Scintillation Dosimetry Research Articles

Cherenkov imaging combined with scintillation dosimetry provides real-time positional and dose monitoring for radiotherapy patients with cardiac implanted electronic devices

Background and purposeCardiac implanted electronic devices (CIED) require dose monitoring during each fraction of radiotherapy, which can be time consuming and may have delayed read-out times. This study explores the potential of Cherenkov imaging combined with scintillation dosimetry as an alternative verification system. Methods and materialsTime-gated, complementary metal–oxide–semiconductor (iCMOS) cameras were used to collect video images of anthropomorphic phantoms and patients undergoing radiation treatment near chest wall cardiac devices. Scintillator discs and optically stimulated luminescence dosimeters (OSLDs) were used for dose measurement. Accuracy of spatial delivery was assessed by overlaying predicted surface dose outlines derived from the treatment planning system (TPS) with the Cherenkov images. Dose measurements from OSLDs and scintillators were compared. ResultsIn phantom studies, Cherenkov images visibly indicated when dose was delivered to the CIED as compared to non-overlapping dose deliveries. Comparison with dose overlays revealed congruence at the planned position and non-congruence when the phantom was shifted from the initial position. Absolute doses derived from scintillator discs aligned well with the OSLD measurements and TPS predictions for three different positions, measuring within 10 % for in-field positions and within 5 % for out-of-field positions. For two patients with CIEDs imaged over 18 fractions, Cherenkov imaging confirmed positional accuracy for all fractions, and dose measured by scintillator discs deviated by <0.015 Gy from the OSLD measurements. ConclusionsCherenkov imaging combined with scintillation dosimetry presents an alternative methodology for CIED monitoring with the added benefit of instantly detecting deviations, enabling timely corrective actions or proper patient triage.

Visual Dose Monitoring for Whole Breast Radiation Therapy Treatments via Combined Cherenkov Imaging and Scintillation Dosimetry

PurposeThis study investigates scintillation dosimetry coupled with Cherenkov imaging for in vivo dose monitoring during whole breast radiotherapy (WBRT). Given recent observations of excess dose to the contralateral breast (CB), in vivo dosimetry (IVD) could help ensure accurate dose delivery and decrease risks of secondary cancer. This work presents a rapid, streamlined alternative to traditional IVD, providing direct visualization of measurement location relative to the treatment field on the patient. Methods and Materials10 WBRT patients consented under an IRB-approved protocol were monitored with scintillation dosimetry and always-on Cherenkov imaging, on both their treated and CB for one to three fractions. Scintillator dosimeters, small plastic discs 1mm thick and 15mm in diameter, were calibrated against optically-stimulated luminescent dosimeters (OSLDs) to generate an integral output-to-dose conversion, where integral output is measured in post-processing through a custom fitting algorithm. The discs have been extensively characterized in a previous study for various treatment conditions including beam energy and treatment geometry. ResultsN=44 dosimetry measurements were evaluated, including 22 treated breast and 22 CB measurements. Following integral output-to-dose calibration, in vivo scintillator dosimeters exhibited high linearity (R2=0.99) with paired OSLD readings across all patients. The difference between scintillation and OSLD dose measurements averaged 2.8% of the prescribed dose, or an absolute dose difference of approximately 7 cGy. ConclusionsIntegration of scintillation dosimetry with Cherenkov imaging offers an accurate, rapid alternative for in vivo dose verification in WBRT, circumventing the limitations of conventional point dosimeters. The additional benefit of visualizing measurement locations relative to the treatment field provides users an enhanced understanding of results and allows for detection of high dose gradients. Future work will explore the applicability of this technique across a broader range of radiotherapy treatments, aiming to streamline IVD practices.

