Presentation Isocenter Verification of a Compact Rotating Gantry for Carbon Ion Therapy

Saotome, Naoya  ,  Furukawa, Takuji  ,  Saraya, Yuichi  ,  Mizushima, Kota  ,  Hara, Yousuke  ,  Tansho, Ryohei  ,  Shirai, Toshiyuki  ,  Noda, Koji

Purpose: At the National Institute of Radiological Sciences (NIRS), we have been commissioning the rotating- gantry system for the carbon-ion radiotherapy in 2015. It is world’s first rotating-gantry with super-conducting magnet and achieved a more compact, lighter rotating gantry than the typical gantry. During the commissioning of the rotating gantry, we adjusted the beam position using a steel sphere located at isocenter and verified the accuracy using a scintillation screen and CCD system. We employ the digital QA system to verify the geometrical accuracy easily and quickly.Methods: The 300 ton rotating gantry can deliver carbon ions having 430 MeV/u to the isocenter over 360 degrees, having the capability of performing three-dimensional scanning irradiation. the mechanical isocenter was verified using the laser tracker system. To verify the coincidence of the isocenter for irradiation system and the patient positioning system, we used a steel sphere located at isocenter. As a part of the verifying of the treatment beam position, scintillation screen viewed by a CCD camera mounted on the gantry downstream of the sphere. Total 201energy carbon beams with that were in the range from 48 to 430 MeV/u were measured sequentially. A starshot test was also performed to verify the gantry angle and beam direction visually using a scintillator block and a CCD camera. For the starshot test, 13 beam energy were selected. Results: From the result of the test using a sphere, the maximum displacement of the beam position was within 0.5mm at all gantry angles. The gantry starshot shows accuracy of the gantry angle was less than 0.5 degree. Conclusion: The isocentricity of the compact super-conducting rotating gantry for carbon ion therapy dedicated to the highly precise treatment were within 1mm. Two of digital measurement system brought high-efficient beam adjusting and commissioning.
59th AnnualMeeting of American association of Physicists in Medicine (AAPM2017)

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