Hounsfield Number Research Articles

ACR benchmark testing of a novel high-speed ring-gantry linac kV-CBCT system.

A new generation cone-beam computed tomography (CBCT) system with new hardware design and advanced image reconstruction algorithms is available for radiation treatment simulation or adaptive radiotherapy (HyperSight CBCT imaging solution, Varian Medical Systems-a Siemens Healthineers company). This study assesses the CBCT image quality metrics using the criteria routinely used for diagnostic CT scanner accreditation as a first step towards the future use of HyperSight CBCT images for treatment planning and target/organ delineations. Image performance was evaluated using American College of Radiology (ACR) Program accreditation phantom tests for diagnostic computed tomography systems (CTs) and compared HyperSight images with a standard treatment planning diagnostic CT scanner (Siemens SOMATOM Edge) and with existing CBCT systems (Varian TrueBeam version 2.7 and Varian Halcyon version 2.0). Image quality performance for all Varian HyperSight CBCT vendor-provided imaging protocols were assessed using ACR head and body ring CT phantoms, then compared to existing imaging modalities. Image quality analysis metrics included contrast-to-noise (CNR), spatial resolution, Hounsfield number (HU) accuracy, image scaling, and uniformity. All image quality assessments were made following the recommendations and passing criteria provided by the ACR. The Varian HyperSight CBCT imaging system demonstrated excellent image quality, with the majority of vendor-provided imaging protocols capable of passing all ACR CT accreditation standards. Nearly all (8/11) vendor-provided protocols passed ACR criteria using the ACR head phantom, with the Abdomen Large, Pelvis Large, and H&N vendor-provided protocols produced HU uniformity values slightly exceeding passing criteria but remained within the allowable minor deviation levels (5-7 HU maximum differences). Compared to other existing CT and CBCT imaging modalities, both HyperSight Head and Pelvis imaging protocols matched the performance of the SOMATOM CT scanner, and both the HyperSight and SOMATOM CT substantially surpassed the performance of the Halcyon 2.0 and TrueBeam version 2.7 systems. Varian HyperSight CBCT imaging system could pass almost all tests for all vendor-provided protocols using ACR accreditation criteria, with image quality similar to those produced by diagnostic CT scanners and significantly better than existing linac-based CBCT imaging systems.

Mechanical properties of atherosclerotic plaques, caps and walls of arterial vessels: a mobile test bench experiments

Within the framework of this study, a methodology and a prototype of a test bench for conducting experiments on compression of biological tissue samples have been developed. The test bench for the implementation of the technique consists of high–precision scales (measuring accuracy up to 0.01 g, maximum weight - 5 kg), an electronic caliper (measuring accuracy up to 0.01 mm) with 3D-printer pads that are attached to grips, as well as video cameras. Thanks to such a mobile stand, it was possible to conduct a series of experiments (a total of 99 tests) to determine the Young's modulus of atherosclerotic plaques and areas of vascular walls removed from the body no later than a few hours. This made it possible to collect a database of the mechanical characteristics of the plaques as close as possible to the real properties. In addition, regression dependences were constructed between the Hounsfield numbers corresponding to dense atherosclerotic deposits discernible on a CT scan and the Young modules obtained during experiments. Such dependencies will further allow determining the mechanical properties of plaques in vivo based on computed tomography data. The technique was verified by mechanical experiments on the universal testing machine Instron 3342 and on a mobile test bench on samples of hard (with pronounced calcification) and soft plaques. 7 experiments were conducted for each type of samples. The results differed by no more than 4.3 % for soft plaques and no more than 9.5 % for hard plaques. To test the inter-expert reliability of the methodology, a number of experiments were conducted with the involvement of two independent participants. Each of the three mobile stand operators performed 5 tests on soft rubber samples. The study of inter-expert reliability allowed us to show the independence of the methodology from the skills and qualifications of the operator.

Multivariate Analysis of Effective Dose and Size-Specific Dose Estimates for Thorax and Abdominal Computed Tomography.

