Verification of proton range, position, and intensity in IMPT with a 3D liquid scintillator detector system

Abstract

Purpose: Intensity-modulated proton therapy (IMPT) using spot scanned proton beams relies on the delivery of a large number of beamlets to shape the dose distribution in a highly conformal manner. The authors have developed a 3D system based on liquid scintillator to measure the spatial location, intensity, and depth of penetration (energy) of the proton beamlets in near real-time. Methods: The detector system consists of a 20 Â 20 Â 20 cc liquid scintillator (LS) material in a light tight enclosure connected to a CCD camera. This camera has a field of view of 25.7 by 19.3 cm and a pixel size of 0.4 mm. While the LS is irradiated, the camera continuously acquires images of the light distribution produced inside the LS. Irradiations were made with proton pencil beams produced with a spot-scanning nozzle. Pencil beams with nominal ranges in water between 9.5 and 17.6 cm were scanned to irradiate an area of 10 Â 10 cm square on the surface of the LS phantom. Image frames were acquired at 50 ms per frame. Results: The signal to noise ratio of a typical Bragg peak was about 170. Proton range measured from the light distribution produced in the LS was accurate to within 0.3 mm on average. The largest deviation seen between the nominal and measured range was 0.6 mm. Lateral position of the measured pencil beam was accurate to within 0.4 mm on average. The largest deviation seen between the nominal and measured lateral position was 0.8 mm; however, the accuracy of this measurement could be improved by correcting light scattering artifacts. Intensity of single proton spots were measured with precision ranging from 3 % for the smallest spot intensity (0.005 MU) to 0.5 % for the largest spot (0.04 MU). Conclusions: Our LS detector system has been shown to be capable of fast, submillimeter spatial localization of proton spots delivered in a 3D volume. This system could be used for beam range, intensity and position verification in IMPT.

Quality assurance in proton beam therapy using a plastic scintillator and a commercially available digital camera

“…Several features of large scintillators enable them to be good candidates for dosimetric measurements of proton beam such as fast response and high spatial resolution 7. Recently, large 3D‐volume liquid scintillator detectors were used to verify proton range and position for scanned proton beams and showed that they were able to provide precise position results within 0.7% and an accuracy in proton range to within 0.3 mm on average 8, 9. However, the materials making up a liquid scintillator are not suitable for hospital environments due to toxicity and the need to deoxygenate the scintillator prior to use to optimize the light output 10.…”

Development of a novel proton dosimetry system using an array of fiber-optic Cerenkov radiation sensors

“…Although proton scanning beam characteristics, such as beam spot size, location, and duration, should be confirmed during the QA process, real-time data are difficult to acquire using a conventional dosimetric system [11][12][13], suggesting the applicability of the proposed AFCRS system. Recent studies showed that scintillator detector system viewed by a CCD camera is capable to measure the spatial location, intensity, and depth of penetration (energy) of the proton beams in realtime [14,15]. Although scintillator detector is a good candidate for the real-time proton dosimeter, there are some limitations.…”

Performance characterization of a 3D liquid scintillation detector for discrete spot scanning proton beam systems

“…First, they are tissue- or water-equivalent, enabling dose detection with minimal field perturbation (Ingram et al 2015). Second, they have high spatial resolution (Archambault et al 2012). Third, they exhibit good temporal resolution, with nanosecond scintillation-response time and detection time in the range of milliseconds.…”