Bogusław Maciejewski
Cancer Center-Institute, Poland
Title: Time factor and dose fractionation in radiotherapy for head and neck cancer
Biography
Biography: Bogusław Maciejewski
Abstract
Results of our studies on dose fractionation and time factor for more than 1000 head and neck cancer cases are presented. For a constant total dose (TCD50) extension of overall treatment time (OTT) significantly decreases tumor cure probability by 1-1.50% per each one day extension of the OTT for laryngeal cancer. Further studies focused on oral cavity and oropharyngeal cancer and showed that due to accelerated repopulation of tumor clonogens starting about week 3 of irradiation of conventional fractionation 5 days/week, about 0.6 Gy/day (Drep) of 2.0 Gy fractions is balanced by repopulation. In early 80-ties it became a basic rationale for altered fractionation (accelerated, hyperfractionation and hybrid fractionation). There were over 50 clinical trials carried out through the next 20 years but meta-analysis of these results has shown only 6-7% overall therapeutic gain, much lower than expected. Because of various fractionation schedules, it is not possible to separate biological effect of dose escalation from that of changes in dose per fraction. When hypofractionated radiosurgery became the object of interest, there is promising perspectives to improve tumor local control at least for some tumor types and sites. The results of these studies will be presented and discussed.