ACPSEM position paper: dosimetry for magnetic resonance imaging linear accelerators

This report provides recommendations on reference dosimetry measurements for MRI-linacs on behalf of the Australiasian College of Physical Scientists and Engineers in Medicine (ACPSEM) MRI-linac working group. There are two configurations considered for MRI-linacs, perpendicular and parallel, referring to the relative direction of the magnetic field and radiation beam, with different impacts on dose deposition in a medium. These recommendations focus on ion chambers which are most commonly used in the clinic for reference dosimetry. Water phantoms must be MR safe or conditional and practical limitations on phantom set-up must be considered. Solid phantoms are not advised for reference dosimetry. For reference dosimetry, IAEA TRS-398 recommendations cannot be followed completely due to physical differences between conventional linac and MRI-linac systems. Manufacturers ’ advice on reference conditions should be followed. Beam quality specification ofTPR20,10 is recommended. The configuration of the central axis of the ion chamber relative to the magnetic field and radiation beam impacts the chamber response and must be considered carefully. Recommended corrections to delivered dose are\({k}_{{Q}_{msr}{Q}_{0}}^{{f}_{msr}{f}_{ref}}\), a correction for beam quality and\({k}_{\overrightarrow{B},{Q}_{msr}}^{{f}_{msr}}\), for the impact of the magnetic field on dosimeter response in the magnetic field. Literature based values for\({k}_{\overrightarrow{B},{Q}_{msr}}^{{f}_{msr}}\) a...
Source: Australasian Physical and Engineering Sciences in Medicine - Category: Biomedical Engineering Source Type: research