Conformation therapy: a method of improving the tumour treatment volume ratio.

Restriction of the volume irradiated is a fundamental tenet of radiotherapy. Conventional two-dimensional treatment results in geometrically shaped high-dose regions, the sizes of which are defined by the greatest dimensions of a tumour mass. Conformation therapy permits a tumour to be considered for treatment as multiple short segments, and the radiation field to be tailored to fit each segment accurately. This paper demonstrates that this results in a reduction of the treatment volume of between 10% and 80%, depending on the shape of the tumour. Also, it is shown that a greater proportion of the high-dose region is occupied by tumour, thus reducing the volume of normal tissue treated to a high dose. Smaller treatment volumes allow the prescription of tumoricidal doses and improve the tolerance of radiation by patients.