The role of Tc-99m (V) DMSA scintigraphy in the evaluation of superscan on bone scintigraphy

Technical note: identifying the prostate cancer 'superscan' by quantitative skeletal scintigraphy

AIM

The risk of failing to recognize the false, normal pattern of the superscan is a real one, with potential consequences for diagnosis and treatment. Quantitative indices of bone activity have previously measured uptake ratios or exposure time. Such estimates from spot images have provided differentiation of the superscan from normal. More recent reports describe quantitative methods for scanning type gamma-cameras, relying upon significant computation, availability of image analysis programmes or the drawing of whole skeletal regions of interest. The aim of this study was to establish a set of reference values for the evaluation of skeletal scintigraphy images, using the whole-body count alone.

MATERIALS AND METHODS

Patients underwent a routine whole-body bone study using the scanning technique. The total counts acquired during the scan were used to compare the skeletal uptake of the radiopharmaceutical between prostate patients showing superscan image patterns (n=38), prostate cancer patients with normal scans (n=40) and a control group (n=40) with normal scans, referred for reasons other than prostate cancer.

RESULTS

Qualitative comparison showed patterns of avid bone uptake with diminished visualization of kidney and bladder activity in the superscan group, and normal scans in the control and prostate patient groups. Quantitation using total counts recorded directly from the whole-body bone scan showed a significantly raised value in the superscan group only (P<0.001). We have established a simple set of objective reference bands to complement visual interpretation of the scan.

CONCLUSION

The whole-body image count alone, with little or no additional processing, is a helpful discriminator for the nuclear medicine superscan. This may assist the identification of this relatively uncommon diffuse metastatic disease in men with prostate cancer and reduce the number of investigations that might otherwise be reported incorrectly as normal.

99Tcm(V)DMSA scintigraphy in skeletal metastases and superscans arising from various malignancies: diagnosis, treatment monitoring and therapeutic implications

Skeletal metastases arising from a wide variety of malignancies including a few cases with superscan appearance were evaluated using (99)Tc(m) MDP bone scanning and (99)Tc(m)(V)DMSA scintigraphy. Whole body planar scans were obtained at 3 h and 24 h after injection of 740 MBq (99)Tc(m) MDP and 5 days later at similar times after injection of 555 MBq of (99)Tc(m)(V)DMSA. A qualitative as well as quantitative comparison was made between the (99)Tc(m) MDP bone scan and the (99)Tc(m)(V)DMSA scan in detection of osseous metastases. The reference methods used for discordant or equivocal lesions were correlative morphological imaging modalities, for example additional conventional radiography, CT or MRI. The present pictorial review deals with the results of qualitative analysis of the study. A total of 75 cases have been evaluated. The vignettes illustrated in the present article demonstrate avid (99)Tc(m)(V)DMSA concentration in skeletal metastases from a wide variety of malignancies and thus expand the potential therapeutic indications for 188/186 Re(V)DMSA. The study also demonstrates the valuable supporting role a (99)Tc(m)(V)DMSA scan can play in the confirmation as well as evaluation of the extent of malignant infiltration in a suspected superscan in routine skeletal scintigraphy. In addition, a (99)Tc(m)(V)DMSA scan detected a number of metastatic lesions in and around joints and regions with previous surgical intervention that were inconclusive in the bone scan. The results in a few patients who were available for repeat scintigraphy following treatment, support the convincing evidence that (99)Tc(m)(V)DMSA accumulation may be a sensitive indicator of patient response to therapy. This might have an important bearing in the context of increasing "cold" bisphosphonate usage in the treatment of skeletal metastases, where skeletal scintigraphy with a radiolabelled bisphosphonate derivative can often be fallacious because of competitive inhibition by the non-labelled form.

