Patient CT Data Research Articles

Surgical planning, manufacturing and implantation of an individualized cervical fusion titanium cage using patient-specific data

Most cervical fusion cages imperfectly mimic the anatomy of the intervertebral disc space. The production of individualized cages might be the next step to further improve spinal implants due to their enhanced load-bearing surface. To evaluate the planning, manufacturing, and implantation of an individualized cervical cage in co-operation with EIT and 3D Systems. A digital 3D model of the patient's cervical spine was rendered from the patients CT data. It was then possible to correct degenerative deformities by digitally repositioning the vertebrae and virtually resecting the osteophytes. The implantation of the cage can be simulated to check the accuracy of the fit. The cage is made of trabecular titanium and manufactured by Direct Metal Printing. The pilot project for the implantation of the first individualized cervical cage ever, resulted in a highly accurate fit. During surgery, the cage self-located into the correct position after suspending distraction due to the implants unique end plate design. Furthermore, it was impossible to move the cage in any direction with the inserting instrument after suspending distraction for the same reason. Thus, it can be assumed that an individualized cervical implant provides excellent primary stability. Preconditions for the manufacturing of individualized cervical fusion cages using specific patient data are given. The implantation is uncomplicated. The improved load-bearing surface will lower the rate of implant dislocation and subsidence. The production of individualized cages at a reasonable price has to be evaluated by spine surgeons and the industry.

A robust noise reduction technique for time resolved CT.

To develop a noise reduction method for time resolved CT data, especially those with significant patient motion. PArtial TEmporal Nonlocal (PATEN) means is a technique that uses the redundant information in time-resolved CT data to achieve noise reduction. In this method, partial temporal profiles are used to determine the similarity (or weight) between pixels, and the similarity search makes use of both spatial and temporal information, providing robustness to patient motion. The performance of the PATEN filter was qualitatively and quantitatively evaluated with nine cardiac CT patient data sets and five CT brain perfusion patient data sets. In cardiac CT, PATEN was applied to reduce noise primarily in the reduced-dose phases created with electrocardiographic (ECG) pulsing. CT number accuracy and noise reduction were evaluated in both full-dose phases and reduced-dose phases between filtered backprojection images and PATEN filtered images. In CT brain perfusion, simulated quarter dose data were obtained by adding noise to the raw data of a routine dose scan. PATEN was applied to the simulated low-dose images. Image noise, time-intensity profile accuracy, and perfusion parameter maps were compared among low-dose, low-dose+PATEN filter, and full-dose images. The noise reduction performance of PATEN was compared to a previously proposed noise reduction method, time-intensity profile similarity (TIPS) bilateral filtering. In 4D cardiac CT, after PATEN filtering, the image noise in the reduced-dose phases was greatly reduced, making anatomical structures easier to identify. The mean decreases in noise values between the original and PATEN images were 11.0% and 53.8% for the full and reduced-dose phases of the cardiac cycle, respectively. TIPS could not achieve effective noise reduction. In CT brain perfusion, PATEN achieved a 55.8%-66.3% decrease in image noise in the low-dose images. The contrast to noise ratio in the axial images was increased and was comparable to the full-dose images. Differentiation of anatomical structure in the PATEN images and corresponding quantitative perfusion parameter maps were preferred by two neuroradiologists compared to the simulated low-dose and TIPS results. The mean perfusion parameters calculated from the PATEN images agreed with those determined from full-dose data to within 12% and 20% for normal and diseased regions. In ECG-gated cardiac CT, where the dose had already been reduced by a factor of 5 in the reduced-dose phases, PATEN achieved a 53.8% noise reduction, which decreased the noise level in the reduced-dose phases close to that of the full-dose phases. In CT brain perfusion, a fourfold dose reduction was demonstrated to be achievable by PATEN filtering, which improved quantitative perfusion analysis. PATEN can be used to effectively reduce image noise to improve image quality, even when significant motion occurred between temporal samples.

