The Future of Radiological Protection


Optimzation of Dose for Adult Chest Computed Tomography Examinations: A Phantom Study

Author(s): Lynn Ninsiima 1, Mary Boadu 2, Stephen Inkoom 3, Benard O. Botwe 4
( 1 Atomic Energy Council, Uganda; 2 Radiological and Medical Sciences Research Institute, Ghana Atomic Energy Commission, Ghana; 3 Radiation Protection Institute, Ghana Atomic Energy Commission, Ghana; 4 Department of Radiography, School of Biomedical & Allied Health Sciences, College of Health Sciences, University of Ghana, Ghana)


In a bid to reduce the stochastic effects of ionizing radiation (like cancer), there is need to optimize the dose received from adult chest CT examinations to As Low As Reasonably Achievable (ALARA) in order to obtain a lower dose to the patients but with acceptable image quality. This, in the end protects patients from the harmful effects of radiation, thus ensuring radiation protection.

The main objective of this study was to optimize the dose received by adult patients who had undergone chest CT examinations. One hundred and seventy patient protocols were collected from the Picture Archiving and Communication System (PACS) of one facility with a Siemens CT machine with 64 slices for a period of about nine months. Parameters including the age, sex, Volumetric Computed Tomography (CTDIvol), and Dose Length Product (DLP) were obtained. The effective dose was estimated by multiplying the DLP by the conversion coefficient of the chest region, and Signal to Noise Ratio (SNR) of the mean protocols was assessed using ImageJ software. Exploitation of the mean existing protocols was done using a RANDO anthropomorphic phantom to obtain protocols that would result in lower patient dose with acceptable image quality. On assessment of the existing patient protocols, the average CTDIvol, DLP and effective dose were 6.99±2.44 mGy, 233.18±89.68 mGy*cm and 3.22±1.24 mSv, respectively. The mean SNR for the existing images for the adult chest CT patients was 16.01±2.55. This fits the Rose model criterion, which states that an image with SNR ≥5 is of acceptable quality, and can be considered for diagnostic purposes. The dose and image assessment of the suggested optimized protocols resulted in a 14.38% reduction in the effective dose with an acceptable SNR of 9.23. It can be concluded that an increase in the pitch while keeping all other scanner parameters as the ones in the routine adult chest CT examinations resulted in a lower dose with an acceptable image quality. The suggested optimized protocols should be utilized at the facility for adult chest CT examinations. This would achieve the major aim of radiation protection to protect patients from the harmful effects of ionizing radiation, in line with the ALARA principle.

Keywords: Optimization; Dose; Computed Tomography; Adult; Image quality