Influence of a perpendicular magnetic field on biological effectiveness of carbon-ion beams

Abstract

Purpose: Our previous study revealed that the application of a magnetic field longitudinal to a carbon-ion beam of 0.1 ≤ B_//≤ 0.6 T enhances the biological effectiveness of the radiation. The purpose of this study is to experimentally verify whether the application of a magnetic field perpendicular to the beam also alters the biological effectiveness.

Methods and materials: Most experimental conditions other than the magnetic field direction were the same as those used in the previous study to allow comparison of their results. Human cancer and normal cells were exposed to low (12 keV/μm) and high (50 keV/μm) linear energy transfer (LET) carbon-ion beams under the perpendicular magnetic fields of $B_{\perp }$= 0, 0.15, 0.3, or 0.6 T generated by a dipole magnet. The effects of the magnetic fields on the biological effectiveness were evaluated by clonogenic cell survival. Doses that would result in the survival of 10%, D₁₀s, were determined for the exposures and analyzed using Student’s t-tests.

Results: For both cancer and normal cells treated by low- and high-LET carbon-ion beams, the D₁₀s measured in the presence of the perpendicular magnetic fields of $B_{\perp }$≥ 0.15 T were not statistically different (p ≫ .05) from the D₁₀s measured in the absence of the magnetic fields, $B_{\perp }$= 0 T.

Conclusions: Exposure of human cancer and normal cells to the perpendicular magnetic fields of $B_{\perp }$≤ 0.6 T did not alter significantly the biological effectiveness of the carbon-ion beams, unlike the exposure to longitudinal magnetic fields of the same strength. Although the mechanisms underlying the observed results still require further exploration, these findings indicate that the influence of the magnetic field on biological effectiveness of the carbon-ion beam depends on the applied field direction with respect to the beam.

Keywords:

• Perpendicular magnetic field
• carbon-ion radiotherapy
• biological effectiveness

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Notes on contributors

Taku Inaniwa

Taku Inaniwa is a Researcher in the field of medical physics. He is a member of Department of Accelerator and Medical Physics at National Institute of Radiological Sciences (NIRS), QST.

Masao Suzuki

Masao Suzuki is a Researcher in the field of radiation biology. He is a member of Department of Basic Medical Sciences for Radiation Damages at NIRS, QST.

Shinji Sato

Shinji Sato is a Technician specialized in electronics. He is a member of Department of Accelerator and Medical Physics at NIRS, QST.

Akira Noda

Akira Noda is a Researcher in the field of accelerator and beam physics. He is a member of Department of Accelerator and Medical Physics at NIRS, QST.

Masayuki Muramatsu

Masayuki Muramatsu is a Researcher in the field of accelerator and beam physics. He is a member of Department of Accelerator and Medical Physics at NIRS, QST.

Yoshiyuki Iwata

Yoshiyuki Iwata is a Researcher in the field of accelerator and beam physics. He is a member of Department of Accelerator and Medical Physics at NIRS, QST.

Nobuyuki Kanematsu

Nobuyuki Kanematsu is a Researcher in the field of medical physics. He is a member of Medical Physics Section at NIRS Hospital, QST.

Toshiyuki Shirai

Toshiyuki Shirai is a Researcher in the field of accelerator and beam physics. He is a director of Department of Accelerator and Medical Physics at NIRS, QST.

Koji Noda

Koji Noda is a Researcher in the field of accelerator and beam physics. He is a director general of NIRS, QST.