A case of mandibular reconstruction with a custom-made mesh plate using three dimensional model created from patient's CT data

A case of mandibular reconstruction with a custom-made mesh plate using three dimensional model created from patient's CT data

Glenoid version by CT scan: an analysis of clinical measurement error and introduction of a protocol to reduce variability.

ObjectiveRecent studies have challenged the accuracy of conventional measurements of glenoid version. Variability in the orientation of the scapula from individual anatomical differences and patient positioning, combined with differences in observer measurement practices, have been identified as sources of variability. The purpose of this study was to explore the utility and reliability of clinically available software that allows manipulation of three-dimensional images in order to bridge the variance between clinical and anatomic version in a clinical setting.Materials and methodsTwenty CT scans of normal glenoids of patients who had proximal humerus fractures were measured for version. Four reviewers first measured version in a conventional manner (clinical version), measurements were made again (anatomic version) after employing a protocol for reformatting the CT data to align the coronal and sagittal planes with the superior-inferior axis of the glenoid, and the scapular body, respectively.ResultsThe average value of clinical retroversion for all reviewers and all subjects was −1.4° (range, −16° to 21°), as compared to −3.2° (range, −21° to 6°) when measured from reformatted images. The mean difference between anatomical and clinical version was 1.9° ± 5.6° but ranged on individual measurements from −13° to 26°. In no instance did all four observers choose the same image slice from the sequence of images.ConclusionsThis study confirmed the variation in glenoid version dependent on scapular orientation previously identified in other studies using scapular models, and presents a clinically accessible protocol to correct for scapular orientation from the patient’s CT data.

SU‐E‐T‐341: DVH‐Based Comparison of True 3D Measurements to a Delta4 System

Purpose:Delta4 dosimetric software can be used to calculate DVH‐based metrics for patient‐specific quality assurance from measurements made by a Delta4 QA device. This study investigates the effectiveness of a novel transform method that transposes measurements made with a full‐density 3D dosimeter onto patient anatomy, enabling the calculation of DVHs. This allows for DVH comparisons from the transformed dose distribution, which are based on true 3D measurements, to those from the Delta4 system, which are based on semi‐3D measurements and interpolation.Methods:A double‐arc VMAT treatment for a head‐and‐neck case was delivered to a 1kg PRESAGE 3D dosimeter inserted into a polyurethane head phantom. The dosimeter was readout using an in‐house optical‐CT scanner to gather full‐density 3D dosimetric data. The transform method is achieved by multiplication of the measured doses with a “transformation matrix” which accounts for heterogeneities and differences in geometry between the patient and the phantom. The transformation matrix is a voxel‐by‐voxel division of the patient planned dose by the phantom planned dose, both calculated in the treatment planning system (Eclipse). The transformed distribution was then overlaid on the patient CT data, enabling the calculation of DVHs. The same VMAT treatment was delivered to the Delta4 phantom and DVH data was calculated using its associated software.Results:The transformed dose distribution showed good agreement with calculated patient values, determined by similarity in dose profiles between the two distributions and a 3D gamma index passing rate of 94.87% for 3%/3mm criteria. For every structure contained within the dosimeter volume, the transformed DVHs demonstrated better agreement than the Delta4 DVHs, when compared to the values calculated in the treatment planning system.Conclusion:The coupled technique of full‐density 3D dose measurements and the presented transform method enables clinical patient‐specific quality assurance data that is more accurate than the semi‐3D Delta4 system.This work was supported by NIH R01CA100835.

MO‐F‐CAMPUS‐I‐03: GPU Accelerated Monte Carlo Technique for Fast Concurrent Image and Dose Simulation

