The availability of lutetium-177 from research reactors

The expected increased clinical use of lutetium-177 (Lu-177, t1/2 6.71 d) will require cost effective routine availability of high levels of this radioisotope with high specific activity. The high 2090 b Lu- 176 thermal neutron capture cross section and apparent low Lu-177 burn-up cross section permit production of high sp. act. Lu-177 by the 'direct' Lu-176(n,γ))Lu-177g route with only low level contamination from the long-lived Lu-177m isomer (t1/2 =160 d). Very high thermal neutron flux (> 2 x 1015 neutrons/cm2/sec) can provide ∼75-90 Ci of Lu-177 per mg of Lu-176 target at saturation, which approaches the theoretical specific activity of 109 Ci/mg. Production of Lu-177 via the 'indirect' Yb-176(n,γ); σ = 2.4 b)Yb-177(t1/2 1.9 h; β- →)Lu-177 route is an attractive alternative since Lu-177m contamination is precluded. However, even the yields of Lu-177 produced by the indirect route (∼300 mCi Lu-177/mg Yb-176) at such very high thermal flux are ∼250 fold lower than by the direct route. In addition, this approach requires the effective separation of no-carrier-added (n.c.a.) Lu-177 from the macroscopic levels of the Yb target. With the lower 'indirect' Lu-177 production yields expected in modest flux reactors, very large enriched Yb-176 targets will be needed, with subsequent target recovery required. Although the effective separation of n.c.a. Lu-177 from Yb target has been demonstrated, it is doubtful that the very high multi-Curies levels of Lu-177 which would be required for extensive clinical trials or routine clinical use could be produced by this approach, which suffers from much lower yields, and costly and time consuming chemical processing. It is thus seems likely that large multi-Curie levels of high specific activity Lu-177 required for routine clinical use can only be cost-effectively produced by the 'direct' route in a high flux reactor with capabilities for on-line access to the reactor core. (author)