The study aimed to compute the effective dose (E) and size-specific dose estimate (SSDE) of routine adult patients undergoing thorax and abdominal computed tomography (CT) imaging and to present their multivariate analysis. All adult thorax and abdominal CT examinations conducted from March 2022 to June 2022 were prospectively included in this study. The Water Equivalent Diameter (Dw) and SSDE of all the examinations were computed from CT dose index volume (CTDIvol) and Dose length product (DLP) displayed on the dose report in the CT console. The multivariate statistical analysis was performed to investigate the correlation of SSDE and E on CTDIvol, Dw area of the region of interest (ROI) (AreaROI), body mass index (BMI), conversion factor (fsize) and hounsfield (HUmean) number in the ROI at 95% level of significance (P < 0.05). The linear regression analysis was performed to investigate the dependence of SSDE and E on other parameters for both abdominal and thorax patients. A total number of 135 (Abdomen = 61 and Thorax = 74) measurements were performed. The mean value of effective dose for abdomen and thorax patients was found to be 7.17 ± 3.94 and 4.89 ± 2.16 mSv, respectively. The SSDE was observed to be 13.24 ± 3.61 and 13.04 ± 3.61 mGy for thorax and abdomen respectively. The multivariate analysis suggests that SSDE for abdominal CT is found significantly dependent on CTDIvol, Dw and fsize with P < 0.05 and E is found to be significantly dependent on DLP, AreaROI, Dw and fsize at 95% level of confidence for abdominal CT imaging. SSDE for thorax CT was found significantly dependent on BMI, CTDIvol, HUmean, Dw and fsize at 95% level of confidence. Furthermore, E was observed dependent on DLP at P < 0.05. The linear regression analysis also shows that E is strongly correlated with DLP (r = 1.0) for both thorax and abdominal CT, further the SSDE was observed strongly correlated with CTDIvol with r = 0.79 and r = 0.86 for abdomen and thorax CT respectively. A strong correlation was observed between BMI and for Dw abdominal CT imaging (r = 0.68). The mean value of SSDE for thorax is slightly greater than abdomen. The average value of effective dose for abdomen and thorax measurements was found to be 7.17 ± 3.94 and 4.89 ± 2.16 mSv and , correspondingly. SSDE for both abdomen and thorax CT is significantly dependent on CTDIvol, Dw and fsize at 95% level of confidence. The strong correlation was also observed E on DLP and SSDE on CTDIvol for both Abdomen and Thorax CT. The strong dependence of Dw on BMI (r = 0.68) is due to the excessive fat concentration around the stomach and abdomen.

A clinical study comparing polymer and gold fiducials for prostate cancer radiotherapy.

Image guidance with gold fiducials improves outcomes of prostate radiotherapy. However, gold produces artefact on CT imaging, interfering with contouring and verification. The purpose of this study was to compare polymer to standard gold fiducials using radiotherapy imaging modalities to assess the visibility and artefact. Twenty eight patients with locally advanced prostate cancer were enrolled, half had three polymer fiducials implanted into the prostate and half underwent insertion of gold fiducials. Patients were imaged with CT, T2 weighted MRI, cone-beam CT (CBCT) and planar KV images. Fiducials were scored for visibility and assessed for CT artefact in surrounding prostate tissue. The artefact was quantified from Hounsfield number histograms and separated into percentile ranges and proportion of voxels in HU normal tissue range of a 2cm sphere surrounding the fiducial. Gold and polymer fiducials were sufficiently visible for CT and CBCT verification. The gold fiducials could be visualized well on KV planar imaging; however, the polymer markers were obscured by pelvic bones. Neither polymer nor gold fiducials could be visualized on MRI. The polymer fiducial produced less artefact than gold on CT, having less voxel spread for the HU percentile ranges and a greater proportion of voxels in the normal tissue range. Polymer fiducials are a more suitable fiducial than gold for CT/CBCT in prostate cancer radiotherapy, demonstrating minimal artefact and good visibility on CT. However, they were not well seen on MRI or KV imaging and thus not suitable for co-registration or planar KV verification.

