (HR = 3.38; 95% CI 1.27-9.37; p = 0.015) and multivariate analysis (HR = 3.33; 1.18-10.07; p = 0.023).

CONCLUSIONS

Pre-treatment bicarbonate predicts for primary tumor control in NSCLC treated with SBRT and may be useful for risk stratification. These findings should be confirmed prospectively.

Management of local recurrences and regional failure in early stage non-small cell lung cancer after stereotactic body radiation therapy

Stereotactic body radiation therapy (SBRT) is a very effective way to treat early stage non-small cell lung cancer (NSCLC) and small oligometastatic lung lesions with consistently high rates of local control, but both local and regional/distant recurrences still occur. The management of recurrences remains unsettled and may entail repeat SBRT, conventionally fractionated external beam RT (EF-EBRT), chemotherapy or surgery. Most patients with local recurrences [within the initial planning target volume (PTV)] can be salvaged successfully with good cancer specific survival. Nonetheless, proximity of the initial SBRT delivery to organs at risk (ribs, blood vessels, airways) may make retreatment more difficult. With attention to detail and careful patient selection, both surgery and reirradiation can be performed safely and effectively. Strategies for management of regional (nodal) recurrences may require conventional therapies tailored to the patterns of failure. The role of immunotherapy in salvage has not been elucidated as yet. We review here data on the available literature concerning salvage of SBRT lung patients.

Research of Biological Dose Conversion Platform Based on a Modified Linear Quadratic Model

The study aimed to develop a novel dose conversion platform by improving linear-quadratic (LQ) model to more accurately describe radiation response for high fraction/acute doses. This article modified the LQ model via piecewise fitting the biological dose curve using different fractionated dose and optimizing the consistency between mathematical model and experimental data to gain a more reasonable transform. That mathematical development of the LQ model further amended certain deviations of various cell curves with high doses and implied the rationality of the present model at low dose range. The modified biologically effective dose model that solved the dilemma of inaccurate LQ model had been used in comparing between hypofractionated and conventional fractioned dose. It has been verified that the calculated values are similar in the treatment of same efficacy, no matter what α/β is, and provided a more rational explanation for significant differences among various hypofractionations. The equivalent uniform dose based on the subsection function could represent arbitrary inhomogeneous dose distributions including high-dose fractions, providing a foundation for the implementation of detailed evaluation of different cell dose effects.

Final report of survival and late toxicities in the Phase I study of stereotactic body radiation therapy for peripheral T2N0M0 non-small cell lung cancer (JCOG0702)

Purpose

A dose escalation study to determine the recommended dose with stereotactic body radiation therapy (SBRT) for peripheral T2N0M0 non-small cell carcinomas (JCOG0702) was conducted. The purpose of this paper is to report the survival and the late toxicities of JCOG0702.

Materials and methods

The continual reassessment method was used to determine the dose level that patients should be assigned to and to estimate the maximum tolerated dose. The starting dose was 40 Gy in four fractions at D₉₅ of PTV.

Results

Twenty-eight patients were enrolled. Ten patients were treated with 40 Gy at D₉₅ of PTV, four patients with 45 Gy, eight patients with 50 Gy, one patient with 55 Gy and five patients with 60 Gy. Ten patients were alive at the last follow-up. Overall survival (OS) for all patients was 67.9% (95% CI 47.3–81.8%) at 3 years and 40.8% (95% CI 22.4–58.5%) at 5 years. No Grade 3 or higher toxicity was observed after 181 days from the beginning of the SBRT. Compared to the toxicities up to 180 days, chest wall related toxicities were more frequent after 181 days.

Conclusions

The 5-year OS of 40.8% indicates the possibility that SBRT for peripheral T2N0M0 non-small cell lung cancer is superior to conventional radiotherapy. The effect of the SBRT dose escalation on OS is unclear and further studies are warranted.

Effect of Tumor Location and Dosimetric Predictors for Chest Wall Toxicity in Single-Fraction Stereotactic Body Radiation Therapy for Stage I Non-Small Cell Lung Cancer

PURPOSE

Dosimetric parameters to limit chest wall toxicity (CWT) are not well defined in single-fraction (SF) stereotactic body radiation therapy (SBRT) phase 2 trials. We sought to determine the relationship of tumor location and dosimetric parameters with CWT for SF-SBRT.

METHODS AND MATERIALS

From a prospective registry of 1462 patients, we identified patients treated with 30 Gy or 34 Gy. Gross tumor volume was measured as abutting, ≤1 cm, 1 to 2 cm, or >2 cm from the chest wall. CWT was prospectively graded according to Common Terminology Criteria for Adverse Events version 3.0, with grade 2 requiring medical therapy, grade 3 requiring procedural intervention, and grade 4 being disabling pain. Grade 1 CWT or radiographic rib fracture was not included. Logistic regression analysis was used to identify the parameters associated with CWT and calculate the probability of CWT with dose.