Purpose:To develop an accurate and fast Monte Carlo (MC) method of simulating CT that is capable of correlating dose with image quality using voxelized phantoms.Methods:A realistic voxelized phantom based on patient CT data, XCAT, was used with a GPU accelerated MC code for helical MDCT. Simulations were done with both uniform density organs and with textured organs. The organ doses were validated using previous experimentally validated simulations of the same phantom under the same conditions. Images acquired by tracking photons through the phantom with MC require lengthy computation times due to the large number of photon histories necessary for accurate representation of noise. A substantial speed up of the process was attained by using a low number of photon histories with kernel denoising of the projections from the scattered photons. These FBP reconstructed images were validated against those that were acquired in simulations using many photon histories by ensuring a minimal normalized root mean square error.Results:Organ doses simulated in the XCAT phantom are within 10% of the reference values. Corresponding images attained using projection kernel smoothing were attained with 3 orders of magnitude less computation time compared to a reference simulation using many photon histories.Conclusion:Combining GPU acceleration with kernel denoising of scattered photon projections in MC simulations allows organ dose and corresponding image quality to be attained with reasonable accuracy and substantially reduced computation time than is possible with standard simulation approaches.

SU‐E‐T‐773: Use of a Commercial TPS for Deriving Exit Dose Distribution for Patient Specific QA with An EPID

Purpose:A method to derive exit dose distributions with a commercial treatment planning system for comparison to Epid measured doses.Methods:In contrast to published methods, we present an approach that uses a treatment planning system (Raystation, Raysearch) to calculate exit dose patterns based on a modified patient CT dataset. The EPID is assumed as water equivalent and therefore is represented as water filled ring in the images. This is done by: ‐Export a renamed copy of the patient CT and plan data set. —Manipulate the CT‐data to a field of view of 1000 mm. — Insert the water filled cylinder ring, centered to the target point. — Manipulate plan file with the new target and dose prescription point. — Import and recalculate dose on the manipulated data set. — Export and extract exit field dose matrix from the cylinder (optional entrance dose). — Calibrate matrix to size and rebin data from the cylinder to EPID equivalent data. — Correct Epid measurement for scatter, position and field size. ‐Evaluate and compare data in Verisoft (PTW). Data manipulation and extraction is done by a simple tool (IDL, Exelis).Results:This method was tested on a Siemens Artiste 6MV for field sizes up to 27×27cm2 limited by used geometry and EPID size. First phantom measurements show good results for fields up to 20×20cm (pass rate > 95% for 3%, 3mm Gamma index) while larger fields have higher discrepancies towards the field edges. This might Result from off axis softening of the beam and the higher sensitivity of the detector to beam scatter.Conclusion:This method might simplify the use of exit dosimetry with the EPID for patient specific QA as it uses the dose calculation of a commercial treatment planning system. The concept was proven by phantom data sets, giving acceptable results.

SU‐E‐T‐470: Importance of HU‐Mass Density Calibration Technique in Proton Pencil Beam Dose Calculation

Purpose:Stoichiometric calibration of Hounsfield Units (HUs) for conversion to proton relative stopping powers (RStPs) is vital for accurate dose calculation in proton therapy. However proton dose distributions are not only dependent on RStP, but also on relative scattering power (RScP) of patient tissues. RScP is approximated from material density but a stoichiometric calibration of HU‐density tables is commonly neglected. The purpose of this work was to quantify the difference in calculated dose of a commercial TPS when using HU‐density tables based on tissue substitute materials and stoichiometric calibrated ICRU tissues.Methods:Two HU‐density calibration tables were generated based on scans of the CIRS electron density phantom. The first table was based directly on measured HU and manufacturer quoted density of tissue substitute materials. The second was based on the same CT scan of the CIRS phantom followed by a stoichiometric calibration of ICRU44 tissue materials. The research version of Pinnacle3 proton therapy was used to compute dose in a patient CT data set utilizing both HU‐density tables.Results:The two HU‐density tables showed significant differences for bone tissues; the difference increasing with increasing HU. Differences in density calibration table translated to a difference in calculated RScP of −2.5% for ICRU skeletal muscle and 9.2% for ICRU femur. Dose‐volume histogram analysis of a parallel opposed proton therapy prostate plan showed that the difference in calculated dose was negligible when using the two different HU‐density calibration tables.Conclusion:The impact of HU‐density calibration technique on proton therapy dose calculation was assessed. While differences were found in the calculated RScP of bony tissues, the difference in dose distribution for realistic treatment scenarios was found to be insignificant.

