Biological effectiveness of fast neutrons on a murine osteosarcoma.
The effect of fast neutrons and gamma rays on a murine osteosarcoma was studied. The NROS tumor, a radiation-induced osteosarcoma in a C3H mouse, was transplanted into the right hind legs of syngeneic female mice and locally irradiated with single or four daily doses of either fast neutrons or gamma rays. The NROS contained 13-30% hypoxic cells. It took approximately 7 days for the NROS tumor to show apparent reoxygenation following gamma ray irradiations. Two assays were used to determine the neutrons' relative biological effectiveness (RBE) to gamma rays: tumor growth delay time and tumor control dose. The largest RBE of 4.5 was obtained at the smallest dose of neutrons examined, followed by a gradual decrease down to 2.3. The tumor growth delay assay indicated that the RBE values of 2.6-3.1 after single doses of fast neutrons increased to 3.1-4.5 after four daily fractions. The 50% tumor control doses were 78.5 Gy and 33.0 Gy after single doses of gamma rays and fast neutrons, resulting in an RBE of 2.3. Fractionated doses increased the RBE to 2.6. Mitotic cells disappeared shortly after irradiation but reappeared 7 days after irradiation.
Ishii
T
T
Department of Orthopedic Surgery, Chiba University, Japan.
Ando
K
K
Koike
S
S
D000818:Animals; D002588:Cesium Radioisotopes; D005214:Fast Neutrons / Q000627:therapeutic use; D005260:Female; D005720:Gamma Rays; D051379:Mice; D008809:Mice, Inbred C3H; D009368:Neoplasm Transplantation; D012516:Osteosarcoma / Q000532:radiotherapy*; D012062:Relative Biological Effectiveness
D002588:Cesium Radioisotopes