In the first 21 months of our study, patterns of care were diverse with respect to clinical utilization, body sites and radiation prescriptions. No patient discontinued treatment due to inability to tolerate daily high-field MR-scans and the acute radiation toxicity experience was encouraging.
Patients were included between February 2019 to October 2020 at seven institutions in four countries. We used descriptive statistics to describe the patterns of care, tolerability (the percentage of patients discontinuing their course early) and safety (grade 3-5 CTCAE v.5 acute toxicity within 3 months after end of treatment).
A total 943 patients participated in the XXX Study, 702 of whom had complete baseline data at the time of this analysis. Patients were primarily male (79%) with a median age of 68 years (range: 22-93), and were treated for 39 different indications. The most frequent indications were prostate (40%), oligometastatic lymph node (17%), brain (12%), and rectal (10%) cancers. The median number of fractions was 5 (range 1-35). Six patients discontinued MR-Linac treatments, but none due to an inability to tolerate repeated high-field MRIs. Of the 415 patients with complete data on acute toxicity at 3 months follow up, eighteen (4%) patients experienced grade 3 acute toxicity related to radiation. No grade 4 or 5 acute toxicity related to radiation was observed.
High-field MR-Linacs, linear accelerators (linac) combined with a diagnostic MRI scanner and online adaptive workflow, potentially give rise to novel online anatomic and response adaptive radiotherapy paradigms. Since the first high-field (1.5T) MR-Linac received regulatory approval in late 2018, little is known about clinical use, patient tolerability of daily high-field MRIs, and toxicity of treatments. Herein we report the initial experience within XXX (XXX), a prospective international registry of the XXX.