IMPACT OF TIME BETWEEN X-RAY FRACTIONS ON ACUTE CHANGES IN THE FUNCTION OF THE URINARY-BLADDER IN THE MOUSE

Noninvasive transurethral cystometry was used in mice anesthetized wit h pentobarbitone to quantify the effect of the interval between X-ray fractions on acute radiation-induced changes in the function of the ur inary bladder. Bladder capacity was defined at intravesical pressures of 10 and 20 mm Hg. A reduction in the storage capacity of the bladder by greater than or equal to 50% of the individual preirradiation cont rol value, occurring at any time during the initial 30 days after radi otherapy, was the quantal end point used for dose-response analysis. F our equal-sized dose fractions were applied with intervals of 0, 0.5, 1, 1.5, 2, 4 and 8 h, respectively. The ED(50) values increased from 1 8.2 Gy (95% confidence interval 16.8-20.6) for single-dose treatment t o 28.1 Gy (26.2-29.9) in the 8-h protocol. Linear-quadratic analysis o f the results, using an indirect repair model and the direct analysis approach, yielded a half-time of repair of 1.2 h (0.9-1.9) with an alp ha/beta ratio of 10.4 Gy. If combined with previous data for split dos es where 1 to 10 fractions were given within less than or equal to 7 d ays (Dorr and Schultz-Hector, Radiat. Res. 131, 35-42, 1992), an even longer repair half-time of 1.2 h (1.3-2.7) was determined. (C) 1995 bg Radiation Research Society