ESTRO 2024 - Abstract Book

S4871

Physics - Quality assurance and auditing

ESTRO 2024

and more important. Based on the International Atomic Energy Agency's "end-to-end" (E2E) audit methodology for on-site verification of IMRT/VMAT dose delivery, voluntary audits have been carried out in Romania since 2019 through a pilot study (under IAEA TC Project ROM6/0/18). The main objective was to evaluate the physical aspects of the overall clinical IMRT/VMAT performance for the head and neck test case.

Material/Methods:

10 institutions (private and public) performing IMRT/VMAT treatments have voluntarily participated in this study, nationwide. There were 12 LINACs and 14 beams measured included, using 6MV and 10MV. The adopted methodology simulated all the steps of an IMRT/VMAT treatment, in an” end-to-end” approach using the anthropomorphic CIRS SHANE phantom. It can accommodate a small volume ion chamber (IC) in four dedicated locations. Based on the IAEA methodology, the audit consisted of two parts: the pre-visit - the centers are asked to create an IMRT/ VMAT treatment based on the IAEA methodology; the on-site visit aims to do dose measurements in dedicated locations - three in planning target volumes (PTVs) and one in the spinal cord (OAR). The algorithms used were AAA and ACUROS XB from Varian, and Monte Carlo from Elekta. The measured doses were compared using the agreement criteria given in the IAEA methodology.

Results:

Most cases returned good agreement for the same type of algorithm in all centres and for each beam quality. It must be said that the number of results is still low to have a conclusive statistical result. Regarding the type “b” algorithm (AAA), all measured values for PTV volumes agreed in the range of -3.9% to +2.7%. For the type “c” algorithms (Monte Carlo and ACUROS XB) the results ranged from -3.3% to +2.9%. Regarding the spinal cord (OAR) the agreement ranged from -4.7% to +0.9% for type "b" algorithm. Considering the patient-specific quality assurance results (global criteria of 3%/3mm, 10% threshold), passing rates ranged from 95.6% to 100% for all considered beams. Nevertheless, during this study, there were identified situations that could have led to suboptimal treatments in terms of dose delivery and were corrected.

Conclusion:

E2E dosimetry audit can contribute to achieving a better understanding of the local performance of radiotherapy implementation of the IMRT/VMAT techniques in clinical practice.

Keywords: dosimetry, anthropomorphic phantom, Head&Neck

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Preliminary results of a multicentre small field dosimetry audit using a novel holder design

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