The influence of using different reconstruction algorithms on sensitivity of quantitative 18F-FDG-PET volumetric measures to background activity variation

Introduction: This study aims to investigate the influence of background activity variation on image quantification in differently reconstructed PET/CT images. Methods: Measurements were performed on a Discovery-690 PET/CT scanner using a custom-built NEMA-like phantom. A background activity level of 5.3 and 2.6 kBq/ml 18F-FDG were applied. Images were reconstructed employing four different reconstruction algorithms: HD (OSEM with no PSF or TOF), PSF only, TOF only, and TOFPSF, with Gaussian filters of 3 and 6.4 mm in FWHM. SUVmax and SUVpeak were obtained and used as cut-off thresholding; Metabolic Tumor Volume (MTV) and Total Lesion Glycolysis (TLG) were measured. The volume recovery coefficients (VRCs), the relative percent error (�MTV), and Dice similarity coefficient were assessed with respect to true values. Results: SUVmax and SUVpeak decreased and MTV increased as function of increasing the background dose. The most differences occur in smaller volumes with 3-mm filter; Non-TOF and Non-PSF reconstruction methods were more sensitive to increasing the background activity in the smaller and larger volumes, respectively. The TLG values were affected in the small lesions (decrease up to 12). In a range of target volumes, differences between the mean �MTV in the high and low background dose varied from -11.8 to 7.2 using SUVmax and from 2.1 to 7.6 using SUVpeak inter reconstruction methods. Conclusion: The effect of the background activity variation on SUV-based quantification in small lesion was more noticeable than large lesion. The HD and TOFPSF algorithms had the lowest and the highest sensitivity to background activity, respectively. © 2018 Iranian Journal of Nuclear Medicine. All Rights Reserved

Monte Carlo study of electron dose distributions produced by the elekta precise linear accelerator

BackgroundMonte Carlo simulation of radiation transport is considered to be one of the most accurate methods of radiation therapy dose calculation and has ability to reduce the uncertainty in the calculated dose to a few percent.Aims(1) To study the efficacy of the MCNP4C Monte Carlo code to simulate the dose distribution in a homogeneous medium produced by electron beams from the Elekta Precise linear accelerator. (2) To quantify the effect of introduction of various components to the simulated geometry for the above machine.Materials/MethodsFull Monte Carlo simulation of the detailed geometry of the Precise treatment head for 8 and 15 MeV energies and 10×10 applicator was performed. Experimental depth dose and lateral profiles at 2cm depth were measured using a P-type diode detector with a 2.5 mm diameter. To quantify the effects of different parts of the treatment head, seven cases were simulated for a 15 MeV beam to reflect increasing levels of complexity, by step-wise introduction of beam divergence, primary and secondary scattering foils, secondary collimators, applicator, Mirror and Mylar screen.ResultsThe discrepancy between measured and calculated data is within 2%/2 mm at both 8 and 15 MeV. In terms of the mean and most probable energies at the surface, the difference wa

Assessment of different MCNP Monte Carlo codes in electron absorbed dose

BackgroundMCNP is a general-purpose Monte Carlo code for simulation of neutrons, photons and electrons or coupled neutron/photon/electron transport. This code is based on ETRAN/ITS codes. There are different versions of this code.AimThis work aims to compare the more recently released MCNP codes with the earlier version in terms of the central axis absorbed dose (CADD), the energy spectrum and the computational efficiency. MCNP codes 4A, 4B, 4C, X and 5 were compared for a 10 MeV electron beam in water.Materials/MethodsThe energy spectra of electrons were scored on the phantom surface and planes 3 and 5cm deep using F2 tally subdivided into 0.1 MeV energy bins. This tally also was repeated for 4A, 4B, 4C and X with smaller energy bins (0.05 MeV). The simulated geometry and other input parameters were kept the same. Both the default and ITS energy indexing algorithms (EIA) were used in 4B, 4C and X, while only the default EIA was employed in 4A and 5.ResultsWith default indexing, X and 5 showed no difference in CADD compared to 4B and 4C and were within 3% of 4A. We found no differences in CADD between codes when 4B, 4C and X were used with ITS indexing. The ITS algorithm improved computational efficiency. For the energy spectrum at the phantom surface, all codes except X show very similar results (within 2%). However, changing the energy indexing to ITS as well as using a 0.05 MeV bin removed this discrepancy at the surface for X code.ConclusionsWhile, under the examined conditions, versions 4B and later behaved similarly in terms of the resulting CADD, the ITS indexing should be used due to its agreement with measurements and computational efficiency

A combined 3D megavoltage CT scanner and portal imager for treatment verification in radiotherapy

SIGLEAvailable from British Library Document Supply Centre-DSC:DXN024241 / BLDSC - British Library Document Supply CentreGBUnited Kingdo

Monte Carlo study of electron dose distributions produced by the elekta precise linear accelerator

