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


METHODS
For 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.


RESULTS
The 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.


CONCLUSIONS
Using 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.
Becker
Julian
J
Department of Radiotherapy and Radio-Oncology, University Medical Center Hamburg-Eppendorf, University of Hamburg, Germany. j.becker@uke.uni-hamburg.de
Brunckhorst
Elin
E
Schmidt
Rainer
R
D001895:Boron / Q000737:chemistry; D002138:Calibration; D003198:Computer Simulation; D019583:Dose Fractionation, Radiation; D006258:Head and Neck Neoplasms / Q000532:radiotherapy; D006801:Humans; D008274:Magnesium / Q000737:chemistry; D008297:Male; D009010:Monte Carlo Method; D009502:Neutrons; D011471:Prostatic Neoplasms / Q000532:radiotherapy; D011879:Radiotherapy Dosage; D050397:Radiotherapy, Intensity-Modulated / Q000295:instrumentation*; D012542:Scattering, Radiation
D008274:Magnesium; D001895:Boron