Dynamic Changes in Tumor Burden in Patients Undergoing PSMA RLT

Area of Science:

• Nuclear medicine
• Oncology
• Radiology

Background:

• Metastatic castration-resistant prostate cancer (mCRPC) poses significant treatment challenges.
• Prostate-specific membrane antigen radioligand therapy (PSMA RLT) is an emerging treatment for mCRPC.
• Monitoring treatment response quantitatively is crucial for optimizing PSMA RLT.

Purpose of the Study:

• To evaluate quantitative changes in total metastatic tumor burden in mCRPC patients undergoing PSMA RLT.
• To assess the utility of SPECT/CT imaging in monitoring treatment response.
• To correlate imaging findings with prostate-specific antigen (PSA) levels.

Main Methods:

• Retrospective analysis of 331 mCRPC patients treated with PSMA RLT at two centers.
• Quantitative measurements of SUVmean, SUVmax, and total tumor volume (TTV) using post-treatment SPECT/CT.
• Calculation of median percentage changes in TTV and correlation with PSA response (PSA50).

Main Results:

• 58.4% of patients achieved PSA50 response.
• Early responders (≥30% TTV reduction between cycles 1-2) showed a 61.3% TTV reduction at cycle 2.
• Minimal responders (<30% TTV reduction) had gradual TTV decreases across cycles.
• A modest correlation between PSA and TTV changes was observed (r=0.318), with 43.6% discordance.
• Early responders had smaller tumor burden reductions in later cycles compared to minimal responders.

Conclusions:

• Dynamic changes in TTV on SPECT/CT are valuable for assessing PSMA RLT efficacy.
• SPECT/CT imaging can help identify early treatment responders and guide RLT strategy adjustments.
• The discordance between PSA and TTV suggests that imaging provides complementary information for treatment monitoring.