Time-course of effects of external beam radiation on 18F-FDG uptake in healthy tissue and bone marrow

Abstract

 Introduction: The utility of PET for monitoring responses to radiation therapy have been complicated by metabolically active processes in surrounding normal tissues. We examined the time-course of ¹⁸F-FDG uptake in normal tissues using small animal-dedicated PET during the 2-month period following external beam radiation. Methods: Four mice received 12Gy of external beam radiation, in a single fraction to the left half of the body. Small animal ¹⁸F-FDG PET scans were acquired at 0 (pre-radiation), 1, 2, 3, 4, 5, 8, 12, 19, 24, and 38 days following irradiation. ¹⁸F-FDG activity in various tissues was compared between irradiated and non-irradiated body halves before, and at each time-point after, irradiation. Results: Radiation had a significant impact on ¹⁸F-FDG uptake in previously healthy tissues, and time-course of effects differed dramatically in different types of tissues. For example, liver tissue demonstrated increased uptake, particularly over days 3-12, with the mean left to right uptake ratio increasing 52% over mean baseline values (p<0.0001); in contrast, femoral bone marrow uptake demonstrated decreased uptake, particularly over days 2-8, with the mean left to right uptake ratio decreasing 26% below mean baseline values (p=0.0005). Significant effects were also seen in lungs and brain. Conclusions: Radiation had diverse effects on ¹⁸F-FDG uptake in previously healthy tissues. These kinds of data may help lay groundwork for a systematically acquired database of the time-course of effects of radiation on healthy tissues, useful for animal models of cancer therapy imminently, as well as interspecies extrapolations pertinent to clinical application eventually.