Scintimetric Characterization of Skeletal Hotspots by Dr.V.Siva’s Retention Ratio in A Diagnostic Referral Center

Aim: This study aims to document the utility of Scintimetric Characterization of the Skeletal Hot Spots seen in the Bone Scans done in this referral center during 2016-2017, in differentiating metastatic and non-metastatic lesions. Materials and Method: The study group consists of 59 patients referred for metastatic evaluation and non-specific bone complaints to our center. The whole body bone scan was done 3hrs after the intravenous injection of 15 to 25mCi of Tc99m MDP using GE Millenium Gamma Camera. The 24hr whole body bone scan was repeated in all those who had focal hot spots in their scans and who accepted voluntarily with the consent of the referring physician. The counts in the focal hot spots at 3 and 24hr bone scan images were calculated using the region ratio count protocol. The Dr.V.Siva’s Retention Ratio was calculated by dividing the3hr counts by the 24hr counts in the focal hotspots. The values of metastatic and nonmetastatic groups were tabulated and analyzed. Results: In our series 35/59 (59%) scans were negative and did not show any focal changes. 24/59 (41%) scans showed focal changes in the form of hot spots. Out of the total 69 hot spots analyzed 31 (45%) had the value of 13.07 ± 1.02 indicating metastatic nature and 38 ( 55%) had the value of 6.07 ± 0.62 confirming the benign nature of the lesions. Thus the metastatic group had the mean value which is almost twice that of the benign group. The statistical evaluation confirmed the significant difference between the two groups. Conclusion: It can be concluded that the Scintimetric characterization of the focal hot spots by Dr.V.Siva’s retention ratio effectively provides useful means to differentiate between the metastatic and non-metastatic lesions in the tertiary referral diagnostic center as well.


Introduction
normal bones show normal uptake and uniform distribution of the tracer. The abnormal regions usually present as focal hot spots due to increased localization of the tracer in the affected bone. This is common to both the neoplastic and benign etiologies. The metastatic lesions tend to be multiple, asymmetric in distribution and can be single as well. The benign lesions tend to be solitary and if multiple normally show symmetrical distribution of the tracer. The utility of 24hr delayed bone scan in differentiating the benign and neoplastic conditions was first shown by Israel O et al. [1]. The counts at the lesion are dived by the counts at the background at4hr scan and the 24hr scan. The ratio of the 24hr lesion / nonlesion value divided by the 4hr lesion / nonlesion value was shown to be different in the Malignant and benign bone disorders. This method proved to be of no clinical value as the resultant ratio was in decimal values and no useful cut off could be arrived at. Therefore by taking the counts only in the lesion at 4hr and 24hr Dr. V.Siva's retention ratio was calculated by dividing the 4hr count by 24hr count as shown in Figure 1. A useful cut off could be arrived at using this ratio as it gave full integers rather than decimal values [2,3]. The utility of this method in the evaluation of skeletal hot spots in the metastatic work up of Carcinoma Prostate had been documented by us [4]. For the first time the scintimetric characterization of the skeletal hot spots was put into use in a tertiary referral diagnostic center at Chennai.

Materials and Methods
The whole-body bone scan was done 3 hours after the intravenous injection of 15 to 25mCi of Tc99m MDP using GE Millenium Gamma Camera. The 24hr whole body bone scan was repeated in all those who had focal hot spots in their scans and who accepted voluntarily with the consent of the referring physician. The study group included59 patients referred for metastatic evaluation and non-specific bone complaints to our center. The counts in the focal hot spots at 3 and 24hr bone scan images were calculated using the region ratio count protocol and tabulated. The Dr.V.Siva's Retention Ratio was calculated by dividing the3hr counts by the 24hr counts in the focal hotspots. The values of metastatic and non-metastatic groups were tabulated and analyzed. The valuesof the malignant and the benign group were shown in Tables 1 & 2 respectively.

Results
In this series 35 35/59 (59%) scans were negative and did not show any focal changes. 24/59 (41%) scans showed focal changes in the form of hot spots. Out of the total 69 hot spots analyzed 31 (45%) had the value of 13.07 ± 1.02 indicating metastatic nature and 38 (55%) had the value of 6.07 ± 0.62 confirming the benign nature of the lesions as per the Dr. V Siva's retention ration calculation method. Thus the metastatic group had the mean value which is almost twice that of the benign group. The statistical evaluation confirmed the significant difference between the two groups as shown in Figure 2. The results of an unpaired t test performed showed t= 12.3and std dev=2.35, degrees of freedom = 67. The probability of this result, assuming the null hypothesis, is less than .0001. The test of two independent sample analysis by equal variance method showed that Mean a-Mean b is 7.0037 with t of +12.3, df 67 and p value of <0.0001 by both one tailed and two tailed methods. Similarly in the unequal variance method the Mean a-Mean b is 7.0037 with t of 11.88, df 51.05 and p value of <0.0001 by both one tailed and two tailed methods.

Discussion
The scitimetric characterization of the skeletal hot spots had been shown to be useful in the differentiation of benign and malignant lesions and also in the evaluation of delayed union of fractures as well by us [5]. Afroza Naznin et.al from INMAS, Bangladesh in their study have reported that the Dr. V. Siva's retention ratio protocol applied on a small number of prostate cancer patients in Bangladesh gave promising results [6]. They had concluded that the inclusion of Dr. V Siva's quantitative parameter in adjunct to conventional bone scintigraphy for the skeletal survey of carcinoma prostate patients can help to narrow down the specificity spectrum of bone scan hot spots being either due to metastasis versus benign disease. A typical method of reporting the scintimetric characterization was introduced in the report of the study as shown in Figure 3.

Conclusion
It can be concluded that the Scintimetric Characterization of the Skeletal Hot spots by Dr.V. Siva'sRetention Ratio significantly helps in the proper management of the patients even in a tertiary diagnostic center too. This concept must be put into test in various institutions world over for further authentication.