An Iterative Method for Computed Tomography Machine Calibration: Attenuation and Dual-Energy Computed Tomography Inversion from the Hounsfield Numbers

Introduction: Photoelectric effect and X-ray scattering determine the attenuation coefficient of materials in diagnostic radiology. This manuscript presents an iterative gradient search method to separate the contributions to attenuation from these two independent sources. This issue assumes importance due to two reasons, including 1) Electron density determination of scanned materials and 2) correct dose calculation in diagnostic radiology. Material and Methods: A special water-filled phantom which was custom-built for simultaneous scanning of 12 samples was used in the current study. Attenuation coefficient equations were iteratively solved to calculate the contributions from x-ray scattering and photoelectric effects. Results: Data converged after five iterations (within 1%). Error in the attenuation coefficient was measured at ±3%. Conclusion: As evidenced by the obtained results, this method can be used to determine the Compton and photoelectric contributions with sufficient accuracy. Moreover, the inversion of Dual- Energy computed tomography (DECT) data for finding electron density and effective atomic number of materials also presents satisfactory results.

Dosimetric study of Hounsfield number correction effect in areas influenced by contrast product in lungs case.

The aim of the study was dosimetric effect quantification of exclusive computed tomography (CT) use with an intravenous (IV) contrast agent (CA ), on dose distribution of 3D-CRT treatment plans for lung cancer. Furthermore, dosimetric advantage investigation of manually contrast-enhanced region overriding, especially the heart. Ten patients with lung cancer were considered. For each patient two planning CT sets were initially taken with and without CA. Treatment planning were optimized based on CT scans without CA. All plans were copied and recomputed on scans with CA. In addition, scans with IV contrast were copied and density correction was performed for heart contrast enhanced. Same plans were copied and replaced to undo dose calculation errors that may be caused by CA. Eventually, dosimetric evaluations based on dose volume histograms (DVHs) of planning target volumes (PTV) and organs at-risk were studied and analyzed using the Wilcoxon's signed rank test. There is no statistically significant difference in dose calculation for the PTV maximum, mean, minimum doses, spinal cord maximum doses and lung volumes that received 20 and 30 Gy, between planes calculated with and without contrast scans (p > 0.05) and also for contrast scan, with manual regions overriding. Dose difference caused by the contrast agent is negligible and not significant. Therefore, there is no justification to perform two scans, and using an IV contrast enhanced scan for dose calculation is sufficient.

Impact of Acquisition Protocols on Accuracy of Dose Calculation Based on XVI Cone Beam Computed Tomography.

Purpose:The objective of this work is to study the impact of acquisition protocols on the accuracy of cone beam computed tomography (CBCT)-based dose calculation and to determinate its limits from image characteristics such as image quality, Hounsfield numbers consistency, and restrictive sizes of volume acquisition, compared to the CT imaging for the different anatomy localizations: head and neck (H&N), thorax, and pelvis.Materials and Methods:In this work, we used a routine on-board imaging CBCT of the XVI system (Elekta, Stockholm, Sweden). Dosimetric calculations performed on CT images require the knowledge of the Hounsfield unit-relative electron density (HU-ReD) calibration curve, which is determined for each imaging technology and must be adapted to the imaging acquisition parameters (filter/field of view). The accuracy of the dose calculation from CBCT images strongly depends on the quality of these images and also on the appropriate correspondence to the electronic densities, which will be used by the treatment planning system to simulate the dose distribution. In this study, we evaluated the accuracy of the dose calculation for each protocol, as already pointed in many studies.Results:As a result, the protocols that give better results in terms of dose calculation are F0S20 for the H&N region and F1M20 for the thoracic and pelvic regions, with an error <2% compared to results obtained with CT images. In addition, the dose distributions obtained with CT and CBCT imaging modalities were compared by two different methods. The first comparison was done by gamma index in three planes (sagittal, coronal, and transverse) with 2%; 2 mm criteria. The results showed good correspondence, with more than 95% of points passed the criteria. We also compared the target volume, the organs at risk (OARs), and the maximum and minimum doses for the three localizations (H&N, thorax, and pelvis) in CT and CBCT imaging modalities using a Rando phantom.Conclusions:The choice of the adequate CBCT acquisition protocol and the appropriate phantom to determine the HU-ReD calibration curve provides a better precision in the calculation of dose on CBCT images. This allows improving the results obtained when using the HU-ReD calibration method for dose calculation in adaptive radiotherapy.

