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Study of Tumor Control and Dose-Volume Dependence for Normal Tissue Toxicity in Patients Treated with Stereotactic Body Radiation Therapy for Loco-Regional Tumor Recurrences in Abdominal and Pelvic Regions

I Dragojevic

I Dragojevic*, D Rahn , V Moiseenko , UC San Diego, La Jolla, CA


SU-F-FS2-6 (Sunday, July 30, 2017) 2:05 PM - 3:00 PM Room: Four Seasons 2

Purpose: To present our early institutional experience of re-irradiation combining conventionally fractionated and SBRT dose data to guide normal tissue sparing, dose prescription, and to analyze outcomes data in abdominal and pelvic cancer patients.

Methods: Six patients who had SBRT re-irradiation to abdominal and pelvic areas, were selected for evaluation. EQD2 and DVH data were obtained, plans were exported from Eclipse (Varian Medical Systems) into deformable registration software, MIM (MIM Software, Inc.). Plan doses were converted to EQD2 and then summed to calculate the cumulative dose to organs at risk (OARs). Follow-up documentation was reviewed for toxicity and survival data.

Results: SBRT is infrequently used for re-irradiation, and clinical experience is extremely limited. Use of deformable co-registration and conversion to EQD2 provides a platform for planning and outcomes data analysis. This is particularly important for previously irradiated normal tissues, which puts them at higher risk of radiation-induced damage. This platform has been in clinical use at our institution and data collected retrospectively for 6 patients who received SBRT re-irradiation of the abdomen and pelvis. Specifically, we report dosimetric data for the following OARs: bowel, rectum, kidneys, and bladder. Dose-volume histograms in the EQD2 space were compared against normal tissue tolerance guidelines used for conventional fractionation. The analysis revealed that for kidneys and bladder, the doses fit within known constraints. However, doses for bowel and rectum occasionally exceeded constraints used for conventional fractionation (for one of the patients, bowel and rectum D 0.1cc doses were 92.9 Gy and 90.1 Gy EQD2 respectively). Only one patient had grade 2 bowel toxicity.

Conclusion: Early experience shows that this approach can be used efficiently effectively to guide planning and report/analyze clinical data. Incidence of toxicity was low, which, given the sample size, is only indicative that this approach provides safe guidance.

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