Conformation therapy at the Royal Free Hospital. A progress report on the tracking cobalt project

A computer-controlled tracking cobalt unit (CCTCU) was commissioned for treating patients in January 1980. The system has proved to be reliable and acceptable in routine use for conventional and conformation therapy. The system comprises a modified TEM MS90 Mobaltron, a Hewlett-Packard System 1000 Model 30 mini-computer and user programmes. Tracking techniques are suitable for the treatment of tumours of the oesophagus, thyroid, bronchus, chains of lymph nodes or medulloblastoma. Tumours 85 cm long can be treated at the isocentre. The high dose volume may be considerably reduced when tracking techniques are used instead of conventional techniques. The major obstacle to the routine use of conformation therapy is treatment planning. Work in progress is designed to produce a computerized planning system linking a CT scanner and the CCTCU. It is expected that the system will produce both a plan optimized in 3-D and the necessary control data in machine readable form within an hour of a patient being scanned. The present planning system is based on a Rad-8 planning system and an Alderson phantom to verify the dose distribution in 3-D. An outline of the tracking technique is given. The computer control system is described briefly, with its methods of use for treating patients. Brief reverence is made to work at other centres using conformation therapy.