Pioneering therapy using a hyperbaric chamber is being used on patients in Plymouth to reduce the side effects of breast cancer treatment.
The Diving Diseases Research Centre (DDRC), which deals with deep sea divers who suffer the bends, is carrying out clinical trials.
Experts believe breathing in pure oxygen in the chamber could relieve a painful side effect of radiotherapy.
The six-week trial is being funded by Cancer Research UK.
Dr Phil Bryson, the medical director at DDRC, said: "We have one particular patient who's taking part in a trial looking at lymphoedema - that's swelling of the arm following radiotherapy.
"What we'll be doing over the next few weeks is giving her the treatment and taking biopsies. She'll be having volumetric measurements of the arm and we'll be noting how she's feeling and how she's doing."
Dr Bryson said the oxygen dissolves into the blood and is taken to the area where the tissue is damaged, which is short of oxygen.
Patient Peggy McKenna, who has suffered from lymphoedema since her breast cancer treatment, said it has affected her life.
"It makes it awfully difficult for you to find clothes to wear - you can't get them on because your arm is too big and that's a problem," she said.
"It aches a little, though not too badly. Generally it's discomfort and it's unpleasant. I've tried many things, but nothing seemed to work."
While patients are breathing in the pure oxygen, under transparent domed hoods, they are able to sit and read or watch a film in a specially built-in screen in the chamber.
The trial is being carried out in conjunction with the Royal Marsden Hospital.