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Monte Carlo Modeling of a Gamma Camera for Sm-153 Imaging in Targeted Radiotherapy and Benchmarking with Measured Data

Asgari, Afrouz | 2013

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 44146 (46)
  4. University: Sharif University of Technology
  5. Department: Energy Engineering
  6. Advisor(s): Sohrabpour, Mostafa; Shokrani, Parvaneh
  7. Abstract:
  8. Metastatic bone is one of the most common causes pain in cancer patients. Because of Sm-153 emits gamma and beta, Sm-153 have been used for both of the diagnosis and treatment of metastases; Also Tc-99m have been used for the detection of metastases. Dosimetric studies in targeted radiotherapy require an accurate quantification of activity existing in different organs of a patient, which can be estimated from scintigraphic images. Quantitative imaging is difficult to perform because of several physical phenomena, such as scatter and attenuation, which lead to errors in activity determination and nuclear medicine image degradation.
    In this work, we must determine the optimal window in such a way that it displays the lowest scatter fraction as well as having a nearly constant linear attenuation coefficient as a function of phantom thickness. Other aim in this study is attenuation correction quantitatively. The experimental of data in this work were obtained from the OBITER SCINTRON gamma camera. We analyzed energy windows by using Tc-99m and Sm-153 radionuclide with RW3 and Teflon bone phantom. We have also used MCNP4C Monte Carlo code for simulation of the performance of the above gamma camera. Based on the results of the simulation as well as experimental work, the performance of WH and ASW windows display of the both results, lowest scatter fraction as well as constant linear attenuation coefficient as a function of phantom thickness. WH and ASW were optimal windows in nuclear medicine imaging for Tc-99m in RW3 phantom and Sm-153 in Teflon bon phantom. Attenuation correction was done for WH and ASW optimal windows and for both of the TC-99m and Sm-153 by using filtered backprojection algorithm. Corrected counts were not affected by the thickness of scattering material. Results of simulation and experimental show that very good agreement between the set of experimental with simulation as well as theoretical values with simulation data were obtained which was nominally less than 7.07% for Tc-99m and less than 8.00% for Sm-153.
    The combination of source distance from the collimator and insertion of scattering material tend to increases the FWHM and FWTM significantly. However the use the Triple Energy Window, TEW, method has been investigated to improve or to reduce the scattered radiation effect on the image quality. TEW method using, TC-99m and Sm-153 radioisotopes, has reduced FWHM and FWTM parameters by 28% and 16% respectively. Extended Triple Energy Window, ETEW, was also studied, and ETEW method was found to be more effective than the TEW method for improvement of the image quality.
    A new method, calculating responses of gamma camera to specific activity of Tc-99m and Sm-153 in RW3 and Teflon phantom has been presented. In this method, response of gamma camera to specific activity of Sm-153 has been calculated for different thicknesses and different radiation angles. Experimental and simulation calibration factors have been calculated for Tc-99m, Sm-153, RW3 and Teflon phantoms. The results show that the average errors obtained from simulation and experiment for Tc-99m and Sm-153 in RW3 phantoms are 4.5% and 3.1% respectively. The average errors obtained from simulation and experiment for Tc-99m and Sm-153 in Teflon phantom are 5.4% and 5.6% respectively. Results show that using the above methods can improve the quality of nuclear medicine images and calculate inherent activity in the body organs
  9. Keywords:
  10. Monte Carlo N-Particle (MCNP)Code ; Single Photon Emission Tomography (SPECT) ; 99m TC ; Metastatic Bone ; Gama Camera ; Scatter Correction ; Attenuation Correction

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