Augmenting the Accuracy of MRI-Based HDR Brachytherapy for Prostate Cancer Using On-Line X-Ray Guidance During Delivery

leads to more conservative treatments. For pelvic tumors, measurement of the rectal wall dose will facilitate optimal treatment delivery. We report on the clinical performance of a fibre optic dosimetry (FOD ) system customized to measure the dose in real time in an array configuration. This system enables definitive assessment of the dose delivered, with the potential for intervention if required. Materials and Methods: An array of FODs in an insertable applicator has been designed and built. The clinician can select to position all the dosimeters along the anterior wall of the rectum or in any other arrangement. Dosimeters were optically interfaced to a light detection system, located outside the treatment bunker. Customized software recorded the dose from each dosimeter as the real time dose rate and as the accumulated dose at that point. Prior to use the dosimeters were simultaneously calibrated in a purpose built jig. Results: The performance of the array was demonstrated first by simulating brachytherapy treatments in a water phantom. Preliminary clinical trial with gynecological patients established that rectal wall dose mapping was convenient and accurate. In Figure 1 the radioopaque markers on the end of the rectal applicator are visible.