Ck. Haston et al., RADIATION-INDUCED LUNG DAMAGE IN RATS - THE INFLUENCE OF FRACTION SPACING ON EFFECT PER FRACTION, International journal of radiation oncology, biology, physics, 28(3), 1994, pp. 633-640
Citations number
21
Categorie Soggetti
Oncology,"Radiology,Nuclear Medicine & Medical Imaging
Purpose: When the linear-quadratic model is used to predict fractionat
ed treatments which are isoeffective, it is usually assumed that each
(equal size) treatment fraction has an equal effect, independent of th
e time at which it was delivered during a course of treatment. Previou
s work by our group has indicated that this assumption may not be vali
d in the context of radiation-induced lung damage in rats. Consequentl
y we tested directly the validity of the assumption that each fraction
has an equal effect, independent of the time it is delivered. Methods
and Materials: An experiment was completed in which fractionated irra
diation was given to whole thoraces of Sprague-Dawley rats. All treatm
ent schedules consisted of eleven equal dose fractions in 36 days give
n as a split course, with some groups receiving the bulk of the doses
early in the treatment schedule, before a 27-day gap, and others recei
ving most of the dose toward the end of the treatment schedule, after
the time gap. To monitor the incidence of radiation-induced damage, br
eathing rate and lethality assays were used. Results: The maximum diff
erences in the LD(50)s and breathing rate ED(50)s for the different fr
actionation schedules were 4.0% and 7.7% respectively. The lethality d
ata and breathing rate data were consistent with results expected from
modelling using the linear-quadratic model with the inclusion of an o
verall time factor, but not the generalized linear-quadratic model whi
ch accounted for fraction spacing. Conclusion: For conventional daily
fractionation, and within the range of experimental uncertainties, the
results indicate that the effect of a treatment fraction does not dep
end on the time at which it is given (its position) in the treatment.
The results indicate no need to extend isoeffect formulae to consider
the effect of each fraction separately for radiation-induced lung dama
ge.