Chamber Array Research Articles

Decomposing a Beam Profile Constancy into Energy and Symmetry Components and Its Evaluation Using an Ionization Chamber Array

We have proposed a new formulation that can decompose the profile constancy defined in the AAPM TG 142 into energy and symmetry constancies by measuring beam profiles using an IC profiler (ICP). Measured profiles were laterally inverted to calculate averaged profiles in the lateral direction, thereby cancelling asymmetric components. Validation tests were performed by comparing the proposed calculation and measured results under various experimental conditions. Calculated profile constancies were further compared to decomposed energy and symmetry constancies. The energy constancy calculated from the averaged beam profile by lateral inversion and the measured PDD(10) constancy agreed within 0.1% when only symmetries were varied. The calculated energy and symmetry constancies, and the measured results agreed within 0.2% when both energies and symmetries were varied. The linac beam profile constancy has been decomposed into energy and symmetry terms. The proposed formulation has been validated by comparing the calculations and the direct measurements using the ICP. We have shown that QA/QC for profile constancy tests can be efficiently performed using the proposed formulation.

Commissioning of a synchrotron-based proton beam therapy system for use with a Monte Carlo treatment planning system

This work tackles the commissioning and validation of a novel combination of a synchrotron-based proton beam therapy system (Hitachi, Ltd.) for use with a Monte Carlo treatment planning system (TPS). Four crucial aspects in this configuration have been investigated: (1) Monte Carlo-based correction performed by the TPS to the measured integrated depth-dose curves (IDD), (2) circular spot modelling with a single Gaussian function to characterize the synchrotron physical spot, which is elliptical, (3) the modelling of the range shifter that enables using only one set of measurements in open beams, and (4) the Monte Carlo dose calculation model in small fields.Integrated depth-dose curves were measured with a PTW Bragg peak chamber and corrected, with a Monte Carlo model, to account for energy absorbed outside the detector. The elliptical spot was measured by IBA Lynx scintillator, EBT3 films and PTW microDiamond. The accuracy of the TPS (RayStation, RaySearch Laboratories) at spot modelling with a circular Gaussian function was assessed.The beam model was validated using spread-out Bragg peak (SOBP) fields. We took single-point doses at several depths through the central axis using a PTW Farmer chamber, for fields between 2 × 2cm and 30 × 30cm. We checked the range-shifter modelling from open-beam data. We tested clinical cases with film and an ionization chamber array (IBA Matrix).Sigma differences for spots fitted using 2D images and 1D profiles to elliptical and circular Gaussian models were below 0.22 mm. Differences between SOBP measurements at single points and TPS calculations for all fields between 5 × 5 and 30 × 30cm were below 2.3%. Smaller fields had larger differences: up to 3.8% in the 2 × 2cm field. Mean differences at several depths along the central axis were generally below 1%. Differences in range-shifter doses were below 2.4%. Gamma test (3%, 3 mm) results for clinical cases were generally above 95% for Matrix and film.Approaches for modelling synchrotron proton beams have been validated. Dose values for open and range-shifter fields demonstrate accurate Monte Carlo correction for IDDs. Elliptical spots can be successfully modelled using a circular Gaussian, which is accurate for patient calculations and can be used for small fields. A double-Gaussian spot can improve small-field calculations. The range-shifter modelling approach, which reduces clinical commissioning time, is adequate.

Experimental Validation of a Real-Time Adaptive 4D-Optimized Particle Radiotherapy Approach to Treat Irregularly Moving Tumors