SU‐E‐T‐226: Correction of a Standard Model‐Based Dose Calculator Using Measurement Data

Purpose:To propose a hybrid method that combines advantages of the model‐based and measurement‐based method for independent dose calculation. Modeled‐based dose calculation, such as collapsed‐cone‐convolution/superposition (CCCS) or the Monte‐Carlo method, models dose deposition in the patient body accurately; however, due to lack of detail knowledge about the linear accelerator (LINAC) head, commissioning for an arbitrary machine is tedious and challenging in case of hardware changes. On the contrary, the measurement‐based method characterizes the beam property accurately but lacks the capability of dose disposition modeling in heterogeneous media.Methods:We used a standard CCCS calculator, which is commissioned by published data, as the standard model calculator. For a given machine, water phantom measurements were acquired. A set of dose distributions were also calculated using the CCCS for the same setup. The difference between the measurements and the CCCS results were tabulated and used as the commissioning data for a measurement based calculator. Here we used a direct‐ray‐tracing calculator (ΔDRT). The proposed independent dose calculation consists of the following steps: 1. calculate D_model using CCCS. 2. calculate D_ΔDRT using ΔDRT. 3. combineResults:D=D_model+D_ΔDRT.Results:The hybrid dose calculation was tested on digital phantoms and patient CT data for standard fields and IMRT plan. The results were compared to dose calculated by the treatment planning system (TPS). The agreement of the hybrid and the TPS was within 3%, 3 mm for over 98% of the volume for phantom studies and lung patients.Conclusion:The proposed hybrid method uses the same commissioning data as those for the measurement‐based method and can be easily extended to any non‐standard LINAC. The results met the accuracy, independence, and simple commissioning criteria for an independent dose calculator.

Determining the Variability of Lesion Size Measurements from CT Patient Data Sets Acquired under “No Change” Conditions

PURPOSE: To determine the variability of lesion size measurements in computed tomography data sets of patients imaged under a “no change” (“coffee break”) condition and to determine the impact of two reading paradigms on measurement variability. METHOD AND MATERIALS: Using data sets from 32 non-small cell lung cancer patients scanned twice within 15 minutes (“no change”), measurements were performed by five radiologists in two phases: (1) independent reading of each computed tomography dataset (timepoint): (2) a locked, sequential reading of datasets. Readers performed measurements using several sizing methods, including one-dimensional (1D) longest in-slice dimension and 3D semi-automated segmented volume. Change in size was estimated by comparing measurements performed on both timepoints for the same lesion, for each reader and each measurement method. For each reading paradigm, results were pooled across lesions, across readers, and across both readers and lesions, for each measurement method. RESULTS: The mean percent difference (±SD) when pooled across both readers and lesions for 1D and 3D measurements extracted from contours was 2.8 ± 22.2% and 23.4 ± 105.0%, respectively, for the independent reads. For the locked, sequential reads, the mean percent differences (±SD) reduced to 2.52 ± 14.2% and 7.4 ± 44.2% for the 1D and 3D measurements, respectively. CONCLUSION: Even under a “no change” condition between scans, there is variation in lesion size measurements due to repeat scans and variations in reader, lesion, and measurement method. This variation is reduced when using a locked, sequential reading paradigm compared to an independent reading paradigm.

An Evaluation of Two Approaches to Skin Bolus Design for Patients Receiving Radiotherapy for Head and Neck Cancers

