The measurement of photoneutrons in the vicinity of a Siemens Primus linear accelerator

This study involves the measurement of photoneutron contamination emitted from a Siemens Primus medical linear accelerator by using BD–PND bubble detectors. Various bubble detectors were arranged around the linac head with the interval of 1 m and at the same height as the isocenter to measure the dose equivalent distribution in the treatment room. The measurements were performed for 15 MV X-rays with 40×40 cm2 and 0×0 cm2 fields and for 15,18, and 21 MeV electrons with 25×25 cm2 electron cone. Neutron dose equivalent rate at the points of measurement in the treatment room decreased with increasing distance to the isocenter. The maximum neutron dose equivalents were at the isocenter, and the values for 15 MV 40×40 and 0×0 cm2 were 1843±90 and 169.9±59.9 μSv per Gy X-ray, respectively. The values for 15, 18 and 21 MeV electrons with 25×25 cm2 cones were 100.0±20.4, 262.7±61.2 and 349.0±29.6 μSv per Gy electron, respectively. The neutron contamination of electrons less than 12 MeV was below the detection limit.