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Correction of percentage depth dose for varying SSD for 8 MV x rays and 60 Co gamma rays
Author(s) -
Agarwal Suresh K.,
Wakley Jack,
Scheele Ronald V.,
Howard Barbara Y.
Publication year - 1974
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 - 10.1118/1.1637274
Subject(s) - gamma ray , percentage depth dose curve , physics , dosimetry , nuclear medicine , quadratic equation , cobalt 60 , mathematics , computational physics , ionization chamber , irradiation , nuclear physics , geometry , ionization , ion , medicine , quantum mechanics
A change of source skin distance results in a significant change in percentage depth dose. The factors P(f 2 ) / P ( f 1 ) by which percentage depth dose at SSD f 1is to be multiplied to find new percentage depth dose at SSD f 2are tabulated and presented in a graphical form, for f 1 = 100 cm and f 2 = 110–140 cm for 8 MV x rays and for f 1 = 80 cm and f 2 = 90–140 cm for 60 Co gamma rays. The use of quadratic and linear equations to calculate this factor have been suggested. The ratios calculated using a quadratic equation agree very well with values from experimental data.