PurposeThis radiation treatment planning study compares two approaches to designing a bolus for patients with head and neck cancer. Our current approach, based on clinical examination, is compared with an alternative approach, based on the patient's computed tomographic image data set, to investigate potential improvements in delivering the prescribed dose to the superficial regions of the clinical target volume (CTV) while limiting the dose to normal skin. MethodsTwelve consecutive head and neck radiotherapy plans requiring a bolus were selected. A clinically placed bolus was designed by a radiation oncologist through physical examination of the patient. A virtual bolus was designed using an algorithm that configured it to overlay only the superficial CTV delineated on the patient's CT data set. These two approaches were compared on the basis of dose-volume histograms of normal skin and the superficial CTV, as well as the total bolus area. ResultsOf 12 patients, the virtual bolus plan resulted in a decrease in the bolus area of at least 4 cm2 for nine patients, an increase in the bolus area of at least 30 cm2 for three patients, and an improvement in the minimum dose to the superficial CTV in six patients. Of these six patients, half had a reduction in the bolus area with a corresponding modest 2% improvement in the minimum dose to the superficial CTV, whereas the other half had an increase in the bolus area with a corresponding dramatic 10%–57% improvement in the minimum dose to the superficial CTV. ConclusionsBasing bolus design on computed tomography image data rather than on clinical examination reduced the area of normal skin under the bolus in 9 patients (75%) and improved dose coverage of the superficial CTV in 3 patients (25%). All plans benefited from the virtual bolus approach because it has been shown to be more appropriate for balancing skin sparing with target coverage.

Sci-Sat AM: Stereo - 08: Stereotactic Ablative Radiotherapy (SABR) for low, intermediate and high risk prostate cancer using Volumetric Modulated Arc Therapy (VMAT) with a 10x Flattening Filter Free (FFF) beam

Purpose: To determine the feasibility of using Volumetric Modulated Arc Therapy (VMAT) with a 10x Flattening Filter Free (FFF) beam for Stereotactic Ablative Radiotherapy (SABR) for low, intermediate and high risk prostate cancer. Methods and Materials: Ten anonymized patient CT data sets were used in this planning study. For each patient CT data set, three sets of contours were generated: 1) low risk, 2) intermediate risk, and 3) high risk scenarios. For each scenario, a single-arc and a double-arc VMAT treatment plans were created. Plans were generated with the Varian Eclipse™ treatment planning system for a Varian TrueBeam™ linac equipped with Millenium 120 MLC. Plans were created using a 10x-FFF beam with a maximum dose rate of 2400 MU/min. Dose prescription was 36.25Gy/5 fractions with the planning objective of covering 99% of the Planning Target Volume with the 95% of the prescription dose. Normal tissue constraints were based on provincial prostate SABR planning guidelines, derived from national and international prostate SABR protocols. Plans were evaluated and compared in terms of: 1) dosimetric plan quality, and 2) treatment delivery efficiency. Results: Both single-arc and double-arc VMAT plans were able to meet the planning goals for low, intermediate and high risk scenarios. No significant dosimetric differences were observed between the plans. However, the treatment time was significantly lower for a single-arc VMAT plans. Conclusions: Prostate SABR treatments are feasible with 10x-FFF VMAT technique. A single-arc VMAT offers equivalent dosimetric plan quality and a superior treatment delivery efficiency, compared to a double-arc VMAT.

Development of patient-specific molecular imaging phantoms using a 3D printer.

The aim of the study was to investigate rapid prototyping technology for the production of patient-specific, cost-effective liquid fillable phantoms directly from patient CT data. Liver, spleen, and kidney volumes were segmented from patient CT data. Each organ was converted to a shell and filling holes and leg supports were added using computer aided design software and prepared for printing. Additional fixtures were added to the liver to allow lesion inserts to be fixed within the structure. Phantoms were printed from an ultraviolet curable photopolymer using polyjet technology on an Objet EDEN 500V 3D printer. The final print material is a clear solid acrylic plastic which is watertight, rigid, and sufficiently durable to withstand multiple assembly and scanning protocols. Initial scans of the phantoms have been performed with Tc-99m SPECT and F-18 PET/CT. The organ geometry showed good correspondence with anatomical references. The methodology developed can be generally applied to other anatomical or geometrical phantoms for molecular imaging.

