ESTRO 2022 - Abstract Book

S711

Abstract book

ESTRO 2022

Conclusion The potential of PBS-PT to reduce heart and lung toxicity compared to IMRT was significant and persistent from Plan to Start. All PBS-PT techniques responded similarly to uncertainties and were sufficiently robust at Plan, and for the majority of patients at Start. Altered breathing patterns between Plan and Start jeopardized target coverage for 3/15 patients with all PBS-PT techniques. Adaptive protocols should therefore include imaging at onset of or early in treatment.

MO-0793 Tissue-specific range uncertainty estimation in proton therapy

C. Olesen 1 , L.P. Muren 1 , U.V. Elstrøm 1 , V.T. Taasti 2

1 Aarhus University Hospital, Danish Centre for Particle Therapy, Aarhus N, Denmark; 2 Maastricht University, Department of Radiation Oncology (MAASTRO), Maastricht, The Netherlands Purpose or Objective Proton therapy is sensitive to range uncertainties, which mainly originate from the CT-based estimation of the proton stopping power ratio (SPR). Range uncertainties are typically accounted for by margins or robust optimization, where tissue- independent (TI) uncertainties (same uncertainty for all tissues) mainly are used. However, it can be assumed that the range uncertainty margins depend on the specific tissues traversed by the protons. The aim of this study was to investigate the differences between range margins based on tissue-specific (TS) and TI range uncertainties. Materials and Methods The CT-based range uncertainties caused by, e.g., CT image noise, beam hardening, and CT-to-SPR conversion inaccuracies were evaluated for lung, soft and bone tissues to quantify the TS range uncertainties (Fig 1). Proton plans were created using matRad for three patients (pelvic, liver, and head-and-neck (HN)) and a thorax phantom, to evaluate the range uncertainties in different tissue compositions. Conventional optimization (i.e., without robust optimization) was used to