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The volume effect in irradiated mouse colorectum
Author(s) -
Skwarchuk Mark William
Publication year - 1998
Publication title -
medical physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.473
H-Index - 180
eISSN - 2473-4209
pISSN - 0094-2405
DOI - 10.1118/1.598361
Subject(s) - irradiation , rectum , fibrosis , volume (thermodynamics) , radiation therapy , nuclear medicine , dosimetry , chemistry , pathology , biology , medicine , physics , quantum mechanics , nuclear physics
One approach for decreasing rectal complications due to prostate irradiation is to reduce the volume of normal tissue irradiated using conformal radiotherapy. A number of mathematical models have been previously developed to describe the change in associated toxicity with a change in irradiated volume, i.e., the “volume effect,” for serial‐type normal tissues, including the rectum. However, limited data are available to test or support these models. One goal of this thesis was to test the hypothesis that there would not be a threshold length, as predicted by the Probability model of the volume effect, in the development of fibrotic obstruction after irradiation of various lengths of C57B1/6 and C3Hf/Kam mouse colorectum. A strain‐dependent threshold length was observed, in contradiction of the Probability model predictions. However, the data could be described if the Probability model was modified to include a threshold volume term, i.e., the Threshold Probability model. The mechanism of the threshold was determined to be epithelial regeneration after irradiation. Strain differences were observed for the incidence, histological time of appearance, and spatial location of fibrosis. However, there were no consistent strain differences in mRNA levels or immunolocalization for the pro‐fibrotic cytokines TGFbeta 1, 2, 3, and TNFalpha. The data indicate the need for volume effect models that account for biologically important processes, such as the effect of epithelial regeneration after irradiation.