Dosimetry Verification For High Dose Rate Brachytherapy Of Cervical Cancer Using Co-60 Source At The Korle-Bu Teaching Hospital

Abstract

Transition from the low dose rate brachytherapy to high dose rate brachytherapy at the National Center for Radiotherapy and Nuclear Medicine, Korle-Bu Teaching Hospital, Accra, Ghana necessitated the performance of dose verification test, which serves an end-to-end quality assurance procedure to verify and validate dose delivery in intracavitary brachytherapy of the cervix and the vaginal walls based on the Manchester system. An in-house water phantom was designed and fabricated from Perspex (poly methyl acrylate) sheets to represent the cervix region of a standard adult patient. The phantom was used to verify the whole dose delivery chain such as the calibration of the cobalt -60 source in use, applicator and source localization method, output of treatment planning with the dedicated treatment planning system and the actual dose delivery process. Since the above factors would influence the final dose delivered, doses were measured at various points within the in-house phantom for a number of clinical implants that were likely to be used to treat a patient based on departmental protocol. The measured doses were compared to those of the treatment planning system. The various implants were immersed into the phantom filled with water, and the doses were measured with samples of calibrated Gafchromic EBT3 films. The Gafchromic film was calibrated against output of a 0.6 cc cylindrical ionization chamber having traceability to a secondary standard dosimetry laboratory with beams from a cobalt-60 teletherapy machine using the International Atomic Energy Agency technical report series 398 protocol. The discrepancies between the measured doses and their corresponding calculated doses obtained with the treatment planning system ranged from - 28.75% to 42.19% (mean of ±12.50). These compared favourably well with those reported in other related publications.