Evaluation of TOPAS MC tool performance in optical photon transport and radioluminescence-based dosimetry

Radiation therapy plays a pivotal role in modern cancer treatment, demanding precise and accurate dose delivery to tumor sites while minimizing harm to surrounding healthy tissues. Monte Carlo simulations have emerged as indispensable tools for achieving this precision, offering detailed insights into radiation transport and interaction at the subatomic level. As the use of scintillation and luminescence dosimetry becomes increasingly prevalent in radiation therapy, there arises a need for validated Monte Carlo tools tailored to optical photon transport applications. In this paper, an evaluation process of the TOPAS (TOol for PArticle Simulation) Monte Carlo tool for Cerenkov light generation, optical photon transport and radioluminescence based dosimetry is presented. Three distinct sources of validation data are utilized: one from a published set of experimental results and two others from simulations performed with the Geant4 code. The methodology employed for evaluation includes the selection of benchmark experiments, making use of opt3 and opt4 Geant4 physics models and simulation setup, with observed slight discrepancies within the calculation uncertainties. Additionally, the complexities and challenges associated with modeling optical photons generation through luminescence or Cerenkov radiation and their transport are discussed. The results of our evaluation suggests that TOPAS can be used to reliably predict Cerenkov generation, luminescence phenomenon and the behavior of optical photons in common dosimetry scenarios.

Real-time Plastic Scintillation Dosimetry of Ultra-High Dose Rate Very High Energy Electrons (VHEE) at CERN CLEAR Facility

Real-time Plastic Scintillation Dosimetry of Ultra-High Dose Rate Very High Energy Electrons (VHEE) at CERN CLEAR Facility

Technical note: Characterization of a multi-point scintillation dosimetry research platform for a low-field MR-Linac.

MRI-guided radiation therapy (MRgRT) requires unique quality assurance equipment to address MR-compatibility needs, minimize electron return effect, handle complex dose distributions, and evaluate real-time dosimetry for gating. Plastic scintillation detectors (PSDs) are an attractive option to address these needs. To perform a comprehensive characterization of a multi-probe PSD system in a low-field 0.35T MR-linac, including detector response assessment and gating performance. A four-channel PSD system (HYPERSCINT RP-200) was assembled. A single channel was used to evaluate repeatability, percent depth dose (PDD), detector response as a function of orientation with respect to the magnetic field, and intersession variability. All four channels were used to evaluate repeatability, linearity, and output factors. The four PSDs were integrated into an MR-compatible motion phantom at isocenter and in gradient regions. Experiments were conducted to evaluate gating performance and tracking efficacy. For repeatability, the maximum standard deviation of repeated measurements was 0.13% (single PSD). Comparing the PSD to reference data, PDD had a maximum difference of 1.12% (10cm depth, 6.64×6.64 cm2). Percent differences for rotated detector setups were negligible (<0.3%). All four PSDs demonstrated linear response over 10-1000 MU delivered and the maximum percent difference between the baseline and measured output factors was 0.78% (2.49×2.49 cm2). Gating experiments had 400 cGy delivered to isocenter with<0.8 cGy variation for central axis measures and<0.7 cGy for the gradient sampled region. Real-time dosimetry measurements captured spurious beam-on incidents that correlated to tracking algorithm inaccuracies and highlighted gating parameter impact on delivery efficiency. Characterization of the multi-point PSD dosimetry system in a 0.35T MR-linac demonstrated reliability in a low-field MR-Linac setting, with high repeatability, linearity, small intersession variability, and similarity to baseline data for PDD and output factors. Time-resolved, multi-point dosimetry also showed considerable promise for gated MR-Linac applications.

Influence of shallow traps on the kinetics of Optically Stimulated Luminescence of the Li and Ce ions co-doped MgB4O7 compound

The presence of point defects associated with shallow traps has been identified as a limiting factor in the design of materials with desirable characteristics for applications such as scintillation and luminescence dosimetry, among others. In this context, this study aims to elucidate the dynamics inherent to the charge carriers in systems containing multiple traps and one single recombination centre. To unravel this complexity, we employed a synergetic approach combining Thermoluminescence (TL) and Optically Stimulated Luminescence (OSL) measurements with kinetic models. Specifically, for the Li and Ce co-doped MgB4O7, we verified that the electron population trapped in shallower traps exhibits a slower decay rate under optical stimulation compared to deeper traps. This behaviour led to a delay in the luminescence emission, as a result of charge re-trapping or even competition with other centres. This phenomenon can be attributed to its low photoionization cross-section associated with a high re-trapping rate, providing a rationale for these remarks. In addition, we observed that the shallow traps have a greater optical than thermal probability of being detrapped, indicating that they were not solely detrapped through thermal stimulation. Also, the magnitude of the thermal probability leads us to believe that there is an electron population different from zero in the conduction band at t = 0 (before optical stimulation). Lastly, this study paves the way for a deeper understanding of charge carrier dynamics in systems of multiple traps, improving the performance of existing materials for scintillation and dosimetry.

