[New criteria for scintigraphic follow-up of bone metastases following radiotherapy. Results of functional scintigraphy using 99mTc-MDP].

After radiation therapy regional 99mTc-MDP clearance by 17 metastatic lesions was determined repeatedly in 13 patients. 99mTc-MDP clearance rates decreased within 14 weeks after irradiation of osteoblastic metastases, but were normalized in only one lesion. In osteolytic lesions 99mTc-MDP clearance increased 4 weeks after completion of radiation therapy indicating reossifications evident from X-ray examinations subsequently. 99mTc-MDP clearance decreased subsequently and returned to normal after 28-50 weeks in 6 out of 11 metastases demonstrating reossification on X-ray. Monitoring of radiation therapy of bone metastases should be adapted to these complex variations of tracer kinetics. The initial increase of tracer accumulation in osteolytic metastases due to bone repair should not be misinterpreted as a local progression of metastatic bone disease.