Lung Insert Research Articles

Improving the Feasibility of Mitigating Phase Errors in 4DCT caused by a Random Reference Breathing Pattern in the Quasar Phantom and the Role of Slice Thickness.

The study aimed to validate a method for minimizing phase errors by combining full-length lung 4DCT (f4DCT) scans with shorter tumor-restricted 4DCT (s4DCT) scans. It assessed the feasibility of integrating two scans one covering the entire phantom length and the other focused on the tumor area. The study also evaluated the impact of Maximum Intensity Projection (MIP) volume and imaging dose for different slice thicknesses (2.5mm and 1.25mm) in both full-length and short target-restricted 4DCT scans. The study utilized the Quasar Programmable Respiratory Motion Phantom, simulating tumor motion with a variable lung insert. The setup included a tumor replica and a six-dot IR reflector marker on the breathing platform. The objective was to analyze volume differences in fMIP_2.5mm compared to sMIP_1.25mm within their respective 4D_MIP CT series. This involved varying breathing periods (2.5s, 3.0s, 4.0s, and 5.0s) and longitudinal tumor sizes (6mm, 8mm, and 10mm). The study also assessed exposure time and expected CTDIvol of s4D_2.5mm and s4D_1.25mm for different breathing periods (5.0s to 2.0s) in the sinusoidal wave motion of the six-dot marker on the breathing platform. Conducting two consecutive 4DCT scans is viable for patients with challenging breathing patterns or when the initial lung tumor scan is in close proximity to the tumor location, eliminating the need for an additional full-length 4DCT. The analysis involves assessing MIP volume, imaging dose (CTDIvol), and exposure time. Longitudinal tumor shifts for 6mm are [16.6-17.2] in fMIP_2.5mm and [16.8-17.5] in sMIP_1.25mm, for 8mm [17.2-18.3] in fMIP_2.5mm and [17.8-18.4] in sMIP_1.25mm, and for 10mm [19-19.9] in fMIP_2.5mm and [19.4-20] in sMIP_1.25mm (p≥ 0.005), respectively. The Quasar Programmable Respiratory Motion Phantom accurately replicated varied breathing patterns and tumor motions. Comprehensive analysis was facilitated through detailed manual segmentation of Internal Target Volumes and Internal Gross Target Volumes.

A practical method for assessing quantitative scanner accuracy with long-lived radionuclides: The ARTnet insert.

To address the problem of using large volumes of long-lived radionuclides in test phantoms to check calibration accuracy of PET and SPECT systems we have developed a test object which (a) contains less radioactivity, (b) has a low total volume, and (c) is easier to store than currently used phantoms, while still making use of readily-available "standardised" test objects. We have designed a hollow acrylic cylindrical insert compatible with the NEMA/IEC PET Body Image Quality (IQ) phantom used in NU 2 performance testing of PET systems. The insert measures 90 mm internal diameter and 70 mm internal height and so is sufficiently large to not be subject to partial volume effects in PET or SPECT imaging. The volume of the insert is approximately 500 mL. It has been designed as a replacement for the standard long cylindrical "lung insert" in the IQ phantom without needing to remove the fillable hollow spheres of the phantom. The insert been tested with 18F, 68Ga and 124I PET/CT and 99mTc, 131I and 177Lu SPECT/CT on scanners that had previously been calibrated for these radionuclides. The scanners were found to produce accurate image reconstructions in the insert with 5% of the true value without any confounding uncertainty from partial volume effects when compared to NEMA NU 2-2018 Phantom measurement. The "ARTnet Insert" is simple to use, inexpensive, compatible with current phantoms and is suitable for both PET and SPECT systems. It does not suffer from significant partial volume losses permitting its use even with the poor spatial resolution of high-energy imaging with 131I SPECT. Furthermore, it uses less radioactivity in a smaller volume than would be required to fill the entire phantom as is usually done. Long-term storage is practical while allowing radioactive decay of the insert contents.

Magnetic-field-modulated radiotherapy (MagMRT) in inhomogeneous medium and its potential applications

