Sci‐Sat AM (1) General‐03: IMRT prostate planning: a graphical rectal NTCP determination

Including the NTCP in the objective function of the inverse IMRT plan optimization would make the planning more effective in the prediction of the post‐radiation effects. However, doing so would lengthen the total planning time. The purpose of this work is to establish a method for rectal NTCP determination, independent of the DVH, as a means of improving the treatment planning efficiency. In this study, IMRT plans of ten randomly selected prostate patients are performed using Pinnacle3 V 6.2b planning system. The DVH control points and prescriptions for contouring of the PTVs and OARs were adapted from the prescriptions of the Radiation Therapy Oncology Group protocol P‐0126. PTVs with margins in the range of 2 to 10 mm and prescribed dose ranging from 70 to 82 Gy were employed in our study. This paper presents a new model for determination of the rectal NTCP (RNTCP). The method uses a special function, named GVN (from Gy, Volume, NTCP). It describes the RNTCP if a volume of 1 cm3 of the intersection between the PTV and rectum is irradiated uniformly by a dose of 1 Gy. The function was “geometrically” normalized using a prostate‐prostate‐ratio (PPR) of the patients' prostates. Also, a correction of the RNTCP for different prescribed doses was used. The argument of the normalized function is the rectum intersection, and parameters are the prescribed dose, prostate volume, PTV margin and PPR.