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A Therapeutic Operating Characteristic (TOC) curve for radiation therapy plots, for all possible treatment doses, the probability of tumor ablation as a function of the probability of radiation-induced complication. Application of this analysis to actual therapeutic situations requires that dose-response curves for ablation and for complication be estimated from clinical data. We describe an approach in which "maximum likelihood estimates" of these dose-response curves are made, and we apply this approach to data collected on responses to radiotherapy for carcinoma of the nasopharynx. TOC curves constructed from the estimated dose-response curves are subject to moderately large uncertainties because of the limitations of available data. These TOC curves suggest, however, that treatment doses greater than 1800 ret may substantially increase the probability of tumor ablation with little increase in the risk of radiation-induced cervical myelopathy, especially for T1 and T2 tumors.

In a comprehensive mycosis fungoides program, 60 patients have been seen with a pathologic diagnosis of this disease. Forty-four patients with advanced disease were referred for radiation therapy. Three treatment techniques were identified in which 14 patients were treated with localized fields using electrons or whole-body electron-beam therapy with doses of less than 3000 rads, 21 patients were treated using the Stanford technique with tissue doses of between 3000 and 4000 rads, and nine patients were treated with six cycles of mechlorethamine, vincristine, prednisone, and procarbazine or cyclophosphamide, vincristine, prednisone, and procarbazine following the electron-beam therapy. The actuarial survival rate was 45% at 1 year for the 14 patients with localized electron-beam therapy, whereas the actuarial survival rates were 83% for patients treated with whole-body electron-beam therapy and 100% for patients treated with whole-body electron-beam therapy followed by four-drug chemotherapy. The recurrence-free interval for these three groups correlates with these observations. A central nervous system recurrence has been observed in the combined-therapy group.

Between May 1974 and March 1983, 44 children with histologically verified cerebellar medulloblastoma were seen for post-operative cranial-spinal irradiation following attempted total tumor removal. Six patients were excluded from review because they received all or part of their treatment at another institution (3 patients) or did not complete the planned course of irradiation (3 patients). All of the 38 remaining patients were treated by a previously described technique on a 4 MeV Linear Accelerator with 55 Gy delivered to the primary tumor site. Prior to December 1978, 19 consecutive children (Group A) had spinal prophylactic doses of 30-40 Gy and brain prophylactic doses of 40-50 Gy. After the date, 25 Gy was given to the cranial-spinal axis of 19 consecutive children (Group B). This lower dose was arbitrarily selected with the hope of reducing morbidity in treated survivors and achieving the same tumor control. Risk factors that define good and poor prognosis were evaluated for each group, and there were no differences noted. Myelography and CSF cytology were not routinely performed. Follow-up for the 38 patients ranges from 20 months to 124 months. For the low risk patients, survival (12/15 or 80%) was independent of cranial-spinal radiation dose (Group A 6/8, Group B 6/7). For the high risk patients survival was poor (9/23 or 39%), not dependent on cranial-spinal radiation dose (Group A 5/11, Group B 4/12), and associated with failure at the primary site (10/14), often with CSF seeding (8/10). The other 4 failures include 2 who had moved outside the United States (details of failure are unknown), 1 with supratentorial, CSF seeding and distant metastases, and 1 with distant metastasis only. There were no isolated spinal failures. This pilot study shows that the prophylactic radiation dose to the cranial-spinal axis can be decreased to 25 Gy without jeopardizing control rate and survival in patients with medulloblastoma.