Treatment of locally advanced lung cancer is limited by toxicity and insufficient local control. Particle therapy could enable more conformal treatment than intensity modulated photon therapy but is challenged by irregular tumor motion, associated range changes, and tumor deformations. We propose a new strategy for robust, online adaptive particle therapy, synergizing 4-dimensional optimization with real-time adaptive beam tracking. The strategy was tested and the required motion monitoring precision was determined. In multiphase 4-dimensional dose delivery (MP4D), a dedicated quasistatic treatment plan is delivered to each motion phase of periodic 4-dimensional computed tomography (4DCT). In the new extension, "MP4D with residual tracking" (MP4DRT), lateral beam tracking compensates for the displacement of the tumor center-of-mass relative to the current phase in the planning 4DCT. We implemented this method in the dose delivery system of a clinical carbon facility and tested it experimentally for a lung cancer plan based on a periodic subset of a virtual lung 4DCT (planned motion amplitude 20mm). Treatments were delivered in a quality assurance-like setting to a moving ionization chamber array. We considered variable motion amplitudes and baseline drifts. The required motion monitoring precision was evaluated by adding noise to the motion signal. Log-file-based dose reconstructions were performed in silico on the entire 4DCT phantom data set capable of simulating nonperiodic motion. MP4DRT was compared with MP4D, rescanned beam tracking, and internal target volume plans. Treatment quality was assessed in terms of target coverage (D95), dose homogeneity (D5-D95), conformity number, and dose to heart and lung. For all considered motion scenarios and metrics, MP4DRT produced the most favorable metrics among the tested motion mitigation strategies and delivered high-quality treatments. The conformity was similar to static treatments. The motion monitoring precision required for D95 >95% was 1.9mm. With clinically feasible motion monitoring, MP4DRT can deliver highly conformal dose distributions to irregularly moving targets.

Intra-Lid Multi-Core Vapor Chamber Architecture for Heterogeneous Electronic Packages: Technology Concept to Prototype Evaluation

Thermal management of future heterogeneous electronic packages with extreme heat fluxes relies on effective spreading of heat in the package lid. Intra-lid integration of vapor chambers is a promising strategy for simultaneous dissipation of large total heat loads and localized high-flux hot spots. However, conventional vapor chambers comprising a single vapor core require relatively thick evaporator wicks to prevent dry out at high total heat loads, thereby imposing a large temperature drop across the wick at the hot spot location. We recently proposed a cascaded multi-core vapor chamber (CMVC) architecture comprising a single-core vapor chamber stacked on an array of smaller footprint vapor cores having relatively thinner wicks. The multi-core array is designed to spread heat from arbitrarily distributed high-flux hot spots before they enter the top vapor chamber having a thicker wick. Then, the top vapor chamber spreads the high total heat loads to the base of the mounted heat sink. To evaluate the proposed CMVC technology, we make a weighted decision to identify an appropriate minimum viable prototype for subsequent design and testing. A reduced-order model is used to determine the dimensions and properties of the wick and vapor core that minimize the temperature drop across the down-selected multi-core vapor chamber architecture for a given power map, considering manufacturing process constraints. Finite element analysis (FEA) simulations are employed to decide a condenser wall thickness that avoids permanent deformation in the vapor chamber architecture under a mechanical load. A prototype is manufactured by a commercial vendor following these parameters and manufacturing constraints. As predicted by the thermal model, experimental characterization of this first-reported multi-core vapor chamber array prototype offers a notable reduction in temperature drop relative to a benchmark solid copper spreader, owing to attenuation of hot spots at a low temperature difference.

Quality assurance of scanned proton beams at different gantry angles using an ionization chamber array in a rotational phantom

PurposeTo implement a single set-up monthly QA procedure for 9 different beam parameters at different gantry angles and evaluate its clinical implementation over a 12 month period. MethodsWe developed a QA procedure using an array detector (PTW Octavius 1500XDR) embedded in a rotational unit (PTW Octavius 4D) at our proton facility. With a single set-up we can monitor field central axis position, field symmetry, field size, flatness, penumbrae, output, spot size, spot position and range at different gantry angles (AAPM TG 224). The set-up is irradiated with homogenous 2D fields with dynamic aperture and spot patterns at five gantry angles. A modular top is used to check the range consistency. Absolute γ analysis were performed to compare measured dose distributions to calculated dose. All other parameters are directly extracted from the measurements. Additionally, the sensitivity of the set-up to small changes in beam parameters were compared to the Lynx detector (IBA). ResultsOver a 12 month period, output, symmetry, and flatness were within ± 2 %; FWHM, spot positions, penumbra widths, and central axis fields were within ± 1 mm. Range differences were all within 1/2 of the energy spacing (±0.6 MeV) relative to baseline. Most (2 %, 2 mm) γ-analysis showed agreement scores higher than 90 %. The sensitivity is comparable to the Lynx detector and measurement time is reduced by 40 %. ConclusionThe time-efficient monthly QA procedure that we developed can accurately be used to measure a large range of beam parameters at different gantry angles, within the TG 224 AAPM recommendations.