Determination of output factor for CyberKnife using scintillation dosimetry and deep learning

Objective. Small-field dosimetry is an ongoing challenge in radiotherapy quality assurance (QA) especially for radiosurgery systems such as CyberKnifeTM. The objective of this work is to demonstrate the use of a plastic scintillator imaged with a commercial camera to measure the output factor of a CyberKnife system. The output factor describes the dose on the central axis as a function of collimator size, and is a fundamental part of CyberKnife QA and integral to the data used in the treatment planning system. Approach. A self-contained device consisting of a solid plastic scintillator and a camera was build in a portable Pelicase. Photographs were analysed using classical methods and with convolutional neural networks (CNN) to predict beam parameters which were then compared to measurements. Main results. Initial results using classical image processing to determine standard QA parameters such as percentage depth dose (PDD) were unsuccessful, with 34% of points failing to meet the Gamma criterion (which measures the distance between corresponding points and the relative difference in dose) of 2 mm/2%. However, when images were processed using a CNN trained on simulated data and a green scintillator sheet, 92% of PDD curves agreed with measurements with a microdiamond detector to within 2 mm/2% and 78% to 1%/1 mm. The mean difference between the output factors measured using this system and a microdiamond detector was 1.1%. Confidence in the results was enhanced by using the algorithm to predict the known collimator sizes from the photographs which it was able to do with an accuracy of less than 1 mm. Significance. With refinement, a full output factor curve could be measured in less than an hour, offering a new approach for rapid, convenient small-field dosimetry.

Magnetic field influence on the light yield from fiber-coupled BCF-60 plastic scintillators of relevance for output factor dosimetry in MR-linacs

Organic plastic scintillators are of interest for ionizing radiation dosimetry in megavoltage photon beams because plastic scintillators have a mass density very similar to that of water. This leads to insignificant perturbation of the electron fluence at the point of measurement in a water phantom. This feature is a benefit for dosimetry in strong magnetic fields (e.g., 1.5 T) as found in linacs with magnetic resonance imaging. The objective of this work was to quantify if the light yield per dose for the scintillating fiber BCF-60 material from Saint-Gobain Ceramics and Plastics Inc. is constant regardless of the magnetic flux density. This question is of importance for establishing traceable measurement in MR linacs using this detector type. Experiments were carried out using an accelerator combined with an electromagnet (max 0.7 T). Scintillator probes were read out using chromatic stem-removal techniques based on two optical channels or full spectral information. Reference dosimetry was carried out with PTW31010 and PTW31021 ionization chambers. TOPAS/GEANT4 was used for modelling. The light yield per dose for the BCF-60 was found to be strongly influenced by the magnitude of the magnetic field from about 1 mT to 0.7 T. The light yield per dose increased (1.3 ± 0.2)% (k = 1) from 1 mT to 10 mT and it increased (4.5 ± 0.9)% (k = 1) from 0 T to 0.7 T. Previous studies of the influence of magnetic fields on medical scintillator dosimetry have been unable to clearly identify if observed changes in scintillator response with magnetic field strength were related to changes in dose, stem signal removal, or scintillator light yield. In the current study of BCF-60, we see a clear change in light yield with magnetic field, and none of the other effects.

Characterization of a 0.8 mm3 Medscint plastic scintillator detector system for small field dosimetry

