title: Dosimetric characteristics of an unshielded p-type Si diode: linearity, photon energy dependence and spatial resolution.
abstract: The unshielded Si diode PTW 60012, used for accurate measurements of the transversal dose profiles of narrow photon beams, has been investigated with regard to its linearity, photon energy dependence and spatial resolution. The diode shows a slight supralinearity, i.e., increase of the response with pulse dose, by 3% over the pulse dose range 0.1 to 0.8 mGy. In p-type silicon, supralinearity results from the increased chance for radiation-induced electrons to escape recombination when the pulse dose increases. Over the energy range from 6 to 15 MV, the response decreases by about 4%. This small variation of the response results from partial compensation between the influences of the secondary electron energy on the mass stopping power ratio silicon/water and on electron backscattering from the silicon chip. The lateral response function of the examined diode has a full half width of 1.3 mm. Dose profiles of 5 mm half-width can still be recorded with negligible error.
authors.affiliation: Medical Radiation Physics Group, University of Oldenburg, and Pius-Hospital, Oldenburg. armand.f.djouguela.ouentcheu@mail.uni-oldenburg.de
authors.forename: Armand
authors.initials: A
authors.lastname: Djouguela
authors.forename: Irmgard
authors.initials: I
authors.lastname: Griessbach
authors.forename: Dietrich
authors.initials: D
authors.lastname: Harder
authors.forename: Ralf
authors.initials: R
authors.lastname: Kollhoff
authors.forename: Ndimofor
authors.initials: N
authors.lastname: Chofor
authors.forename: Antje
authors.initials: A
authors.lastname: Rühmann
authors.forename: Kay
authors.initials: K
authors.lastname: Willborn
authors.forename: Bjoern
authors.initials: B
authors.lastname: Poppe
mesh_terms: D000327:Adsorption; D006801:Humans; D054023:Lasers, Semiconductor; D017785:Photons / Q000627:therapeutic use*; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D012825:Silicon
chemical_list: D012825:Silicon