title: The response of mouse skin to irradiation with neutrons from the 62 MV cyclotron at Clatterbridge, U.K.
abstract: Acute skin reactions on mouse feet were used to measure the effect of 62 MeV p-Be neutrons from the cyclotron at Clatterbridge, U.K. The results were compared with the response to 16 MeV d-Be neutrons from the cyclotron at Hammersmith, 4 MeV d-Be neutrons from the van de Graaff accelerator at the Gray Laboratory, and 250 kVp X-rays. Up to 16 equal radiation fractions were given alone, or 16 fractions followed by "top-up" doses of 4 MeV d-Be neutrons to study the effect of neutron doses less than 1 Gy per fraction. For equivalent skin reactions, 9-16% more dose (total neutron + gamma) was needed with p(62)-Be neutrons compared with d(16)-Be neutrons. This did not vary significantly between 1 and 16 fractions. The top-up studies indicated that this figure might rise to approximately 14-32% at very low doses of neutrons, the value depending on the method of analysis of the data. The data indicate that the "standard" clinical protocol of 1.47 Gy per fraction (N + gamma dose) in 12 fractions given at Hammersmith with d(16)-Be neutrons would correspond to a dose of 1.64 Gy per fraction (N + gamma) at Clatterbridge using a similar regime of p(62)-Be neutrons. d(4)-Be neutrons were more effective than d(16)-Be neutrons by a factor of 1.6 over the whole range of dose per fraction studied (0.05-14.5 Gy per fraction of d(4)-Be neutrons). Relative to X-rays, the RBE for p(62)-Be neutrons was 1.6 +/- 0.02 for a single X-ray dose of 30 Gy, rising to 2.9 +/- 0.04 for an X-ray dose per fraction of 4.6 Gy given 16 times. The full-course fractionation data and the top-up data together indicate an extrapolated limiting RBE at vanishingly small doses per fraction of 4.2-4.8 depending on the method of analysis. The X-ray data were well-fitted by a linear-quadratic (LQ) model of dose-fractionation, with alpha/beta = 8.6 +/- 1.5 Gy. The LQ model also provides a fairly good description of the neutron responses, alpha/beta being large (greater than 24) reflecting predominantly linear underlying dose-responses for all the neutron beams. This in turn reflects the small variation observed in the relative effectiveness between the 3 neutron beams with changes in dose per fraction.
authors.affiliation: Gray Laboratory, Mount Vernon Hospital, Northwood, Middlesex, U.K.
authors.forename: M C
authors.initials: MC
authors.lastname: Joiner
authors.forename: S B
authors.initials: SB
authors.lastname: Field
mesh_terms: D000818:Animals; D004307:Dose-Response Relationship, Radiation; D005260:Female; D051379:Mice; D008954:Models, Biological; D009502:Neutrons; D011829:Radiation Dosage; D012062:Relative Biological Effectiveness; D012867:Skin / Q000528:radiation effects*