Breathing-motion-compensated robotic guided stereotactic body radiation therapy : Patterns of failure analysis

The tumor core boost study: A feasibility study of radical dose escalation to the central part of large tumors with an integrated boost in the palliative treatment setting

PURPOSE

For patients with large tumors palliative radiotherapy often is the only local treatment option. To prevent toxicity the administered doses are low. Dose escalation to the tumor could be an option to better smyptom control and prolong local control rates. In this prospective study we used a very pragmatic approach with a simultaneously integrated boost (SIB) to an almost geometrically defined tumor core to achieve this. The primary endpoint was to demonstrate feasibility.

METHOD

Patients with solid tumors > 4 cm in diameter of different histologies were eligible in this single arm, prospective, multi-institutional clinical feasibility trial with two treatment concepts: 5 × 5 Gy with an integrated boost to the tumor core of 5 × 10 Gy or 10 × 3 Gy with a boost of 10 × 6 Gy. The objective of dose escalation in this study was to deliver a minimum dose of 150% of the prescribed dose to the gross tumor volume (GTV) tumor core and to reach a maximum of at least 200% in the tumor core.

RESULTS

In all, 21 patients at three study sites were recruited between January 2019 and November 2020 and were almost evenly spread (9 to 12) between the two concepts. The treated planning target volumes (PTV) averaged 389.42 cm³ (range 49.4-1179.6 cm³). The corresponding core volumes were 72.85 cm³ on average (range 4.21-338.3 cm³). Dose escalation to the tumor core with mean doses of 167.7-207.7% related to the nonboost prescribed isodose led to PTV mean doses of 120.5-163.3%. Treatment delivery and short-term follow-up was successful in all patients.

CONCLUSIONS

Palliative radiotherapy with SIB to the tumor core seems to be a feasible and well-tolerated treatment concept for large tumors. The applied high doses of up to 50 Gy in 5 fractions (or 60 Gy in 10 fractions) did not cause unexpected side effects in the 42 day follow-up period. Further research is needed for more information on efficacy and long-term toxicity.

Planning benchmark study for SBRT of liver metastases: Results of the DEGRO/DGMP working group stereotactic radiotherapy and radiosurgery

PURPOSE

To investigate, if liver SBRT treatment planning can be harmonized across different treatment planning systems, delivery techniques and institutions by using a specific prescription method and to minimize the knowledge gap concerning inter-system and inter-user differences. To provide best practice guidelines for all used techniques.

METHODS

A multiparametric specification of target dose (GTV_D50%, GTV_D0.1cc, GTV_V90%, PTV_V70%) with a prescription dose of GTV_D50% = 3 × 20 Gy and OAR limits were distributed with CTs and structure sets from three liver metastases patients. Thirty-five institutions provided 132 treatment plans using different irradiation techniques. These plans were first analyzed for target and OAR doses. Four different renormalization methods were performed (PTV_Dmin, PTV_D98%, PTV_D2%, PTV_Dmax). The resulting 660 treatments plans were evaluated regarding target doses in order to study the effect of dose renormalization to different prescription methods. A relative scoring system was used for comparisons.

RESULTS

GTV_D50% prescription can be performed in all systems. Treatment plan harmonization was overall successful with standard deviations for D_max, PTV_D98%, GTV_D98% and PTV_Dmean of 1.6 Gy, 3.3 Gy, 1.9 Gy and 1.5 Gy, respectively. Primary analysis showed 55 major deviations from clinical goals in 132 plans, while in only <20% of deviations GTV/PTV dose was traded for meeting OAR limits. GTV_D50% prescription produced the smallest deviation from target planning objectives and between techniques, followed by the PTV_Dmax, PTV_D98%, PTV_D2% and PTV_Dmin prescription. Deviations were significant for all combinations but for the PTV_Dmax prescription compared with GTV_D50% and PTV_D98%. Based on the various dose prescription methods, all systems significantly differed from each other, while GTV_D50% and PTV_D98% prescription showed the least differences between the systems.

CONCLUSIONS

This study showed the feasibility of harmonizing liver SBRT treatment plans across different treatment planning systems and delivery techniques when a sufficient set of clinical goals is given.

Radiomics for prediction of radiation-induced lung injury and oncologic outcome after robotic stereotactic body radiotherapy of lung cancer: results from two independent institutions

OBJECTIVES

To generate and validate state-of-the-art radiomics models for prediction of radiation-induced lung injury and oncologic outcome in non-small cell lung cancer (NSCLC) patients treated with robotic stereotactic body radiation therapy (SBRT).

