Frameless,Real-Time Surface Imaging-Guided Radiosurgery System

Stereotactic radiosurgery (SRS) refers to the delivery of a single, high dose of radiation to a precisely defined target. ¹ This is achieved by using multiple, noncoplanar radiation beams that converge on the target lesion. ^2,3 The goal of SRS is to deliver highly conformal radiation therapy in an attempt to ablate the lesion, while minimizing damage to the surrounding normal tissue. SRS has proven to be a safe and efficacious treatment option for many lesions that are surgically inaccessible or are associated with unacceptable surgical morbidity. ^{4 –6} Due to the precision required for the planning and execution of SRS, implementation historically required the surgical attachment of a frame to the patient's skull. ⁷ The frame is, in turn, rigidly mounted to the treatment table to minimize patient movement during treatment. Subsequent technological advances included the development of frameless SRS, where patient positioning is monitored through serial X-rays or externally attached fiducials. ^8,9 Whereas these systems have been proven accurate, ^10,11 they result in additional radiation to the patient and an increase of time and complexity in treatment delivery. ^12,13 To overcome these issues, we here provide a 9-minute 51-second video illustration of what can be described as a third generation SRS technology where patient immobilization is monitored by video surface imaging cameras designed to detect and monitor the surface contour of the patient's facial features. The system, AlignRT (VisionRT Ltd.), utilizes three ceiling-mounted nonionizing camera pods that capture facial landmarks of the patient and, in turn, builds a three-dimensional surface image of the patient. Each pod consists of three cameras (two for stereovision, one for texture), a speckle flash unit for static imaging, and a speckle projector for dynamic imaging. Once the surface rendering is complete, the system monitors any cranial displacement from the initial position. Radiation delivery is halted, if significant and sustained displacements occur, and resumed only after the patient returned to the initial position. We termed this system as Surface Imaging-Guided Stereotactic Radiosurgery (SIG SRS). We previously demonstrated that the physical accuracy and the clinical efficacy of SIG SRS are comparable to the frame-based X-ray or external fiducial-based systems. ^14,15 We have treated more than 350 patients with the AlignRT system. In terms of clinical efficacy, we have analyzed the outcome of our first 44 patients with 115 intracranial metastases treated with SIG SRS. ¹⁴ The median follow-up for all patients was 6.0 months, with a range of 0.3–21.6 months. Actuarial 6- and 12-month local control was 90% and 76%, respectively. Regional failure was noted in 16 patients (46%). The median actuarial overall survival was 7.7 months. ¹⁴ These results are comparable to those achieved using conventional frame-based systems, ^16,17 frameless systems with serial X-ray monitoring, ^10,18 as well as external fiducial systems. ^8,9 In this study, we provide a video documentation of the SIG SRS procedure based on minimal patient immobilization and patient monitoring with a video surface imaging system. This treatment constitutes a step forward in patient comfort and treatment speed, while maintaining accuracy and clinical results seen with previous stereotactic immobilization systems.

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