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I. Cibulskaite et al. / Medical Physics in the Baltic States 7 (2009) 72 - 75 Table 2 Scatter dose in planar Si volume Scatter dose, Gy (mA s) -1 Construction 25 kV 28 kV 30 kV 0.1 mm Si, 1,258*10 without coating - 1,236*10 12 - 1,356*10 12 - 12 0.1 mm Si with 1,259*10 0.001 mm SiO2 coating - 1,239*10 12 - 1,359*10 12 - 12 0.1 mm Si with 1,260*10 0.001 mm a-C:H coating - 1,238*10 12 - 1,361*10 12 - 12 0.1 mm Si with 1,260*10 0.001mm carbon coating, containing SiOx - 1,238*10 12 - 1,360*10 12 - 12 0.1mm Si with 1,272*10 0.1 mm carbon coating, containing SiOx - 1,288*10 12 - 1,413*10 12 - 12 However these coatings also have to provide almost the same or better protective properties as the often used relative thick free standing polymeric foils do. 4. Conclusions The calculation of the total and scatter doses in Si samples coated by protective coatings were performed using Monte Carlo based modeling code EGSnrc. The modeling of (25-32) keV the X-ray photons interaction processes with mentioned material allowed to investigate the scatter contribution to the registered dose thought obtained total and scatted doses results. The 75 criterion of the scatter contribution is scatter to total dose ratio. Combination of the scatter modelling results obtained from Monte Carlo calculations with the manufacturing technological parameters of the experimental coatings, allows to get coatings that have good protective features, with possibly low scatter dose to total dose ratio and in this way to optimise the construction of ionising radiation detector that are suitable for low energy X-ray photon doses recording. As the modelling results shows, the influence of the thin (< 1 μm) DLC coatings containing SiOx , to X-ray scattering processes within detector material was negligible. 5. References 1. Kawrakow I.; Rogers D.W.O. The EGSnrc Code System. Monte Carlo Simulation of Electron and Photon Transport. National Reasearch Council of Canada. 2003. http://www.irs.inms.nrc.ca 2. Rogers D.W.O., Kawrakow I., Seuntjens J.P., Walters B.R.B., Mainegra-Hing E. NRC User Codes for EGSnrc. NRCC Report PIRS-702, 2005. 3. Dosimetric Aspects of Mammography. Report 6 of the Netherlands Commission on Radiation Dosimetry, 1993. 4. Cranley B. J. Gilmore, G. W. A. Fogarty, and L. Desponds, IPEM Report 78. Catalogue of Diagnostic X-Ray Spectra and other Data. The Institute of Physics and Engineering in Medicine IPEM; CD-Rom Edition 1997. Electronic Version prepared by D. Suttond, 1997.
MEDICAL PHYSICS IN THE BALTIC STATES 7 (2009) Proceedings of International Conference “Medical Physics 2009” 8 - 10 October 2009, Kaunas, Lithuania APPLICATION OF A SYNTHETIC DIAMOND DETECTOR FOR THE MEASUREMENT OF RELATIVE DOSE DISTRIBUTIONS IN RADIOTHERAPY N. KAZUCHITS*, M. RUSETSKYI*, A. SHULENKOV**, V. KUKUSHKIN***, S. MARTYNOV***, V. KHRUNOV***, J. TUZOV***, G. GATSKEVICH****, D. KANDYBOVICH**** * Belarussian State University, 220030 Minsk, Belarus; ** UP Minskii NII Radiomaterialov 220024 Minsk, Belarus; *** Institute in Physical and Technical Problems 141980 Dubna, Moscow Region; **** N.N. Alexandrov National Cancer Centre of Belarus Minsk, Belarus Abstract: The suitability of a synthetic diamond for the measurement of relative dose distributions in selected radiotherapy applications was studied. The performance of the synthetic diamond detector was analyzed by comparison with that of natural diamond detector produced by a Physikalisch-Technische Werkstatten (Freiburg, Germany) (PTW). The synthetic diamond detector is concluded to be suitable for relative dose measurements, especially when high response and high spatial resolution are required. Keywords: Diamond, detector, sensitivity, γ-rays, dose rate 1. Introduction Diamond is the attractive material for radiation detectors fabrication. The main advantage of this material is its radiation hardness. For application of diamond detectors in radiotherapy it is necessary to note two additional features – chemical inertness and “tissue equivalence”. The last feature is due to atomic number of the carbon (Z=6) is similar to the effective atomic number of the human soft tissue (Z=7,4). At present time natural diamond radiation detectors for radiotherapy are under the commercial production [1]. However, such detectors are rather expensive because of only a small part of natural diamond crystals is suitable for dosimetry application. Another material for radiation detectors production is high-pressure high-temperature (HPHT) synthetic diamond [2, 3]. Both natural and HPHT synthetic diamonds have practically the same physical properties [4]. The electronic applications of the HPHT material are restricted by a high concentration of the nitrogen and inhomogeneity of the crystals. Nevertheless, the improvement of the HPHT technology enables to consider synthetic diamond detectors as a future commercial product. In general, both natural and HPHT synthetic diamonds require a complex selection for dosimetry application. The purpose of this work is to compare characteristics of HPHT synthetic diamond detector with PTW natural diamond detector. Sensitivity, temporal current 76 stability and current linearity with dose rate were measured in high-energy photon beam. 2. Details of experiment The HPHT synthetic diamond crystals produced by “Adamas-BSU” company (Minsk, Belarus) were used in our experiments. Diamond plates 0,3 mm thickness were cut from as-grown crystals. After pre-selection by UV-photoconductivity method the detector structures were fabricated on the diamond plates. For this purpose it was performed an ion implantation of boron into both surfaces of diamond followed by high temperature (1400 ºC) annealing in vacuum. Finally, the Ti+Au contacts were deposited on both boron-doped layers. Prepared structures were tested using calibrated 137 Cs irradiation source of Federal State Unitary enterprise «Institute in Physical and Technical Problems» (Dubna, Russia). Leakage current, sensitivity, preirradiation dose, stability and linearity of current with dose rate were measured. The best samples were hermetically sealed in plastic cases for certification in Basic laboratory of metrological service of the Russian centre of science of radiology and surgical technologies (St. Petersburg). Certification was carried out while γ-rays 60 Co irradiated detectors were submerged in the water phantom. Experimental results are related to the best synthetic diamond detector.
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