Physical validation of a Monte Carlo‐based, phantom‐derived approach to computed tomography organ dosimetry under tube current modulation

Stepusin, Elliott J.; Long, Daniel J.; Ficarrotta, Kayla R.; Hintenlang, David E.; Bolch, Wesley E.

doi:10.1002/mp.12461

Cited by 11 publications

(11 citation statements)

References 26 publications

(72 reference statements)

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“…Each patient‐specific phantom was then converted to a discrete array of voxel elements using an in‐house MATLAB (MathWorks, Natick, MA, USA) script. Finally, to be usable in the radiation transport code MCNPX v2.70 (Los Alamos National Laboratory, Los Alamos, NM, USA) for the previously validated CT dosimetry methodology, the voxel elements were converted to a 1‐D array, referred to as a lattice file . Table shows each of the patients used in this study, including their height, weight, body mass index (BMI), BMI classification, and age (for pediatric patients only).…”

Section: Methodsmentioning

confidence: 99%

“…In order to estimate this value in the computational phantoms, the elemental composition of each voxel and the energy spectra for the exam must be known, which they are in this study. The energy spectra of a Toshiba Aquilion ONE scanner was previously computationally defined and is stored in discrete 1 keV bins . The methods for obtaining these spectra are described in Turner et al .…”

Section: Methodsmentioning

confidence: 99%

“…A set of standard body CT exams were simulated for each patient‐specific phantom and each of its five matched phantoms as well as the entire reference family. The exams were modeled using the previously validated methodology that accounts for TCM . The six torso exams modeled were as follows: chest–abdomen–pelvis (CAP), chest–abdomen (CA), abdomen–pelvis (AP), chest (C), abdomen (A), and pelvis (P).…”

Section: Methodsmentioning

confidence: 99%

“…Alternatively, for clinically viable CT dose estimates, patients must be matched to other computational phantoms (e.g., members of a patient‐dependent phantom library) for which CT organ doses have previously been computed. The purpose of this study is to investigate the impact of various patient‐phantom matching metrics on the accuracy of patient organ dose utilizing a previous validated CT dosimetry methodology, one that accounts for tube current modulation (TCM) …”

Section: Introductionmentioning

confidence: 99%

“…The purpose of this study is to investigate the impact of various patientphantom matching metrics on the accuracy of patient organ dose utilizing a previous validated CT dosimetry methodology, one that accounts for tube current modulation (TCM). 7,8 2. MATERIALS AND METHODS…”

Section: Introductionmentioning

confidence: 99%

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Assessment of different patient‐to‐phantom matching criteria applied in Monte Carlo–based computed tomography dosimetry

et al. 2017

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Overall, these data suggest that matching a patient to a computational phantom in a library is superior to matching to a reference phantom. Water equivalent diameter is the superior matching metric, but it is less feasible to implement in a clinical and retrospective setting. For these reasons, height-and-weight matching is an acceptable and reliable method for matching a patient to a member of a computational phantom library with regard to CT dosimetry.

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Section: Methodsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 3 more Smart Citations

Assessment of different patient‐to‐phantom matching criteria applied in Monte Carlo–based computed tomography dosimetry

et al. 2017

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Calibration strategies for use of the nanoDot OSLD in CT applications

Scarboro

Cody

Stingo

et al. 2018

J Applied Clin Med Phys

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Aluminum oxide based optically stimulated luminescent dosimeters (OSLD) have been recognized as a useful dosimeter for measuring CT dose, particularly for patient dose measurements. Despite the increasing use of this dosimeter, appropriate dosimeter calibration techniques have not been established in the literature; while the manufacturer offers a calibration procedure, it is known to have relatively large uncertainties. The purpose of this work was to evaluate two clinical approaches for calibrating these dosimeters for CT applications, and to determine the uncertainty associated with measurements using these techniques. Three unique calibration procedures were used to calculate dose for a range of CT conditions using a commercially available OSLD and reader. The three calibration procedures included calibration (a) using the vendor‐provided method, (b) relative to a 120 kVp CT spectrum in air, and (c) relative to a megavoltage beam (implemented with 60Co). The dose measured using each of these approaches was compared to dose measured using a calibrated farmer‐type ion chamber. Finally, the uncertainty in the dose measured using each approach was determined. For the CT and megavoltage calibration methods, the dose measured using the OSLD nanoDot was within 5% of the dose measured using an ion chamber for a wide range of different CT scan parameters (80–140 kVp, and with measurements at a range of positions). When calibrated using the vendor‐recommended protocol, the OSLD measured doses were on average 15.5% lower than ion chamber doses. Two clinical calibration techniques have been evaluated and are presented in this work as alternatives to the vendor‐provided calibration approach. These techniques provide high precision for OSLD‐based measurements in a CT environment.