Objective. To study the effects of magnetic field gradients on the dose deposition in an inhomogeneous medium and to present the benefits offered by magnetic-field-modulated radiotherapy (MagMRT) under multiple radiation beams. Approach. Monte Carlo simulations were performed using the Geant4 simulation toolkit with a 7 MV photon beam from an Elekta Unity system. A water cuboid embedded with material slabs of water, bone, lung or air was used to study the effects of MagMRT within inhomogeneous medium. Two cylindrical water phantoms, with and without a toroidal lung insert embedded, were used to study the effects of MagMRT under single, opposing or four cardinal radiation beams. Optimized magnetic field variations in the form of a wavelet were used to induce dose modulation within the material slabs or at the iso-center of the phantoms. Main results. The magnitudes of the dose enhancement and reduction induced by the magnetic field gradients become more prominent in a medium of lower density. A maximum dose increase of 6.5% and a decrease of 4.8% were found inside bone, while an increase of 20.4% and a decrease of 13.9% were found in lung tissue. Under multiple radiation beams, the dose enhancement can be induced at the iso-center while the dose reduction occurs in regions around the tumor. For the case with four cardinal beams irradiating a homogeneous water cylinder, an 8.4% of dose enhancement and a 2.4% of dose reduction were found. When a toroidal lung insert was embedded, a maximum dose enhancement of 9.5% and a reduction of 17.0% were produced for anterior-posterior opposing fields. Significance. With an optimized magnetic field gradient, MagMRT can induce a dose boost to the target while producing a better sparing to the surrounding normal tissue, resulting in a sharper dose fall-off in all directions outside the target volume.

Comparison of image quality and spatial resolution between 18F, 68Ga, and 64Cu phantom measurements using a digital Biograph Vision PET/CT

BackgroundPET nuclides can have a considerable influence on the spatial resolution and image quality of PET/CT scans, which can influence diagnostics in oncology, for example. The individual impact of the positron energy of 18F, 68Ga, and 64Cu on spatial resolution and image quality was compared for PET/CT scans acquired using a clinical, digital scanner.MethodsA Jaszczak phantom and a NEMA PET body phantom were filled with 18F-FDG, 68Ga-HCl, or 64Cu-HCl, and PET/CT scans were performed on a Siemens Biograph Vision. Acquired images were analyzed regarding spatial resolution and image quality (recovery coefficients (RC), coefficient of variation within the background, contrast recovery coefficient (CRC), contrast–noise ratio (CNR), and relative count error in the lung insert). Data were compared between scans with different nuclides.ResultsWe found that image quality was comparable between 18F-FDG and 64Cu-HCl PET/CT measurements featuring similar maximal endpoint energies of the positrons. In comparison, RC, CRC, and CNR were degraded in 68Ga-HCl data despite similar count rates. In particular, the two smallest spheres of 10 mm and 13 mm diameter revealed lower RC, CRC, and CNR values. The spatial resolution was similar between 18F-FDG and 64Cu-HCl but up to 18% and 23% worse compared with PET/CT images of the NEMA PET body phantom filled with 68Ga-HCl.ConclusionsThe positron energy of the PET nuclide influences the spatial resolution and image quality of a digital PET/CT scan. The image quality and spatial resolution of 68Ga-HCl PET/CT images were worse than those of 18F-FDG or 64Cu-HCl despite similar count rates.

Development of a new quantification method using partial volume effect correction for individual energy peaks in 111In-pentetreotide SPECT/CT

Objective(s):Somatostatin receptor scintigraphy (SRS) using 111In-pentetreotide has no established quantification method. The purpose of this study was to develop a new quantitative method to correct the partial volume effect (PVE) for individual energy peaks in 111In-pentetreotide single-photon emission computed tomography (SPECT).Methods:Phantom experiments were performed to construct a new quantitative method. In the phantom experiments, a NEMA IEC body phantom was used. Acquisition was performed using two energy peaks (171 keV and 245 keV) on the SPECT/CT system. The volume of interest was set at each hot sphere and lung insert in the SPECT images of each energy peak, and the recovery coefficient (RC) was calculated to understand the PVE. A new quantitative index, the indium uptake index (IUI), was calculated using the RC to correct the PVE. The quantitative accuracy of the IUI in the hot sphere was confirmed. Case studies were performed to clarify the quantitative accuracy. In a case study, the relationship between the IUI and the Krenning score, which is used as a visual assessment, was evaluated for each lesion.Results:The obtained RCs showed that the energy peak at 171 keV was faster in recovering the effect of PVE than that at 245 keV. The IUI in the 17-mm-diameter hot sphere was overestimated by 4.8% and 8.3% at 171 keV and 245 keV, respectively, compared to the actual IUIs. The relationship between IUI and Krenning score was rs=0.773 (p<0.005) at sum, rs=0.739 (p<0.005) at 171 keV, and rs=0.773 (p<0.005) at 245 keV.Conclusion: We have developed a new quantification method for 111In-pentetreotide SPECT/CT using RC-based PVE correction for an individual energy peak of 171 keV. The quantitative accuracy of this method was high even for accumulations of less than 20 mm, and it showed a good relationship with the Krenning score; therefore, the clinical usefulness of IUI was demonstrated.

