Radiation pneumonitis after hypofractionated radiotherapy: Evaluation of the LQ(L) model and different dose parameters

Abstract

Purpose: To evaluate the linear quadratic (LQ) model for hypofractionated radiotherapy within the context of predicting radiation pneumonitis (RP) and to investigate the effect if a linear (L) model in the high region (LQL model) is used. Methods and Materials: The radiation doses used for 128 patients treated with hypofractionated radiotherapy were converted to the equivalent doses given in fractions of 2 Gy for a range of α/β ratios (1 Gy to infinity) according to the LQ(L) model. For the LQL model, different cut-off values between the LQ model and the linear component were used. The Lyman model parameters were fitted to the events of RP grade 2 or higher to derive the normal tissue complication probability (NTCP). The lung dose was calculated as the mean lung dose and the percentage of lung volume (V) receiving doses higher than a threshold dose of xGy (Vx). Results: The best NTCP fit was found if the mean lung dose, or Vx, was calculated with an α/β ratio of 3 Gy. The NTCP fit of other α/β ratios and the LQL model were worse but within the 95% confidence interval of the NTCP fit of the LQ model with an α/β ratio of 3 Gy. The V50 NTCP fit was better than the NTCP fit of lower threshold doses. Conclusions: For high fraction doses, the LQ model with an α/β ratio of 3 Gy was the best method for converting the physical lung dose to predict RP. Copyright © 2010 Elsevier Inc.