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  4. Dosimetric Evaluation On Single-Isocenter Versus Multiple-Isocenter Frameless Volumetric Modulated Arc Radiosurgery for Simultaneous Treatment of Multiple Intracranial Metastases

Dosimetric Evaluation On Single-Isocenter Versus Multiple-Isocenter Frameless Volumetric Modulated Arc Radiosurgery for Simultaneous Treatment of Multiple Intracranial Metastases

Z Huang1,2*, Y Feng1 , C Luo3 , T Liu4, D Zhu2, S Lo5 , N Mayr5 , W Yuh5 , (1) East Carolina Univ, Greenville, NC, (2) Saint Thomas Rutherford Hospital, Murfreesboro, TN, (3) University Hospitals Cleveland Medical Center, Mentor, OH, (4) Methodist Hospital, Houston, TX, (5) University of Washington, Seattle, WA

Presentations

(Sunday, 7/14/2019)  

Room: ePoster Forums

Purpose: The aim of this study is to provide a comparison between single-isocenter and multiple-isocenter planning technique and evaluation of plan quality for the multi-lesion, single-isocenter versus multiple-isocenter stereotactic ablative radiotherapy of the intracranial metastasis.

Methods: From dosimetric pointview, we performed a comparison between single-isocenter and multiple-isocenter treatment planning of 5 patients undergoing frameless VMAR for multiple intracranial metastases in 2017. A total of 9 metastases (median 3 per patient, range 2-4) were treated to a median dose of 24.4 Gy (range, 20-30 Gy). 2 patients were treated with single fractionation and 1 patient was treated with fractionated SRS. Follow-up including clinical examination and magnetic resonance imaging (MRI) occurred every 3 months. Conformal index (CI) was defined as the ratio of the volume covered by 100% prescription dose to the target volume. Homogeneity index (HI) was defined as the ratio of maximum dose in PTV to prescription dose. Q-Ratio of the minimal dose in PTV to prescription dose was reported as well as doses to critical structures such as optic nerves, chiasm, brainstem, eyes, lens.

Results: The average CI was 1.01 and 0.97 for single-isocenter versus multiple-isocenter treatment planning for these 9 metastatic masses. There was no difference in both Q and HI (0.92 and 0.92; 1.22 and 1.21, respectively). The maximum doses to left optic nerve, right optic nerve, and optical chiasm were higher in single-isocenter than multiple-isocenter plans (3.74 vs 1.49 Gy, 1.72 vs. 1.49 Gy, 2.12 vs.1.84 Gy, and 3.73 vs. 2.72 Gy, repectively). However, the maximum dose to brainstem was lower in single-isocenter than multiple-isocenter plans (6.28 vs. 6.61 Gy).

Conclusion: The single-isocenter frameless VMAR for multiple intracranial metastases provide a promising technique that may provide similar quality of treatment planning compared to multiple-isocenter planning radiosurgery.

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