Postoperative irradiation in oral cavity and oropharyngeal tumours. Prognostic factors and dose-time relationships

In a retrospective study, local tumor control in 75 patients with oral cavity and oropharyngeal squamous cell carcinomas postoperatively irradiated was analysed with respect to initial tumor volume (T stage), regional nodal status (N stage), normalized total dose and time of treatment. The following conclusion were drawn: 1) overall treatment time and specially the time interval between surgery and radiotherapy influenced strongly the probability of tumor control: 2) an increase of 0.16 Gy/day, on average, was required for a constant control rate: 3) this increase in dose was attributed to the residual to surgery tumor clonogens growth rare: 4) such tumor growth seems to be a major determinant of failure in protracted treatments; 5) an average of 5-6 Gy was required to obtain an isocontrol dose 50% (TCD50) in T-3-T-4 tumors with respect to T-1-T-2 tumors; 6) the probability of local control was less likely in patients with clinically positive lymph nodes. It can be stared, as a general conclusion of this study, that postoperative irradiation of oral cavity and oropharyngeal tumors should be performed in the shortest time compatible with no reduction of dose below that necessary to assure tumor control.