Hydrogel-based microfluidic device with multiplexed 3D in vitro cell culture

Microfluidic devices that combine an extracellular matrix environment, cells, and physiologically relevant perfusion, are advantageous as cell culture platforms. We developed a hydrogel-based, microfluidic cell culture platform by loading polyethylene glycol (PEG) hydrogel-encapsulated U87 glioblastoma cells into membrane-capped wells in polydimethyl siloxane (PDMS). The multilayer microfluidic cell culture system combines previously reported design features in a configuration that loads and biomimetically perfuses a 2D array of cell culture chambers. One dimension of the array is fed by a microfluidic concentration gradient generator (MCGG) while the orthogonal dimension provides loading channels that fill rows of cell culture chambers in a separate layer. In contrast to typical tree-like MCGG mixers, a fractional serial dilution of 1, ½, ¼, and 0 of the initial solute concentration is achieved by tailoring the input microchannel widths. Hydrogels are efficiently and reproducibly loaded in all wells and cells are evenly distributed throughout the hydrogel, maintaining > 90% viability for up to 4 days. In a drug screening assay, diffusion of temozolomide and carmustine to hydrogel-encapsulated U87 cells from the perfusion solution is measured, and dose–response curves are generated, demonstrating utility as an in vitro mimic of the glioblastoma microenvironment.

Overall Accuracy of Single-Isocenter Multiple Metastases SRS Treatments over Time: Comparison of Two Commercially Available Methods

<h3>Purpose/Objective(s)</h3> Single isocenter stereotactic radiosurgery (SI-SRS) is an efficient approach for dose delivery to multiple brain metastases since the treatment duration is considerably reduced, compared to the standard method of the isocenter placement at each tumor center. However, the complexity of this technique results in increased sensitivity to geometric and dosimetric uncertainties during plan delivery, thus patient-specific quality assurance procedures of high accuracy are mandatory. This study presents the investigation into the consistency of this technique, using the a 4D dose verification system and 3D printed head phantoms. <h3>Materials/Methods</h3> A treatment plan with two brain metastases was delivered four times in the period of one month on a Linac, to evaluate the reproducibility of the SI-SRS technique. The targets had a concave (2.4 cc) and a spherical (1.5 cc) shape, placed at a distance of 5 cm. Dose prescription was set to 8 Gy for both targets and a treatment plan of a single fraction using four Hyperarc beams, one full coplanar arc and three half noncoplanar arcs, arranged with a single isocenter automatically located on the center of the distance between the two targets was created. Before plan delivery, Winston-Lutz (WL) tests were performed to determine the diameter of the sphere containing the radiation isocenter for various positions of the collimator, gantry and couch. The dose distribution was recalculated on 4D geometry and measured with the 1000 SRS ion chamber array. The head phantom accommodated a film insert and the irradiation procedure consisted of positioning, imaging and plan delivery as if it was the real patient. Gamma analysis was performed for 3%/1mm acceptance criteria using a dose threshold of 1 Gy for films and 10% of maximum dose for 4D. <h3>Results</h3> The Root Mean Square (RMS) variation of the isocenter was 0.71±0.15 mm for gantry, 0.66±0.14 mm for collimator and 0.87±0.22 mm for couch, validating that the isocenter diameter was within the tolerance of 1 mm before each measurement. Gamma analysis revealed a mean passing rate (GPR) of 93.2%±0.07% for 4D measurements, compared to 91.2%±1.8% for the film ones. The reduced GPR in the case of the head phantom is expected, since it is an End-to-End QA procedure, incorporating not only the plan delivery uncertainties, but also the ones related to image registration and couch rotation. <h3>Conclusion</h3> Both QA methods showed a good agreement with each other and the calculated dose distribution having GPRs above 90% for the 3%/1mm criteria, rendering them suitable for verification of SRS plans' dosimetric and spatial accuracy. The standard deviation of the GPRs revealed that the plan delivery was consistent between the measurements, demonstrating high reproducibility and accuracy of the SI-SRS technique.

