201T1 and 99Tcm-J001X macrophage scintigraphy: two radionuclide imaging techniques for the surveillance of acute localized radiation over-exposures.

The therapeutic or surgical management of acute localized irradiation is very complicated due to the delayed occurrence of ionizing radiation effects. There is a great need for non-invasive imaging techniques to delineate healthy from exposed tissues. Such a technique should be of value considering that spread of damage can occur from apparently silent fibrotic foci. Of the scintigraphic procedures, 99 Tc m first-pass scintigraphy has already been recommended by the International Atomic Energy Agency (IAEA) for the evaluation of irradiated tissues. In order to improve the scintigraphic surveillance of accidental over-exposures, the potentials of 20 Tl and 99 Tc m -J001X were evaluated on an experimental porcine model reproducing the late fibrotic effect encountered after localized irradiation. J001X, an acylated poly-(1,3)-galactoside of bacterial origin, was used for the functional imaging of the inflammatory reaction which took place after irradiation. This scintigraphy, based on targeting of activated macrophages recruited by lesions, was performed together with 201 Tl scans for the assessment of blood perfusion and cellular metabolism. Our results demonstrate that these two radiopharmaceuticals provide reliable information for the management of accidental localized over-exposure, J001X allowing the assessment of the inflammatory reaction and 201 Tl-chloride being mainly useful for imaging the delayed onset of fibrosis.