A comparison of breast and lung doses from chest CT scans using organ-based tube current modulation (OBTCM) vs. Automatic tube current modulation (ATCM).

Rick R Layman,Chris Cagnon,Hyun J Kim,Michael Mcnitt-Gray,Ei Ne Chou,Maryam Bostani,Anthony J Hardy,Dianna Cody

doi:10.1002/acm2.13198

Abstract

PurposeThe purpose of this work was to estimate and compare breast and lung doses of chest CT scans using organ‐based tube current modulation (OBTCM) to those from conventional, attenuation‐based automatic tube current modulation (ATCM) across a range of patient sizes.MethodsThirty‐four patients (17 females, 17 males) who underwent clinically indicated CT chest/abdomen/pelvis (CAP) examinations employing OBTCM were collected from two multi‐detector row CT scanners. Patient size metric was assessed as water equivalent diameter (Dw) taken at the center of the scan volume. Breast and lung tissues were segmented from patient image data to create voxelized models for use in a Monte Carlo transport code. The OBTCM schemes for the chest portion were extracted from the raw projection data. ATCM schemes were estimated using a recently developed method. Breast and lung doses for each TCM scenario were estimated for each patient model. CTDIvol‐normalized breast (nDbreast) and lung (nDlung) doses were subsequently calculated. The differences between OBTCM and ATCM normalized organ dose estimates were tested using linear regression models that included CT scanner and Dw as covariates.ResultsMean dose reduction from OBTCM in nDbreast was significant after adjusting for the scanner models and patient size (P = 0.047). When pooled with females and male patient, mean dose reduction from OBTCM in nDlung was observed to be trending after adjusting for the scanner model and patient size (P = 0.085).ConclusionsOne specific manufacturer’s OBTCM was analyzed. OBTCM was observed to significantly decrease normalized breast relative to a modeled version of that same manufacturer’s ATCM scheme. However, significant dose savings were not observed in lung dose over all. Results from this study support the use of OBTCM chest protocols for females only.

Highlights

Computed tomography (CT) was first introduced in the 1970s, and the technology has rapidly evolved making it an important and highly utilized diagnostic tool for clinicians
This study considered organ doses from organ-based tube current modulation (OBTCM) relative to automatic tube current modulation (ATCM) for females, males, and pooled populations, with the pooled being used to determine the effects of having one OBTCM protocol used for both females and males
This study focused on the impact of this technique on organ dose, investigating the potential radiation dose reduction or penalty to the breast in female patients and lung in male and female patients from an OBTCM chest exam relative to an ATCM chest exam that is typically used in the clinical setting

Summary

Introduction

Computed tomography (CT) was first introduced in the 1970s, and the technology has rapidly evolved making it an important and highly utilized diagnostic tool for clinicians. In 2007, an estimated 62 million CT exams were performed annually with an annual growth rate of 12.5% from 2008 to 2009.1,2 The increased utilization of CT procedures, and the frequency of exams per patient, has raised concern about potential carcinogenic health risk from the associated radiation, despite the fact that the potential cancer risk associated with a single CT scan is considered to be very low or non-existent.[1,3] Another important aspect when considering radiation-related carcinogenesis is the radiation dose to radiosensitive organs, such as the breast. ATCM adjusts the x-ray tube current along the angular and/or longitudinal direction to optimize the dose distribution based on the patient’s overall attenuation and provide overall improved image quality at a reduced radiation dose.[10]

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