Can radiobiological parameters derived from squamous cell carcinoma of the head and neck be used to predict local control in anal cancer treated with chemoradiation?

Abstract

Parameters have been derived in head and neck cancer to account for the additional biological effective dose provided by synchronous chemotherapy. The purpose of this study was to establish whether such parameters could be used to predict local control differences in anal cancer. In anal cancer two randomised trials of radiotherapy vs chemoradiotherapy and two trials randomising between different synchronous chemotherapy regimens were identified. To predict differences in local control between the arms of the first two studies, a global value of 9.3 Gy for the chemotherapy biologically effective dose was employed. For the last two trials, values specific to differing chemotherapy schedules were derived. These values were added to the calculated biological effective dose for the radiotherapy component in order to predict local control outcomes in anal cancer trials. The predicted difference in local control using the global value of 9.3 Gy for the addition of synchronous chemotherapy in the trials of radiotherapy vs radiotherapy and synchronous chemotherapy was 24.6% compared with the observed difference of 21.4%. Using schedule-specific values for the contribution of chemotherapy, the predicted differences in local control in the two trials of differing synchronous chemotherapy schedules were 7.2% and 12% compared with the observed 18% and 0%. The methods initially proposed require modification to result in adequate prediction. If the decreased cisplatin dose intensity employed in anal cancer is modelled, more satisfactory predictions for such trials can be achieved. This revised modelling may be hypothesis generating.