Evaluation of novel AI-based extended field-of-view CT reconstructions.

PurposeModern computed tomography (CT) scanners have an extended field‐of‐view (eFoV) for reconstructing images up to the bore size, which is relevant for patients with higher BMI or non‐isocentric positioning due to fixation devices. However, the accuracy of the image reconstruction in eFoV is not well known since truncated data are used. This study introduces a new deep learning‐based algorithm for extended field‐of‐view reconstruction and evaluates the accuracy of the eFoV reconstruction focusing on aspects relevant for radiotherapy.MethodsA life‐size three‐dimensional (3D) printed thorax phantom, based on a patient CT for which eFoV was necessary, was manufactured and used as reference. The phantom has holes allowing the placement of tissue mimicking inserts used to evaluate the Hounsfield unit (HU) accuracy. CT images of the phantom were acquired using different configurations aiming to evaluate geometric and HU accuracy in the eFoV. Image reconstruction was performed using a state‐of‐the‐art reconstruction algorithm (HDFoV), commercially available, and the novel deep learning‐based approach (HDeepFoV). Five patient cases were selected to evaluate the performance of both algorithms on patient data. There is no ground truth for patients so the reconstructions were qualitatively evaluated by five physicians and five medical physicists.ResultsThe phantom geometry reconstructed with HDFoV showed boundary deviations from 1.0 to 2.5 cm depending on the volume of the phantom outside the regular scan field of view. HDeepFoV showed a superior performance regardless of the volume of the phantom within eFOV with a maximum boundary deviation below 1.0 cm. The maximum HU (absolute) difference for soft issue inserts is below 79 and 41 HU for HDFoV and HDeepFoV, respectively. HDeepFoV has a maximum deviation of −18 HU for an inhaled lung insert while HDFoV reached a 229 HU difference. The qualitative evaluation of patient cases shows that the novel deep learning approach produces images that look more realistic and have fewer artifacts.ConclusionTo be able to reconstruct images outside the sFoV of the CT scanner there is no alternative than to use some kind of extrapolated data. In our study, we proposed and investigated a new deep learning‐based algorithm and compared it to a commercial solution for eFoV reconstruction. The deep learning‐based algorithm showed superior performance in quantitative evaluations based on phantom data and in qualitative assessments of patient data.

Reduction of margin to compensate the respiratory tumor motion by the analysis of dosimetric internal target volume in lung SBRT with nonuniform volume prescription method.

To develop a dosimetric internal target volume (ITV) margin (DIM) for respiratory motion in lung stereotactic body radiotherapy (SBRT) and to evaluate DIM with a nonuniform volume prescription (NVP) and the point prescription (PP). Volumetric modulated arc therapy (VMAT) treatment plans with PP and NVP were created on a heterogeneous programmable respiratory motion phantom, with a tumor (30-mm diameter) inside a cylindrical lung insert. The tumor was defined as the gross tumor volume (GTV), equal to the clinical target volume (CTV). Five-millimeter and 0-mm margins were used for the ITV and setup margins, respectively. The phantom was moved in cranio-caudal direction with a biquadratic sinusoidal waveform with a 4-s cycle and an amplitude of ±5-10mm. The interplay effect was evaluated by measuring the dose profile with a film in the sagittal plane for different respiratory periods and different initial respiratory phases. DIM was based on the respiratory motion amplitude that satisfied 100% and 95% coverage of the prescribed dose by the minimum dose of the CTV. Moreover, the absolute dose was measured with and without respiratory motion for NVP by a pinpoint chamber. The dose difference in the tumor region due to the interplay effect was within 1.0%. The gamma passing rate was over 95.1% for different respiratory periods and 98.6% for different initial respiratory phases. DIM with PP was almost equivalent to the margin of the respiratory motion. However, DIM with NVP was 2.0 and 1.8 times larger than the margin of the respiratory motion for the 100% and 95% coverage of the prescribed doses, respectively. The interplay effects experienced between the MLC sequence and tumor motion were negligible for NVP. The DIM analysis revealed that the margin to compensate the respiratory tumor motion could be reduced by more than 44-50% for NVP in SBRT.

A deep neural network for fast and accurate scatter estimation in quantitative SPECT/CT under challenging scatter conditions.

