The Prognostic Value of Quantitative Bone SPECT/CT Before <sup>223</sup>Ra Treatment in Metastatic Castration-Resistant Prostate Cancer
Helmut Dittmann, Sabine Kaltenbach, Matthias Weissinger, Francesco Fiz, Peter Martus, Maren Pritzkow, Juergen Kupferschlaeger, Christian la Fougère
Abstract
Radiolabeled bisphosphonates such as <sup>99m</sup>Tc-3,3-diphosphono-1,2-propanodicarboxylic acid (<sup>99m</sup>Tc-DPD) typically show intense uptake in skeletal metastases from metastatic castration-resistant prostate cancer (mCRPC). Extensive bone involvement is regarded as a risk factor for mCRPC patients treated with <sup>223</sup>Ra-dichloride (<sup>223</sup>Ra). The aim of this study was to quantify <sup>99m</sup>Tc-DPD uptake by means of SPECT/CT before <sup>223</sup>Ra and compare the results with the feasibility of treatment and overall survival (OS). <b>Methods:</b> Sixty consecutive mCRPC patients were prospectively included in this study. SPECT/CT of the central skeleton covering the skull to the mid-femoral level was performed before the first cycle of <sup>223</sup>Ra. The bone compartment was defined by means of low-dose CT. Emission data were corrected for scatter, attenuation, and decay supplemented by resolution recovery using dedicated software. The Kaplan–Meier estimator, <i>U</i> test, and Cox regression analysis were used for statistics. <b>Results:</b> Total <sup>99m</sup>Tc-DPD uptake of the central skeleton varied between 11% and 56% of injected dose (%ID) or between 1.8 and 10.5 %ID/1,000 mL of bone volume (%ID/L). SUV<sub>mean</sub> ranged from 1.9 to 7.4, whereas the SUV<sub>max</sub> range was 18–248. Patients unable to complete <sup>223</sup>Ra treatment because of progression and/or cytopenia (<i>n</i> = 23) showed significantly higher uptake (31.9 vs. 25.4 %ID and 6.0 vs. 4.7 %ID/L; <i>P</i> < 0.02). OS after <sup>223</sup>Ra (median, 15.2 mo) was reduced to 7.3 mo in cases of skeletal uptake that was 26 %ID or higher, as compared with 30.8 mo if lower than 26 %ID (<i>P</i> = 0.008). Similar results were obtained for %ID/L and SUV<sub>mean</sub>. SUV<sub>max</sub> did not correlate with survival. %ID/L was identified as an independent prognostic factor for OS (hazard ratio, 1.381 per unit), along with number of previous treatment lines. <b>Conclusion:</b> Quantitative SPECT/CT of bone scans performed at baseline is prognostic for survival in mCRPC patients treated with <sup>223</sup>Ra.