All ETDs from UAB

Advisory Committee Chair

Claudiu T Lungu

Advisory Committee Members

Alfred A Bartolucci

Steven M Becker

Riedar K Oestenstad

Sharon L White

Michael V Yester

Document Type

Dissertation

Date of Award

2011

Degree Name by School

Doctor of Public Health (DrPH) School of Public Health

Abstract

Purpose: Shielding considerations are important for designing a positron emission tomography/computed tomography (PET/CT) imaging facility, because of the high energy (511 keV) of electron-positron annihilation photons. Since radiation emitted from patients administered PET radiopharmaceuticals includes lower-energy scattered photons, a given thickness of lead attenuates more of the radiation than it would for a monoenergetic beam of 511 keV photons. A more accurate determination of the effective attenuation coefficient of lead for the spectra of photon energies emitted from PET/CT patients could reduce the shielding requirements necessary to adequately protect public health. In this work, the spectra of energies emitted from 14 patients of different Body Mass Index (BMI) are presented. Methods: The radiation spectra emitted from adult patients injected with F-18 FDG at The Kirklin Clinic PET/CT Center were measured through an unleaded wall, and a wall that contains 15.9 mm of lead. The spectra were corrected for radioactive decay time, distance from the patient, detection efficiency of the sodium iodide detector at different energies, and normalized to an injected activity of 15 mCi. The counts were summed to produce a measure of the quantity of transmitted radiation. The shielded wall sums were divided by the unshielded wall sums to determine the radiation transmission factor for each patient. Results: An effective linear attenuation coefficient of c = 0.226/mm was measured in this work. The results were not significantly affected by differences in patient BMI. For a particular lead shielding thickness, new broad-beam transmission factors calculated using c = 0.226/mm are less than the corresponding broad-beam transmission factors in lead at 511 keV given by American Association of Physicists in Medicine Task Group 108. Conclusions: Since much of the 511 keV annihilation radiation is scattered in the human body, a spectrum of photon energies interacts with the lead shielding. This results in an increase in the effective attenuation coefficient for lead compared to a monoenergetic beam of 511 keV photons. Because of these effects, current shielding designs for PET/CT imaging facilities using lead shielding may result in safety margins that are higher than originally calculated to adequately protect public health.

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