Intraoperative Dosimetry for Prostate Brachytherapy Using Fluoroscopy and Ultrasound

The use of brachytherapy or implantation of radioactive sources into the prostate for adenocarcinoma has advantages over external beam radiation in that a very high dose can be delivered to the tumor while limiting the doses to the surrounding normal tissue (i.e., bowel and bladder). It is established that outcomes after treatment with brachytherapy are related to the technical quality of source placement within the gland. Accurate placement of the radioactive sources with achievement of optimum dose distributions within the prostate is key to the success of brachytherapy with regard to both killing tumor as well as minimizing toxicity. Due to factors such as deformations of the prostate during needle insertion, needle deviation from intended path during insertion, prostatic edema from needle trauma, and relaxation of tissues as well as source migration after needle removal, the actual source positions upon completion of the procedure may fail to accurately match their intended placement, resulting in variations from the idealized dosimetric plan. One way to overcome this complex problem is to have the capability of visualizing the sources once they are in the prostate and then continuously updating the dosimetric plan in real time. To this end, we have developed a mechanism whereby ultrasound and fluoroscopy are quantitatively integrated to allow for real-time visualization of source positions intraoperatively. A prior Phase I study performed by this group evaluated a prototype version of this mechanism, resulting in the successful treatment of 6 patients with true intraoperative dynamic dosimetry. Dosimetric outcomes within this cohort of patients was excellent, and the intraoperative doses predicted by the system more accurate than that predicted by the current standard method (ultrasound-based dosimetry).