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An Investigation of Dose Reduction in Head and Neck CT with the Use of Organ Exposure Modulation

Luttrell, Kyle C

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2016, Master of Science in Biomedical Sciences (MSBS), University of Toledo, Biomedical Sciences (Medical Physics: Diagnostic Radiology).
An Abstract of An Investigation of Dose Reduction in Head and Neck CT with the Use of Organ Exposure Modulation by Kyle Luttrell Submitted to the Graduate Faculty as partial fulfillment of the requirements for the Master of Science in Biomedical Science Degree in Medical Physics The University of Toledo August 2016 Purpose: To investigate the use of organ exposure modulation (OEM) in head and neck CT to reduce the dose to radiosensitive organs such as the lens of the eye and thyroid. Methods: The Toshiba Aquilion ONE CT scanner was used to perform multiple scans of the head and neck on a RANDO phantom using the clinically-used technique without OEM and an OEM technique. For the brain protocol, the scanner reported CTDIVOL, measured in the head phantom, for the fixed mA and OEM techniques was 42.7 mGy and 37.3 mGy respectively. For the head/neck protocol, the scanner reported CTDIVOL, measured in the body phantom, for the current technique and OEM technique was 5.4 mGy and 4.8 mGy respectively. Dose was measured with optically stimulated luminescent dosimeters (OSLDs) affixed to the surface of the RANDO phantom at position of the eyes, both sides of the head, and posterior of the head for the brain scan and the eyes and thyroid for the head/neck scan. The OSLDs had been calibrated free-in-air against a pencil ion chamber at the CT scanner isocenter. Additionally, the fixed mA and OEM techniques were used to scan the ACR phantom for the purpose of assessing image noise and contrast-to-noise ratio (CNR). Results: On average dose to the lens of the eyes for the head scan using the fixed mA protocol was measured to be 42.0±4.9 mGy while the OEM technique was 29.5±4.6 mGy, representing a 29.8% dose reduction. Radiation dose to the sides and posterior of the head was on average reduced by 10.2±3.5%. Image noise evaluated in the ACR phantom was increased on average by 6.3%. The CNR using the fixed mA technique was found to be 1.82 while the OEM technique was 1.55. For the head/neck scan, the average dose to the lens of the eyes and the thyroid for the current protocol was measured to be 59.1±0.84 mGy and 17.4±1.2 mGy respectively. The dose to the eye lens and thyroid using an OEM protocol was measured to be 45.0±0.69 mGy and 21.8±0.9 mGy respectively, representing a dose savings of 23.8% to the eyes and an increase in dose of 25.6% to the thyroid. Image noise was increased on average by 16.9%. The CNR using the current protocol was found to be 1.123 while the OEM technique was 0.922. Conclusions: For the head scan, dose to the lens of the eye was reduced, by using an OEM protocol, by 29.8%. The dose reduction corresponded to a slight increase in image noise and decrease in CNR. However, the CNR remains well above the acceptable criteria of 1.0 set forth by ACR for adult head scans. For the head/neck scan, dose to the lens of the eye was reduced by 23.8%, however dose to the thyroid increased by 25.6%. This dose reduction resulted in an increase in image noise and once again a decrease in CNR. CNR for the head and neck protocol was reduced below the minimum of 1.0 set forth by the ACR. All-in-all OEM protocols reduced dose to the eye lens with an increase in dose to the thyroid. Image quality remained relatively adequate with the exception of the CNR for the head and neck protocol. OEM would be a viable option for head protocols. With further development of the head and neck technique, CNR can be increase above the minimum limit and the OEM protocol could become a viable option for head and neck protocols as well.
Ishmael Parsai, Ph.D. (Committee Chair)
Kerry Krugh, Ph.D. (Advisor)
Nicholas Sperling, Ph.D. (Committee Member)
58 p.

Recommended Citations

Citations

  • Luttrell, K. C. (2016). An Investigation of Dose Reduction in Head and Neck CT with the Use of Organ Exposure Modulation [Master's thesis, University of Toledo]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=mco1470320019

    APA Style (7th edition)

  • Luttrell, Kyle. An Investigation of Dose Reduction in Head and Neck CT with the Use of Organ Exposure Modulation. 2016. University of Toledo, Master's thesis. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=mco1470320019.

    MLA Style (8th edition)

  • Luttrell, Kyle. "An Investigation of Dose Reduction in Head and Neck CT with the Use of Organ Exposure Modulation." Master's thesis, University of Toledo, 2016. http://rave.ohiolink.edu/etdc/view?acc_num=mco1470320019

    Chicago Manual of Style (17th edition)