Intraoperative radiotherapy for locally advanced prostate cancer: treatment technique and ultrasound-based analysis of dose distribution.

Background: To present the technique and dose distribution of intraoperative radiotherapy (IORT) for prostate cancer. Patients and Methods: Pelvic lymphadenectomy, prostate IORT and radical retropubic prostatectomy was performed in 11 prostate cancer patients. Prostate thickness and rectum depth were measured with intraoperative ultrasound. IORT was delivered by a mobile linear accelerator in the operating room (electron beam, 12 Gy at 90% isodose). Results: The mean preoperative probability of organ-confined disease was 10% (Memorial Sloan Kettering Cancer Center nomograms). Mean prostate thickness, width and length were 3.4 cm, 4.6 and 4.9 cm, respectively. Mean rectum depth was 3.3 cm. Mean doses to the posterior prostate capsule, 5-mm lateral prostate margins and at the subsequent uretheral stump area were 4.6 Gy, 8.7 Gy and 11.3 Gy, respectively. Maximum mean rectal dose was 4.9 Gy. Conclusion: IORT appeared a feasible approach for prostate cancer, showing a satisfactory dose coverage to the prostate bed with relatively low rectal dose. However, high variability in dose distribution calls for further study of patient selection criteria and dosimetry. Radical prostatectomy is a well-accepted treatment for prostate cancer (1). Several retrospective series and two recent large randomized trials demonstrated an improved biochemical and clinical progression-free survival in patients with positive margins or pT3 treated with postoperative radiotherapy (2-4). External beam postoperative irradiation (EBRT) consists of a seven week schedule and may be correlated with significant side- effects. Moreover, the geometric uncertainties in defining the target area and organ motion issues may jeopardize the benefit of postoperative radiotherapy (5). Alternative approaches are being sought. Intraoperative radiotherapy (IORT), usually combined with EBRT, has been used for many years for various locally advanced tumors (6). This approach offers several radiobiological, physical and clinical advantages. Recently, IORT using an electron beam (IOERT) has been proposed prospectively at the European Institute of Oncology, Milan, Italy, for intermediate- and high-risk prostate cancer patients, candidates for radical prostatectomy. The aim of our study was to present this IOERT technique and to analyze its dose distribution. Toxicity as well as tumor control data will be the subject of a future report when longer follow-up data are available.