(UroToday.com) The 2024 GU ASCO annual meeting featured a prostate cancer session and a presentation by Dr. Hong Song discussing the clinical utility of rapid post-therapy whole-body digital SPECT/CT in evaluating early treatment response of 177Lu-PSMA-617 treatment. 177Lu-PSMA-617 radioligand therapy represents a significant advancement for metastatic castration resistant prostate cancer (mCRPC) and currently post-therapy SPECT-CT is conducted 24 hours after infusion. Multi-detector cadmium-zinc-telluride based whole-body digital SPECT/CT is a new generation of imaging system. The objective of this study was to assess the clinical utility of rapid post-therapy whole-body SPECT/CT scan in evaluating early treatment response of 177Lu-PSMA-617 treatment.
This study retrospectively reviewed patients with progressive mCRPC who were treated with at least two cycles of 177Lu-PSMA-617 at Stanford University from June 2022 to June 2023. Post-therapy whole-body digital SPECT/CT (GE StarGuide) was performed from vertex to mid-thigh at 1-2 hours after 177Lu-PSMA-617 infusion, and post-therapy SPECT/CT images were quantified with MIM software. 177Lu-PSMA positive lesions were delineated with liver parenchyma uptake as cut-off, and 177Lu-PSMA positive total tumor volume, tumor SUVmax, and SUVmean were obtained. Post-therapy SPECT/CT image after cycle 1 was used as baseline for comparison with SPECT/CT after cycles 2 and 3. Overall survival, PSA progression free survival as defined by PCWG3, and PSA decline > 50% from baseline (PSA50) at any time after treatment were measured. Changes in post-therapy SPECT/CT were correlated with clinical outcomes to assess quantitative SPECT/CT as a tool for early treatment response.
There were 68 patients treated with 177Lu-PSMA of which 56 patients (mean age 76 ± SD 8 years; range 60-93 years) who were imaged with at least two post-therapy SPECT/CT were included in the analysis. The following compares all patients to those who received at least two SPECT/CTs:
Post-therapy whole body SPECT/CT was acquired in approximately 12 mins, and all scanned patients tolerated the rapid whole-body SPECT/CT well. As shown are representative images of same-day post-therapy SPECT/CT for these patients:
With a median follow up of 10 months, median PSA progression free survival was 5.0 months (range 1.0-15 months), 33 of 56 patients (58.9%) achieved PSA50 at any time after treatment, and 42 of 56 patients (75%) were alive at data cutoff. Quantitative analysis of SPECT/CT images showed that 36 of 56 patients (64%) had a >30% decrease in Lu-PSMA positive total tumor volume on early follow-up post-therapy SPECT/CT after cycle 2 or 3:
Kaplan-Meier survival analysis showed that a >30% decrease in Lu-PSMA positive total tumor volume was associated with longer overall survival (median not reached vs 6 months, p = 0.008) and longer PSA progression free survival (6 months vs 1 month, p < 0.001):
However, a decrease in SUVmax or SUVmean was not associated with PSA progression free survival or overall survival.
Dr. Song concluded his presentation by discussing the clinical utility of rapid post-therapy whole-body digital SPECT/CT in evaluating early treatment response of 177Lu-PSMA-617 treatment with the following take-home points:
- This study showed successful implementation of same day post-therapy whole-body digital SPECT/CT following 177Lu-PSMA-617, with quantification of 1-2 hours post-therapy SPECT/CT images as a promising method for assessing treatment response
- Future research directions include improving methods for predicting and evaluating treatment response, expanding the utility of the whole-body SPECT/CT system in post-therapy evaluation in 177Lu-PSMA-617, and possibly to alpha emitter imaging
Presented by: Hong Song, MD, PhD, Stanford University, Palo Alto, CA
Written by: Zachary Klaassen, MD, MSc – Urologic Oncologist, Associate Professor of Urology, Georgia Cancer Center, Wellstar MCG Health, @zklaassen_md on Twitter during the 2024 American Society of Clinical Oncology Genitourinary (ASCO GU) Cancers Symposium, San Francisco, CA, January 25th – January 27th, 2024