PURPOSE: To fit @entity137 data of @entity1 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 @entity1 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 @entity6110 ( @entity6110 ), according to the LQ model with/without including a time factor y (fixing a/b  =  5  Gy). The 3-year risks of severe @entity3832 , @entity322 , and @entity811 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 @entity850 , @entity322 , and @entity811 were, respectively, 6.6%, 4.8%, and 3.3% in the group treated in 2004-2010. The best-fitted a/b values were 0.81  Gy and 0.74  Gy for @entity322 and @entity811 , respectively, with the classic LQ formula. When fixing a/b  =  5  Gy, best-fit values for y were, respectively, 0.66  Gy/d and 0.85  Gy/d. Sensitivity analyses showed reasonable values for y (0.6-1.0  Gy/d), with comparable goodness of fit for a/b values between 3.5 and 6.5  Gy. Likelihood ratio tests showed that the fits with/without including y were equivalent. The resulting multivariable backward logistic models in the whole population included @entity6110 , pT4, and use of antihypertensives (area under the curve [AUC]  =  0.72) for @entity322 and @entity6110 , pT4, and year of surgery (AUC  =  0.80) for @entity811 . Stenosis data could not be fitted: a 4-variable model including only clinical factors (acute @entity137 , pT4, year of surgery, and use of antihypertensives) was suggested (AUC  =  0.73). CONCLUSIONS: The unexpected impact of moderate hypofractionation on severe @entity322 and @entity811 after postprostatectomy radiation therapy may be explained by a bladder a/b value <1  Gy or, radiobiologically more plausible, by introducing a time factor likely to represent a previously hypothesized consequential component of late effect.

Modelling the impact of fractionation on late XXXX after postprostatectomy radiation therapy.

@entity1 :: ('9606', 'Species') :: ['patients'] @entity137 :: ('MESH:D064420', 'Disease') :: ['urinary toxicity'] @entity322 :: ('MESH:D014549', 'Disease') :: ['incontinence'] @entity850 :: ('MESH:D003251', 'Disease') :: ['stenosis'] @entity6110 :: ('MESH:D017029', 'Disease') :: ['BED', 'biological equivalent dose'] @entity3832 :: ('MESH:D014525', 'Disease') :: ['urethral stenosis'] @entity811 :: ('MESH:D006417', 'Disease') :: ['hematuria']
@entity137 :: (MESH:D064420,Disease) :: ['urinary toxicity']
