Investigation of the neutron contamination in IMRT deliveries with a paired magnesium and boron coated magnesium ionization chamber system

Background and PurposePhoton beams used in IMRT treatments with high energies (>10 MV) are contaminated with neutrons. Measurement of this neutron dose is of significance to the overall risk estimate of high energy radiotherapy.Materials and methodsFor measuring neutron doses a paired magnesium and boron coated magnesium chamber system was used. All measurements were performed inside the solid water phantom EasyCube using abdominal extensions. 4 different clinical treatment plans were studied.ResultsThe measured neutron dose showed to be homogeneous inside the phantom and increased with increased number of applied monitor units. The sum over all fractions showed neutron doses of 1 - 2 mGy, depending on the kind of treatment.ConclusionsUsing large conversion factors of 25 Sv/Gy, none of the studied treatment plans exceeded dose equivalents of 50 mSv for the whole treatment. This dose equivalent has to be considered whole body dose due to the homogeneous distribution of neutrons.