The Effect of Crystalline Lens Radiation Exposure Reduction on CT Examination and CTDI Inspection

Abstract

In an April 2011 statement, the International Commission on Radiological Protection announced that a switch from an annual 150-mSv crystalline lens radiation dosage safety limit should prevent exposure over an average period of 5 years from exceeding 50 mSv and 20 mSv in a single year. The crystalline lens is rarely an examination target, but incidentally this often provides incoming radiation during computed tomography (CT) examinations of the head and neck and, incidentally, the temporal bone. This study aimed to determine the effect of crystalline lens radiation exposure reduction when using ODM, ASiR (40%), and the Bi shield as dose-by-dose reduction measures during head CT examination and to conduct a comparative inspection of the computed tomography dose index (CTDI) indication level on the CT console when using radioactivity dose reduction measures and measured values. I measured head images according to time and while using each reduction measure along with a TLD element to evaluate the radiation exposure dose of the crystalline lens as well as the SD and CT levels at the eyeball and temporal lobe in the images. When using ODM, the crystalline lens radioactivity dose reduction rate ranged from 11%–15% and the images did not differ significantly from those collected under normal time conditions. With ASiR (40%), the crystalline lens radioactivity dose reduction rate ranged from 37%–39%, the image SD levels increased by approximately 1.0 in both areas, and a change was observed in the CT level. However, the artifactual phenomena were not acceptable and could be ignored at the clinical level. When ODM and ASiR (40%) were combined, the crystalline lens radioactivity dose reduction rate was 37%–39%, an effect similar to that achieved with the Bi shield. SD levels of the eyeball significantly increased while using the Bi shield, but the image obtained while using ODM and ASiR (40%) in combination hardly differed from that obtained with ASiR (40%) alone. Therefore, I think that the combined use of ODM and ASiR (40%) is an effective CT device reduction measure. The CTDI measurement experiment measured the central area of the phantom as well as 5 points (top and bottom, right and left), and these measurements were averaged. The measurements decreased at the center and upper points when using ODM and overall when using ASiR (40%). The CTDI indication level on the CT console decreased similarly to the measured value. The measurements obtained while using ODM and ASiR (40%) in combination increased by approximately 8.2%–9.0% relative to the measured values and indication level. Similar relative errors were obtained under all conditions with regard to ODM and ASiR (40%), suggesting that the changes in the CTDI indication levels on the CT console were appropriate.

This study suggested that ODM, ASiR, and the Bi shield were useful radiation exposure reduction measures.