The sigmoid colon and bladder shielding in whole pelvic irradiation at prostate cancer (forward planned IMRT from Institute of Oncology Ljubljana)

Abstract

Background. The whole pelvic irradiation (WPI) is again gaining the important role in radiotherapy of prostate cancer. With the conformal irradiation of the large fields that are covering the pelvic nodes, the extra damage is done to sigmoid colon and urinary bladder. Sparing the region between the iliac nodes is necessary since the dose delivered to the organs at risk that are partly included in the mentioned area (the sigmoid colon and bladder) can be importantly reduced. Methods. We are presenting a possible way of shielding the central region between iliac nodes that does not need to be irradiated. Dose volume histograms of standard box technique and technique with additional central shielding of sigmoid colon and urinary bladder in WPI are compared in 10 patients. Results. Applying the described shielding technique 30 to 45 % or in some cases even up to 55% of the sigmoid colon that would with standard box technique be irradiated at doses from 30 to 50 Gy is spared, and also around 10% of the bladder that would receive 45-55 Gy is spared. Conclusions. In the whole pelvic irradiation (WPI) in prostate radiotherapy the sparing of the region between the iliac nodes is crucial since it allows the dose delivered to the sigmoid colon to be reduced to the recommended restrictions. Since the sigmoid colon benefits most from described shielding, the technique is addressed as the Sigmoid Colon Shielding (SCS). The SCS technique is in use at our department at Institute of Oncology in Ljubljana.