Medical uses of cyclotrons: treatment and diagnosis

The application of cyclotrons in medicine was foreseen very early in their development. The two main uses were expected to be production of artificial radionuclides and treatment of cancer with neutrons; today these are still the main uses together with activation analysis, radiobiology and treatment with charged-particle beams. The first cyclotron designed exclusively for medical use is the one at Hammersmith Hospital: there are now at least ten in different countries and many more which are applied to medical problems for part of the time. Neutron therapy was initiated from the desire to use a form of radiation whose effects were less dependent on the concentration of oxygen in tumours. Assessment of the value of neutron therapy has been plagued by technical difficulties with existing machines: poor penetration, beams fixed in the horizontal position, poor collimation, lack of adjustable field and hazards from radioactivity. New machines at present in production are designed to overcome these problems. Direct use of charged-particle beams is an attractive idea but high energies are needed for useful penetration into the body and ions heavier than He are needed to give reduced dependence on oxygen. Neutron beams have also been used for measurement of total-body Ca and N by activation analysis in vivo. The dose received by the patient has to be severely limited but sufficient precision can be obtained to aid medical research. Production of radionuclides remains the principal medical use of cyclotrons. 15O and 11C are particularly important and their use demands that the cyclotron should be in the hospital. Positron-emission tomography is now beginning to allow us to measure functional parameters in the brain, lungs and heart. This is the area in which the most exciting new developments seem likely