Purpose: Beam availability for neutron therapy at the National Accelerator Centre at Faure, South Africa is such that treatment fractions are given at irregularly spaced intervals. Such treatment scheduling may not be optimal.
Methods: Investigations were made using the acute skin reaction of the mouse foot to determine the effect of different numbers of regularly and irregularly spaced fractions of p(66)/Be neutrons. Assessment of results was both by average skin reaction and by ED50 values for the incidence of moist desquamation as established by probit analysis.
Results: Different numbers of fractions (between 6 and 11) and different times between fractions did not appear to affect the mouse foot response significantly when fractionation was completed within 11 days, i.e. before repopulation began to have an effect. When overall treatment times were longer than 11 days, the mouse foot responses to 6 and 9 fractions with variable interfraction times were similar, provided the overall treatment times were the same and the fractions were at least 24 h apart. The alpha/beta ratio was 87 +/- 27 (SE) Gy for the early response of the BALB/c mouse foot skin to p(66)/Be neutrons.
Conclusions: The response of mouse skin to fractionated p(66)/Be neutrons was independent of fraction number or interfraction time, provided that the overall treatment time was the same.