1. Modelling the impact of fractionation on late urinary toxicity after postprostatectomy radiation therapy.
- Author
-
Fiorino C, Cozzarini C, Rancati T, Briganti A, Cattaneo GM, Mangili P, Di Muzio NG, and Calandrino R
- Subjects
- Aged, Area Under Curve, Dose-Response Relationship, Radiation, Humans, Incidence, Linear Models, Male, Middle Aged, Postoperative Period, Prostatic Neoplasms surgery, Radiation Injuries epidemiology, Relative Biological Effectiveness, Sensitivity and Specificity, Time Factors, Dose Fractionation, Radiation, Hematuria epidemiology, Prostatectomy, Prostatic Neoplasms radiotherapy, Radiation Injuries complications, Urethral Stricture epidemiology, Urinary Incontinence epidemiology
- Abstract
Purpose: To fit urinary toxicity data of patients treated with postprostatectomy radiation therapy with the linear quadratic (LQ) model with/without introducing a time factor., Methods and Materials: Between 1993 and 2010, 1176 patients were treated with conventional fractionation (1.8 Gy per fraction, median 70.2 Gy, n=929) or hypofractionation (2.35-2.90 Gy per fraction, n=247). Data referred to 2004-2010 (when all schemes were in use, n=563; conventional fractionation: 316; hypofractionation: 247) were fitted as a logit function of biological equivalent dose (BED), according to the LQ model with/without including a time factor γ (fixing α/β = 5 Gy). The 3-year risks of severe urethral stenosis, incontinence, and hematuria were considered as endpoints. Best-fit parameters were derived, and the resulting BEDs were taken in multivariable backward logistic models, including relevant clinical variables, considering the whole population., Results: The 3-year incidences of severe stenosis, incontinence, and hematuria were, respectively, 6.6%, 4.8%, and 3.3% in the group treated in 2004-2010. The best-fitted α/β values were 0.81 Gy and 0.74 Gy for incontinence and hematuria, respectively, with the classic LQ formula. When fixing α/β = 5 Gy, best-fit values for γ were, respectively, 0.66 Gy/d and 0.85 Gy/d. Sensitivity analyses showed reasonable values for γ (0.6-1.0 Gy/d), with comparable goodness of fit for α/β values between 3.5 and 6.5 Gy. Likelihood ratio tests showed that the fits with/without including γ were equivalent. The resulting multivariable backward logistic models in the whole population included BED, pT4, and use of antihypertensives (area under the curve [AUC] = 0.72) for incontinence and BED, pT4, and year of surgery (AUC = 0.80) for hematuria. Stenosis data could not be fitted: a 4-variable model including only clinical factors (acute urinary toxicity, pT4, year of surgery, and use of antihypertensives) was suggested (AUC = 0.73)., Conclusions: The unexpected impact of moderate hypofractionation on severe incontinence and hematuria after postprostatectomy radiation therapy may be explained by a bladder α/β value <1 Gy or, radiobiologically more plausible, by introducing a time factor likely to represent a previously hypothesized consequential component of late effect., (Copyright © 2014 Elsevier Inc. All rights reserved.)
- Published
- 2014
- Full Text
- View/download PDF