ESTRO 2022 - Abstract Book

S1533

Abstract book

ESTRO 2022

obtained. Other particles, such as neutrons or alpha particles, can also be tracked. The GPU implementation further increases the speed of the code. Benchmark MC simulations with PENH-NUCL [1,2] and TOPAS [3] have been used to test GHMCp dose predictions and activation maps in homogeneous and heterogeneous phantoms. A realistic prostate treatment plan consisting of 1610 pencil beams with energies from 100 MeV to 155 MeV was also simulated. A performance study to assess the speed gain reached with GHMCp has been performed. Results Good results have been obtained with the GHMCp code when compared to the reference MC codes in terms of gamma evaluation, with more than 99% voxels fulfilling 3%-3 mm criteria in all homogeneous and heterogeneous phantoms and more than 96% voxels in the prostate MCTP. Figure 1 shows dose distribution in the prostate MCTP from PENH-NUCL and GHMCp. GHMCp was proved to be about 10000 times faster than PENH-NUCL (1 core) and 800 times faster than TOPAS (16 cores), for similar statistical uncertainty.

Figure 1. Dose distribution in the prostate MCTP calculated with GHMCp (NVIDIA GeForce GeForce RTX 2080 Ti with 4352 CUDA Cores) (a) and PENH-NUCL (1 core of Intel Xeon CPU E5-2650 0 @ 2.00GHz) (b).

Conclusion The GHMCp is a fast and versatile computation tool that allows changing from one MC physics to another, the easily incorporation of secondary particles, and that calculates dose and activation maps within seconds, which makes it possible real time calculations and inverse dose planning.

PO-1731 Investigating proton therapy as a treatment option for pregnant breast cancer patients

R. Ahmad 1 , E. Baer 2 , K. Pile 1 , C. Collins-Fekete 1 , S. Gulliford 3 , S. Wickers 3 , M. Hawkins 1

1 University College London, Department of Medical Physics and Biomedical Engineering, London, United Kingdom; 2 University College London, Department of medical Physics and Biomedical Engineering, London, United Kingdom; 3 University College London Hospitals NHS Foundation Trust, Department of Radiotherapy Physics, London, United Kingdom Purpose or Objective The Steering Committee on Clinical Practice Guidelines for the Care and Treatment of Breast Cancer states that pregnancy is an absolute contraindication for breast irradiation (Whelan et al., 2003) due to the developing foetus being highly radiosensitive. Particularly, the effect of scattered radiation in conventional x-ray treatments is of concern. We investigate proton therapy as a treatment option for pregnant breast cancer patients. A phantom was used to estimate doses to the foetus from intensity-modulated proton therapy (IMPT) during the first trimester of pregnancy. Materials and Methods We use a virtual anthropomorphic phantom (Xu et al., 2007) in the early gestational period of pregnancy, segmented into major organs and tissues. The phantom includes a 3-month-old foetus, segmented into foetal soft tissue and brain. For all segments in the phantom, the relative stopping powers are calculated voxel-wise using corresponding elemental compositions and densities from Chen et al., 2004 (maternal/foetal tissues) and ICRU 46 (remaining tissues), with mean excitation energies ( I -values) from ICRP 44 and Bär et al., 2018. Treatment planning was performed in Eclipse, with planning target volumes created by a therapeutic radiographer for the right and left breast. Four IMPT plans were generated (40 Gy (RBE), 15 fractions) using spot scanning and single field optimisation, each with a Lexan range shifter (5 cm water equivalent thickness) to degrade the proton energy for shallow range: 1) Single field (315°) and 2) two fields (0°, 315°) to the right breast; 3) single field (45°) and 4) two fields (0°, 45°) to the left breast. Following parametrisation of the beam properties, treatment plans were imported into TOPAS (Perl et al., 2012), simulating total absorbed and equivalent neutron doses, scored for the foetal brain and soft tissue. Results Total absorbed doses and equivalent neutron doses to the foetus with and without range shifter are displayed in Table 1. The average foetal dose (std) across all four plans was 0.044 (0.008) mGy and 0.39 (0.09) mSv for the total