# IBA myQA SRS Detector for CyberKnife Robotic Radiosurgery Quality Assurance
###### Abstract  
The IBA myQA(r) SRS high-resolution solid-state detector was evaluated in the context of robotic radiosurgery delivered using CyberKnife(r). The performance was investigated for periodic machine delivery quality assurance (DQA) and patient-specific treatment verification. myQA(r) SRS is a 140 \(\times\) 120 mm CMOS matrix with 400 \(\upmu\)m resolution, allocated in a cylindrical ABS phantom topped by a hemispheric cap. Evaluations included: periodic DQA tests, angular response, dose-rate dependence and Iris variable aperture collimator field size measurements. For patient-specific QA various intracranial targets were studied (Gamma Index, 3%/1 mm agreement criteria), taking into account also the detector's angular response. Results for periodic DQA were in accordance with the machine commissioning data. Dose-rate dependence was confirmed, and angular response tests resulted in a signal decay >5% when beams were delivered outside a \(\pm\)50\({}^{\circ}\) amplitude cone with respect to the vertical direction. Concerning patient-specific QA, >50\({}^{\circ}\) angled beams elimination led to a Gamma Index passing rates improvement ranging between +3% and +115%. IBA myQA(r) SRS proved to be a suitable device for many CyberKnife(r) constancy DQA checks, providing high-resolution real-time results. Patient-specific Gamma tests showed high passing rates once angular dependence corrections were performed, even in high complexity treatments such as those for trigeminal neuralgia targets. IBA myQA SRS; CyberKnife; robotic radiosurgery; SRS; quality assurance; pre-treatment QA +
Footnote †: journal: Medical Computing  
Accepted: 30 July 2022  
Published: 2 August 2022
expanded in complexity, but resources have been inadequate to handle this ever-increasing complexity [2]. Stereotactic radiosurgery (SRS) is a typical example of an advanced radiotherapy technique becoming an essential tool in the management of a growing number of malignant and benign conditions. The accuracy of dose administration in such a technique, delivering precisely-targeted high-dose sessions, is of paramount importance to guarantee both the clinical outcome and the absence of severe toxicities. As stated by the report of AAPM Task Group No. 135, a mistaken delivered dose or beam displacement errors may result \"_in inaccurate estimates of accumulated dose as well as inaccurate estimates of the steepness and location of the high dose gradient regions that may be designed to protect adjacent critical structures and organs at risk_\" [3]. A comprehensive QA program is therefore all the more important, but the challenges of such a program are still exacerbated by a lack of efficient and accurate equipment [4]. DQA tests are generally performed by means of ionization chambers, solid-state point detectors, or radiochromic films [4; 5]. Recently, 2D and 3D detector arrays are increasingly being used in SRS, even just for specific tasks like planar dose mapping [6; 7]. Despite this, their use in clinical practice is still hindered by drawbacks and limitations. While point measurements are inappropriate for achieving full information about the intended dose distribution, radiochromic films need special handling care and are time-consuming tools. A device combining a contiguous high resolution and a bidimensional active area capable of performing both periodic DQA tests and accurate dose map comparisons is still needed, particularly when it comes to robotic radiosurgery. In spring 2021, a new high-resolution detector was released for clinical use by IBA (myQA(r) SRS, IBA Dosimetry GmbH, Schwarzenbruck, Germany) for SRS and stereotactic body radiotherapy (SBRT) QA of treatments delivered with conventional linear accelerators (linac). Systems such as Varian Ethos(tm)/Halcyon(tm) and CyberKnife(r) MLC, Iris, or Cones are also supported, but validation testing for the CyberKnife is still work in progress. myQA(r) SRS is therefore not available for sale for these systems.