Testing of an enhanced leaf model for improved dose calculation in a commercial treatment planning system.

With the ever-increasing complexity of dynamic radiotherapy treatments, dose calculation algorithms are challenged to accurately calculate the dose resulting from small, on- and off-axis multileaf collimator (MLC) aperture movements. Although the currently available Eclipse (Varian Medical Systems, Palo Alto) dose calculation algorithms still use a simplified, binary MLC model, a more advanced and detailed modeling of the MLC could be beneficial for the dose calculation precision of high-end treatments. To improve the modeling of the MLC in the dose calculation algorithms of the Eclipse treatment planning system, an enhanced MLC attenuation model was constructed through ray tracing through the actual leaf designs for the most commonly used Varian MLC types. The enhanced leaf model (ELM) thus includes the rounded leaf tip shape, the drive screw cutout, and the leaf body thickness. The purpose of this work is to test out this new model and explore possible improvements compared to the previous model. Dose calculations were performed in a research Eclipse environment equipped with the original and enhanced MLC model. Measurements were performed on TrueBeam and on Halcyon dual MLC treatment units. Dedicated static and dynamic MLC test plans were designed to challenge the dose calculation and highlight differences between both models while keeping the experimental setup simple in order to minimize measurement uncertainties. Measurements were performed with single ion chambers, 2D ion chamber arrays and film. The improved MLC model considerably improves the accuracy of the dose calculation for the test fields used in this study. For the TrueBeam MLC, improvements are most prominent for off-axis dose delivery through narrow (static or dynamic) MLC gaps. For 3mm narrow sweeping gap deliveries at 12cm off-axis, the advanced model agrees within 2% with the measurement, in contrast to the 12% deviation observed with the original MLC model. For the Halcyon MLC, improvements are especially prominent when the leaves of both MLC stacks are aligned, regardless of their position in the field. Sweeping gap measurements improve from a 7%-10% deviation with the original model to within 2% with the new model. Although test fields designed in this study emphasize the flaws in the original MLC dose calculation model, the enhanced MLC model resolves all of the observed discrepancies, showing excellent on- and off-axis agreements with all of the performed measurements.

An integrated microfluidics platform with high-throughput single-cell cloning array and concentration gradient generator for efficient cancer drug effect screening

BackgroundTumor cell heterogeneity mediated drug resistance has been recognized as the stumbling block of cancer treatment. Elucidating the cytotoxicity of anticancer drugs at single-cell level in a high-throughput way is thus of great value for developing precision therapy. However, current techniques suffer from limitations in dynamically characterizing the responses of thousands of single cells or cell clones presented to multiple drug conditions.MethodsWe developed a new microfluidics-based “SMART” platform that is Simple to operate, able to generate a Massive single-cell array and Multiplex drug concentrations, capable of keeping cells Alive, Retainable and Trackable in the microchambers. These features are achieved by integrating a Microfluidic chamber Array (4320 units) and a six-Concentration gradient generator (MAC), which enables highly efficient analysis of leukemia drug effects on single cells and cell clones in a high-throughput way.ResultsA simple procedure produces 6 on-chip drug gradients to treat more than 3000 single cells or single-cell derived clones and thus allows an efficient and precise analysis of cell heterogeneity. The statistic results reveal that Imatinib (Ima) and Resveratrol (Res) combination treatment on single cells or clones is much more efficient than Ima or Res single drug treatment, indicated by the markedly reduced half maximal inhibitory concentration (IC50). Additionally, single-cell derived clones demonstrate a higher IC50 in each drug treatment compared to single cells. Moreover, primary cells isolated from two leukemia patients are also found with apparent heterogeneity upon drug treatment on MAC.ConclusionThis microfluidics-based “SMART” platform allows high-throughput single-cell capture and culture, dynamic drug-gradient treatment and cell response monitoring, which represents a new approach to efficiently investigate anticancer drug effects and should benefit drug discovery for leukemia and other cancers.

