Spot-scanning proton therapy for targets with adjacent cardiac implantable electronic devices - Strategies for breast and head & neck cancer.

Abstract

Cardiac implantable electronic device (CIED) malfunctions can be induced by secondary neutron dose from spot-scanning proton therapy. A recent in-vitro study investigating secondary neutron dose to CIEDs up to 7mSv per fraction found that exposure of secondary neutrons in this range was clinically manageable. This study presents decision algorithms proposed by a national expert group for selection of patients with breast and head & neck (H&N) cancer with CIEDs adjacent to target for proton therapy based on the 7mSv threshold. Ten patients with breast cancer and five with H&N cancer were included in the study. Five patients with breast cancer received photon therapy with CIED and proton plans were retrospectively created. The remaining patients received proton therapy without CIED and a worst-case position of a virtual CIED was retrospectively delineated. Secondary neutron dose was estimated as ambient dose equivalent H*(10) using Monte Carlo simulations. For patients with breast cancer and with contralateral CIED, the secondary neutron dose to the CIED was below 7mSv per fraction for CTV<1500cm3 in 2Gy fractions and CTV<1000cm3 in 2.67Gy fractions. The secondary neutron dose to the CIED was below 7mSv per fraction for all patients with H&N cancer. Simulations of neutron exposure suggest that proton therapy is feasible for most patients with CIED adjacent to target. This forms the basis for decision algorithms for selection of patients with CIED for proton therapy.