ESTRO 37 Abstract book

S993

ESTRO 37

Heidelberg, Germany 5 National Centre of Oncological Hadrontherapy CNAO, Medical Physics, Pavia, Italy 6 University of Pavia, Department of Physics, Pavia, Italy 7 Heidelberg Ion-beam Therapy Center HIT, Heidelberg, Germany Purpose or Objective A treatment plan recalculation platform, FROG (Fast Recalculation and Optimization on GPU), for the four ions ( 1 H, 4 He, 12 C, 16 O) available at the Heidelberg Ion-beam Therapy Center (HIT) has been developed in-house, capable of accurate physical dose, dose-averaged linear energy transfer (LET D ) and biological dose (e.g. LEM, MKM, etc.) computation within minutes. For improved dose estimation in patient cases with moderate to severe bone and soft-tissue heterogeneity, a novel pencil beam model has been derived from Monte Carlo simulation, explicitly accounting for the pencil beam interactions within the HIT beam applications and monitoring system (BAMS). Material and Methods FLUKA Monte Carlo simulations for depth and lateral dose were performed for the four ions, incorporating a detailed geometry of the HIT beam-line [1]. Particles impinging the high Z materials of the BAMS were flagged during simulation and scored separately from the primary beam. Double Gaussian (DG) and Triple Gaussian (TG) parameterizations of the lateral spreading in water were performed. Spread out Bragg peaks (SOBPs) in water and various patient cases were simulated with the Monte Carlo code and recalculated in the FROG platform for comparison. Pencil beam splitting was executed in FROG following a beamlet superposition approach [2]. Results FROG recalculations of the SOBPs in water for the four ions are in agreement with the Monte Carlo results, with a maximal variation of ~1.5% occurring for Carbon ions, which can be attributed to limitations of TG parameterization. Recalculation of patient cases demonstrates excellent agreement with Monte Carlo simulation as shown for example in Figure 1 for a two- field proton chordoma case. A comparison in terms of lateral dose distributions calculated by means of FLUKA and FROG is reported in Figure 2.

not change the fraction of plans with high Γ pass rates significantly.

Conclusion Despite the lack of correlation of the metrics in the study, all plans passed the Γ(3%, 3mm) analysis, and little variation in complexity between the analyzed plans was observed. The results form a statistical basis for evaluating future plans, which are likely to have high dosimetric accuracies if they have similar complexities as plans which have already passed QA. Plans with deviating values should be evaluated more carefully. Future studies will include other diagnosis groups, where larger variations in plan complexity may be expected. Ref: [1] A. L. McNiven [2] L. Masi [3] D. Willis EP-1838 FROG: a novel GPU-based approach to the pencil beam algorithm for particle therapy S. Mein 1,2 , T. Tessonnier 3 , B. Kopp 1,4 , K. Choi 5,6 , T. Haberer 7 , J. Debus 1,4,7 , A. Abdollahi 1,4,7 , A. Mairani 5,7 1 German Cancer Research Center DKFZ, Imaging and Radiation Oncology, Heidelberg, Germany 2 Heidelberg University, Physics Faculty, Heidelberg, Germany 3 Centre François Baclesse - Caen, Radiation Oncology, Caen, France 4 Heidelberg University Clinic, Radiation Oncology,

Figure 1: FLUKA and FROG plan recalculation from a two- field proton chordoma patient.