Introduction

Peptide receptor radionuclide therapy (PRRT) is an effective treatment option for patients with well-differentiated somatostatin receptor-expressing neuroendocrine tumours (NETs)¹. While PRRT is considered a well-tolerated form of treatment, physiological uptake in normal tissues can lead to radiation induced organ toxicity. For the majority of patients, the kidneys will be the dose-limiting organ for a typical treatment schedule of ¹⁷⁷LuDOTA-TATE PRRT².

⁶⁸GaDOTA-TATE imaging of patients with NETs has shown that tumour sequestration is a major factor leading to a sink effect that decreases activity concentration in healthy tissues, particularly the renal parenchyma³.  Conversely, if a patient responds well during PRRT, a reduction in tumour burden could cause an increase in renal dose via a reduction in the sink effect.

Aims

1. To determine if patient response on ⁶⁸GaDOTA-TATE imaging leads to the reduction of the tumour sink effect.
2. To compare change in the sink effect between patients with high liver doses and low liver doses from response to PRRT.

Methods

From approximately 100 patients treated with PRRT in our facility, we retrospectively selected 2 groups of 10 patients, ones with the highest and others with the lowest liver dose estimated from ¹⁷⁷LuDOTA-TATE dosimetry studies.

Volumes of interest were placed on the liver and kidneys of the pre- and post-therapy ⁶⁸GaDOTA-TATE images to measure the change in tracer uptake. The liver VOI was chosen as a surrogate marker of overall whole body metastatic disease.

Results

A decrease in liver uptake showed a non-linear increase in kidney uptake. This result suggests that patients that respond well during PRRT may have varied, increased renal dose from cycle-to-cycle. This is contrary to the suggestion that that the cycle-to-cycle renal radiation dose can be predicted from a single precedent cycle with good accuracy based on a near zero change in the renal dose difference4.