Scientific Abstracts and Sessions

Purpose: A simple method for verifying the dose point kernel of Ir-192 source used in HDR brachytherapy using Kodak EDR2 film in a spiralphantom. Method and Materials: A spiral solid water phantom availablefrom Gammex International for IMRT QA was modified for this study. A CT scan image of the phantom was acquired with a 10 x 12 inch filmloaded in the spiral groove. A 3.5 mm long 8.5 Ci pellet of Ir-192 in aNucletron HDR system was driven to a snugly fitting catheter located at the center of the phantom. The film loaded in the groove was exposed for adwell time calculated to deliver doses within the linear range of the film. Acalibration film was processed with each film exposed in the groove. The film was scanned with a Vidar 16-bit scanner and analyzed using the RITfilm analysis software. The isodose map and dose profile along the lengthof the spiral were calculated to a number of selected distances from the center of the source. The conversion of film optical density to dose wasprocured by measuring the dose at selected points in solid water sheets witha 0.6 cc Farmer ion chamber. The nC recorded at selected distances from the source was converted to cGy using the TG-21 formalism. Results:The measured dose point kernel measured with the film was compared withpublished data. Corrections for obliquity and sensitivity of the chamber with energy were ignored since these are less than 2 %. The dose profile forIr-192 was found to be in close agreement with published data.Conclusion: A simple film exposed in a spiral phantom can be employedto verify the dose point kernels required for Ir-192 and other radionuclides being considered for HDR and LDR brachytherapy.