Dose reduction evaluation in radiosensitive tissues for head CT scans using two phantoms and bismuth eye shielding

Abstract

Computed tomography is the imaging technique that most contributes to increasing the population average dose. Head scanning protocols have a very high dose in patients due to the small thicknesses of the slice for 3D image reconstruction. In this sense, radiosensitive tissues, such as the eye lenses and the thyroid, receive significant doses, as they are close to or in the irradiated field. The objective of this work is to present data on the variation of absorbed dose in the eye lenses and thyroid, with and without the use of bismuth eye shielding in head CT scans, and also to analyze the best dose-to-noise ratio in order to observe whether there is a decrease in image quality capable of rendering the proposed protocols useless. The method is based on head scans testing optimized protocols for the radiology service. Two male phantoms, one anthropomorphic and the other made in polymethyl methacrylate (PMMA), were used in the tests and radiochromic films were used to measure the absorbed dose values. The films were placed in the eye lenses and thyroid regions. Scans were performed on a GE CT scanner with 64-channel, Light Speed model. The obtained data allowed to observe the dose variation in the tissues and to conclude which of used protocols presented has the best noise-to-dose ratio for the use of the bismuth eye shielding. The results obtained will be important to suggest a complementary procedure for the optimization of head CT scans.