Dosimetry audit service in Italy: Results of the partnership between Italian Association of Medical Physics (AIFM) and Italian National Institute of Ionizing Radiation Metrology (ENEA-INMRI).

Purpose: The Italian National Institute of Ionizing Radiation Metrology (ENEA-INMRI) and the Italian Association of Medical Physics (AIFM) offer a certified audit service to radiotherapy (RT) centers for reference dosimetry.

Methods: Audits are provided for photon beams in the range 6-18 MV including flattening filter free C-arm Linac, CyberKnife and TomoTherapy beams. A dosimeter consisting of a set of TLD chips embedded in a PMMA waterproof holder is used. TLDs are calibrated in terms of absorbed dose to water in the ENEA-INMRI reference Co γ-beam. Correction factors accounting for energy dependence, signal reproducibility and response stability are applied to evaluate absorbed dose. For each beam audited, irradiation of two dosimeters with 2 Gy is required in reference conditions, according to the international dosimetry protocols. Audit performance is evaluated in terms of theEscore: it is satisfactory if |E| ≤ 1.0.

Results: Audit was successfully performed for 94beams in 34 ItalianRTcenters. Nominal beam energies analysed were 6 MV (38.3 %), 6 MV FFF (33.0 %), 10 MV (12.8 %), 10 MV FFF (4.2 %), 15 MV (9.6 %) and 18 MV (2.1 %). TheEscores are normally distributed with 95 % of data between -0.54 and 0.7; 99.5 % of values are in the range [-1.0,1.0] and 81.1 % are in the optimal range [-0.5,0.5]. As for the single unsatisfactory result, data from the form filled in by the RT center allowed ENEA-INMRI to identify an error in the measurement setup.

Conclusions: Results of remote audits have shown excellent performance of Italian RT centers.