Inter‐ and Intrafraction Motion for Stereotactic Radiosurgery in Dogs and Cats Using a Modified Brainlab Frameless Stereotactic Mask System

Abstract

Precise and accurate patient positioning is necessary when doing stereotactic radiosurgery (SRS) to ensure adequate dosing to the tumor and sparing of normal tissues. This prospective cross-sectional study aimed to assess feasibility of a commercially available modified frameless SRS positioning system for use in veterinary radiotherapy patients with brain tumors. Fifty-one dogs and 12 cats were enrolled. Baseline and verification CT images were acquired. The verification CT images from 32 dogs and five cats had sufficient images for fusion to baseline CT images. A rigid box-based fusion was performed to determine interfraction motion. Forty-eight dogs and 11 cats were assessed for intrafraction motion by cine CT. Seventy percent of dogs and 60% of cats had interfraction 3D vector translational shifts >1 mm, with mean values of 1.9 mm in dogs, and 1.8 mm in cats. In dogs muscle wasting was weakly correlated with translational shifts. The maximum angular interfraction motion observed was 6.3° (roll), 3.5° (pitch), and 3.3° (yaw). There was no correlation between angular interfraction motion and weight, brachycephaly, or muscle wasting. Fifty-seven percent of dogs and 50% of cats had respiration-related intrafraction motion. Of these, 4.5% of dogs and 10% of cats had intrafraction motion >1 mm. This study demonstrates the modified Brainlab system is feasible for SRS in dogs and cats. The smaller cranial size and difference in anatomy increases setup uncertainty in some animals beyond limits usually accepted in SRS. Image-guided positioning is recommended to achieve clinically acceptable setup accuracy (<1 mm) for SRS.

Treatment of MRI‐Diagnosed Trigeminal Peripheral Nerve Sheath Tumors by Stereotactic Radiotherapy in Dogs

“…Thermoplastic masks, vacuum‐locked moldable bags, dental molds for bite blocks, and nonmigrating fiducials imbedded in tumors aid in replicating the dog and PTV positioning for subsequent treatments . External mobilization devices help position the body for treatment, and several immobilization systems have previously been evaluated for radiotherapy of the head and neck in dogs …”

“…The thermoplastic mask was molded to the dog's head to immobilize the skull. The stereotactic target positioner box was locked onto the sled, and the CT origin coordinates were aligned to the box with the CT positioning lasers …”

“…The stereotactic target positioner box was locked onto the sled, and the CT origin coordinates were aligned to the box with the CT positioning lasers. 10 A noncontrast CT with 120 kV and 150 mA with 1 mm collimation was performed. Contrast-enhanced images with 1 mm collimation were acquired with iodinated contrast medium i at a dose of 740 mg I/kg.…”

“…Stereotactic radiotherapy can be delivered with a linear accelerator via a multileaf collimator (MLC) system or a cone‐based system for beam collimation. A frameless SRT system with a body support sled has been developed, including a stereotactic box affixed to the sled at the head to eliminate the need for an affixed head frame, and a set of cones that attach to the machine head, creating circular fields of a defined diameter for beam delivery …”

“…A frameless SRT system with a body support sled has been developed, including a stereotactic box affixed to the sled at the head to eliminate the need for an affixed head frame, and a set of cones that attach to the machine head, creating circular fields of a defined diameter for beam delivery. 10 Intracranial peripheral nerve sheath tumors (PNST) are relatively uncommon tumors in dogs. 11 dogs with intracranial PNST have one or more of the following clinical signs: ipsilateral masticatory muscle atrophy, loss of facial sensation, and Horner's syndrome.…”