The potential of <sup>223</sup>Ra and <sup>18</sup>F-fluoride imaging to predict bone lesion response to treatment with <sup>223</sup>Ra-dichloride in castration-resistant prostate cancer.
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<h4>Purpose</h4>The aims of this study were to calculate bone lesion absorbed doses resulting from a weight-based administration of <sup>223</sup>Ra-dichloride, to assess the relationship between those doses and corresponding <sup>18</sup>F-fluoride uptake and to assess the potential of quantitative <sup>18</sup>F-fluoride imaging to predict response to treatment.<h4>Methods</h4>Five patients received two intravenous injections of <sup>223</sup>Ra-dichloride, 6 weeks apart, at 110 kBq/kg whole-body weight. The biodistribution of <sup>223</sup>Ra in metastatic lesions as a function of time after administration as well as associated lesion dosimetry were determined from serial <sup>223</sup>Ra scans. PET/CT imaging using <sup>18</sup>F-fluoride was performed prior to the first treatment (baseline), and at week 6 immediately before the second treatment and at week 12 after baseline.<h4>Results</h4>Absorbed doses to metastatic bone lesions ranged from 0.6 Gy to 44.1 Gy. For individual patients, there was an average factor difference of 5.3 (range 2.5-11.0) between the maximum and minimum lesion dose. A relationship between lesion-absorbed doses and serial changes in <sup>18</sup>F-fluoride uptake was demonstrated (r<sup>2</sup> = 0.52). A log-linear relationship was demonstrated (r<sup>2</sup> = 0.77) between baseline measurements of <sup>18</sup>F-fluoride uptake prior to <sup>223</sup>Ra-dichloride therapy and changes in uptake 12 weeks after the first cycle of therapy. Correlations were also observed between both <sup>223</sup>Ra and <sup>18</sup>F-fluoride uptake in lesions (r = 0.75) as well as between <sup>223</sup>Ra absorbed dose and <sup>18</sup>F-fluoride uptake (r = 0.96).<h4>Conclusions</h4>There is both inter-patient and intra-patient heterogeneity of absorbed dose estimates to metastatic lesions. A relationship between <sup>223</sup>Ra lesion absorbed dose and subsequent lesion response was observed. Analysis of this small group of patients suggests that baseline uptake of <sup>18</sup>F-fluoride in bone metastases is significantly correlated with corresponding uptake of <sup>223</sup>Ra, the associated <sup>223</sup>Ra absorbed dose and subsequent lesion response to treatment.
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Clinical Trials, Phase I as Topic
Prostatic Neoplasms, Castration-Resistant
Positron Emission Tomography Computed Tomography
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European journal of nuclear medicine and molecular imaging, 2017, 44 (11), pp. 1832 - 1844