Feasibility assessment of proton treatment for ventricular tachycardia-treatment planning study

Background: Photon radiotherapy has been demonstrated as an emergent role for ablation of ventricular tachycardia (VT). Compare to photon radiotherapy, proton with rapidly distal fall off is an advantage in radiotherapy. Therefore, the feasibility assessment of a single fraction proton irradiation for VT instead of the photon therapy is investigated in this study. Methods: Two patients treated with and an implantable cardioverter-defibrillator (ICD) implantation and repeated catheter ablations were retrospective selected for study. Targeted lesions in image set, including left ventricular summit and right ventricular outflow tract septum and nearby organs at risk, were contoured by cardiologist and radiation oncologist. The target dose coverage and dose in organs at risk by using the photon volumetric arc therapy, proton wobbling and proton pencil beam scanning treatment technique were evaluated respectively. Results: In comparison of dose volume parameters and isodose distributions including R30, R50 [ratio of the 50% and 30% of prescription isodose volume to the volume of planning target volume (PTV)] among three different techniques. The conformal index and homogeneity index in all type of treatment plans are demonstrated to deliver a conformal, homogeneous dose to the target area. And, showing no difference in the proton wobbling and proton pencil beam technique in nearly all result. Conclusions: This treatment planning study indicated that using the proton beam to treat VT is a feasible therapeutic option. Compared to photon therapy treatment planning, proton can offer lower radiation dose to heart and lung with the same conformal index. Nevertheless, several issues require consideration in future studies, including accurate patient localization, motion margin evaluation of respiration and heartbeat, dose measurement, and verification of small field irradiation.