Dose fraction, dose rate and iso-effect relationships for normal tissue responses
article
An analysis is presented of responses of a variety of normal tisues in animals to fractionated irradiations. It is shown that the influence of fractionation can be described on the basis of a simple formula relating the effectiveness for induction of cellular effects to the dose per fraction: F(D) = a1D + a2D2. The ratio a1/a2 is derived as an essential parameter for the description of fractionation effects. It is concluded that the values of a1/a2 for responses of various tissues range widely from 2 to 10 Gy. On the basis of the review of radiobiological data, a formalism is developed for the analysis and prediction of iso-effect relations for tissue tolerance, which can be used as an alternative to the nominal standard dose (NSD) formula of Ellis and its derived equations. An essential characteristic of the formalism is that three groups of tissue responses are distinguished which can be described with respect to fractionation effects by average values of a1/a2 = 10; 5 and 2.5 Gy, respectively. These groups comprise a 1: a.o. skin and intestine; 2: connective tissue; 3: a.o. lung and vascular system. Dose rate effects can be described by a similar formalism. For the calculation of equivalent total doses to be applied in clinical treatments, a concept denoted Extrapolated Tolerance Dose (ETD) or Extrapolated Response Dose (ERD) is introduced. ETD is the tolerance dose for an infinite number of very small fractions. This concept is shown to be useful for the summation of different fractionated schedules and of low dose rate treatments. A number of examples is presented illustrating similarities and differences in comparison with calculations based on the NSD formula. An important feature of the described formalism is that it is directly based on radiobiological insights and it provides a more logical concept to account for the diversity of tissue responses than the assumption of different exponents of N and T in the NSD formula.
Topics
biological modelmethodologynonhumanradiation doseradiation dose fractionationreviewtherapyanimalcell survivalhumanmouserabbitradiation exposureradiation injuryradiation responseratAnimalCell SurvivalDose-Response Relationship, RadiationHumanMiceRabbitsRadiation Injuries, ExperimentalRadiotherapy DosageRats
TNO Identifier
229261
ISSN
03603016
Source
International Journal of Radiation Oncology Biology Physics, 8(11), pp. 1981-1997.
Pages
1981-1997
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