2258 - Are Smaller Clinical Target Volume Margins Safe In Radiotherapy for Glioblastomas and High-Grade Gliomas? A Systematic Review and Meta-Analysis

03:00pm - 04:00pm ET

Poster Hall - Exhibit Hall A

Screen: 13

POSTER

Presenter(s)

Nicole Wisener, MSc, BMSc - University of Ottawa, Ottawa, ON

N. Wisener¹, D. Chen², J. Detsky^3,4, D. Dinakaran^4,5, H. Soliman^3,4, C. L. Tseng^4,5, K. L. Zeng^4,5, A. Sahgal^3,4, and H. Chen^4,5; ¹University of Ottawa, Ottawa, ON, Canada, ²University of Toronto, Toronto, ON, Canada, ³Department of Radiation Oncology, Odette Cancer Centre, Sunnybrook Health Sciences Centre, University of Toronto, Toronto, ON, Canada, ⁴Department of Radiation Oncology, University of Toronto, Toronto, ON, Canada, ⁵Department of Radiation Oncology, Odette Cancer Centre, Sunnybrook Health Sciences Centre, Toronto, ON, Canada

Purpose/Objective(s): Radiotherapy for high-grade gliomas (HGGs), including glioblastoma (GBM), has traditionally used large clinical target volume (CTV) margins, although this approach is being increasingly challenged. This study aims to systematically review comparative evidence on larger vs. smaller CTV margins in radiotherapy for GBM and non-GBM HGG, assessing overall survival (OS), progression-free survival (PFS), toxicity, and quality of life (QOL). We hypothesized that smaller margins would not compromise OS, PFS, or QOL, nor increase toxicity.

Materials/Methods: This PRISMA-guided systematic review (PROSPERO #CRD420251022791) included retrospective/prospective comparative effectiveness studies (CESs) and randomized controlled trials (RCTs) reporting OS, PFS, disease control, toxicity, and/or QOL from the MEDLINE, Embase, Scopus, and Cochrane CENTRAL. Case reports, reviews, guidelines, communications and abstract-only studies were excluded. Where available, Kaplan-Meier OS and PFS curves were digitized and data were extracted for meta-analysis with random-effects models.

Results: Of 1311 records reviewed, 13 studies were identified for full data abstraction. Five were RCTs and 8 were retrospective cohort studies. A total of 1729 patients with 1732 lesions were analyzed across all studies, with the majority (78%) being GBM patients. Overall, 899 lesions were treated using larger radiotherapy margins, while 833 lesions used smaller margins. Though the definitions of larger vs. smaller CTV margins varied across studies, larger margins were generally characterized by inclusion of all peritumoral edema within the CTVs and larger (2-3 cm) gross tumor volume (GTV) to CTV expansions, whereas smaller margins typically reflected a direct CTV expansion of <2 cm around GTV without inclusion of all peritumoral edema. Overall, no study reported inferior outcomes with smaller CTV margins when directly compared to larger CTV margins, regardless of target definitions used. Meta-analysis revealed a trend towards better OS for smaller margins, with low between-study heterogeneity (Pooled HR = 0.87 [0.75-1.01], I2 = 5%). There was no significant difference between margin sizes for PFS, with moderate heterogeneity (Pooled HR = 0.91 [0.75-1.11], I2 = 51%). Rates of marginal failure ranged from 2%-55% in the larger margin group and 0%-9% in the smaller margin group, with no statistically significant difference found in any study. Reported radiation necrosis rates ranged from 0%-34% for larger margins and from 0% to 21% for smaller margins, with one study showing a statistically significant difference in favour of smaller margins.

Conclusion: Existing comparative effectiveness literature uniformly supports that smaller CTV margin sizes do not compromise clinical outcomes in patients receiving radiotherapy for GBM and non-GBM HGG.