SU‐E‐J‐72: Geant4 Simulations of Spot‐Scanned Proton Beam Treatment Plans

Purpose:To evaluate density inhomogeneities which can effect dose distributions for real‐time image gated spot‐scanning proton therapy (RGPT), a dose calculation system, using treatment planning system VQA (Hitachi Ltd., Tokyo) spot position data, was developed based on Geant4.Methods:A Geant4 application was developed to simulate spot‐scanned proton beams at Hokkaido University Hospital. A CT scan (0.98 × 0.98 × 1.25 mm) was performed for prostate cancer treatment with three or four inserted gold markers (diameter 1.5 mm, volume 1.77 mm3) in or near the target tumor. The CT data was read into VQA. A spot scanning plan was generated and exported to text files, specifying the beam energy and position of each spot. The text files were converted and read into our Geant4‐based software. The spot position was converted into steering magnet field strength (in Tesla) for our beam nozzle. Individual protons were tracked from the vacuum chamber, through the helium chamber, steering magnets, dose monitors, etc., in a straight, horizontal line. The patient CT data was converted into materials with variable density and placed in a parametrized volume at the isocenter. Gold fiducial markers were represented in the CT data by two adjacent voxels (volume 2.38 mm3). 600,000 proton histories were tracked for each target spot. As one beam contained about 1,000 spots, approximately 600 million histories were recorded for each beam on a blade server. Two plans were considered: two beam horizontal opposed (90 and 270 degree) and three beam (0, 90 and 270 degree).Results:We are able to convert spot scanning plans from VQA and simulate them with our Geant4‐based code. Our system can be used to evaluate the effect of dose reduction caused by gold markers used for RGPT.Conclusion:Our Geant4 application is able to calculate dose distributions for spot scanned proton therapy.

MO‐E‐17A‐05: Individualized Patient Dosimetry in CT Using the Patient Dose (PATDOSE) Algorithm

Purpose:Radiation dose to the patient undergoing a CT examination has been the focus of many recent studies. While CTDIvol and SSDE‐based methods are important tools for patient dose management, the CT image data provides important information with respect to CT dose and its distribution. Coupled with the known geometry and output factors (kV, mAs, pitch, etc.) of the CT scanner, the CT dataset can be used directly for computing absorbed dose.Methods:The HU numbers in a patient's CT data set can be converted to linear attenuation coefficients (LACs) with some assumptions. With this (PAT‐DOSE) method, which is not Monte Carlo‐based, the primary and scatter dose are computed separately. The primary dose is computed directly from the geometry of the scanner, x‐ray spectrum, and the known patient LACs. Once the primary dose has been computed to all voxels in the patient, the scatter dose algorithm redistributes a fraction of the absorbed primary dose (based on the HU number of each source voxel), and the methods here invoke both tissue attenuation and absorption and solid angle geometry. The scatter dose algorithm can be run N times to include Nth‐scatter redistribution. PAT‐DOSE was deployed using simple PMMA phantoms, to validate its performance against Monte Carlo‐derived dose distributions.Results:Comparison between PAT‐DOSE and MCNPX primary dose distributions showed excellent agreement for several scan lengths. The 1st‐scatter dose distributions showed relatively higher‐amplitude, long‐range scatter tails for the PAT‐DOSE algorithm then for MCNPX simulations.Conclusion:The PAT‐DOSE algorithm provides a fast, deterministic assessment of the 3‐D dose distribution in CT, making use of scanner geometry and the patient image data set. The preliminary implementation of the algorithm produces accurate primary dose distributions however achieving scatter distribution agreement is more challenging. Addressing the polyenergetic x‐ray spectrum and spatially dependent scatter fractions will improve algorithm accuracy.Funding Support: UC Davis Clinical and Translational Science Center (CTSC) Award; NIH IMSD Student Fellowship; Saxon Student FellowshipDisclosure: PATENT Royalties from Samsung for dosimetry algorithm

SU‐E‐J‐134: An Augmented‐Reality Optical Imaging System for Accurate Breast Positioning During Radiotherapy

