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Physical factors affecting absorbed dose to the skin from cobalt‐60 gamma rays and 25‐MV x rays
Author(s) -
Gag William F.,
Horton John L.
Publication year - 1979
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 - 10.1118/1.594583
Subject(s) - cobalt 60 , dosimetry , percentage depth dose curve , gamma ray , backscatter (email) , ionization chamber , absorbed dose , materials science , radiation , nuclear medicine , scattering , optics , dose profile , ionization , physics , irradiation , medicine , ion , nuclear physics , telecommunications , wireless , quantum mechanics , computer science
When there is an absence of scattering material adjacent to the skin on the exit side of a megavoltage beam the dose to the skin is less than would be calculated using depth dose tables or isodose distributions measured in “semi‐infinite” phantoms. Ionization measurements using a thin‐window parallel‐plate chamber show that the dose at 4 mg/cm 2 from the exit surface is 14% to 16% less for cobalt‐60 gamma rays and about 8% less for 25‐MV x rays compared to the dose with full backscatter. As the angle of incidence increases the skin dose increases due to radiation scattered toward the surface. A method for the calculation of skin doses from tangential therapy beams is described.