Destruction simulation for the inhomogeneous body by finite element method using computed tomography data

The work is devoted to modelling the bone organ destruction using the finite element method and taking into account the CT data. In order to evaluate the model, the simulation results for the femur are presented. Such an approach allows to individualize the simulation of the organ and determines the relevance of the study. Numerical studies using the finite element method were performed, an eight-node finite element with linear approximation was used. A linear formulation for an inhomogeneous elastic body was considered. Young’s modulus and ultimate stress were determined using power functions. The dependence of mechanical properties on the optical density was assumed, which, in turn, was determined by linear relationships depending on the Hounsfield numbers. For discretization by the finite element method, the distribution of the mechanical properties of the material for each element was performed according to tomography data. After solving, the stress-strain state problem safety factor was calculated in each node. Based on the calculated safety factor, a decision is made either to thicken the mesh or to remove the finite element. The paper presents the results of calculations using the method for two problems: an inhomogeneous sample and specimen with averaged mechanical properties. The numerical results in these problems illustrate the significant differences in the results of the stress-strain state of the organ and allow us to judge the nature of the destruction of the organ.

Study of radiation interaction parameters for organic compounds at gamma photon energies different from available standard radioisotopes

The present work emphasizes on the transmission of gamma photons, having energies in the range (241.8–401.8 keV) obtained by Compton scattering technique, to determine mass-attenuation coefficients (μm), molar-extinction coefficients (ε), mass-energy absorption coefficient (μen/ρ), effective atomic number (Zeff), mean free path (MFP), half value layer (HVL), total atomic (σt.a) and electronic (σt.el) cross-sections, and Hounsfield number (H) of various organic compounds like Alcohols, Aldehydes, Ketones, Esters, Amines, Benzene compounds and Water, and further used as radiation shielding. The WinXcom software package is used to compare the experimentally deduced radiation interaction parameters with theory. The theoretical and experimental results are in good agreement within permissible experimental uncertainty. The radiation shielding parameters have been found to vary with gamma-ray energy and effective atomic number for these organic compounds under present investigations.

Pancreatic Fibrosis and Chronic Pancreatitis: Mini-Review of Non-Histologic Diagnosis for Clinical Applications.

Pancreatic fibrosis is the dominant reversible pathological change and diagnostic factor in early chronic pancreatitis, defined by a mechanistic approach proposed in 2016. Main guidelines for chronic pancreatitis were published by the American Pancreas Association in 2014, the Japanese Society of Gastroenterology in 2015, and United European Gastroenterology in 2017. All three sets of guidelines mentioned that the staging of chronic pancreatitis is important but challenging. There are various image modalities for the non-histologic diagnosis of pancreatic fibrosis: (1) shear wave elastography, such as an acoustic radiation force impulse with a cut-off value of 1.4 m/s; (2) strain elastography using grades of strain; (3) endoscopic ultrasonography using the Rosemont criteria or endoscopic ultrasound criteria for early chronic pancreatitis proposed by the Japan Pancreas Society; (4) computed tomography using the Hounsfield scale or number of micro-calcifications; and (5) magnetic resonance imaging using the apparent diffusion coefficient and the T1w flash and T2w HASTE sequences. The clinical applications are to (1) evaluate pancreatic tumors and inflammatory disease; (2) monitor dyspepsia with early chronic pancreatitis; (3) monitor individuals with a high risk of pancreatic cancer; (4) analyze a fatty pancreas with fibrosis; (5) predict a fistula after pancreatic surgery; and (6) predict outcomes for chronic pancreatitis or pancreatic cancer. The selection of tools will be dependent on the clinical scenario. Conclusion: There are various modalities for the non-histologic diagnosis of pancreatic fibrosis. The selection of the optimal device will be dependent on the clinical scenario.

