BLADDER AND RECTUM DOSE VARIATIONS AMONG BRACHYTHERAPY APPLICATIONS IN INOPERABLE CERVICAL CARCINOMA PATIENTS RECEIVING DEFINITIVE RADIOTHERAPY

AIM: To investigate the variation of rectum and bladder doses between brachytherapy fractions and the effect of optimization on rectum and bladder doses in patients with inoperable cervical carcinoma receiving definitive radiotherapy. MATERIALS AND METHODS: Our treatment protocol for inoperable cervical carcinoma includes 5 brachytherapy applications after external radiotherapy. In each brachytherapy fraction treatment planning was done and plan was optimized to achieve rectal and bladder doses under tolerance limit. Treatment was undergone according to these optimized plans. Rectum and bladder dose variations between fractions were compared retrospectively. In addition, a dosimetric study was done: Rectum and bladder doses were calculated with using the first plan's source positions in later fractions. RESULTS: Rectal and bladder doses were different in each fraction in both the treatment plans and dosimetric study plans. Only 4 of 5 fractions of brachytherapy could be done in 4 patients since mean rectal doses were higher than 85% of point A doses. When source arrangement of the first fraction was used in later fractions, mean rectal doses were more than 85% of point A dose in 6 of 10 patients. CONCLUSION: Rectum and bladder doses vary due to tumor response and application geometry between brachytherapy fractions. Therefore, treatment should be planned and optimized for each brachytherapy fraction and critical organ doses must be kept in tolerance limit.

Keywords: cervical carcinoma, brachytherapy, and dosimetry