Rectum Dose Analysis Employing a Multi-purpose Brachytherapy Phantom

Purpose: It is difficult to reproduce a brachytherapy measurement because of changes in the rectal shape during inter-fraction. We constructed a multi-purpose brachytherapy phantom (MPBP) and reproduced the same conditions found in actual therapy. We further attempted to apply the measured optimal dose to reduce rectal complications. Methods: A measured dose was administered at rectal reference point R1 using a diode detector in four patients who used a tandem and ovoid in brachytherapy for carcinoma of the cervix. A total number of 20 rectal dose measurements were performed five times per patient. In addition, discrepancies in the set-up of the diode detector were analyzed with each repetitive measurement. After reproducing the same conditions as found in actual therapy using a multi-function applicator (MFA) in the multi-purpose brachytherapy phantom con-structed for this study, the dose was measured at reference points in the rectum using a ther-moluminescence dosimeter (TLD). Results: According to the discrepancies measured in the set-up using a diode detector, Patient 1 showed a maximum value of 11.25+ 0.95 mm in the Y direction, Patients 2 and 3 exhibited 9.90+ 2.40 mm and 20.85+ 4.50 mm in the Z direction, respectively. Patient