The time course of development of late side effects after irradiation of the prostate with multiple fractions per day

Abstract

Background and purpose. A group of patients with prostate cancer was irradiated in the early 1980s with a TID schedule, resulting in a very high frequency of side effects. The time course of development of severe late complications was evaluated. Materials and methods. We retrospectively reviewed the records of 91 patients with prostate cancer, irradiated on a linear accelerator or a cobalt unit between 1980 and 1983. They received a split-course irradiation with multiple fractions per day (MFD) up to a nominal dose of 60 Gy. The rate of development of severe late urological and gastrointestinal complications, grade 3 or more according to the RTOG scoring system, was analysed. Results. The 5-year actuarial incidence of urological complications was 51%. After a lag time of a few months, patients develop ‘first events’ at a nearly constant rate of 10% for 5 years after treatment. Subsequent events (‘all events’) seem to continue to appear even after 5 years. The actuarial incidence at 5 years of gastrointestinal complications was 14%, with no new events developing later than 3 years after treatment. Conclusions. The irradiation schedule used resulted in an unacceptable high incidence of late side effects, probably due to incomplete repair between fractions. MFD fractions to the pelvis should be avoided, unless sufficient time in between fractions can be allowed. Moreover, the fact that after this treatment schedule with very pronounced biological effects, new severe complications continued to develop up to 5 years after therapy, indicates that sufficiently long follow-up time has to be respected when investigating new radiation techniques for pelvic tumours.