The relationship between technical parameters of external beam radiation therapy and complications for localized prostate cancer

Background: This study was performed to review retrospectively the clinical course of chronic rectal bleeding as a complication of external beam radia tion therapy for localized prostate cancer and to analyze the relationship between technical parameters of radiation therapy and the complications. Methods: Seventy-one patients with stages A2, B and C were treated with loc al-field radiotherapy (total dose 52.5-66 Gy, daily dose 2.0-3.28 Gy, field area 30-81 cm(2), number of fields 3-15 ports, planning simulations X-ray or CT-based) between 1989 and 1998 at three institutions. The protocols wer e consistent during this same period at these institutions. Results: Multivariate analysis revealed pretreatment PSA and Gleason sum to be statistically significant predictors of 5 year prostatic specific antig en (PSA) relapse-free rates in a median follow-up period of 42 months (rang e 12-119 months). The significant risk factors for higher grading of acute morbidity were a biological equivalent dose, alpha/beta = 10(BED10) greater than or equal to 65 Gy, dose per fraction greater than or equal to 3.0 Gy, field area greater than or equal to 42 cm(2), fewer ports and X-ray planni ng simulation. However, no parameter was associated with higher grading of late morbidity. Eleven patients (15.4%) experienced a late GI complication: grade 1 (4.2%), grade 2 (9.8%), grade 3 (1.4%). The median time to occurre nce of rectal bleeding was 12 months after radiotherapy and the mean durati on of morbidity was 11 months. Conclusions: Higher total dose and dose per fraction, larger field area, fe wer ports and X-ray simulation increased the grades of acute morbidity. A m ajority of chronic rectal bleedings were transient and responded to conserv ative treatment.