Author: Jamieson Baker, Emel Calugaru, Yijian Cao, Jenghwa Chang, Jessica Jung, Jian Liu, Cindy Pham, Anurag Sharma, John Starner, Ching-Ling Teng, Michael A. Trager, Gabriella Wernicke 👨🔬
Affiliation: Northwell, Northwell Health, Radiation Medicine, Northwell Health, Hofstra University Medical Physics Program 🌍
Purpose: Our hospital network has options to treat recurrent glioblastoma (GBM) with surgically targeted Cesium-131 brachytherapy, external beam stereotactic radiotherapy (SRT) with Varian TrueBeam, Halcyon, or Gamma Knife. This report analyzed the dosimetric features for each modality.
Methods: Eight consecutive recurrent GBM patient from 2022-2024 with Cs-131 Gamma Tile (GT) implants intraoperatively were retrospectively replanned for SRT. Brachytherapy prescription were 60Gy (n=6) and 80Gy (n=2) at 5mm depth. Post-op resection cavities (RC) were contoured on post-implant CT and replanned fSRS (6Gy x 5) with Varian TrueBeam (TB) , Varian Halcyon (HAL) and Gamma Knife (GK). 1mm margin were added to resection cavities for planning and plans were normalized to PTV100% = 99.0% for TB and HAL, PTV100% = 99.5% for GK to according to institutional criteria. Dosimetric parameters were analyzed as conformity index (CI), gradient index (GI), dose median, dose maximum (HI), depth dose at 0-1mm, 5-6mm and 10-11mm from the cavity surface, and V243Gy of normal brain. Statistical significance is defined as p<0.01 by Wilcoxon signed rank test.
Results: Median RC volume is 13.1cc (8.1-40.6cc). Median dose to PTV is 108.2% (range, 106.9-109.5%), 108.2% (106.9%-109.5%), and 137% (125.3-179.9%) prescription dose (Rx) for TB, HAL, and GK respectively, and 113.5% (range, 56.6%-237.7%) Rx to RC+5mm for GT. Dose inhomogeneity defined as the standard deviation (STD) to the mean dose is highest in GT (p = 0.008): STD = 137.9% (48.2-168.2%), 21.15% (15.1-30%), 4.65% (3.9-5.8%), 3.64% (3.3-4.9%) for GT, GK, HAL, and TB respectively. GI is smallest in TB (p = 0.008). Significant dose fall off is highest in TB at = 1cm from the RC (p= 0.008).
Conclusion: This report highlighted differential dosimetric characteristics when treating recurrent GBM with Gamma Tile, Varian TrueBeam, Halcyon and Gamma Knife. Further investigation is needed for clinical significance because of different dosimetry.