Comparison of Computed Tomographic Hounsfield Numbers with Ultrasonographic Categorization of the Fatty Liver Disease

Material and Methods: It was a Cross sectional analytical study. By Purposive sampling 227 Patients of FLD were sampled from Radiology Department AL Razi Healthcare MM Alam Road Lahore and Radiology Department Shalamar Hospital Shalamar Road Lahore. The data was collected for 9 months. Patients of both gender of age between 20-80 years, who underwent both CT and USG scans of abdomen and with Ultrasonographic diagnosis of diffuse FLD was included. The USG categories of FLD were compared with mean Liver CTHFN. Statistical analysis was done by ANOVA; p value of CTHFN was found significant for each Ultrasonographic category of FLD.

The advantages of carbon fiber based orthopedic devices in patients who have to undergo radiotherapy.

Background and Objectives:The modern approach to primary and secondary muscular skeletal tumors is multidisciplinary. The right combination of chemotherapy, surgery and radiotherapy (RT) makes obtaining local and distant disease more likely. When surgery is indicated, radiotherapy often has a fundamental role as an adjuvant treatment; however, the titanium alloy instrumentations interfere with Radiotherapy setting, decreasing its effectiveness. It is common opinion that carbon fiber-reinforced devices are convenient in case of adjuvant RT in muscular skeletal oncology. The aim of the study is to support this intuition with experimental data, verifying the more accurate estimation of the delivered dose during RT, comparing Carbon Fiber-Reinforced PEEK (CFRP) plates with titanium-alloy orthopedic devices in order to evaluate their effects on target volume identification and dose distribution for radiation treatment.Methods:Phantoms were then irradiated with a linear accelerator Varian 2100 C/D with photon beams of 6 and 15 MV energies. Absorbed dose in the point of interest was verified by EBT3 gafchromic films above and below the two materials. Images from CT simulations were also analyzed in terms of Hounsfield numbers in patients with titanium and carbon fiber orthopedic implants in the spine or in the femur.Results:For a 6 MV photon beam, the doses measured just under the titanium-alloy plate were less than approximately 20% of the value calculated by the TPS. For a 15 MV beam energy, these differences were slightly lower. Using CFRP plate, the difference between measured and calculated doses was within ±3% for both energies, which was comparable with the statistical uncertainties. In the cases of simulated treatment of humerus titanium implants, the difference varies in range ± 10% with hot spot of + 10% and cold spot of -15%.Conclusions:The use of CFRP for orthopedic devices and implants provides a valuable advantage in identifying the target due to the reduction of artifacts. Clear imaging of the soft tissues surrounding the bone is useful and reduces the discrepancies between calculated/delivered and measured doses, generating a more homogeneous dose distribution. Furthermore, there is a significant benefit in detecting the state of disease in CT imaging during the follow-up of treated patients. In-vivo studies are encouraged to verify whether a more effective radiotherapy leads to a decrease in local recurrence and local progression. (www.actabiomedica.com)

Additive Manufacture of Lung Equivalent Anthropomorphic Phantoms: A Method to Control Hounsfield Number Utilizing Partial Volume Effect

Abstract Anthropomorphic radiotherapy phantoms require tissue-equivalent materials to achieve Hounsfield units (HU) that are comparable to those of human tissue. Traditional manufacturing methods are limited by their high-cost and incompatibility with patient-specific customization. Additive manufacture (AM) provides a significant opportunity to enable manufacture of patient-specific geometries at relatively low cost. However, AM technologies are currently limited in terms of available material types, and consequently enable very little variation in achievable HU when standard manufacturing parameters are used. This work demonstrates a novel method whereby the partial volume effect (PVE) is utilized to control the HU of an AM material, in particular, enabling low HU in the range typical of lung tissue. The method enables repeatable design of lung HU and is compatible with commercial machines using standard print parameters. A custom algorithm demonstrates the clinical application of the method, whereby patient-specific computed tomography (CT) data are algorithmically calibrated according to AM print parameters and confirmed to be robust as a custom anthropomorphic radiotherapy phantoms.

