Y Wu¹, Y Zhang¹, B Erickson², L Lay³, M Alber⁴, J Adamson⁵*, (1) Duke Kunshan University, Kunshan, CN, (2) Duke University Medical Physics Graduate Program, Durham, NC, (3) Louisiana State University, Baton Rouge, LA, (4) Scientific Rt, (5) Duke University Medical Center, Durham, NC

• 
  J Adamson

PO-GePV-T-246 (Sunday, 7/10/2022)   [Eastern Time (GMT-4)]

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Purpose: Dosimetric recalculation using linear accelerator trajectory files is becoming increasingly common with a number of software now commercially available. The trajectory files include high temporal resolution measurements (20ms), but commercial analysis software typically down-samples the measured data to the resolution of the original DICOM-RT treatment plan control points. We investigate whether this down-sampling results in any appreciable dosimetric effects.

Methods: We utilized a secondary Monte Carlo dose calculation algorithm (SciMoCa) to quantify the dosimetric effect of down-sampling for 10 IMRT/VMAT plans from various sites including head and neck, breast e-comp, prostate, lung SBRT, spine SBRT, and multifocal SRS. The plans are made by Eclipse TPS and delivered by Varian TrueBeam Linacs. The statistical nature of the Monte Carlo algorithm enables accurate dose calculation in the same timeframe for DICOM-RT plans with both high resolution (trajectory file) and low resolution (down-sampled to DICOM-RT control points). We quantified the differences in PTV D99%, D95%, D1%, Dmean, D50%, and V100%. To evaluate effects on normal tissue, we quantified the differences in ring structures surrounding the PTV at distances of 0-3mm, 3-6mm, and 6-9mm; dose indices for ring structures included Dmean, D99%, D50%, and D1%.

Results: Differences between dose calculated at high and low resolution was minimal, with most differences being within 0.1%. The maximum observed differences were on the order of 0.5% for the PTV D1%, which was observed for SRS VMAT and Breast e-comp. Differences were systematic and statistically significant for PTV D99%, PTV D95%, and Ring_3-6mm Dmean, but were clinically irrelevant (0.1%).

Conclusion: Down-sampling linear accelerator trajectory file data to the resolution of the DICOM-RT plan did not appear to have any appreciable effect on the dosimetric accuracy of log-file based analysis.

Funding Support, Disclosures, and Conflict of Interest: Dr. Adamson reports ownership of Clearsight RT LLC which is unrelated to this work.

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