Validation of a digital method for patient-specific verification of VMAT treatment using a 2D ionisation detector array

VMAT treatment involves the delivery of complex beam parameters including the dynamic multi-leaf collimators (MLC) from a linac. The use of a detector array has become a standard method to verify the treatment accuracy before the treatment planned is delivered to the patient with some limitations. This study aims to evaluate the accuracy of a high-resolution, digital method using linac log data for VMAT treatment verification. The log data was obtained from a Versa HD (Elekta ltd., Crawley, UK) linac during VMAT treatment. All the dynamic treatment parameters including MLC position, and MLC speed, were recorded at the rate of 4 Hz in the log data. The treatment delivery was also measured simultaneously using an Octavius 1500 2D ionisation chamber array (PTW, Freiburg, Germany) during the log data measurements. The parameters were extracted and analysed using algorithms written in MATLAB (MathWorks, Natick, MA). The results demonstrated that the log data can track MLC leaves with an accuracy of 1 mm at speeds ranging from 3.04 to 3.40 cm/s. Evaluation of the fluence generated for the VMAT delivery using log data was shown to agree well with the planned dose distribution measured in the 2D detector array, with an average gamma pass rate of 97.5% at 3%/3 mm. Log data obtained a higher gamma pass rate of 98.5% compared to the 2D detector array of 97.5%. The digital linac log data provides the basis for an essential high-resolution real-time verification tool that may be used for routine VMAT verification.

Electrical Characterization of Micron-Sized Chambers Used as a Depot for Drug Delivery

Implantable drug delivery devices have emerged as a quintessential therapeutic platform for curing chronic ailments that require enhanced and localized drug concentrations. A typical device encompasses an array of tiny reservoirs or chambers to store drug formulations before their release inside a biological milieu. With the recent progress in biocompatible and biodegradable materials, it has become readily possible to fabricate chambers for rapid and on-demand drug release. However, to deal with an emerging diagnostic and therapeutic conundrum, new paradigms are required to devise chambers with multifunctional capabilities. In this article, we present micrometer-sized chambers that are fabricated by a patterned film base to realize their structure in an array formation. The microchambers are fabricated from a polylactic acid matrix and modified with a range of conducting species using the layer-by-layer (LBL) assembly technique. For electrical response characterization of microchambers, a complementary split ring resonator (CSRR) is used to estimate the loss tangent. A proof of concept is also discussed that the conductive nature of microchambers can be envisioned to perform thermal therapy and drug delivery in response to electromagnetic radiations.

Controlled Rehydration of Dried Reagents for Robust Multiplex Digital PCR.

Digital polymerase chain reaction (dPCR) is emerging as a powerful method for nucleic acid detection due to its unprecedented sensitivity and precision. However, most current dPCR platforms are inherently limited by their low multiplexing ability due to primer-pair cross interactions and spectral overlap of available fluorophores. Here, we present a novel and robust method for multiplexing dPCR that is free from primer dimerization and fluorescence channel number limitation, enabling highly precise and multiplexed detection of nucleic acid targets. By prestoring target-specific primers and probes in different storage chambers, the method physically separates reactions and thus avoids the primer-pair cross interactions and spectral overlap of different fluorescent probes that usually occur within a single-tube reaction. Furthermore, a dissolvable delay valve (DDV) is embedded between each pair of the reagent prestorage chamber and reaction microwell array. Such a DDV configuration allows full reconstitution of the prestored reagents and then generates a uniform concentration distribution of the reconstituted reagents across the entire reaction microwell array, which is favorable for achieving reliable and robust multiplex dPCR assays. We demonstrated the feasibility of this method by performing an eight-plex dPCR assay targeting the seven most common point mutations in Kirsten rat sarcoma viral oncogene homologue (KRAS) and a reference sequence (wild-type KRAS allele).

