Radiation Oncology ??Biology ??Physics ARS 63rd Annual Meeting 67

and the surgery groups were statistically significant at 90% confidence for both four-year symptom-free survival and seven-year total survival; and significant to 95% confidence for five-year total survival. Total five- year survival of the high-dose group was also significantly greater than the low-dose radiation group at 95% confidence. Reported risks of radia- tion myelitis at different sections of the spinal column are discussed and weighed against benefits of treatment with different radiation doses. Postoperative courses of radiation to 7000 rads are recomnended for sacral, coccygeal, lumbar and cervical chordomas. For the rare case of thoracic chordoma, routine postoperative radiation is not recomnended and a single course of 4000 rads is advised in management of recurrent tumor.

(77) BRAIN TOLEFWJCE UNIT: A METHOD TO ESTIMATE RISK OF BRAIN INJURY FOR VARIOUS DOSE SCHEDULES

Richard D. Pezner, M.D.* and John 0. Archambeau,

RADIATION

M.D.

Division of Radiation Oncology City of Hope National Medical Center

Duarte, Cal ifornia 91010

A mathematica1 formula for tolerante of the brain and optic nerves to irradiation has been derived. It is expressed in terms of brain tolerante units (btu) where Tissue Dose (rad) = btu x ND.45 x TogD3.

It appears to more real istical ly ref lect brain tolerante than Ell is’ N.S.D. formula. A dose-tolerante curve has been proposed to ana I yze relative risk of brain injury for different dose schedules. Dose schedu I es with a btu value of less than 1050 appear to have very low risk of complication unless exacerbating factors such as chemotherapy capable of crossing the blood-brain barrier or CNS infection are also present. The btu formula may be able to better evaluate risk-benef it comparisons of different dose schedules in treating various tumors of the brain, sellar region and extracranial sites.

(78) MEDULLOBLASTOMA IN ADULTS: IMPROVED SURVIVAL WITH SUPERVOLTAGE RADIATION THERAPY

Gene Kopelson, M.D.,l Rita M. Linggood, M.D.,l and George M. Kleinman, M.D.'

'Department of Radiation Medicine and 'Neuropathology Laboratory of the Department of Pathology, Massachusetts Genera1 Hospital, Boston, Mass. 02114

From 1962-June 1979, 16 adults (> 16 years of age) received postoperative neuraxis radiation therapy for medullöblastoma. An actuarial 10 year survival rate of 51% was achieved, with the major site of recurrence post-irradiation in the posterior fossa. Compared to previous pediatrie series, adults present with more advanced disease at the primary site, demonstrate more visceral metastases, and fare less wel1 after tuaor recurrence. Patients with high T-stage, high M-stage, and males showed the highest relapse rates. Compared to prior series of adult patients, the demonstrated improved survival is attributed to increased doses delivered to the posterior fossa.