MO-FG-202-07: Real-Time EPID-Based Detection Metric For VMAT Delivery Errors.

Passarge, M; Fix, Michael; Manser, Peter; Stampanoni, M F M; Siebers, J V (June 2016). MO-FG-202-07: Real-Time EPID-Based Detection Metric For VMAT Delivery Errors. Medical physics, 43(6), p. 3713. American Association of Physicists in Medicine AAPM 10.1118/1.4957310


To create and test an accurate EPID-frame-based VMAT QA metric to detect gross dose errors in real-time and to provide information about the source of error.


A Swiss cheese model was created for an EPID-based real-time QA process. The system compares a treatmentplan- based reference set of EPID images with images acquired over each 2° gantry angle interval. The metric utilizes a sequence of independent consecutively executed error detection METHODS: a masking technique that verifies infield radiation delivery and ensures no out-of-field radiation; output normalization checks at two different stages; global image alignment to quantify rotation, scaling and translation; standard gamma evaluation (3%, 3 mm) and pixel intensity deviation checks including and excluding high dose gradient regions. Tolerances for each test were determined. For algorithm testing, twelve different types of errors were selected to modify the original plan. Corresponding predictions for each test case were generated, which included measurement-based noise. Each test case was run multiple times (with different noise per run) to assess the ability to detect introduced errors.


Averaged over five test runs, 99.1% of all plan variations that resulted in patient dose errors were detected within 2° and 100% within 4° (∼1% of patient dose delivery). Including cases that led to slightly modified but clinically equivalent plans, 91.5% were detected by the system within 2°. Based on the type of method that detected the error, determination of error sources was achieved.


An EPID-based during-treatment error detection system for VMAT deliveries was successfully designed and tested. The system utilizes a sequence of methods to identify and prevent gross treatment delivery errors. The system was inspected for robustness with realistic noise variations, demonstrating that it has the potential to detect a large majority of errors in real-time and indicate the error source. J. V. Siebers receives funding support from Varian Medical Systems.

Item Type:

Conference or Workshop Item (Abstract)


04 Faculty of Medicine > Department of Haematology, Oncology, Infectious Diseases, Laboratory Medicine and Hospital Pharmacy (DOLS) > Clinic of Radiation Oncology > Medical Radiation Physics

UniBE Contributor:

Fix, Michael, Manser, Peter


500 Science > 530 Physics
600 Technology > 610 Medicine & health




American Association of Physicists in Medicine AAPM




Beatrice Scheidegger

Date Deposited:

27 Feb 2017 16:09

Last Modified:

05 Dec 2022 15:01

Publisher DOI:


PubMed ID:


Uncontrolled Keywords:

Dosimetry; Error correction; Gamma rays; Image guided radiation therapy; Medical imaging; Radiation treatment; Real time information delivery; Science funding; Testing procedures


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