An integrated microfluidic chip-mass spectrometry system for rapid antimicrobial resistance analysis of bacteria producing β-lactamases

Bacteria producing β-lactamases have become a major issue in the global public health field. To restrain the development of drug resistance and reduce the abuse of antibiotics, it is very important to rapidly identify bacteria producing β-lactamases and put forward a reasonable treatment plan. Here, an integrated microfluidic chip-mass spectrometry system was proposed for rapid screening of β-lactamase-producing bacteria and optimization of β-lactamase inhibitor dosing concentration. The concentration gradient generator followed by an array of bacterial culture chambers, as well as micro-solid-phase extraction columns was designed for sample pretreatment before mass analysis. By using the combination system, the process of the hydrolysis of antibiotics by β-lactamase-producing bacteria could be analyzed. To validate the feasibility, four antibiotics and two antibiotic inhibitors were investigated using three strains including negative control, SHV-1 and TEM-1 strains. SHV-1 and TEM-1 strains were successfully distinguished as the β-lactamase producing strains. And the acquired optimal concentrations of β-lactamase inhibitors were in accordance with the results by that obtained from the traditional microdilution broth method. The total analysis time only needed around 2 h, which was faster than conventional methods that require a few days. The technique presented herein provides an easy and rapid protocol for β-lactamase resistance related studies, which is important for the inhibition of antimicrobial resistance development and the reduction of antibiotics abuse.

Comparison of pencil beam and Monte Carlo calculations with ion chamber array measurements for patient-specific quality assurance

ObjectiveTo determine under what conditions and criteria comparisons between calculations made with the current clinical treatment planning system (Syngo) and an in-house built TPS (TIMPS) would allow skipping of in-beam portal-specific measurements. MethodsMeasurements were made with an array of 24 ion chambers in a water phantom for 227 proton and 313 carbon ion portals with and without a range shifter (RS). These measurements were compared with calculations performed with Syngo and TIMPS using metrics of average dose difference and Gamma index. ResultsFor proton portals without RS, if a Gamma comparison between TIMPS and Syngo passed using criteria of 90% of tested points being within 3% and 3 ​mm, then 74% of measurements would agree with both TIMPS and Syngo. For proton portals with RS, more than 80% of measurements would agree with both calculations using the same criteria. For carbon ion portals without RS, if a Gamma evaluation between TIMPS and Syngo passed with criteria of 90% of tested points being within 2% and 2 ​mm, 85% of measurements would agree with both calculations. For carbon ion portals with RS, if a Gamma evaluation between TIMPS and Syngo passed with criteria of 90% of tested points being within 3% and 3 ​mm, 60% of measurements would agree with both calculations. ConclusionsBoth the pencil beam algorithm in Syngo and the FDC algorithm in TIMPS can provide accurate dose calculations in water for most clinical portals. For about 75% of portals, physicists can perform comparisons of calculations instead of phantom measurements to verify Syngo calculations thereby saving a large amount of beam time. There are some portals, however, such as for low-energy protons without RS and high-energy carbon ions, where agreement between the two calculations and measurements are not yet satisfactory to allow the elimination of all measurements.

Double-layer acoustic metasurface for the suppression of the Mack second mode in hypersonic boundary-layer flow

An acoustic metasurface consisting of two layers of perforated plates is proposed for suppression of the Mack second mode in hypersonic boundary-layer flow. The upper layer with very tiny holes is permeable to acoustic waves and hardly alters the background hypersonic boundary-layer flow, offering rather low resistive and inductive components of surface acoustic impedance. The bottom layer with large and sparse square holes is attached to a rigid wall surface and forms a periodic array of chambers, each covering multiple holes of the upper layer, which can adjust the impedance phase by working as a capacitive component. Based on a linear stability analysis of hypersonic boundary-layer instability, such an acoustic metasurface satisfying the required surface impedance is designed and numerically investigated. The results show that the metasurface can efficiently suppress the Mack second mode over a relatively wide bandwidth. This work provides an alternative strategy for the design of porous walls for hypersonic boundary-layer stabilization.

A 2D strip ionization chamber array with high spatiotemporal resolution for proton pencil beam scanning FLASH radiotherapy.

