ESTRO 37 Abstract book

S998

ESTRO 37

Results Figure 1 shows that for both fields 1.5 × 10 cm² and 2 × 10 cm², the output correction factors for Exradin A1SL and A26 vary by less than 0.1 %. The larger corrections on IBA CC01 (1.4 %) and PTW 31010 (0.5 %) in 1.5 × 10 cm² field size are mainly due to the high density material of the electrode and volume averaging, respectively. The generic beam quality correction values for Exradin A1SL in 6 MV FFF photon beam for different field sizes are listed in Table 1. The correction values for Exradin A1SL over all field sizes are within 0.1 %. The agreement between the Monte Carlo and measured chamber readings averaged over all field sizes are found to be 0.14 %, 0.06 %, 0.23 % and 0.42 % for Exradin A1SL, A26, IBA- CC01 and PTW-31010 respectively.

MC as complementary TPS engine in CCB. We focus on cross-commissioning with the clinical TPS, implementation of the beam model, development of quality assurance (QA) strategies etc. The advantage of the MC tool for patient treatment plan verification will be demonstrated on treatment plans of patients treated at CCB. Material and Methods The GPU-accelerated MC-TPS 'Fred” (Schiavi et al. 2017; University of Rome) is currently investigated at CCB. The physical beam model used in the TPS at CCB Krakow has been implemented in Fred and validated against experimentally measured data and Eclipse TPS calculations. Lateral and depth-dose distributions of proton pencil beams as well as various dose cubes placed at varying depths in water were analyzed according to the QA protocols. Dose distributions computed with Fred MC code were compared with water phantom measurements for dozens of patients treated in Krakow proton centre using clinical volumetric indices and gamma index method. Results A good agreement between single beam dose distribution computations performed with Fred and TPS was obtained. A phase space characterising Krakow proton centre beam model was built in Fred and validated using single beams, Quality Assurance fields, and patient dose distributions obtained from measurements in water phantom and from TPS calculations. We find that the GPU-accelerated MC code Fred offers superior computation speed and improved accuracy with respect to analytical TPS. In fact, in Fred a dose distribution computation can be performed with a tracking rate exceeding 106 primaries per second reducing the computation time for a 5x5x10cm3 field to less than one minute (2 GPUs, 24 CPU threads). Conclusion Moreover, MC methods can support time consuming medical physics protocols helping reducing the time for experimental patient treatment plan verification measurements in water phantom. Thanks to the high performance of GPU-accelerated TPS tools, patient treatment plan dose computation time is reduced to seconds and can be extended to biological dose recalculation with variable RBE towards an improved patient treatment at CCB in the future. EP-1849 Verification of the physics model of the TPS for asymmetric fields through Monte Carlo simulations S. Brovchuk 1 , S. Cora 2 , P. Francescon 2 1 Kyiv Regional Oncology Dispensary, Radiotherapy department, Kyiv, Ukraine 2 “San Bortolo” Hospital, Med Phys Dept, Vicenza, Italy Purpose or Objective The outcome of a radiotherapy treatment is correlated to the accuracy in the dose delivered to the patient. The dose calculation accuracy depends both on the type of algorithm used and on the physics model created in the TPS with the measurements acquired during the commissioning of the accelerator. Verification of the accuracy of the physics model in situations different from the standard measurements used for the commissioning, can be done either with comparisons with measurements or with Monte Carlo (MC) simulations. Although MC is mostly used in medical physics field as a research tool, in clinical practice it can be also used as independent method for checking commissioned data, dose calculation distributions obtained from the commercial TPS and, in case a new treatment planning techniques are introduced. The last issue was the focus of the present work, as one isocenter 3DCRT planning for the treatment of breast and supraclavicular lesions was recently introduced in our department.

Conclusion Despite the fact that the intermediate field sizes of 1.5 × 10 cm² and 2 × 10 cm² represent lateral non-equilibrium conditions, the correction for the Exradin A1SL and A26 chambers are unity to within 0.1 %. Expanding the calibration methodology from msr to intermediate non- equilibrium fields will also require a method to measure the beam quality which is part of our further studies. EP-1848 GPU-accelerated Monte Carlo TPS for treatment plan verification at CCB Krakow proton therapy centre A. Rucinski 1 , G. Battistoni 2 , M. Durante 3 , J. Gajewski 4 , M. Garbacz 1 , N. Krah 5 , P. Olko 1 , V. Patera 6 , I. Rinaldi 7 , A. Skrzypek 1 , F. Tommasino 8 , E. Scifoni 3 , A. Schiavi 6 1 Institute of Nuclear Physics PAN, Proton Radiotherapy Group, Krakow, Poland 2 INFN, Sezione di Milano, Milano, Italy 3 Trento Institute for Fundamental Physics and Applications, TIFPA, Trento, Italy 4 Institute of Nuclear Physics PAN, Cyclotron Centre Bronowice CCB, Krakow, Poland 5 CNRS, CREATIS UMR5220- U1206, Lyon, France 6 Sapienza University of Rome, SBAI, Rome, Italy 7 CNRS/IN2P3 and Lyon 1 University, UMR 5822, Lyon, France 8 University of Trento / Trento Institute for Fundamental Physics and Applications, Department of Physics / TIFPA, Trento, Italy Purpose or Objective In proton beam therapy Monte Carlo (MC) simulations explicitly take into account many details of the interactions of particles with human tissue. They are considered to be the most reliable tool to reproduce the complexity of the mixed irradiation field in heterogeneous tissues and can also account for variable radiobiological effectiveness. Until recent years, the use of MC simulations in clinical routine was limited by the computational time. The advent of GPU cards pushed the development of MC-based treatment planning system (TPS) with a significant reduction of calculation time. Bronowice Cyclotron Center (CCB) Krakow proton beam therapy centre in Poland offers proton treatment to head and neck patients since October 2016. In the first year 70 patients were treated with pencil beam scanning. In this contribution, we report on our ongoing work to establish