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

Abstract

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. 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. 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. 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.