METHODS

Radiomics models were generated from the planning CT images of 110 patients with primary, inoperable stage I/IIa NSCLC who were treated with robotic SBRT using a risk-adapted fractionation scheme at the University Hospital Cologne (training cohort). In total, 199 uncorrelated radiomic features fulfilling the standards of the Image Biomarker Standardization Initiative (IBSI) were extracted from the outlined gross tumor volume (GTV). Regularized models (Coxnet and Gradient Boost) for the development of local lung fibrosis (LF), local tumor control (LC), disease-free survival (DFS) and overall survival (OS) were built from either clinical/ dosimetric variables, radiomics features or a combination thereof and validated in a comparable cohort of 71 patients treated by robotic SBRT at the Radiosurgery Center in Northern Germany (test cohort).

RESULTS

Oncologic outcome did not differ significantly between the two cohorts (OS at 36 months 56% vs. 43%, p = 0.065; median DFS 25 months vs. 23 months, p = 0.43; LC at 36 months 90% vs. 93%, p = 0.197). Local lung fibrosis developed in 33% vs. 35% of the patients (p = 0.75), all events were observed within 36 months. In the training cohort, radiomics models were able to predict OS, DFS and LC (concordance index 0.77-0.99, p < 0.005), but failed to generalize to the test cohort. In opposite, models for the development of lung fibrosis could be generated from both clinical/dosimetric factors and radiomic features or combinations thereof, which were both predictive in the training set (concordance index 0.71- 0.79, p < 0.005) and in the test set (concordance index 0.59-0.66, p < 0.05). The best performing model included 4 clinical/dosimetric variables (GTV-D_mean, PTV-D_95%, Lung-D_1ml, age) and 7 radiomic features (concordance index 0.66, p < 0.03).

CONCLUSION

Despite the obvious difficulties in generalizing predictive models for oncologic outcome and toxicity, this analysis shows that carefully designed radiomics models for prediction of local lung fibrosis after SBRT of early stage lung cancer perform well across different institutions.

Liver SBRT with active motion-compensation results in excellent local control for liver oligometastases: An outcome analysis of a pooled multi-platform patient cohort

BACKGROUND

Local treatment of metastases in combination with systemic therapy can prolong survival of oligo-metastasized patients. To fully exploit this potential, safe and effective treatments are needed to ensure long-term metastases control. Stereotactic body radiotherapy (SBRT) is one means, however, for moving liver tumors correct delivery of high doses is challenging. After validating equal in-vivo treatment accuracy, we analyzed a pooled multi-platform liver-SBRT-database for clinical outcome.

METHODS

Local control (LC), progression-free interval (PFI), overall survival (OS), predictive factors and toxicity was evaluated in 135 patients with 227 metastases treated by gantry-based SBRT (deep-inspiratory breath-hold-gating; n = 71) and robotic-based SBRT (fiducial-tracking, n = 156) with mean gross tumor volume biological effective dose (GTV-BED_α/β=10Gy) of 146.6 Gy₁₀.

RESULTS

One-, and five-year LC was 90% and 68.7%, respectively. On multivariate analysis, LC was significantly predicted by colorectal histology (p = 0.006). Median OS was 20 months with one- and two-year OS of 67% and 37%. On multivariate analysis, ECOG-status (p = 0.003), simultaneous chemotherapy (p = 0.003), time from metastasis detection to SBRT-treatment (≥2months; p = 0.021) and LC of the treated metastases (≥12 months, p < 0.009) were significant predictors for OS. One- and two-year PFI were 30.5% and 14%. Acute toxicity was mild and rare (14.4% grade I, 2.3% grade II, 0.6% grade III). Chronic °III/IV toxicities occurred in 1.1%.

CONCLUSIONS

Patient selection, time to treatment and sufficient doses are essential to achieve optimal outcome for SBRT with active motion compensation. Local control appears favorable compared to historical control. Long-term LC of the treated lesions was associated with longer overall survival.

Quality assurance for dynamic tumor tracking

The purpose of this work was to develop a treatment plan verification routine for a linear accelerator dedicated to SBRT treatments with gimbal based dynamic tumor tracking using three commercially available phantoms. The accelerator system has two special features: It operates with a rotation of the ring shaped gantry instead of a couch rotation and target motion can be compensated for via a gimbal system (dynamic tumor tracking, DTT). DTT plans were each measured with the three different phantoms. Afterwards the measured dose distribution was compared with the calculated dose distribution via global Gamma Index analysis (3mm / 3%, threshold: 10%). The global gamma pass rates were on average (93.5±7.2) % for ArcCHECK, (98.0±2.6) % for OCTAVIUS® 4D and (98.4±4.2) % for MatriXX Evolution. All three systems could be used for quality assurance with ring rotations and DTT, however, each with limitations.