Objective. Plastic scintillator detectors (PSDs) have demonstrated ability to meet requirements of small field dosimetry. Medscint developed a 1 mm long, 1 mm diameter cylindrical PSD with effective volume of 0.8 mm3. Clinically relevant, small field dosimetric properties of this detector, combined with a novel scintillation dosimetry system—HYPERSCINT RP-200, and HYPERDOSE analysis software were evaluated in this study. Approach. This novel scintillator-based dosimetry system was characterized with 6 MV-WFF and 10 MV-FFF x-ray beams delivered by Varian TrueBeamTM linear accelerator. The detector was characterized for leakage, short-term repeatability, dose response linearity, angular response, dose rate response, and field size dependence for radiation field sizes of 0.25 × 0.25 to 10 × 10 cm2. Measured detector specific output ratios were compared with microDiamond output factors to determine small field output correction factors, Main results. The dosimetry system showed excellent short-term repeatability with standard deviation of only 0.04 ± 0.01%. It demonstrated good dose linearity with variations less than 1.0% for 14.4 cGy and above. The dosimetry system was found to be independent of dose rate and angle of irradiation, with deviations for both below 0.5%. Leakage was found to be comparable to background readings. For 6 MV-WFF energy beams, detector specific output ratios for field sizes down to 1 × 1 cm2 agreed with output factors measured with PTW TN60019 microDiamond, thus, equates to unity for these field sizes. For 10 MV-FFF energy beams, detector specific output ratios for field sizes down to 2 × 2 cm2 agreed with PTW TN60019 microDiamond output factors, thus, equates to unity for these field sizes. for field sizes down to 0.5 × 0.5 cm2 were determined to be within 6% of unity for both 6 MV-WFF and 10 MV-FFF energy beams. Significance. The HYPERSCINT RP-200 dosimetry system coupled with a 0.8 mm3 PSD showed excellent dosimetric properties and was found to be clinically relevant for relative dosimetry down to field sizes of 0.5 × 0.5 cm2 and potentially smaller.

Point scintillator dosimetry in ultra-high dose rate electron “FLASH” radiation therapy: A first characterization

FLASH radiation therapy is a novel technique combining ultra-high dose rates (UHDR) with very short treatment times to strongly decrease normal tissue toxicity while preserving the anti-tumoral effect. However, the radiobiological mechanisms and exact conditions for obtaining the FLASH-effect are still under investigation. There are strong indications that parameters defining the beam structure, such as dose per pulse, instantaneous dose rate and pulse repetition frequency (PRF) are of importance. UHDR irradiations therefore come with dosimetric challenges, including both dose assessment and temporal ones. In this work, a first characterization of 6 real-time point scintillating dosimeters with 5 phosphors (Al2O3:C,Mg; Y2O3:Eu; Al2O3:C; (C38H34P2)MnBr4 and (C38H34P2)MnCl4, was performed in an UHDR pulsed electron beam. The dose rate independence of the calibration was tested by calibrating the detector at conventional and UHDR. Dose rate dependence was observed, however, further investigation, including intermediate dose rates, is needed. Linearity of the response with dose was tested by varying the number of pulses and a linearity with R2> 0.9989 was observed up to at least 200 Gy. Dose per pulse linearity was investigated by variation of the pulse length and SSD. All point scintillators showed saturation effects up to some extent and the instantaneous dose rate dependence was confirmed. A PRF dependence was observed for the Al2O3:C,Mg and Al2O3:C- based point scintillators. This was expected as the luminescence decay time of these materials exceeds the inter-pulse time.

Time-resolved plastic scintillator dosimetry in MR linear accelerators without image distortion

One of the newest developments within radiotherapy is the integration of Magnetic Resonance (MR) scanners and Megavoltage X-rays from linear accelerators into the new MR-Linacs. Some MR-Linacs are able to perform gated treatments based on continuously acquired 2D MR images taken during dose delivery, which has the potential to reduce margins required for tumor coverage. We have developed a dosimetry system that can provide time-resolved, dose-per-pulse, dosimetry without distorting the MR images in order to characterize this technology. The system is based on a plastic BCF-60 scintillation detector (PSD) coupled to an optical PMMA fiber cable. The detector was placed in a plastic tube filled with water and inserted into the piston of a dynamic MRI compatible phantom to be treated on a ViewRay MRIdian 0.35 T MR-Linac. The piston performed a sinusoidal movement to simulate a breathing cycle of either 4 or 8 s. We demonstrate that the detector system is able to provide real-time dose-per-pulse measurements without causing distortions in the MR images. The time-resolved dosimetry system revealed systematic dose rate transients during gated treatments that lasted about 1 s in every gating sequence where the beam turned on and off. Detection of such effects require real time dosimetry which does not interfere with the MRI based gating.

Pre-clinical and clinical evaluation of the HYPERSCINT plastic scintillation dosimetry research platform for in vivo dosimetry during radiotherapy.

