Phase I trials involving radiation therapy, quantifying the risks

Introduction: Over one third of cancer patients receive radiation therapy (RT) at some point. Our purpose was to quantify the risks to patients associated with enrolment onto RT-based phase I trials.

Methods: All phase I and phase I/II clinical trials involving RT published in English between 2001 and 2010 were identified via a PubMed search. For pragmatic reasons, we focused on trials from 2001, 2005 and 2009. For each trial we calculated a 'toxicity ratio' equal to the number of grade 3/4/5 toxic events divided by the number of patients in the trial. Linear regression was used to determine which variables were associated with higher toxicity ratios.

Results: There were a total of 33 treatment-related deaths, and 1812 acute grade 3/4 toxicities among the 2994 subjects in 98 trials. The median toxicity ratio over 98 trials was 0.46 (95% confidence interval (CI) 0.34 to 0.58). Multivariate regression analysis showed that toxicity ratios were significantly higher in trials with chemotherapy (P = 0.002) and in trials for cancers of the head-and-neck (P < 0.001). The median toxicity ratio in chemotherapy trials was 0.60 (95% CI: 0.48 to 0.72) compared with trials without chemotherapy 0.08 (95% CI: 0.03 to 0.13).

Conclusions: Although the risk of grade 5 toxicity is low, the risk of major toxicity is significant in phase I RT trials. These values are comparable to published risk estimates for phase I non-RT trials.