Outcome of patients treated with cobalt and 6 MV in head and neck cancers.

BACKGROUND: Since 1992, we have been using a 6-MV linear accelerator instead of a cobalt machine. The aim of the study is to evaluate the impact of this on neck control, particularly on postoperative patients in which subcutaneous tissues are at risk.
METHOD: A retrospective study including all of 1,452 consecutive patients treated by definitive or postoperative radiotherapy between 1989 and 1997. All stages and subsites of the head/neck were included. Local and neck control were evaluated by the Kaplan Meier method, and comparisons were made between the cobalt and the 6-MV subgroups with a subsequent Cox analysis. For neck control analysis, the postoperative patients were divided in low and high risk (extracapsular extension [ECE], >two nodes, or T4).
RESULTS: Radical radiotherapy: A better local control (LC) is observed with 6 MV than with cobalt, but neck control was similar. Postoperative radiotherapy: A better LC is observed with 6 MV. In high-risk patients, the neck control was higher for the cobalt group (79%) vs 60% for the 6-MV group (p = .09 and .03 in a Cox model).
CONCLUSION: In postoperative patients at high risk for neck relapse, cobalt seems to give a better neck control. We are currently doing a prospective study in which a bolus is added for half the treatment when patients at high risk for neck relapse are treated with 6 MV.