The Characteristic of Profile and Depth Dose of Neutron Clinac iX 15 MV

Abstract

Several previous studies described that radiation neutrons are produced by 10 MV X-ray beams operated linac. This study was performed to exercise the characteristic of profile and neutron depth dose for 15 MV X-ray beams and also to evaluate the contribution of neutron dose to the patient. The experiment used Linac iX with 15 MV X-ray beam, TLD-100, TLD-600, and phantom. The phantom was designed to evaluate the dose profile at cross-plane and diagonal axis. TLDs were calibrated separately by gamma and neutron sources. Gamma calibration was carried out using 137Cs source whereas neutron calibration was done using 252Cf source at BATAN Facility. Neutron dose equivalents were calculated on cross-plane and diagonal axis in 10 cm × 10 cm fields at 15 positions from the central axis, on the phantom surface and depths of 2 cm, 3 cm, and 15 cm. The percentage maximum neutron dose equivalent distributions were obtained around of 3 cm depth for cross-plane and diagonal axis. Furthermore, the dose profile of neutron at different depths and off-axis position are not symmetrical. Neutron dose in out-of-field had no significant response compared to the in-field. The relative neutron dose in out-of-field is 27% and 24% normalized to the maximum neutron dose at each depth on cross-plane and diagonal axis respectively.

Evaluation of the linac neutron dose profile for various depths and field sizes: a Monte Carlo study

“…The direct neutron measurement using TLD-600 and TLD-100 pair has been performed in Varian Clinac iX 15 MV. The result shows that the highest measured neutron dose equivalent is 0.298 mSv/Gy [23]. According to ICRP 103, the highest radiation weighting factor will be in the range of ∼1 MeV neutrons [9].…”