(Sunday, 7/12/2020) [Eastern Time (GMT-4)]
Room: AAPM ePoster Library
Purpose: To develop a dosimetry framework for reconstructing radiotherapy organ dose for a retrospective epidemiological study of late effects within the National Wilms Tumor Study (NWTS). We describe the methods and workflow for how organ doses will be reconstructed for ~5000 patients in the cohort.
Methods: Patient radiotherapy plans are reconstructed from original paper records. As CT images are not available, body size-dependent computational human phantoms were selected from a library as surrogate anatomies for the dosimetry. Patients were matched to phantoms based on gender, height, and weight (increments of 10-cm and 5-kg). As needed, missing height/weight variables were imputed according to standard growth charts. A DICOM-CT and corresponding Structure file containing the organ contours for each phantom are imported into a treatment planning system (TPS) for reconstruction of the fields from the paper records. The plans are reconstructed by a medical physicist under the supervision of a radiation oncologist familiar with the protocols used during the NTWTS trials. As the TPS is inaccurate in the out-of-field region, Monte Carlo simulation is performed to improve the organ dose calculation. In-house scripts are used to automatically convert the DICOM-RT to input files for simulation using the XVMC code.
Results: A full patient-phantom matching was performed for the NWTS cohort. Radiotherapy plans were reconstructed for the first 300 patients and exported from the TPS for Monte Carlo dosimetry. Doses are calculated for more than 100 organs pre-defined in the phantoms. The NWTS patients were treated with a variety of photon energies: Co-60(30%), 2MV(2%), 4MV(43%), 6MV(12%), 8MV(4%), 10MV(6%), and other/unknown(3%). The most common treatment fields were: abdomen(15%), right-flank(28%), left-flank(35%), chest+other fields(22%).
Conclusion: The organ dosimetry for the NWTS cohort will be used to understand causes of late effects following radiotherapy and will provide valuable information for developing dose tolerance criteria for mitigating toxicity.
Keywords
Dosimetry, Radiation Risk, Monte Carlo
Taxonomy
TH- External Beam- Photons: out of field dosimetry/risk analysis
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