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

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Abstract
Background: This study was performed to review retrospectively the clinical course of chronic rectal bleeding as a complication of external beam radiation 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 local-field radiotherapy (total dose 52.5–66 Gy, daily dose 2.0–3.28 Gy, field area 30–81 cm2, number of fields 3–15 ports, planning simulations X-ray or CT-based) between 1989 and 1998 at three institutions. The protocols were 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 antigen (PSA) relapse-free rates in a median follow-up period of 42 months (range 12–119 months). The significant risk factors for higher grading of acute morbidity were a biological equivalent dose, α/β = 10(BED10) ≥65 Gy, dose per fraction ≥3.0 Gy, field area ≥42 cm2, fewer ports and X-ray planning 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 occurrence of rectal bleeding was 12 months after radiotherapy and the mean duration of morbidity was 11 months. Conclusions: Higher total dose and dose per fraction, larger field area, fewer ports and X-ray simulation increased the grades of acute morbidity. A majority of chronic rectal bleedings were transient and responded to conservative treatment.

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