Prognostic Value of SPECT-CT Quantitative Indices for the Response Assessment of Bone Metastatic Prostate Carcinoma

Prostate adenocarcinoma is one of the most common cancer in men, and bone its most frequent distant metastasis location. 5-year survival has greatly increased these last two decades, with wide differences between countries. Nevertheless, the prognosis of castrate-resistant bone metastatic prostate cancer (BMPC) remains poor.

PCWG (Prostate Cancer Working Group) 2 has proposed in 2007 criteria to evaluate response to treatment for prostate cancer. There are based on composite data, including clinical signs (such as general condition and bone pain), Prostatic Specific Antigen (PSA) variation, CT scan (RECIST criteria) and bone scan. The scintigraphic part is based on whole body planar acquisition, and on the assessment of new uptakes. These bone scan criteria are simplistic, because only a visual analysis is possible, without consideration of changes in intensity. Moreover, these criteria consider the bone scan as a planar imaging, and it has been shown that Single Photon Emission Computed Tomography (SPECT) improved sensitivity, specificity, positive and negative predictive values in oncologic context. Finally, "PCWG2 (Prostate Cancer Working Group 2) recognizes that there are no validated criteria for response on radionuclide bone scan".

To reflect bone metastasis burden, a quantitative analysis method for bone scintigraphy, the Bone Scan Index (BSI), had been tested. BSI is based on the uptake of whole body planar imaging. While baseline BSI seemed to offer a poor correlation with overall survival (OS), on-treatment changes in BSI appeared to be a decent response marker. But a volumetric quantitative biomarker may improve the accuracy of this assessment.

The recent development of a new SPECT quantification tool (xSPECT Quant® tool, Siemens) could offer good performances on therapeutic assessment. The objective of this study is to assess the interest of this new quantitative volumetric method in bone scan response evaluation of BMPC.