Revised radiobiological modelling of the contribution of synchronous chemotherapy to the rate of grades 3-4 mucositis in head and neck cancer.

IntroductionBiological effective dose (BED) calculations modelled on reduced accelerated repopulation when synchronous chemotherapy is delivered significantly correlate with observed differences in local control in randomised trials of platinum-based chemoradiation. The purpose of this study was to examine whether a similar relationship existed in the context of grades 3-4 mucositis. MethodsBiological effective dose from radiotherapy and synchronous chemotherapy was calculated using three different models: AB using the additional BED attributable to chemotherapy and standard repopulation parameters; zero repopulation (ZRP) using zero correction for repopulation; and variable t(p) (Vt(p)) using a variable doubling time for mucosal stem cell repopulation. The correlation between the percentage change in biological effective dose between trial arms, and the observed percentage change in the rate of grades 3-4 mucositis was examined by using the Pearson product-moment correlation. ResultsWith the AB model, there were no significant correlations with observed differences in rates of grades 3-4 mucositis. With either the ZRP or Vt(p) models, significant correlations were observed. A value of 5 days for the doubling time during repopulation (T-p) was associated with the most significant correlation (P=0.002). ConclusionModels where the dose lost due to accelerated repopulation is reduced imply a therapeutic loss from the use of synchronous chemotherapy when only local control and the rate of acute grades 3-4 mucositis are considered.