OUTLINE: Patients receive irinotecan IV over 90 minutes beginning within 24 hours of radiotherapy on days 1, 8, 15, and 22. External beam radiotherapy is administered 5 days per week for 5.5-6 weeks starting on day 1 concurrent with chemotherapy. Cohorts of 3-6 patients are treated until the maximum tolerated dose (MTD) has been determined. The MTD is defined as the dose level at which the incidence of dose limiting toxicity is no greater than one-third of the patients treated at that dose level. Once the MTD has been determined, additional patients receive irinotecan at the dose level below the MTD with external beam radiation therapy on the same treatment schedule as above. Patients are followed at 4 weeks after treatment, then every 3 months for 2 years, and then every 6 months for 3 additional years.