Calcul de dose de radiothérapie à partir de tomographies coniques : état de l’art

In external beam radiotherapy, the dose planning is currently based on computed tomography (CT) images. A relation between Hounsfield numbers and electron densities (or mass densities) is necessary for dose calculation taking heterogeneities into account. In image-guided radiotherapy process, the cone beam CT is classically used for tissue visualization and registration. Cone beam CT for dose calculation is also attractive in dose reporting/monitoring perspectives and particularly in a context of dose-guided adaptive radiotherapy. The accuracy of cone beam CT-based dose calculation is limited by image characteristics such as quality, Hounsfield numbers consistency and restrictive sizes of volume acquisition. The analysis of the literature identifies three kinds of strategies for cone beam CT-based dose calculation: establishment of Hounsfield numbers versus densities curves, density override to regions of interest, and deformable registration between CT and cone beam CT images. Literature results show that discrepancies between the reference CT-based dose calculation and the cone beam CT-based dose calculation are often lower than 3%, regardless of the method. However, they can also reach 10% with unsuitable method. Even if the accuracy of the cone beam CT-based dose calculation is independent of the method, some strategies are promising but need improvements in the automating process for a routine implementation.

Developing and characterizing MR/CT-visible materials used in QA phantoms for MRgRT systems.

Synthetic tissue equivalent (STE) materials currently used to simulate tumor and surrounding tissues for IROC-Houston's anthropomorphic head and thorax QA phantoms cannot be visualized using magnetic resonance (MR) imaging. The purpose of this study was to characterize dual MR/CT-visible STE materials that can be used in an end-to-end QA phantom for MR-guided radiotherapy (MRgRT) modalities. Over 80 materials' MR, CT, and dosimetric STE properties were investigated for use in MRgRT QA phantoms. The materials tested included homogeneous and heterogeneous materials to simulate soft tissue/tumor and lung tissues. Materials were scanned on a Siemens' Magnetom Espree 1.5T using four sequences, which showed the materials visual contrast between T1- and T2-weighted images. Each material's Hounsfield number and electron density data was collected using a GE's CT Lightspeed Simulator. Dosimetric properties were examined by constructing a 10×10×20cm3 phantom of the selected STE materials that was divided into three sections: anterior, middle, and posterior. Anterior and posterior pieces were composed of polystyrene, whereas the middle section was substituted with the selected STE materials. EBT3 film was inserted into the phantom's midline and was irradiated using an Elekta's Versa 6MV beam with a prescription of 6Gy at 1.5cm and varying field size of: 10×10cm2 , 6×6cm2 , and 3×3cm2 . Measured film PDD curves were compared to planning system calculations and conventional STE materials' percent depth dose (PDD) curves. The majority of the tested materials showed comparable CT attenuation properties to their respective organ site; however, most of the tested materials were not visible on either T1- or T2-weighted MR images. Silicone, hydrocarbon, synthetic gelatin, and liquid PVC plastic-based materials showed good MR image contrast. In-house lung equivalent materials made with either silicone- or hydrocarbon-based materials had HUs ranging from: -978 to -117 and -667 to -593, respectively. Synthetic gelatin and PVC plastic-based materials resembled soft tissue/tumor equivalent materials and had HUs of: -175 to -170 and -29 to 32, respectively. PDD curves of the selected MR/CT-visible materials were comparable to IROC-Houston's conventional phantom STE materials. The smallest field size showed the largest disagreements, where the average discrepancies between calculated and measured PDD curves were 1.8% and 5.9% for homogeneous and heterogeneous testing materials, respectively. Gelatin, liquid plastic, and hydrocarbon-based materials were determined as alternative STE substitutes for MRgRT QA phantoms.

