Proliferation and apoptosis after whole-body irradiation: longitudinal PET study in a mouse model

A reliable method for regional in vivo imaging of radiation-induced cellular damage would be of great importance for the detection of therapy-induced injury to healthy tissue and the choice of adequate treatment of radiation emergency patients in both civilian and military events. This study aimed to investigate in a mouse model if positron emission tomography (PET) imaging with proliferation and apoptosis markers is potentially suitable for this purpose.

Four groups, including twenty mice (wild-type C57BL/6) each, were whole-body irradiated with 0 Gy, 0.5 Gy, 1 Gy, and 3 Gy and examined by PET over a six-month period at defined time points. 3'-[¹⁸F]fluoro-3'-deoxythymidine ([¹⁸F]FLT) and 2-(5-[¹⁸F]fluoropentyl)-2-methyl malonic acid ([¹⁸F]ML-10) were used to visualise proliferation and apoptosis. Regional standard uptake values were compared with respect to irradiation dose over time. Histologic data and peripheral blood cell values were correlated with the PET results.

The hematopoietic bone marrow showed a significantly increased [¹⁸F]FLT signal at early time points after radiation exposure (day 3 and day 7). This correlated with blood parameters, especially leukocytes, and histological data. A significantly increased [¹⁸F]FLT signal also occurred in the gastrointestinal tract and thymus at early time points. An increased [¹⁸F]ML-10 signal related to irradiation doses was observed in the bone marrow on day 8, but there was a high variability of standard uptake values and no correlation with histological data.

[¹⁸F]FLT showed potential to visualise the extent, regional distribution and recovery from radiation-induced cellular damage in the bone marrow, gastrointestinal tract and thymus. The potential of [¹⁸F]FLT imaging to assess the extent of bone marrow affected by irradiation might be especially useful to predict the subsequent severity of hematopoietic impairment and to adapt the therapy of the bone marrow reserve. [¹⁸F]ML-10 PET proved to be not sensitive enough for the reliable detection of radiation induced apoptosis.