Relative clinical influence of tumor dose versus dose per fraction on the occurrence of late normal tissue morbidity following larynx radiotherapy.

Abstract

A study was made of 242 cases of T2 No glottic cancer treated by definitive radiotherapy over a 15-year period. The aim was to examine the relative influences of tumor biological dose (indicated by locoregional control) versus dose per fraction on the occurrence of late normal tissue effects; in addition, the impact of cord mobility on outcome was analyzed. The 5-year survival corrected for intercurrent deaths was 84% and local disease-free (larynx and/or nodes) survival was 76%. Using Cox regression analysis the only factor significant for local control was cord mobility (p < 0.0001) which also had an effect on overall survival (p < 0.0001); subdivision of T2 glottic staging should be reintroduced into staging classifications. It is evident that comparison of clinical results between centers is potentially prejudiced by an array of factors relating not only to fractionation differences but also variation in clinical and organizational aspects of care. Nevertheless, using other published data for comparison, it seems likely that the serious morbidity rate of 4.1% seen in this study is due in some part to the high tumor biological dose (resulting in high local control). The influence of fraction size was difficult to discern as equivalence in local control was not seen in the data chosen.