Related Experiment Video
Updated: Jan 12, 2026
A Whole Body Dosimetry Protocol for Peptide-Receptor Radionuclide Therapy PRRT: 2D Planar Image and Hybrid 2D+3D SPECT/CT Image Methods
Published on: April 24, 2020
Concordance between single-time-point and multiple-time-point dosimetry in 177 Lu-PSMA-I&T therapy for metastatic
Nathaly Barbosa Parada1, Carlos Granados1, Edwin Pulido2
1Unit of Diagnostic Imaging and Nuclear Medicine.
Purpose:
To quantify concordance between single-time-point (STP) and multiple-time-point (MTP) dosimetry for organs-at-risk (OARs) and lesions in 177 Lu-PSMA-I&T.
Methods:
Thirteen men with metastatic castration-resistant prostate cancer underwent quantitative SPECT/CT at ~20, ~48, and ~120 h posttherapy. Lesions <3.0 cc were excluded. Time-activity curves (TACs) were fit with automatic model-order selection (parameters ≤ data points); accepted fits required R2 > 0.90. STP activity-time integrals were estimated with the Hänscheid formalism. Agreement metrics included paired median differences, Lin's concordance, and Bland-Altman bias/limits of agreement.
Results:
For OARs, STP at ~48 h matched MTP with minimal bias (parotids Δ = 0.00 Gy/GBq, P = 0.475; kidneys Δ = 0.02, P = 0.157). Lesion concordance improved with later imaging (STP2-STP3), whereas ~20 h STP underestimated lesion dose coefficients (all lesions Δ = +0.36 Gy/GBq; +57.4%). TAC modeling favored mono-exponential kinetics in most lesions (83%) and kidneys, with mixed behavior in parotids.
Conclusion:
A single quantitative scan at ~48 h provides OAR dosimetry concordant with MTP, while lesion estimates are best captured at ~48-120 h. Early STP imaging (~20 h) should not be used alone for lesions. Findings support a pragmatic, concordance-oriented dosimetry workflow for routine 177 Lu-PSMA-I&T care.
