Radiobiology of neutrons
Tumor responses depend on a number of factors, of which the intrinsic radiosensitivity of the cells and their oxygenation condition can be considered as most important. Variations of the sensitivity in the cell cycle and differences between resting and proliferating cells are considered to play a smaller part. Large differences in intrinsic cellular sensitivity and in RBE values of fast neutrons have been observed for impairment of the clonogenic capacity of cells in culture and in experimental tumors. For most of the treatments commonly applied in radiotherapy, doses per fraction are smaller than 5 Gy of photons and 1.5 Gy of neutrons. In these dose ranges, the survival curves of mammalian cells can be described by the formula: S(D)/S(O) = exp - (a/sub 1/D + a/sub 2/D/sup 2/). Values of a/sub 1/ range between 10/sup -1/ and 1 Gy/sup -1/ for photons; they are a factor of 3 to 10 larger for fast neutrons, depending on the type of cell and the neutron energy spectrum. However, a direct correlation between cellular sensitivity and the magnitude of RBE values has not been established. The influence of fractionation is described by the value of a/sub 1//a/sub 2/. It is shown that for several important normal tissues these values are smaller than for cells from a number of experimental tumors. Therefore, with X rays, more sparing of normal tissues is obtained than for these tumors, and the application of neutrons is not expected to provide an advantage in this respect. The presence of hypoxic cells in experimental tumors has been well established. It has been observed, however, that for daily fractionated treatments with doses of less than 3 Gy of photons, the influence of hypoxia is much smaller than for single large doses, because of the process of reoxygenation.
- Research Organization:
- Radiobiological Inst. TNO, Rijswijk, Finland
- OSTI ID:
- 5241768
- Journal Information:
- Int. J. Radiat. Oncol., Biol. Phys.; (United States), Vol. 8:12
- Country of Publication:
- United States
- Language:
- English
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63 RADIATION, THERMAL, AND OTHER ENVIRON. POLLUTANT EFFECTS ON LIVING ORGS. AND BIOL. MAT.
FAST NEUTRONS
RADIOBIOLOGY
RBE
ANOXIA
CELL CYCLE
CELL PROLIFERATION
FRACTIONATED IRRADIATION
MATHEMATICAL MODELS
OXYGEN ENHANCEMENT RATIO
RADIOTHERAPY
X RADIATION
BARYONS
BIOLOGY
ELECTROMAGNETIC RADIATION
ELEMENTARY PARTICLES
FERMIONS
HADRONS
IONIZING RADIATIONS
IRRADIATION
MEDICINE
NEUTRONS
NUCLEAR MEDICINE
NUCLEONS
RADIATIONS
RADIOLOGY
THERAPY
550603* - Medicine- External Radiation in Therapy- (1980-)
560152 - Radiation Effects on Animals- Animals