A major challenge for accurate quantitative SPECT imaging of some radionuclides is the inadequacy of simple energy window-based scatter estimation methods, widely available on clinic systems. A deep learning approach for SPECT/CT scatter estimation is investigated as an alternative to computationally expensive Monte Carlo (MC) methods for challenging SPECT radionuclides, such as 90Y. A deep convolutional neural network (DCNN) was trained to separately estimate each scatter projection from the measured 90Y bremsstrahlung SPECT emission projection and CT attenuation projection that form the network inputs. The 13-layer deep architecture consisted of separate paths for the emission and attenuation projection that are concatenated before the final convolution steps. The training label consisted of MC-generated "true" scatter projections in phantoms (MC is needed only for training) with the mean square difference relative to the model output serving as the loss function. The test data set included a simulated sphere phantom with a lung insert, measurements of a liver phantom, and patients after 90Y radioembolization. OS-EM SPECT reconstruction without scatter correction (NO-SC), with the true scatter (TRUE-SC) (available for simulated data only), with the DCNN estimated scatter (DCNN-SC), and with a previously developed MC scatter model (MC-SC) were compared, including with 90Y PET when available. The contrast recovery (CR) vs. noise and lung insert residual error vs. noise curves for images reconstructed with DCNN-SC and MC-SC estimates were similar. At the same noise level of 10% (across multiple realizations), the average sphere CR was 24%, 52%, 55%, and 67% for NO-SC, MC-SC, DCNN-SC, and TRUE-SC, respectively. For the liver phantom, the average CR for liver inserts were 32%, 73%, and 65% for NO-SC, MC-SC, and DCNN-SC, respectively while the corresponding values for average contrast-to-noise ratio (visibility index) in low-concentration extra-hepatic inserts were 2, 19, and 61, respectively. In patients, there was high concordance between lesion-to-liver uptake ratios for SPECT reconstruction with DCNN-SC (median 4.8, range 0.02-13.8) compared with MC-SC (median 4.0, range 0.13-12.1; CCC = 0.98) and with 90Y PET (median 4.9, range 0.02-11.2; CCC = 0.96) while the concordance with NO-SC was poor (median 2.8, range 0.3-7.2; CCC = 0.59). The trained DCNN took ~ 40s (using a single i5 processor on a desktop computer) to generate the scatter estimates for all 128 views in a patient scan, compared to ~ 80min for the MC scatter model using 12 processors. For diverse 90Y test data that included patient studies, we demonstrated comparable performance between images reconstructed with deep learning and MC-based scatter estimates using metrics relevant for dosimetry and for safety. This approach that can be generalized to other radionuclides by changing the training data is well suited for real-time clinical use because of the high speed, orders of magnitude faster than MC, while maintaining high accuracy.

Digital Solid-State SPECT/CT Quantitation of Absolute 177Lu Radiotracer Concentration: In Vivo and In Vitro Validation.

The accuracy of 177Lu radiotracer concentration measurements using quantitative clinical software was determined by comparing in vivo results for a digital solid-state cadmium-zinc-telluride SPECT/CT system with in vitro sampling. Methods: First, image acquisition parameters were assessed for an International Electrotechnical Commission body phantom emulating clinical count rates loaded with a lung insert and 6 hot spheres with a 12:1 target-to-background ratio of 177Lu solution. Then, the data of 28 whole-body SPECT/CT scans of 7 patients who underwent 177Lu prostate-specific membrane antigen radioligand therapy were retrospectively analyzed. Three users analyzed SPECT/CT images for in vivo urinary bladder radiotracer uptake using quantitative software. In vitro radiopharmaceutical concentrations were calculated using urine sampling obtained immediately after each scan, scaled to SUVs. Any in vivo or in vitro identity relations were determined by linear regression (ideally, slope = 1 and intercept = 0), within a 95% confidence interval. Results: Phantom results demonstrated lower quantitative error for acquisitions using the 113-keV 177Lu energy peak rather than including the 208-keV peak, given that only low-energy collimation was available in this camera configuration. In the clinical study, 24 in vivo-in vitro pairs were eligible for further analysis, with 4 having been rejected as outliers (via Cook distance calculations). All linear regressions (R2 ≥ 0.82, P < 0.0001) provided identity in vivo-in vitro relations (95% confidence interval), with SUV averages from all users giving a slope of 0.96 ± 0.13, an intercept of -0.07 ± 0.46 g/mL, and an average residual difference of 19.5%. In acquisitions with the lower-energy 177Lu energy peak, solid-state SPECT/CT imaging provided an accuracy to within approximately 20% of in vivo urinary bladder radiotracer concentrations. Conclusion: This noninvasive in vivo quantitation method can potentially improve diagnosis, patient management, and treatment response assessment and provide data essential to 177Lu dosimetry.