Tumor-dose-rate variations during robotic radiosurgery of oligo and multiple brain metastases

Purpose

For step-and-shoot robotic stereotactic radiosurgery (SRS) the dose delivered over time, called local tumor-dose-rate (TDR), may strongly vary during treatment of multiple lesions. The authors sought to evaluate technical parameters influencing TDR and correlate TDR to clinical outcome.

Material and methods

A total of 23 patients with 162 oligo (1–3) and multiple (>3) brain metastases (OBM/MBM) treated in 33 SRS sessions were retrospectively analyzed. Median PTV were 0.11 cc (0.01–6.36 cc) and 0.50 cc (0.12–3.68 cc) for OBM and MBM, respectively. Prescription dose ranged from 16 to 20 Gy prescribed to the median 70% isodose line. The maximum dose-rate for planning target volume (PTV) percentage p in time span s during treatment (TDR_s,p) was calculated for various p and s based on treatment log files and in-house software.

Results

TDR_60min,98% was 0.30 Gy/min (0.23–0.87 Gy/min) for OBM and 0.22 Gy/min (0.12–0.63 Gy/min) for MBM, respectively, and increased by 0.03 Gy/min per prescribed Gy. TDR_60min,98% strongly correlated with treatment time (ρ = −0.717, p < 0.001), monitor units (MU) (ρ = −0.767, p < 0.001), number of beams (ρ = −0.755, p < 0.001) and beam directions (ρ = −0.685, p < 0.001) as well as lesions treated per collimator (ρ = −0.708, P < 0.001). Median overall survival (OS) was 20 months and 1‑ and 2‑year local control (LC) was 98.8% and 90.3%, respectively. LC did not correlate with any TDR, but tumor response (partial response [PR] or complete response [CR]) correlated with all TDR in univariate analysis (e.g., TDR_60min,98%: hazard ration [HR] = 0.974, confidence interval [CI] = 0.952–0.996, p = 0.019). In multivariate analysis only concomitant targeted therapy or immunotherapy and breast cancer tumor histology remained a significant factor for tumor response. Local grade ≥2 radiation-induced tissue reactions were noted in 26.3% (OBM) and 5.2% (MBM), respectively, mainly influenced by tumor volume (p < 0.001).

Conclusions

Large TDR variations are noted during MBM-SRS which mainly arise from prolonged treatment times. Clinically, low TDR corresponded with decreased local tumor responses, although the main influencing factor was concomitant medication.

Stereotactic body radiotherapy (SBRT) in patients with lung metastases - prognostic factors and long-term survival using patient self-reported outcome (PRO)

OBJECTIVES

The present study aims to evaluate long-term side-effects and outcomes and confirm prognostic factors after stereotactic body radiotherapy (SBRT) of pulmonary lesions. This is the first work that combines the investigated data from patient charts and patient-reported outcome (PRO) up to 14 years after therapy.

MATERIALS AND METHODS

We analyzed 219 patients and 316 lung metastases treated between 2004 and 2019. The pulmonary lesions received a median dose and dose per fraction of 35 Gy (range: 14-60.5 Gy) and 8 Gy (range: 3-20 Gy) to the surrounding isodose. During the last 1.5 years of monitoring, we added PRO assessment to our follow-up routine. We sent an invitation to a web-based survey questionnaire to all living patients whose last visit was more than 6 months ago.

RESULTS

Median OS was 27.6 months. Univariate analysis showed a significant influence on OS for KPS ≥90%, small gross tumor volume (GTV) and planning target volume (PTV), the absence of external metastases, ≤3 pulmonary metastases, and controlled primary tumor. The number of pulmonary metastases and age influenced local control (LC) significantly. During follow-up, physicians reported severe side-effects ≥ grade 3 in only 2.9% within the first 6 months and in 2.5% after 1 year. Acute symptomatic pneumonitis grade 2 was observed in 9.7%, as grade 3 in 0.5%. During PRO assessment, 39 patients were contacted, 38 patients participated, 14 participated twice during follow-up. Patients reported 15 cases of severe side effects (grade ≥ 3) according to PROCTCAE classification. Severe dyspnea (n = 6) was reported mostly.

