Prospective estimation of organ dose in CT under tube current modulation

Abstract

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...

CT breast dose reduction with the use of breast positioning and organ‐based tube current modulation

“…The maximum line integrals of attenuation coefficients () from all detector bins at was selected as the basis to generate tube current profile at . The tube current profile was modeled as where and are the fixed and attenuation‐based modulated mA, respectively, ud ( θ ) is the maximum line integrals of attenuation coefficients calculated at , and is the modulation strength . A typical averaged modulation strength level ( α = 0.5) was used.…”

Organ localization: Toward prospective patient‐specific organ dosimetry in computed tomography

“…There have been a number of advances in that direction, incorporating the knowledge of organ location and the TCM profile toward organ dosimetry. 9 However, the knowledge of the organ location is still a major factor in that process.…”

“…Once the knowledge of patient geometry (organ location and body contour) are properly accounted for, these information should be combined with the knowledge of the TCM profile to assess the local irradiation condition of the organ to enable organ dose estimation. 9 The body contour, TCM, and the integration of these components are beyond the scope of the current investigation. They will be addressed in subsequent studies.…”

Application of the 4-D XCAT Phantoms in Biomedical Imaging and Beyond

“…In the following study 80 , a selected clinical patient, represented by a particular XCAT phantom, was optimally matched (based upon trunk height) with another XCAT phantom in the library to obtain a representation of the patient’s anatomy. The organ dose from a clinical abdominopelvic CT protocol was calculated for the two phantoms and compared.…”

“…Predicted and simulated organ dose for a patient undergoing a clinical abdominopelvic CT imaging protocol 80 .…”