UCLA Journal of Radiation Oncology SPRING 2024 - Flipbook - Page 38
UCLA RADIATION ONCOLOGY JOURNAL
perform a randomized controlled trial for every new treatment paradigm. While some endpoints
require robust prospective data and extended time periods to measure, such as disease-specific and
overall survival, there are other relevant endpoints, such as acute toxicity, which can be determined
in a shorter timeframe. Thus, the widespread use of MRgRT need not be delayed until longer-term
endpoints are met, similar to the intuition around and the adoption of IMRT.76,77 It should also be noted
that level I evidence is similarly not reasonable nor a required threshold for the creation of a new
Current Procedural Terminology (CPT) code to, for example, capture the work and practice expense of
MR-guided adaptive radiation therapy. Therefore, we must carefully consider the evidence threshold
required for widespread adoption of MRgRT and associated processes of care. Fortunately, efforts are
already ongoing to ensure the appropriate accumulation of data for the introduction of MRgRT.78
Additional Opportunities for Value with Disruptive Workflows
While the advantages of MRgRT with respect to cancer outcomes make it appealing from the value
perspective, additional value may come from the disruptive workflows inherent to MRI simulation and
adaptive processes of care. These aspects relate to the structure and process components of the value
equation describe above. Regarding the MRgRT simulation process, being able to omit CT simulation
improves value from the patient and system perspectives through reduced appointments, radiation
exposure, and overall healthcare congestion, among other factors. Instrumental to this process is
the use of synthetic CTs, in which MRI simulation images are converted to synthetic CT data (eg,
Hounsfield Units) necessary for dose calculation and treatment planning, which are actively being
studied and validated.43, 44, 45 Additionally, use of both CT and MRI simulations for treatment planning,
which is increasingly the case for disease sites where soft tissue resolution is paramount such as central
nervous system, head and neck, and gastrointestinal tumors,42 can introduce errors during the image
registration process,79 introducing yet another opportunity for improvement in outcomes with MRIonly workflows.
However, there are multiple potential advantages of MRI simulation in and of itself compared with CT
simulation, which invite additional opportunities for innovation and improving value. For example,
the superior soft tissue visualization with MRI allows for improved target delineation such that
MRI simulation-based target delineation notably results in smaller clinical target volumes (CTVs) in
prostate80 and cervical cancer.81 Furthermore, when combined with online adaptive planning in lung
cancer, MRI-based planning resulted in smaller PTVs than would have been generated from an internal
target volume (ITV) approach.82 Additionally, a recent small retrospective study found that the use of
MRI simulation was associated with improved local control in nasopharyngeal cancer, particularly
in stage T4 disease, compared with PET/CT simulation, which was proposed to be the result of full
visualization of disease extent with MRI.83 MRI-only workflows have been developed84, 85 (Fig. 4), and
the feasibility and safety of a same-day MRI-only simulation with an adaptive MRgRT workflow was
recently demonstrated in palliative radiotherapy cases with encouraging results.86 The improved value
to the patient provided by this accelerated process is apparent in the palliative setting, where symptom
control and minimizing treatment length are emphasized, though this expedited workflow would
certainly benefit all patients, especially those receiving a single fraction of radiation or travelling from
great distances. Further in the future, with the real-time motion management and plan adaptation
capabilities of MRgRT, the concept of the PTV may be rendered obsolete, and future treatments might
be planned based solely on the gross tumor volume (GTV) or CTV, which would allow for further
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