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Dosimetric Comparison of Gamma Knife(R) IconTM and Linear Accelerator-Based FSRT Plans for the Re-Irradiation of Large (> 14 Cc) Recurrent Glioblastomas

M Schelin*, H Liu, W Shi, Y Yu, K Mooney, Thomas Jefferson University, Philadelphia, PA


(Sunday, 7/12/2020)   [Eastern Time (GMT-4)]

Room: AAPM ePoster Library

Purpose: To investigate dosimetric differences between clinically deliverable Leksell Gamma Knife® (GK) Icon™ and linear accelerator-based FSRT plans on the basis of normal brain sparing for re-irradiation of large (> 14cc) recurrent glioblastomas (GBM).

Methods: Eight patients with large, recurrent GBM (PTV mean = 40cc, range 17-75cc) were treated using re-irradiation via linac-based FSRT with a dose of 35Gy in 10 fractions. For each patient, a new GK FSRT plan was created in Leksell GammaPlan® V11 (LGP) with identical treatment volumes and the same target coverage goal, PTV V100% > 95%. To maintain clinical deliverability, the LGP optimization included a planning goal of treatment time < 20 minutes, with an absolute maximum treatment time of 40 minutes. Dosimetric comparisons of the two plans were performed in MIM. For both plan types, target coverage, conformity index (CI), gradient index (GI), normal brain V4, V12, V20, and treatment time were recorded. Statistical significance was measured using the two-tailed, paired t-test with p<0.05.

Results: The GK FSRT plans had significantly (p<0.05) lower mean values of normal brain V12 (-21.3%) and V20 (-24.9%), and a lower mean V4 (-5.34%). There was an increase in target coverage (mean = 2.25%, max = 22.0%) and CI (mean = 3.33%, max = 33.8%), and a decrease in GI (mean = -15.1%, max = -52.2%), but these differences were not statistically significant. All OAR doses were clinically acceptable. The mean GK treatment time was 18 minutes (max = 26 minutes), significantly increased compared to the linac-based plans (mean = 5 minutes, max = 8 minutes).

Conclusion: Clinically deliverable GK FSRT plans decrease normal brain dose compared to standard linac-based FSRT for the re-irradiation of large, recurrent glioblastomas. GK FSRT has the potential to improve patient outcomes for this patient population by reducing the risk of CNS toxicities.


Gamma Knife, Stereotactic Radiosurgery, Brain


TH- External Beam- Photons: gammaknife

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