Abstract
Magnetic resonance imaging guided radiotherapy is a recent development that has the
potential to revolutionise radiotherapy with the integration of magnetic resonance imaging
and a conventional linear accelerator. MRI can clearly observe the changes in shape and
position of target volumes during radiation delivery due to its high soft tissue contrast,
allowing for online, and potentially real time, treatment plan adaptations, whilst providing no
additional radiation to the patient from imaging.
While this technology could increase the effectiveness of radiation treatment, avoiding
unnecessary irradiation of healthy tissue and delivering more precise treatment of target
volumes that have undergone translations and shape deformations, thorough methods of
evaluating the accuracy of adapted treatment plans using the MR-guided systems is essential.
Within this project, a novel assessment methodology has been designed, developed,
evaluated, and finally implemented within an audit of clinical MR-linac systems. The devised
workflow uses a 3D printed pelvis phantom which can be configured to create a wide range
of clinically relevant adaptive radiotherapy scenarios. Clear imaging is possible within both
computed tomography and magnet resonance imaging, enabling the creation of reference
treatment plans, and adapted treatment plans where the prostate and organs at risk have
undergone precise changes in both shape and position. Dosimetry measurements obtained are
compared with calculated doses from the treatment planning system, providing an evaluation
of the accuracy of adaptive radiotherapy. Through the application of this workflow, the high
capabilities of MR-guided systems to treat volumes that have experienced significant changes
has been demonstrated. This innovative assessment methodology provides a beneficial
quality assurance process for online adaptive radiotherapy, as well as future plans consisting
of further developments to allow assessments with real time adaptive radiotherapy treatments.