A Real-time Scintillating Fiber Detector to Improve Patient Safety in External Beam Radiation Therapy

Abstract

The purpose of this study is to improve patient safety in radiation oncology by implementing real time verification of fluence delivered during external beam radiation therapy using a radiation hard scintillating fiber sensor array architecture and real time data acquisition hardware. Radiation oncology patients undergo highly complicated treatment procedures in which delivered dose should be controlled, recorded, and verified for quality and safety. Currently, radiation treatment cumulative dose is measured prior to delivery, which is not sensitive to temporal variations that could occur during imaging or treatment. Therefore, the actual quality and safety of the radiation therapy procedure is unknown and any deviation from the intended dose cannot be identified, thus cannot be corrected. To address this gap in patient safety, we developed scintillating fiber array sensors with real time data acquisition hardware to implement real time fluence verification of photon and electron beams. These on line detectors can operate on a wide range of clinical devices through modification of sensor element geometry and front end electronics operating parameters. This common technological platform provides a simplified method to construct low cost radiation based modality specific dosimeters. As an example, we developed and tested a scintillating fiber array for linac external beam radiation therapy with plastic encapsulated scintillating fibers and photodetectors integrated in a monolithic configuration. This detector has high speed front end amplifiers for real time acquisition and verification of the pulsed linac output during treatment. We determined the detector sensitivity and linearity response with respect to beam intensity and field size for the clinical range of photon beam energies. The scintillating fiber spatial detection sensitivity is 2.3 mV/mm with a statistical error of 0.5 mV. Fiber linearity response with respect to beam intensity and field size was within 2% for all tested beams. The front end amplifiers have a time response of 250 nsec. The fiber dosimeter has a maximum beam attenuation of 2.4% and is used in an online transmission configuration for in vivo treatment delivery accuracy monitoring. The development of this technology addresses the urgent need for in vivo real time quality assurance of external beam therapy to increase patient safety. The developed linear fiber array has high spatial and temporal resolution to provide accurate dose verification, thus providing therapists real time feedback of external beam treatment fluence with minimum beam attenuation to increase patient safety. Configurations for other external beam treatment devices such as tomotherapy machines could be done with little design modification.