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Lung dose corrections for 6‐ and 15‐MV x rays
Author(s) -
Mackie T. R.,
ElKhatib E.,
Battista J.,
Scrimger J.,
Van Dyk J.,
Cunningham J. R.
Publication year - 1985
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 - 10.1118/1.595691
Subject(s) - monte carlo method , dosimetry , nuclear medicine , computation , radiation treatment planning , computational physics , physics , radiation , slab , absorbed dose , imaging phantom , materials science , radiation therapy , optics , computer science , mathematics , algorithm , radiology , statistics , medicine , geophysics
We have measured the radiation dose in simple heterogeneous phantoms and compared our results with those obtained by various methods of computation. Dose data were obtained both within and distal to simulated regions of lung in order to test the ratio of tissue–air ratios (TAR), Batho, and equivalent TAR methods. These procedures are used routinely in manual and computer‐aided planning of radiation therapy, but have been validated primarily for cobalt‐60 radiation. Tests performed with 6‐ and 15‐MV x rays reveal that incorrect doses can be computed within or near to a low‐density medium, particularly when the field size is small. In these cases, electronic equilibrium is not achieved in the lateral direction, thereby violating an implicit assumption of all the above calculation methods. We quantify the errors in dose calculation for simple slab phantoms, and support our interpretation with a Monte Carlo simulation in which the energy transported by charged particles away from sites of x‐ray interactions is considered directly.