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  4. Dosimetric Evaluation of a Cone-Based and a MLC-Based Treatment Planning Technique for Multiple Brain Metastases Stereotactic Radiosurgery (SRS)

Dosimetric Evaluation of a Cone-Based and a MLC-Based Treatment Planning Technique for Multiple Brain Metastases Stereotactic Radiosurgery (SRS)

N Vallone1*, J Brindle1,2, Z Saleh1,2, M Schwer1,2, T Dipetrillo1,2, J Hepel1,2, T Kinsella1,2, K Leonard1,2, P Koffer1,2, E Yu1,2,Y Yang1,2, (1) Brown University, Providence, RI (2) Rhode Island Hospital, Providence, RI

Presentations

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

Room: AAPM ePoster Library

Purpose:
Several treatment planning methods are available for multiple brain metastases stereotactic radiosurgery (SRS). This study dosimetrically compared an MLC-based automatic planning with a cone-based manual planning approach in terms of normal tissue sparing and target coverage.

Methods:
Cone plans were previously planned for 10 patients with 2-5 targets (treated in 1-3 plans) with CyberKnife MultiPlan (v5.2, Sunnyvale, CA). MLC plans were then created in Brainlab Elements Multiple Brain Mets module (v2.0, Munich, Germany) with single iso center for a TrueBeam STx with HDMLC (6XFFF). MR/CT images and structures were imported into Elements to eliminate variables. Dosimetric parameters including PTV coverage, maximum dose (Dmax), Conformity Index (CI), Homogeneity Index (HI), Volume normal brain receiving 12Gy (V12Gy) and 3Gy (V3Gy), Dmax to OARs, and beam-on time were obtained and analyzed using a two-tailed paired student t-test.

Results:
PTV coverage was above 99.1% and 99.5% for cone and MLC plans, with Dmax averages of 118% and 120% respectively. CI for MLC plans was 1.42 ± 0.067 compared to 4.88 ± 3.90 for cone plans, with no significant difference for HI. V12Gy and V3Gy were reduced by 3.07 ± 3.78cc and 134 ± 212cc for MLC plans, which also provided lower dose to all OARs including brainstem, cochleae, eyes, lenses, optical chiasm, and optic nerves. Total MUs decreased by 8243 ± 9652 for MLC plans, resulting in a beam-on time reduction of 14.3 ± 12.1 mins. All MLC plans finished within 10 mins while each cone plan took about 3 hours on average.

Conclusion:
Both cone-based and MLC-based planning produced clinically acceptable plans. MLC plans provided significantly superior normal tissue sparing with equivalent PTV coverage, while requiring less beam-on and planning time. This study demonstrated that automatic MLC planning is an effective alternative to cone-based planning for multiple brain metastases SRS.

Keywords

Radiosurgery, Optimization

Taxonomy

TH- External Beam- Photons: intracranial stereotactic/SBRT

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