43. CBCT dose calculation: accuracy assessment of four different methods

Introduction Cone Beam CT (CBCT) images aim at target volume repositioning before treatment fraction. These images may be used for dose calculation in order to dosimetrically quantify anatomical variations that occurs during treatment. The main limits are image quality, Hounsfield numbers (HU) consistency and CBCT reconstruction size. This study aims to assess accuracy of several CBCT dose calculation methods. Methods This study deals with four CBCT (XVI, Elekta) and CT image sets acquired on the same day in context of weekly dose planning of one H&N patient treated with VMAT technique. CT-CBCT sets were used to quantify CBCT dose calculation accuracy by investigating four methods: (i) use of a density to HU relation from phantom CBCT image (phantom HU-D relation), (ii) use of a density to HU relation from patient CBCT image (patient HU-D relation), (iii) density override by three classes threshold (air, soft tissues, bone) and (iv) elastic deformation (Admire, Elekta) between planning CT and CBCT image, by creating a pseudo-CT. After rigid registration, plan characteristics are projected on CBCT images (or pseudo-CT) with Pinnacle v.9.10 (Philips). Dose distribution comparison between CT-based (reference) and CBCT-based calculation was performed by a gamma analysis in 2D and 3D ( γ 2D and γ 3D, criteria: 2%/2 mm, 30% threshold). Then, dose differences were reported in terms of 95% target coverage, parotid glands mean dose (Dmean) and PRV spinal cord maximum dose (D2%). Results On average, γ 3D (percentage of points with gamma The gamma analysis showed location of discrepancy areas: near body contour, regarding shoulders and in presence of heterogeneities ( Fig. 1 ). These differences can be explained by the poor image quality and the HU inconsistency of CBCT images in some areas. The method with pseudo-CT seems to be the best to pass over these issues because densities come from planning CT. Conclusions The four evaluated methods show that dose differences can reach 5% for parotid glands and are lower than 2% for spinal cord and target volumes. The 3D gamma analysis results (2%/2 mm) are higher than 95% for three among four methods. However, additional uncertainties have to be taken into consideration in case of CBCT image delineation and/or calculation on truncated images. This preliminary study shows CBCT dose calculation feasibility to quantify impact of patient anatomical variations during treatment and trigger a new plan based on CT if necessary. The future work is real delivered dose monitoring, based on CBCT image, in perspective of dose guided adaptive radiotherapy.

