[¹⁷⁷Lu]Lu-PSMA SPECT/CT for early response assessment using quantitative RECIP 1.0

Area of Science:

• Nuclear Medicine
• Oncology
• Radiopharmaceutical Therapy

Background:

• Metastatic castration-resistant prostate cancer (mCRPC) requires effective prognostic tools for treatment stratification.
• Lutetium-177 (¹⁷⁷Lu) labeled PSMA radioligand therapy (RLT) is a promising treatment for mCRPC.
• Early assessment of treatment response can guide therapeutic decisions.

Purpose of the Study:

• To evaluate the prognostic value of the Response Evaluation Criteria in PSMA imaging (RECIP 1.0) at the second cycle of ¹⁷⁷Lu-PSMA-RLT.
• To assess the predictive capability of RECIP 1.0 for progression-free survival (PSA-PFS) and overall survival (OS) in mCRPC patients.

Main Methods:

• Retrospective analysis of 136 mCRPC patients treated with ≥2 cycles of [¹⁷⁷Lu]Lu-PSMA-I&T.
• 24-hour post-therapy SPECT/CT imaging at cycles 1 and 2 to measure SUVmean, SUVmax, and total tumor volume (TTV).
• Patients classified as RECIP-PD (progressive disease) or RECIP-non-PD; survival analysis using Cox regression and Kaplan-Meier curves.

Main Results:

• RECIP 1.0 classification at cycle 2 significantly predicted shorter PSA-PFS and OS (HR=3.6 and HR=3.1, respectively; p<0.001).
• Increased SUVmean, TTV increase ≥20%, and new lesions were associated with poorer outcomes.
• RECIP 1.0 demonstrated high prognostic accuracy (Harrell's C-index: PSA-PFS=0.80, OS=0.78).

Conclusions:

• Quantitative RECIP 1.0 applied to cycle 2 ¹⁷⁷Lu-PSMA SPECT/CT serves as an independent prognostic tool.
• It enables early identification of mCRPC patients unlikely to benefit from continued ¹⁷⁷Lu-PSMA-RLT.
• Prospective validation is recommended before clinical implementation for treatment management changes.