We have found an effective way of containing and then delivering this highly potent element directly into cancer cells

Dr David Scheinberg

They have also worked against samples of cells from a range of human cancers in the lab.

These include leukaemia, lymphoma, breast, ovarian, neuroblastoma, and prostate cancers.

The nanogenerators consist of radioactive atoms contained inside molecular cages and attached to antibodies which target specific types of cancer.

Inside a cancer cell, the atom decays by giving off high energy alpha particle radiation which tears through the cell's DNA and proteins.

Dr David Scheinberg, from the Memorial Sloan-Kettering Cancer Centre in New York, who led the scientific team, said: "We have found an effective way of containing and then delivering this highly potent element directly into cancer cells."

20 years

It took 20 years to develop the technology to the point where it was both effective and safe.

The mouse tests, modelling prostate cancer and widespread lymphoma, showed that a single low dose treatment could extend life.

The researchers, whose work was published in the journal Science, also found that very low concentrations could kill human cell cultures.

At the heart of each "bomb" is an atom of the radioactive element actinium-225.

When actinium decays, it produces a series of three daughter atoms, each of which gives off its own alpha particle.

"You get four times the punch from one atom," said Dr Scheinberg.

Keeping the generator inside the cell greatly reduced the possibility of alpha particles damaging healthy cells.

The team plans to apply to the US Food and Drug Administration for permission to begin human trials next year.

Leukaemia will probably be the first cancer the technique is tested on.

The research is published in the journal Science.