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Purpose/objective(s): Compared to conventional TBI techniques, VMAT TBI has been shown to provide superior lung sparing while maintaining target coverage. However, one of the significant barriers preventing widespread VMAT TBI implementation is the time-consuming treatment planning process. To overcome this issue, we developed an in-house automated treatment planning process for VMAT TBI and evaluated the resulting dosimetric plan quality against manually generated treatment plans.Materials/methods: Application Programming Interface (API) scripting was utilized to interface with a commercial treatment planning system. Two scripts were built to facilitate autoplanning: the first generates optimization structures, creates the plan, places the beams, and sets the optimization constraints using user-defined input. The second uses the output from the first script to run successive VMAT optimizations, where the plan quality is evaluated after each iteration and the optimization objectives are adjusted according to dosimetric deviation of each constraint from its objective. The optimization loop proceeds until either all plan objectives are met, or the number of iterations reaches a user-defined maximum. Nine patients previously treated in our clinic with VMAT TBI were used to evaluate the efficacy of the proposed autoplanning process. The plan quality of the produced auto plans was evaluated by comparing against the manually generated clinical plans. The clinically relevant metrics, including global Dmax, PTV V110%, lungs and lungs-1cm Dmean, kidneys Dmean, and bowel Dmax, were analyzed. All plans were normalized to deliver 100% of the prescription dose to 90% of the PTV. All dosimetric comparisons between the auto and manual plans were made with the dose expressed as a percentage of the prescription dose. Paired t-test was used to compare the dosimetric indices between auto and manual plans.Results: No significant differences were observed between the manual and autoplan global Dmax (P < 0.893), PTV V110% (P < 0.734), kidneys Dmean (P = 0.351), and bowel Dmax (P < 0.473). Statistically significant decreases in the Dmean to the lungs and lungs-1cm volumes of 5.4% ± 6.4% (P < 0.024) and 6.8% ± 7.4% (P < 0.017), respectively, were obtained with the autoplans as compared to the manual plans. The required time for treatment planning (i.e., contouring and planning) ranged from approximately 2-3 days for the manual plans as compared to approximately 3-5 hours for the autoplans.Conclusion: Superior lung sparing with the same target coverage and similar global Dmax were observed with the autoplans as compared to the manual treatment plans. Large reductions in planning time were obtained using the developed autoplanning scripts as compared to manual planning, thus reducing the required effort of the treatment planning team and making VMAT TBI a more accessible treatment technique. The developed scripts will be made open-source and freely available to the public in the near future. [ABSTRACT FROM AUTHOR]

Purpose/objective(s): The first clinical biology-guided radiation therapy (BgRT) system - RefleXion X1 - is installed and is being commissioned for clinical use at our institution. The system delivers 6MV-FFF beam via 50 firing positions at 850 cGy/min dose rate on 60 rpm rotating gantry with the couch advancing in 2.1 mm increments. Collimation is achieved through a binary multi-leaf collimator system composed of 64 (6.25 mm width at 850 cm SAD) leaves and 10mm or 20mm jaws. The purpose of this study was to compare the treatment plan quality and delivery efficiency for SBRT cases without PET-guidance.Materials/methods: Five lung cancer patients (50 Gy/4fx) with motion-inclusive PTV previously treated with VMAT SBRT were selected for this retrospective study. For each VMAT plan a corresponding plan was generated on the RefleXion treatment planning system (TPS) using our institutional planning constraints. VMAT SBRT plans used 1-2 partial arcs with 10MV-FFF energy and 2400 MU/min dose rate. RefleXion SBRT plans used all 50 firing positions and 1 cm jaw collimation. As plan normalization option does not yet exist in the RefleXion TPS, the plans were optimized to achieve PTV D95% coverage with 100% of prescription dose to the best of planner's ability. All clinically relevant metrics in this study, including plan PTV D95%, PTV D1%, 50% isodose volume (I50%), Conformity Index (CI), organs at risk constraints, and treatment time were analyzed and compared between VMAT and RefleXion plans using paired t-tests.Results: Clinically acceptable plans were obtained with both techniques. The average PTV volume was 14.1 ± 6.4cc. For VMAT and RefleXion plans, no statistically significant difference was observed in PTV D95%, PTV D1%, CI or I50%. Ipsilateral lung volume spared at 12.4 Gy (VS12.4) was slightly greater (31.6cc increase, P < 0.035) and skin Dmax was slightly lower (1.4 Gy decrease, P < 0.038) for RefleXion plans. Treatment beam-on time was significantly longer for RefleXion plans (23.4min increase, P < 0.0002).Conclusion: RefleXion TPS provided comparable plan quality to lung SBRT VMAT plans. Treatment beam-on time is significantly longer for the RefleXion system. [ABSTRACT FROM AUTHOR]