Radiotherapy

In cancer biology, imaging and therapy are inextricably linked. In the case of the proposed Beamline 10 at the Australian Synchtrotron, the capabilities designed for excellent imaging are also ideally suited for the study and development of novel radiotherapy techniques.

The major problems with the radiotherapy lie in determining the extent of the spread of the disease and delivering sufficient radiation to the tumour without damaging surrounding healthy tissues. These problems are particularly acute in tumours where the surrounding tissue is extremely sensitive. Synchrotron radiation is able to deliver high doses only to the targetted areas significantly better than current clinical techniques. Three methods are currently under investigation at overseas synchrotrons: photon activation therapy (PAT), computed tomography (CT) therapy, and microbeam radiation therapy.

Photon activation and CT therapy both use specific X-ray energies that are preferentially absorbed by an element that has been delivered into the tumour. In PAT a chemical agent such as cis-platinum, which is also used in chemo-therapy, is introduced and concentrates in the tumour. By choosing the correct energy the X-ray beam interacts preferentially in the tumour and delivers a highly localized dose. CT therapy also uses a contrast agent such as iodine and that also concentrates in the tumour. It takes advantage of beam spreading effects and stereotactic methods to spare normal tissues.

Perhaps the most exciting possibility is MRT. Here, extremely large radiation doses are applied to tissues in an array of micrometre-thick highly collimated X-ray beams. The extraordinary aspect of microbeam radiation is that it spares healthy tissue far better than large-area beams of the same dose, and yet the tumour is still damaged. The method has been used with great effectiveness to deliver doses in excess of 1000 Gy to live animals; a dose of 10 Gy delivered using conventional methods is lethal. The reason for this effect is unknown but is a fertile area for further study

It is possible that therapies utilizing this effect may revolutionize the treatment of some kinds of cancers which are currently untreatable. A string programme of research into the nature of this effect, together with determining the most effective way of delivering the dose, is planned to be a significant activity on the Australian Synchrotron. However, it should be noted that much research will be required before MRT could be considered for clinical application.