Design of a Reconfigurable Quality Assurance Phantom for Verifying the Spatial Accuracy of Radiosurgery Treatments for Multiple Brain Metastases

Radiation therapy frequently involves highly customized and complex treatments, employing sophisticated equipment, that require extensive patient-specific validation to verify the accuracy of the treatment plan as part of the clinical quality assurance (QA) process. This paper introduces a novel, reconfigurable QA phantom developed for the spatial validation of radiosurgery treatments of multiple brain metastases (MBM). This phantom works in conjunction with existing electronic portal imaging detector (EPID) technology to rapidly verify MBM treatment plans with submillimeter accuracy. The device provides a 12x12x12cm(3) active volume and multiple, independently configurable markers, in the form of 3mm diameter radiopaque spheres, which serve as surrogates for brain lesions. The device is lightweight, portable, can be setup by a single operator, and is adaptable for use with external beam radiotherapy (EBRT) techniques and stereotactic linear accelerators (LINACs). This paper presents the device design and fabrication, along with initial testing and validation results both in the laboratory, using a coordinate measuring machine (CMM) and under simulated clinical conditions, using a radiosurgery treatment plan with 15 lesions. The device has been shown to place markers in space with a 0.45mm root-mean-square error, which is satisfactory for initial clinical use. The device is undergoing further testing under simulated clinical conditions and improvements to reduce marker positional error.