Influence of interfraction interval on the efficacy and toxicity of hyperfractionated radiotherapy in combination with concurrent daily chemotherapy in Stage III non-small-cell lung cancer

Purpose: To investigate the influence of the interfraction interval (IFI) on treatment outcome and toxicity in hyperfractionated (HF) radiotherapy (RT) for Stage III non-small-cell lung cancer. Methods and Materials: Data for 301 patients treated with 1.2 Gy b.i.d. to a total of 69.6 Gy and concurrent chemotherapy in our 3 prospective studies were analyzed. The chemotherapy regimen was either (1) 50 mg each of carboplatin and etoposide (CE) given on RT days (163 patients) or (2) 30 mg of CE on RT days and 100 mg of CE on Saturdays and Sundays during the RT course (138 patients). An IFI of 4.5-5 h or 5.5-6 h had been nonrandomly assigned for each patient, and this interval was kept throughout the treatment. Results: No difference was observed in treatment outcome due to the chemotherapy protocol, and the 2 groups were combined. Patients treated with the shorter IFI had a better local control rate (38% at 5 years) and survival rate (30% at 5 years) than those treated with the longer interval (23% and 14%, respectively; p<0.001). However, female patients and those with a high Karnofsky performance status score (KPS), weight loss of ≤5% in the previous 6 months, or Stage IIIA disease had been more often treated with the shorter IFI, and these characteristics were associated with better treatment outcome. In multivariate analysis, only gender, KPS, and weight change proved to be significant prognostic factors influencing both local control and survival, and the effect of IFI was not significant. The incidence of Grade 4 acute esophagitis tended to be higher in the shorter interval group (p=0.072), but there were no differences in the incidence of late or other acute RT-related toxicities between the 2 groups. Conclusions: The possible influence of the IFI on local control and survival could not be verified using multivariate analysis. To better understand the influence of the IFI, randomized studies with more patients and wider ranges of intervals (e.g., 5 h vs. 8 h) seem to be necessary