Radio frequency shielding for a linac-MRI system.

The real-time operation of a linac-MRI system will require proper radio frequency (RF) shielding such that the MRI images can be acquired without extraneous RF noise from the linac. We report on the steps taken to successfully shield the linac from the MRI such that the two devices can operate independently of one another. RF power density levels are reported internally and externally to the RF cage which houses the linac and MRI. The shielding effectiveness of the RF cage has been measured in the frequency range 1-50 MHz and is presented. Lastly MRI images of two phantoms are presented during linac operation. This work illustrates that the accelerating structure of a linac and an MRI can be housed within the same RF cage. The 6 MV linac can be operated to produce radiation with no measurable degradation in image quality due to RF effects.