RESUMO
This study aims to develop and test software for assessing and reporting doses for standard patients undergoing computed tomography (CT) examinations in a 320 detector-row cone-beam scanner. The software, called SimDoseCT, is based on the Monte Carlo (MC) simulation code, which was developed to calculate organ doses and effective doses in ICRP anthropomorphic adult reference computational phantoms for acquisitions with the Aquilion ONE CT scanner (Toshiba). MC simulation was validated by comparing CTDI measurements within standard CT dose phantoms with results from simulation under the same conditions. SimDoseCT consists of a graphical user interface connected to a MySQL database, which contains the look-up-tables that were generated with MC simulations for volumetric acquisitions at different scan positions along the phantom using any tube voltage, bow tie filter, focal spot and nine different beam widths. Two different methods were developed to estimate organ doses and effective doses from acquisitions using other available beam widths in the scanner. A correction factor was used to estimate doses in helical acquisitions. Hence, the user can select any available protocol in the Aquilion ONE scanner for a standard adult male or female and obtain the dose results through the software interface. Agreement within 9% between CTDI measurements and simulations allowed the validation of the MC program. Additionally, the algorithm for dose reporting in SimDoseCT was validated by comparing dose results from this tool with those obtained from MC simulations for three volumetric acquisitions (head, thorax and abdomen). The comparison was repeated using eight different collimations and also for another collimation in a helical abdomen examination. The results showed differences of 0.1 mSv or less for absolute dose in most organs and also in the effective dose calculation. The software provides a suitable tool for dose assessment in standard adult patients undergoing CT examinations in a 320 detector-row cone-beam scanner.
Assuntos
Tomografia Computadorizada de Feixe Cônico/instrumentação , Método de Monte Carlo , Imagens de Fantasmas , Tomógrafos Computadorizados , Tomografia Computadorizada por Raios X/métodos , Adulto , Tomografia Computadorizada de Feixe Cônico/métodos , Bases de Dados Factuais , Feminino , Humanos , Masculino , Doses de Radiação , SoftwareRESUMO
The measurement of the ambient dose equivalent H*(10) with automatic real-time radioactivity monitors using gamma-ray spectrometry provides valuable information at short integration times and serves as an alternative to conventional peak analysis of spectra. In this paper, a full methodology for the calculation of this quantity using Monte Carlo (MC) simulations is described and applied to real spectrometric measurements with LaBr3(Ce) scintillation detectors. The methodology involves the calculation of the fluence-to-H*(10) conversion factors and a method for obtaining the fluence from gamma-ray spectra. The combination of these two elements makes it possible to calculate the H*(10). The obtained results are compared with the H*(10) measurements of a Geiger-Müller (GM) detector. Finally, the necessary activity concentration to produce a certain increment on the H*(10) is discussed for some isotopes. This is used to discuss the analysis capabilities of the spectrometric detectors when compared to GM ones.
RESUMO
OBJECTIVE: The purpose of this study was to estimate the patient dose from perfusion CT examinations of the brain, lung tumors, and the liver on a cone-beam 320-MDCT scanner using a Monte Carlo simulation and the recommendations of the International Commission on Radiological Protection (ICRP). MATERIALS AND METHODS: A Monte Carlo simulation based on the Electron Gamma Shower Version 4 package code was used to calculate organ doses and the effective dose in the reference computational phantoms for an adult man and adult woman as published by the ICRP. Three perfusion CT acquisition protocols--brain, lung tumor, and liver perfusion--were evaluated. Additionally, dose assessments were performed for the skin and for the eye lens. Conversion factors were obtained to estimate effective doses and organ doses from the volume CT dose index and dose-length product. RESULTS: The sex-averaged effective doses were approximately 4 mSv for perfusion CT of the brain and were between 23 and 26 mSv for the perfusion CT body protocols. The eye lens dose from the brain perfusion CT examination was approximately 153 mGy. The sex-averaged peak entrance skin dose (ESD) was 255 mGy for the brain perfusion CT studies, 157 mGy for the lung tumor perfusion CT studies, and 172 mGy for the liver perfusion CT studies. CONCLUSION: The perfusion CT protocols for imaging the brain, lung tumors, and the liver performed on a 320-MDCT scanner yielded patient doses that are safely below the threshold doses for deterministic effects. The eye lens dose, peak ESD, and effective doses can be estimated for other clinical perfusion CT examinations from the conversion factors that were derived in this study.
Assuntos
Encéfalo/diagnóstico por imagem , Fígado/diagnóstico por imagem , Neoplasias Pulmonares/diagnóstico por imagem , Método de Monte Carlo , Doses de Radiação , Radiometria/métodos , Tomografia Computadorizada por Raios X/métodos , Feminino , Humanos , Masculino , Imagens de FantasmasRESUMO
PURPOSE: To estimate organ dose and effective dose for patients for cardiac CT as applied in an international multicenter study (CORE320) with a 320-Detector row CT scanner using Monte Carlo (MC) simulations and voxelized phantoms. The effect of positioning of the arms, off-centering the patient and heart rate on patient dose was analyzed. METHODS: A MC code was tailored to simulate the geometry and characteristics of the CT scanner. The phantoms representing the adult reference male and female were implemented according to ICRP 110. Effective dose and organ doses were obtained for CT acquisition protocols for calcium scoring, coronary angiography and myocardial perfusion. RESULTS: For low heart rate, the normalized effective dose (E) for cardiac CT was higher for female (5.6 mSv/100 mAs) compared to male (2.2 mSv/100 mAs) due to the contribution of female breast tissue. Averaged E for female and male was 11.3 mSv for the comprehensive cardiac protocol consisting of calcium scoring (1.9 mSv); coronary angiography including rest cardiac perfusion (5.1 mSv) and stress cardiac perfusion (4.3 mSv). These values almost doubled at higher heart rates (20.1 mSv). Excluding the arms increased effective dose by 6-8%, centering the patient showed no significant effect. The k-factor (0.028 mSv/mGy.cm) derived from this study leads to effective doses up to 2-3 times higher than the values obtained using now outdated methodologies. CONCLUSION: MC modeling of cardiac CT examinations on realistic voxelized phantoms allowed us to assess patient doses accurately and we derived k-factors that are well above those published previously.