Abstract
Background: Volumetric modulated arc therapy (VMAT) is the standard of care for many clinical indications, but should only be considered with proper technical support and quality assurance (QA) in place. Despite the high accuracy of VMAT systems, errors can be present and adequate verification is required. Dosimetric VMAT verification systems have a broadly similar analysis philosophy. However, many factors influence the analyses and the subsequent QA outcome, based on which the plan will pass or fail.Aim: This study investigated various factors that influence the dosimetric impact and detectability of known linac component deviations on VMAT QA, including geometries, tissue densities, gamma criteria and dose–volume differences.Setting: Universitas Hospital (Annex), Bloemfontein, South Africa.Methods: Deliberate multi-leaf collimator (MLC)-bank offsets were introduced on four different VMAT plans of the prostate, nasopharynx and brain. Measured reference dose sets were compared to measured QA results, using the IBA Dolphin© detector and Compass© software for three dosimetric scenarios. Gamma pass rates over a range of criteria from 1%/2-mm to 4%/4-mm in the total volumes and per structure, as well as dose–volume differences were studied.Results: Gamma tests in the total patient/phantom did not sufficiently detect errors. The calculation media did not influence the QA outcome greatly. However, the detection geometry affected the results. Per structure gamma analyses provided superior error detection, although still missed some clinically relevant differences. The addition of dose–volume analyses highlighted several important errors.Conclusion: Volumetric modulated arc therapy using only total volume gamma analyses can easily overlook clinically relevant errors. The choice of gamma criterion is crucial. Verification with at least a per structure gamma test in combination with dose–volume checks is recommended, especially in small target volume cases.
Highlights
The complexity of volumetric modulated arc therapy (VMAT) requires considerable linear accelerator component analysis and verification to guarantee the integrity of treatment plan quality and treatment delivery accuracy
Volumetric modulated arc therapy and intensity modulated radiotherapy (IMRT), the precursor to VMAT, offer several advantages over conventional radiotherapy treatment and have been promulgated as a standard of care for a large selection of cancer treatment sites. 3,4,5,6 to maintain treatment integrity, adequate emphasis should be placed on the execution and interpretation of quality assurance (QA) to be aligned with clinical and technical requirements
We investigated several analyses metrics, phantom geometries and dosimetry settings often used for VMAT QA to study the dosimetric impact and detectability of known linac component deviations, in particular the multi-leaf collimator (MLC)
Summary
The complexity of volumetric modulated arc therapy (VMAT) requires considerable linear accelerator (linac) component analysis and verification to guarantee the integrity of treatment plan quality and treatment delivery accuracy. Component malfunctions and deviations from planned treatment positions or values may occur, VMAT delivery with linacs from various manufacturers has been found to be dosimetrically accurate.[7,8,9] To identify treatment delivery errors, deviations or miscalibrations of linac components, patient-specific QA via dosimetric plan verification and dose recalculation[10,11,12] generally follows the acceptance of a clinical treatment plan These can be performed with a wide range of dosimetry systems, ranging from radiation detector arrays 13,14,15 to linac logfiles.[16,17] http://www.sajo.org.za. Many factors influence the analyses and the subsequent QA outcome, based on which the plan will pass or fail
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
