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Background: The TRS‑483, an IAEA/AAPM International Code of Practice on dosimetry of small static photon fields, underwent testing via an IAEA coordinated research project (CRP). Alongside small field output factors (OFs) measurements using active dosimeters by CRP participants, the IAEA Dosimetry Laboratory received a mandate to formulate a remote small field dosimetry audit method using its passive dosimetry systems. Purpose: This work aimed to develop a small field dosimetry audit methodology employing radiophotoluminescent dosimeters (RPLDs) and radiochromic films. The methodology was subsequently evaluated through a multicenter pilot study with CRP participants. Methods: The developments included designing and manufacturing a dosimeter holder set and the characterization of an RPLD system for measurements in small photon fields using the new holder. The audit included verification of small field OFs and lateral beam profiles for small fields. At first, treatment planning system (TPS) calculated OFs were checked against a reference data set that was available for conventional linacs. Second, calculated OFs were verified through the RPLD measurement of point doses in a machine‐specific reference field, 4 cm × 4 cm, 2 cm × 2 cm, and 1 cm × 1 cm, corresponding size circular fields or nearest achievable field sizes. Lastly, profile checks in in‐plane and cross‐plane directions were done for the two smallest fields by comparing film measurements with TPS calculations at 20%, 50%, and 80% isodose levels. Results: RPLD correction factors for small field measurements were approximately unity. However, they influenced the dose determination's overall uncertainty in small fields, estimated at 2.30% (k = 1 level). Considering the previous experience in auditing reference beam output following the TRS‐398 Code of Practice, the acceptance limit of 5% for the ratio of the dose determined by RPLD to the dose calculated by TPS, DRPLD/DTPS, was considered adequate. The multicenter pilot study included 15 participants from 14 countries (39 beams). Consistent with the previous findings, the results of the OF check against the reference data confirmed that TPSs tend to overestimate OFs for the smallest fields included in this exercise. All except three RPLD measurement results were within the acceptance limit, and the spread of results increased for smaller field sizes. The differences between the film measured and TPS calculated dose profiles were within 3 mm for most of the beams checked; deviated results revealed problems with TPS commissioning and calibration of the treatment unit collimation systems. Conclusion: The newly developed small field dosimetry audit methodology proved effective and successfully complemented the CRP OF measurements by participants with RPLD audit results. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Background Purpose Methods Results Conclusions In 2021, a Technical Meeting was hosted by the International Atomic Energy Agency (IAEA) where it was recommended that a standardized method for assessing the accuracy of film dose calculations should be established.To design an audit that evaluates the accuracy of film dosimetry processes. To propose a framework for identifying out‐of‐tolerance results and to perform an international pilot study to test the audit design.Six members of an international Dosimetry Audit Network (DAN) developed an audit for radiochromic film dosimetry. A single host center provided the materials to each participating DAN member to conduct the audits. Materials included: (1) a set of two irradiated audit films (10 Sq: 10 cm × 10 cm, 15 Sq: 15 cm × 15 cm), (2) a reference calibration film set, and (3) a blank sheet of film. The participants were blinded to the dose and tasked with producing dose maps using their standard film dosimetry process. Average Region‐Of‐Interest (ROI: 2 cm × 2 cm) dose was measured from the dose maps and compared to the known dose. In the audit, all participants used their local scanning and software protocols. Film calibration was performed in two distinct ways: (1) using a calibration film set which was provided by the host center and (2) using a calibration film set which was locally irradiated. Several variations of the audit were also performed to examine how scanning and software processing can affect film dosimetry results. In the first variation of the audit (VariantA), a set of film scans was processed using five different software solutions. In the second variation of the audit (VariantB), all films were scanned on the same scanner and processed using two in‐house software solutions.Taking one film scan from each participant, the standard deviations (1σ) (SD) in the dose returned from the host calibration and returned from the local calibration were ±7.2% and ±6.5% respectively, with variations from −12.4% to 12.9% of the known dose. The larger dose variations in the data set were attributed to the corrections applied for variations in scanner brightness during processing and incorrectly assigned calibration doses. When the raw image data set was processed by an expert user of each software solution (VariantA) the SDs were ±2.7% and ±3.7% for in‐house and vendor‐based software, respectively. When the films were scanned on a single scanner and processed with the two in‐house software solutions (VariantB) the results had a SD of ±2.3%.An audit has been designed and tested for radiotherapy film dosimetry at an international level. A framework for diagnosing issues within a film dosimetry process has been proposed that could be used to audit centers that use film as a dosimeter. Incorporating quality assurance throughout the film process is important in obtaining accurate and consistent film dosimetry. A better understanding of vendor‐based software systems is necessary for users to process accurate and consistent film dosimetry. [ABSTRACT FROM AUTHOR]