Verification of brachytherapy dosimetry with radiochromic film

The aim of this work is to empirically validate the optimized dose distribution calculated by the Nucletron Brachytherapy Planning System (v. 13.3) at a distance of 1.0 cm from a stepping source of high-dose-rate-iridium 192 (192Ir). The longitudinal dose distribution at 1.0 cm from a straight pathway of multiple-source positions is measured using radiochromic film and compared with the planning system's calculated results. The optical density of the exposed films was determined with a modified Scanditronix film scanner, and the film was calibrated with 192Ir using manually calculated exposure times. A calibration equation was used to convert scanner output to dose. Our results illustrate the significance of exacting geometry in the experimental setup due to the inverse square law and the small distances involved. The dose distribution calculated by the Nucletron Brachytherapy Planning System (v. 13.3), at a distance of 1.0 cm, is validated to within +/-4% of the measured dose distribution. The advantages and limitations of radiochromic film as a dosimetry tool are also addressed in this work.