WFU Physics Colloquium

Exposure to ionizing radiation from medical procedures has skyrocketed in the last three decades, owing largely to the increase in diagnostic imaging procedures. Computed tomography is a powerful and invaluable tool in the diagnosis of disease, but it is essential that the radiation risks be appropriately quantified so that clinicians are in the best possible position to assess the risks and benefits associated with its use. Our group uses sophisticated small animal lung tumorigenesis models to investigate the carcinogenic risks of low dose radiation.

As a tangential investigation, NASA seeks to evaluate the low dose radiation risks associated with long-term space flight. Megavoltage linear accelerators were utilized to model the effects of high-energy space radiation in conjunction with hyperoxic and low-gravity environmental conditions. Dosimetry was quantified with ionization chamber and optically stimulated luminescent dosimeter measurements to verify a uniform, homogeneous dose distribution that allowed for unanesthetized rodent irradiation in specially designed chambers. The results suggested that astronauts exposed to space radiation while breathing 100% oxygen during an extra-vehicular activity do not have a greater risk of developing radiation-induced tumors.

This work focuses on the rigorous dosimetry that must be the foundation for any radiation experiment. Ionization chamber measurements provided the dosimetry standard and facilitated the design of an irradiation protocol for 100 kVp x-rays. From this, radiochromic film dosimetry was performed to examine the spatial dose distributions. Optically stimulated luminescent dosimeters were implanted in mouse lung cavities and utilized for in vivo dose verification of our models. To enhance our tumor analysis capabilities, an efficient, high-resolution 7T MRI scanning protocol was implemented to permit longitudinal tracking of tumor growth rate.

Our cancer-susceptible murine model has consistently shown a dose-independent, gender-dependent increased carcinogenic risk following exposures to radiation doses as low as 1.25 mGy, suggesting that the carcinogenic potential of low dose radiation could be underestimated in cancer prone populations. While other groups have previously studied some aspects of this model individually, the combination of a sensitive in vivo mouse model using a clinical CT scanner as the radiation source with an organ specific endpoint represents a completely novel implementation in the field of radiation risk.