BACKGROUND: Although the pharmacokinetic profiles and clinical efficiency of ⁸⁹SrCl₂ as an agent of choice in extensive metastatic bone disease have been studied widely, the relationship of its efficiency to perfusion of metastases remains unresolved. Hence we aimed to compare the clinical and radiological manifestations of regression of metastatic bone disease in prostate cancer with results of pre-treatment scanning with ^99mTc-MIBI as a blood flow marker.
MATERIALS AND METHODS: Sixteen patients with bone metastatic spread of prostate cancer (on average 9 s.d. 3 bone metastases on ^99mTc-MDP scan) were treated with ⁸⁹SrCl₂ (Metastron, Amersham plc) and studied during post-injection followup. In each patient whole-body ^99mTc-MDP (3–4h post-injection of 510 MBq) and ^99mTc-MIBI (10 min post-injection of 510 MBq) scans were performed before injection of 150 MBq of ⁸⁹SrCl₂ and 3 and 6 months after. Mean count ratio (metastasis/normal bone) was calculated for ^99mTc-MDP scans for all metastases. ^99mTc-MIBI uptake was employed as a marker of local neoplastic blood flow in metastases, and quantified in a manner similar to ^99mTc-MDP study as (metastasis/ normal bone) pixel count ratio. MRI T1 and T2 scanning were used for anatomic followup of metastases.
RESULTS: All patients demonstrated substantial improvement in severity of pain syndrome with full release from pain in ten. The ^99mTc-MDP follow-up revealed a decrease in the number of «hot» metastatic uptake sites from 9 s.d. 3 to 5 s.d. 3 (p<0.01) with a simultaneous decrease of normal bone ratio in remaining hot spots on ^99mTc-MDP scans from 2.79 s.d. 0.45 to 1.83 s.d. 0.18 (p<0.05) after 3 months and further to 1.44 s.d. 0.43 (p<0.05) after 6 months. Metastases with ^99mTc-MIBI pre-treatment (metastasis/background) index over 1.5 and anatomic cross-dimensions below 19 mm demonstrated near-full regression when studied using ^99mTc-MDP and MRI 3 and 6 months after injection of ⁸⁹SrCl₂. A significant correlation was observed between pre-treatment ^99mTc-MIBI (Mts/Bg) ratio and decrease in ^99mTc-MDP metastatic uptake (r=0.84, p<0.005).
CONCLUSION: Metastases with anatomic dimensions smaller than 20 mm and persistent blood supply can be effectively cured with ⁸⁹Sr. The ^99mTc-MIBI scan of bone metastases is of predictive value for prognosis of success of systemic ⁸⁹Sr therapy in prostate cancer.