Session Item

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).

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.

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).

Figure 1: Cardiac conduction node exposure during mediastinal Hodgkin lymphoma irradiation with volumetric modulated arc therapy (VMAT) or intensity modulated proton therapy (IMPT) with deep-inspiration breath-hold (DIBH). Mean (A) and maximum (B) doses delivered to the heart, to the sino-atrial node (SAN) and to the atrio-ventricular node (AVN). 

The SAN can be substantially exposed during mediastinal HL radiotherapy with DIBH-VMAT. Mean heart dose is poorly representative of conduction node exposure. Proton therapy significantly reduces radiation doses to the cardiac conduction system and might consequently be considered in case of underlying rhythmic or conduction disorders.