SU-E-T-73: Investigation of Dose Reconstruction Using the Dosimetry Check Platform for Different Anatomical Sites

Abstract

Purpose: to evaluate the dependence of the anatomical site being treated when using the Dosimetry Check software for patient specific IMRTquality assurance. Methods: Seventeen step and shoot IMRT patients were used to evaluate the dependence of the treatment site on the performance of the Dosimetry Check software (Math Resolution, LLC, Maryland). The treatments were delivered using a Varian Novalis Tx with an HD 120 MLC system. Integrated images for each patient were taken with an aSi1000 EPID (Varian Medical Systems). An integrated image was taken for each individual field and imported into the Dosimetry Check software. Using the Pinnacle treatment planningsoftware, the CT scans, structure file, plan file, and dose file were exported and then imported in to the Dosimetry Check software. The software then used the imported fluence fields to calculate the absolute dose and dose volume histogram to compare with the reference data exported from the treatment planning system. Gamma analysis was used to compare the measured data with the reference data. A 3% ‐ 3mm criteria normalized to the prescription dose with a 5% dose threshold was used. Results: Some treatment site dependence was observed. Of the fivesites investigated, two showed very similar results. In the remaining sites, the liver patients showed very strong agreement between measured data and reference data while the lung and H/N patients barely met our passing criteria. Conclusions: Dosimetry Check is an independent dose calculation software that uses a pencil beam algorithm. Pencil beam algorithms are fast but are also known to over‐estimate dose in low density heterogeneities. That should be a consideration for dose reconstruction with H/N and lung patients.