Intraoperative HDR brachytherapy for rectal cancer using a flexible intraoperative template: standard plans versus...

HDR intraoperative brachytherapy (IOBT) is applied to locally advanced rectal tumors using a 5 mm thick flexible intraoperative template (FIT). To reduce the procedure time, treatment planning is performed using standard plans that neglect the curvature of the FIT. We have calculated the individual treatment plan, based on the real geometry of the FIT, and the dose at clips placed during surgery. A mean treatment dose of 9.55+/-0.21 Gy was found for the individual plan, compared to the prescribed 10 Gy (P<0.0001) The mean central dose was 10.03+/-0.10 Gy in the standard plan and 9.20+/-0.32 Gy in the individual plan (P<0.0001) The mean dose at the corners of the FIT was 10.3 Gy in the standard plan and ranged between 10.3 and 10.5 Gy in the individual plan. In 63% of the clips, the dose was larger than 15.0 Gy, which is equivalent to a gap between the FIT and the target smaller than 5 mm. In 18% of the clips, the dose was smaller than 13.0 Gy indicating that locally the gap was larger than 5 mm. Clinical practice will have to prove if these small dose deviations influence the clinical outcome.