Impact of Fractionation and Dose in a Multivariate Model for Radiation-Induced Chest  Wall XXXX .

@entity1 @entity2 @entity5 @entity158
PURPOSE: To determine the role of @entity1 / @entity5 characteristics, radiation dose, and fractionation using the linear-quadratic (LQ) model to predict stereotactic body radiation therapy-induced grade >= 2 chest wall @entity158 (CWP2) in a larger series and develop clinically useful constraints for @entity1 treated with different fraction numbers. METHODS AND MATERIALS: A total of 316 @entity2 in 295 @entity1 were treated with  stereotactic body radiation therapy in 3 to 5 fractions to 39 to 60  Gy. Absolute dose-absolute volume chest wall (CW) histograms were acquired. The raw dose-volume histograms (a/b  =      Gy) were converted via the LQ model to equivalent doses in 2-Gy fractions (normalized total dose, NTD) with a/b from 0 to 25  Gy in 0.1-Gy steps. The Cox proportional hazards (CPH) model was used in univariate and multivariate models to identify and assess CWP2 exposed to a given physical and NTD. RESULTS: The median follow-up was 15.4  months, and the median time to development of CWP2 was 7.4  months. On a univariate CPH model, prescription dose, prescription dose per fraction, number of fractions, D83cc, distance of @entity5 to CW, and body mass index were all statistically significant for the development of CWP2. Linear-quadratic correction improved the CPH model significance over the physical dose. The best-fit a/b was 2.1  Gy, and the physical dose (a/b  =      Gy) was outside the upper 95% confidence limit. With a/b  =  2.1  Gy, VNTD99Gy was most significant, with median VNTD99Gy  =  31.5  cm(3) (hazard ratio 3.87, P<.001). CONCLUSION: There were several predictive factors for the development of CWP2. The LQ-adjusted doses using the best-fit a/b  =  2.1  Gy is a better predictor of CWP2 than the physical dose. To aid dosimetrists, we have calculated the physical dose equivalent corresponding to VNTD99Gy  =  31.5  cm(3) for the 3- to 5-fraction groups.
