UNIty-Based MR-Linac Guided AdapTive RadiothErapy for High GraDe Glioma: a Phase 2 Trial (UNITED Trial)

Glioblastoma (GBM) is a high grade glioma (brain tumor) that is treated with surgery or biopsy followed by radiotherapy (RT) given daily over 3 or 6 weeks with or without an oral chemotherapy. Radiation is targeted to the visible residual tumor on magnetic resonance imaging (MRI) images plus a large margin of 15 to 30 mm to account for possible cancer cells outside the visible tumor and for potential growth or shifts in tumor position throughout the prolonged RT course. Standard RT uses MRI to create a reference plan (with large margins) and treats that same volume every day. This exposes a large amount of healthy brain tissue to radiation leading to toxicity and reduced quality of life.

A new technology, the MR-Linac, combines an MRI scanner and a Linac (radiation delivery machine) into one unit. This allows for "adaptive" RT by obtaining an updated MRI scan each day just prior to treatment, adapting the RT plan to take into account any changes in the tumor or the patient's anatomy on that given day. This allows for a smaller (5 mm) margin on the visible tumor as its position can be tracked daily. The goal of this study is to use adaptive RT with small margins to demonstrate that the local control of the visible tumor is not compromised compared to the large volumes used with standard non-adaptive RT, while determining whether smaller margins lead to decreased radiation toxicity and therefore improved quality of life by minimizing radiation exposure.