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

Objectives
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.Materials And Methods
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.Results
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.Conclusion
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.Clinical Relevance
Salivary radioactivity of patients undergoing 177Lu-RLT poses minimal risk to oral healthcare workers.