PurposeThe purpose of this work is to evaluate the Hyperscint‐RP100 scintillation dosimetry research platform (Hyperscint‐RP100, Medscint Inc., Quebec, QC, Canada) designed for clinical quality assurance (QA) for use in in vivo dosimetry measurements.MethodsThe pre‐clinical evaluation of the scintillator was performed using a Varian TrueBeam linear accelerator. Dependency on field size, depth, dose, dose rate, and temperature were evaluated in a water tank and compared to calibration data from commissioning and annual QA. Angularity was evaluated with a 3D printed phantom. The clinical evaluation was first performed in two cadaver dogs, and then in three companion animal dogs receiving radiation therapy for nasal tumors. A treatment planning CT scan was performed for cadavers and clinical patients. Prior to treatment, the probe was inserted into the radiation field. Radiation was then delivered and measured with the scintillator. For cadavers, the treatment was repeated after making an intentional shift in patient position to simulate a treatment error.ResultsIn the preclinical measurements the dose differed from annual measurements as follows: field size −0.77 to 0.43%, depth dose −0.36 to 1.14%, dose −0.54 to 2.93%, dose rate 0.3 to 3.6%, and angularity −1.18 to 0.01%. Temperature dependency required a correction factor of 0.11%/°C. In the two cadavers, the dose differed by −1.17 to 0.91%. The device correctly detected the treatment error when the heads were intentionally laterally shifted. In three canine clinical patients treated in multiple fractions, the detected dose ranged from 98.33 to 103.15%.ConclusionResults of this new device are promising although more work is necessary to fully validate it for clinical dosimetry.

Time-Resolved Plastic Scintillator Dosimetry in Mr Linear Accelerators Without Image Distortion

Time-Resolved Plastic Scintillator Dosimetry in Mr Linear Accelerators Without Image Distortion

Comparative optic and dosimetric characterization of the HYPERSCINT scintillation dosimetry research platform for multipoint applications

This study introduces the HYPERSCINT research platform (HYPERSCINT-RP100, Medscint Inc., Quebec, Canada), the first commercially available scintillation dosimetry platform capable of multi-point dosimetry through the hyperspectral approach. Optic and dosimetric performances of the system were investigated through comparison with another commercially available solution, the Ocean Optics QE65Pro spectrometer. The optical characterization was accomplished by measuring the linearity of the signal as a function of integration time, photon detection efficiency and spectral resolution for both systems under the same conditions. Dosimetric performances were then evaluated with a 3-point plastic scintillator detector (mPSD) in terms of signal to noise ratio (SNR) and signal to background ratio (SBR) associated with each scintillator. The latter were subsequently compared with those found in the literature for the Exradin W1, a single-point plastic scintillator detector. Finally, various beam measurements were realized with the HYPERSCINT platform to evaluate its ability to perform clinical photon beam dosimetry. Both systems were found to be comparable in terms of linearity of the signal as a function of the intensity. Although the QE65Pro possesses a higher spectral resolution, the detection efficiency of the HYPERSCINT is up to 1000 time greater. Dosimetric measurements shows that the latter also offers a better SNR and SBR, surpassing even the SNR of the Exradin W1 single-point PSD. While doses ranging from 1 to 600 cGy were accurately measured within 2.1% of the predicted dose using the HYPERSCINT platform coupled to the mPSD, the Ocean optics spectrometer shows discrepancies up to 86% under 50cGy. Similarly, depth dose, full width at half maximum region of the beam profile and output factors were all accurately measured within 2.3% of the predicted dose using the HYPERSCINT platform and exhibit an average difference of 0.5%, 1.6% and 0.6%, respectively.

3D source tracking and error detection in HDR using two independent scintillator dosimetry systems.

