Optical imaging provides rapid verification of static small beams, radiosurgery, and VMAT plans with millimeter resolution

Abstract

Purpose: We demonstrate the feasibility of optical imaging as a quality assurance tool for static small beamlets, and pretreatment verification tool for radiosurgery and volumetric-modulated arc therapy (VMAT) plans. Methods: Small static beams and clinical VMAT plans were simulated in a treatment planning system (TPS) and delivered to a cylindrical tank filled with water-based liquid scintillator. Emission was imaged using a blue-sensitive, intensified CMOS camera time-gated to the linac pulses. For static beams, percentage depth and cross beam profiles of projected intensity distribution were compared to TPS data. Two-dimensional (2D) gamma analysis was performed on all clinical plans, and the technique was tested for sensitivity against common errors (multileaf collimator position, gantry angle) by inducing deliberate errors in the VMAT plans control points. The technique's detection limits for spatial resolution and the smallest number of control points that could be imaged reliably were also tested. The sensitivity to common delivery errors was also compared against a commercial 2.5D diode array dosimeter. Results: A spatial resolution of 1 mm was achieved with our imaging setup. The optical projected percentage depth intensity profiles agreed to within 2% relative to the TPS data for small static square beams (5, 10, and 50 mm 2 ). For projected cross beam profiles, a gamma pass rate >99% was achieved for a 3%/1 mm criteria. All clinical plans passed the 3%/3 mm criteria with >95% passing rate. A static 5 mm beam with 20 Monitor Units could be measured with an average percent difference of 5.5 AE 3% relative to the TPS. The technique was sensitive to multileaf collimator errors down to 1 mm and gantry angle errors of 1°. Conclusions: Optical imaging provides ample spatial resolution for imaging small beams. The ability to faithfully image down to 20 MU of 5 mm, 6 MV beamlets prove the ability to perform quality assurance for each control point within dynamic plans. The technique is sensitive to small offset errors in gantry angles and multileaf collimator (MLC) leaf positions, and at certain scenario, it exhibits higher sensitivity than a commercial 2.5D diode array.

Optimization of in vivo Cherenkov imaging dosimetry via spectral choices for ambient background lights and filtering

“…8 The imaging technique has been also used to characterize irradiation sources' spatial and temporal profiles (dose profiles, source strength, position, and dwell time) for all aforementioned treatment modalities. [9][10][11][12] Correlating dose delivery to Cherenkov emission from patients requires corrections associated with imaging perspective, anatomy, and tissue optical properties 3 that vary from patient to patient and establishing such correction factors is well underway. 5 Furthermore, it is worth noting that while Cherenkov light is emission in the ultraviolet and blue wavelength, emission from tissue is predominantly red and infrared weighted due to the optical absorption of water, hemoglobin, and fat.…”

Dosimetry for FLASH Radiotherapy: A Review of Tools and the Role of Radioluminescence and Cherenkov Emission

“…Optical imaging of scintillation using cameras during external beam radiotherapy has already been widely implemented [88,94,95]. In a recent study [96], a time-gated intensified CMOS camera was used to image complex stereotactic radiosurgery (SRS) plans at high dose-rates in a radioluminescent phantom. The authors were able to resolve complex and highly modulated dose distributions spatially and temporally.…”

Technical Note: Single‐pulse beam characterization for FLASH‐RT using optical imaging in a water tank

“…Optical imaging of radioluminescence has been shown to successfully image small beams and complex stereotactic radiosurgery plans. 23 Additionally, the technique was also used successfully to image high dose rate scanned proton pencil beams and was shown to be independent of any dose rate dependencies up to dose rates of~20 Gy/s. 24 In both cases, however, only 2D projected dose distributions were measured and important central axis information was lost.…”