CONCLUSION

We could confirm excellent local control and low toxicity rates. PROs improve and complement follow-up care. They are an essential measure in addition to the physician-reported outcomes. Future research must be conducted regarding the correct interpretation of PRO data.

Performance of Makerless Tracking for Gimbaled Dynamic Tumor Tracking

BACKGROUND AND PURPOSE

The purpose of this work is to report the workflow and the accuracy of the new markerless dynamic tumor tracking (MLDTT) method of the Vero 4DRT system introduced with ExacTrac 3.6.1.

MATERIAL AND METHODS

Phantom measurements were performed to assess the accuracy of the MLDTT algorithm by using the QA-tool which is provided by the vendor. A patient breathing curve was used as the motion trajectory of the phantom and the target positions detected by the MLDTT algorithm were compared to the defined positions. Furthermore, eight patients have been treated with MLDTT between May 2018 and July 2019. A log-file analysis is used to evaluate MLDTT treatment data.

RESULTS

The accuracy of the MLDTT detection is 0.12mm ± 0.12mm, 0.12mm ± 0.11mm, 0.20mm ± 0.21mm for the x-, y-, z-direction, respectively. These values are comparable to the accuracy of marker based DTT at the Vero system. The median treatment time was 21min 34seconds and 175kV images were acquired during treatment for monitoring the target motion.

CONCLUSION

The accuracy of the MLDTT algorithm is comparable to the marker based approach and the accuracy reported for the XSight Lung of the CyberKnife. Eight patients were treated successfully using MLDTT and the treatment times are comparable to a standard DTT treatment.

Method for a motion model based automated 4D dose calculation

The Vero system can treat intra-fractionally moving tumors with gimbaled dynamic tumor tracking (DTT) by rotating the treatment beam so that it follows the motion of the tumor. However, the changes in the beam geometry and the constant breathing motion of the patient influence the dose applied to the patient. This study aims to perform a full 4D dose reconstruction for thirteen patients treated with DTT at the Vero system at the Universitätsklinikum Erlangen and investigates the temporal resolution required to perform an accurate 4D dose reconstruction. For all patients, a 4DCT was used to train a 4D motion model, which is able to calculate pseudo-CT images for arbitrary breathing phases. A new CT image was calculated for every 100 ms of treatment and a dose calculation was performed according to the current beam geometry (i.e. the rotation of the treatment beam at this moment in time) by rotating according to the momentary beam rotation, which is extracted from log-files. The resulting dose distributions were accumulated on the planning CT and characteristic parameters were extracted and compared. [Formula: see text]-evaluations of dose accumulations with different spatial-temporal resolutions were performed to determine the minimal required resolution. In total 173 700 dose calculations were performed. The accumulated 4D dose distributions show a reduced mean GTV dose of 0.77% compared to the static treatment plan. For some patients larger deviations were observed, especially in the presence of a poor 4DCT quality. The [Formula: see text]-evaluation showed that a temporal resolution of 500 ms is sufficient for an accurate dose reconstruction. If the tumor motion is regarded as well, a spatial-temporal sampling of 1400 ms and 2 mm yields accurate results, which reduces the workload by 84%.

Comparative analysis between interstitial brachytherapy and stereotactic body irradiation for local ablation in liver malignancies

PURPOSE

Interstitial high-dose-rate brachytherapy (BT) is an alternative treatment option to stereotactic body radiotherapy (SBRT) for the ablative treatment of liver malignancies. The aim of the present comparative planning study was to reveal the possibilities and limitations of both techniques with regard to dosimetric properties.

METHODS AND MATERIALS

Eighty-five consecutive patients with liver malignancy diagnosis were treated with interstitial BT between 12/2008 and 09/2009. The prescription dose of BT varied between 15 and 20 Gy, depending on histology. For dosimetric comparison, virtual SBRT treatment plans were generated using the original BT planning CTs. Additional margins reflecting the respiratory tumor motion were added to the target volumes for SBRT planning.

RESULTS

The mean PTV_BT was 34.7 cm³ (0.5-410.0 cm³) vs. a mean PTV_SBRT of 73.2 cm³ (6.1-593.4 cm³). Regarding the minimum peripheral dose (D_99.9), BT achieved the targeted prescription dose of 15 Gy/20 Gy better without violating organ at risk constraints. The dose exposure of the liver was significantly influenced by treatment modality. The liver exposure to 5 Gy was statistically lower with 611 ± 43 cm³ for BT as compared with 694 ± 37 cm³ for SBRT plans (20-Gy group, p = 0.001), corresponding to 41.8% vs. 45.9% liver volume, respectively.

