SU‐FF‐T‐92: A Dosimetric Analysis of IMRT Used to Replace and Mimic HDR Brachytherapy in the Treatment of Gynecologic Malignancy

Abstract

Purpose: To evaluate the ability of intensity modulated radiation therapy (IMRT) to mimic the dose distribution of high‐dose rate (HDR) intracavitary brachytherapy in the treatment of gynecologic malignancy, including regions of high dose in the target volume while limiting doses to organs at risk (OAR). Methods: The HDR treatment planning CT scans of 4 patients with gynecologic malignancy were used in creating 3 different types of IMRT treatment plans. HDR dose levels were contoured and exported as volumes to the IMRT treatment planning system. The IMRT300% and IMRT100% plans were designed to mimic V300%(HDR) and V100%(HDR), respectively. No attempt was made to spare the OAR. Results of IMRT300% and IMRT100% were used to determine the limitations of IMRT in order to create IMRTTx: a compromised plan, designed to replicate the V100%(HDR) and the highest isodose volume possible, while sufficiently sparing the OARs. Results: The IMRT300% and IMRT100% plans showed an increase in V50% by a factor of 10 and 2, respectively. The IMRTTx plan mimicked V200%(HDR) to within a mean of 16.4% while concurrently replicating V100%(HDR) to within a mean of 79.7%. An associated mean of 510% and a mean D2cc increase of 61.7% and 102.7% for the bladder and rectum were realized. Moreover, for the patients who received supplementary conventional external‐beam radiation therapy (CXRT), nodal treatment was integrated with IMRTTx in order to replace CXRT. The nodal mean D90(IMRT) was within 3.9% of D90(CXRT). For all patients, IMRTTx OAR doses were below the regions of interest (ROI) constraints used clinically. Conclusion: The present study suggests that IMRT may be capable of mimicking HDR brachytherapy in the treatment of gynecologic malignancy. As V200%(HDR) and V100%(HDR) are mimicked, increased V50% and OAR doses must be accepted. Compliance to clinical ROI constraints can be achieved.