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SU‐F‐T‐286: Calculation‐Based Patient Specific IMRT QA Detects Potential Errors That Measurement‐Based QA Does Not
Author(s) -
Mossahebi S,
Langen K,
Guerrero M,
Yi B,
Lu W,
Kalavagunta C,
Prado K,
Chen S
Publication year - 2016
Publication title -
medical physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.473
H-Index - 180
eISSN - 2473-4209
pISSN - 0094-2405
DOI - 10.1118/1.4956426
Subject(s) - nuclear medicine , medicine , head and neck , radiology , medical physics , surgery
Purpose: Calculation‐based patient‐specific IMRT/VMAT QA, as a DICOM‐RT‐based plan verification system, has been commissioned and is currently being used at our institution. We report our investigation of IMRT/VMAT plan verification failures/warnings out of more than 1,000 plans verified over an 18‐month period. Methods: Seven patients with QA failures/warnings from our calculation‐based IMRT/VMAT QA were selected. Dose to 95% of PTV volume (D95%) and mean PTV dose with a difference of greater than 3%, a global gamma passing rate of less than 95%, and a mean dose difference to organ at risk (OAR) larger than 5% were set as the failure/warning criteria. The treatment sites of the selected patients included pelvis, leg, head and neck, brain, and breast. Measurement‐based IMRT/VMAT QA was done on each patient using MapCHECK2. Root cause analysis (RCA) was performed on all patients to investigate the IMRT/VMAT failures/warnings. Results: All seven patients’ plans passed measurement‐based IMRT/VMAT QA with a gamma passing rate of more than 95%. Our RCA of patients showed the IMRT/VMAT QA failures detected by the calculation‐based method were mainly due to inclusion of the skin in PTV, and tissue heterogeneity effects particularly at tissue‐air and tissue‐bone interfaces. Conclusion: Calculation‐based IMRT/VMAT QA can detect potential failures which cannot be detected by standard measurement‐based QA.