A comparison of methods to estimate organ doses in CT when utilizing approximations to the tube current modulation function

Khatonabadi, M; Zhang, Di; Mathieu, Kelsey Boitnott; Kim, Hee Jin; Lu, Peiyun; Cody, Dianna D.; DeMarco, John J.; Cagnon, Chris H.; McNitt‐Gray, Michael F.

doi:10.1118/1.4736807

Cited by 35 publications

(36 citation statements)

References 30 publications

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“…Khatonabadi et al studied the organ dose for 32 chest and 39 abdominopelvic exams for a clinical CT system (Sensation 64, Siemens Healthcare, Forchheim, Germany). 12 The study developed an organ-specific CTDI vol to effectively account for the local radiation field under tube current modulation. Li et al estimated organ dose for chest and abdominopelvic scans for a XCAT phantom under five modulation strengths.…”

Section: Discussionmentioning

confidence: 99%

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Prospective estimation of organ dose in CT under tube current modulation

Tian

Segars

et al. 2015

Medical Physics

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Purpose: Computed tomography (CT) has been widely used worldwide as a tool for medical diagnosis and imaging. However, despite its significant clinical benefits, CT radiation dose at the population level has become a subject of public attention and concern. In this light, optimizing radiation dose has become a core responsibility for the CT community. As a fundamental step to manage and optimize dose, it may be beneficial to have accurate and prospective knowledge about the radiation dose for an individual patient. In this study, the authors developed a framework to prospectively estimate organ dose for chest and abdominopelvic CT exams under tube current modulation (TCM). Methods: The organ dose is mainly dependent on two key factors: patient anatomy and irradiation field. A prediction process was developed to accurately model both factors. To model the anatomical diversity and complexity in the patient population, the authors used a previously developed library of computational phantoms with broad distributions of sizes, ages, and genders. A selected clinical patient, represented by a computational phantom in the study, was optimally matched with another computational phantom in the library to obtain a representation of the patient's anatomy. To model the irradiation field, a previously validated Monte Carlo program was used to model CT scanner systems. The tube current profiles were modeled using a ray-tracing program as previously reported that theoretically emulated the variability of modulation profiles from major CT machine manufacturers Li et al., [Phys. Med. Biol. 59, 4525-4548 (2014)]. The prediction of organ dose was achieved using the following process: (1) CTDI vol -normalized-organ dose coefficients (h organ ) for fixed tube current were first estimated as the prediction basis for the computational phantoms; (2) each computation phantom, regarded as a clinical patient, was optimally matched with one computational phantom in the library; (3) to account for the effect of the TCM scheme, a weighted organ-specific CTDI vol [denoted as (CTDI vol ) organ,weighted ] was computed for each organ based on the TCM profile and the anatomy of the "matched" phantom; (4) the organ dose was predicted by multiplying the weighted organ-specific CTDI vol with the organ dose coefficients (h organ ). To quantify the prediction accuracy, each predicted organ dose was compared with the corresponding organ dose simulated from the Monte Carlo program with the TCM profile explicitly modeled. Results: The predicted organ dose showed good agreements with the simulated organ dose across all organs and modulation profiles. The average percentage error in organ dose estimation was generally within 20% across all organs and modulation profiles, except for organs located in the pelvic and shoulder regions. For an average CTDI vol of a CT exam of 10 mGy, the average error at full modulation strength (α = 1) across all organs was 0.91 mGy for chest exams, and 0.82 mGy for abdominopelvic exams. relation to a targeted level of image q...

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Section: Discussionmentioning

confidence: 99%

“…The prior studies have been able to use the concept of regional CTDI vol in conjunction with organ dose coefficients to assess organ dose. 1,12 However, the methodology has been applied to a limited number of human models, and is further oriented toward retrospective dose estimation for specific models.…”

Section: Introductionmentioning

confidence: 99%

Prospective estimation of organ dose in CT under tube current modulation

Tian

Segars

et al. 2015

Medical Physics

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“…However, due to the voxelized models entirely originating from image data none of the voxelized models include the image data corresponding to the over-ranging region. 33 As a result, the simulated organ doses may slightly underestimate actual dose since there is no dose contribution due to scatter from the over-ranging region; this is assumed to be an insignificant contribution for the organs of interest in this study as they are bigger organs and are not adjacent to the boundaries of the scan region.…”

Section: Iib Simulated Ct Examsmentioning

confidence: 99%

The feasibility of a regional CTDI_vol to estimate organ dose from tube current modulated CT exams

