Access Type

Open Access Dissertation

Date of Award

January 2016

Degree Type

Dissertation

Degree Name

Ph.D.

Department

Medical Physics

First Advisor

Frank F. Dong

Second Advisor

Otto Muzic

Abstract

Purpose: This work investigated several topics related to dosimetry in soft tissue from fluoroscopic X-ray beams; first, it investigated the X-ray beam spectra and air kerma rates available for clinical use on state-of-the-art fluoroscopes using spectral (copper [Cu]) filtration; second, it investigated the fluoroscopic X-ray beam characteristics of first half-value layer (HVL), second HVL, homogeneity coefficients (HCs), and backscatter factors (BSFs) across the full range of available beam qualities; and third, it investigated the energy dependence of kerma-area-product (KAP)-meters measuring the radiation output of the fluoroscope. Materials and Methods: A state-of-the-art Siemens Artis Zee fluoroscope was operated in the service mode to allow for manual control of the technique factors (kVp, mA, ms, and Cu). Free-in-air measurements were made to determine HVLs and KAP-meter accuracy. BSFs were determined across a large range of X-ray field sizes and beam spectra with polymethyl-methacrylate. Percent depth doses (PDDs) and X-ray beam profiles were acquired across a similar range of X-ray beam spectra using a PTW water tank and a Spokas ionization chamber for the PDD measurements and a solid state dosimeter for the beam profile measurements. Results: Fluoroscopic dose rate and technique parameter curves are reported for several state-of-the-art fluoroscopes, illustrating differences in approach among vendors and establishing the basis for investigation of the X-ray beam characteristics (HVLs, HCs, BSFs, and PDDs). These X-ray beam characteristics are reported across a large range of clinically available X-ray beam spectra, providing the necessary foundation for dosimetry in soft tissue from these beams. Additionally, the accuracy of the displayed Ka,r and correction coefficients determined using the American Association of Physicists in Medicine Task Group 190 methodology is reported across a similar range of X-ray beam spectra. Conclusion: The content of this research provides the necessary foundation for determining radiation dose at depth in soft tissue from state-of-the-art fluoroscopes. The results from this research can be used to assess dose at depth in soft tissue from fluoroscopically guided interventions, to determine fetal dosimetry from fluoroscopically guided interventions, and to validate dose modeling software.

Download

Share

COinS