CONCLUSIONS

To the best of our knowledge, this is the first report on the comparison of clinically treated liver BT treatments with virtually planned SBRT treatments. The planning study showed a superior outcome of BT regarding dose coverage of the target volume and exposed liver volume. Nevertheless, further studies are needed to determine ideal applicability for each treatment approach.

Geometrical tracking accuracy and appropriate PTV margins for robotic radiosurgery of liver lesions by SBRT

Purpose: To assess the geometrical accuracy and estimate adequate PTV margins for liver treatments using the Synchrony respiratory tracking system. Material and methods: Treatment log files are analyzed for 72 liver patients to assess tracking accuracy. The tracking error is calculated as the quadratic sum of the correlation, the predictor and the beam positioning errors. Treatment target rotations and rigid body errors reported by the system are also evaluated. The impact of uncorrected rotations is assessed by rotating the planned dose distribution and reassessing target coverage. Total PTV margins are estimated by summing in quadrature tracking errors and rigid body errors. Relationships are explored between tracking errors, model linearity and motion amplitudes of internal and external markers. Results: Margins of 3, 2, 2 mm in SUP-INF, LT-RT and ANT-POST directions, respectively, are sufficient to account for tracking and beam positioning errors for 95% of patients. If rigid body error is also considered, margins increase to 4 mm isotropic. Rotations could not be corrected for 92% of patients due to imperfect fiducial implantation and limitations in the magnitude of corrections that the system can apply. Uncorrected rotations would lead to average estimated dose reductions of 2.7% ± 5.8% of the prescribed dose for D99 of GTVs (5 mm PTV expansion) in which the target was well covered in the original plan (28 of 31 GTVs). 80% of tracking models exhibit near linear correlation between internal and external marker motions with small tracking errors (<2.2 mm). Conclusions: Isotropic PTV margins considering tracking errors and target rigid body errors could be used for liver SBRT treatments if rotational corrections can be calculated accurately so that systematic rotational offsets can be avoided. The linearity of the internal and external breathing motions might be useful for other types of treatment modalities for liver cancer.

Radiomic analysis of planning computed tomograms for predicting radiation-induced lung injury and outcome in lung cancer patients treated with robotic stereotactic body radiation therapy

OBJECTIVES

To predict radiation-induced lung injury and outcome in non-small cell lung cancer (NSCLC) patients treated with robotic stereotactic body radiation therapy (SBRT) from radiomic features of the primary tumor.

METHODS

In all, 110 patients with primary stage I/IIa NSCLC were analyzed for local control (LC), disease-free survival (DFS), overall survival (OS) and development of local lung injury up to fibrosis (LF). First-order (histogram), second-order (GLCM, Gray Level Co-occurrence Matrix) and shape-related radiomic features were determined from the unprocessed or filtered planning CT images of the gross tumor volume (GTV), subjected to LASSO (Least Absolute Shrinkage and Selection Operator) regularization and used to construct continuous and dichotomous risk scores for each endpoint.

RESULTS

Continuous scores comprising 1-5 histogram or GLCM features had a significant (p = 0.0001-0.032) impact on all endpoints that was preserved in a multifactorial Cox regression analysis comprising additional clinical and dosimetric factors. At 36 months, LC did not differ between the dichotomous risk groups (93% vs. 85%, HR 0.892, 95%CI 0.222-3.590), while DFS (45% vs. 17%, p < 0.05, HR 0.457, 95%CI 0.240-0.868) and OS (80% vs. 37%, p < 0.001, HR 0.190, 95%CI 0.065-0.556) were significantly lower in the high-risk groups. Also, the frequency of LF differed significantly between the two risk groups (63% vs. 20% at 24 months, p < 0.001, HR 0.158, 95%CI 0.054-0.458).

CONCLUSION

Radiomic analysis of the gross tumor volume may help to predict DFS and OS and the development of local lung fibrosis in early stage NSCLC patients treated with stereotactic radiotherapy.

In-vivo treatment accuracy analysis of active motion-compensated liver SBRT through registration of plan dose to post-therapeutic MRI-morphologic alterations

BACKGROUND/PURPOSE

In-vivo-accuracy analysis (IVA) of dose-delivery with active motion-management (gating/tracking) was performed based on registration of post-radiotherapeutic MRI-morphologic-alterations (MMA) to the corresponding dose-distributions of gantry-based/robotic SBRT-plans.

