  Two full rotating gantry with different nozzles (Multipurpose nozzle with
MLC, Scanning Dedicated nozzle) with conventional cyclotron system is installed
and under commissioning for various proton treatment options at Samsung Medical
Center in Korea. The purpose of this study is to investigate neutron dose
equivalent per therapeutic dose, H/D, to x-ray imaging equipment under various
treatment conditions with monte carlo simulation. At first, we investigated H/D
with the various modifications of the beam line devices (Scattering, Scanning,
Multi-leaf collimator, Aperture, Compensator) at isocenter, 20, 40, 60 cm
distance from isocenter and compared with other research groups. Next, we
investigated the neutron dose at x-ray equipments used for real time imaging
with various treatment conditions. Our investigation showed the 0.07 ~ 0.19
mSv/Gy at x-ray imaging equipments according to various treatment options and
intestingly 50% neutron dose reduction effect of flat panel detector was
observed due to multi- leaf collimator during proton scanning treatment with
multipurpose nozzle. In future studies, we plan to investigate experimental
measurement of neutron dose and validation of simulation data for x-ray imaging
equipment with additional neutron dose reduction method.
