Relationship of time dose factors to tumor control and complications in the treatment of Cushing's disease by irradiation

The records of the Radiotherapy Division of the Radiology Department of Vanderbilt University Hospital were reviewed for the period 1952–1970. During those 19 years 45 patients with a well-documented diagnosis of Cushing's disease were treated initially by external irradiation of the pituitary. All of the patients were treated with megavoltage equipment using photons. When the results of irradiation are compared against total doses of radiation, it is evident that the control rate is unsatisfactory at doses less than 4000 rad and the maximum benefits of irradiation are evident in the 4500–5000 rad dose range. It is also clear that the complication rate increases as the dose exceeds 4800 rad. If the various treatment regimens of irradiation are converted to “equivalent” doses by the Nominal Standard Dose (NSD) or Time-Dose-Fractionation (TDF) methods, the relationship between “dose” and efficacy of therapy and complications is demonstrated. In order to reduce the possibility of treatment-related morbidity, the use of three or more small (4 × 4 cm) treatment portals or rotational techniques is recommended to a pituitary dose of 4600–5000 rad treating 5 days a week for 5–6 weeks.