Decision-making between DCA and VMAT in Linac-based SRS for brain lesions: A dosimetric analysis based on tumor size
Lara Caglayan1, Davide Scafa1, Patrick Eich1
1Department of Radiation Oncology, University Hospital Bonn, Bonn, Germany.
Introduction:
Linac-based SRS provides a highly precise noninvasive treatment option for intracranial lesions. DCA and VMAT are commonly used Linac-based techniques. There are no standardized guidelines for technique selection, particularly considering the geometric properties of the lesions. We thus sought to compare DCA and VMAT to define a workflow for clinical decision-making. This study introduces Qasym, a novel parameter quantifying lesion asymmetry, and compares the dosimetric performance of DCA and VMAT.
Materials And Methods:
Between 2018 and 2021, a total of 89 brain metastases from 24 patients with lesion volumes up to 4.3 cm3 were included. VMAT and DCA plans were created for each lesion with identical field parameters, resulting in a total of 178 evaluable plans. The parameters included the CI, DSI, and MUs. Various approaches for quantifying asymmetry were explored and their impact on CI and DSI was investigated. Additionally, we introduced the novel Qasym index, designed to quantify lesion asymmetry.
Results:
VMAT resulted in lower CI values, especially for volumes exceeding 2 cm3. With a prescription dose of 20 Gy, DSI90% values were comparable between VMAT and DCA for < 2 cm3, while VMAT achieved lower values for larger volumes. VMAT showed higher DSI50% and DSI25% values for < 2 cm3, which reversed for larger volumes. V2Gy values were similar for both techniques for < 2 cm3 but were lower for VMAT in larger volumes. Qasym significantly correlated with CI (p < 0.01). Analysis of ΔCI% and ΔDSI% revealed that VMAT outperformed DCA for lesions > 2 cm3 and smaller volumes with a Qasym > 1.2. DCA required significantly fewer MUs (p < 0.01).
Conclusion:
This study provides detailed dosimetric information on two commonly applied planning techniques for Linac-based SRS treatment for brain metastases. These findings might support decision making for optimal technique selection upon volumetric features. Qasym provides a practical tool for these purposes.
