P Tsiamas*, W Cruz, W Fontenot, J Limmer, Texas Oncology - Houston, TX

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  P Tsiamas

PO-GePV-T-185 (Sunday, 7/25/2021)   [Eastern Time (GMT-4)]

Purpose: Comparing Stereotactic plans patient QA between Sun Nuclear’s SRS Mapcheck (SRSMC), Varian’s Electronic Portal Dosimetry (EPID) suite and Gafchromic film (EBT-3).

Methods: For this evaluation the three different QA process mentioned above (EPID, SRSMC, EBT-3 films) were used. Two different EPID resolutions were used, an aSi-500 and an aSi-1000. Patients were selected based on their lesion size and site in order to review a spectrum of sites and sizes. Lesion sizes were specifically chosen to test the robustness of the QA processes. All plans included in the study were re-planned (Eclipse v15.6) as multiple field IMRT fields in order to have a direct comparison between the different QA methods. Plans were delivered on two different Varian-iX machines, each one having a different Eclipse model with a different CT curve. Data normalization was performed based on the Eclipse models and CT curves in order to exclude variations related with these factors. QA passing rates were set to 95% (2% - 2mm). Total number of calculation points, passing and failing points were recorded and evaluated for each one of the techniques used

Results: Time of setup, ease of use, accuracy, resolution, dependability, and dependencies were examined when comparing the 4 (SRSMC, EBT-3, aSi1000, aSi500) different QA devices. EPID aSi-1000 had the highest resolution while the lowest was for SRSMC. Gamma analysis showed that for 93.8% of the cases SRSMC had higher passing rates than EPID results, though the gamma passing rate standard deviation among the different measurements did not exceed 2% (average difference was 0.87%). Comparison between aSi-500 and aSi-1000 showed that passing rates for aSi-1000 was higher for 84.4% of the cases.

Conclusion: Comparison between the different patient QA processes showed that aSi1000 will be an appropriate system for SRS QA.

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Keywords

Not Applicable / None Entered.

Taxonomy

TH- External Beam- Photons: Quality Assurance - IMRT/VMAT

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