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SU‐FF‐T‐92: A Dosimetric Analysis of IMRT Used to Replace and Mimic HDR Brachytherapy in the Treatment of Gynecologic Malignancy
Author(s) -
Lamba M,
Weatherford J,
Elson H,
Kassing W
Publication year - 2009
Publication title -
medical physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.473
H-Index - 180
eISSN - 2473-4209
pISSN - 0094-2405
DOI - 10.1118/1.3181565
Subject(s) - medicine , nuclear medicine , brachytherapy , radiation treatment planning , radiation therapy , dosimetry , radiology
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 IMRT 300% and IMRT 100% plans were designed to mimic V 300%(HDR) and V 100%(HDR) , respectively. No attempt was made to spare the OAR. Results of IMRT 300% and IMRT 100% were used to determine the limitations of IMRT in order to create IMRT Tx : a compromised plan, designed to replicate the V 100%(HDR) and the highest isodose volume possible, while sufficiently sparing the OARs. Results: The IMRT 300% and IMRT 100% plans showed an increase in V 50% by a factor of 10 and 2, respectively. The IMRT Tx plan mimicked V 200%(HDR) to within a mean of 16.4% while concurrently replicating V 100%(HDR) to within a mean of 79.7%. An associated meanV 50 % ( IMRT )V 50 % ( HDR )of 510% and a mean D 2cc 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 IMRT Tx in order to replace CXRT. The nodal mean D 90(IMRT) was within 3.9% of D 90(CXRT) . For all patients, IMRT Tx 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 V 200%(HDR) and V 100%(HDR) are mimicked, increased V 50% and OAR doses must be accepted. Compliance to clinical ROI constraints can be achieved.