Recurrence distance analysis for clinical target volume optimization in glioblastoma

Purpose To analyze the pattern of failure in patients with glioblastoma through recurrence distance analysis, and to evaluate the feasibility of reduced and personalized clinical target volume (CTV-)margins. Methods This study included 201 patients with IDH-wildtype glioblastoma who received standard chemoradiation between 2012 and 2022 and subsequently developed tumor recurrence. From these patients, clinical variables, radiotherapy treatment plans, and imaging data were collected. The recurrence distance was defined as the minimum isotropic expansion from the gross tumor volume (GTV) required to encompass 80% of the recurrence volume (RD 80 ). Multiple linear regression modeling with backward elimination was performed to identify variables that correlate with the RD 80 . Results Median time between the last radiotherapy fraction and progressive disease was 6.8 months (IQR: 4.1–11.8 months). The median RD 80 was 1.2 mm (IQR: 0–6.0 mm). For 80% of the patients in our cohort, the RD 80 was ≤10.4 mm. In the final multiple linear regression model, the log-transformed GTV volume (β = −0.70, p = 3.9e-7), involvement of the subventricular zone (β = 0.53, p = 0.019) and involvement of the subgranular zone (β = 0.51, p = 0.032) were significantly associated with the log-transformed RD 80 . Conclusion This work highlights the potential of reduced CTV-margins in patients with glioblastoma, supporting further prospective evaluation.