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Session: Quality Improvement and Outcomes [Return to Session]

Investigating the Ability of Patient-Specific QA Devices to Detect Changes in Dose Distribution Due to MLC Positioning Errors in Stereotactic Radiotherapy Plans

S James1,2, E Elder2-3, C Huh1, A Al-Basheer1*, J Barrett1, F Mostafaei1, (1) Augusta University, (2) Georgia Institute of Technology, (3) Emory University


SU-H430-IePD-F7-6 (Sunday, 7/10/2022) 4:30 PM - 5:00 PM [Eastern Time (GMT-4)]

Exhibit Hall | Forum 7

Purpose: The goal of this study is to test the sensitivity of a Patient-Specific QA Devices (PSQA) to changes in dose distribution due to MLC positioning errors during plan delivery.

Methods: Ten VMAT SBRT/SRS treatment plans were created with 6FFF or 10FFF beam energies using Eclipse 15.6. A MATLAB script was used to create two MLC positioning error scenarios from the original treatment plan: an MLC near central axis (CAX) that is lagging by 2mm and an MLC near CAX that is stuck outside of the field. The original plan and both error plans were delivered on a MatriXX Resolution (IBA Dosimetry, Schwarzenbruck, Germany), an ArcCHECK (Sun Nuclear, Melbourne, FL), and a myQA SRS (IBA Dosimetry, Schwarzenbruck, Germany). Each plan was analyzed with 3%/3mm, 2%/2mm, 2%/1mm, and 1%/1mm gamma criteria. The difference in gamma pass rates from the original plan to each error plan for each criteria were calculated and averaged.

Results: The IBA Matrixx Resolution average difference in gamma passing rates were -0.51%, -0.33%, -1.98%, -2.68% for the 2mm lag plan and 0.09%, 1.44%, 1.37%, and 2.04% for the stuck MLC plan for 3%/3mm, 2%/2mm, 2%/1mm, and 1%/1mm gamma criteria, respectively. The SNC ArcCHECK average difference in gamma passing rates were 0.78%, -0.53%, -0.34%, 1.69% for the 2mm lag plan and 1.43%, 3.16%, 5.13%, and 6.87% for the leaf stuck plan. The IBA myQA SRS detector average difference in gamma passing were -0.02%, 0.12%, 1.34%, 1.73% for the 2mm lag plan and 0.18%, 1.77%, 6.16%, and 5.97% for the stuck MLC plan.

Conclusion: High resolution detectors performed better for both types of scenarios for MLC positioning errors. Changes in passing rate became most apparent using the 2%/1mm gamma criteria.


Stereotactic Radiosurgery, Quality Assurance, MLC


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

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