An on-site dosimetry audit for high-energy electron beams

Abstract

A R T I C L E I N F O Keywords:Absorbed dose to water Audit Code of practice Dosimetry Electron beam Radiation therapy A B S T R A C T Background and purpose: External dosimetry audits are powerful quality assurance instruments for radiotherapy. The aim of this study was to implement an electron dosimetry audit based on a contemporary code of practice within the requirements for calibration laboratories performing proficiency tests. This involved the determination of suitable acceptance criteria based on thorough uncertainty analyses. Materials and methods: Subject of the audit was the determination of absorbed dose to water, D w , and the beam quality specifier, R 50,dos . Fifteen electron beams were measured in four institutes according to the Belgian-Dutch code of practice for high-energy electron beams. The expanded uncertainty (k = 2) for the D w values was 3.6% for a Roos chamber calibrated in 60 Co and 3.2% for a Roos chamber cross-calibrated against a Farmer chamber. The expanded uncertainty for the beam quality specifier, R 50,dos , was 0.14 cm. The audit acceptance levels were based on the expanded uncertainties for the comparison results and estimated to be 2.4%. Results: The audit was implemented and validated successfully. All D w audit results were satisfactory with differences in D w values mostly smaller than 0.5% and always smaller than 1%. Except for one, differences in R 50,dos were smaller than 0.2 cm and always smaller than 0.3 cm. Conclusions: An electron dosimetry audit based on absorbed dose to water and present-day requirements for calibration laboratories performing proficiency tests was successfully implemented. It proved international traceability of the participants value with an uncertainty better than 3.6% (k = 2).

Comparison of Dosimetry Protocols for Electron Beam Radiotherapy Calibrations and Measurement Uncertainties

“…These authors reported uncertainty (k = 1) in the absorbed dose to water of 1.5% for an electron beam. In another study, de Prez et al [18] reported a combined standard uncertainty (k = 1) for the absorbed dose to water in electron beams in the range 1.6-1.8%. These values compare well with the results of the current study.…”

The role of dosimetry audit in achieving high quality radiotherapy

“…Several of these could create a systematic error for every patient treatment on a given machine. However data from centres that strictly follow a code of practice (such as the Belgian-Dutch NCS-18 CoP [40]) can give very high standards of compliance [10].…”

“…Dosimetry audit is a key component in quality management programmes in radiotherapy, playing an important role in the safe implementation of new treatment modalities and techniques [1] , [2] , [3] , [4] . National and large scale audits provide data which can help to create, sustain and increase standards as well as have the potential to identify issues which may cause harm to patients, thus improving both quality and safety [1] , [4] , [5] , [6] , [7] , [8] , [9] , [10] , [11] , [12] , [13] . They can also help to reduce variability in dose delivered to the patient both nationally, internationally and within multi-institutional trials [3] , [13] , [14] , [15] , [16] .…”

IAEA/WHO postal dosimetry audit methodology for electron beams using radio photoluminescent dosimeters

“…Dosimetry audits focused mainly on photon beams 1,2 starting from beam output in reference and non-reference conditions, [3][4][5][6][7][8] to more advanced end-to-end audits. [9][10][11][12][13] There have been fewer audits focusing on high energy electron beams [14][15][16][17][18] based on air-kerma dosimetry codes of practice (CoPs).A global assessment of remote dosimetry audits demonstrated a high demand for electron beam audits and also indicated that they were more prone to errors as compared to photon beams. 19 The IAEA/WHO dosimetry audit program aims to accommodate Member States who do not have access to any dosimetry audits, offering cost-free services.…”