UCLA Journal of Radiation Oncology SPRING 2024 - Flipbook - Page 35
UCLA RADIATION ONCOLOGY JOURNAL
Outcomes
The ability of a treatment or technology to improve oncologic outcomes, such as toxicity or disease
control, is a crucial component of value in radiation oncology and healthcare as a whole. Multiple
studies have started to report on the clinical outcomes of MRgRT in a variety of cancer sites.50 While
these data are mostly retrospective in nature, there exist some high-quality prospective studies which
begin to confirm the theoretical benefits of MRgRT with respect to cancer outcomes.
The recently published MIRAGE clinical trial34 randomized men with clinically localized prostate
cancer to either CTgRT or MRgRT and sought to evaluate whether reductions in isotropic planning
target volume (PTV) margins from 4 mm to 2 mm, enabled by MRgRT, would reduce the risk of acute
genitourinary (GU) and gastrointestinal (GI) toxicity from SBRT. Indeed, the incidence of physicianreported acute GU (24.4% versus 43.4%, 56.2% relative reduction) and GI (0.0% versus 10.5%, 100%
relative reduction) toxicities were improved in the MRgRT arm, as were patient-reported toxicity
outcomes. In the economic analyses discussed above, relative reductions in toxicity of 7-54% were
needed for MRgRT to become cost-effective compared with CTgRT,51, 52 a threshold which was met
and indeed exceeded by the results of this trial. Additionally in this trial, patients in the CTgRT arm
required fiducial placement whereas those in the MRgRT arm did not, adding further cost savings to
the healthcare system otherwise unaccounted for with MRgRT. However, this trial also demonstrated
some of the economic concerns with MRgRT, including the need for 2 simulation scans (CT and
MRI) in the healthcare system where this single institution study was carried out and increased postimaging treatment delivery times with MRI versus CT guidance (median 1133 seconds versus 232
seconds). Nevertheless, a rigorously demonstrated decrease in radiation-associated toxicity should not
be overlooked as it not only improves patient health-related quality of life, but it also reduces acute
hospital encounters related to treatment toxicity which can be associated with high costs, procedures,
and overall burden for patients, providers, and the healthcare system. Drawing parallels between
MRgRT and other historical innovations in radiation oncology, namely IMRT, recall that the widespread
adoption of this novel technology was primarily spurred by its associated improvements in normal
tissue sparing and toxicity,53, 54, 55 and perhaps an analogous implementation threshold would be
worthwhile for MRgRT.
While the MIRAGE trial demonstrated the toxicity benefits that MRgRT can provide without daily
adaptation, the SMART trial further demonstrated the potential advantages of MRgRT by incorporating
adaptive planning.56 In this multi-center, single-arm phase II trial of MRgRT in borderline resectable
or locally advanced pancreatic cancer, patients were treated to an unprecedented dose of 50 Gy in 5
fractions, and on-table adaptive re-planning was used if the original radiation plans recomputed onto
the daily anatomy would not meet treatment constraints. This resulted in adaptive planning being
performed in 93.1% of fractions. Overall, there were low rates of acute grade 3 or higher GI toxicity
probably (2.2%) and definitely (0%) related to radiation therapy at the augmented dose. Furthermore,
this study also reported noteworthy oncologic outcomes including 1 year local control (82.9%),
distant progression free survival (50.6%), and overall survival (65.0%). Previous research of MRgRT in
inoperable pancreatic cancer found that dose-escalation above a biologically effective dose 10 (BED10)
of 70 Gy, which was primarily achievable by adaptive MRgRT, was associated with improved overall
survival without an increase in toxicity.57 In fact, patients treated with dose-escalated adaptive MRgRT
experienced less toxicity than patients treated at a lower BED10 without adaptive radiation therapy. The
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