Diabetes mellitus: A predictor for late radiation morbidity

Purpose: Given the high frequency of diabetes, as well as prostate cancer i n the elderly population, we sought to determine whether diabetic patients treated with three-dimensional conformal external-beam radiotherapy (3DCRT) had an increased risk of late gastrointestinal (GI) or genitourinary (GU) complications. Methods and Materials: Nine-hundred forty-four prostate cancer patients wer e treated between April 1989 and October 1996 using 3DCRT. Median patient a ge was 69 years (range 48-89), median center of prostate dose was 7211 cGy (range 6211-8074) and median follow-up was 36 months (range 2-99). Patients were evaluated every 6 months with digital rectal examinations, serum PSAs and symptom questionnaires. Radiation morbidity was quantified using Radia tion Therapy Oncology Group (RTOG) and modified Late Effects Normal Tissue Task Force (LENT) scales. Patients with a preexisting history of either Typ e I or Type I[I diabetes mellitus were coded as diabetics. Results: One hundred twenty-one patients had diabetes (13% of total). Rates of acute morbidity did not differ between diabetics and nondiabetics; howe ver, diabetics experienced significantly more late grade 2 GI toxicity (28% vs. 17%,p = 0.011) and late grade 2 GU toxicity (14% vs. 6%,p = 0.001). Th ere was a trend toward increased late grade 3 and 4 GI complications in dia betics, but not for late grade 3 and 4 GU complications; however, the total number of recorded events for these categories was small. Examining the on set of late toxicity, diabetics developed GU complications earlier than non diabetics (median: 10 months vs. 24 months, p = 0.02). Considering age, dos e, rectal blocking, field size, and history of diabetes in a stepwise multi variate regression model for late grade 2 GI toxicity, dose (p = 0.0001), d iabetes (p = 0.0110), and rectal blocking (p = 0.0163) emerged independentl y predictive for complications. For late grade 2 GU toxicity, only the pres ence of diabetes remained independently significant (p = 0.0014). Conclusion: Diabetes mellitus is common in the elderly prostate cancer popu lation. Diabetics are at a significant risk for the development of late gra de 2 GI and GU complications after external-beam radiotherapy for prostate cancer. While diabetes, radiation dose, and rectal blocking predict for lat e GI complications, only the presence of diabetes influences late GU morbid ity. Physicians may consider treatment modifications for diabetic patients, particularly those patients wishing to enter dose-escalation studies. Furt her study of the relationship between diabetes and late radiation complicat ions is needed. (C) 1999 Elsevier Science Inc.