Khatonabadi¹,

Kim²,

Lu³

et al. 2013

Medical Physics

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Purpose: In AAPM Task Group 204, the size-specific dose estimate (SSDE) was developed by providing size adjustment factors which are applied to the Computed Tomography (CT) standardized dose metric, CTDI vol . However, that work focused on fixed tube current scans and did not specifically address tube current modulation (TCM) scans, which are currently the majority of clinical scans performed. The purpose of this study was to extend the SSDE concept to account for TCM by investigating the feasibility of using anatomic and organ specific regions of scanner output to improve accuracy of dose estimates. Methods: Thirty-nine adult abdomen/pelvis and 32 chest scans from clinically indicated CT exams acquired on a multidetector CT using TCM were obtained with Institutional Review Board approval for generating voxelized models. Along with image data, raw projection data were obtained to extract TCM functions for use in Monte Carlo simulations. Patient size was calculated using the effective diameter described in TG 204. In addition, the scanner-reported CTDI vol (CTDI vol,global ) was obtained for each patient, which is based on the average tube current across the entire scan. For the abdomen/pelvis scans, liver, spleen, and kidneys were manually segmented from the patient datasets; for the chest scans, lungs and for female models only, glandular breast tissue were segmented. For each patient organ doses were estimated using Monte Carlo Methods. To investigate the utility of regional measures of scanner output, regional and organ anatomic boundaries were identified from image data and used to calculate regional and organ-specific average tube current values. From these regional and organ-specific averages, CTDI vol values, referred to as regional and organ-specific CTDI vol , were calculated for each patient. Using an approach similar to TG 204, all CTDI vol values were used to normalize simulated organ doses; and the ability of each normalized dose to correlate with patient size was investigated. Results: For all five organs, the correlations with patient size increased when organ doses were normalized by regional and organ-specific CTDI vol values. For example, when estimating dose to the liver, CTDI vol,global yielded a R 2 value of 0.26, which improved to 0.77 and 0.86, when using the regional and organ-specific CTDI vol for abdomen and liver, respectively. For breast dose, the global CTDI vol yielded a R 2 value of 0.08, which improved to 0.58 and 0.83, when using the regional and organ-specific CTDI vol for chest and breasts, respectively. The R 2 values also increased once the thoracic models were separated for the analysis into females and males, indicating differences between genders in this region not explained by a simple measure of effective diameter. Conclusions: This work demonstrated the utility of regional and organ-specific CTDI vol as normalization factors when using TCM. It was demonstrated that CTDI vol,global is not an effective normalization factor in TCM exams where attenuation (and therefore tu...

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“…In the case of TCM simulations, an additional text file with information on individual table location, tube angle, and tube current value throughout the scan was utilized in the simulation. Validation of this MC simulation package under a variety of conditions including TCM has been previously reported . This work used the computational and storage services of the Hoffman2 Shared Cluster provided by the UCLA Institute for Digital Research and Education's Research Technology Group.…”

Section: Methodsmentioning

confidence: 99%

Estimating fetal dose from tube current‐modulated (TCM) and fixed tube current (FTC) abdominal/pelvis CT examinations

et al. 2019

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Purpose The purpose of this work was to estimate scanner‐independent CTDIvol‐to‐fetal‐dose coefficients for tube current‐modulated (TCM) and fixed tube current (FTC) computed tomography (CT) examinations of pregnant patients of various gestational ages undergoing abdominal/pelvic CT examinations. Methods For 24 pregnant patients of gestational age from <5 to 36 weeks who underwent clinically indicated CT examinations, voxelized models of maternal and fetal (or embryo) anatomy were created from abdominal/pelvic image data. Absolute fetal dose (Dfetus) was estimated using Monte Carlo (MC) simulations of helical scans covering the abdomen and pelvis for TCM and FTC scans. Estimated TCM schemes were generated for each patient model using a validated method that accounts for patient attenuation and scanner output limits for one scanner model and were incorporated into MC simulations. FTC scans were also simulated for each patient model with multidetector row CT scanners from four manufacturers. Normalized fetal dose estimates, nDfetus, was obtained by dividing Dfetus from the MC simulations by CTDIvol. Patient size was described using water equivalent diameter (Dw) measured at the three‐dimensional geometric centroid of the fetus. Fetal depth (DEf) was measured from the anterior skin surface to the anterior part of the fetus. nDfetus and Dw were correlated using an exponential model to develop equations for fetal dose conversion coefficients for TCM and FTC abdominal/pelvic CT examinations. Additionally, bivariate linear regression was performed to analyze the correlation of nDfetus with Dw and fetal depth (DEf). For one scanner model, nDfetus from TCM was compared to FTC and the size‐specific dose estimate (SSDE) conversion coefficients (f‐factors) from American Association of Physicists in Medicine (AAPM) Report 204. nDfetus from FTC simulations was averaged across all scanners for each patient (nDfetus¯). nDitalicfetus¯ was then compared with SSDE f‐factors and correlated with Dw using an exponential model and with Dw and DEf using a bivariate linear model. Results For TCM, the coefficient of determination (R2) of nDfetus and Dw was observed to be 0.73 using an exponential model. Using the bivariate linear model with Dw and DEf, an R2 of 0.78 was observed. For the TCM technology modeled, TCM yielded nDfetus values that were on average 6% and 17% higher relative to FTC and SSDE f‐factors, respectively. For FTC, the R2 of nDitalicfetus¯ with respect to Dw was observed to be 0.64 using an exponential model. Using the bivariate linear model, an R2 of 0.75 was observed for nDitalicfetus¯ with respect to Dw and DEf. A mean difference of 0.4% was observed between nDitalicfetus¯ and SSDE f‐factors. Conclusion Good correlations were observed for nDfetus from TCM and FTC scans using either an exponential model with Dw or a bivariate linear model with both Dw and DEf. These results indicate that fetal dose from abdomen/pelvis CT examinations of pregnant patients of various gestational ages may be reasonably estimated with mod...

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A comparison of methods to estimate organ doses in CT when utilizing approximations to the tube current modulation function

Cited by 35 publications

References 30 publications

Prospective estimation of organ dose in CT under tube current modulation

Prospective estimation of organ dose in CT under tube current modulation

The feasibility of a regional CTDI_vol to estimate organ dose from tube current modulated CT exams

Estimating fetal dose from tube current‐modulated (TCM) and fixed tube current (FTC) abdominal/pelvis CT examinations

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A comparison of methods to estimate organ doses in CT when utilizing approximations to the tube current modulation function

Cited by 35 publications

References 30 publications

Prospective estimation of organ dose in CT under tube current modulation

Prospective estimation of organ dose in CT under tube current modulation

The feasibility of a regional CTDIvol to estimate organ dose from tube current modulated CT exams

Estimating fetal dose from tube current‐modulated (TCM) and fixed tube current (FTC) abdominal/pelvis CT examinations

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The feasibility of a regional CTDI_vol to estimate organ dose from tube current modulated CT exams