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Beam Output Audit results within the EORTC Radiation Oncology Group network
© The Author(s). 2016
Received: 29 August 2016
Accepted: 25 November 2016
Published: 15 December 2016
Beam Output Auditing (BOA) is one key process of the EORTC radiation therapy quality assurance program. Here the results obtained between 2005 and 2014 are presented and compared to previous results.
For all BOA reports the following parameters were scored: centre, country, date of audit, beam energies and treatment machines audited, auditing organisation, percentage of agreement between stated and measured dose.
Four-hundred and sixty-one BOA reports were analyzed containing the results of 1790 photon and 1366 electron beams, delivered by 755 different treatment machines. The majority of beams (91.1%) were within the optimal limit of ≤ 3%. Only 13 beams (0.4%; n = 9 electrons; n = 4 photons), were out of the range of acceptance of ≤ 5%. Previous reviews reported a much higher percentage of 2.5% or more of the BOAs with >5% deviation.
The majority of EORTC centres present beam output variations within the 3% tolerance cutoff value and only 0.4% of audited beams presented with variations of more than 5%. This is an important improvement compared to previous BOA results.
In 1982 the European Organisation for Research and Treatment of Cancer - Radiation Oncology Group (EORTC-ROG started a quality assurance (QA) program in radiation therapy (RTQA). ) In 1986 a Beam Output Audit (BOA) program was incorporated in this RTQA program [1, 2]. This RTQA process is in essence a verification of the dose delivery under reference conditions at the accruing site and defines, with the facility questionnaire the RTQA Level 1 . It is a dose measurement performed by a national or international auditor, independent from the site, and the results are fed back to EORTC headquarters . Published BOA data measured by an independent body and collected in the perspective of a trial coordination organization is scarce. A description of the method with mailed Thermoluminescence dosemeters (TLDs) and the results for the 1987–1989 and 1987–1992 periods have been published earlier [1, 5]. Themain goal of this paper is to present the BOA results from 2005 to 2014 stemming from European and non-European centres participating in EORTC trials.
Materials and methods
There are a number of EORTC-ROG minimum requirements that centres should fulfill to get their BOA approved by the EORTC-ROG . First and foremost, the audit must be performed independently from the centre, including at least the highest and lowest photon energy. The date of measurement should not be longer ago than 2 years at the time a request to participate in a new trial is received from a centre by the EORTC. Flattened beams and flattening filter free beams are considered as different energies. Electron beams are optional, unless the centre wants to participate in a study with electron treatments. All measurements need to be preferably within the 3% agreement, but measurements up to and including 5% are also accepted . The institutions are notified of the decision of the EORTC and are alerted if beams are within the 3 to 5% range if applicable. If a site does not fulfil the 5% tolerance for a single machine or beam the site is not authorized to use that combination of treatment unit type and energy. The EORTC currently distinguishes 3 treatment unit types: standard linear accelerator, rotational and robotic. The auditor’s primary standard has to have a clear traceability back to a national or international primary standard and the measurements must take place under standard conditions.
BOA reports capture the following parameters: centre, country, date of audit, beam energies and treatment machines audited, auditing organisation and the measured and stated dose. In addition to the mandatory measurements under standard conditions, a commercial service provider (called EQUAL) also reported the measurements they performed on the beam axis under non-standard conditions (wedged beams, field size 15x20cm, field size 7x7cm, at SSD of 105, 110 and 115 cm). Additionally, the number of treatment machines was collected for each centre based upon the latest EORTC facility questionnaire.
Most of the audits were performed by EQUAL. Most other different auditing bodies can be brought back to the common denominator of national organizations.
Summary of all beam results
Photon beams (%)
Electron beams (%)
Total (451 BOA reports)
Photon beam results from the EQUAL audits for non-standard conditions
Percentage depth dose (%)
Beam output variation open beams (%)
Beam output variation wedged beams (%)
Wedge transmission factor
When comparing the current results with earlier reported results an important difference can be seen. An evaluation over a time period of 6 years (1987–1992), auditing 55 institutes showed 2.5% of the beams with a higher discrepancy than 7% between stated and measured dose . The 1998 EQUAL program, auditing 102 centres, noted a rate of 3% of the photon beam outputs in reference conditions showing deviations outside the acceptance level of 5%  and the IAEA 1998–2001 postal results for 526 photon and 791 Co-60 beams revealed 16% of the beams having a discrepancy outside the 5% limit and even 1.3% (17 beams) with a discrepancy of more than 20%, with, in general, worse results for the Co-60 beams than for the photon beams . Other old reports stemming from over 10 to 23 years ago also reported significant discrepancies [8–11]. Dutreix and co-workers found 37 out of 125 beams outside the 3% optimal level and observed that 16 out of 22 beams with deviations between 3 to 6% and all 15 beams with a deviation of more than 6% were from centres not participating in BOAs within the previous 5 years (8). Izewska and Andreo observed that Only 65% of those hospitals who received TLDs for the first time had results within the acceptance limits, while more than 80% of the users that had benefitted from a previous TLD audit were successful .
In the current results, covering reports coming throughout a much wider part of the world, only 0.2% of the photon beams were found to be higher than the acceptance level.
Another feasibility study by the European-Commission Network verifying mailed dosimetry for electron beams was initiated in the late nineties. In total 300 (91.5%) out of 328 beams were found to be within the tolerance level of 5% . Currently only 0.7% of all the electron beams were found to be out of this range.
Overall good results could also be seen for the measurements in non-standard conditions. The percentage number of all photon beams – standard and non-standard conditions - within the non-optimal level of acceptance from the 1998 EQUAL program are 14% and those outside of acceptance level are 4%, while the presented results have 6.5 and 0.1% of the beams in these categories of acceptance .
The difference in our results to those found in literature might be caused by the presence of a bias, as our dataset only contains BOA-reports from centres participating in EORTC lead radiotherapy trials. Additionally, centres might have provided only a selection of their BOA data to the EORTC.
More recent publications on RTQA results in trials suggest that the main sources of protocol deviations are not due to beam output deviations under reference conditions. Deviations are more likely to be related to ambiguousness in the trial protocol, delineation variations and dose calculation and optimization problems in trial specific treatment plans . Other trial RTQA procedures, which are more and more harmonized globally, like benchmark exercises, individual case reviews and complex dosimetry checks are able to detect such protocol deviations and nowadays mitigate the need for BOAs in the context of trial RTQA [4, 14].
It can be defended that omitting the request of a BOA would make trial RTQA easier, faster and less costly without loss of RT quality within trials.
Our analysis shows that only 0.2 and 0.7% of all photon and electron BOA results, respectively, were found discrepant in respect to a 5% cutoff level, which is a substantial improvement compared to previous BOA results.
We want to acknowledge all the people within the EORTC Radiation Oncology Group Quality Assurance team for fruitful discussions related to the topic addressed in this paper.
This work has been supported by the “Vlaamse Liga tegen Kanker”, Belgium, through the EORTC Charitable Trust in the scope of the “Emmanuel van der Schueren” fellowship allocated to Dr. Melissa Christiaens.
Availability of data and materials
The data cannot be shared as it could be maybe traceable to individual institutions which we do not have the right to disclose.
CH and MC drafted the manuscript. All authors participated in the analysis of the data described in this paper. All authors read and approved the final manuscript.
The author declares that he/she has no competing interests.
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