ABSTRACT
Radiobiological effects depend greatly on the nature of the tissue in question and how the physical dose is received which is defined by the treatment time, dose rate, and fractionation scheme. An important component of comparing the efficacy of various fractionation and dose rate regimes is their effect on tumor control and normal tissues. The expectations for a therapeutic gain from the implementation of these treatment schedules are mainly based on radiobiological modeling. Radiotherapy is often the primary treatment of locally advanced squamous cell head and neck cancer, but the optimal fractionation schedule has been controversial. The aim of clinical radiotherapy is to obtain for each cancer patient the highest probability of tumor control while minimizing the probability of late complications. The patients those who were put on the hyperfractionation method were treated with parallel opposing fields in the head and neck region same as the conventional fractionation patients.
