Dose Assessment of the Rectum during Brachytherapy of the Cervix Using Gafchromic Films

Abstract

Internal radiation therapy, refers to as brachytherapy, involve putting a source of radiation with high photon in or near a cancerous tissues. The type of brachytherapy used most often to treat cervical cancer is known as intracavitary brachytherapy. Unfortunately however, the radiation source placed in the cervix irradiate the normal tissues of rectum and other nearby organs during intracavitary brachytherapy of the cervix treatment. This high doses received by parts of the rectum is a concern for clinicians and the general public. The aim of this study is to assess the dose delivered to the rectum using Gafchromic films and compare it with the optimized dose calculated by the Brachy Prowess 4.60 Treatment Planning System (TPS) reports for empirical validation and system verification. Fletcher suite applicators were used to perform thirty (30) different clinical insertions on the constructed cervix phantom and results evaluated. The mean difference between the doses calculated by the TPS and the doses measured by the Gafchromic film for the rectum at the distance of 0.5cm from the edges of the film was 23.1% (range -42.42 to +40.41). At a distance of 1.5cm for the rectum the mean was 22.5% (range -49.45 to +46.48). The TPS calculated maximum dose was typically higher than the measured maximum dose. However, in some cases, the measured doses were found to be higher than the doses calculated by the TPS. This is due to positional inaccuracies of the sources during treatment planning. It is recommended that in vivo dosimetry should be performed in addition to computation.