The Kinetics of Repair of Sublethal Radiation-Induced Damage in Pig Skin: Studies with Multiple Interfraction Intervals

The kinetics of the repair of radiation-induced sublethal damage (SLD) was studied for the epidermis of the pig. A total of either 7 or 14 interfraction intervals with incomplete repair was achieved by giving 28 fractions either as 7 × 2 fractions/day plus a top-up dose of 17 Gy (half tolerance) or...

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Bibliographic Details
Published in:Radiation research 1996-05, Vol.145 (5), p.586-594
Main Authors: G. J. M. J. van den Aardweg, Hopewell, J. W., Guttenberger, R.
Format: Article
Language:English
Subjects:
Animals
Beta Particles
Biological and medical sciences
Biological effects of radiation
Dose fractionation
Dose-Response Relationship, Radiation
Epidermis - pathology
Epidermis - radiation effects
Female
Fractionation
Fractions
Fundamental and applied biological sciences. Psychology
Ionizing radiations
Kinetics
Musical intervals
Probability
Radiation damage
Radiation dosage
Radiation Tolerance
Radiotherapy
Skin
Skin - pathology
Skin - radiation effects
Strontium
Swine
Time Factors
Tissues, organs and organisms biophysics
Yttrium Radioisotopes
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Summary:The kinetics of the repair of radiation-induced sublethal damage (SLD) was studied for the epidermis of the pig. A total of either 7 or 14 interfraction intervals with incomplete repair was achieved by giving 28 fractions either as 7 × 2 fractions/day plus a top-up dose of 17 Gy (half tolerance) or as 14 × 2 fractions/day. The dose per fraction ranged from 1.96-4.82 Gy. A total of 9 intervals ranging from 0.17 h up to 8 h between fractions was used. The incidence of moist desquamation, as an estimate of acute epidermal response, was used as an end point to establish dose-effect relationships. The data were analyzed using either the incomplete repair model of Thames, assuming monoexponential repair kinetics, or a modified version of the incomplete repair model, assuming bi-exponential repair of sublethal damage. Both methods of analysis allowed for the longer overnight interval between fractions. Analysis assuming monoexponential repair gave a T1/2 of 0.74 h for the combined data, although there was a trend toward a longer half-time when only the longer interfraction intervals (>1.0 h) were used in the analysis. A further analysis using the modified version of an incomplete repair model gave a fast and a slow component of repair with significantly different half-times of 0.09 and 4.5 h, respectively. Varying the number of incomplete repair intervals by replacing half the number of fractions with a single half-tolerance top-up dose did not modify the kinetics of repair significantly, in terms of either the repair half-times or the proportion of repair associated with a fast and slow component. Reanalysis of data published previously for 3 and 4 fractions using the modified incomplete repair model again resulted in two components of repair, represented by the significantly different half-times of 0.17 and 3.0 h. These values were similar to those obtained from the multiple-fraction experiment. These data clearly demonstrate that an acutely responding tissue is associated with a long T1/2 for the repair of SLD which is independent of the dose per fraction. For accelerated fractionation schedules in the clinic, using multiple fractions per day, these results suggest a need to control the intervals between fractions carefully and when appropriate to reduce the total dose to avoid serious normal-tissue complications.
ISSN:0033-7587
1938-5404
DOI:10.2307/3579277