Biophysics & Radiotherapy
Narges Araste; Hossein Tavakoli-Anbaran
Volume 27, Issue 1 , May and June 2020, , Pages 17-26
Abstract
Background: The Compton scattered annihilation gammas between PET detectors reduce spatial resolution by making an incorrect Line of Response. This paper, by presenting a new method, tried to remove these errors from PET imaging. In this way, the detectors were insulated so that scattered gammas from ...
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Background: The Compton scattered annihilation gammas between PET detectors reduce spatial resolution by making an incorrect Line of Response. This paper, by presenting a new method, tried to remove these errors from PET imaging. In this way, the detectors were insulated so that scattered gammas from a detector can not enter other detectors of the PET ring. Method: First of all, the Siemens PET BiographTM 6 scanner ring was simulated and then all detectors of this ring were isolated to resolve this error and investigate its impact on the Response Function of PET detectors. Results: The analysis of the results of simulation showed that, the isolation of PET detectors reduced counts of detectors in the energy window, especially at the lower threshold (350 to 400 keV). This reduction with a spherical soft issue was less than without that. So that the maximum of the relative percentage difference for counts of detectors between connect and disconnect them was 70% (in 400 keV) and 12% (in 350 keV) in the absence and presence of soft tissue, respectively. Conclusion: Although the isolation of the detectors boosted the resolution of PET, it removed some true coincidences and reduced the sensitivity of PET; there for, it did not have much effect on image quality of PET. Also, a slight decrease in the count, with the soft tissue, shows the greater effect of the isolation of PET-detectors in improving image quality in abdominal imaging in comparison with other imaging such as head and neck imaging.
Golshan Mahmoodi; Parvaneh Shokrani; Alireza Amo Heidari; Maryam Atared; Ali Hosseinzadeh
Volume 22, Issue 2 , May and June 2015, , Pages 397-409
Abstract
Back ground and purpose: To treatment of malignant pleural mesoteloma, in the absence of IMRT, photon beam and lung shield was used for treatment and then electron beam was used to treat shielding area. Photon dose distribution is influenced by inhomogeneity media, lateral electronic disequilibrium at ...
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Back ground and purpose: To treatment of malignant pleural mesoteloma, in the absence of IMRT, photon beam and lung shield was used for treatment and then electron beam was used to treat shielding area. Photon dose distribution is influenced by inhomogeneity media, lateral electronic disequilibrium at interfaces, the block in middle of the field and narrow field. This study compares Monte Carlo (MC) with conventional treatment planning system (TPS) calculations for photon beam radiation therapy of malignant pleural mesoteloma (MPM) using lung island shield.
Methods and Materials: Photon dose distribution using lung island shield calculated by three methods: 1) MC 2) TPS 3) Film dosimetry in anthropomorphic phantom. MC commissioned by film dosimetry and TPS dose calculation accuracy investigated by MC simulation.
Results: Accuracy of treatment head simulation and tomographic phantom dose distribution was verified by matching percent depth dose (PDD) and dose profile in water phantom and film dosimetry in anthropomorphic phantom in two fields of with and without lung shield respectively.
Conclusion:Compare to MC, TPS: 1) overestimates pleura dose coverage (90% prescribed dose) 3-12 mm and the dose in under the lung shield region 10-50% and 2) underestimated the dose profile width 1-16 mm in low dose region (< 50% prescribed dose) and the dose in out of field region 6-100%.
Ebrahim Golmakani; Reza Ganji; Mohsen Abad; Homa Rezaee moghaddam; Mehdi Bakhshabadi; Mohammad Mehrpoyan; Mohsen Khosoabadi; Ramin Shahraeini
Volume 21, Issue 5 , September and October 2014, , Pages 808-818
Abstract
Background: The aim of this study is to assess of dose enhancement effect in tumour in presence of 10B, 157Gd, 10B nanoparticles and 157Gd nanoparticles in radiotherapy through neutron capture by Monte Carlo method.
Materials and Methods: A 252Cf brachytherapy source AT model was simulated by Monte ...
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Background: The aim of this study is to assess of dose enhancement effect in tumour in presence of 10B, 157Gd, 10B nanoparticles and 157Gd nanoparticles in radiotherapy through neutron capture by Monte Carlo method.
Materials and Methods: A 252Cf brachytherapy source AT model was simulated by Monte Carlo method code MCNPX and its TG-43 parameters were calculated and compared with previous corresponding data. This 252Cf brachytherapy source was used as a neutron source in neutron capture therapy. Dose enhancement factor was compared in tumour in presence of 10B, 157Gd, 10B nanoparticles and 157Gd nanoparticles for the concentrations of 100, 200 and 500 ppm of each capture agents in neutron capture. For this aim, around the 252Cf source, a spherical soft tissue phantom and a tumour containing each capture agents were considered.
Results: Calculated air kerma strength and dose rate constant for 252Cf source equals to 0.306 cGycm2/hµg and 5.782 cGy/Uh respectively. Among examined agents, maximum DEF belonged to 10B and 10B nanoparticles in concentration of 500 ppm. These values were reported as 1.06 and 1.08 respectively.
Conclusion: IN this study, air kerma strength and dose rate constant indicate difference of %7.27 and %1.10 with other corresponding values. In dose enhancement point of view, capture agents containing 10B are more useful in neutron capture therapy. In the same concentrations, dose enhancement factor for capture agents in nanoparticles form is higher than the presence of capture agents in atomic form. So, it is preferable to use of nanoparticle capture agent rather than atomic form. However, it should be noted that before clinical usage of this agents, other medical, chemical and physical criteria should be considered, for their comparison, in selection of capture agents in neutron capture therapy.
Mohsen Khosroabadi; Mehdi Bakhshabadi; Alireza Golshan; Mohammad Mehrpoyan
Volume 21, Issue 2 , May and June 2014, , Pages 320-331
Abstract
Background: One of the ways to treat prostate cancer is brachytherapy using low-energy sources, such as iodine-125 (125I). The purpose of this study was to assess dose enhancement factor in tumors in the presence of various nanoparticles in prostate tumor, and the effect of these nanoparticles on isodose ...
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Background: One of the ways to treat prostate cancer is brachytherapy using low-energy sources, such as iodine-125 (125I). The purpose of this study was to assess dose enhancement factor in tumors in the presence of various nanoparticles in prostate tumor, and the effect of these nanoparticles on isodose curves in prostate cancer brachytherapy using Monte Carlo simulation.
Materials and Method: 125I brachytherapy source model SL-125/SH-125 was simulated using Monte Carlo MCNPX code. TG-43 parameters were calculated and verified. Dose enhancement factors were evaluated in presence of Fe2O3, Ag, Gd, Pt and Au nanoparticles in central cross section of the tumor in concentrations of 7, 18 and 30 mg/ml.
Results: Dose rate constant obtained 0.954 cGyh-1U-1. Maximum dose enhancement factors for Fe2O3, Ag, Gd, Pt and Au were 1.79, 1.32, 1.14, 1.15 and 1.27, respectively. Also, the 100% isodose line shifted toward the central point of the spherical tumor and the 100% isodose line shifted outward. Dose enhancement factors had no rule in increasing or decreasing by atomic number of nanoparticles.
Conclusion: Regarding to the simulation results, it can be concluded that nanoparticles presence in tumor leads to dose increase inside the tumor and dose decrease outside the tumor. Therefore, we can reduce treatment time and activity. So, the clinical use of these nanoparticles is recommended to enhance prostate brachytherapy dose.