Direct dosimetric comparison of linear accelerator vs. Gamma Knife fractionated stereotactic radiotherapy (fSRT) of large brain tumors

Emel Calugaru; Zachary Whiting; Brandon Delacruz; Daniel Ma; Barbara Garcia; Anuj Goenka; Jenghwa Chang

doi:10.1016/j.meddos.2022.09.006

Direct dosimetric comparison of linear accelerator vs. Gamma Knife fractionated stereotactic radiotherapy (fSRT) of large brain tumors

Med Dosim. 2023;48(1):31-36. doi: 10.1016/j.meddos.2022.09.006. Epub 2022 Dec 8.

Authors

Emel Calugaru¹, Zachary Whiting², Brandon Delacruz², Daniel Ma¹, Barbara Garcia², Anuj Goenka¹, Jenghwa Chang³

Affiliations

¹ Radiation Medicine Department, Northwell Health, New Hyde Park, New York 11042, USA.
² Department of Physics and Astronomy, Hofstra University, Hempstead, New York 11549, USA.
³ Radiation Medicine Department, Northwell Health, New Hyde Park, New York 11042, USA; Department of Physics and Astronomy, Hofstra University, Hempstead, New York 11549, USA. Electronic address: jchang24@northwell.edu.

PMID: 36503990
DOI: 10.1016/j.meddos.2022.09.006

Abstract

The purpose of this study was to directly compare the plan quality of Gamma Knife (GK) (Elekta, Stockholm, Sweden)- vs linear accelerator (LINAC)-based delivery techniques for fractionated stereotactic radiotherapy (fSRT) of large brain metastases. Eighteen patients with clinical target volumes (CTVs) larger than 9.5 cc were selected to generate comparative plans for the prescription dose of 9 Gy × 3 fractions, utilizing the Eclipse (Varian, Palo Alto, US) vs Leksell GammaPlan (LGP) (Elekta, Stockholm, Sweden) treatment planning systems (TPS). Each GK plan was first developed using LGP's automatic planning, followed by manual adjustments/refinements. The same MRI and structures, including CTVs and organs at risk, were then DICOM-transferred to the Eclipse TPS. Volumetric Modulated Arc Therapy (VMAT) and Dynamic Conformal Arc (DCA) plans for a Truebeam, with high-definition multi-leaf collimators (MLCs), were developed on these MR images and structures using a single isocenter and 3 non-coplanar arcs. No planning target volume (PTV) margins were added, and no heterogeneity correction was used for either TPS. GK plans were prescribed to the 50% isodose line, and Eclipse VMAT and DCA plans allowed a maximum dose up to 170% and ∼125%, respectively. Gradient index (GI), Paddick Conformity Index (PCI), V₂₀_GyRind, and V₄_GyRind of all 3 techniques were calculated and compared. One-way analysis of variance (ANOVA) was performed to determine the statistical significance of the differences of these planning indices for the 3 planning techniques. A total of eighteen treatment targets were analyzed. Median CTV volume was 14.4 cc (range 9.5 cc - 55.9 cc). Mean ± standard deviation of PCI were 0.85 ± 0.03, 0.90 ± 0.03, and 0.72 ± 0.11 for GK, VMAT and DCA plans, respectively. They were respectively 2.64 ± 0.17, 2.46 ± 0.18, and 2.83 ± 0.48 for GI; 15.33 ± 8.45 cc, 10.47 ± 4.32 cc and 23.51 ± 16 cc for V₂₀_GyRind; and 316.28 ± 138.35 cc, 317.81 ± 108.21 cc, and 394.85 ± 142.16 cc for V₄_GyRind. The differences were statistically significant with p < 0.01 for all indices, except for V₄_GyRind (p > 0.129). In conclusion, a direct dosimetric comparison using the same MRI scan and contours was performed to evaluate the plan quality of various fSRT delivery techniques for CTV > 9.5 cc. LINAC VMAT plans provided the best dosimetric outcome in regard to PCI, GI, and V₂₀_GyRind. GK outcomes were similar to LINAC VMAT plans while LINAC DCA outcomes were significantly worse. Even though GK has a smaller physical penumbra, LINAC VMAT outperformed GK in this study due to enhanced penumbra sharpening and better beam optimization.

Keywords: Fractionated stereotactic radiotherapy; Gamma knife; Treatment planning.

MeSH terms

Brain Neoplasms* / radiotherapy
Brain Neoplasms* / secondary
Humans
Particle Accelerators
Radiosurgery* / methods
Radiotherapy Dosage
Radiotherapy Planning, Computer-Assisted / methods
Radiotherapy, Intensity-Modulated* / methods