Development of a multi-fraction radiation protocol for intracerebral human glioblastoma xenografts

Patients with malignant gliomas are typically treated by surgery, radiation therapy and chemotherapy. Fractionated radiotherapy consists of 30 daily doses of 1.8 to 2 Gy given over a 6-week period. We have investigated a multi-fraction radiation protocol in which rats bearing intracerebral tumors are irradiated once daily for 10 days with a 2-day break in the middle. This scheme simulates the first third of a typical human radiation protocol, and it is a practical scheme to conduct in the laboratory. U-87 MG or U-251 MG human glioblastoma cells were implanted into the right caudate-putamens of male athymic rats. We irradiated rats using an irradiation jig that allowed us to deliver Cesium-137 photons at a dose rate of 280 cGy/minute selectively to the portion of the head containing the tumor. This device adequately shields all other parts of rat, including the critically sensitive oropharynx. Animals received the first radiation dose when intracerebral tumors were ∼20 mg in size. Untreated U-87 MG tumor-bearing rats died with a median survival of 23 days, while tumor bearing rats that were given ten 1-Gy doses died with a median survival of 28.5 days. Untreated U-251 MG tumor-bearing rats died with a median survival of 34.5 days, while tumor-bearing rats that were given ten 1-Gy doses died with a median survival of 58 days. However, 5 of 14 of these rats had a lifespan >68 days and were considered cured. A daily dose of 0.75 Gy produced a median survival of 43 days, but again 2 rats had a lifespan >70 days. Currently, we are seeking a dose that causes reproducible tumor growth delay of 1 to 2 weeks, without curing any animals, to use in future studies that combine radiation with other anti-tumor agents