RESUMEN
INTRODUCTION: This study assessed the incidence of late rectal toxicities and evaluated potential predictive factors for late proctitis in patients treated with prostate-specific intensity-modulated radiotherapy in Hong Kong. METHODS: This retrospective longitudinal observational study included patients with localised prostate cancer who were treated with intensity-modulated radiation therapy in an oncology unit in Hong Kong between January 2007 and December 2011, and who had >1 year of follow-up. Clinical, pharmacological, and radiation parameters were recorded. Toxicities were measured by Common Terminology Criteria for Adverse Events version 4. RESULTS: In total, 232 patients were included in this analysis. The mean follow-up time was 7.3 ± 2.1 years and 46.5% of the patients had late rectal toxicities. Late proctitis occurred in 30.5% of patients; 25% of the patients with late proctitis exhibited grade ≥2 toxicity. Median onset times for late proctitis and rectal bleeding were 15 and 18.4 months, respectively. Multivariable regression showed increased odds for the occurrence of late proctitis in patients with older age (odds ratio [OR]=1.11, 95% confidence interval [CI]=1.04-1.19, P=0.003), higher V70 (OR=1.08, 95% CI=1.01-1.15, P=0.027), and presence of acute rectal toxicities (OR=4.47, 95% CI=2.37-8.43, P<0.001). Antiplatelet use was not significantly associated with the occurrence of late proctitis (OR=1.98, 95% CI=0.95-4.14, P=0.07). CONCLUSIONS: The incidence of late rectal toxicities was considerable among patients in this study. Clinicians should consider the possibility of late proctitis for patients with older age, acute rectal toxicities, and higher V70. High doses to rectal volumes should be limited because of the significant association with V70.