Diabetes mellitus: a predictor for late radiation morbidity.

PURPOSE: Given the high frequency of diabetes, as well as prostate cancer in 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 were treated between April 1989 and October 1996 using 3DCRT. Median patient age 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 Radiation Therapy Oncology Group (RTOG) and modified Late Effects Normal Tissue Task Force (LENT) scales. Patients with a preexisting history of either Type I or Type II 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; however, 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). There was a trend toward increased late grade 3 and 4 GI complications in diabetics, but not for late grade 3 and 4 GU complications; however, the total number of recorded events for these categories was small. Examining the onset of late toxicity, diabetics developed GU complications earlier than nondiabetics (median: 10 months vs. 24 months, p = 0.02). Considering age, dose, rectal blocking, field size, and history of diabetes in a stepwise multivariate regression model for late grade 2 GI toxicity, dose (p = 0.0001), diabetes (p = 0.0110), and rectal blocking (p = 0.0163) emerged independently predictive for complications. For late grade 2 GU toxicity, only the presence of diabetes remained independently significant (p = 0.0014).

CONCLUSION: Diabetes mellitus is common in the elderly prostate cancer population. Diabetics are at a significant risk for the development of late grade 2 GI and GU complications after external-beam radiotherapy for prostate cancer. While diabetes, radiation dose, and rectal blocking predict for late GI complications, only the presence of diabetes influences late GU morbidity. Physicians may consider treatment modifications for diabetic patients, particularly those patients wishing to enter dose-escalation studies. Further study of the relationship between diabetes and late radiation complications is needed.