A Monte Carlo study on dose enhancement and photon contamination production by various nanoparticles in electron mode of a medical linac

The aim of this study is the evaluation of electron dose enhancement and photon contamination production by various nanoparticles in the electron mode of a medical linac. MCNPX Monte Carlo code was used for simulation of Siemens Primus linac as well as a phantom and a tumor loaded with nanoparticles. Electron dose enhancement by Au, Ag, I and Fe2O3 nanoparticles of 7, 18 and 30 mg/ml concentrations for 8, 12 and 14 MeV electrons was calculated. The increase in photon contamination due to the presence of the nanoparticles was evaluated as well. The above effects were evaluated for 500 keV and 10 keV energy cut-offs defined for electrons and photons. For 500 keV energy cut-off, there was no significant electron dose enhancement. However, for 10 keV energy cut-off, a maximum electron dose enhancement factor of 1.08 was observed for 30 mg/ml of gold nanoparticles with 8 MeV electrons. An increase in photon contamination due to nanoparticles was also observed which existed mainly inside the tumor. A maximum photon dose increase factor of 1.07 was observed inside the tumor with Au nanoparticles. Nanoparticles can be used for the enhancement of electron dose in the electron mode of a linac. Lower energy electron beams, and nanoparticles with higher atomic number, can be of greater benefi t in this field. Photons originating from nanoparticles will increase the photon dose inside the tumor, and will be an additional advantage of the use of nanoparticles in radiotherapy with electron beams

A Monte Carlo study on dose enhancement and photon contamination production by various nanoparticles in electron mode of a medical linac

The aim of this study is the evaluation of electron dose enhancement and photon contamination production by various nanoparticles in the electron mode of a medical linac. MCNPX Monte Carlo code was used for simulation of Siemens Primus linac as well as a phantom and a tumor loaded with nanoparticles. Electron dose enhancement by Au, Ag, I and Fe2O3 nanoparticles of 7, 18 and 30 mg/ml concentrations for 8, 12 and 14 MeV electrons was calculated. The increase in photon contamination due to the presence of the nanoparticles was evaluated as well. The above effects were evaluated for 500 keV and 10 keV energy cut-offs defined for electrons and photons. For 500 keV energy cut-off, there was no significant electron dose enhancement. However, for 10 keV energy cut-off, a maximum electron dose enhancement factor of 1.08 was observed for 30 mg/ml of gold nanoparticles with 8 MeV electrons. An increase in photon contamination due to nanoparticles was also observed which existed mainly inside the tumor. A maximum photon dose increase factor of 1.07 was observed inside the tumor with Au nanoparticles. Nanoparticles can be used for the enhancement of electron dose in the electron mode of a linac. Lower energy electron beams, and nanoparticles with higher atomic number, can be of greater benefit in this field. Photons originating from nanoparticles will increase the photon dose inside the tumor, and will be an additional advantage of the use of nanoparticles in radiotherapy with electron beams

On Models, Bounds, and Estimation Algorithms for Time-Varying Phase Noise

In this paper, first, a new discrete-time model of phase noise for digital communication systems, which is a more accurate model compared to the classical Wiener model, is proposed based on a comprehensive continuous-time representation of time-varying phase noise, and statistical characteristics of this model are derived. Next, the non-data-aided (NDA) and decision-directed (DD) maximum-likelihood (ML) estimators of time-varying phase noise, using the proposed discrete-time model are derived. To evaluate the performance of the proposed estimators, the Cramer-Rao lower bound (CRLB) for each estimation approach is derived and by using Monte-Carlo simulations it is shown that the mean-square error (MSE) of the proposed estimators converges to the CRLB at moderate signal-to-noise ratios (SNR). Finally, simulation results show that the proposed estimators outperform existing estimation methods as the variance of the phase noise process increases

Effect of photon energy spectrum on dosimetric parameters of brachytherapy sources

The aim of this study is to quantify the influence of the photon energy spectrum of brachytherapy sources on task group No. 43 (TG-43) dosimetric parameters

Effect of photon energy spectrum on dosimetric parameters of brachytherapy sources

AIM: The aim of this study is to quantify the influence of the photon energy spectrum of brachytherapy sources on task group No. 43 (TG-43) dosimetric parameters. BACKGROUND: Different photon spectra are used for a specific radionuclide in Monte Carlo simulations of brachytherapy sources. MATERIALS AND METHODS: MCNPX code was used to simulate 125I, 103Pd, 169Yb, and 192Ir brachytherapy sources. Air kerma strength per activity, dose rate constant, radial dose function, and two dimensional (2D) anisotropy functions were calculated and isodose curves were plotted for three different photon energy spectra. The references for photon energy spectra were: published papers, Lawrence Berkeley National Laboratory (LBNL), and National Nuclear Data Center (NNDC). The data calculated by these photon energy spectra were compared. RESULTS: Dose rate constant values showed a maximum difference of 24.07% for 103Pd source with different photon energy spectra. Radial dose function values based on different spectra were relatively the same. 2D anisotropy function values showed minor differences in most of distances and angles. There was not any detectable difference between the isodose contours. CONCLUSIONS: Dosimetric parameters obtained with different photon spectra were relatively the same, however it is suggested that more accurate and updated photon energy spectra be used in Monte Carlo simulations. This would allow for calculation of reliable dosimetric data for source modeling and calculation in brachytherapy treatment planning systems

Evaluation of vertebral artery variations and arterial dominance in cervical CT angiographic images in Iranian population

Purpose: The aim of the present study was to determine the characteristics and variations in the origin of vertebral arteries (VA), its level of entry into the transverse foramen, VA diameter, Length of VA, and VA dominance. Methods: A total of 250 adult patients (143 males and 107 females) were enrolled (Mean age: 60.92±13.44) and scanned with Computerized Tomography angiography (CTA). Results: The VA entered the C6 transverse foramen in 97.8% of specimens. Abnormal entrance of VA was observed in 4.4% of specimens. The mean length of prevertebral (V1) right and left VA was 81.38±14.38 mm and 82.49±14.16 mm. The mean length of the intraforaminal segment (V2) of the right and left VA was 81.38±14.375mm and 82.49±14.162mm and showed sexual dimorphism. The mean diameter of the right and left VA was 3.297±0.85 and 3.676±0.88, respectively. We found 1(0.4%) left and 1(0.4%) right VA emerging from the aortic arch. The mean right and left VA diameters were 3.28 ± 0.83 mm and 3.6±0.88mm, respectively. A total of 90(0.36) patients were right dominant and 160(0.64) patients were left-dominant. The right VA of aortic arch origin entered the 4th cervical transverse foramina, whereas the left VA entered the 7th cervical transverse foramina. We found that 22(8.8%) of the right and 1 (0.4%) of the left vertebral arteries had distal origin. The results did not show any relationship between gender and origin of VA, diameter of VA, and level of entry. A significant relationship was observed between gender and VA length (P=0.0001). Discussion: The present study confirms the presence of anomalous in the VA route. Knowledge of such anatomical variations is important in interpreting CTA and may reduce the risk of intraoperative VA injury