RESULTS

This study included 146 lesions. The median follow-up time was 23.8 months. The 5-year local control, distant metastasis, and overall survival rates were 91.8%, 19.2%, and 28.7%, respectively. Grade 2 to 4 CWT was 30.6% for lesions abutting the chest wall, 8.2% for ≤1 cm from the chest wall, 3.8% for 1 to 2 cm from the chest wall, and 5.7% for >2 cm from the chest wall. Grade ≥3 CWT was 1.4%. Tumor abutment (odds ratio [OR]: 6.5; P = .0005), body mass index (OR: 1.1; P = .02), rib D1cc (OR: 1.01/Gy; P = .03), chest wall D1cc (OR: 1.08/Gy; P = .03), and chest wall D5cc (OR: 1.10/Gy; P = .01) were significant predictors for CWT on univariate analysis. Tumor abutment was significant for CWT (OR: 7.5; P = .007) on multivariate analysis. The probability of CWT was 15% with chest wall D5cc at 27.2 Gy and rib D1cc at 30.2 Gy.

CONCLUSIONS

The rate of CWT with SF-SBRT is similar to the rates published for fractionated SBRT, with most CWT being low grade. Tumor location relative to the chest wall is not a contraindication to SF-SBRT, but the rates increase significantly with abutment. Rib D1cc and chest wall D1cc and D5cc may be used as predictors of CWT.

Comparison of Single- and Five-fraction Regimens of Stereotactic Body Radiation Therapy for Peripheral Early-stage Non-small-cell Lung Cancer: A Two-institution Propensity-matched Analysis

PURPOSE

To evaluate differences in local control (LC), disease-specific (DC), and overall survival (OS) of patients with early-stage non-small-cell lung cancer (NSCLC) treated with single- (SF) versus 5-fraction (FF) stereotactic body radiation therapy (SBRT) at 2 institutions.

PATIENTS AND METHODS

Peripheral early-stage NSCLC cases treated with a median dose of 30 Gy in SF or a median dose of 50 Gy in FF were included per institutional practice. Kaplan-Meier and Cox models were used to assess survival. A matched-pair analysis was performed to account for imbalances. Toxicities including Common Terminology Criteria for Adverse Events (CTCAE) grade 3 pneumonitis, chest wall pain requiring long-acting narcotics, and hospitalization for respiratory events 6 months posttreatment were recorded.

RESULTS

A total of 163 lesions were treated between 2007 and 2015; 65 received SF SBRT and 98 received FF SBRT. Most tumors were T1 (n = 92) and T2 (n = 34) lesions and had adenocarcinoma (n = 77) and squamous cell carcinoma (n = 46) histologies, respectively. In the matched cohort, there were no differences in OS, LC, DC, or progression-free survival between the groups. LC and OS at 1 year in the matched cohort was 95% and 88%, and 87% and 84% in the SF and FF cohorts, respectively. There was 1 grade 3 pneumonitis in the FF group, and 9 total hospitalizations post-SBRT, 3 (5%) in the SF group and 6 (6%) in the FF group.

CONCLUSIONS

No statistically significant differences were seen in LC or DC following SF or FF SBRT in this matched cohort of peripheral lesions. No grade 4 or higher toxicities were reported.

Stereotactic MR-Guided Online Adaptive Radiation Therapy (SMART) for Ultracentral Thorax Malignancies: Results of a Phase 1 Trial

Purpose

Stereotactic body radiation therapy (SBRT) is an effective treatment for oligometastatic or unresectable primary malignancies, although target proximity to organs at risk (OARs) within the ultracentral thorax (UCT) limits safe delivery of an ablative dose. Stereotactic magnetic resonance (MR)–guided online adaptive radiation therapy (SMART) may improve the therapeutic ratio using reoptimization to account for daily variation in target and OAR anatomy. This study assessed the feasibility of UCT SMART and characterized dosimetric and clinical outcomes in patients treated for UCT lesions on a prospective phase 1 trial.

Methods and Materials

Five patients with oligometastatic (n = 4) or unresectable primary (n = 1) UCT malignancies underwent SMART. Initial plans prescribed 50 Gy in 5 fractions with goal 95% planning target volume (PTV) coverage by 95% of prescription, subject to strict OAR constraints. Daily real-time online adaptive plans were created as needed to preserve hard OAR constraints, escalate PTV dose, or both, based on daily setup MR image set anatomy. Treatment times, patient outcomes, and dosimetric comparisons were prospectively recorded.

Results

All initial and daily adaptive plans met strict OAR constraints based on simulation and daily setup MR imaging anatomy, respectively. Four of the 5 patients received ≥1 adapted fraction. Ten of the 25 total delivered fractions were adapted. A total of 30% of plan adaptations were performed to improve PTV coverage; 70% were for reversal of ≥1 OAR violation. Local control by Response Evaluation Criteria in Solid Tumors was 100% at 3 and 6 months. No grade ≥3 acute (within 6 months of radiation completion) treatment-related toxicities were identified.

Conclusions

SMART may allow PTV coverage improvement and/or OAR sparing compared with nonadaptive SBRT and may widen the therapeutic index of UCT SBRT. In this small prospective cohort, we found that SMART was clinically deliverable to 100% of patients, although treatment delivery times surpassed our predefined, timing-based feasibility endpoint. This technique is well tolerated, offering excellent local control with no identified acute grade ≥3 toxicity.