2-DIMENSIONAL FILM DOSIMETRY APPLICATION IN HETEROGENEOUS MATERIALS EXPOSED TO MEGAVOLTAGE PHOTON BEAMS

Measurement of dose within tissues and tissue interfaces having sharp density discontinuities and heterogeneities (such as in the lung, esop hagus, and rectum) is essential for treatment plan verification and ac curate prediction of the prescribed dose. This study examines the feas ibility and utility of simplifying standard film dosimetry to measure dose distributions deposited by megavoltage beams in tissue substitute s (such as cork for lung) and anthropomorphic phantoms which closely r esemble human tissues having large density heterogeneities and having sharp tissue interfaces. In addition, film dosimetry determined the do se distribution involving superposition of multiple radiation fields a nd helped evaluate the accuracy of a commercial treatment planning pro gram which incorporates tissue heterogeneity effects through the ''eff ective path length'' algorithm. This study shows that these treatment planning programs and simple calculations overestimate the dose delive red within the lower density material in heterogeneous regions. (C) 19 97 American Association of Physicists in Medicine.