Purpose: In stereotactic radiosurgery (SRS) with single-isocentric treatments for brain metastases, rotational setup errors may cause considerable dosimetric effects. We assessed the dosimetric effects on HyperArc plans for single and multiple metastases.
Methods: For 29 patients (1-8 brain metastases), HyperArc plans with a prescription dose of 20-24 Gy for a dose that covers 95% (D95% ) of the planning target volume (PTV) were retrospectively generated (Ref-plan). Subsequently, the computed tomography (CT) used for the Ref-plan and cone-beam CT acquired during treatments (Rot-CT) were registered. The HyperArc plans involving rotational setup errors (Rot-plan) were generated by re-calculating doses based on the Rot-CT. The dosimetric parameters between the two plans were compared.
Results: The dosimetric parameters [D99% , D95% , D1% , homogeneity index, and conformity index (CI)] for the single-metastasis cases were comparable (P > 0.05), whereas the D95% for each PTV of the Rot-plan decreased 10.8% on average, and the CI of the Rot-plan was also significantly lower than that of the Ref-plan (Ref-plan vs Rot-plan, 0.93 ± 0.02 vs 0.75 ± 0.14, P < 0.01) for the multiple-metastases cases. In addition, for the multiple-metastases cases, the Rot-plan resulted in significantly higher V10Gy (P = 0.01), V12Gy (P = 0.02), V14Gy (P = 0.02), and V16Gy (P < 0.01) than those in the Ref-plan.
Conclusion: The rotational setup errors for multiple brain metastases cases caused non-negligible underdosage for PTV and significant increases of V10Gy to V16Gy in SRS with HyperArc.
Keywords: HyperArc; multiple brain metastases; radiosurgery; rotational setup error.
© 2019 The Authors. Journal of Applied Clinical Medical Physics published by Wiley Periodicals, Inc. on behalf of American Association of Physicists in Medicine.