IAEA methodology for on-site end-to-end IMRT/VMAT audits: an international pilot study

Abstract

Background: The IAEA has developed and tested an on-site, end-to-end IMRT/VMAT dosimetry audit methodology for head and neck cases using an anthropomorphic phantom. The audit methodology is described, and the results of the international pilot testing are presented. Material and methods: The audit utilizes a specially designed, commercially available anthropomorphic phantom capable of accommodating a small volume ion chamber (IC) in four locations (three in planning target volumes (PTVs) and one in an organ at risk (OAR)) and a Gafchromic film in a coronal plane for the absorbed dose to water and two-dimensional dose distribution measurements, respectively. The audit consists of a pre-visit and on-site phases. The pre-visit phase is carried out remotely and includes a treatment planning task and a set of computational exercises. The on-site phase aims at comparing the treatment planning system (TPS) calculations with measurements in the anthropomorphic phantom following an end-to-end approach. Two main aspects were tested in the pilot study: feasibility of the planning constraints and the accuracy of IC and film results in comparison with TPS calculations. Treatment plan quality was scored from 0 to 100. Results: Forty-two treatment plans were submitted by 14 institutions from 10 countries, with 79% of them having a plan quality score over 90. Seventeen sets of IC measurement results were collected, and the average measured to calculated dose ratio was 0.988 ± 0.016 for PTVs and 1.020 ± 0.029 for OAR. For 13 film measurement results, the average gamma passing rate was 94.1% using criteria of 3%/3 mm, 20% threshold and global gamma. Conclusions: The audit methodology was proved to be feasible and ready to be adopted by national dosimetry audit networks for local implementation.

A multi‐institutional evaluation of small field output factor determination following the recommendations of IAEA/AAPM TRS‐483

“…The proposed linac-typecurves along with the proposed tolerance limits can be used as initial quality assurance for the accreditation for clinical trials followed my more detailed experimental procedures. [4][5][6] Unfortunately, the larger inter-linac variation of the Siemens Primus could not be followed up as the machines were decommissioned. When operating this linac type with field sizes smaller than 1 cm x 1 cm, a larger inter-linac variation might be expected compared to state-of -the-art linacs and frequent checks of the SFOFs are necessary.…”

“…Approximately 67% of the centers participating in the present study were also participating in clinical trials involving stereotactic radiotherapy and/or intensity modulated radiotherapy techniques where accurate dosimetry of small fields is essential. The proposed linac‐type‐curves along with the proposed tolerance limits can be used as initial quality assurance for the accreditation for clinical trials followed my more detailed experimental procedures 4–6 …”

“…2 These effects can also influence the results of dosimetry audits and need to be considered separately. [3][4][5][6] The determination of SFOFs is challenging as the ratio of detector readings is in general not equal to the ratio of dose. 1,7,8 Additionally, the use of appropriate detectors and accurate positioning of these detectors in small fields are essential to minimize the experimental uncertainty.…”

Comprehensive end-to-end test for intensity-modulated radiation therapy for nasopharyngeal carcinoma using an anthropomorphic phantom and EBT3 film

“…Most extant studies on the end-to-end test are based on considerably simple phantoms (12)(13)(14)(15)(16) . Recently, anthropomorphic phantoms that realistically simulate anatomically accurate patient tissue heterogeneities were introduced to end-to-end IMRT/VMAT dosimetry audit methodology and monthly QA protocol for external beam radiation therapy treatment (17,18) . To the best of the authors' knowledge,…”

IAEA support to radiotherapy dosimetry

“…Individual follow-up of poor results (using a 5% acceptance limit between the stated and measured dose) was initiated in 1996 and this has facilitated a more in-depth analysis of the audit results. Kazantsev et al [10] presents the results of an international pilot study of an on-site end-to-end audit methodology for head and neck treatment using advanced technologies that was developed though an IAEA coordinated research project. The methodology not only tests the integrity of treatment delivery, but also includes aspects of imaging and treatment planning quality assurance.…”