# Minimising the impact of stable 208Pb on recovery of 212Pb from a generator

## TL;DR

This paper models how stable 208Pb accumulates in 212Pb generators over time and determines optimal elution times to maximize radiopharmaceutical efficiency.

## Contribution

The study introduces a matrix-based model to calculate optimal elution times for 212Pb generators while accounting for 208Pb accumulation.

## Key findings

- Optimal elution time for 224Ra generators is 16.5 hours, achieving 6997 MBq 212Pb/nmol total Pb.
- Optimal elution time for 228Th generators is 19.2 hours, achieving 6566 MBq 212Pb/nmol total Pb.
- Current 208Pb levels in literature do not hinder pre-clinical or clinical molar activity requirements.

## Abstract

Stable 208Pb will accumulate over time in all 212Pb generators, forming an increasing proportion of the Pb atoms and potentially impacting the efficiency of chelation of 212Pb. This paper models the accumulation of 208Pb in 212Pb-parent generators with time, calculates the optimal elution time with respect to effective specific activity (ESA) of the 212Pb produced, and considers whether the presence of 208Pb could prevent the required molar activities (Am) being achieved. A matrix calculation was utilised to model the decay of 224Ra and 228Th parents in generators and the associated accumulation of 208Pb with time. This model was used to calculate the optimal elution times for each generator with respect to ESA and Am.

The optimal elution time with respect to Am of 212Pb is 16.5 h for a 224Ra generator (61.0% of 224Ra starting activity, Am = 6997 MBq 212Pb/nmol total Pb) and 19.2 h for a 228Th generator (71.4% of 228Th starting activity, Am = 6566 MBq 212Pb/nmol total Pb).

The limited data available in literature shows the level of 208Pb present in these studies does not prevent attainment of the required molar activities for pre-clinical or clinical work. However, with other chelators and under other conditions this may not be the case. The authors would encourage others to measure and report the level of 208Pb in 212Pb generator eluates alongside radiolabelling results and the max Am of the radiopharmaceutical 212Pb (vector molecule (VM)) achieved.

The online version contains supplementary material available at 10.1186/s41181-025-00357-4.