Purpose: The influence of treatment parameters, such as (a) fraction size and (b) average and maximum dose (as derived from three-dimensional (3D) distributions), on the incidence of pericarditis was analyzed. To understand and predict the dose and volume effect on the pericardium, a normal tissue-complication probability model was tested with these complication data.
Methods and materials: Patients (n = 57) entered in 3 consecutive University of Michigan protocols of combined modality for treatment of localized esophageal carcinoma, and having 3D treatment planning for radiation therapy were the subject of this study. Univariate and multivariate analyses were performed to determine the significance of the effect of fraction size and dose parameters on the development of any grade of pericarditis. Dose distributions were corrected for the biological effect of fraction size using the linear-quadratic method. Normal tissue complication probability (NTCP) was calculated with the Lyman model.
Results: Nonmalignant pericardial effusions occurred in 5 of the 57 patients; all effusions were in patients who received treatment with 3.5 Gy daily fractions. On multivariate analysis, no dose factor except fraction size predicted pericarditis, until the dose distributions were corrected for the effect of fraction size ("bio"-dose). Then, both "bio-average" and "bio-maximum" dose were significant predictive factors (p = 0.014). NTCPs for the patients with pericarditis range from 62% to 99% for the calculations with the "bio"-dose distributions vs. 0.5% to 27% for the uncorrected distributions.
Discussion: A normal tissue complication probability (NTCP) model predicts a trend towards a high incidence of radiation pericarditis for patients who have high complication probabilities. It is important to correct the dose distribution for the effects of fractionation, particularly when the fraction size deviates greatly from standard (2.0 Gy) fractionation.