# Radioactivity levels in the saliva of patients undergoing targeted radioligand therapy with [177Lu]Lu-PSMA-I&T and [177Lu]Lu-DOTA-TOC

## TL;DR

This study measures radioactive levels in saliva of patients undergoing radioligand therapy, finding minimal risk to healthcare workers.

## Contribution

The study provides new data on salivary radioactivity levels and their decay for two types of radioligand therapies.

## Key findings

- Salivary radioactivity peaks 2 hours post [177Lu]Lu-DOTA-TOC and 4 hours post [177Lu]Lu-PSMA-I&T.
- PSMA-I&T patients show ten times higher radioactivity turnover in saliva compared to DOTA-TOC patients.
- Radiation exposure to medical staff from patient saliva is considered minimal.

## Abstract

The number of patients receiving radioligand therapy (RLT) has risen sharply in recent years. This raises concerns about possible risks to dental healthcare workers due to their exposure to the patients and their saliva. We therefore set about to measure the salivary radioactivity in patients undergoing 177Lu–RLT.

We recruited in-house RLT patients receiving [177Lu]Lu -DOTA-TOC (n = 6) or [177Lu]Lu-PSMA-I&T (n = 14). We measured the radioactivity concentrations in 1 ml saliva samples collected before and 0.5, 2, 4, 21, 27, and 45 h post application of the radioligands, with additional samples collected at 51 and 69 h for [177Lu]Lu-PSMA-I&T patients. The biological half-life (BHL) and area under the curve (AUC) were calculated for the radioactivity of the saliva for both cohorts.

Both cohorts exhibited increases in salivary radioactivity, attaining peaks at 2 h p.i. of [177Lu]Lu-DOTA-TOC and 4 h p.i. of [177Lu]Lu-PSMA-I&T, and presenting with a significant decrease until the patients discharge. The median peak concentration for [177Lu]Lu-PSMA-I&T was four-fold higher than for the [177Lu]Lu-DOTA-TOC group. For PSMA-patients, the BHL was 14 h and the mean AUC was 895 kBqh/ml. For DOTA-TOC patients, these values were 8.5 h and 96 kBqh/ml, respectively.

Salivary radioactivity peaks earlier and at lower levels in [177Lu]Lu-DOTA-TOC patients compared to [177Lu]Lu-PSMA-I&T, which shows longer retention and ten times higher radioactivity turnover in saliva. However, radiation exposure to medical staff by the patents saliva can be considered minimal.

Salivary radioactivity of patients undergoing 177Lu-RLT poses minimal risk to oral healthcare workers.