SU-GG-T-248: Dose-Escalation for a Dominant Intraprostatic Lesion Using a Combination of IMRT and VMAT

Abstract

Purpose: To study the feasibility of boosting the dosedelivered to a dominant intraprostatic lesion (DIL), identified by functional imaging, requiring higher dose for better tumorcontrol using Intensity‐Modulated Radiation Therapy(IMRT) and Volumetric Modulated Arc Therapy (VMAT). Materials and Methods:Treatment planning was performed on 2 patient CT‐scans with hypothetical DIL (1/8 the size of the prostate) in the inferior‐posterior‐left side of the prostate using Pinnacle treatment planning system (Philips Medical Systems). Three types of plan were generated, (A1) 10 Gy 5‐field IMRT boost to the DIL‐PTV followed by 76 Gy 5‐field IMRT to the Prostate‐PTV, (A2) 10 Gy VMAT boost to the DIL‐PTV followed by 76 Gy 5‐field IMRT to the Prostate‐PTV and (A3) 10 Gy VMAT boost to the DIL‐PTV followed by 76 Gy VMAT to the Prostate‐PTV. Plans were delivered using Varian clinac and verified using MapCheck and MapPhan (Sun Nuclear). Results: For plans A1, A2 and A3, the DIL‐PTV received a mean dose of 87.0±0.7 Gy, 86.4±0.4 Gy and 87.5±0.8 Gy respectively, and the Prostate‐PTV — DIL‐PTV received a mean dose of 77.9±1.1 Gy, 77.7±0.7 Gy and 78.1±1.3 Gy respectively. All three plans did not exceed the normal tissue tolerances from the guidelines of the RTOG 0126. Plan A2 had a slightly lower dose to the rectum and bladder. All the plans were delivered and verified successfully. The plan A3 had better dose conformity to DIL‐PTV. Conclusions: This study demonstrates the feasibility of using any of the three treatment methods in treating a DIL without exceeding normal tissue tolerances. However, considering the speed of VMAT delivery over the 5‐field IMRT and better conformality of the dose distribution, a VMAT boost to a DIL followed by a VMAT to the Prostate‐PTV is a preferable treatment option for DIL dose‐escalation. Research sponsored by CIHR.