Detection and quantification of Ra uptake in bone metastases of patients with castration resistant prostate carcinoma, with the aim of determining the absorbed dose in the metastases.

Purposes: To obtain the necessary acquisition and calibration parameters in order to evaluate the possibility of detecting and quantifying Ra uptake in bone metastases of patients treated for castration resistant prostate carcinoma. Furthermore, in the cases in which the activity can be quantified, to determine the absorbed dose.

Material And Methods: Acquisitions from a Petri dish filled with Ra were performed in the gamma camera. Monte Carlo simulations were also performed to study the partial volume effect. Formulae to obtain the detection and quantification limits of Ra uptake were applied to planar images of two patients 7 days post-administration of 55kBq/kg of Ra. In order to locate the lesions in advance, whole-body scans and SPECT/CT images were acquired after injecting Tc-HDP.

Results: The optimal energy window was found to be at 82keV with a medium-energy collimator MEGP. Of the lesions found in the patients, only those that had been detected in both the AP and PA projections could be quantified. These lesions were those which had shown a higher Tc-HDP uptake. The estimated values of absorbed doses ranged between 0.7Gy and 7.8Gy.

Conclusions: Of the lesions that can be detected, it is not possible to quantify the activity uptake in some of them, which means that the absorbed dose cannot be determined either. This does not mean that the absorbed dose in these lesions can be regarded as negligible.