For photon beam sizes lower than 2cm×2cm no absorbed-dose-to-water (D w) primary standards are available for determining the possible influence of field size on the dosimeter response. In this work, D w measurements performed in 1cm×1cm photon beams at PTB using alanine and synthetic diamond dosimeters were compared in order to assess the reliability of the two dosimetric systems in such a small field size. The ratio of D w values measured by diamond dosimeters to D w values measured by alanine was 0.991±1.5% (1 SD) and 1.007±1.3% (1 SD) for 6MV and 10MV photon beams, respectively. This shows that both systems are capable of accurately measuring D w in small fields.
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