Thesis (MTech Biomedical Technology)--Cape Peninsula University of Cape Town, 2005In clinical radiotherapy, experiments are performed to determine optimal conditions of
the radiation prior to radiotherapy. These experiments focus on the relative biological
effectivness(RBE) determination and are predominantly applied in high linear energy
transfer (LET) radiations i.e. fast neutrons, as the RBE values for such radiations vary
greatly. In general, the RBE of a certain radiation relative to a given reference radiation
flCo gamma) varies widely with the energy, dose, dose rate, fractionation, type of tissue
and end-point used.
Experience with neutron therapy at iThemba LABS has shown that treatment with more
fractions and lower doses per fraction may be beneficial for some patients. To calculate
the iso-effective treatment dose needed, an appropriate alp ratio for early effects is
needed. In this study, the repair of mouse jejunum was measured for split-dose
irradiations to determine if a suitable alP ratio for neutrons could be estimated using the
known value for gamma rays and the applicable RBE.. Crypt stem cell survival was
measured 3.5 days after split-dose exposures to p(66)/Be neutrons and 6OCo gamma rays.
Dose response curves for both treatment modalities and for both acute and fractionated
exposures were constructed by counting crypts of Leiberkhiin at the base of the villi in
haematoxylin and Eosin-stained sections of mouse jejunum. Using a RBE value of 1.64
and an alP ratio of 7Gy noted for tbe fractionated photon exposures, an alP ratio of 11.5
IV
could be estimated for neutrons
