Room: Exhibit Hall | Forum 5
Purpose: Adaptive radiotherapy (ART) strategies, such as, dose scaling, deforming dose distribution, and re-computing on the new anatomy have achieved mixed results. Their main limitations are increased clinical resources needed for contouring, re-planning, plan evaluation, and quality assurance. Manual segmentation of OARs is a major contributor in treatment delays and dose delivery errors. We propose a novel and efficient ART technique based on contouring a limited set of image slices adjacent to PTV.
Methods: Treatment planning data were evaluated for 10 previously treated prostate cancer patients: prescription dose 78Gy in 39 fractions with 6MV volumetric arc therapy (VMAT). The proposed ART method was tested by contouring OARs (bladder, rectum, femurs and penile bulb) on a limited number of CT slices (3â€“5 cm from the PTV edge). The extent of partial OAR (P_OAR) contours was determined by examining the original treatment plan and only including slices with significant OAR exposure (> 50% prescription dose). DVH data for P_OARs then served as dose constraints for adaptive re-planning. To test the efficacy of the method, treatment plans were re-generated on P_OARs and the resulting dose parameters for PTV/OARs) compared with the original plan.
Results: The proposed ART method reduced average contouring time by a factor of four. Treatment plans generated with P_OARs were dose equivalent for PTV and within <5% for OARs. In some cases, the plan quality was improved since high-dose OAR regions were included in plan optimization. RTOG dose constraints were met for each patient. The method is superior to atlas based auto-segmentation (ABAS) and deformable image registration (DIR) methods which are prone to contouring uncertainties.
Conclusion: The proposed ART method allows efficient adaptation to daily anatomic and setup changes with reduced burden on clinical resources.
Not Applicable / None Entered.