METHODS

Forty targets in two patient cohorts were evaluated: (1) gantry-based SBRT (deep-inspiratory breath-hold-gating; GS) and (2) robotic SBRT (online fiducial-tracking; RS). The planning-CT was deformably registered to the first post-treatment contrast-enhanced T1-weighted MRI. An isodose-structure cropped to the liver (ISL) and corresponding to the contoured MMA was created. Structure and statistical analysis regarding volumes, surface-distance, conformity metrics and center-of-mass-differences (CoMD) was performed.

RESULTS

Liver volume-reduction was -43.1 ± 148.2 cc post-RS and -55.8 ± 174.3 cc post-GS. The mean surface-distance between MMA and ISL was 2.3 ± 0.8 mm (RS) and 2.8 ± 1.1 mm (GS). ISL and MMA volumes diverged by 5.1 ± 23.3 cc (RS) and 16.5 ± 34.1 cc (GS); the median conformity index of both structures was 0.83 (RS) and 0.80 (GS). The average relative directional errors were ≤0.7 mm (RS) and ≤0.3 mm (GS); the median absolute 3D-CoMD was 3.8 mm (RS) and 4.2 mm (GS) without statistically significant differences between the two techniques. Factors influencing the IVA included GTV and PTV (p = 0.041 and p = 0.020). Four local relapses occurred without correlation to IVA.

CONCLUSIONS

For the first time a method for IVA was presented, which can serve as a benchmarking-tool for other treatment techniques. Both techniques have shown median deviations <5 mm of planned dose and MMA. However, IVA also revealed treatments with errors ≥5 mm, suggesting a necessity for patient-specific safety-margins. Nevertheless, the treatment accuracy of well-performed active motion-compensated liver SBRT seems not to be a driving factor for local treatment failure.

Clinical outcomes following advanced respiratory motion management (respiratory gating or dynamic tumor tracking) with stereotactic body radiation therapy for stage I non-small-cell lung cancer

Purpose

To report the outcomes of stereotactic body radiation therapy (SBRT) for stage I non-small-cell lung cancer (NSCLC) according to respiratory motion management method.

Methods

Patients with stage I NSCLC who received SBRT from 2007 to 2015 were reviewed. Computed tomography (CT) simulation with four-dimensional CT was performed for respiratory motion assessment. Tumor motion >1 cm in the craniocaudal direction was selectively treated with advanced respiratory management: either respiratory gating to a pre-specified portion of the respiratory cycle or dynamic tracking of an implanted fiducial marker. Comparisons were made with internal target volume approach, which treated all phases of respiratory motion.

Results

Of 297 patients treated with SBRT at our institution, 51 underwent advanced respiratory management (48 with respiratory gating and three with tumor tracking) and 246 underwent all-phase treatment. Groups were similarly balanced with regard to mean age (P=0.242), tumor size (P=0.315), and histology (P=0.715). Tumor location in the lower lung lobes, as compared to middle or upper lobes, was more common in those treated with advanced respiratory management (78.4%) compared to all-phase treatment (25.6%, P<.0001). There were 17 local recurrences in the treated lesions. Kaplan-Meier analyses showed that there were no differences with regard to mean time to local failure (91.5 vs 98.8 months, P=0.56), mean time to any failure (73.2 vs 78.7 months, P=0.73), or median overall survival (43.3 vs 45.5 months, P=0.56) between patients who underwent advanced respiratory motion management and all-phase treatment.

Conclusion

SBRT with advanced respiratory management (the majority with respiratory gating) showed similar efficacy to all-phase treatment approach for stage I NSCLC.

Prognostic factors in stereotactic body radiotherapy of lung metastases

PURPOSE

The aim of this study was to evaluate prognostic factors in patients with lung metastases who undergo lung stereotactic body radiotherapy (SBRT).

MATERIALS AND METHODS

A total of 87 patients with 129 lung metastases who underwent SBRT between November 2004 and May 2012 were enrolled in this retrospective study. The patient collective consisted of 54 men (62.1%) and 33 women (37.9%); the median age was 65 years (range 36-88). The Karnofsky performance index was ≥70% (median 90%) for all cases, but one (60%). Adverse effects were categorized using the CTCAE 4.0 classification system. Retrospective analyses regarding patients' characteristics, progression-free survival (PFS), overall survival (OS), disease-specific survival (DSS), and local tumor control rates (LTC) were performed.