Experimental measurements of two-dimensional (2D) dose rate distributions in proton pencil beam scanning (PBS) FLASH radiation therapy (RT) are currently lacking. In this study, we characterize a newly designed 2D strip-segmented ionization chamber array (SICA) with high spatial and temporal resolution and demonstrate its applications in a modern proton PBS delivery system at both conventional and ultrahigh dose rates. A dedicated research beamline of the Varian ProBeam system was employed to deliver a 250-MeV proton PBS beam with nozzle currents up to 215nA. In the research and clinical beamlines, the spatial, temporal, and dosimetric performances of the SICA were characterized and compared with measurements using parallel-plate ion chambers (IBA PPC05 and PTW Advanced Markus chamber), a 2D scintillator camera (IBA Lynx), Gafchromic films (EBT-XD), and a Faraday cup. A novel reconstruction approach was proposed to enable the measurement of 2D dose and dose rate distributions using such a strip-type detector. The SICA demonstrated a position accuracy of 0.12±0.02mm at a 20-kHz sampling rate (50μs per event) and a linearity of R2 >0.99 for both dose and dose rate with nozzle beam currents ranging from 1 to 215nA. The 2D dose comparison to the film measurement resulted in a gamma passing rate of 99.8% (2mm/2%). A measurement-based proton PBS 2D FLASH dose rate distribution was compared to simulation results and showed a gamma passing rate of 97.3% (2mm/2%). The newly designed SICA demonstrated excellent spatial, temporal, and dosimetric performances and is well suited for commissioning, quality assurance, and a wide range of clinical applications in proton PBS clinical and FLASH-RT.

Potential of a Second-Generation Dual-Layer Spectral CT for Dose Calculation in Particle Therapy Treatment Planning.

In particle therapy treatment planning, dose calculation is conducted using patient-specific maps of tissue ion stopping power ratio (SPR) to predict beam ranges. Improving patient-specific SPR prediction is therefore essential for accurate dose calculation. In this study, we investigated the use of the Spectral CT 7500, a second-generation dual-layer spectral computed tomography (DLCT) system, as an alternative to conventional single-energy CT (SECT) for patient-specific SPR prediction. This dual-energy CT (DECT)-based method allows for the direct prediction of SPR from quantitative measurements of relative electron density and effective atomic number using the Bethe equation, whereas the conventional SECT-based method consists of indirect image data-based prediction through the conversion of calibrated CT numbers to SPR. The performance of the Spectral CT 7500 in particle therapy treatment planning was characterized by conducting a thorough analysis of its SPR prediction accuracy for both tissue-equivalent materials and common non-tissue implant materials. In both instances, DLCT was found to reduce uncertainty in SPR predictions compared to SECT. Mean deviations of 0.7% and 1.6% from measured SPR values were found for DLCT- and SECT-based predictions, respectively, in tissue-equivalent materials. Furthermore, end-to-end analyses of DLCT-based treatment planning were performed for proton, helium, and carbon ion therapies with anthropomorphic head and pelvic phantoms. 3D gamma analysis was performed with ionization chamber array measurements as the reference. DLCT-predicted dose distributions revealed higher passing rates compared to SECT-predicted dose distributions. In the DLCT-based treatment plans, measured distal-edge evaluation layers were within 1 mm of their predicted positions, demonstrating the accuracy of DLCT-based particle range prediction. This study demonstrated that the use of the Spectral CT 7500 in particle therapy treatment planning may lead to better agreement between planned and delivered dose compared to current clinical SECT systems.

On the potential of 2D ion chamber arrays for high-dose rate remote afterloading brachytherapy quality assurance

