Michael T. Munley PhD, Presenter: Nothing to Disclose

Joseph Moore, Abstract Co-Author: Nothing to Disclose

Matthew Walb, Abstract Co-Author: Nothing to Disclose

Jennifer McBride, Abstract Co-Author: Nothing to Disclose

Scott Isom MS, Abstract Co-Author: Nothing to Disclose

Kenneth T. Wheeler, Abstract Co-Author: Nothing to Disclose

Mark S. Miller PhD, Abstract Co-Author: Nothing to Disclose

To determine if there is a CT dose below which no excess tumor formation occurs in a mouse model of cancer prone populations.

Bitransgenic mice that conditionally expressed a mutant human Ki-rasG12C gene in a doxycycline (DOX) inducible and lung specific manner were used to measure excess lung tumor formation after low dose CT exposures. Lung specific expression of the mutant Ki-ras transgene product in these mice results in the formation of small hyperplastic foci and very early stage adenomas that do not normally progress to more severe tumor types even after a year of continuous DOX treatment. This transgenic mouse model thus recapitulates the earliest stages of lung tumor formation. Mice were either sham-irradiated or received a single exposure of whole-body 100 keV CT radiation using a clinical scanner. Doses examined included 0, 1.25, 5, 10, 30, 50, 65 and 80 mGy. At 9 months after irradiation, the mice were euthanized, their lungs excised, and the number of lung tumors determined.

Significant excess tumor formation was observed in irradiated mice and appeared to be independent of dose between 1.25 - 80 mGy. The excess tumor formation was greater in females than in males.

Previous data obtained from this model indicated that the carcinogenic risk from fractionated low dose CT exposures (80 - 160 mGy total dose) is i] significantly increased compared to non-irradiated controls, and ii] is restricted to populations expressing cancer susceptibility genes. The data presented here demonstrate that decreasing the dose may not decrease the carcinogenic risk and therefore, the carcinogenic risk from low dose CT exposure may be underestimated for cancer prone populations when using the Linear No-Threshold model. (Supported by NIH CA136910)

Low dose CT exposure appears to increase the carcinogenic risk independent of radiation dose for cancer prone populations.

Munley, M, Moore, J, Walb, M, McBride, J, Isom, S, Wheeler, K, Miller, M, Excess Tumor Formation After a Single CT Exposure Appears to be Independent of Dose Between 1.25 - 80 mGy.  Radiological Society of North America 2012 Scientific Assembly and Annual Meeting, November 25 - November 30, 2012 ,Chicago IL. http://archive.rsna.org/2012/12020616.html