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MR Guided Adaptive Radiotherapy Improves Target Coverage and OAR Sparing: Dosimetric Analysis of 1185 Adaptive Fractions and 4 Years Experience

D Yang*, H Kim, O Green, B Cai, L Henke, J Cammin, B Gu, H Li, H Gach, Washington University School of Medicine, St. Louis, MO

Presentations

(Sunday, 7/12/2020)   [Eastern Time (GMT-4)]

Room: AAPM ePoster Library

Purpose: data in limited patient numbers indicate MRI guided online adaptive radiotherapy (MRGRT) for abdominal cancers could spares critical GI OARs. This study assesses all previously adapted fractions of the Viewray (VR) Co-60 machine at our institution. Dosimetry metrics on patients’ treatment day anatomy between adapted plans vs original plans are compared. The aims are to determine the reasons and corresponding rates necessitating plan adaptations and to quantify target coverage changes.


Methods: abdominal cancer patients (N=137) previously treated with MRGRT on the VR Co-60 machine from 2015 to 2019 are included. Sites were pancreas (98), adrenal (11) and unspecified abdomen (28). A total 961 (81.1%) out of 1185 fractions were adapted. Plan adaptation conditions were 1) the target was edited, or 2) any critical OAR constraints were violated, or 3) target coverage was significantly worse (V95 reduction >10%). For each adapted fraction, dose was calculated using a Monte Carlo engine for both the original plans and the adapted plans. MATLAB scripts were developed to 1) process treatment plan data files, 2) identify the case-specific targets and OARs, 3) compute DVH metrics (V95%Rx and D95% for the targets, and V>constraint for the OARs), and 4) analyze the results.


Results: of 961 adapted fractions were processed. The analysis shows that 1) critical OARs were edited for 100% cases, 2) targets were edited for 9.4% cases, 3) critical OAR constraints were violated for 90.5% cases by the original plans, 4) optimization objectives were edited for 3.4% cases and 5) all critical OAR constraints were met in all adapted plans, 6) target coverages were improved for 92.4% cases with the adapted plans.


Conclusion: more than 4 years, results continue to confirm that adapted plans provided significantly better target coverage while preventing violation of critical OAR constraints.

Download ePoster [PDF]

Funding Support, Disclosures, and Conflict of Interest: Hyun Kim received research funding from Viewray. Olga Green received travel support from Viewray.

Keywords

MRI, Dose, Statistical Analysis

Taxonomy

TH- External Beam- Photons: adaptive therapy

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