Shortages of rare nuclear isotopes that rapidly shrink tumours threaten to undermine the development of breakthrough treatments in which health companies have invested billions of dollars, experts in the nascent radiopharmaceuticals field have warned.

By combining a nuclear isotope with an antibody, the microscopic drugs — also known as radioligands — deliver a toxic payload directly to cancer cells. But actinium-225, the most common isotope used in the experimental treatment, whose decaying protons and neutrons emit powerful “alpha” radiation, is in increasingly low supply.

Reliant largely on dwindling supplies from Soviet and American cold war-era stockpiles of precursor radioactive materials, companies have struggled to obtain enough actinium to treat the thousands of patients being enrolled in clinical trials.