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), V20GyRind, and V4GyRind 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 V20GyRind; and 316.28 ± 138.35 cc, 317.81 ± 108.21 cc, and 394.85 ± 142.16 cc for V4GyRind. The differences were statistically significant with p < 0.01 for all indices, except for V4GyRind (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 V20GyRind. 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
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Article info
Publication history
Published online: December 08, 2022
Accepted:
September 29,
2022
Received in revised form:
August 19,
2022
Received:
June 5,
2022
Footnotes
Previous Presentations: Part of this work was presented at the 63rd AAPM Virtual Annual Meeting, July 25-July 29, 2021.
Taxonomy: TH- External Beam- Photons: intracranial stereotactic/SBRT.
Identification
Copyright
© 2022 American Association of Medical Dosimetrists. Published by Elsevier Inc. All rights reserved.