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Toward automated and personalized organ dose determination in CT examinations — A comparison of two tissue characterization models for Monte Carlo organ dose calculation with a Therapy Planning System

2019

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Purpose Computed tomography (CT) is a versatile tool in diagnostic radiology with rapidly increasing number of examinations per year globally. Routine adaption of the exposure level for patient anatomy and examination protocol cause the patients' exposures to become diversified and harder to predict by simple methods. To facilitate individualized organ dose estimates, we explore the possibility to automate organ dose calculations using a radiotherapy treatment planning system (TPS). In particular, the mapping of CT number to elemental composition for Monte Carlo (MC) dose calculations is investigated. Methods Organ dose calculations were done for a female thorax examination test case with a TPS (Raystation™, Raysearch Laboratories AB, Stockholm, Sweden) utilizing a MC dose engine with a CT source model presented in a previous study. The TPS's inherent tissue characterization model for mapping of CT number to elemental composition of the tissues was calibrated using a phantom with known elemental compositions and validated through comparison of MC calculated dose with dose measured with Thermo Luminescence Dosimeters (TLD) in an anthropomorphic phantom. Given the segmentation tools of the TPS, organ segmentation strategies suitable for automation were analyzed for high contrast organs, utilizing CT number thresholding and model‐based segmentation, and for low contrast organs utilizing water replacements in larger tissue volumes. Organ doses calculated with a selection of organ segmentation methods in combination with mapping of CT numbers to elemental composition (RT model), normally used in radiotherapy, were compared to a tissue characterization model with organ segmentation and elemental compositions defined by replacement materials [International Commission on Radiological Protection (ICRP) model], frequently favored in imaging dosimetry. Results The results of the validation with the anthropomorphic phantom yielded mean deviations from the dose to water calculated with the RT and ICRP model as measured with TLD of 1.1% and 1.5% with maximum deviations of 6.1% and 8.7% respectively over all locations in the phantom. A strategy for automated organ segmentation was evaluated for two different risk organ groups, that is, low contrast soft organs and high contrast organs. The relative deviation between organ doses calculated with the RT model and with the ICRP model varied between 0% and 20% for the thorax/upper abdomen risk organs. Conclusions After calibration, the RT model in the TPS provides accurate MC dose results as compared to measurements with TLD and the ICRP model. Dosimetric feasible segmentation of the risk organs for a female thorax demonstrates a possibility for automation using the segmentation tool available in a TPS for high contrast organs. Low contrast soft organs can be represented by water volumes, but organ dose to the esophagus and thyroid must be determined using standardized organ shapes. The uncertainties of the organ doses are small compared to the overall uncertainty, at least an order...

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Physical validation of a Monte Carlo‐based, phantom‐derived approach to computed tomography organ dosimetry under tube current modulation

Abstract: Overall, these data suggest that the Monte Carlo-based dosimetry presented in this work is viable for CT dosimetry. Additionally, for CT exams with TCM, local attenuation weighting of organ dose contributions from precomputed axial dosimetry libraries increases organ dose accuracy.

Cited by 11 publications

References 26 publications

Assessment of different patient‐to‐phantom matching criteria applied in Monte Carlo–based computed tomography dosimetry

Assessment of different patient‐to‐phantom matching criteria applied in Monte Carlo–based computed tomography dosimetry

Calibration strategies for use of the nanoDot OSLD in CT applications

Toward automated and personalized organ dose determination in CT examinations — A comparison of two tissue characterization models for Monte Carlo organ dose calculation with a Therapy Planning System

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