Towards standardization of absolute SPECT/CT quantification: a multi-center and multi-vendor phantom study

Absolute quantification of radiotracer distribution using SPECT/CT imaging is of great importance for dosimetry aimed at personalized radionuclide precision treatment. However, its accuracy depends on many factors. Using phantom measurements, this multi-vendor and multi-center study evaluates the quantitative accuracy and inter-system variability of various SPECT/CT systems as well as the effect of patient size, processing software and reconstruction algorithms on recovery coefficients (RC).MethodsFive SPECT/CT systems were included: Discovery™ NM/CT 670 Pro (GE Healthcare), Precedence™ 6 (Philips Healthcare), Symbia Intevo™, and Symbia™ T16 (twice) (Siemens Healthineers). Three phantoms were used based on the NEMA IEC body phantom without lung insert simulating body mass indexes (BMI) of 25, 28, and 47 kg/m2. Six spheres (0.5–26.5 mL) and background were filled with 0.1 and 0.01 MBq/mL 99mTc-pertechnetate, respectively. Volumes of interest (VOI) of spheres were obtained by a region growing technique using a 50% threshold of the maximum voxel value corrected for background activity. RC, defined as imaged activity concentration divided by actual activity concentration, were determined for maximum (RCmax) and mean voxel value (RCmean) in the VOI for each sphere diameter. Inter-system variability was expressed as median absolute deviation (MAD) of RC. Acquisition settings were standardized. Images were reconstructed using vendor-specific 3D iterative reconstruction algorithms with institute-specific settings used in clinical practice and processed using a standardized, in-house developed processing tool based on the SimpleITK framework. Additionally, all data were reconstructed with a vendor-neutral reconstruction algorithm (Hybrid Recon™; Hermes Medical Solutions).ResultsRC decreased with decreasing sphere diameter for each system. Inter-system variability (MAD) was 16 and 17% for RCmean and RCmax, respectively. Standardized reconstruction decreased this variability to 4 and 5%. High BMI hampers quantification of small lesions (< 10 ml).ConclusionAbsolute SPECT quantification in a multi-center and multi-vendor setting is feasible, especially when reconstruction protocols are standardized, paving the way for a standard for absolute quantitative SPECT.

An affordable custom phantom for measurement of linac time delay in gated treatments with irregular breathing.

Respiratory gated treatments are now common in order to reduce tumour motion uncertainties due to breathing. One issue associated with gated treatments is the time delay between the gating system and the linear accelerator. In this study we develop and characterise an affordable phantom to be used in routine and patient specific quality assurance (QA) of the Varian Real-Time Position Management™ (RPM) system. A photodiode has been incorporated into the phantom in order to estimate the time delay. A commercial Quasar phantom was customised to incorporate two stepper motors which independently control an anterior-posterior abdomen/thorax moving plate, and an inferior-superior moving lung insert. A photodiode placed in the path of the radiation is used to measure when beam on/off occurs. Two Arduino microcontroller boards have been utilised to control the motors, read the photodiode and write to an SD card. The measured beam on/off, correlated to the known positions of the phantom is compared to the gate window for RPM. The time delay was measured for sinusoidal movements with a period of 7.50s and 3.75s, and for three patient breathing traces. For the sinusoidal movements, time delays of 150 ± 34ms and 39 ± 34ms were measured, for 7.50s and 3.75s periods, respectively. In the case of the patients' breathing traces time delays of 135 ± 26ms, 137 ± 34ms and 129 ± 28ms were measured. An affordable motion phantom has been developed for routine and patient specific QA of respiratory gating systems. It is capable of reproducing a patient's breathing waveform and performing time delay measurements with a photodiode. Results indicate a time delay of the order of 0.1-0.2s for the RPM system.

A depth dose study between AAA and AXB algorithm against Monte Carlo simulation using AIP CT of a 4D dataset from a moving phantom

To identifying depth dose differences between the two versions of the algorithms using AIP CT of a 4D dataset. Motion due to respiration may challenge dose prediction of dose calculation algorithms during treatment planning. The two versions of depth dose calculation algorithms, namely, Anisotropic Analytical Algorithm (AAA) version 10.0 (AAAv10.0), AAA version 13.6 (AAAv13.6) and Acuros XB dose calculation (AXB) algorithm version 10.0 (AXBv10.0), AXB version 13.6 (AXBv13.6), were compared against a full MC simulated 6X photon beam using QUASAR respiratory motion phantom with a moving chest wall. To simulate the moving chest wall, a 4cm thick wax mould was attached to the lung insert of the phantom. Depth doses along the central axis were compared in the anterior and lateral beam direction for field sizes 2×2cm2, 4×4cm2 and 10×10cm2. For the lateral beam direction, the moving chest wall highlighted differences of up to 105% for AAAv10.0 and 40% for AXBv10.0 from MC calculations in the surface and buildup doses. AAAv13.6 and AXBv13.6 agrees with MC predictions to within 10% at similar depth. For anterior beam doses, dose differences predicted for both versions of AAA and AXB algorithm were within 7% and results were consistent with static heterogeneous studies. The presence of the moving chest wall was capable of identifying depth dose differences between the two versions of the algorithms. These differences could not be identified in the static chest wall as shown in the anterior beam depth dose calculations.

