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Survey Results of Current Standards for Verifying Patient Positioning and Dose Delivery in IMRT

H Mehrens*, S Kry , D Followill , UT MD Anderson Cancer Center, Houston, TX


(Tuesday, 7/16/2019) 10:00 AM - 10:30 AM

Room: Exhibit Hall | Forum 4

Purpose: To describe and report results from a survey of current standards for verifying patient positioning and dose delivery in IMRT.

Methods: The survey was included as part of IROC-Houston’s Facility Questionnaire. The survey was available to 2,681 sites. Results were limited to those institutions that updated the questionnaire in 2017, resulting in 1,455 respondents. The purpose of this survey was to understand the use of treatment positioning verification and delivered dose verification in IMRT. The survey was broken into two main sections. First, two questions about the methods and frequency of patient imaging for setup verification. Second, eight questions about the methods, tools, and interpretation of patient specific IMRT dose delivery quality assurance (QA).

Results: Verification of patient positioning was performed mostly by either kV imaging and/or MV Portal imaging (87%). Patient imaging was performed daily for 64% of the respondents. Patient specific IMRT QA was performed most frequently with a 2D diode array (53%) followed by ion chamber point dose measurement (39%) and EPID measurements (27%). The vast majority of sites (81%) use planar measurements to assess agreement utilizing absolute dose (88%). For planar measurements, the loosest criteria was 5%/5 mm with ≥ 90% pixels passing and the tightest criteria was 1%/3 mm with ≥ 90% pixels passing indicating a large variability in passing criteria. The most common criteria used was 3%/3 mm with ≥ 95% of pixels passing (49%). If IMRT QA did not meet their passing criteria, the most common action taken was to simply re-measure with the same setup, followed by moving to a new calculation point and re-measuring.

Conclusion: The survey provides a snapshot of the current state of patient positioning and dose verification for IMRT radiotherapy. This provides guidance, at least in terms of consensus practice, for clinics across the county.

Funding Support, Disclosures, and Conflict of Interest: This work received funding from the NIH/NCI grant #CA180803.


Quality Assurance


TH- External beam- photons: Quality Assurance - IMRT

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