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Unwanted photon and neutron radiation resulting from collimated photon beams interacting with the body of radiotherapy patients
Author(s) -
Ing H.,
Nelson W. R.,
Shore R. A.
Publication year - 1982
Publication title -
medical physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.473
H-Index - 180
eISSN - 2473-4209
pISSN - 0094-2405
DOI - 10.1118/1.595137
Subject(s) - collimated light , photon , neutron , monte carlo method , physics , radiation , dosimetry , spectral line , beam (structure) , nuclear physics , optics , nuclear medicine , medicine , laser , statistics , mathematics , astronomy
Monte Carlo calculations have been made to determine the energies delivered by photons and neutrons to the human body irradiated by collimated photon beams. The beams were monoenergetic and ranged from 100 keV to 40 MeV. The energy deposition in the body was sorted into two regions: inside and outside the irradiated volume. Most of the results obtained were for a beam size of 100 cm 2 although some calculations were also made for 600 cm 2 beams. The effect of beam size on energy deposition in the two regions was investigated for 60 Co gamma rays. Graphs are presented which give the integral doses delivered by neutrons and photons to the two regions for therapy beams of various energies. These graphs can be used to calculate the integral doses which are delivered inside and outside the treatment volume for photon spectra from most medical accelerators. Calculations of energy deposition were also made for the spectra from two particular accelerators. These were done using Monte Carlo as well as by simply “folding” the spectra into the results for monoenergetic photons. The results obtained by both methods were in good agreement and indicated that the integral doses deposited outside the treatment volume by neutrons are more than two orders of magnitude smaller than those deposited by scattered photons.