Affiliations: [a] Radiation Therapy, Summa Health Cancer Institute, Akron, Ohio, USA
| [b] Department of Medical Physics, Memorial Sloan Kettering Cancer Center, New York, NY, USA
| [c] Department of Radiation Oncology, University of Nebraska Medical Center, Omaha, Nebraska, USA
Correspondence:
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Corresponding author: Mutian Zhang, PhD, Radiation Therapy, Summa Health Cancer Institute, 161 N Forge Street, Akron, Ohio, OH 44304, USA. Tel.: +1 330 375 7868; E-mail: mutian_zhang@hotmail.com.
Abstract: BACKGROUND:Versa HD linear accelerators (linacs) are used for stereotactic radiosurgery treatment. However, the mechanical accuracy of such systems remains a concern. OBJECTIVE:The purpose of this study was to evaluate the accuracy of an Elekta Versa HD linac. METHODS:We performed measurements with a ball bearing phantom to calculate the rotational isocenter radii of the linac’s gantry, collimator, and table, and determine the relative locations of those isocenters. We evaluated the accuracy of the cone-beam computed tomography (CBCT) guidance with a film-embedding head phantom and circular cone-collimated radiation beams. We also performed dosimetric simulations to study the effects of the linac mechanical uncertainties on non-coplanar cone arc delivery. RESULTS:The mechanical uncertainty of the linac gantry rotation was 0.78 mm in radius, whereas that of the collimator and the table was <0.1 mm and 0.33 mm, respectively. The axes of rotation of the collimator and the table were coinciding with and 0.13 mm away from the gantry isocenter, respectively. Experiments with test plans demonstrated the limited dosimetric consequences on the circular arc delivery given the aforementioned mechanical uncertainties. End-to-end measurements determined that the uncertainty of the CBCT guidance was≤1 mm in each direction with respect to the reference CT image. CONCLUSIONS:In arc delivery, the mechanical uncertainties associated with the gantry and the table do not require remarkable increases in geometric margins. If large enough, the residual setup errors following CBCT guidance will dominate the overall dosimetric consequence. Therefore, the Versa HD linac is a valid system for stereotactic radiosurgery using non-coplanar arc delivery.
Keywords: Linear accelerator, stereotactic radiosurgery, mechanical uncertainty, cone-beam CT guidance
