Abstract
BackgroundThe shape of the dose-response curve at low doses differs from the linear quadratic model. The effect of a radio-adaptive response is the centre of many studies and well known inspite that the clinical applications are still rarely considered.MethodsWe studied the effect of a low-dose pre-irradiation (0.03 Gy – 0.1 Gy) alone or followed by a 2.0 Gy challenging dose 4 h later on the survival of the HT29 cell line (human colorectal cancer cells) and on the GM637 cell line (human fibroblasts).Results0.03 Gy given alone did not have a significant effect on both cell lines, the other low doses alone significantly reduced the cell survival. Applied 4 h before the 2.0 Gy fraction, 0.03 Gy led to a significant induced radioresistance in GM637 cells, but not in HT29 cells, and 0.05 Gy led to a significant hyperradiosensitivity in HT29 cells, but not in GM637 cells.ConclusionA pre-irradiation with 0.03 Gy can protect normal fibroblasts, but not colorectal cancer cells, from damage induced by an irradiation of 2.0 Gy and the application of 0.05 Gy prior to the 2.0 Gy fraction can enhance the cell killing of colorectal cancer cells while not additionally damaging normal fibroblasts. If these findings prove to be true in vivo as well this may optimize the balance between local tumour control and injury to normal tissue in modern radiotherapy.
Highlights
The shape of the dose-response curve at low doses differs from the linear quadratic model
A pre-irradiation with 0.03 Gy can protect normal fibroblasts, but not colorectal cancer cells, from damage induced by an irradiation of 2.0 Gy and the application of 0.05 Gy prior to the 2.0 Gy fraction can enhance the cell killing of colorectal cancer cells while not damaging normal fibroblasts
If these findings prove to be true in vivo as well this may optimize the balance between local tumour control and injury to normal tissue in modern radiotherapy
Summary
The shape of the dose-response curve at low doses differs from the linear quadratic model. It is widely accepted that the shape of the dose-response curve at low doses differs from the linear quadratic model [1]. Hyperradiosensitivity or adaptive responses (i.e. a biopositive effect induced by a low priming dose and identified after application of a higher challenging dose) may occur at low doses of irradiation. The radio-adaptive response was first recognized 1984, when Olivieri et al demonstrated that human lymphocytes exposed to low concentrations of radioactive thymidine show fewer chromatid aberrations caused by a 1.5 Gy challenging dose than those not pre-exposed to irradiation [2]. A radio-adaptive response seems to be associated (page number not for citation purposes)
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