Purpose:Breast radiotherapy, particularly electronic compensation, may involve large dose gradients and difficult patient positioning problems. We have developed a simple self‐calibrating augmented‐reality system, which assists in accurately and reproducibly positioning the patient, by displaying her live image from a single camera superimposed on the correct perspective projection of her 3D CT data. Our method requires only a standard digital camera capable of live‐view mode, installed in the treatment suite at an approximately‐known orientation and position (rotation R; translation T).Methods:A 10‐sphere calibration jig was constructed and CT imaged to provide a 3D model. The (R,T) relating the camera to the CT coordinate system were determined by acquiring a photograph of the jig and optimizing an objective function, which compares the true image points to points calculated with a given candidate R and T geometry. Using this geometric information, 3D CT patient data, viewed from the camera's perspective, is plotted using a Matlab routine. This image data is superimposed onto the real‐time patient image, acquired by the camera, and displayed using standard live‐view software. This enables the therapists to view both the patient's current and desired positions, and guide the patient into assuming the correct position. The method was evaluated using an in‐house developed bolus‐like breast phantom, mounted on a supporting platform, which could be tilted at various angles to simulate treatment‐like geometries.Results:Our system allowed breast phantom alignment, with an accuracy of about 0.5 cm and 1 ± 0.5 degree. Better resolution could be possible using a camera with higher‐zoom capabilities.Conclusion:We have developed an augmented‐reality system, which combines a perspective projection of a CT image with a patient's real‐time optical image. This system has the potential to improve patient setup accuracy during breast radiotherapy, and could possibly be used for other disease sites as well.

Development of a Manufacturing Process of Temporal Bone Surgery Models Using Rapid Prototyping

Cochlear implant surgery on highly hearing impaired and deaf patients presents surgeons with major medical challenges. In advance of the operation, the surgeon must gain the necessary dexterity and topographical knowledge in the field of microsurgery. For these purposes human cadaver specimens are usually used but they are not sufficiently available. Therefore, our group from the University of Magdeburg researches and develops a manufacturing process for producing individual anatomical facsimile models (AFM) of the human ear bone, which originally simulate the cavity structure of the inner ear (cochlea, semicircular canals) by using rapid prototyping methods. For this production a variety of biomechanical data of the human ear bone are needed to recreate the later models with the same biomechanical properties. By using these obtained biomechanical data and the individual patient's CT data, stereolithography models of UV-sensitive epoxy resin can be produced. The models can be emulated to the biomechanical properties of the human bone by varying the curing process of the epoxy resin. Thus, the authentic drilling and milling properties give the surgeon the possibility to develop the skills needed in dealing with microsurgical instruments. At the same time the authenticity of the AFM promotes the study of the anatomical structure and the orientation of anatomical landmarks.

Dosimetric evaluation of MapCHECK 2 and 3DVH in the IMRT delivery quality assurance process

Based on per-field data, 3 dose-volume histogram (DVH) is designed to calculate 3-dimensional (3D) dose using patient-computed tomography (CT) for an intensity-modulated radiation therapy (IMRT) delivery quality assurance (DQA) process measured with diode detector arrays. In this study, the characteristics and suitability of 3DVH for an IMRT DQA process were evaluated by assessment of clinically applied results. The DQA plans were prepared with a 2D diode detector array (MapCHECK 2) for 20 IMRT patients (10 with head and neck cancer and 10 with prostate cancer), and the matching rate between the calculated dose and the measured dose was analyzed. The relative dose differences between the original IMRT plan and the recalculated plan by 3DVH were evaluated for tumor target and organs at risk (OARs). Confidence limits (CLs) were determined for quantification of the degree of agreement that should be expected in each DQA method. The individual CLs for DQA accuracy of 3D dosimetric evaluation in the tumor target and OARs were also calculated to evaluate the differences compared with conventional 2D-based DQA results. The matching rates were sufficient to validate the accuracy of IMRT DQA analyses and the calculated CL values were reasonable values considering the normal criteria of our institution. The 3DVH analysis generally had better matching rate than per-field measurement analysis and the CL values for OARs were better than those for the planning target volume (PTV). The usefulness of the 3DVH tool was verified for IMRT DQA from the point of view of dose evaluation in the corresponding patient's CT data. It also enables dosimetric evaluation in each important structure (PTV and OARs), which can promote more effective evaluation of DQA error in terms of tumor treatment and side effects.

