Purpose: We wanted to study the influence of the time factor in a combination of external irradiation and brachytherapy from a retrospective study of 370 squamous cell carcinomas of soft palate and tonsil.
Patients and methods: From 1977 to 1993, 370 soft palate and tonsillar carcinomas were treated at the Centre Alexis Vautrin. All patients received external irradiation (ERT) with a minimum dose to the tumour of 45 Gy, followed by low dose rate brachytherapy by Iridium 192 using the technique of plastic tubes; 22 patients received neo-adjuvant chemotherapy. We treated 85 T1, 159 T2, 117 T3 and nine T4 or TX carcinomas; 128 of these had palpable nodes. There were 267 men and 24 women. The median age was 55 years (range 33-81 years).
Results: The median duration of the total treatment was 57 days. The rate of local control was 88% at 5 years when the treatment time was 7 weeks and 74% when it was 9 weeks (P = 0.001). The rates of overall survival at 5 years were 63 and 44%, respectively (P < 0.0001). For the interval between external irradiation and brachytherapy the series was divided into three groups, i.e. patients treated with a delay inferior or equal to 16 days (2 weeks), patients for which the interval was between 16 and 20 days and patients treated with a delay greater than 20 days (3 weeks). The rates of local control and overall survival at 5 years were not significantly different in the two first groups so we amalgamated these two groups and compared them with the third group. In this way the time cut-off for the delay between external irradiation and brachytherapy was 20 days. At 5 years, the rate of local control was 85% for the group for which the interval was inferior to 3 weeks and 73% when the delay was greater (P = 0.01). The rates of overall survival at 5 years were 59 and 38%, respectively (P < 0.001). Multivariate analysis confirmed that protraction of treatment was a factor for poorer local control. This factor was independent of the other prognostic factors.
Conclusion: The total duration of irradiation and the delay between external irradiation and brachytherapy were significant prognostic factors for local control and overall survival of soft palate and tonsil carcinomas. The overall duration should not be greater than 7 weeks (external irradiation, 5 weeks plus a delay of 12-15 days between ERT and brachytherapy). The delay should never be greater than 20 days, but a boost should be considered to make up for the loss of local control.