Estimating radiation doses from multidetector CT using Monte Carlo simulations: effects of different size voxelized patient models on magnitudes of organ and effective dose

Abstract

The purpose of this work is to examine the effects of patient size on radiation dose from CT scans. To perform these investigations, we used Monte Carlo simulation methods with detailed models of both patients and multidetector computed tomography (MDCT) scanners. A family of three-dimensional, voxelized patient models previously developed and validated by the GSF was implemented as input files using the Monte Carlo code MCNPX. These patient models represent a range of patient sizes and ages (8 weeks to 48 years) and have all radiosensitive organs previously identified and segmented, allowing the estimation of dose to any individual organ and calculation of patient effective dose. To estimate radiation dose, every voxel in each patient model was assigned both a specific organ index number and an elemental composition and mass density. Simulated CT scans of each voxelized patient model were performed using a previously developed MDCT source model that includes scanner specific spectra, including bowtie filter, scanner geometry and helical source path. The scan simulations in this work include a whole-body scan protocol and a thoracic CT scan protocol, each performed with fixed tube current. The whole-body scan simulation yielded a predictable decrease in effective dose as a function of increasing patient weight. Results from analysis of individual organs demonstrated similar trends, but with some individual variations. A comparison with a conventional dose estimation method using the ImPACT spreadsheet yielded an effective dose of 0.14 mSv mAs(-1) for the whole-body scan. This result is lower than the simulations on the voxelized model designated 'Irene' (0.15 mSv mAs(-1)) and higher than the models 'Donna' and 'Golem' (0.12 mSv mAs(-1)). For the thoracic scan protocol, the ImPACT spreadsheet estimates an effective dose of 0.037 mSv mAs(-1), which falls between the calculated values for Irene (0.042 mSv mAs(-1)) and Donna (0.031 mSv mAs(-1)) and is higher relative to Golem (0.025 mSv mAs(-1)). This work demonstrates the ability to estimate both individual organ and effective doses from any arbitrary CT scan protocol on individual patient-based models and to provide estimates of the effect of patient size on these dose metrics.

Patient‐specific radiation dose and cancer risk estimation in CT: Part II. Application to patients

“…While patientspecific dose estimations have been pursued in the past, they were either limited to providing dose for only the imaged part of the body 16,30 or limited to patients whose cadavers had undergone a whole-body scan. 31 Although the dose and risk estimates reported in our study were strictly patientspecific only for the segmented organs inside the image volume, as these organs receive the highest dose, the resultant effective dose and risk index estimates were indicative of the specific patients in their entirety.…”

“…31,32 Due to the size-based pediatric CT protocols in use at our institution, which use lower scan techniques for smaller patients, organ and effective dose received by the newborn patient was comparable to that of the teenager patient ͑Table III, last column͒. However, when the risks of cancer incidence were assessed, the newborn patient had about ten times greater risk of thyroid cancer than the teenager patient ͑Table IV, last column͒ due to age and gender differences.…”

Radiation Dose to the Fetus for Pregnant Patients Undergoing Multidetector CT Imaging: Monte Carlo Simulations Estimating Fetal Dose for a Range of Gestational Age and Patient Size

“…A previously validated multidetector CT source model was created by using Monte Carlo simulation-based techniques (14)(15)(16)(17)(18). The CT scanner modeled was a LightSpeed 16 (GE Medical Systems).…”

Estimating peak skin and eye lens dose from neuroperfusion examinations: Use of Monte Carlo based simulations and comparisons to CTDIvol, AAPM Report No. 111, and ImPACT dosimetry tool values

“…In addition, usually patients with smaller size receive higher organ dose when the same scanning technique is used. 12,14,15,26 However, only small differences of peak skin and eye lens dose were observed in this study because this study focuses specifically on the patient head region. Third, tube current modulation (TCM) was not explicitly modeled in this study and all the simulations were performed at fixed tube current.…”