Abstract
Purpose: The purpose of this study was to simulate and validate organ doses from different computed tomography (CT) localizer radiograph geometries using Monte Carlo methods for a population of patients. Methods: A Monte Carlo method was developed to estimate organ doses from CT localizer radiographs using PENELOPE. The method was validated by comparing dosimetry estimates with measurements using an anthropomorphic phantom imbedded with thermoluminescent dosimeters (TLDs) scanned on a commercial CT system (Siemens SOMATOM Flash). The Monte Carlo simulation platform was then applied to conduct a population study with 57 adult computational phantoms (XCAT). In the population study, clinically relevant chest localizer protocols were simulated with the x-ray tube in anterior–posterior (AP), right lateral, and PA positions. Mean organ doses and associated standard deviations (in mGy) were then estimated for all simulations. The obtained organ doses were studied as a function of patient chest diameter. Organ doses for breast and lung were compared across different views and represented as a percentage of organ doses from rotational CT scans. Results: The validation study showed an agreement between the Monte Carlo and physical TLD measurements with a maximum percent difference of 15.5% and a mean difference of 3.5% across all organs. The XCAT population study showed that breast dose from AP localizers was the highest with a mean value of 0.24 mGy across patients, while the lung dose was relatively consistent across different localizer geometries. The organ dose estimates were found to vary across the patient population, partially explained by the changes in the patient chest diameter. The average effective dose was 0.18 mGy for AP, 0.09 mGy for lateral, and 0.08 mGy for PA localizer. Conclusion: A platform to estimate organ doses in CT localizer scans using Monte Carlo methods was implemented and validated based on comparison with physical dose measurements. The simulation platform was applied to a virtual patient population, where the localizer organ doses were found to range within 0.4%–8.6% of corresponding organ doses for a typical CT scan, 0.2%–3.3% of organ doses for a CT pulmonary angiography scan, and 1.1%–20.8% of organ doses for a low-dose lung cancer screening scan.
Original language | English |
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Pages (from-to) | 5262-5272 |
Number of pages | 11 |
Journal | Medical Physics |
Volume | 46 |
Issue number | 11 |
DOIs | |
State | Published - Nov 1 2019 |
Externally published | Yes |
Funding
ES receives grant support from GE Healthcare and Siemens Healthcare. The content is solely the responsibility of the authors and does not necessarily represent the official views of the National Institutes of Health. Research reported in this publication was supported by the National Institutes of Health under award number R01EB‐001838. The authors thank Dr. Juan Carlos Ramirez Giraldo for his help with clarifying localizer acquisition CTDI vol and arranging the scanning session. The authors acknowledge Clifford G Hammer at Medical Radiation Research Center, University of Wisconsin, for providing the TLD support. Finally, the authors thank Dr. Ehsan Abadi for his assistance in CT simulations.
Keywords
- Monte Carlo
- computed tomography
- dosimetry
- localizer radiograph
- simulation study
- topogram