Predictive Value of Potential Doubling Time for Radiotherapy of Head and Neck Tumor Patients: Results from the EORTC Cooperative Trial 22851

R epopulation of surviving cells between doses in a fractionated radiotherapy schedule could potentially limit tumor control. Such repopulation would increase the effective number of cells needed to be killed, leading to a greater chance of surviving cells remaining after standard dose radiotherapy in rapidly growing tumors. This has been recognized to play a significant role in head and neck tumors, and in other sites] -3 One way to circumvent this problem is to give the radiotherapy in a shorter overall time, ie, accelerated radiotherapy. The EORTC Radiotherapy group instituted a randomized phase III trial in 1985 to test this approach in head and neck tumors (trial 22851). Methods to monitor tumor proliferation rates have developed over the last decade to a point where they can be applied to measurements of human tumors in situ, necessitating taking, in some cases, only a single biopsy. 4-9 These methods were applied in the present trial to test the potential of these methods in predicting those patients who are at risk from conventional radiotherapy due to the presence of a relatively rapidly growing tumor. Their addition to a randomized trial is the best means of testing the usefulness of predictive assays, although it represents a retrospective analysis, ie, correlations with outcome are done at the end of the trial. Depending on predictive success, future trials could be designed in which the treatment is dependent on the predictor. This article reports on the results of the cell kinetic data obtained to date in EORTC trial 22851 and how these data correlate with outcome. This represents an update of a previous report. ~ A corn