Incremental diagnostic utility of systematic whole body SPECT/CT for bone scintigraphy in initial staging of cancer patients

Objectives The use of SPECT/CT has been shown to increase the diagnostic performance of bone scintigraphy for staging of malignancies. A systematic whole body (WB) SPECT/CT may allow further improvement. However, this would be balanced by higher dosimetry and longer acquisition time. The aim of this study was to assess the incremental diagnostic utility of a systematic WB SPECT/CT acquisition for bone scintigraphy in initial staging of cancer patients.

Methods Consecutive patients referred for bone scintigraphy for initial staging of malignancy from February to June 2014 were analyzed. All patients underwent a two-bed WB SPECT/CT acquisition of the trunk (from the cervical spine to the proximal femora) on a Symbia/Intevo T6 gamma-camera. Images were interpreted by two nuclear medicine physicians in a 3-step procedure. Firstly, only WB planar images were used; secondly, one additional single bed SPECT/CT chosen based on planar images was used; finally, WB planar and SPECT/CT images were available for interpretation. Lesions were classified as benign, equivocal or suspicious for metastasis. A per-lesion, per-anatomical region and per-patient analysis was performed.

Results 102 patients were analyzed (prostate n = 67, breast n = 17, lung n = 6, bladder n = 6, kidney n = 4, other n = 2). In a per-lesion analysis, the number of equivocal and suspicious lesions was 91 and 241 using WB planar images, 17 and 259 using a single-bed SPECT/CT acquisition and 11 and 269 using WB SPECT/CT images, respectively. In a per-anatomical region analysis, the number of equivocal and suspicious regions was 67 and 57 using WB planar images, 10 and 63 using one single-bed SPECT/CT and 7 and 71 using WB SPECT/CT, respectively. In a per-patient analysis, the diagnostic conclusion was “no evidence of disease”, “equivocal” or “evidence of disease” in 35, 53 and 14 patients using WB planar images, 77, 6 and 19 patients using an additional single-bed SPECT/CT and 76, 7 and 19 using WB SPECT/CT images, respectively. Only one patient had a different diagnostic conclusion based on systematic WB SPECT/CT (equivocal scan) as compared with the single-bed SPECT/CT (no evidence of disease). Guided biopsy of the equivocal lesion did not show malignancy.

Conclusions As previously demonstrated, adding a single-bed SPECT/CT to whole body planar bone scintigraphy reduced the proportion of indeterminate results for initial staging of malignancy. Although a systematic WB SPECT/CT acquisition slightly increased the number of suspicious anatomical regions as compared with one single bed SPECT/CT acquisition, there was no benefit in terms of patient’s management, the only discrepancy resulting in an unnecessary biopsy. Further taking into account dosimetric considerations and acquisition time, it does not appear to have an incremental diagnostic utility to perform a systematic WB SPECT/CT acquisition for bone scintigraphy in initial staging of cancer patients.