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Some Unique Radiation-Safety Related Challenges with Installation of a MR-Linac

G Pang, Odette Cancer Centre and Department of Radiation Oncology, University of Toronto, Toronto, ON, CA


(Sunday, 7/12/2020)   [Eastern Time (GMT-4)]

Room: AAPM ePoster Library

Purpose: Compared to conventional Linacs, there are some unique radiation safety related challenges during installation of a MR-Linac. The purpose of this work is to review these challenges and provide solutions based on our experience with a MR-Linac.

Methods: A new MR-Linac (Elekta) was installed and commissioned. Measures were taken to address some unique radiation-safety issues during room design, machine installation and commissioning. These include: (1) The room must be shielded for both ionizing radiation and MR fields with the Faraday cage being placed inside the radiation shielding; (2) For a room without a maze, there is potentially a direct line of sight from the x-ray target through an air gap under the shielding door. This is because the x-ray target of a MR-Linac can go below the floor level. We designed a shielding door that goes below the floor level to avoid the problem; (3) Due to the unusual large size of the gantry we had to cut a hole in the roof to deliver the machine and then covered the hole with a concrete layer; (4) There are only a few locations inside the room where EPOs and LPO can be installed due to the presence of Faraday cage. A large mirror was used in order to view the whole room at the location of LPO; (5) Conventional radiation survey meters usually do not work in a strong magnetic field. Measurement of activation inside the room was done within a short time window in commissioning, during which the Linac was running but no magnetic field was applied. (6) Radiation monitoring badges for staff were modified to make them MR safe.

Results: Regulatory compliance was met and an operating licence was obtained.

Conclusion: Care must be taken to address some unique radiation safety issues with installation of a MR-Linac.


Radiation Protection, MRI, Linear Accelerator


IM/TH- MRI in Radiation Therapy: MRI/Linear accelerator combined (general)

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