Image-based dosimetry for 225AcAc-PSMA-I&T therapy and the effect of daughter-specific pharmacokinetics

Abstract Purpose Although 221 Fr and 213 Bi have sufficient gamma emission probabilities, quantitative SPECT after 225 AcAc-PSMA-I 221 Fr, 24 ± 6/38 ± 11 h; 78 keV, 23 ± 7/39 ± 13 h. The 213 Bi-to- 221 Fr kidney SUV ratio increased by an average of 9% from 24 to 48 h. Urine analysis revealed an increasing 213 Bi-to- 225 Ac ratio (24 h, 0. 98 ± 0. 15; 48 h, 1. 08 ± 0. 09). Mean kidney and lesion absorbed doses were 0. 17 ± 0. 06 and 0. 36 ± 0. 1 {Sv}ₑ₁₄=5 Sv RBE = 5 /MBq using 221 Fr and 213 Bi SPECT images, compared to 0. 16 ± 0. 05/0. 18 ± 0. 06 and 0. 36 ± 0. 1/0. 38 ± 0. 1 {Sv}ₑ₁₄=5 Sv RBE = 5 /MBq considering either the 221 Fr or 213 Bi SPECT. Conclusion SPECT/CT imaging and urine analysis showed minor differences of up to 10% in the daughter-specific pharmacokinetics. These variances had a minimal impact on the lesion and kidney dosimetry which remained within 8%.