TU‐D‐BRB‐01: PET/CT Guided Dose Redistribution for HDR Interstitial Brachytherapy of Cervical Cancer

Purpose: Advances in functional imaging may allow identification and targeting of tumor sub‐volumes based on their biological characteristics, allowing selective boosting of dose to radio‐resistant sub‐volumes during treatment planning. The purpose of this study was to redistribute high dose regions toward the PET‐hot regions as identified on PET/CT images during High‐Dose‐Rate (HDR) brachytherapy for cervical cancer while maintaining a clinically acceptable DVH. Material and Methods: FDG‐PET and CT images were acquired and registered. The tumor volume was contoured and segmented into sub‐volumes based on their Standardized Uptake Values (SUV) in PET images. The sub‐volumes with higher SUV were considered metabolically active and therefore required higher radiation dose. The integral tumor was prescribed a uniform dose from external beams followed by a boost dose delivered by HDR interstitial brachytherapy. The HDR treatment plan was optimized using a home‐brew software implementation of an Adaptive Simulated Annealing (ASA) algorithm. The tumor dose was then redistributed by increasing and decreasing the prescription dose to sub‐volumes with higher and lower SUV respectively such that the integral tumor prescription dose was kept constant. A routine cervical cancer case with both uniform and PET‐guided plans is presented. Both plans were optimized based on a generalized Equivalent Uniform Dose (gEUD) cost function and renormalized to V100=95% of prescribed dose to the integral PTV. Their isodose distributions and DVHs were compared. Results: The PET‐guided plan had larger hot spots in and near the PET sub‐volume while the DVH of PTV was kept the same as that of the uniformly prescribed plan. Doses to critical organs were also reduced in the PET‐guided plan. Conclusions: The approach described used PET/CT imaging guiding dose redistribution within PTV so that the hot spots encompass metabolically active tumor sub‐volumes. An IRB approved treatment protocol is underway to study the clinical efficiency of this approach.