Biodistribution and dosimetry for combined [177Lu]Lu-PSMA-I&T/[225Ac]Ac-PSMA-I&T therapy using multi-isotope quantitative SPECT imaging
Astrid Delker, Mirjam Schleske, Grigory Liubchenko, I. Berg, Mathias J. Zacherl, Matthias Brendel, Franz Josef Gildehaus, Mikhail Rumiantcev, Sandra Resch, Kerstin Hürkamp, Vera Wenter, Lena M. Unterrainer, Peter Bartenstein, Sibylle Ziegler, Leonie Beyer, Guido Böning
Abstract
Abstract Purpose Quantitative SPECT for patient-specific dosimetry is a valuable tool in the scope of radionuclide therapy, although its clinical application for 225 Ac-based treatments may be limited due to low therapeutic activities. Therefore, the aim of this study was to demonstrate the feasibility of clinical quantitative low-count SPECT imaging during [ 177 Lu]Lu-PSMA-I&T/[ 225 Ac]Ac-PSMA-I&T treatment. Methods Eight prostate cancer patients (1000 MBq/8 MBq [ 177 Lu]Lu-PSMA-I&T/[ 225 Ac]Ac-PSMA-I&T) received a single-bed quantitative 177 Lu/ 225 Ac SPECT/CT acquisition (1 h) at 24 h post treatment (high-energy collimator, 16 projections p. head à 3.5 min, 128 × 128 pixel). The gamma peak at 440 keV (width: 10%) of the progeny 213 Bi was imaged along with the peak at 208 keV (width: 15%) of 177 Lu. Quantification included CT-based attenuation and window-based scatter correction plus resolution modelling. Gaussian post-filtering with a full-width-half-maximum of 30 mm and 40–45 mm was employed to match the signal-to-noise ratio of 225 Ac and 177 Lu, respectively. Results Kidney ( r = 0.96, p < 0.01) and lesion ( r = 0.94, p < 0.01) SUV for [ 177 Lu]Lu-PSMA-I&T and [ 225 Ac]Ac-PSMA-I&T showed a strong and significant correlation. Kidney SUV were significantly higher ( p < 0.01) for [ 225 Ac]Ac-PSMA-I&T (2.5 ± 0.8 vs. 2.1 ± 0.9), while for [ 177 Lu]Lu-PSMA-I&T lesion SUV were significantly higher ( p = 0.03; 1.8 ± 1.1 vs. 2.1 ± 1.5). For absorbed dose estimates, significant differences regarding the kidneys remained, while no significant differences for lesion dosimetry were found. Conclusion Quantitative low-count SPECT imaging of the peak at 440 keV during [ 225 Ac]Ac-PSMA-I&T therapy is feasible. Multi-isotope imaging for [ 177 Lu]Lu-PSMA-I&T/[ 225 Ac]Ac-PSMA-I&T therapy indicates accumulation of free 213 Bi in the kidneys.