Determination of Effective Dose from Neutrons and Scatter photons in 3D, IMRT and VMAT

Abstract

The scatter photons and neutrons from high energy photon beams (more than 10 MV) will increase the undesired dose to the patient and the staff working in linear accelerator room. This undesired dose which is found at out-of-field area can increase the probability of secondary malignancy. The purpose of this study is to determine the equivalent dose of scatter photons and neutrons generated by 3 different treatment techniques: 3D-conformal, IMRT and VMAT. The measurement was performed using two types of the Optically Stimulation Luminescence (OSL and OSLN) detectors in the Alderson Rando phantom that was irradiated by 3 different treatment techniques following the actual prostate cancer treatment plans. The scatter photon and neutron equivalent dose were compared among the 3 treatments techniques at the surface in the out-of-field area and the critical organs. Maximum equivalent dose of scatter photons and neutrons was found when using the IMRT technique. The neutrons showed average equivalent doses of 0.26, 0.63 and 0.31 mSv/Gy at abdominal surface region which was 20 cm from isocenter for 3D, IMRT and VMAT, respectively. The scattered photons equivalent doses were 6.94, 10.17 and 6.56 mSv/Gy for 3D, IMRT and VMAT, respectively. For the 7 organ dose measurements, the scattered neutron and photon equivalent doses in out of field from the IMRT plan were highest. At the liver which was the nearest organ at out of field, the average equivalent dose were 0.73, 10.23 mSv/Gy for neutron and photon, respectively. The result revealed that the scatter equivalent doses for neutron and photon were higher for IMRT. The equivalent doses for VMAT were slightly higher than 3D. So the suitable treatment techniques should be selected to benefit the patient and the treatment room staff.