Fast [177Lu]Lu-PSMA SPECT/CT with dual-energy acquisition and Monte Carlo-based scatter correction

Whole-body post-therapy SPECT/CT plays an important role in [177Lu]Lu-PSMA-617 (LuPSMA) radiopharmaceutical therapy for verifying biodistribution, assessing treatment response, and performing radiation dosimetry. However, conventional dual-head NaI(Tl)-based scanners typically require lengthy scans, which can be resource-intensive and challenging for patient compliance, limiting their routine use in clinical practice. This study explores reducing acquisition duration using dual-energy peaks to increase count statistics and Monte Carlo-based scatter correction (MCS) to maintain image quality and quantitative accuracy under low-count conditions. LuPSMA scans (33 studies from 29 patients) covering mid-thigh to vertex (3 bed positions) were acquired using a dual-head NaI(Tl)-based scanner (Siemens Intevo) with both 208 and 113 keV photopeaks and corresponding scatter windows. Full-duration 12 min/bed acquisitions were reconstructed using MCS (Hermia SPECT Reconstruction, Hermes) and the scanner’s energy-window-based scatter correction (EWS), where MCS reconstruction at 12 min/bed served as the reference standard. Shorter-duration projections (1.5, 3, and 6 min/bed) were synthetically generated and reconstructed using MCS. Image quality metrics, including bias, coefficient of variation (CV), contrast ratio (CR), and signal-to-noise ratio (SNR), were evaluated across segmented organs and tumors. MCS reconstructions at 1.5–6 min/bed showed < 6% bias in mean organ uptake (median ~ 2%) relative to the 12 min/bed MCS (reference), significantly lower (p < 0.01) than the bias for 12 min/bed EWS (median ~ 3%). For mean tumor uptake, 3–6 min/bed MCS showed < 10% bias (median ~ 5%), with no significant difference from 12 min/bed EWS (median ~ 6%). CR remained consistent across all reconstructions (median ~ 5). MCS at 12 min/bed had slightly better CV, CR, and SNR than EWS at 12 min/bed, though differences were not statistically significant. MCS at 6 min/bed was not significantly different from either full-duration reconstruction. Visual assessments supported these findings, with MCS benefits over EWS more pronounced at lower count levels. These findings indicate that using dual-energy acquisition with MCS, scan times as short as 3–6 min/bed on conventional NaI(Tl)-based scanners maintain sufficient image quality for lesion detection, therapy monitoring, and dosimetry. These reductions in scan time could facilitate the routine implementation of post-LuPSMA SPECT/CT in clinical practice.