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

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.