WBS is a widely used and highly sensitive imaging modality to detect the bone metastases in cancer patient. However, its specificity is limited in accurately diagnosing a bone lesion due to uptake in other benign conditions (e.g., degenerative changes, fractures, infections, and trauma) [11]. SPECT is able to expose accurate localization and characterization of more bone lesions[2]. Although some patients undergo SPECT scan, there are some lesions still remain equivocal. Combined the anatomical information of CT with functional information of SPECT, SPECT/CT can enable more accurate localization and characterization of lesions using. For the vertebrae where the location of a lesion determines whether it is classified as malignant or benign. The study shows that most of the benign lesions were within the facet joints or at the end plate of the vertebral bodies whereas the malignant lesions were predominantly within the pedicles and vertebral bodies [12]. The management of a patient mostly based on diagnosis and clinical staging. But bone metastasis or benign bone disease is detected by bone scintigraphy or other imaging methods may influence the diagnosis and clinical staging of patient. Most of the time, the existence of bone metastasis may result in the change of treatment such as radiotherapy or radionuclide therapy. In our study, the diagnosis of 42(37.5%) patients had been changed based on SPECT/CT, which is also founded by other studies. Thanuja Mahaletchumy et al. [13], found 32% patients had their diagnosis altered in their study. Ndlovu et al.[14], recorded an alteration of diagnosis in 40.5% of patients in their study. Meanwhile, 4 patients received chemotherapy for the diagnosis was changed from benign to malignant and 6 patients avoided overtreatment for the diagnosis was changed from malignant to benign (Fig. 2,3). Of the 32 equivocal patients, 21 were found to be benign and 11 were found to be malignant based on SPECT/CT, but only 6 patients received changed treatment plan for other organs metastases. The diagnostic coincidence rate of SPECT/CT is 90.2% when a definitive diagnosis was made. This is lower than a study by Zhao et al. (95.7%) [15]༌but higher than the study by Horger et al. [16](85%).
We observed the role of SPECT/CT in the interpretation of each bone lesion in the lesion-based analysis. Not only SPECT/CT reduced the number of equivocal lesions (12.5%) compared to WBS and SPECT, but also resulted in improved accuracy in the characterization of these lesions, further supporting the value of its clinical application.
And we found that bone lesions commonly affected the spine and ribs, which is corroborated with other studies[2, 6, 13]. In our study, SPECT/CT significantly decreased the number of equivocal lesions at all bone regions, and the reduction was statistically significant in the proportion of equivocal lesions in the spine (P < 0.004)[14]. These findings suggest that SPECT/CT enhances the confidence diagnosis equivocal lesions which at almost all the bone sites. Specially, using SPECT/CT to scan spine will be most beneficial to patients for degenerative changes frequently occur at this region. This is also found in the study of Thanuja Mahaletchumy et al.,[13] It’s difficult to distinguish the benign changes from bone metastasis by WBS and SPECT alone. In the present study, we found that even though some bone lesions were detected by the CT component of the SPECT/CT which were not seen on WBS and SPECT imaging, it did not change the final diagnosis of the patients.
Many previous studies showed that only one region SPECT/CT commonly used in an area with equivocal lesions found by WBS.[4,17−18] We performed whole-body SPECT/CT from the base of the skull to the proximal femurs in all the patients no matter they have definite benign or malignant lesions on WBS. For these patients with lesions detected by WBS supporting the diagnosis of benign or malignant bone disease, even we founded additional lesions on SPECT/CT, the overall diagnosis would not be changed. But these findings could help us to confirm the true range of bone metastases. So, not only the equivocal lesions but also the other definitive benign or malignant lesions on WBS could be evaluated by the whole-body SPECT/CT.
Our study has some limitations. First was that the patients did not receive any biopsy of the bone lesions. Theoretically, our study should combine pathologic findings to confirm the diagnoses of malignant or benign lesion, but it’s not practical or necessarily ethical to perform bone biopsy for every lesion. Secondly, considering the findings based on MRI, plain radiography, follow-up bone scan, and CT as reference, it’s difficult to confirm the common reference standard in patients. Furthermore, the decision on which imaging methods to use as the reference standard in some of the patients was left to the referring physician.