What can reveal on-site end-to-end audit? The experience from national dosimetry audit group

Result code in IS VaVaI

<a href="https://www.isvavai.cz/riv?ss=detail&h=RIV%2F86652052%3A_____%2F17%3AN0000041" target="_blank" >RIV/86652052:_____/17:N0000041 - isvavai.cz</a>

Result on the web

<a href="https://www.sciencedirect.com/science/article/pii/S0167814017320947?via%3Dihub" target="_blank" >https://www.sciencedirect.com/science/article/pii/S0167814017320947?via%3Dihub</a>

DOI - Digital Object Identifier

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Result language

angličtina

Original language name

What can reveal on-site end-to-end audit? The experience from national dosimetry audit group

Original language description

National Radiation Protection Institute performs on-site audits in the Czech Republic. In total, 53 on-site end-to-end audits for prostate and 16 for H&N/brain radiotherapy were performed. Prostate case was verified in the national run for all centres using IMRT in 2013 and repeated for majority of centres with upgrade/installation of new linacs in 2014-2016. There was a pilot run with head phantom in 2016. Majority of results were within tolerances. All results were analysed to describe the most interesting findings and the weakest points. Absorbed doses with ionisation chambers and plane doses with EBT3 films were measured in the pelvic or head phantom. Following aspects can be assessed: unit calibration, TPS model accuracy for reference field, MLC accuracy, CT numbers to RED conversion in terms of its influence to dose, phantom geometrical offset at the couch, optimisation constraints, radiobiological plan parameters calculated from DVHs. Anthropomorphic phantoms (pelvic and head) with benchmark PTVs and OARs were used. Three sets of audit results were analysed: prostate audit national run, repeated prostate audit, H&N/brain audit pilot run. Methodology is applicable to C-arm linacs, Tomotherapy, Leksell Gamma Knife, and proton beams. H&N/brain audit is more complex than prostate one, and chamber cavity volume is taken into account more carefully which enables to keep tight tolerances. Centres which participated in the previous run did not perform better than centres which participated for the first time in prostate audit. However, results were sufficient in all cases. There was not significant improvement in results with installations of new linac and TPS. Better MLC performance was observed but CT number to RED was still the problematic point. Differences in planning approaches can be seen. Weakest point for the head audit was the phantom positioning on the couch (despite using IGRT). Tolerances for film evaluation depend on the dose gradient in the direction perpendicular to the film plane. We use 95% or 90% (4%/3mm) for gamma index for prostate/ H&N or brain plans respectively. In future, pseudo-3D gamma analysis will be implemented. It is not straighforward to identify the causes of deviations, especially when they lie within tolerance limits. Nevertheless, it is possible to identify systematic errors which might be vendor dependent, user dependent, or TPS dependent. These can help to optimise the national quality standard in radiotherapy. We recommend not to use rigid marks on phantom but let the centre apply their own fixation and positioning procedure. We recommend to include CT scanning process and identical „patient“ set-up procedure employing RTTs. When designing audit methodology, it is necessary to analyze pilot run results first and then optimise procedure dependent tolerances. The contribution was presented at the conference ESTRO 36 and published in journal Radiotherapy and Oncology, Volume 123, Supplement 1, Pages S951–S952.

Czech name

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Czech description

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Type

O - Miscellaneous

CEP classification

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OECD FORD branch

20601 - Medical engineering

Project

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Continuities

I - Institucionalni podpora na dlouhodoby koncepcni rozvoj vyzkumne organizace

Publication year

2017

Confidentiality

S - Úplné a pravdivé údaje o projektu nepodléhají ochraně podle zvláštních právních předpisů