Sr-89 therapy: Strontium kinetics in disseminated carcinoma of the prostate

Abstract

Strontium kinetics were investigated in a group of 14 patients receiving ⁸⁹Sr palliation for metastatic bone disease secondary to prostatic carcinoma. Using ⁸⁵Sr as a tracer, total body strontium retention R(t) was monitored for a 3 month period following ⁸⁹Sr administration, and at 90 days was found to vary from 11% to 88% and to correlate closely with the fraction of the skeleton showing scintigraphic evidence of osteoblastic metastatic involvement. Strontium renal plasma clearance varied from 1.6 l/day to 11.6 l/day, and in nine patients was significantly reduced compared with values found in healthy adult men, probably due to increased renal tubular reabsorption associated with the disturbance of calcium homoeostasis. Renal clearance rate was the principal factor determining R(t) for t<6 days, and was an important secondary factor at later times. Over the interval 30 days t<90 days, R(t) was closely fitted by the power law function R(t)=R ₃₀ (t/30)^-b, with R ₃₀ and b showing the close correlation expected from the effect of R(t) on strontium recycling. The correction of the data for this effect to determine the true skeletal release rate is described. Measurement of localized strontium turnover in individual metastatic deposits from whole body profiles and scintigraphic images gave retention curves that typically rose to a plateau by 10 days after therapy, and then decreased very slowly. In contrast, retention curves for adjacent normal trabecular bone showed more rapid turnover, peaking at 1 day and subsequently decreasing following a t^-0.2 power law function. The changes in strontium kinetics found in metastatic bone disease are favourable to the objectives of ⁸⁹Sr therapy.