ESTRO 2022 - Abstract Book

S1527

Abstract book

ESTRO 2022

RBE.

PO-1726 Exploration of RBE optimization in proton arc therapy

H. Henjum 1 , S. Pilskog 1,2 , C. H. Stokkevåg 3,2 , J. Tjelta 3,2 , K. S. Ytre-Hauge 1

1 University of Bergen, Institute of Physics and Technology, Bergen, Norway; 2 Haukeland University Hospital, Department of Oncology and Medical Physics, Bergen, Norway; 3 University of Bergen, Institute for Physics and Technology, Bergen, Norway Purpose or Objective In clinical proton therapy a relative biological effectiveness (RBE) of 1.1 is used, although it is known that the RBE varies and depends on several factors as the LET, tissue type and dose. This has given rise to several different variable RBE models which aim to give a more accurate description of the effects of protons. Proton arc therapy (PAT) is an emerging treatment modality and has showed promise in improving both target coverage and reducing linear energy transfer (LET) in organs at risk (OARs). In the current study we further investigate the potential of RBE based optimization in PAT, employing both full and pruned arc configurations in treatment of complex tumours surrounding critical OARs. Materials and Methods Intensity modulated proton therapy (IMPT) and PAT plans for a paediatric ependymoma patient were created. The PAT plans consisted of a 240° arc, where the front of the patient received no fields (Figure 1a). Additionally, the pencil beam spots in the arc plan (denoted full PAT plan) with the highest energies in each direction were removed to create a pruned