A Novel Method of Quantitative Planar Scintigraphy for Theranostic Applications—Experimental Validation and Clinical Evaluation
Abstract
Purpose
Post-therapy quantitative imaging is essential for dosimetry-guided precision cancer treatment in theranostics. Although SPECT is the typical choice for post-therapy quantification, its routine clinical use is constrained by scanner availability, acquisition time, and workflow complexity. To mitigate these limitations, we propose a novel method for quantitative planar scintigraphy that exploits the similarity in biodistribution between diagnostic radiotracers (typically PET-based) and their therapeutic counterparts. This study presents experimental phantom validation and preliminary clinical evaluation of the proposed approach.
Methods
With this method, planar images were simulated by in-house software from diagnostic PET using device-specific imaging models and acquisition parameters. For each organ of interest, a conversion constant relating activity concentration measured in simulated planar images to volumetric activity concentration from diagnostic PET was derived and applied to physically acquired planar images to estimate volumetric activity concentration. Experimental validation was performed using ⁹⁹ᵐTc-filled cylindrical phantoms and scanned on an Intevo SPECT/CT system (Siemens Healthineers) following NEMA protocols, with evaluation of planar sensitivity and system volume sensitivity. For clinical evaluation, two anonymized datasets from patients treated with ¹⁷⁷Lu-DOTATATE, curated and publicly released by University of Michigan researchers, were utilized. Estimated activity concentrations from planar images were compared with SPECT-derived reference values in the kidneys, spleen, and liver parenchyma across four post-therapy time points.
Results
In phantom experiments, planar sensitivity and system volume sensitivity derived from simulated data agreed with experimental measurements within 10% for both LEHR and LEAP collimators. In clinical evaluation, differences between planar-based estimates and SPECT reference values were −7% ± 9% for patient A and −8% ± 15% for patient B.
Conclusion
The proposed method accurately reproduces planar imaging characteristics and demonstrates good preliminary agreement with SPECT-based quantification, supporting its feasibility as a practical alternative to SPECT for post-therapy quantitative imaging in theranostic applications.