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High Energy Gamma Detection for Minimally Invasive Surgery

Chapman, Gregg James

Abstract Details

2017, Doctor of Philosophy, Ohio State University, Electrical and Computer Engineering.
Intraoperative detection of radio-labeled cancer has become a standard of care for some forms of cancer surgery. Most commercially available gamma detection probes are designed for use with low energy radioisotopes. Many new radiotracers exhibit positron emission which ultimately decays into two 511 kilo-electron volts (KeV) high energy gamma emissions. Gamma detection probes capable of capturing this energy require heavy side shielding to block off-axis radiation, making them both large and cumbersome for intraoperative use. Moreover, minimally invasive surgical procedures, performed either laparoscopically or robotically, are rapidly replacing open procedures in many areas of surgical oncology. To detect high energy radioisotopes with a gamma detection probe capable of being introduced into the surgical field laparoscopically, a significant change to the approach of intraoperative gamma detection is required. Gamma detection probes must be re-designed with both increased sensitivity at high energy, and an alternative to the heavy metal shielding. The necessity for side shielding can be eliminated by using two detectors in combination with software to limit the field of view. To achieve increased sensitivity, the detection system can be configured to detect a broader energy range that includes gamma counts from Compton scattered radiation. Compton scattered radiation is the result of incomplete photoelectric absorption within the detection crystal. In currently marketed designs, it is excluded from the accumulation of gamma counts because it reduces the spatial resolution of the probe. A third methodology is required to recover this loss of spatial resolution associated with the expanded energy range. A statistical basis for probe positivity can be used to improve the spatial accuracy of the radiation source measurement. This research investigates the viability of applying these three methodologies to reduce the diameter of gamma radiation probes while simultaneously increasing the sensitivity at an energy of 511 KeV. A positive outcome defines the parameters for a subsequent implementation of laparoscopic and robotic probes to be used for the detection of positron emitting radionuclides. It is evident from the study that a detector pair can limit the field of view without the use of side shielding. When the energy range is expanded to include Compton scattered radiation, probe sensitivity is increased by two orders of magnitude. A statistical criterion for probe positivity recovers the loss of spatial resolution associated with the use of a wider energy acceptance range. The statistical criterion is also capable of differentiating a radiation source from background at tumor-to-background ratios as low as 1.1-to-1 if the gamma counts are sufficiently high. The data also suggests that the depth of the radiation source may be calculated using the count rates from the detector pair, under limited conditions. However, further investigation is required. Surface mapping of the radioactivity emitted from phantom models demonstrates that the ratio of two detector counts is a more sensitive indicator of spatial differences in radioactivity compared to count rates from a single detector. This finding suggests that a new criterion for probe positivity based on count rate ratios may improve localization of radio-labeled tumors.
Robert Lee, PhD (Advisor)
Marvin White, PhD (Committee Member)
Edward Martin, Jr./MD (Committee Member)
222 p.

Recommended Citations

Citations

  • Chapman, G. J. (2017). High Energy Gamma Detection for Minimally Invasive Surgery [Doctoral dissertation, Ohio State University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=osu1500525997308215

    APA Style (7th edition)

  • Chapman, Gregg. High Energy Gamma Detection for Minimally Invasive Surgery. 2017. Ohio State University, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=osu1500525997308215.

    MLA Style (8th edition)

  • Chapman, Gregg. "High Energy Gamma Detection for Minimally Invasive Surgery." Doctoral dissertation, Ohio State University, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=osu1500525997308215

    Chicago Manual of Style (17th edition)