RESULTS

On univariate and multivariate analysis OS, DSS, and PFS were significantly (p < 0.05) better for patients with ≤3 lung metastases; no extrathoracic metastases at the time of the SBRT; a gross tumor volume (GTV) <7.7 cm³ and patients that received a staging that included positron emission tomography with fluorine 18 fluorodeoxyglucose/computed tomography (FDG-PET/CT) imaging. Furthermore, a longer OS was observed if newly diagnosed metastases during follow-up were limited to the lung (median survival: 43.7 months versus 21.7 months; p = 0.023).

CONCLUSION

The number and pattern of metastases, and the size of the target volume are strong predictors for the outcome of patients receiving SBRT of lung tumors. FDG-PET/CT should be part of pretherapeutic staging before SBRT.

Non-coplanar VMAT combined with non-uniform dose prescription markedly reduces lung dose in breath-hold lung SBRT

BACKGROUND AND PURPOSE

In this retrospective treatment planning study, the effect of a uniform and non-uniform planning target volume (PTV) dose coverage as well as a coplanar and non-coplanar volumetric modulated arc therapy (VMAT) delivery approach for lung stereotactic body radiation therapy (SBRT) in deep inspiration breath-hold (DIBH) were compared.

MATERIALS AND METHODS

For 46 patients with lesions in the peripheral lungs, three different treatment plans were generated: First, a coplanar 220° VMAT sequence with a uniform PTV dose prescription (UC). Second, a coplanar 220° VMAT treatment plan with a non-uniform dose distribution in the PTV (nUC). Third, a non-coplanar VMAT dose delivery with four couch angles (0°, ±35°, 90°) and a non-uniform prescription (nUnC) was used. All treatment plans were optimized for pareto-optimality with respect to PTV coverage and ipsilateral lung dose. Treatment sequences were delivered on a flattening-filter-free linear accelerator and beam-on times were recorded. Dosimetric comparison between the three techniques was performed.

RESULTS

For the three scenarios (UC, nUC, nUnC), median gross tumor volume (GTV) doses were 63.4 ± 2.5, 74.4 ± 3.6, and 77.9 ± 3.8 Gy, and ipsilateral V10Gy lung volumes were 15.7 ± 6.1, 13.9 ± 4.7, and 12.0 ± 5.1%, respectively. Normal tissue complication probability of the ipsilateral lung was 3.9, 3.1, and 2.8%, respectively. The number of monitor units were 5141 ± 1174, 4104 ± 786, and 3657 ± 710 MU and the corresponding beam-on times were 177 ± 54, 143 ± 29, and 148 ± 26 s.

CONCLUSION

For SBRT treatments in DIBH, a non-uniform dose prescription in the PTV, combined with a non-coplanar VMAT arc arrangement, significantly spares the ipsilateral lung while increasing dose to the GTV without major treatment time increase.

Clinical Results of Mean GTV Dose Optimized Robotic-Guided Stereotactic Body Radiation Therapy for Lung Tumors

Introduction

We retrospectively evaluated the efficacy and toxicity of gross tumor volume (GTV) mean dose optimized stereotactic body radiation therapy (SBRT) for primary and secondary lung tumors with and without robotic real-time motion compensation.

Materials and methods

Between 2011 and 2017, 208 patients were treated with SBRT for 111 primary lung tumors and 163 lung metastases with a median GTV of 8.2 cc (0.3–174.0 cc). Monte Carlo dose optimization was performed prioritizing GTV mean dose at the potential cost of planning target volume (PTV) coverage reduction while adhering to safe normal tissue constraints. The median GTV mean biological effective dose (BED)₁₀ was 162.0 Gy₁₀ (34.2–253.6 Gy₁₀) and the prescribed PTV BED₁₀ ranged 23.6–151.2 Gy₁₀ (median, 100.8 Gy₁₀). Motion compensation was realized through direct tracking (44.9%), fiducial tracking (4.4%), and internal target volume (ITV) concepts with small (≤5 mm, 33.2%) or large (>5 mm, 17.5%) motion. The local control (LC), progression-free survival (PFS), overall survival (OS), and toxicity were analyzed.

Results

Median follow-up was 14.5 months (1–72 months). The 2-year actuarial LC, PFS, and OS rates were 93.1, 43.2, and 62.4%, and the median PFS and OS were 18.0 and 39.8 months, respectively. In univariate analysis, prior local irradiation (hazard ratio (HR) 0.18, confidence interval (CI) 0.05–0.63, p = 0.01), GTV/PTV (HR 1.01–1.02, CI 1.01–1.04, p < 0.02), and PTV prescription, mean GTV, and maximum plan BED₁₀ (HR 0.97–0.99, CI 0.96–0.99, p < 0.01) were predictive for LC while the tracking method was not (p = 0.97). For PFS and OS, multivariate analysis showed Karnofsky Index (p < 0.01) and tumor stage (p ≤ 0.02) to be significant factors for outcome prediction. Late radiation pneumonitis or chronic rip fractures grade 1–2 were observed in 5.3% of the patients. Grade ≥3 side effects did not occur.

