2014 - Dosimetric Evaluation of Ablative Stereotactic MR-Guided Adaptive Radiation Therapy for Anatomically Unfavorable Metastatic Colorectal Cancer
Presenter(s)
T. Bejarano1, R. Herrera2, E. Y. Y. Akdemir3, A. Kaiser1, R. Kotecha4, Y. Weiss2, M. D. Hall3, Y. Lee1, S. Davis2, M. J. Flakus2, R. P. Tolakanahalli1, A. Gutierrez2, K. E. Mittauer1, and M. D. Chuong1; 1Department of Radiation Oncology, Miami Cancer Institute, Baptist Health South Florida, Miami, FL, 2Department of Oncological Sciences, Herbert Wertheim College of Medicine, Florida International University, Miami, FL, 3Miami Cancer Institute, Miami, FL, 4Miami Cancer Institute, Baptist Health South Florida, Miami, FL
Purpose/Objective(s): Stereotactic MR-guided oART (SMART) facilitates dose escalation for anatomically unfavorable tumors in proximity to radiosensitive organs-at-risk (OARs). Rigorous dosimetric validation is critical to optimizing the therapeutic ratio. SMART may be particularly beneficial for radioresistant tumors including metastatic colorectal cancer (mCRC) for which a biologically effective dose (BED10) >100 Gy10 has shown enhanced long-term local control (LC). This study evaluates the dosimetric quality and consistency of SMART plans for mCRC by analyzing key performance indicators. To our knowledge, this is the first MRL dosimetric plan analyses on mCRC.
Materials/Methods: We retrospectively evaluated 33 mCRC patients and 51 lesions treated with 50 SMART plans on a 0.35 T MRL at a single institution. Median prescribed dose was 50 Gy (range: 30-60 Gy) in 5 fractions (range: 1-6 fractions). The planning target volume (PTV) was delineated according to institutional standards and cropped out of adjacent OARs. Dose distributions were optimized using step-and-shoot IMRT. The dosimetric evaluation included 100% prescription isodose volume to target volume (PITV), the 50% isodose volume to target volume (R50%), homogeneity index (HI) the dose received by 2% of target volume (TV) to dose received by 98% of TV, target coverage (TC) the TV receiving the prescribed dose to the TV, and the maximum dose at 2 cm from the target boundary to the total dose (Max D2cm). Statistical analysis was conducted for each parameter to assess plan quality and dose gradient characteristics across the cohort.
Results: The mean volume of gastrointestinal (GI) OARs within 5 mm of lesions was 1.11 ± 1.91cc (median: 0.26). Mean PITV, R50%, and HI were 1.07 ± 0.36 (median: 1.09), 5.63 ± 2.68 (median: 4.72), and 1.51 ± 0.31 (median: 1.35), respectively. TC was robust with mean of 0.86 ± 0.22 (median: 0.95). Max D2cm showed a mean of 0.51 ± 0.06 (median: 0.52). Gross tumor volume (GTV) mean was 50.95 ± 12.40 Gy (median: 53.40). PTV mean was 48.11 ± 11.36 Gy (median: 51.68), while PTV D90 mean was 43.13 ± 9.82 Gy (median: 44.60). Mean prescribed BED10 was 107.67 ± 28.24 Gy10 (median: 100).
Conclusion: To our knowledge this is the first MRL dosimetric plan analyses on mCRC. Our SMART plans achieved superior conformity, target coverage, and dose gradient while maintaining an ablative prescribed dose for mCRC lesions in frequent proximity to GI OAR. These findings can be used as institutional benchmarks for SMART plan quality and support continued investigation correlating dosimetric indices with clinical outcomes.