Site-specific dosimetry of metastatic lesions in 186Re Therapy

The aim of this study is to obtain the optimum absorbed dose of bone and bone marrow in order to, by radiotherapeutic molecular application, reach the maximum palliative results. ¹⁸⁶Re - HEDP was infused in 11 patients with multiple skeletal metastases. The patients received a bolus injection of 1295MBq (35mCi) of ¹⁸⁶Re - HEDP, which in bone pain palliation from multiple metastases has proved to be highly justified and efficient. Scintigraphic acquisition of metastatic spots was completed by Elscint Apex SPX (revised by GE Healthcare) gamma camera. Planar data -anterior and posterior images- of patients, were acquired and used for an estimation of the dose in the specific lesions, according to the MIRD schema. Single photon emission computed tomography (SPECT) study of the same patients was completed and tomographic slices reconstructed; edged threshold was used and voxels number in each slice was measured. The total number of voxels in all reconstructed slices was added to produce the metastasis volume. The MIRDOSE 3.1 software was used for the calculation of spot-site absorbed dose and the comparison with normal bone tissue absorbed dose. Quantification of metastasis regions on skeleton was calculated of data obtained from whole - body scintigraphic images and SPECT slices of the metastatic spots volumes. We calculated the Metastatic to Normal Bone absorbed Dose Ratio (M/N) ratio and the Bone to Bone Marrow absorbed Dose ratio (B/RM ratio). Quantitative scintigraphic images analysis provides more realistic absorbed dose estimates for each individual. The dose rate- volume histogram of a target and relative indices provide information in assessing tumor control probability.