Rectum and lung normal tissue complication probability: a retrospective analysis depending on different numbers of fractions and different dose-limits

Abstract

Rectal bleeding and lung pneumonitis are the most common side effect following prostate and lung external radiotherapy treatments. To assess retrospectively rectum and lung normal tissue complication probability (NTCP) at different dose-volume limits changing the number of fractions, 40 patients, half treated for prostate cancer and half treated for lung disease using a conformal radiotherapy treatment (3DCRT) or an intensity-modulated radiation treatment (IMRT) were included in our study. Rectum and lung complications were analysed changing the number of fractions and adjusting the total dose keeping the dose-volume limits fixed as per original standard dose plan (2 Gy/daily). Three different sets of parameters, two linear-quadratic and one seriality model, were employed to evaluate rectum and lung NTCP using Biosuite software. An increased in rectum and lung complications was observed at low dose-volume values when the number of fraction was reduced from 38 given at 2 Gy/day to 5 given at 8 Gy/day. NTCP differences were substantially reduced to an average value of 4% when VD>40 Gy for rectum and VD >20Gy for lung treatments were considered. A lower NTCP coefficient of variation was obtained for V70 and V30 for rectum and lung respectively. Results indicate that more consideration should be given to the low dose-volume limits when the number of fractions are reduced and the dose per fraction increased in prostate and lung treatment to take under control rectum and lung toxicity for both 3DCRT and IMRT treatments. *Correspondence to: Antonella Bufacchi, Medical Physics Department, S. Giovanni Calibita Fatebenefratelli Hospital and PIOXI Clinic, Rome, Italy, E-mail: ant.buf@tiscali.it