Document Type : Original Article
Authors
1
Medical Physics Research Center, Mashhad University of Medical Sciences, Mashhad, Iran;Department of Medical Physics, School of Medicine, Mashhad University of Medical Sciences, Mashhad, Iran
2
Department of Medical Physics, School of Medicine, Mashhad University of Medical Sciences, Mashhad, Iran;Department of Medical Physics and Biomedical Engineering, Faculty of Medicine, Tehran University of Med
3
Department of Medical Physics, School of Medicine, Mashhad University of Medical Sciences, Mashhad, Iran
4
Medical Physics Research Center, Mashhad University of Medical Sciences, Mashhad, Iran;Department of Medical Physics, School of Medicine, Mashhad University of Medical Sciences, Mashhad, Iran;4Department of Medical Phys
Abstract
Objective
The dose-response relationship of radiation-induced bystander effect (RIBE) is controversial at high dose levels. The aim of the present study is to assess RIBE at high dose levels by examination of different endpoints.
Materials and Methods
This experimental study used the medium transfer technique to induce RIBE. The cells were divided into two main groups: QU-DB cells which received medium from autologous irradiated cells and MRC5 cells which received medium from irradiated QU-DB cells. Colony, MTT, and micronucleus assays were performed to quantify bystander responses. The medium was diluted and transferred to bystander cells to investigate whether medium dilution could revive the RIBE response that disappeared at a high dose.
Results
The RIBE level in QU-DB bystander cells increased in the dose range of 0.5 to 4 Gy, but decreased at 6 and 8 Gy. The Micronucleated cells per 1000 binucleated cells (MNBN) frequency of QU-DB bystander cells which received the most diluted medium from 6 and 8 Gy QU-DB irradiated cells reached the maximum level compared to the MNBN frequency of the cells that received complete medium (P < 0.0001). MNBN frequency of MRC5 cells which received the most diluted medium from 4 Gy QU-DB irradiated cells reached the maximum level compared to MNBN frequency of cells that received complete medium (P < 0.0001).
Conclusion
Our results showed that RIBE levels decreased at doses above 4 Gy; however, RIBE increased when diluted conditioned medium was transferred to bystander cells. This finding confirmed that a negative feedback mechanism was responsible for the decrease in RIBE response at high doses. Decrease of RIBE at high doses might be used to predict that in radiosurgery, brachytherapy and grid therapy, in which high dose per fraction is applied, normal tissue damage owing to RIBE may decrease.
Keywords
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