SummaryBackgroundMonte Carlo simulation of radiation transport is considered to be one of the most accurate methods of radiation therapy dose calculation and has ability to reduce the uncertainty in the calculated dose to a few percent.Aims(1) To study the efficacy of the MCNP4C Monte Carlo code to simulate the dose distribution in a homogeneous medium produced by electron beams from the Elekta Precise linear accelerator. (2) To quantify the effect of introduction of various components to the simulated geometry for the above machine.Materials/MethodsFull Monte Carlo simulation of the detailed geometry of the Precise treatment head for 8 and 15 MeV energies and 10×10 applicator was performed. Experimental depth dose and lateral profiles at 2cm depth were measured using a P-type diode detector with a 2.5 mm diameter. To quantify the effects of different parts of the treatment head, seven cases were simulated for a 15 MeV beam to reflect increasing levels of complexity, by step-wise introduction of beam divergence, primary and secondary scattering foils, secondary collimators, applicator, Mirror and Mylar screen.ResultsThe discrepancy between measured and calculated data is within 2%/2 mm at both 8 and 15 MeV. In terms of the mean and most probable energies at the surface, the difference was <0.2 MeV for the majority of cases and the maximum deviation was no more than 0.3 MeV.ConclusionsThe results obtained with MCNP4C agree well with measured electron dose distributions. Inclusion of all the main components of the treatment head in the simulated geometry is necessary to avoid discrepancies of about 5% compared to measurements

Impact of image reconstruction methods on quantitative accuracy and variability of FDG-PET volumetric and textural measures in solid tumors

Objective: This study aims to assess the impact of different image reconstruction methods on PET/CT quantitative volumetric and textural parameters and the inter-reconstruction variability of these measurements. Methods: A total of 25 oncology patients with 65 lesions (between 2017 and 2018) and a phantom with signal-to-background ratios (SBR) of 2 and 4 were included. All images were retrospectively reconstructed using OSEM, PSF only, TOF only, and TOFPSF with 3-, 5-, and 6.4-mm Gaussian filters. The metabolic tumor volume (MTV) and total lesion glycolysis (TLG) were measured. The relative percent error (�MTV and �TLG) with respect to true values, volume recovery coefficients, and Dice similarity coefficient, as well as inter-reconstruction variabilities were quantified and assessed. In clinical scans, textural features (coefficient of variation, skewness, and kurtosis) were determined. Results: Among reconstruction methods, mean �MTV differed by -163.5 ± 14.1 to 6.3 ± 6.2 at SBR2 and -42.7 ± 36.7 to 8.6 ± 3.1 at SBR4. Dice similarity coefficient significantly increased by increasing SBR from 2 to 4, ranging from 25.7 to 83.4 between reconstruction methods. Mean �TLG was -12.0 ± 1.7 for diameters > 17 mm and -17.8 ± 7.8 for diameters � 17 mm at SBR4. It was -31.7 ± 4.3 for diameters > 17 mm and -14.2 ± 5.8 for diameters � 17 mm at SBR2. Textural features were prone to variations by reconstruction methods (p < 0.05). Conclusions: Inter-reconstruction variability was significantly affected by the target size, SBR, and cut-off threshold value. In small tumors, inter-reconstruction variability was noteworthy, and quantitative parameters were strongly affected. TOFPSF reconstruction with small filter size produced greater improvements in performance and accuracy in quantitative PET/CT imaging. Key Points: � Quantitative volumetric PET evaluation is critical for the analysis of tumors. � However, volumetric and textural evaluation is prone to important variations according to different image reconstruction settings. � TOFPSF reconstruction with small filter size improves quantitative analysis. © 2018, European Society of Radiology

Assessment of adaptive response of gamma radiation in the operating room personnel exposed to anesthetic gases by measuring the relative gene expression changes KU80, LIGASE1 and P53

Background: Some operating room personnel are occupationally exposed to genotoxic agents such as anesthetic gases and ionizing radiation. Adaptive response, as a defense mechanism, will occur when cells become exposed to a low dose of factors harming DNA (priming dose), which in the subsequent exposure to higher dose of those factors (challenging dose), show more resistance and sensibility. Objective: The aim of this study was to investigate adaptive response or synergy of ionizing radiation in the operating room personnel exposed to anesthetic gases by evaluation of the relative gene expression changes of effective genes for DNA repair such as Ku80, Ligase1 and P53. Material and Methods: In this case-control study, 20 operating room personnel and 20 nurses (who were not present in the operating room) as controls were studied. Venous blood samples were drawn from participants. In order to evaluate the adaptive response, a challenging dose of 2Gy gamma radiation was applied to blood samples. Moreover, RNA extraction and cDNA synthesis were performed. Gene expression level was studied by RT-qPCR and compared with the control group. Results: Ligase1 and P53 expression in the operating room personnel was signifi-cantly higher than that of the control group before irradiation (P�0.001). Statistically, there was no significant difference in the Ku80 and P53 expression in the operating room personnel before and after irradiation. Conclusion: Given the findings of this study, exposure to challenging dose of gamma radiation can induce adaptive response in expression of Ku80 and P53 genes in operating room personnel. © 2020, Shiraz University of Medical Sciences. All rights reserved