The aim of this study is to perform three-dimensional (3D) source position reconstruction by combining in vivo dosimetry measurements from two independent detector systems. Time-resolved dosimetry was performed in a water phantom during HDR brachytherapy irradiation with Ir source using two detector systems. The first was based on three plastic scintillator detectors and the second on a single inorganic crystal (CsI:Tl). Brachytherapy treatments were simulated in water under TG-43U1 conditions, including a HDR prostate plan. Treatment needles were placed in distances covering a range of source movement of 120mm around the detectors. The distance from each dwell position to each scintillator was determined based on the measured dose rates. The three distances given by the mPSD were recalculated to a position along the catheter (z) and a distance radially away from the mPSD (xy) for each dwell position (a circumference around the mPSD). The source x, y, and z coordinates were derived from the intersection of the mPSD's circumference with the sphere around the ISD based on the distance to this detector. We evaluated the accuracy of the source position reconstruction as a function of the distance to the source, the most likely location for detector positioning within a prostate volume, as well as the capacity to detect positioning errors. Approximately 4000 source dwell positions were tracked for eight different HDR plans. An intersection of the mPSD torus and the ISD sphere was observed in 77.2% of the dwell positions, assuming no uncertainty in the dose rate determined distance. This increased to 100% if 1σ search regions were added. However, only 73(96)% of the expected dwell positions were found within the intersection band for 1(2) σ uncertainties. The agreement between the source's reconstructed and expected positions was within 3mm for a range of distances to the source up to 50mm. The experiments on a HDR prostate plan, showed that by having at least one of the detectors located in the middle of the prostate volume, reduces the measurement deviations considerably compared to scenarios where the detectors were located outside of the prostate volume. The analysis showed a detection probability that, in most cases, is far from the random detection threshold. Errors of 1(2)mm can be detected in ranges of 5-25 (25-50)mm from the source, with a true detection probability rate higher than 80%, while the false probability rate is kept below 20%. By combining two detector responses, we enabled the determination of the absolute source coordinates. The combination of the mPSD and the ISD in vivo dosimetry constitutes a promising alternative for real-time 3D source tracking in HDR brachytherapy.

Technical note: characterization of spectral changes with measurement geometry and magnetic field strength in light guides used for scintillation dosimetry

The purpose of this work was to characterize the stem-effect signal and the Cerenkov light ratio (CLR) in various light guides as functions of measurement geometry and magnetic field strength. Two PMMA-, two silica-, and one polystyrene-based light guides were considered in this work. Spectra measurements were performed as functions of depth, fiber-beam angle, and magnetic field strength using an optical spectrometer. All measurements were performed using a clinical linear accelerator at a nominal photon beam energy of 6 MV. Depths ranging from 1 cm to 10 cm, fiber-beam angles ranging from 90 degrees to 30 degrees, and magnetic field strengths ranging from 0 T to ± 1.40 T were investigated. The CLR was calculated from each spectrum by taking the ratio of the integral signal between 400 nm and 500 nm to the integral signal between 500 nm and 600 nm. A maximum increase of 80.5% in the stem-effect signal was observed in the magnetic field. Variations in spectral shape and, consequently, the CLR were observed for all of the fibers as functions of magnetic field strength and measurement geometry, particularly for wavelengths less than 400 nm. The plastic fibers exhibited decreases in the CLR as a function of magnetic field strength at all depths investigated, whereas the silica fibers exhibited increases in the CLR with decreasing magnetic field strength. A maximum variation of 11.1% in the CLR was observed for the polystyrene fiber due to the magnetic field. The sensitivity of the CLR to the magnetic field decreased as the fiber-beam angle decreased. The measured spectral response, shape, and CLR were found to be sensitive to the applied magnetic field strength and polarity where the variations in response were unique to each fiber.

Tomographic-based 3D scintillation dosimetry using a three-view plenoptic imaging system.

