Quantitative Imaging of Patients Undergoing Radiotherapy for Primary Gliomas Using A 1.5 Tesla MR Linac

Abstract

The introduction of a 1.5 Tesla MR-Linac (MRL) allows for the acquisition of diagnostic quality MR images, either as ancillary studies during treatment on a conventional Linac (cLinac) or seamlessly during treatment on the MRL. We present the first in human experience imaging and treating primary brain tumors using a 1.5 Tesla MRL. Between February of 2019 and January of 2020 a total of 4 patients with gliomas have been treated using the MRL, with daily quantitative MR (qMR) and 3 patients had weekly acquisition of qMR images while undergoing treatment on a cLinac in a prospective imaging trial (NCT03500081). A detailed log during each treatment was obtained for the duration and changes in treatment time. Quantitative MR sequences (IVIM, T1 and T2 mapping) were acquired for patients treated on the MRL while adaptive planning was performed and during beam delivery. Patients treated on the MRL had daily acquisition of qMR sequences. Patients treated on cLinac were scheduled for weekly qMR imaging. qMR sequences obtained are in Table 1. Independent, FDA approved, commercially available software was used for qMRI processing and radiomic feature extraction. Six patients with WHO Grade IV tumors were treated with 60 Gy, while one WHO Grade II tumor of the brainstem was treated to 59.4Gy. The median patient age was 60. Median follow up is 4.7 months, four patients have progressed. Patients treated on the MRL had a median table time of 28 minutes including daily adaptation and optimization of IMRT plan, physician review, treatment and all qMR imaging. Weekly imaging sessions for patients treated on cLinac ranged from 15-33 minutes. Analysis of the qMR data demonstrated variable % change in median values within the Gross Target Volume (Table 1). ADC, T1, and T2 parameters ranged from (-0.2 – 25%), (-1 – 36%), and (3-22%) within the GTV, respectively. Changes in quantitative T1 (14-36%) and T2 (15-22%) within the GTV over the course of treatment were observed in the recurring patients. We present a first in human experience of imaging and treating primary gliomas with a 1.5 Tesla MR. It was feasible to treat patients on the MRL and obtain qMR imaging without additional table time. It was also feasible to integrate weekly imaging into a standard clinical work flow without increasing time. While entirely exploratory and hypothesis generating, highly unique changes in qMRI parameters were seen in those patients who developed progression. This presents an unparalleled opportunity for collection, validation, and future interventional trial integration of MR biomarkers of radiation response in primary glioma. Table 1: % Change Median Value for GTV.Tabled 1Abstract 2641; TablePatientMachineIVIMADCDSLOWDFASTFMAPT1MapT2Map1MRL7-0.25-0.2-10-132-17252415-258153-21141311-536154151812313314225conventional2761167-7-3 Open table in a new tab