The technique, known as prone radiation and common practice in the US, is helpful for women with larger breasts who are harder to treat in the traditional position lying on their back.
When patients receive radiotherapy - a powerful form of X-ray radiation which destroys cancer cells - to their left breast, the heart is also at risk of receiving radiation, due to its location on that side of the chest.
This can damage the heart muscle, causing a condition called cardiotoxicity, and can lead to symptoms and complications one to two years after treatment. Chemotherapy also increases the risk.
Such radiotherapy also raises the risk of death from cardiac-related causes such as pericarditis - swelling around the heart that causes chest pain, coronary artery disease, heart attack or heart rhythm problems.
Treatments that shield or reduce the heart from radiation are vital now that breast cancer patients are living longer.
Javeria Iqbal, senior breast radiographer at the Royal Free Hospital, London, is one of a team at the hospital leading the new technique.
She says: “When delivering radiotherapy, it is important that the whole breast receives the radiation, but that other parts of the body are affected as little as possible.”
One commonly used technique in patients with cancer in their left breast is called deep inspiration breath hold (DIBH).
By taking a deep breath in and holding it in the lungs for 20 to 25 seconds, the chest wall is lifted away from the heart during treatment.
This creates a gap between the heart and the breast receiving treatment, reducing the risk of damage.
A special mouthpiece - a spirometer - measures the breath. If the patient coughs or needs to take a breath, the device senses it and cuts off the delivery of radiation.
“The problem is that not all patients can hold their breath for this time, or can tolerate the mouthpiece," says Iqbal.
While patients lie on their back during radiotherapy, large or less-firm breasts - more than a D-cup size - can spread or hang to the sides, making them difficult to treat safely. And since the radiographers are treating a bigger area to target the cancer, they are creating more radiation which means an extra risk to the heart.
Prone radiotherapy means that even large-breasted patients can safely have the whole breast treated while minimising damage to the heart. This is because by lying on their front, the patient’s breast cannot spread in all directions, as they naturally fall to the front.
The radiographer uses different angles, directing radiation tangentially from two sides at the breast. Iqbal says that the technique has already shown reduced radiation doses to the heart in comparison to the usual method.