SU-E-T-642: PET-Image TCP-Driven Biological Planning for Cervical Cancer High- Dose Rate Brachytherapy

Abstract

Purpose: Tumor metabolic activities obtained from PET studies may facilitate targeted dose delivery to improve local tumor control. We perform feasibility tests on TCP‐driven PET‐image‐guided dose escalation in high‐ dose‐rate‐brachytherapy(HDR). Quality and robustness of plans, TCP, and potential outcome significance are evaluated. Methods: CT and 18F‐ fluorodeoxyglucosebased‐PET images are obtained for cervical cancer patients. Planning‐target‐volumes(PTV) and critical structures are delineated. Enhanced PET signal defines boost‐target‐volume(BTV). HDR plans are optimized to deliver 35Gy Ir‐192 to PTV and 37–40Gy to BTV following 45Gy external‐beam‐radiotherapy. Each dwell location is modeled via two variables: a binary variable to indicate whether a radioactive seed will be deposited and a continuous variable to denote dwell time. The treatment planning model ensures 95% PTV‐coverage. The objective seeks rapid dose fall‐off from the prescribed dose while maximizing TCP. For each patient‐case, we compare 3 plans: 1)standard HDR plan, 2)escalation with same PTV prescription dose, and 3)escalation with reduced PTV prescription dose. Results: Standard plans have TCP values 48% to 73%. In all patients(15), escalated plans of >=37Gy to BTV result in slight reduction in rectum and bladder dose, and 40Gy for over 99% of BTV. TCP values range from 81% to 96%. When BTV is less than 15% of PTV, dose escalation and standard plans have virtually identical PTV dose. When BTV occupies over 20% of PTV, dose escalation to PET intrinsically increases PTV dose(1–5%). When PTV is prescribed 33Gy, independent of BTV, escalation can be achieved while dose to PTV, bladder and rectum are reduced. Conclusions: The presented algorithm allows for PET‐enhanced treatment, which facilitates targeted delivery of escalated dose and potential improvements in clinical outcome. Our study reveals significant improvement in tumor control and organs‐at‐risk dose reduction. Clinical studies for PET hot‐HDR dose re‐steering are in progress to test its feasibility, validate its importance, and measure potential gain in clinical outcome. The work of the first author is partially supported by funds from the National Science Foundation.