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Improved lung dose calculation using tissue–maximum ratios in the Batho correction
Author(s) -
ElKhatib E.,
Battista J. J.
Publication year - 1984
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 - 10.1118/1.595495
Subject(s) - cobalt 60 , irradiation , dosimetry , cobalt , nuclear medicine , materials science , isotopes of cobalt , radiation , lung , physics , optics , medicine , nuclear physics , metallurgy
We have reexamined the Batho power law for computing the dose within and beyond lung irradiated with small and large fields of cobalt‐60 and 6‐MV x rays. Using slab phantoms consisting of two materials, agreement between calculated and measured doses was within 2% inside lung for 6‐MV x irradiation, but much poorer (9%) for cobalt‐60 irradiation. For cobalt‐60 irradiation, tissue–air ratios (TARs) were used initially in the Batho equation, while for 6‐MV x rays, tissue–maximum ratios (TMRs) were used. When we substituted TMR values instead of TAR values for cobalt‐60, we found marked improvement by nearly 5% in the accuracy of dose calculated within lung. This was confirmed by numerical comparison of the Batho expression with an analytic solution of the primary and first‐scattered radiation. We therefore encourage the use of TMRs for cobalt‐60 radiation, expecially for larger radiation fields, and provide measured data tables for field sizes up to 50×50 cm 2 , and depths up to 30 cm. In addition to unifying the dosimetry for all megavoltage irradiation, this approach improves the accuracy of doses calculated within lung.