EURAMET.RI(I)-S7 comparison of alanine dosimetry systems for absorbed dose to water measurements in gamma- and x-radiation at radiotherapy levels

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The National Physical Laboratory (NPL), the Physikalisch-Technische Bundesanstalt (PTB) and the Laboratoire National Henri Becquerel (LNE-LNHB) are involved in the European project 'External Beam Cancer Therapy', a project of the European Metrology Research Programme. Within this project, the electron paramagnetic resonance (EPR)/alanine dosimetric method has been chosen for performing measurements in small fields such as those used in IMRT (intensity modulated radiation therapy). In this context, these three National Metrology Institutes (NMI) wished to compare the result of their alanine dosimetric systems (detector, modus operandi etc) at radiotherapy dose levels to check their consistency. This EURAMET.RI(I)-S7 comparison has been performed with the support of the Bureau International des Poids et Mesures (BIPM) which collected and distributed the results as a neutral organization, to ensure the comparison was 'blind'.Irradiations have been made under reference conditions by each laboratory in a 60Co beam and in an accelerator beam (10 MV or 12 MV) in a water phantom of 30 cm × 30 cm × 30 cm in a square field of 10 cm × 10 cm at the reference depth. Irradiations have been performed at known values of absorbed dose to water (Dw) within 10% of nominal doses of 5 Gy and 10 Gy, i.e. between 4.5 Gy and 5.5 Gy and between 9 Gy and 11 Gy, respectively. Each participant read out their dosimeters and assessed the doses using their own protocol (calibration curve, positioning device etc) as this comparison aims at comparing the complete dosimetric process.The results demonstrate the effectiveness of the EPR/alanine dosimetry systems operated by National Metrology Institutes as a method of assuring therapy level doses with the accuracy required. The maximum deviation in the ratio of measured to applied dose is less than 1%.Main text.To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database kcdb.bipm.org/.The final report has been peer-reviewed and approved for publication by EURAMET, according to the provisions of the CIPM Mutual Recognition Arrangement (MRA).