Study on the adequacy of use semiconductor detectors for dosimetric evaluations in radiotherapy with electron beams

The limited range of the electrons allows to treat particularly superficial structures, by limiting the dose on more depth tissues, because the electron beam presents a marked down falling after the buildup region. The radiation beam in a determined medium is characterized by a distribution versus depth in the medium curve - DDP (Depth dose percentage, and from that curve come clinical parameters used in characterization of electron beam are defined. The semiconductor detectors, more specifically the silicon diodes, are used in large scale in measurements of absorbed dose in radiotherapeutic treatment with electron beams. However, researchers from Medicine School of the Yale University point out the inadequacy of diode using for dose axial profile, in clinical parameter surveys. Contra position reports available in the literature justify this work, describing a adequacy study of semiconductor detectors using on procedures of clinical dosimetry with electron beams. Dose axial profile measurements were performed at Varian Clinac 2100 C of the Servico de Radioterapia do Instituto de Radiologia do Hospital das Clinicas de Sao Paulo, Brazil. DDP measurements with silicon diode present clinical parameters R100 (maximum depth dose 0 and R50 (maximum 50 percent of dose) compatible with the values obtained with the ionization chamber for the same beam conditions. (author)