ESTRO 2024 - Abstract Book

S4893

Physics - Quality assurance and auditing

ESTRO 2024

2456

Proffered Paper

Remote EPID-based dosimetric audit results with clinically relevant IMRT dose evaluation criterion

Peter Greer 1,2 , Joerg Lehmann 1,2 , Alisha Moore 3

1 Calvary Mater Newcastle Hospital, Radiation Oncology, Newcastle, Australia. 2 University of Newcastle, Physics, Newcastle, Australia. 3 TROG Cancer Research, Clinical Trials, Newcastle, Australia

Purpose/Objective:

The Virtual Epid Standard Phantom Audit (VESPA) method was initiated in 2015 for dosimetric auditing of centres participating in clinical trials. It is a Level-II (TPS-planned) audit for IMRT or VMAT performed remotely without cost to the participating centre. To date 70 audits have been performed remotely in 15 different countries (Fig 1.). The aim of this work was to evaluate the audit results with respect to recommended clinical IMRT dose evaluation criteria as defined in the AAPM Task Group 218 report.

Material/Methods:

For the VESPA process, centres transfer their benchmarking plan to a cylindrical phantom in the treatment planning system (TPS) and calculate dose in the phantom. The plan is delivered, and images recorded in-air on the electronic portal imaging device (EPID). The data is sent to the central site for analysis where the dose in the (virtual) cylindrical phantom is reconstructed using an image to 3D dose conversion algorithm and compared to the TPS dose. All audit results were regenerated with a single EPID to dose conversion algorithm using a batch-processing method. Results were assessed against the TG218 gamma (g) criteria recommended for in-house IMRT dose evaluation (3%,2mm, 10% dose threshold). The percentage of points with g-value ≤ 1 was used. A case was considered passed (Optimal Level) if ≥ 95% of points meet g ≤ 1. A case was considered passed (tolerance level) if ≥ 90% and < 95% of points meet g ≤ 1. A case was considered to fail (Action Level) if < 90% of points meet g ≤ 1.