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HIT cancerous tumours with radiation at just the right time and you can boost
your killing power. That’s the message coming from a model of how cancer cells
behave.

Cancerous cells are more resistant to radiation at certain times in their
life cycle. They are particularly impervious when they’re duplicating their DNA,
since they are actively checking for mistakes in the genetic code and repairing
them. At that point “they’re relatively bulletproof,” says Norman Kirkby, a
biochemical engineer from the University of Surrey.

Radiologists would like to treat patients when most cancer cells are in a
more vulnerable phase. But it’s difficult to know when to strike since cells
don’t synchronise their life cycles, and there can be a host of different cell
types within a single tumour. So Kirkby developed a computer model that mimics
the complex behaviour of several cell lines. He explained his work at the
Institute of Physics Simulation and Modelling Applied to Medicine conference in
London this week. Susan Short from the Gray Cancer Institute in north-west
London tested the sensitivity of a brain cancer cell line called T98G to varying
amounts of radiation. When Kirkby plugged Short’s data into his model, he found
that 40 to 50 per cent more cells died after doses of 0.5 grays three times a
day over 6 weeks, than on the normal treatment of 2 grays once a day. That might
not make a big difference to the death rate for patients with brain cancer, he
says, but it would help reduce side effects by cutting patients’ overall
exposure to radiation.

Kirkby hopes the same principle will work for other cancers, and he is
designing more complex models that should be able to pinpoint the best times to
treat tumours to within about 15 minutes. But he admits that hospitals might
find it impossible to organise treatments that precisely.