Evaluation of Organs-at-Risk Sparing for Glioblastoma Patients Using a Small-Margin Weekly Adaptive Protocol on a 1.5T MR-Linac
Abstract
Purpose: To assess the dosimetric impact on organs-at-risk (OARs) and target coverage of a small-margin weekly adaptive treatment for glioblastoma delivered on an MR-Linac.
Methods and materials: The UNIty-Based MR-Linac Guided AdapTive Radiation thErapy for High GraDe Glioma (UNITED) phase 2 prospective trial used a 5 mm clinical target volume (CTV) margin compared to conventional 1.5 to 3 cm CTV margins. Margin reduction was supported by weekly administration of gadolinium contrast and adaptation to gross tumor volume changes using onboard MR imaging. In the present study, dosimetric data from 29 patients with UNITED plans (PUNITED) treated with 60 Gy in 30 fractions were retrospectively replanned with conventional margins (PConv) and compared. For each patient, 6 weekly adapted and 1 conventional margin nonadapted plan were included in the analysis. Relevant OAR dose metrics were compared using Friedman tests followed by Nemenyi post hoc analysis (α = 0.005, corrected for multiple comparisons).
Results: A substantial and statistically significant reduction in irradiated normal brain volume was achieved with the median V60Gy lowered from 146.3-157.3 cm3 (range of median weekly values) with PConvto 84.2-93.4 cm3 for PUNITED (P < .0001). The median max dose to the brainstem and optic chiasm was reduced from 56.1 Gy to 49.0 Gy (P = .0001) and from 41.5 Gy to 38.4 Gy (P < .0001), respectively. In addition to OAR sparing, 10 of 29 patients experienced suboptimal target coverage…
How strong is the evidence?
Evidence Hub reads this as a clinical trial, done in people. Its evidence level is 3 of 5 (Moderate · trial / cohort / secondary analysis). Trials without a large randomized design, cohorts and secondary analyses give moderate evidence. Reported size: 29 participants or records.
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