To demonstrate the feasibility of a three-plenoptic camera projection, scintillation-based dosimetry system for measuring three-dimensional (3D) dose distributions of static photon radiation fields. Static x-ray photon beams were delivered to a cubic plastic scintillator volume embedded within acrylic blocks. For each beam, three orthogonal projections of the scintillating light emission were recorded using a multifocus plenoptic camera. Experimental 3D reconstructions of the light distribution were obtained using an iterative maximum likelihood-expectation maximization (ML-EM) algorithm. For this purpose, the elements of the system matrix representing the contribution of the scintillator volume voxels to the camera sensor pixels were calculated using optical design software. A reconstruction-specific correction was applied to light reconstructions to account for scintillating light imaged by the camera but not directly resulting from dose deposition. Cross beam profiles (CBPs) and percentage depth dose (PDD) curves were compared to treatment planning system data for square fields. Three-dimensional and 3D gamma analyses were performed for concave-shaped dose distributions and the Pearson correlation coefficient and reconstruction error were employed to assess the quality of the measured relative 3D dose distributions. A full and accurate model of the plenoptic camera-based scintillation dosimetry system was implemented using the light ray tracing capabilities of optical design software. With this model, light distributions were successfully reconstructed over a volume of 60×60×60mm at a resolution of 2mm. For relative 3D measurements of square radiation fields of , and compared with treatment planning system reference distributions, the maximum root-mean-square error of the CBPs evaluated at two different depths was of 3.2%, 1.2%, and 1.1%, respectively; as for the corresponding linearly fitted PDDs of the square fields, the slopes of the reconstructed dose distributions overestimated those of the reference distributions by at most 0.2%/cm. The 2D gamma passing rate with a criterion of 2%/2mm for the concave-shaped photon field was of 61.6%, 66.1%, and 76.4% using one, two, and three plenoptic projections; the respective success rates become 77.1%, 87.5%, and 94.9% using a criterion of 3%/3mm. The 3D correlation coefficient for the corresponding reconstructions was of 0.688, 0.905, and 0.976, respectively. Three-dimensional light distributions emitted from within a plastic scintillator volume were successfully recovered using optical design software to establish a complete tomographic model of a plenoptic camera-based prototype. The tomographic model can equivalently extend to dynamic dose delivery measurements, providing temporal resolution limited by the camera's exposure time. This feasibility study enables a simplified design-to-implementation process for volumetric scintillation dosimetry prototypes toward fully meeting the clinical needs of 3D dose measurements for static and dynamic delivery techniques.

Technical Note: A novel dosimeter improves total skin electron therapy surface dosimetry workflow.

PurposeThe novel scintillator‐based system described in this study is capable of accurately and remotely measuring surface dose during Total Skin Electron Therapy (TSET); this dosimeter does not require post‐exposure processing or annealing and has been shown to be re‐usable, resistant to radiation damage, have minimal impact on surface dose, and reduce chances of operator error compared to existing technologies e.g. optically stimulated luminescence detector (OSLD). The purpose of this study was to quantitatively analyze the workflow required to measure surface dose using this new scintillator dosimeter and compare it to that of standard OSLDs.MethodsDisc‐shaped scintillators were attached to a flat‐faced phantom and a patient undergoing TSET. Light emission from these plastic discs was captured using a time‐gated, intensified, camera during irradiation and converted to dose using an external calibration factor. Time required to complete each step (daily QA, dosimeter preparation, attachment, removal, registration, and readout) of the scintillator and OSLD surface dosimetry workflows was tracked.ResultsIn phantoms, scintillators and OSLDs surface doses agreed within 3% for all data points. During patient imaging it was found that surface dose measured by OSLD and scintillator agreed within 5% and 3% for 35/35 and 32/35 dosimetry sites, respectively. The end‐to‐end time required to measure surface dose during phantom experiments for a single dosimeter was 78 and 202 sec for scintillator and OSL dosimeters, respectively. During patient treatment, surface dose was assessed at 7 different body locations by scintillator and OSL dosimeters in 386 and 754 sec, respectively.ConclusionScintillators have been shown to report dose nearly twice as fast as OSLDs with substantially less manual work and reduced chances of human error. Scintillator dose measurements are automatically saved to an electronic patient file and images contain a permanent record of the dose delivered during treatment.

Variable periodic time operated fibre-coupled dosimetry system using Ag-activated RPL glasses with build-up

We report the demonstration of a variable periodic time operated fibre-coupled dosimetry system using Ag-activated phosphate glass based on radiophotoluminescent (RPL) phenomenon. In order to overcome the inevitable “build-up” effect occurring in RPL glasses during and after X-ray irradiation, pertinent experiments are designed and carried out. The RPL intensities for four successive sequences, namely, the pre-dose, X-ray exposure, build-up and optical bleaching processes, are examined for the orange and blue RPL bands. Build-up curves and corresponding build-up rates are measured for different excitation wavelengths, analytically evaluated, and compared with those of a real-time fibre plastic scintillation dosimetry system. In addition, the orange RPL signal dependence on temperature and variable interval is examined for three successive sequences. The quick response of the dosimetry system developed here to the on/off switching operations is confirmed using seven successive sequences.

63 Characterization of a scintillation dosimetry system for in vivo dose verification in brachytherapy

63 Characterization of a scintillation dosimetry system for in vivo dose verification in brachytherapy