A Nonparametric Method for the Derivation of α/β Ratios from the Effect of Fractionated Irradiations

Multifractionation isoeffect data are commonly analysed under the assumption that cell survival determines the observed tissue or tumour response, and that it follows a linear-quadratic dose dependence. The analysis is employed to derive the α/β ratios of the linear-quadratic dose dependence, and different methods have been developed for this purpose. A common method uses the so-called Fe plot. A more complex but also more rigorous method has been introduced by Lam et al. (1979). Their method, which is based on numerical optimization procedures, is generalized and somewhat simplified in the present study. Tumour-regrowth data are used to explain the nonparametric procedure which provides α/β ratios without the need to postulate analytical expressions for the relationship between cell survival and regrowth delay

Kinetics of Recovery from Sublethal Radiation Damage in four Murine Tumors.

The kinetics of repair of sublethal radiation damage (SLD) was studied in four transplantable C3H mouse tumors, i.e. mammary carcinoma AT17, fibrosarcoma SSK2, and squamous cell carcinomas AT51 and AT478. Tumors were irradiated with 4 fractions of 300 kV X-rays given under local hypoxia at intervals ranging from 0 to 6 h. Radiation response was measured by growth delay, which was directly analyzed using a general curve description based on the extended linear-quadratic model (exponential repair kinetics). In contrast to existing methods all growth delay values were utilized to estimate the α/β ratios and the half-times as well as their confidence limits in a non-linear least squares analysis. The half-times were 42, 44, 54 and 31 min, respectively. It is concluded that repair of SLD is virtually complete after 5 h in these tumors. This is also due to the relatively small proportion of repairable damage in these tumors reflected in their α/β values, which were 38, 30, 54 and 42 Gy, respectively

Intrazelluläre Erholung - Grundlagen der Hyperfraktionierung.

The radiobiological basis of a hyperfractionated radiation therapy versus conventional fractionation with respect to therapeutic gain, i.e., improved normal tissue sparing for the same level of tumour cell inactivation, will be presented. Data on the recovery potential of various tissues as well as the kinetics of repair will be given. The problem of incomplete repair with short irradiation intervals will be discussed

Intrazelluläre Erholung--Grundlage der Hyperfraktionierung.

The radiobiological basis of a hyperfractionated radiation therapy versus conventional fractionation with respect to therapeutic gain, i.e., improved normal tissue sparing for the same level of tumour cell inactivation, will be presented. Data on the recovery potential of various tissues as well as the kinetics of repair will be given. The problem of incomplete repair with short irradiation intervals will be discussed