Temporal patterns of selected late toxicities in patients treated with brachytherapy or brachytherapy plus external beam radiation for prostate adenocarcinoma

Abstract

What's known on the subject? and What does the study add? While the frequencies and severity of late toxicities following prostate brachytherapy are well known, less has been published with regard to time to first onset. Several series with limited median follow-up have published time to onset. An extensive analysis of timing to late toxicity following brachytherapy for cervical cancer has also been published. This study is the largest of its kind with the longest median follow-up to capture very late events. It can provide a basis for physician and patient education about when late toxicities can reasonably be expected to occur. The study also shows that a significant amount of erectile dysfunction might be more age related than radiation induced. • To assess the timing of first onset of late rectal bleeding, late haematuria and erectile dysfunction (ED) following brachytherapy with or without external beam radiation therapy (EBRT) for prostate adenocarcinoma. • To identify treatment factors and patient characteristics that affect the time to first onset. • In all, 2046 patients were definitively treated for prostate adenocarcinoma with a full (125) I or (103) Pd implant or a partial (103) Pd implant followed by EBRT with 6 years median follow-up (range 2-17 years). • Patients were selected for an event of Radiation Therapy Oncology Group (RTOG) grade 2 or greater rectal bleeding, ≥RTOG grade 2 haematuria, or a drop in the Mount Sinai Erectile Dysfunction Score from potent to impotent (excluding patients who received androgen deprivation therapy). • Life tables were generated to calculate actuarial incidence rates of toxicity. • Wilcoxon rank sum and Cox regression were utilized to identify treatment factors affecting time to onset. • The incidence rate per 1000 patients for 0-2 years, 2-5 years and 5-10 years following radiation for rectal bleeding is 14.3, 15.9 and 6.5, respectively; for haematuria, 14.0, 8.2 and 1.3, respectively; and for ED, 82.4, 48.2 and 42.2, respectively. • Just 5% of rectal bleeding occurs after 5 years from radiation vs 18% of haematuria cases and 22% of ED. • On multivariate analysis, time to first onset of rectal bleeding was affected by the addition of EBRT only whereas the time to onset of haematuria was affected by the biological effective dose of the radiation and the addition of EBRT. • The only factor on multivariate analysis to affect time to onset of ED was the age of the patient at treatment, independent of radiation dose or technique. • Unique temporality to first onset of selected toxicities was observed in patients after radioactive implant for prostate adenocarcinoma with or without EBRT. • Clinicians and patients should be counselled when to expect late toxicities. • The only factor to affect time to onset of ED is the age of the patient, suggesting possible over-reporting of radiation-induced ED in the light of normal age-related events.