COBALT BEAM THERAPHY

Press, Volume XCII, Issue 27795, 21 October 1955, Page 12

COBALT BEAM THERAPHY

EQUIPMENT AND USE DESCRIBED

UNIT FOR CHRISTCHURCH HOSPITAL

Although super-voltage equipment capable of delivering more than 20,000,000 volts was in use, the optimal dose medically‘ was 1,000,000 to 10,000,000 volts and, with an output equivalent to about 3,000,000 volts, the cobalt beam unit to be given to Christchurch by Sir Arthur Sims seemed the most desirable here for efficiency and simplicity, said Dr. A. J. Campbell, senior radiotherapist at the Christchurch Hospital, to the mathematics and physics section of the Canterbury branch of the Royal Society of New Zealand last evening.

Mor* voltage meant deeper penetration and greater tumour dose. The cobalt unit gave this without high voltage supply, cables, or tubes so that jn essence it was a radiotherapist’s dream, Dr. Campbell said. There was a head containing the radio-active cobalt, the table for the patient, and a control panel no more complicated than a radio—a marked contrast to the “Wurlitzer organ console” and other equipment of even a conventiofial Xray unit. Likely Patients Cobalt beam therapy was not the cure-all for cancer, Dr. Campbell said. Although intentions might be modified after staff had been overseas, it was planned to treat: (1) tumours m relation to bone and cartilage (mouth and larynx) in which results should be considerably better than orthodox radiotherapy and the effects of radiation much less; (2) deep-seated tumours of limited size where orthodox methods entailed complicated positioning of the patient (bladder, oesophagus, lung); (3) radio-resistant tumours not responding otherwise (soft tissue, brain, and certain inoperable glands). The hospital would probably not treat cases suitable for standard techniques, radio-sensitive tumours, and certain bone conditions. Over-all, treatment time might range from four to 10 weeks, but none would be undertaken without firm histologically proved diagnosis of patients fit to attend daily. The visible effects of cobalt beam therapy were usually slight redness of the skin after four or five weeks, going on to bronzing, with possibly,dry scaling after persisted treatment, but there would be nothing like the reaction of ordinary therapy and less discomfort, Dr. Campbell said. The hospital physicist (Mr R. A. Borthwick) was associated with Dr. Campbell, and explained the theory and practice of radiation and its varying absorption in bone, muscle, and fat. A high-energy unit gave less scattering and raised the dose without attack from multiple fields. He agreed that cobalt 60 was most suitable for Christchurch. Cobalt Source Shown A cobalt “source” (about the size of four stacked florins) and its surrounding “capsule” (the size of a conventional projector lens) were demonstrated by Mr Borthwick, and he explained the heavily-shielded transit container from which they were loaded into a beam unit and the spent ones extracted for reactivation. Supplies seemed assured as “sources” were produced in Britain, France, and the United States. The head of a cobalt beam unit weighed about a ton. Mr Borthwick said. The bulk was lead sheathing surrounded by steel in case this protection was melted by exterior fire from other sources. The aperture for the beam from the cobalt was lined with tungsten and the shutter was hydraulically operated, with automatic closing in case of any failure. As an aid to focusing, a light beam corresponded with the cobalt beam. Once the output was measured, there was ifo need for such frequent checking as with X-ray units because the rate of loss was known.

The treatment room was walled in concrete with a four-inch lead glass observation window, Mr Borthwick said. Automatic mechanism prevented the beam being applied unless the room doors were locked.

The most significant development in cobalt beam units was a rotating and oscillating head, which was always centred on the tumour but flashed rapidly over the body area in contrast to the fixed beam. This machine. Mr Borthwick said, could do almost anything.