Dosimetry and linac acceptance for the 1.5 T MRI-Linac

Abstract

This thesis concerns the Unity MRI-linac (and its prototypes). The overall aim was to ensure that the MRI-linac was safe and effective for clinical use, and could be introduced into the clinic. To this end it was necessary to identify and solve issues related to reference dosimetry in a magnetic field, acceptance testing of a new system in a new physical configuration, and beam characterisation in a magnetic field.

Results and analysis are provided. A major contribution was the development of a reference dosimetry framework that allows dosimetry to be performed at an MRI-Linac by the local clinical physicist using standard equipment, and where all correction factors can be independently verified.

Additional contributions included evidence of the consistency of ion chamber magnetic field correction factors; evidence of the suitability of a microDiamond small-field detector; a linac acceptance procedure that can be performed by local clinical physicists, and; the first beam characterisation data suitable for modeling the radiation beam in the treatment planning system, such that the system could then be used to plan and deliver radiation treatments.