Objective. To investigate the potential of 2D ion chamber arrays to serve as a standalone tool for the verification of source strength, positioning and dwell time, within the framework of 192Ir high-dose rate brachytherapy device quality assurance (QA). Approach. A commercially available ion chamber array was used. Fitting of a 2D Lorentzian peak function to experimental data from a multiple source dwell position irradiation on a frame-by-frame basis, facilitated tracking of the source center orthogonal projection on the array plane. For source air kerma strength verification, Monte Carlo simulation was employed to obtain a chamber array- and source-specific correction factor of calibration with a 6 MV photon beam. This factor converted the signal measured by each ion chamber element to air kerma in free space. A source positioning correction was also applied to lift potential geometry mismatch between experiment and Monte Carlo simulation. Main results. Spatial and temporal accuracy of source movement was verified within 0.5 mm and 0.02 s, respectively, in compliance with the test endpoints recommended by international professional societies. The source air kerma strength was verified experimentally within method uncertainties estimated as 1.44% (k = 1). The source positioning correction method employed did not introduce bias to experimental results of irradiations where source positioning was accurate. Development of a custom jig attachable to the chamber array for accurate and reproducible experimental set up would improve testing accuracy and obviate the need for source positioning correction in air kerma strength verification. Significance. Delivery of a single irradiation plan, optimized based on results of this work, to a 2D ion chamber array can be used for concurrent testing of source position, dwell time and air kerma strength, and the procedure can be expedited through automation. Chamber arrays merit further study in treatment planning QA and real time, in vivo dose verification.

Evaluating Proton Dose and Associated Range Uncertainty Using Daily Cone-Beam CT.

PurposeThis study aimed to quantitatively evaluate the range uncertainties that arise from daily cone-beam CT (CBCT) images for proton dose calculation compared to CT using a measurement-based technique.MethodsFor head and thorax phantoms, wedge-shaped intensity-modulated proton therapy (IMPT) treatment plans were created such that the gradient of the wedge intersected and was measured with a 2D ion chamber array. The measured 2D dose distributions were compared with 2D dose planes extracted from the dose distributions using the IMPT plan calculated on CT and CBCT. Treatment plans of a thymoma cancer patient treated with breath-hold (BH) IMPT were recalculated on 28 CBCTs and 9 CTs, and the resulting dose distributions were compared.ResultsThe range uncertainties for the head phantom were determined to be 1.2% with CBCT, compared to 0.5% for CT, whereas the range uncertainties for the thorax phantom were 2.1% with CBCT, compared to 0.8% for CT. The doses calculated on CBCT and CT were similar with similar anatomy changes. For the thymoma patient, the primary source of anatomy change was the BH uncertainty, which could be up to 8 mm in the superior–inferior (SI) direction.ConclusionWe developed a measurement-based range uncertainty evaluation method with high sensitivity and used it to validate the accuracy of CBCT-based range and dose calculation. Our study demonstrated that the CBCT-based dose calculation could be used for daily dose validation in selected proton patients.

Water-conscious management strategies reduce per-yield irrigation and soil emissions of CO2, N2O, and NO in high-temperature forage cropping systems

Agricultural soils are important sources of greenhouse gases carbon dioxide (CO2) and nitrous oxide (N2O), as well as nitric oxide (NO), a precursor to tropospheric ozone. Management approaches that constrain these emissions can limit future warming and improve regional air quality, especially in high-temperature agroecosystems where soil emissions are high. Subsurface drip irrigation is a promising management solution that can limit emissions via targeted rhizosphere access to water and nitrogenous fertilizers. In complementary field studies in southern California, we compared per-yield irrigation and soil emissions in surface- and drip-irrigated field plots growing alfalfa (Medicago sativa L.) and sudangrass (Sorghum bicolor ssp. Sudanese), two forage crops with differing fertilizer requirements. For each study, we monitored soil temperature, moisture, and emission responses to irrigation in both spring and summer using a custom automated chamber array that recorded measurements every 30 minutes. We found that, compared to furrow irrigation, drip irrigation in sudangrass increased hay yield by 6% and per-yield soil CO2 emissions by 9% while it decreased irrigation demand by 49%, N2O emissions by 59%, and NO by 49%. In alfalfa, drip irrigation increased yield by 7% while decreasing irrigation by 1%, per-yield soil CO2 emissions by 59%, N2O by 38%, and NO by 20%. In both crops, differences between irrigation types were strongest in summer months, when high temperatures produced large pulses of N2O and NO in sudangrass and CO2 in alfalfa following flood irrigation relative to small pulses following drip irrigation. As agriculture intensifies in warmer climates, implementation of subsurface drip irrigation can help reduce the emission of soil emissions that affect Earth’s climate and regional air quality.