Non-invasive Quantitative Characterization of Skeletal Metastasis in Carcinoma Prostate by Tc99m MDP Bone Scans Using Dr. V. Sivas Retention Ratio in Correlation with Serum PSA Levels

Background: In patients suffering from carcinoma prostate the incidence of skeletal metastases had been found to be very high. The presence of skeletal metastasis could be inferred by the multiple focal hotspots in the skeletal tissue. The metastatic nature of the hotspots could be inferred by multiple lesions, asymmetric distribution with increased tracer concentration. In the case of Solitary focal spot in the bone scan metastatic nature could not be attributed to it. The invasive biopsy procedure could only confirm or discard the metastatic involvement. A new non-invasive Scintimetric characterization and evaluation of skeletal hot spots in bone scans of carcinoma prostate patients was proposed and tested. Materials and methods: The bone scan was done 4 and 24 hours after intravenous injection of 15 to 25 mCi of Tc99m Methylene Di-Phosponate with adequate hydration using the e-cam Siemens dual head gamma camera with e-cam whole body acquisition protocol in 75 patients with biopsy proven carcinoma prostate. Metastatic involvement was seen in 53 patients and was negative in 22. The Serum PSA levels were obtained from the Patient medical records were tabulated. The 185 focal hotspots in various sites in 34 patients were characterized using the temporal scintimetric method. Both 4 and 24hr bone scan images were selected using the general display protocol. Then with the help of the region ratio processing protocol the 4 and 24hr anterior and posterior images were selected separately. Maximum counts in the selected regions were then tabulated. Then the 4/24hr Dr. V. Siva’s retention ratio was derived by dividing the 4hr counts of the focal hotspots with 24hr counts along with the Israel’s 24/4hr ratio as well. Similarly 4/24hr Dr.V.Siva’s retention ratio of whole body scan total counts at 4 and 24hr scans was also calculated.The results were compared and analysed. Results: The mean of 4/24hr Dr. V. Siva’s retention ratio was found to be 12.32 ± 3.3 and that of 24/4hr Israel’s ratio to be 0.08 ± 0.02 for Focal hot spot evaluation. The 4/24hr Dr. V. Siva’s retention ratio was derived by dividing the total whole body counts at 4 and 24hr whole body bone scan was 12.21 ± 2.78 which wascloser to the Focal hot spot retention ratio. The Total PSA, Free PSA and the %PSA Values were 61.8, 19.2 and 26.8 in the Metastatic positive group and 34.5, 6.8 and 12.8 in the negative group respectively. Conclusion: Scintimetric characterization of the skeletal hot spots provided a non-invasive means for identifying the underlying pathology to enable proper management decisions. The 4/24hr Dr. V. Siva’s retention ratio was useful clinically because of its whole integer value, unlike the Israel’s 24/4hr ratio which was in decimal value. The utility of the scintimetric characterization in inferring the metastatic nature of the lesion was confirmed through biopsy of the site afflicted followed by histopathological examination.