A new experimental system for irradiating tumors in mice using a linear accelerator under specific pathogen-free conditions

We developed a reliable system for the irradiation of xenografted tumors in mice which allows for accurate local irradiation under specific pathogen-f ree conditions. The system presented here consists of acrylic supports for mice and an acrylic box connected to a pump through 0.22 mu m pore-sized fi lters. Mice with xenotransplanted tumors growing on their right hind legs w ere set on the supports and put into the box in a laminar flow hood. The tu mors of 7 mice were irradiated simultaneously with X-rays of 6 and 10 MV ge nerated by a linear accelerator at a dose rate of 3.1-4.7 Gy/min. The air w as ventilated through filters during irradiation in the closed box. Microor ganism tests confirmed that no bacteria entered or left the box. One of the significant characteristics of this setup is that it allows for irradiatio n under conditions of acute hypoxia, which is obtained using an integrated tourniquet. The dose variation among 7 tumors was less than 1%. The rest of the mouse's body was shielded effectively by a half-field technique and a lead block. As a result, the whole body dose for the mice was 0-4% of the t otal dose absorbed by the tumor. Due to the high dose rate and the ability to irradiate 7 mice simultaneously under specific pathogen-free conditions, this new system can be considered a time-saving and valuable tool for radi ation oncology research.