(Saturday, 3/30/2019)
Room: Exhibit Hall
Purpose: Determine local process-based patient specific quality assurance action limits using Halcyon 2.0 and multiple measurement devices to (1) evaluate agreement with universal action limits recommended by TG-218 and (2) provide reference to other clinics with similar equipment.
Methods: Ten plans were developed for Halcyon 2.0 via the TG119 test suite with both IMRT and VMAT techniques as well as 28 clinical plans from a variety of sites including: brain, head and neck, lung, breast, abdomen, and pelvis. Six additional breast VMAT plans were created using the two-isocenter technique, which includes an automatic longitudinal shift. A new feature available with Halcyon 2.0, the dynamically flattened beam, was used for an AP/PA spine and four field box, as well as included in ten field-in-field breast plans. All plans (56) were measured with an ion chamber, portal dosimetry, MatriXX within MULTICube phantom, ArcCheck, and Delta4. Action limits were calculated and compared to TG-218 recommendations.
Results: Fifty-three out of the 56 plans are within 3% for ion chamber measurements with an average expected to measured ratio of 1.007 (0.7%) for all plans. The average Gamma passing rates with a 3% dose difference and 2mm distance-to-agreement (global normalization, 10% threshold) criteria for all plans are: PD – 99.9%, MatriXX – 91.6%, ArcCheck – 98.7%, and Delta4 – 99.2%. Therefore, the local action limits will be set at: PD – 99%, MatriXX – 72%, ArcCheck – 95%, and Delta4 – 96%.
Conclusion: Halcyon plan deliveries using IMRT, VMAT, two-isocenter technique, and dynamically flattened beams successfully passed patient-specific QA with multiple measurement devices. Calculated action limits bettered the recommendations of TG-218 (90% with 3%/2mm) using portal dosimetry, ArcCheck, and Delta4. MatriXX action limits are lower due to the measurement geometry and inability to use an inclinometer to apply angular corrections.
Funding Support, Disclosures, and Conflict of Interest: Financial support was provided by Varian Medical Systems
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