Simulation of realistic linac motion improves the accuracy of a Monte Carlo based VMAT plan QA system

PurposeTo investigate the use of a software-based pre-treatment QA system for VMAT, which incorporates realistic linac motion during delivery. MethodsA beam model was produced using the GATE platform for GEANT4 Monte Carlo dose calculations. Initially validated against static measurements, the model was then integrated with a VMAT delivery emulator, which reads plan files and generates a set of dynamic delivery instructions analogous to the linac control system. Monte Carlo simulations were compared to measurements on dosimetric phantoms for prostate and head and neck VMAT plans. Comparisons were made between calculations using fixed control points, and simulations of continuous motion utilising the emulator. For routine use, the model was incorporated into an automated pre-treatment QA system. ResultsThe model showed better agreement with measurements when incorporating linac motion: mean gamma pass (Γ<1) over 5 prostate plans was 100.0% at 3%/3mm and 97.4% at 2%/2mm when compared to measurement. For the head and neck plans, delivered to the anatomical phantom, gamma passes were 99.4% at 4%/4mm and 94.94% at 3%/3mm. For example simulations within patient CT data, gamma passes were observed which are within our centre’s tolerance for pre-treatment QA. ConclusionsThrough comparison to phantom measurements, it was found that the incorporation of a realistic linac motion improves the accuracy of the model compared to the simulation of fixed control points. The ability to accurately calculate dose as a second check of the planning system, and determine realistic delivery characteristics, may allow for the reduction of machine-based pre-treatment plan QA for VMAT.

Automated attenuation-based selection of tube voltage and tube current for coronary CT angiography: Reduction of radiation exposure versus a BMI-based strategy with an expert investigator

BackgroundRecently developed automated algorithms use the topogram and the corresponding attenuation information before coronary CT angiography (CTA) to allow for an individualized anatomic-based selection of tube current (mAs) and voltage (kV). ObjectivesThe value of these algorithms in reducing the associated radiation exposure was evaluated. MethodsOne hundred patients underwent coronary CTA with dual-source CT with prospectively electrocardiogram-triggered axial data acquisition. In all patients, tube parameters (current and voltage) were suggested by both an experienced investigator according to the patient's body mass index (BMI; calculated as weight divided by height squared; kg/m2) and by an automated software according to attenuation values of the initial topogram. The first 50 consecutive patients (group 1) underwent coronary CTA with dual-source CT with tube parameters suggested by the experienced investigator (BMI-based tube parameters), whereas in another 50 consecutive patients (group 2) CT data acquisition was performed with tube settings of the automated software. Subsequently, subjective image quality (4-point rating score from 0 = nondiagnostic to 3 = excellent image quality), image noise (SD of CT number within the aortic root), as well as signal- and contrast-to-noise ratios and mean effective radiation doses, were compared between both groups. ResultsBoth groups showed comparable image quality parameters (group 1 vs 2: noise, 28.1 ± 6.0 HU vs 29.9 ± 5.4 HU, P = .12; signal-to-noise ratio, 16.4 ± 3.9 vs 16.8 ± 4.1, P = .54; contrast-to-noise ratio, 18.6 ± 4.1 vs 19.2 ± 4.3, P = .49; 4-point rating score, 2.8 ± 0.3 vs 2.9 ± 0.3, P = .81). Tube voltage, current, and mean effective radiation dose for groups 1 and 2 were 111 ± 12 kV and 108 ± 12 kV (P = .18), 361 ± 32 mAs and 320 ± 48 mAs (P < .001), and 2.3 mSv (25th; 75th percentile, 1.5; 2.8 mSv) and 1.4 mSv (25th; 75th percentile, 1.1; 1.9 mSv) (P < .001), respectively. ConclusionsAutomated attenuation-based selections of individualized tube parameters are superior to BMI-based selections with expert oversight and show a potential for reduction of radiation exposure in coronary CTA, and image quality is maintained.