Three-dimensional thoracoscopic vertebral body replacement at the thoracolumbar junction.

The aim is to stabilize the thoracolumbar spine with athoracoscopically implanted vertebral body replacement (VBR). To improve intraoperative depth perception and orientation, implantation is performed under three-dimensional (3D) thoracoscopic vision. Vertebral burst fractures at the thoracolumbar junction (A4AOSpine classification), pseudarthrosis, and posttraumatic instability with increasing kyphosis. Severe pulmonary dysfunctions, pulmonary or thoracic infections, previous thoracic surgery, and pulmonary adhesions. The patient is lying in aright lateral decubitus position. Localization of the fractured vertebra. Minimally invasive transthoracic approach. Perform single lung ventilation and insert the 3D thoracoscope two intercostal spaces above the working portal. Utilization of special binocular glasses for 3D vision of the operation field and secure resection of the fractured vertebra. Measurement of the bony defect and insertion of the expandable cage. Control of correct cage position under fluoroscopy. Insertion of achest tube and inflate the left lung. Chest × ray Remove chest tube when output is <500 ml/24 h Early mobilization on the ward 6weeks no weight-bearing >5 kg RESULTS: Between 2012 and 2017, 12patients received aVBR under 3D thoracoscopic vision. After amean follow up of 26months, no cage dislocation was noticed and all patients recovered from the initial back pain. Complications were notable in two cases (17%) with asmall pneumothorax after removal of the chest tube and postoperative pneumonia in one patient (8%). All responded to conservative treatment. Revision surgery was not necessary.

EP-1745: Differences in central line dose profiles for RayStation, Eclipse and Pinnacle, around a lung insert

EP-1745: Differences in central line dose profiles for RayStation, Eclipse and Pinnacle, around a lung insert

Evaluation of dose calculation accuracy of various algorithms in lung equivalent inhomogeneity: Comparison of calculated data with Gafchromic film measured results.

To evaluate dose calculation accuracy of various algorithms in lung equivalent inhomogeneity comprising tumor within it and comparison with Gafchromic film data. Gafchromic film measured central axis absorbed dose in lung insert (-700 Hounsfield unit [HU]), in racemosa wood cylindrical inhomogeneity (-725 HU) and at three surfaces of tumor (-20 HU) created in cylindrical inhomogeneity, put in the cavity of computerized imaging reference systems (CIRS) thorax phantom were compared with convolution (CON), superposition (SP), fast SP (FSP), and X-ray voxel Monte Carlo (XVMC) algorithms calculated dose using 6 MV beams of field size 2 cm × 2 cm, 3 cm × 3 cm, 4 cm × 4 cm, 5 cm × 5 cm, and 8 cm × 8 cm. XVMC was in good agreement with film measured results for all selected field sizes except 3 cm × 3 cm. SP under estimated by 5.7% at the center of the lung insert while deviation up to 6% was found at the cent of wood inhomogeneity in 2 cm × 2 cm. Except CON, increase in dose from proximal to the central surface of the tumor and then dose falloff from central to the distal surface for field size 2 cm × 2 cm to 4 cm × 4 cm was recorded. The change in film measured percentage depth dose from 2 cm × 2 cm to 3 cm × 3 cm field sizes was found -8% however for consecutive field size(s) larger than 3 cm × 3 cm this difference was less. CON and FSP produced overestimated results. Out of four algorithms, XVMC found consistent with measured data. The electronic disequilibrium within and at the interface of inhomogeneity make the accurate dose predictions difficult. These limitations results in deviations from the expected results of the treatments.

Development of pelvis phantom for verification of treatment planning system using convolution, fast superposition, and superposition algorithms

