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MO_1_2458 - Subventricular Zone (SVZ) Radiation Dose and Outcomes in Patients with Glioblastoma Multiforme (GBM)

Monday, October 22
10:45 AM - 12:15 PM
Location: Innovation Hub, Exhibit Hall 3

Subventricular Zone (SVZ) Radiation Dose and Outcomes in Patients with Glioblastoma Multiforme (GBM)
H. Chaudhry Jr, and A. Goenka; Northwell Health, Lake Success, NY

Purpose/Objective(s): The relationship of glioblastoma multiforme (GBM) to neural stem cell regions in the human subventricular zone (SVZ) remains an active area of investigation. Variable findings regarding radiation dosage and tumor control patterns have been described. To investigate this, we looked at patients treated with radiation therapy and concurrent temozolomide to see if incidental dose to the SVZ impacted treatment outcomes. We further subdivided the SVZ into 4 zones, to see if dose to specific zones may better correlate with outcomes.

Materials/Methods: We retrospectively identified all patients at our institution between 2014 and 2016 that were treated for pathologically confirmed GBM and received radiation therapy to a dose of 60 Gy with concurrent temozolomide, without enrollment on clinical trial. 45 patients were identified. The bilateral SVZ (SVZb) was contoured on treatment plans as a 3-mm margin around the ventricles and subdivided into four bilateral zones (frontal (SVZf), insular (SVZin), parietal occipital (SVZpo) and anterior temporal (SVZat). The ipsilateral zone closest to the tumor was classified as the proximal SVZ compartment.

Results: Median LC and OS were 7.7 months and 14.9 months, respectively. The median age was 58 years (range: 23-79 years) and median KPS was 80. 24 patients (53%) underwent GTR, 14 patients STR (31%) and 7 were biopsied (15.6%). Two patients had documented IDH mutations. The tumors were lateralized to the right (n=21) and left (n=24) cerebral hemispheres and located in the frontal (n=12), parietal (n=11), temporal (n=17), occipital (n=2) and multifocal (n=3) lobes. Median SVZi dose was 49.9 Gy (range: 26.5-60.9 Gy), proximal SVZ compartment median dose was 60.3 Gy (range: 11.2-62.0 Gy) and the ipsilateral SVZat median dose was 58.0 Gy (range: 3.7 Gy-61.7 Gy). We did not see a difference in LC associated with dose to the SVZi when analyzed as dose >43 Gy (LC at 6 months, 44% vs. 55%, p=0.42) or as a continuous variable (p=0.67). Dose >60 Gy to the proximal SVZ compartment was also not associated with LC (p=0.29) or OS (p=0.38). Median dose >60 Gy to the SVZat was associated with a trend towards detriment in LC (6 months, 56% vs. 38%, p=0.07) and a significant decrease in OS (6 months, 73% vs. 37%, p=0.01). On multivariate analysis, when including age (p<0.01, HR 1.04) and extent of resection (GTR vs. STR/biopsy, p=0.72), SVZat continued to be independently significant (p<0.01, HR 4.5).

Conclusion: Our data suggests that greater dose to the SVZi may not change local recurrence patterns in patients with GBM. There however seems to be a suggestion that dose >60 Gy to the SVZat may result in a decrease in OS. We hypothesize that this may be due to increased dose to the hippocampal stem cell regions. Further investigation is needed to confirm the results of this study.

Author Disclosure: H. Chaudhry: None. A. Goenka: None.

Huma Chaudhry, MD

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