A new concept for verifying the isocentric alignment of the proton-rotational gantry for radiation control

  • Takahiro KatoEmail author
  • Yuhei Yamazaki
  • Tatsuhiko Sagara


The purpose of this study was to introduce the modified Winston–Lutz (mWL) test and to evaluate its feasibility. This is a new method to completely absorb the proton beam around the isocenter inside a phantom for radiation control. The mWL test was performed using a 14-cm-diameter acrylic Lucy 3D QA Phantom for a passive-scattering proton beam gantry. The energy of the unmodulated proton beam was adjusted such that the residual range was < 130 mm, and the energy of the proton beam was completely lost around the isocenter. The radiation field was formed with a multi-leaf collimator at 8.6 × 8.6 mm2 in the isocenter plane. The phantom was loaded with a 4-mm-diameter tungsten ball, and the EBT3 was set up at the isocenter. The proton beam was irradiated at gantry angles with 45° steps, and the isocenter deviation of the proton beam was measured and subsequently analyzed. Although the radiation field penumbra was blurred under the influence of scattered radiation due to placement in the phantom compared to the traditional WL test placed in the air, evaluation of the beam axis accuracy was possible. The results confirmed that the maximum total displacement was less than 0.9 mm, and the specifications of the device were met. The mWL test is feasible and effective to reduce the building activation in proton beam treatment facilities. Thus, it can be considered a useful method that sufficiently satisfies the shielding calculation conditions.


Proton beam Radiation control Rotational gantry Winston–lutz test 


Compliance with ethical standards

Conflict of interest

The authors have no conflicts of interest to declare.

Ethical approval

This article does not contain any studies performed with human participants or animals.


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Copyright information

© Japanese Society of Radiological Technology and Japan Society of Medical Physics 2019

Authors and Affiliations

  1. 1.Preparing Section for New Faculty of Medical ScienceFukushima Medical UniversityFukushima CityJapan
  2. 2.Department of Radiation Physics and TechnologyKoriyamaJapan

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