Background: The cost of commercial pelvis phantom is a burden to the quality assurance in radiotherapy of small and/or low-income radiotherapy centers. That an algorithm is accurate with short treatment time is a prized asset in treatment planning. Objectives: The purpose of this study was to develop a hybrid algorithm that has balance between accuracy and treatment time and design a pelvis phantom for evaluating the accuracy of a linear accelerator monitor unit. Materials and Methods: A pelvis phantom was designed using Plaster of Paris, styrofoam and water with six hollows for inserting materials mimicking different biological tissues, and the ionization chamber. Computed tomography images of the phantom were transferred to the CMS XiO treatment planning system with three different algorithms. Monitor units were obtained with clinical linear accelerator with isocentric setup. The phantom was tested using convolution (C), fast superposition (FSS), and superposition (S) algorithms with respect to an established reference dose of 1 Gy from a large water phantom. Data analysis value was done using GraphPad Prism 5.0. Results: FSS algorithm showed better accuracy than C and S with bone, lung, and solid water inhomogeneous insert. C algorithm was better in terms of treatment time than S. There was no statistically significant difference between the mean doses for all the three algorithms against the reference dose. The maximum percentage deviation was ±4%, which was below ±5% International Commission on Radiation Units and Measurement minimal limit. Conclusion: This algorithm can be employed in the calculation of dose in advance techniques such as intensity-modulated radiation therapy and RapidArc by radiotherapy centers with multiple algorithm system because it is easy to implement. The materials used for the construction of the phantom are very affordable and simple for low-budget radiotherapy centers.

Experimental verification of 4D Monte Carlo simulations of dose delivery to a moving anatomy.

To evaluate a novel 4D Monte Carlo simulation tool by comparing calculations to physical measurements using a respiratory motion phantom. We used a dynamic Quasar phantom in both stationary and breathing states (sinusoidal motion of amplitude of 1.8cm and period of 3.3s) for dose measurements on an Elekta Agility linear accelerator. Gafchromic EBT3 film and the RADPOS 4D dosimetry system were placed inside the lung insert of the phantom to measure dose profiles and point-dose values at the center of the spherical tumor inside the insert. Both a static 4×4cm2 field and a VMAT plan were delivered. Static and 4D Monte Carlo simulations of the treatment deliveries were performed using DOSXYZnrc and a modified version of the defDOSXYZnrc user code that allows modeling of the continuous motion of both machine and patient. DICOM treatment plan files and linac delivery log files were used to generate corresponding input files. The phantom motion recorded by RADPOS during beam delivery was incorporated into the input files for the 4DdefDOSXYZnrc simulations. For stationary phantom simulations, all point-dose values from MC simulations at the tumor center agreed within 1% with film and within 2% with RADPOS. More than 98% of the voxels from simulated dose profiles passed a 1D gamma of 2%/2-mm criteria against measured dose profiles. Similar results were observed when applying a 2D gamma analysis with a 2%/2-mm criteria to compare 2D dose distributions of Monte Carlo simulations against measurements. For simulations on the moving phantom, MC-calculated dose values at the center of the tumor were found to be within 1% of film and within 2σ of experimental uncertainties which are 2.8% of the RADPOS measurements. 1D gamma comparisons of the dose profiles were better than 91%, and 2D gamma comparisons of the 2D dose distributions were found to be better than 94%. Our 4D Monte Carlo method using defDOSXYZnrc can be used to accurately calculate the dose distribution in continuously moving anatomy for various treatment techniques. This work, if extended to deformable anatomies, can be used to reconstruct patient delivered dose for use in adaptive radiation therapy.

Commissioning Monte Carlo algorithm for robotic radiosurgery using cylindrical 3D-array with variable density inserts

IntroductionTo commission the Monte Carlo (MC) algorithm based model of CyberKnife robotic stereotactic system (CK) and evaluate the feasibility of patient specific QA using the ArcCHECK cylindrical 3D-array (AC) with Multiplug inserts (MP). ResultsFour configurations were used for simple beam setup and two for patient QA, replacing water equivalent inserts by lung. For twelve collimators (5–60mm) in simple setup, mean (SD) differences between MC and RayTracing algorithm (RT) of the number of points failing the 3%/1mmgamma criteria were 1(1), 1(3), 1(2) and 1(2) for the four MP configurations. Tracking fiducials were placed within AC for patient QA. Single lung insert setup resulted in mean gamma-index 2%/2mm of 90.5% (range [74.3–95.9]) and 82.3% ([66.8–94.5]) for MC and RT respectively, while 93.5% ([86.8–98.2]) and 86.2% ([68.7–95.4]) in presence of largest inhomogeneities, showing significant differences (p<0.05). DiscussionAfter evaluating the potential effects, 1.12g/cc PMMA and 0.09g/cc lung material assignment showed the best results. Overall, MC-based model showed superior results compared to RT for simple and patient specific testing, using a 2%/2mm criteria. Results are comparable with other reported commissionings for flattening filter free (FFF) delivery. Further improvement of MC calculation might be challenging as Multiplan has limited material library. ConclusionsThe AC with Multiplug allowed for comprehensive commissioning of CyberKnife MC algorithm and is useful for patient specific QA for stereotactic body radiation therapy. MC calculation accuracy might be limited due to Multiplan’s insufficient material library; still results are comparable with other reported commissioning measurements using FFF beams.

