Search

Within 1 yr after localized irradiation of a hind limb with single (1756 rads) or fractionated (4650 rads in 3 wk) x-ray doses, radiation-induced osteosarcomas were observed in four of nine single-dose rabbits and two of 11 fractionated-dose rabbits. Tumors were observed in the proximal tibia in five cases and the distal femur in one case. In terms of production of osteoid or osseous tissue, three tumors were well differentiated, one slightly differentiated, and two (spindle-cell tumors) undifferentiated. This report summarizes the Tc-99m pyrophosphate (TcPPi) imaging and autoradiographic, radiographic, and histologic studies of these osteosarcomas. The four differentiated osteosarcomas were detected 1--2.5 mo earlier by TcPPi imaging than by radiography, whereas the two undifferentiated tumors were suspected 2 wk or 3.5 mo earlier radiographically. Autoradiograms showed TcPPi localization in bone produced by differentiated osteosarcomas, and in regions of reactive bone resorption and formation peripheral to tumors. The results support a recommendation for combined radiographic and scintigraphic techniques for the early detection of osteosarcomas.

Quantitative Tc-99m pyrophosphate bone imaging was carried out in locally irradiated and control areas of New Zealand albino rabbits to determine the potential role of bone imaging in assessing the time course of radiation effects in bone and surrounding tissues. In vitro Tc-99m tissue assays, and serial radiographs. from the irradiated and contralateral limbs were obtained at regular intervals over the first 12 mo following irradiation for comparison with quantitative results from the camera studies. The autoradiographic localization of TcPPi was also studied in the x-irradiated and contralateral bones of the rabbits. The results show that TcPPi bone imaging is a sensitive in vivo indicator of early radiation effects upon vasculature and bone remodeling. The findings suggest that the quantitative bone-imaging technique may be useful in the evaluation of the effects of treatment modalities on the skeleton.

Histologic and tracer techniques were used to investigate and document alterations in bone pathophysiology subsequent to irradiation of the left hind limb of rabbits. Numerous time-dependent changes were observed. Among these were an inflammatory response shortly after irradiation, and an increase in the remodeling of cortical bone, which peaked between 3 and 6 mo after irradiation. The changes in bone remodeling correlated with changes in vascular patency in a manner consistent with the hypothesis that radiation damage in mature bone is mediated primarily through alterations in the fine vasculature. The findings of this study provide important information on the time course of changes in bone pathophysiology following regional irradiation. They are used in the second of this series of papers to help establish which mechanisms are responsible for postirradiation alterations in the localization of Tc-99m pyrophosphate in these rabbits.