Development of a frameless stereotactic radiosurgery system based on real-time 6D position monitoring and adaptive head motion compensation

Abstract

Stereotactic radiosurgery delivers radiation with great spatial accuracy. To achieve sub-millimeter accuracy for intracranial SRS, a head ring is rigidly fixated to the skull to create a fixed reference. For some patients, the invasiveness of the ring can be highly uncomfortable and not well tolerated. In addition, placing and removing the ring requires special expertise from a neurosurgeon, and patient setup time for SRS can often be long. To reduce the invasiveness, hardware limitations and setup time, we are developing a system for performing accurate head positioning without the use of a head ring. The proposed method uses real-time 6D optical position feedback for turning on and off the treatment beam (gating) and guiding a motorcontrolled 3D head motion compensation stage. The setup consists of a central control computer, an optical patient motion tracking system and a 3D motion compensation stage attached to the front of the LINAC couch. A styrofoam head cast was custom-built for patient support and was mounted on the compensation stage. The motion feedback of the markers was processed by the control computer, and the resulting motion of the target was calculated using a rigid body model. If the target deviated beyond a preset position of 0.2 mm, an automatic position correction was performed with stepper motors to adjust the head position via the couch mount motion platform. In the event the target deviated more than 1 mm, a safety relay switch was activated and the treatment beam was turned off. The feasibility of the concept was tested using five healthy volunteers. Head motion data were acquired with and without the use of motion compensation over treatment times of 15 min. On average, test subjects exceeded the 0.5 mm tolerance 86% of the time and the 1.0 mm tolerance 45% of the time without motion correction.

Correction of motion‐induced misalignment in co‐registered PET/CT and MRI (T1/T2/FLAIR) head images for stereotactic radiosurgery

“…( 17 , 18 ) Therefore, diagnostic images can be utilized through volumetric image registration with a level of accuracy sufficient for SRS. In a trend of increasing clinical implementations of image‐guided frameless SRS, ( 25 , 26 ) where stereotactic imaging is not possible, the 3DVIR could be applied to achieve the accuracy of stereotactic imaging for target delineation and localization, and to perform image‐guided stereotactic setup for frameless SRS delivery.…”

STAT RAD: A Potential Real-Time Radiation Therapy Workflow

“…X-ray or CT image guidance prior to radiation delivery on the treatment unit is routinely employed in the clinic. Methods for optical tracking of markers on the patient surface or tracking of the patient's skin surface itself are available to ensure consistent patient positioning after image guidance and during treatment, known as intra-fractional motion (Wagner et al, 2007;Wiersma et al, 2010). This provides a method without ionizing radiation for confirming patient position that can be used real-time during treatment delivery.…”

Clinical experience with two frameless stereotactic radiosurgery (fSRS) systems using optical surface imaging for motion monitoring

“…Early approaches to intratreatment motion monitoring involved the application of an array of six infrared reflective markers mounted on a tray held by the patient via a bite-block. (9,10) The speed of motion tracking was up to 30 frames per second (fps) with six degrees of freedom (6DOF), provided that the bite-block maintained the rigid relationship between the tray and the head. More recently, intratreatment motion monitoring has shifted toward markerless approaches using video-based optical surface imaging (OSI), reducing the need for patient compliance and simplifying fSRS treatment.…”