Vaginal Applicators in High-Dose Rate Brachytherapy for Endometrial Carcinoma: A Dosimetric Study

OBJECTIVE Intracavitary brachytherapy is one of the most important methods of gynecological cancer treatment. The effect of attenuation by the applicators is not considered in the dose calculation method released by the AAPM TG-43. In this study, the attenuation due to various segmented vaginal cylinders made up of polyetheretherketone was measured. METHODS A plan created by the treatment planning system (TPS) for the patient was executed using Gafchromic films that were taped on the surface of the applicator, and the dose recorded on the films was measured. The same plan was also executed using a well-type ionization chamber. First, a water equivalent material, Elasto-Gel was used in a well-type ionization chamber for charge collection, and then a segmented vaginal cylinder was used for charge collection measurement; thus, the attenuation due to the various segmented vaginal cylinders was obtained. RESULTS The doses recorded on the Gafchromic films were measured and showed that the TPS overestimated the dose for the segmented vaginal applicators and that the maximum overestimation of the dose was 4.75% for 35 mm diameter vaginal cylinders. This was further confirmed by calculating the percentage attenuation due to vaginal cylinders using a well-type ionization chamber. CONCLUSION Due to the attenuation by the various applicators used in vaginal vault brachytherapy, it can be concluded that due to overestimation of dose by the TPS, the dose actually received by the target and the organs at risk in vaginal vault brachytherapy are less and needs to be considered for actual dose estimation.