Interim PET/CT scans predict which NET patients will benefit most from peptide receptor radionuclide therapy | Research

The takeaway

Changes in whole tumor volume and total receptor expression on interim 68Ga-DOTA-TOC PET/CT after 2 PRRT cycles significantly predicted progression-free survival in 24 NET patients (HR 3.3-3.9).

HR 3.9 for poor responders
Patients with <21% reduction in total receptor expression on interim PET had nearly 4x higher risk of disease progression during PRRT

What the researchers found

High ΔWTV (≥-10%): HR 3.053 (p=0.049); high ΔTRE (≥-21%): HR 3.567 (p=0.028) for shorter PFS. Both remained significant in multivariate analysis adjusted for WHO grade (HR 3.345 and 3.894). 66.7% of patients experienced progression.

Why it matters

PRRT is expensive and involves radiation exposure. Early identification of non-responders after 2 cycles could guide decisions about continuing PRRT versus switching to alternative therapies, improving both outcomes and resource utilization.

How the study worked

Retrospective analysis of 24 NET patients with basal and interim (after 2 PRRT cycles) 68Ga-DOTA-TOC PET/CT. Kaplan-Meier survival analysis, log-rank tests, and Cox proportional hazards regression.

What this study cannot tell us

Small sample (n=24). Retrospective single-center design. Cut-off thresholds need prospective validation. PFS used as endpoint rather than overall survival.

How to read the evidence

Small retrospective study with appropriate statistical methodology. Hypothesis-generating; needs prospective validation.

When this study was published

Published in 2025.

The bigger picture

Precision medicine in PRRT: rather than treating all patients the same, interim imaging can personalize treatment by identifying responders early. This approach could optimize outcomes while reducing unnecessary radiation in non-responders.

Questions still open

Should non-responders identified at interim stop PRRT or switch to combination therapy?
Can these PET parameters be standardized across institutions?
Would adding blood-based biomarkers improve predictive accuracy?

Common questions

What is interim PET/CT in PRRT?

It is a scan performed after 2 of the typical 4 treatment cycles of PRRT. By comparing tumor size and receptor expression with the pre-treatment scan, doctors can identify patients who are responding to treatment versus those who are not—potentially allowing earlier treatment adjustments.

Why is early response assessment important?

PRRT involves radioactive peptides that expose the body to radiation. If a patient is not responding after 2 cycles, continuing treatment provides radiation exposure without benefit. Early identification of non-responders allows switching to alternative therapies sooner.

Read the original research

Prognostic value of interim [68Ga]Ga-DOTA-TOC PET/CT in patients with neuroendocrine tumour who underwent peptide receptor radionuclide therapy.

European radiology, 35(5), 2559-2568

View on PubMed ↗Publisher’s paper ↗

Citation

Shin, Eonwoo; Kim, Yong-Il; Yoo, Changhoon; Shin, Yeokyeong; Ryoo, Baek-Yeol; Lee, Dong Yun; Ryu, Jin-Sook. (2025). Prognostic value of interim [68Ga]Ga-DOTA-TOC PET/CT in patients with neuroendocrine tumour who underwent peptide receptor radionuclide therapy.. European radiology, 35(5), 2559-2568. https://doi.org/10.1007/s00330-024-11116-5