Lack of Impact of Expansion Size From Gross Tumor Volume to Planning Target Volume on Control Rates and Patterns of Recurrence in Fractionated Radiotherapy for WHO Grade 1 Meningiomas.

Objectives: For single-fraction stereotactic radiosurgery (SRS) for WHO grade I meningiomas, no-GTV or minimal-GTV to PTV margin is an accepted practice. We evaluated whether there is a control difference based on GTV to PTV expansion size for fractionated RT.

Methods: Eighty-seven patients with WHO grade 1 meningioma were identified from an institutional database, treated with either conventional immobilization and radiation treatment delivery techniques (cRT) with 5 to 20 mm PTV expansions or fractionated stereotactic radiotherapy (fSRT) with ≤3 mm GTV to PTV expansions. Kaplan-Meier estimators were used for local failure-free survival (LFFS), marginal-failure-free survival (MFFS), and distant failure-free survival (DFFS) analysis.

Results: The median follow-up duration was 9.0 years. Twenty-five patients (29%) received cRT and 62 patients (71%) received fSRT. The median dose was 54 Gray. There were 4 local (5%), 1 marginal (1%), and 1 distant failure (1%). The fSRT and cRT groups each had 2 local failures; 3/4 local failures occurred in areas near critical organs at risk. For cRT versus fSRT, 5-year and 10-year LFFS were 100% versus 98% (P=0.46) and 94% versus 96% (P=0.34), 5-year and 10-year MFFS were 100% versus 100% and 100% versus 92% (P=0.004), and 5-year and 10-year DFFS were 100% versus 98% at both time points (P=0.65 and P=0.67, respectively).

Conclusions: In this patient cohort, there was no local control benefit for larger GTV-to-PTV expansions. For patients with tumors not eligible for SRS, fractionated stereotactic treatment workflow with ≤3 mm PTV expansions is an effective approach for WHO grade 1 meningiomas.