Clinical Implementation and Accuracy Evaluation of a Novel Intrafraction Cone-beam Computed Tomography Technique for Stereotactic Radiosurgery and Radiotherapy.

PURPOSE: To evaluate the clinical implementation and setup accuracy of real-time intrafraction cone-beam computed tomography imaging during stereotactic radiosurgery and stereotactic radiotherapy.

MATERIALS AND METHODS: Ten patients treated with intracranial SRS/SRT were retrospectively analyzed. All patients were immobilized using the Fraxion stereotactic head system and treated with volumetric-modulated arc therapy (VMAT) on a linear accelerator (Elekta Versa HD). A custom intrafraction cone-beam computed tomography (CBCT) preset was developed in X-ray volume imaging to acquire kV projections during each VMAT arc. Translational (X, Y, and Z) and rotational (pitch, roll, and yaw) errors were calculated by registering intrafraction CBCT to the planning CT using a 6D match and mean values were compared with SRS tolerance thresholds (0.5 mm and 1°).

RESULTS: The mean intrafraction translational errors were 0.4 mm (lateral), 0.3 mm (longitudinal), and 0.4 mm (vertical), while rotational errors were 0.3° in (pitch), 0.3° in (roll), and 0.4° in (yaw), all within SRS tolerances. Real-time intrafraction CBCT provided clinically acceptable volumetric images with minimal scatter, enabled continuous motion monitoring during VMAT delivery, eliminated additional CBCT scans and couch adjustments, and reduced treatment time by approximately 3-5 min per arc.

CONCLUSION: Real-time intrafraction CBCT imaging enables highly accurate, efficient, and reproducible setup verification during SRS/SRT. The workflow maintains sub-millimeter precision, reduces treatment duration, and enhances clinical confidence in dose delivery. This approach represents a significant advancement in stereotactic image-guided radiation therapy and warrants the evaluation for extracranial SBRT applications.