RESUMEN
For improving radiotherapy treatment results, altered fractionation (AF) is one of the most important biological factors to modify the conventional fractionation schedule. AF is classified into two categories. One is decreasing in dose-per-fraction and increasing in total dose, so-called hyperfractionation (HF), which expands the difference in radio-sensitivity between tumor and normal tissue. On the other hand, shortening of overall treatment time, so-called accelerated hyperfractionation (AHF), prevents accelerated repopulation of tumor cells during radiotherapy. AF is rarely recognized as a standard therapy despite many reports about its efficacy against various cancers, totally. This is often used for head and neck cancer. However, the problem is that they usually improve local-control, but do not always improve survival. Although AHF is recognized as one of a standard treatment for small cell lung cancer, it is still objectionable and disputable. Besides these, efficacy of AF against non-small cell lung cancer, bladder cancer and malignant glioma, has been reported. However, AF is not considered as a standard treatment. Accompanied with spread out of stereotactic irradiation, dose-fractionation-time relationship becomes to be more important subject, especially hypofractionation, to clarify the new aspect of AF.
