Contrasted study on the opening degree of blood-brain barriier after radiation therapy with SPECT and MRI

The blood-brain barrier(BBB) is the largest barrier responsible for preventing direct contact between chemotherapeutic drugs in blood and tumors in brain, the permeability of BBB incease at different degree after brain irradiation in clinical brain tumors radiotherapy. Methods: In our study, 26 patients with metastatic brain tumors(21 cases in pr/mary lung carcinoma, 5 cases in breast carcinoma) were accepted the full brain irradiation. The detructive effects of radiation on the BBB were determined by the 99mTc-DTPA SPECT and the concentration ratio of methotrexate(MTX) in cerebrospinal fluid(CSF) and blood, the brain MRI before and after radiotherapy were retrospective contrasted study with SPECT. Results: the degree of destructive effect on the BBB was directly proportional to radiation doses. After a dose of 20Gy radiation to brain, the permeability of BBB inceased markedly(P<0.01). But in cases the dexamethasone(DXM) was administrated to decease the brain edema during radiotherapy, the permeability inceased less than that in patients without DXM(P<0.05). Conclutions: After 20Gy irradiation, the BBB would gradually open. At this time, chemotherapy is the best choice to improving the therapeutic effect. Dexamethasone was found to cause the decease in BBB permeability but no significant remission of brain edema. So, if the combination of radiotherapy and chemotherapy in treatment of metastatic brain tumors will be plan, the dexamethasone may be not used in expecting to deceasing the side effect and that no affecting the therapeutic effect. (authors)