Cobalt 60 teletherapy for cancer: a revived treatment modality for the 21/sup st/ century

Using a modern, commercial, 3D treatment planning system, we have been able to demonstrate that comparable quality external beam treatment plans can be achieved using a cobalt unit, when compared to current practice on a linear accelerator fitted with a multi-leaf collimator (MLC). Other lesions that we have found to show equal promise include small to medium breasts, parotid gland, maxilliary antrum and oesophagus. The reduced energy dependence that is suggested in IMRT plans would, of course, require a well designed beam compensation system to be a practical and efficient alternative to MLC based linac treatments. However, for conformal radiotherapy, divergent blocks provide the gold standard of 'beams eye view' conformality with their 'infinitely small' leaf width resolution. In general, MLC's can increase the penumbra of linac beams up to and beyond conformally blocked cobalt fields.