Evidence that 99mTc-(V)-DMSA uptake is mediated by NaPi cotransporter type III in tumour cell lines

In vivo studies have demonstrated that pentavalent technetium-99m dimercaptosuccinic acid [(99m)Tc-(V)-DMSA] may be a useful tumour imaging agent. Several studies have suggested that (99m)Tc-(V)-DMSA uptake may be related to the structural similarity between the (99m)Tc-(V)-DMSA core and the PO(4)(3-) anion. As phosphate ions enter cells via NaPi cotransporters, we investigated whether (99m)Tc-(V)-DMSA uptake is mediated by NaPi cotransporters. (99m)Tc-(V)-DMSA and phosphate uptake kinetics were compared in three cancer cell lines (MCF-7, G152 and MG-63) under several conditions (with and without sodium and NaPi cotransporter inhibitor and at different pH). Determination of molecular NaPi cotransporter mRNA expression was performed by reverse-transcriptase polymerase chain reaction (Rt-PCR) assay. Results obtained in the presence of NaPi inhibitor, in sodium-free medium and at alkaline pH showed that (99m)Tc-(V)-DMSA accumulation is linked to NaPi cotransporter functionality. MCF-7 and G152 exhibited the same tracer uptake, whereas MG-63 showed the highest phosphate accumulation and the lowest (99m)Tc-(V)-DMSA uptake. These results were in accordance with mRNA NaPi expression, i.e. all cell lines expressed NaPi type III but MG-63 also co-expressed NaPi type I. The total level of NaPi cotransporter was highly correlated with phosphate accumulation, while the level of type III was related to (99m)Tc-(V)-DMSA uptake. We have demonstrated that (99m)Tc-(V)-DMSA uptake is specifically mediated by NaPi type III in cancer cells.

Recent advances in 99mTc radiopharmaceuticals

99mTc radiopharmaceuticals play an important role in widespread applications of nuclear medicine. When 99mTc radiopharmaceuticals first came into use, major efforts were directed toward the development of 99mTc radiopharmaceuticals for bone imaging and for the excretory functions of the liver and kidneys. In the past 20 years, a significant advance has been made in technetium chemistry, which provided 99mTc radiopharmaceuticals for assessment of regional cerebral and myocardial blood flow. Recent efforts have been directed toward the design of 99mTc-labeled compounds for estimating receptor or transporter functions. A number of bifunctional chelating agents that provide 99mTc labeled proteins and peptides of high in vivo stability with high radiochemical yields have also been developed. More recently, organometallic technetium and rhenium compounds have been introduced as another class of 99mTc radiopharmaceutical design. In this manuscript, recent progress in 99mTc radiopharmaceuticals is reviewed with the major emphasis laid on key innovations in this field to provide the 99mTc radiopharmaceuticals available today.

99mTc(V)-DMSA scintigraphy in monitoring the response of bone disease to vitamin D3 therapy in renal osteodystrophy

Renal osteodystrophy (ROD) is a common and serious complication for uremic patients and patients are treated with 1,25-dihydroxyvitamin D3. The bone scanning agent 99mTc-phosphate has also been used to evaluate in ROD but it is not clear that bone scintigraphy has a role in the follow-up of treatment. In this study 99mTc(V)-DMSA scintigraphy was performed in eleven patients [age 40.7 +/- 17.3 (mean +/- SD) yr] with ROD before and after vitamin D3 therapy. Images were obtained after hemodialysis performed following tracer injection to maintain normal blood levels of the radiopharmaceutical and to reduce soft tissue activity. Lumbar vertebra-to-soft tissue uptake ratios (LUR) were quantified with the planar 99mTc(V)-DMSA images. Alkaline phosphatase and parathyroid hormone levels after treatment had significantly decreased compared with pre-therapy. In all patients there was visually decreased uptake in bone structures after treatment. After treatment the mean LUR ratio was significantly lower than those of before treatment (3.59 +/- 2.63 vs. 1.65 +/- 0.62; p = 0.01). LUR values were correlated with pre-therapy alkaline phosphatase and parathyroid hormone. These findings indicate that 99mTc(V)-DMSA scintigraphy is sensitive in evaluating the response of ROD to vitamin D3 therapy.