Conclusion

Robotic SBRT is a safe and effective treatment for lung tumors. Reducing the PTV prescription and keeping high GTV mean doses allowed the reduction of toxicity while maintaining high local tumor control. The use of real-time motion compensation is strongly advised, however, well-performed ITV motion compensation may be used alternatively when direct tracking is not feasible.

Additional chemotherapy improved local control and overall survival after stereotactic body radiation therapy for patients with oligo-recurrence

Background

Oligo-recurrence has been considered to confer improved prognosis than other oligometastatic conditions, and stereotactic body radiation therapy (SBRT) is considered as an option of local therapy for lung or liver metastases. The purpose of this study was to investigate the efficacy and safety of SBRT for lung and liver oligo-recurrent lesions and evaluate predictive factors for local control and prognosis.

Methods

This retrospective study included patients who presented with 1–3 matachronous lung or liver metastases, and treated with SBRT between May 2013 and March 2016 at a single institution. All patients harbored a controlled primary lesion. Patients with < 6 months of follow-up were excluded. Local control, progression free survival, and overall survival rates were analyzed according to the Kaplan–Meier product limit method. Univariable log-rank and multivariable Cox regression analyses were performed to clarify predictive factors for local control and prognosis. Toxicity was graded according to the Common Terminology Criteria for Adverse Events, version 4.0.

Results

Seventy-six patients with a total of 70 and 44 lung and liver lesions were included. The median follow-up period was 21 (range, 7–43) months. The 1-year local control, progression-free survival and overall survival rates were 89, 38 and 96%, respectively. Smaller gross tumor volume and additional chemotherapy after SBRT were significant predictive factors for better local control (p = 0.005 and p = 0.047), and the presence of a single metastatic lesion was a significant factor of good progression free survival (p = 0.008). Additional chemotherapy after SBRT was not a significant predictive factor but conferred to better overall survival (p = 0.078). Among colorectal cancer patients, post SBRT chemotherapy was significantly associated with better OS (p = 0.025). Over grade 3 adverse event was seen in only one patient.

Conclusion

SBRT is a safe and effective treatment for patients with lung and liver oligo-recurrence. Additional chemotherapy after SBRT improved local control, and single metastatic lesion was a significant predictive factor of better PFS in this study. Among colorectal cancer patients, additional chemotherapy after SBRT significantly associated better OS.

Optimizing the prescription isodose level in stereotactic volumetric-modulated arc radiotherapy of lung lesions as a potential for dose de-escalation

BACKGROUND

To derive and exploit the optimal prescription isodose level (PIL) in inverse optimization of volumetric modulated arc radiotherapy (VMAT) as a potential approach to dose de-escalation in stereotactic body radiotherapy for non-small cell lung carcinomas (NSCLC).

METHODS

For ten patients, inverse Monte Carlo dose optimization was performed to cover 95% PTV by varying prescription isodose lines (PIL) at 60 to 80% and reference 85%. Subsequently, these were re-normalized to the median gross tumor volume dose (GTV-based prescription) to assess the impacts of PTV and normal tissue dose reduction.

RESULTS

With PTV-based prescription, GTV mean dose was much higher with the optimized PIL at 60% with significant reduction of normal lung receiving 30 to 10 Gy (V 30-10Gy ), and observable but insignificant dose reduction to spinal cord, esophagus, ribs, and others compared with 85% PIL. Mean doses to the normal lung between PTV and GTV was higher with 60-70% PIL than 85%. The dose gradient index was 5.0 ± 1.1 and 6.1 ± 1.4 for 60 and 85% PIL (p < 0.05), respectively. Compared with the reference 85% PIL plan using PTV-base prescription, significant decreases of all normal tissue doses were observed with 60% and 70% PIL by GTV-based prescription. Yet, the resulting biological effective (BED) mean doses of PTV remain sufficiently high, ranging 104.2 to 116.9 Gy α/β = 10.

CONCLUSIONS

Optimizing the PIL with VMAT has notable advantage of improving the dosimetric quality of lung SBRT and offers the potential of dose de-escalation for surrounding tissues while increasing the GTV dose simultaneously. The clinical implication of re-normalizing plans from PTV-prescription at 60-70% to the GTV median dose requires further investigations.