35. Evaluation and validation of the use of Orthopedic Metal Artifact Reduction algorithm (O-MAR) for dose calculation in radiotherapy

Introduction O-MAR algorithm mitigates artifacts caused by metal objects in CT images. Initially developed for diagnostic CT images, O-MAR may also prove useful to address CT images used for dose calculation in radiotherapy. Indeed, metal artifacts severely degrade dose calculation accuracy and are usually manually corrected by assigning electron density to 1 g cm −3 . Nevertheless, this process is long, inaccurate and operator-dependent. Moreover, it only applies to soft tissue area. The aim of this study is to evaluate and validate the use of O-MAR on dosimetric CT images for patients with metallic implants (orthopedic and dental). Method The capability of O-MAR to restore real Hounsfield Units (HU) was evaluated on cylindrical phantom considering various inserts (solid water, lung and cortical bone). CT images (Philips BigBore®) were acquired without metal (reference) and with 2 artificial hip joints, with and without O-MAR correction. Same experiment was made with dental implants. The impact of O-MAR on dose calculation was evaluated on previous images using the treatment planning system (TPS) CMS XIO for a 6MV photon beam and for various clinical ballistics on 3 TPS (CMS XIO, IplanRT et Tomotherapy®). Results obtained with O-MAR correction were also compared with those obtained on CT images manually corrected, which are the standard of practice in our institution. For each case, 3D distribution of local percent difference dose was analyzed excluding doses lower than 10% of the prescribed dose. Finally, O-MAR was applied to patients CT images. Results HU measurements show that artefacts have limited impact on lung insert but significant impact on solid water and cortical bone inserts with a difference of 100HU and 250HU respectively. O-MAR effectively reduces these differences to 40HU in solid water and 90HU in cortical bone. Moreover, O-MAR is more effective than manual correction to reduce impact of artefacts on dose calculation. In the phantom with 2 artificial hip joints, for a single 6MV photon beam, the percentage of pixels with a local percent difference dose >+/−1% (PLPD1%) is 5.2% without correction, 2.3% with manual correction and 1.2% with O-MAR. Similar analysis considering 7 IMRT beams (XIO) gives a PLPD1% of 9.5%, 5.7% and 4.4% respectively. O-MAR effectively corrects patients CT images with artificial hip joints. However, for dental implants, some manual re-working remains necessary after O-MAR correction. Conclusion For orthopedic implants, O-MAR is effective to correct metallic artefacts. Comparing with manual correction, O-MAR results in a considerable saving in time and increases accuracy of dose calculation. For dental implants, although manual correction is still required, time saving remains substantial.

Practical reconstruction protocol for quantitative (90)Y bremsstrahlung SPECT/CT.

To develop a practical background compensation (BC) technique to improve quantitative (90)Y-bremsstrahlung single-photon emission computed tomography (SPECT)/computed tomography (CT) using a commercially available imaging system. All images were acquired using medium-energy collimation in six energy windows (EWs), ranging from 70 to 410 keV. The EWs were determined based on the signal-to-background ratio in planar images of an acrylic phantom of different thicknesses (2-16 cm) positioned below a (90)Y source and set at different distances (15-35 cm) from a gamma camera. The authors adapted the widely used EW-based scatter-correction technique by modeling the BC as scaled images. The BC EW was determined empirically in SPECT/CT studies using an IEC phantom based on the sphere activity recovery and residual activity in the cold lung insert. The scaling factor was calculated from 20 clinical planar (90)Y images. Reconstruction parameters were optimized in the same SPECT images for improved image quantification and contrast. A count-to-activity calibration factor was calculated from 30 clinical (90)Y images. The authors found that the most appropriate imaging EW range was 90-125 keV. BC was modeled as 0.53× images in the EW of 310-410 keV. The background-compensated clinical images had higher image contrast than uncompensated images. The maximum deviation of their SPECT calibration in clinical studies was lowest (<10%) for SPECT with attenuation correction (AC) and SPECT with AC + BC. Using the proposed SPECT-with-AC + BC reconstruction protocol, the authors found that the recovery coefficient of a 37-mm sphere (in a 10-mm volume of interest) increased from 39% to 90% and that the residual activity in the lung insert decreased from 44% to 14% over that of SPECT images with AC alone. The proposed EW-based BC model was developed for (90)Y bremsstrahlung imaging. SPECT with AC + BC gave improved lesion detectability and activity quantification compared to SPECT with AC only. The proposed methodology can readily be used to tailor (90)Y SPECT/CT acquisition and reconstruction protocols with different SPECT/CT systems for quantification and improved image quality in clinical settings.