ESTRO 2022 - Abstract Book

S152

Abstract book

ESTRO 2022

Conclusion We could not confirm our hypothesis that lymphoma-specific ABAC performs better than ABAC developed using BC patients. The disappointing performance of ABAC tools for breast contouring in young lymphoma patients suggests more sophisticated methods might be needed in this complex population, e.g. specific atlases to account for variations in arm position and different dense tissue distribution in the breast. We also found ESTRO guidelines need small adaptations to contour ‘breast as an OAR’, which needs further exploration. The different performance between right and left breasts may be due to differences in heart and lung shape and is the subject of ongoing work.

PD-0175 Cardiac conduction system exposure during modern radiation therapy for mediastinal Hodgkin lymphoma

P. Loap 1 , A. Mirandola 2 , L. De Marzi 1 , A. Barcellini 2 , V. Vitolo 2 , A. Iannalfi 2 , R. Dendale 1 , E. Orlandi 2 , Y. Kirova 1

1 Institut Curie, Department of Radiation Oncology, Paris, France; 2 Centro Nazionale di Adroterapia Oncologica, Radiation Oncology Clinical Department, Pavia, Italy Purpose or Objective Radiation-induced arrhythmias and conduction disorders are frequent adverse events of mediastinal Hodgkin lymphoma radiotherapy. Exposition of cardiac conduction system during mediastinal Hodgkin lymphoma (HL) radiotherapy has never been studied, despite increasing use of volumetric modulated arc therapy (VMAT) which tends to expose larger volume to low dose bath. We evaluated conduction node exposure during mediastinal HL irradiation with VMAT and estimated the potential dosimetric benefit with intensity modulated protontherapy (IMPT). Materials and Methods Atrioventricular (AVN) and sinoatrial (SAN) nodes were retrospectively delineated according to published guidelines on the simulation CT scans of 20 localized unfavorable mediastinal HL cancer patients treated in a consolidative setting with deep- inspiration breath-hold (DIBH) VMAT. IMPT treatment was re-planned on the simulation CT scans. Mean and maximum doses to the SAN and to the AVN were retrieved and compared. Correlation coefficients were calculated between doses to the SAN, to the AVN and to the whole heart. Results For VMAT irradiation, the SAN mean dose was 7.0 Gy [range: 0.0-24.3 Gy] and the SAN maximum dose was 13.2 Gy [0.2- 29.4 Gy]; the AVN mean dose was 2.1 Gy [0.0-16.7 Gy] and the AVN maximum dose was 2.7 Gy [0.0-19.4 Gy]. IMPT significantly reduced SAN mean dose to 1.7 Gy [0.0-11.1 Gy] (p<0.01), SAN maximum dose to 5.5 Gy [0.1-25.8 Gy] (p<0.01), AVN mean dose to 0.1 Gy [0.0-1.1 Gy] (p<0.01), and AVN maximum dose to 0.2 Gy [0.0-2.8 Gy] (p<0.01) ( Figure 1 ). For VMAT, correlations were strong between mean doses to the heart and to the SAN (r=0.85) and between mean doses to the heart and to the AVN (r=0.94); they were moderate between maximum doses to the heart and to the SAN (r=0.63) and weak between maximum doses to the heart and the AVN (r=0.38). After IMPT replanning, correlations became moderate between mean doses to the heart and to the SAN (r=0.64) but remain strong between mean doses to the heart and to the AVN (r=0.86); they became unsignificant between maximum doses to the heart and to the SAN (r=0.24) and remained weak between maximum doses to the heart and to the AVN (r=0.31).