Sharp focus aids cancer treatment

University of Florida scientists have developed new technology to precisely target radiation beams at cancerous tumours found on the body’s internal organs.

The new system, now being sold commercially, is reported to employ three-dimensional imaging and optic guidance techniques to ensure that radiation therapy is directed only at tumours.

Conventional radiotherapy beams used to target tumours located anywhere but the head — such as in the prostate, breast or lung — typically include an extra margin to account for the uncertainty of a tumour’s location.

This uncertainty exists primarily because internal organs are not fixed in place; they can shift around slightly in relationship to a patient’s skin.

Through the new system, technicians can view up-to-the-minute 3-D ultrasound images of a tumour and receive step-by-step computer guidance in positioning the patient on the treatment table. Because there is no longer uncertainty about the tumour’s position, the radiation of surrounding normal tissue can be minimised.

‘Since we have better positioning and can avoid normal tissue, we’re also going to be trying to determine if we can improve cure rates by increasing the dose of radiation given to certain tumours and do it without getting increased side effects,’ said Frank J. Bova, the A.E. and B.W. Einstein professor of neurosurgery.

A clinical trial involving 120 patients is comparing the technology, dubbed SonArray, with conventional radiation targeting in patients with prostate cancer.

In the conventional treatment group, the tumour and a surrounding margin of 1 to 2 centimetres will be irradiated, said Dr. John Buatti, the University of Iowa’s director of radiation oncology. In the SonArray group, the surrounding margin will be smaller — from 0.2 to 1 centimetres. Both groups will receive the same radiation dose.

The groups will be evaluated to determine whether the new system reduces the incidence of adverse effects that often accompany radiation to the prostate, such as problems with bladder, bowel and sexual functioning.

In most cancer centres today, radiation oncologists design a patient’s radiation therapy using noninvasive computed tomography (or CT) images taken in the days or hours leading up to treatment.

The patient’s body is marked on the skin to indicate where the radiation should be directed. In some centres, the patient also is positioned to lie in a body mould as an extra measure to try to make sure the tumour is in the location indicated by the earlier CT scans.

‘Skin marks can help you get close, but they still may be a centimetre or two off-target,’ Bova said. ‘We know that the relationship between external skin marks and internal organs is not fixed.’

In the UF system, the treatment also is planned using CT scans, but at the actual time of therapy, the tumour’s location is again identified through a three-dimensional ultrasound scan.

‘We also use a laser optic guidance system that enables us to know the exact position of the tumour in the treatment room based upon the ultrasound images. We are able to determine where every pixel in the room is,’ added Bova.