Aim: This paper analyses whether the timing of interruptions during radiotherapy of squamous cell carcinomas of the head and neck influences treatment results.
Patients and methods: Hundred and ninety-two patients irradiated with curative intent between 1975 and 1985 (63% after surgery and 37 as primary treatment) were analysed with regard to the occurrence, timing, duration and causes of treatment interruptions. In a multivariate analysis, these factors as well as stage, site, extent of surgery etc. were related to 5-year survival rates.
Results: Interruptions of the prescribed course of radiotherapy decreased the survival rate from 61% to 28%. No adverse effect of a break was seen if it occurred during the first 3 weeks whereas survival dropped to 18 to 25% with a break later in the course of radiotherapy.
Conclusion: Timing of treatment interruption in squamous cell carcinomas is a crucial factor determining the chances of tumor cure. The detrimental effect of treatment interruptions increases as treatment progresses. This finding supports the hypothesis that tumor clonogen repopulation accelerates towards the end of radiotherapy of squamous cell carcinomas.