Dosimeter with a photodiode base evaluation by IEC 731 standard and its application in X and gamma radiation field parameters determination and in vivo dosimetry

This work presents a dosimeter with a photodiode base, characterized as field class instrument, for determination of X and gamma radiation field parameters, which are specified in the ISO 4037-1 Standard, and for in vivo dosimetry. Three photodiode models performance, a commercially available (Siemens) and two special others (Hamamatsu), were compared with the ionization chamber's, using the limits established in the IEC 731 Standard as requirement. The long-term stability and the energy dependence tests have shown results higher than the limits but, in special situations, as X-ray beams monitoring, these deficiencies have no influence on the dosimeter performance. The photodiode Siemens has shown uncertainty of 7% for determination of the radiation field diameter, against 4% from the ionization chamber, 16% from the photographic emulsion and 18% from the TDL. At the rotation test, in a water phantom, none of the models has shown satisfactory results. However, using two photodiodes, it was obtained a dosimeter that overcomes these deficiencies, and it could be used for in vivo dosimetry. The relation between the output signal, from the proposed dosimeter, and the phantom depth, has shown agreement of 0,7% with the depth dose distribution curve. So, the dosimeter has shown its capability to evaluate the absorbed dose correctly. (author)