A new model for determining the MTD during phase-I trials in pediatric oncology

The primary goal of phase I studies in oncology is to determine the MTD (Maximum Tolerated Dose) for a drug. This MTD is determined with respect to an accepted risk (usually 33%) to see a limiting toxity for patients. In this paper we propose a new mathematical model to determine the MTD. An important feature of this model is that the limiting toxicity can be formulated as a combination of several basic graded toxicities such as hematologic or neurological. Another feature is the possibility to take into account several patient covariates to individualize the determination of the MTD. The model is a bayesian model where some prior information has been considered. The model is expected to work better than traditional empirical schemes for determining the MTD because it uses at every step all the available information on patients, and adds some major improvements as compared with existing CRM strategies because it uses whole data made available, including low-grades toxicities. Finally the model has been validated with a retrospective data set on 17 patients from a phase I study on paclitaxel in pediatric oncology. Calculated MTDs for each patient were found to be markedly different than the doses actually given following a traditional dose-escalation methodology. Results suggest that our new model provides a better and safer way to drive dose-escalation in phase-I trials as compared with traditional schemes.