Abstract ID: 29 Assessment of neutron dose equivalent during line scanning proton therapy using dynamic multi-leaf collimator

Abstract

The purpose of this study was to evaluate the neutron dose equivalent from proton nuclear interactions with the multi-leaf collimator (MLC) during line scanning proton therapy. We generated a wobbling mode plan, a scanning mode plan, and a dynamic MLC with scanning mode plan with a field size of 7 cm and 12 cm, a maximum proton energy of 150 MeV. A Monte Carlo study was performed using the GEANT4 code (version 10.01.p01) [1] for our virtual machine based on the multi-purpose proton nozzle. In the wobbling mode, scanning mode, and scanning mode with dynamic MLC, the neutron dose equivalent generated through the nozzle was compared using the 12 cm diameter receptor. The receptors were located at the distance of r = 0, 25, 50, 100, 150, and 200 cm from the isocenter. In both field size conditions, the neutron dose equivalent in the scanning mode were 96.6%, 98.7%, 98.7%, 98.4%, 98.2%, and 97.9% lower than the wobbling mode in each receptor position, respectively. However, the neutron doses equivalent using line scanning with MLC to reduce the lateral penumbral width were 53.0%, 91.8%, 90.0%, 90.2%, 92.0%, and 91.6%, respectively, compared to the wobbling mode. The use of dynamic MLC in the scanning increases the neutron dose equivalent, but the use of dynamic MLC can reduce the dose to the organ at risk around the target and avoid disadvantages of the conventional scanning proton therapy [2] . However, according to the results of this study, secondary cancer caused by the effect of neutron dose increased when scanning with dynamic MLC is not negligible [3]