ESTRO 2022 - Abstract Book

S1593

Abstract book

ESTRO 2022

0.01 monitor units (Fig. 1). The plans from the three treatment modalities offered equivalent target coverage. For the proton plans, relative biological effectiveness (RBE) variations were included by calculating both the proton dose with (1) a fixed RBE of 1.1 (as applied clinically), or (2) with variable RBE incorporating dose-averaged linear energy transfer (LETd), as RBE=1+0.055xLETd (PMB 2018;63:225009). The LETd distribution was calculated from the Eclipse treatment planning software. Relative risks (RRs) of brain radiation-induced SC, based on the organ equivalent dose concept (Theor Biol Med Model 2011;8:27), were analyzed and compared by applying a brain-specific full mechanistic dose-response model for carcinoma induction.

Results SC risks were lowest applying PAT-surrogate, with a median RR of 0.92 when compared to IMPT and 0.53 when compared to VMAT (RBE=1.1). The median RR for IMPT vs. VMAT was 0.58. For ranking of the plans according the SC risks, the same patterns were seen across all five patients (Fig. 2). Including variable RBE did not influence the SC risks estimates considerably, especially when investigating PAT-surrogates where the median in RR was identical for RBE=1.1 and RBE(LET). For IMPT vs. VMAT, the median RR was 0.58 for RBE=1.1 vs. 0.57 for RBE(LET) (Fig. 2).

Conclusion Despite an increased low-dose bath with PAT-surrogate vs. IMPT, a tendency towards SC risk-reduction was seen for PAT- surrogate in centrally located tumors. Compared to VMAT plans, SC risks were halved with both proton modalities. However, these results are based on the assumption that the RBE for cell inactivation and cell mutation/cancer induction are equivalent, which remains to be clarified.

PO-1786 Exploratory analysis of anatomical regions associated with Dysphagia measured with the MDADI

A. Carver 1 , A. Hartley 2 , D. Mcnulty 3 , H. Mehanna 4

1 University Hospitals Birmingham NHS Foundation Trust, Medical Physics, Birmingham, United Kingdom; 2 University Hospitals Birmingham NHS Foundation Trust, Oncology, Birmingham, United Kingdom; 3 University Hospitals Birmingham NHS Foundation Trust, Health Informatics, Birmingham , United Kingdom; 4 University Hospitals Birmingham NHS Foundation Trust, ENT, Birmingham , United Kingdom Purpose or Objective The DeEscalate study compared the use of Cisplatin and Cetuximab in combination with radiotherapy in the treatment of Human-Papillomavirus (HPV) positive cancer of the oropharynx. As part of the study the MD Anderson Dysphagia Inventory