Background: Several large randomised studies from western Europe and the USA have shown that accelerated fractionation of radiotherapy might be beneficial in the treatment of squamous-cell carcinoma of the head and neck (HNSCC). The aim of this study--the International Atomic Energy Agency (IAEA) ACC trial--was to determine whether accelerated fractionation could be applied in developing countries, where there are fewer therapeutic resources and where tumour burdens can be heavier.

Methods: Between Jan 6, 1999, to March 31, 2004, nine centres from Asia, Europe, the Middle East, Africa, and South America recruited patients with HNSCC of the larynx, pharynx, and oral cavity who were eligible for curative radiotherapy. Patients were randomly assigned in this open-label trial to receive an accelerated regimen of six fractions of radiotherapy per week (n=458) or to receive a conventional radiotherapy regimen of five fractions per week (n=450), receiving a total dose of 66-70 Gy in 33-35 fractions. Patients were stratified by tumour localisation, T classification, histopathological grade, and institution. Randomisation was done by a central computer-generated balanced randomisation algorithm. The primary endpoint was locoregional control, analysed for all eligible patients, irrespective of whether or not they had completed the course of radiotherapy. This trial is registered with ClinicalTrials.gov, number NCT00120211.

Findings: Six patients in the accelerated group and two in the conventional group were excluded from analyses because of withdrawal of consent or missing data. The planned total radiotherapy dose was received by 418 (92%) of the 452 eligible patients in the accelerated radiotherapy group and 413 (92%) of the 448 patients in the conventional radiotherapy group. Median treatment time was 40 days in the accelerated group and 47 days in the conventional group. The 5-year actuarial rate of locoregional control was 42% in the accelerated group versus 30% in the conventional group (hazard ratio [HR] 0.63, 95% CI 0.49-0.83; p=0.004). Acute morbidity in the form of confluent mucositis was noted in 45 patients in the accelerated group and 22 patients in the conventional group (2.15, 1.27-3.35); severe skin reactions were noted in 87 patients in the accelerated group and 50 patients in the conventional group (1.91, 1.31-2.79). There were no significant differences in late radiation side-effects.

Interpretation: An accelerated schedule of radiotherapy for HNSCC was more effective than conventional fractionation, and since it does not require additional resources, might be a suitable new worldwide standard baseline treatment for radiotherapy of HNSCC.

Funding: International Atomic Energy Agency, Coordinated Research Project (IAEA-CRP E.3.30.18), the Danish Cancer Society, the Danish Strategic Research Council, and the Lundbeck Centre for Interventional Research in Radiation Oncology (CIRRO).