Dose assessment in high dose rate brachytherapy with cobalt-60 source for cervical cancer treatment: a phantom study

Transition from low dose rate brachytherapy to high dose rate brachytherapy at our department necessitated the performance of dose verification test, which served as 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 constructed from Perspex sheets to represent the cervix region of a standard adult patient. The phantom was used to verify the whole dose delivery chain such as calibration of the cobalt-60 source in use, applicator, and source localization method, the output of treatment planning with dedicated treatment planning system, and actual dose delivery process. Since the above factors would influence the final dose delivered, doses were measured with calibrated gafchromic EBT3 films at various points within the in-house phantom for a number of clinical implants that were used to treat a patient based on departmental protocol. The measured doses were compared to those of the treatment planning system. The discrepancies between measured doses and their corresponding calculated doses obtained with the treatment planning system ranged from -29.67 to 40.34% (mean of +/- 13.27%). These compared similarly to other studies.