Biologic basis of radiation therapy.

The biologic effects of ionizing radiation are well understood. The limitations of radiation therapy time-dose schemes typically used in veterinary medicine are also well understood. Before expensive and potentially toxic combinations of treatment, such as radiation combined with chemotherapy or radiation combined with hyperthermia, can be fully understood, the effect of optimizing the manner in which radiation itself is administered must first be defined. This will only occur after a sufficient period of observation after improvement of the radiation time-dose schemes in use today. Also, when evaluating historic data regarding the response of canine and feline tumors to irradiation, the time-dose scheme used must be considered. Many papers were published based on coarsely fractionated schemes using large doses per fraction and relatively low total doses. Thus, the response rates published must be tempered by the fact that it may be possible to obtain better tumor control rates using smaller doses per fraction and a larger total dose.