ESTRO 2022 - Abstract Book

S1298

Abstract book

ESTRO 2022

plans. A standard setup of 2 posterior beams at gantry angles of 165 and 195 degrees were used. Scenario-based robust optimization with 7mm setup error and 3% relative stopping power prediction error (range) robustness was used. Results Mean dose to OARs and the total scanned volume (proton vs VMAT) showed relevant OAR dose reductions for the majority of patients and for all OARs, with largest absolute reductions for pancreas and right kidney (4-6 Gy), and largest relative reductions for stomach and right kidney (90%-96%); see Figure & Table. The total sum of mean dose reductions (kidney L + kidney R + stomach + pancreas) was in the range of 15-20 Gy in 4 patients (all PAO), 10 Gy in 1 patient and 3 Gy in 1 patient (both PAO+PAI: case nr 5 & 6 in Figure). Compared to the historical APPA group, we observed that with VMAT dose levels to the stomach decreased and dose to the kidneys increased. With proton therapy, low dose levels to both kidney and stomach can be achieved.

Conclusion We demonstrated that with proton therapy clinically meaningful OAR dose reductions can be achieved with respect to SPC risks in a proportion of the seminoma patient group, compared to modern RT with VMAT. Risk reductions of other late effects (e.g. diabetes) can be expected as well. For young seminoma patients with unfavorable dose distributions to OARs with a VMAT plan, proton therapy would therefore be a superior treatment option.

PO-1519 Reassessment of neutron contamination during breast treatment for different configurations

A. Dabach 1 , P. Steven 1 , A. Taieb Mokaddem 1 , M. De Saint-Hubert 2 , O. Van Hoey 2 , I. Chiairi 1 , M. Machiels 1 , P. Poortmans 1 , D. Verellen 1 1 Iridium Network, Radiotherapy, Antwerpen, Belgium; 2 Belgian Nuclear Research Centre, Dosimetric Applications, Mol, Belgium Purpose or Objective Early assessment of neutron contamination in IMRT applications was based on delivery techniques [1,2]. Recently these delivery techniques have been optimized and made more efficient with respect to the number of MU required for a certain dose. In fact, the number of MU for many IMRT or VMAT treatments required for a certain fraction dose are now comparable to those required for 3D-conformal techniques. Furthermore, with the Covid-19 pandemic, a new hypofractionated breast