SU‐F‐T‐559: High‐Resolution Scintillating Fiber Array for In‐Vivo Real‐Time SRS and SBRT Patient QA

Abstract

Purpose: A high‐resolution scintillating fiber detector was built for in‐vivo real‐time patient specific quality assurance (QA). The detector is designed for stereotactic body radiotherapy (SBRT) and stereotactic radiosurgery (SRS) to monitor treatment delivery and detect real‐time deviations from planned dose to increase patient safety and treatment accuracy. Methods: The detector consists of two high‐density scintillating fiber arrays layered to form an X‐Y grid which can be attached to the accessory tray of a medical linac for SBRT and cone SRS treatment QA. Fiber arrays consist of 128 scintillating fibers embedded within a precision‐machined, high‐transmission polymer substrate with 0.8mm pitch. The fibers are coupled on both ends to high‐sensitivity photodetectors and the output is recorded through a high‐speed analog‐to‐digital converter to capture the linac pulse sequence as treatment delivery progresses. The detector has a software controlled 360 degree rotational system to capture angular beam projections for high‐resolution beam profile reconstruction. Results: The detector was validated using SRS cone sizes from 6mm to 34mm and MLC defined field sizes from 5×5mm2 to 100×100mm2. The detector output response is linear with dose and is dose rate independent. Each field can be reconstructed accurately with a spatial resolution of 0.8mm and the current beam output is displayed every 50msec. Dosimetric errors of 1% with respect to the treatment plan can be identified and clinically significant deviations from the expected treatment can be displayed in real‐time to alert the therapists. Conclusion: The high resolution detector is capable of reconstructing beam profiles in real‐time with submillimeter resolution and 1% dose resolution. This system has the ability to project in‐vivo both spatial and dosimetric errors during SBRT and SRS treatments when only a non‐clinically significant fraction of the intended dose was delivered. The device has the potential to establish new standards for in‐vivo patient specific QA.