[The observation of edema in the substantia alba during postoperative brain irradiation. The role of computed tomographic studies].

BACKGROUND: The aim of our study was to determine on CT whether a relation exists between a radiation-induced brain edema, treated with diuretics and its corresponding Houndsfield Units (HU). PATIENTS AND METHODS: Seventy-five patients (age 20 to 65 years, suffering from headaches but without hypertension brain tumors or cerebral arteriosclerosis were examined as a reference group. Three slices with 8 mm thickness, 24 mm apart in the upper, middle and lower third of the brain were obtained to measure the HU of the white matter. The second group consisted of 20 patients with brain tumors, which underwent brain surgery. HU of the white matter were measured before radiation and after 10, 20, 30, 40 and 50 Gy. If a reduction in density was detected, diuretic therapy with 40 mg furosemide per o.s. was initiated. If no increase in density was found on follow-up additional therapy with glycerine (4.5 g/kg body weight) was started. In this cases follow-up was on day 4 after initiation of diuretics. If clinical symptoms suggested an increasing in intracranial pressure, CT-examination was performed immediately. Therapy was started according to measurement results. The third group consisted of 64 patients with brain tumors, that underwent postsurgical radiation therapy. Prior to radiation therapy 40 mg furosemide per o.s. were given. CT-examinations, intensified diuretic therapy and follow-up examinations were performed as in group 2. If, despite therapy, the HU decreased, infusion of mannites was added. The second and third group of patients received radiation therapy with telecobalt and/or a linear accelerator (6 and 9 MeV X-ray).
RESULTS: In the first group white matter density was > 30 HU. In the second group white matter density was between 25 and 29 HU prior to diuretic therapy. Under 25 HU a continuous headache, vertigo and confusion ensued. Diuretic therapy was intensified until the measured values reached 25 to 29 HU. Forty-seven of 64 patients in the third group had 25 to 29 HU prior to radiation therapy. Despite prophylactic diuretic therapy in 28 cases density decreased to 20 to 24 HU. Improvement was achieved with an additional glycerine per o.s. The measured values reached again 25 to 29 HU. In 1 case the values dropped under 20 HU. Additional mannite infusion was necessary. In 17 of 64 patients white matter density was > 30 HU prior to radiation therapy, dropping to 25 to 29 HU during radiation. Prophylactic diuretic administration kept the values in this range. A correlation between age of the patient, radiation source, total dose, tumor histology and degree of change in HU was not found.
CONCLUSION: Measurements of HU can serve as a good indicator for spontaneous or diuretic induced changes of a white matter edema during radiation therapy.