A Cyclotron Decommissioning Radiological Assessment Exercise Performed by Student Mentees Underrepresented in the Radiation Safety Profession

Abstract

Cyclotrons used in nuclear medicine imaging accelerate protons, deuterons, and helium ions to bombard a target, which produces nuclear reactions that generate positron-emitting radionuclides. Secondary neutrons are nonuniformly emitted in these reactions and induce heterogeneous activation of the cyclotron components and concrete vault enclosure. This poses radioactive waste management complications when decommissioning a cyclotron facility, since the objective is to ensure that exposures are within regulatory limits and as low as reasonably achievable (ALARA). The McGovern Medical School in The University of Texas Health Science Center in Houston housed a Scanditronix MC40 cyclotron that produced short-lived radioisotopes for Positron Emission Tomography (PET) imaging from 1984 to 2001 until Tropical Storm Allison rendered it inoperable. The purpose of this study was to provide underrepresented Science, Technology, Engineering and Mathematics (STEM) students an ALARA experience with a practical problem encountered in the radiation safety profession. Gamma dose rate measurements were performed with both a Mirion InSpectorTM 1000 spectrometer and Fluke 451P survey meter in the vault at locations identified as hotspots based on preliminary scoping surveys with the Ludlum model 44-9 detector. However, gamma spectra were measured with the spectrometer exclusively at hotspots along the west wall. Results indicated the maximum gamma dose rate of 129 ± 31 nSv h−1 was about 2 times background near the central beam transport line of the now inoperable cyclotron. Furthermore, gamma emission peaks were identified in the spectra from trace amounts of 60Co and 152Eu in the vault’s concrete walls.

A 30-Year Radiation Safety Prospectus Describing Organizational Drivers, Program Activities, and Outcomes

“…This first sharp decline is made even more compelling when viewed within the context of the concurrent growth of the research enterprise. The single peak of increase in 2019 is due to the decommissioning of a cyclotron unit, as described by Zapata et al (2021). A portion of the radioactive waste cost reduction through the 30-y period can also be attributed to the decrease in the use of non-clinical radioactive materials.…”

Response to Mark Harvey Regarding the Educational Curricula for Students Interested in Health Physics

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WE WOULD like to voice our concurrence with Mark Harvey's recent Health Physics Journal Letter to the Editors regarding the educational curricula for students interested in health physics.As Harvey mentions, here at UTHealth, we have experienced a significant shift in the use of radiation sources over the past 30 y, from mainly benchtop research with radioactive materials to an increased use of x-ray producing devices and lasers (Gutierrez and Emery 2022). We are similarly supportive of Harvey's comments about specifically supporting HBCU institutions in this regard, which is an effort that could be led by the Health Physics Society.Our joint effort with Harvey and his students regarding the characterization of our cyclotron as part of decommissioning efforts proved to be mutually educational, with the students not only learning basic health physics but also the process to move their work forward through the publication process so that others can learn from it (Zapata et al 2021).

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“…Our joint effort with Harvey and his students regarding the characterization of our cyclotron as part of decommissioning efforts proved to be mutually educational, with the students not only learning basic health physics but also the process to move their work forward through the publication process so that others can learn from it (Zapata et al 2021).…”

Radiation Safety Education Adjustment in the Future: An HBCU’s Response to Trends in Health Physics

“…The UTHealth program also supported a cyclotron radioactive material license in the 1990s; however, the cyclotron sustained considerable damage from Tropical Storm Allison in 2001. Activated components of the cyclotron were managed by the UTHealth Radiation Safety staff until the unit was decommissioned and the corresponding license was terminated (Zapata et al 2021). Over the 30-y period, the authors noted reductions in dosimetry and waste disposal costs at the beginning of their evaluation despite the gradual growth in the UTHealth research enterprise.…”