Six degrees of freedom CBCT‐based positioning for intracranial targets treated with frameless stereotactic radiosurgery

• Type of Material: Article
• Authors: Anees Dhabbaan, Emory University; Eduard Schreibmann, Emory University; Arsalan Siddiqi, Emory University; Eric Elder, Emory University; Timothy Fox, Emory University; Tomi Ogunleye, Emory University; Natia Esiashvili, Emory University; Walter J Curran, Emory University; Ian Crocker, Emory University; Hui-Kuo Shu, Emory University
• Language: English
• Date: 2012-01-01
• Publisher: American Association of Physicists in Medicine
• Publication Version: Final Published Version
• Copyright Statement: © 2012 The Authors.
• License: Creative Commons Attribution 3.0 Unported
• Final Published Version (URL): http://dx.doi.org/10.1120/jacmp.v13i6.3916
• Title of Journal or Parent Work: Journal of Applied Clinical Medical Physics
• ISSN: 1526-9914
• Volume: 13
• Issue: 6
• Start Page: 215
• End Page: 225
• Keywords: RADIATION-THERAPY; INITIAL CLINICAL-EXPERIENCE; Science & Technology; cone beam CT; registration; CONE-BEAM CT; Life Sciences & Biomedicine; six degrees of freedom; Radiology, Nuclear Medicine & Medical Imaging; REPOSITIONING ACCURACY; SYSTEM; COMPUTED-TOMOGRAPHY; LINEAR-ACCELERATOR; stereotactic frameless radiosurgery; QUALITY-ASSURANCE; BRAIN METASTASES; IMAGE-GUIDED RADIOTHERAPY
• Research Categories: Health Sciences, Radiology; Health Sciences, Oncology

Abstract

Frameless radiosurgery is an attractive alternative to the framed procedure if it can be performed with comparable precision in a reasonable time frame. Here, we present a positioning approach for frameless radiosurgery based on in-room volumetric imaging coupled with an advanced six-degrees-of-freedom (6 DOF) image registration technique which avoids use of a bite block. Patient motion is restricted with a custom thermoplastic mask. Accurate positioning is achieved by registering a cone-beam CT to the planning CT scan and applying all translational and rotational shifts using a custom couch mount. System accuracy was initially verified on an anthropomorphic phantom. Isocenters of delineated targets in the phantom were computed and aligned by our system with an average accuracy of 0.2 mm, 0.3 mm, and 0.4 mm in the lateral, vertical, and longitudinal directions, respectively. The accuracy in the rotational directions was 0.1°, 0.2°, and 0.1° in the pitch, roll, and yaw, respectively. An additional test was performed using the phantom in which known shifts were introduced. Misalignments up to 10 mm and 3° in all directions/rotations were introduced in our phantom and recovered to an ideal alignment within 0.2 mm, 0.3 mm, and 0.4 mm in the lateral, vertical, and longitudinal directions, respectively, and within 0.3° in any rotational axis. These values are less than couch motion precision. Our first 28 patients with 38 targets treated over 63 fractions are analyzed in the patient positioning phase of the study. Mean error in the shifts predicted by the system were less than 0.5 mm in any translational direction and less than 0.3° in any rotation, as assessed by a confirmation CBCT scan. We conclude that accurate and efficient frameless radiosurgery positioning is achievable without the need for a bite block by using our 6DOF registration method. This system is inexpensive compared to a couch-based 6 DOF system, improves patient comfort compared to systems that utilize a bite block, and is ideal for the treatment of pediatric patients with or without general anesthesia, as well as of patients with dental issues. From this study, it is clear that only adjusting for 4 DOF may, in some cases, lead to significant compromise in PTV coverage. Since performing the additional match with 6 DOF in our registration system only adds a relatively short amount of time to the overall process, we advocate making the precise match in all cases.