Can Optical Surface Imaging Replace Non-coplanar Cone-beam Computed Tomography for Non-coplanar Set-up Verification in Single-isocentre Non-coplanar Stereotactic Radiosurgery and Hypofractionated Stereotactic Radiotherapy for Single and Multiple Brain Metastases?

Aims: To conduct a direct comparison regarding the non-coplanar positioning accuracy between the optical surface imaging system Catalyst HD (TM) and non-coplanar cone-beam computed tomography (NC-CBCT) in intracranial single-isocentre non-coplanar stereotactic radiosurgery (SRS) and hypofractionated stereotactic radiotherapy (HSRT).Materials and methods: Twenty patients with between one and five brain metastases who underwent single-isocentre non-coplanar volumetric modulated arc therapy (NC-VMAT) SRS or HSRT were enrolled in this study. For each non-zero couch angle, both Catalyst HD (TM) and NC-CBCT were used for set-up verification prior to beam delivery. The set-up error reported by Catalyst HD (TM) was compared with the set-up error derived from NC-CBCT, which was defined as the gold standard. Additionally, the dose delivery accuracy of each non-coplanar field after using Catalyst HD (TM) and NC-CBCT for set-up correction was measured with SRS MapCHECK (TM).Results: The median set-up error differences (absolute values) between the two positioning methods were 0.30 mm, 0.40 mm, 0.50 mm, 0.15 degrees, 0.10 degrees and 0.10 degrees in the vertical, longitudinal, lateral, yaw, pitch and roll directions, respectively. The largest absolute set-up error differences regarding translation and rotation were 1.5 mm and 1.1 degrees, which occurred in the longitudinal and yaw directions, respectively. Only 35.71% of the pairs of measurements were within the tolerance of 0.5 mm and 0.5 degrees simultaneously. In addition, the non-coplanar field with NC-CBCT correction yielded a higher gamma passing rate than that with Catalyst HD (TM) correction (P < 0.05), especially for evaluation criteria of 1%/1 mm with a median increase of 12.8%.Conclusions: Catalyst HD (TM) may not replace NC-CBCT for non-coplanar set-up corrections in single-isocentre NC-VMAT SRS and HSRT for single and multiple brain metastases. The potential role of Catalyst HD (TM) in intracranial SRS/HSRT needs to be further studied in the future.(c) 2023 Published by Elsevier Ltd on behalf of The Royal College of Radiologists.