RESUMO
BACKGROUND: Considering the increasing simultaneous application of magnetic resonance imaging (MRI) for more precise photon radiotherapy, it will be likely for particle radiotherapy to adopt MRI for future image guiding. It will then be imperative to evaluate the potential biological effects of a magnetic field (MF) on particle irradiation. This study explores such effects on the highly radiosensitive TK6 lymphoblastoid human cell line. METHODS: The following three parameters were measured after irradiation with either carbon ion or proton beams using spread out Bragg peaks and applying different doses within a perpendicular 1.0 T MF: (1) cell survival fraction (14 days postirradiation), (2) treatment-specific apoptosis, which was determined through the measurement of population in the sub-G1 phase, and (3) cell cycle progression by means of flow cytometry. These were compared to the same parameters measured without an MF. RESULTS: The clonogenic assay in both treatment groups showed almost identical survival curves with overlapping error bars. The calculated α values with and without an MF were 2.18 (σ=0.245) and 2.17 (σ=0.234) for carbon ions and 1.08 (σ=0.138) and 1.13 (σ=0.0679) for protons, respectively. Similarly, the treatment-specific apoptosis and cell cycle progression showed almost identical curves with overlapping error bars. A two-sample, unpooled t-test analysis was implemented for comparison of all mean values and showed p-values >0.05. CONCLUSION: No statistically significant difference in biological response of the TK6 cells was observed when they were irradiated using spreadout Bragg peaks within a perpendicular 1.0 T MF as compared to those, which received the same dose without the MF. This should serve as another supporting piece of evidence toward the implementation of MRI in particle radiotherapy, though further research is necessary.
RESUMO
BACKGROUND: The implementation of magnetic resonance imaging (MRI) guided radiotherapy (RT) continues to increase. Very limited in-vitro data on the interaction of ionizing radiation and magnetic fields (MF) have been published. In these experiments we focused on the radiation response in a MF of the TK6 human lymphoblastoid cells which are known to be highly radiosensitive due to efficient radiation-induced apoptosis. METHODS: Clonogenicity was determined 12-14 days after irradiation with 1-4 Gy 6 MV photons with or without a 1.0 Tesla MF. Furthermore, alterations in cell cycle distribution and rates of radiation induced apoptosis (FACS analysis of cells with sub-G1 DNA content) were analyzed. RESULTS: Clonogenic survival showed an exponential dose-dependence, and the radiation sensitivity parameter (α = 1.57/Gy) was in accordance with earlier reports. Upon comparing the clonogenic survival between the two groups, identical results within error bars were obtained. The survival fractions at 2 Gy were 9% (without MF) and 8.5% (with MF), respectively. CONCLUSION: A 1.0 Tesla MF does not affect the clonogenicity of TK6 cells irradiated with 1-4 Gy 6MV photons. This supports the use of MRI guided RT, however ongoing research on the interaction of MF and radiotherapy is warranted.