13. Comparison of algorithms AAA and Acuros (AxB) on heterogenous medium

Introduction A Boltzman equation based algorithm is now implemented on the Eclipse treatment planning system for calculating the dose distribution. Acuros performances are announced to be close to the Monte Carlo ones. However, implementing a new algorithm in routine is not without consequences, even if the dose calculation is more realistic. The aim of this study is to compare the algorithms AxB (V13.6) and AAA (V13.6) with gafchromic films measures for simple situations (bone phantom and air cavity phantom).Then, the PTV coverage on patients will be compared between AAA and AxB algorithms. Methods First, dose calculations and measures were done on a bone phantom composed of a hollow bone with an air cavity, placed in a water tank, and on an air cavity phantom made of 2 cm, 4 cm and 8 cm height of air surrounded by water equivalent RW3 plates. For this latter phantom, Acuros calculations were repeated assigning Hounsfield numbers to −1000 inside the air cavity. Squared fields irradiations were realized at fixed monitor units. For the bone phantom, a unique measure was done with a film perpendicular to the beam direction. For the air cavity phantom, measures were repeated with films perpendicular to the beam in 1 cm step. Calculated profiles and film measurements previously calibrated were overlaid. Dose distribution of 3 patients treated on a vertebra and 4 patients for whom the PTV encompassed sinus, previously calculated with AAA algorithm, were compared with the dose calculated with Acuros algorithm. PTV coverage at 95% was reported and compared for both algorithms. Results Mean differences of 1.8% and 2.6% were observed on the bone phantom between Acuros algorithm and film, and between AAA algorithm and film, respectively. Concerning the air cavity phantom, differences between algorithms and films measurements increased when the cavity height increased, and were on average larger with the AAA algorithm: for 8 cm height: 26.8% vs 7.7%, for 4 cm height: 10.2% vs 5.8%, for 2 cm height: 2.0% vs 1.9%. Acuros calculations were closer to the film on the first cm but larger discrepancies appeared at the end of the air cavity ( Fig. 1 ). This phenomenon was in part corrected by HU correction (mean of −958 before correction against −1000 after correction) but on the contrary a difference in dose for the first cm was involved ( Fig. 1 ). Finally, for both localizations on patient treatment planning, a mean loss of about 2% in PTV coverage was found with the algorithm Acuros with doses holes phenomena in air and/or in bone. Without prescribed dose or coverage objectives adaptation, final dose calculation with Acuros would lead to an increase of the delivered dose. Conclusions Either in bone or in air cavity, decreases in PTV dose coverage for patients were in agreement with observations on phantoms. Moreover, it seems that the Acuros algorithm is extremely sensitive to a small HU variation. Further measurements are in progress to quantify the impact of HU variation on Acuros calculations, in particular due to artefacts on CT images.

On the prediction of X-ray dose deviations and the influence of CT scan protocols

Abstract Patients undergoing computerized tomography (CT) scans for tumor localization and treatment planning are frequently scanned using pre-set customized exposure protocols for optimal imaging of different anatomical sites. The question arises if these scanning protocols will produce a deviation in the Hounsfield number for a given tissue that can afterwards be used to predict the resulting dose calculation deviation due to this. The question is also if the deviation in the Hounsfield number of a tissue is large enough to affect dose calculation clinically significant. A study was devised in which a RMI phantom was scanned with five different scanning protocols and two CT beam energies at 120 and 135 kV. To assess the effect of insert configuration, Hounsfield number measurements were repeated for high density RMI inserts in the center and outer rings in the phantom. For each material insert the standard deviation of the Hounsfield number was calculated. To assist in dose prediction a series of DOSXYZnrc Monte Carlo calculations were carried out for beam qualities between 6 and 16 MV for a range of Hounsfield numbers calculated for bone and water. This provided information on how the depth dose varied as a function of Hounsfield number variation. Lastly, a series of treatment plans were setup for absorbed dose calculation using the RMI insert electron densities vs Hounsfield relations measured above. The absorbed dose of corresponding plans with the largest Hounsfield number variation were subtracted to find the dose discrepancies. It was found that the dose discrepancies in tissue types could be indicated by the deviation of the Hounsfield number due to different scanning protocols. The calculated dose difference were in all cases within 3%.

Integral Dose-Based Inverse Optimization May Reduce Side Effects in Radiotherapy of Prostate Carcinoma.

The purpose of this work is to apply a novel inverse optimization approach, based on utilization of quantitative imaging information in the optimization function, to prostate carcinoma. This new inverse optimization algorithm relies upon quantitative information derived from computed tomography (CT) imaging studies. The Hounsfield numbers of the CT voxels are converted to physical density, which in turn is used to calculate voxel mass and the corresponding integral dose, by summation over the product of dose and mass in each dose voxel. This integral dose is used for plan optimization through its global minimization. The optimization results are compared to the optimization results derived from most commonly used dose-volume-based inverse optimization, where objective functions are formed as summation over all dose voxels of the squared differences between voxel doses and user specified doses. The data from 25 prostate plans were optimized with dose-volume histogram (DVH) and integral dose (energy) minimization objective functions. The results obtained with the energy- and DVH-based optimization schemes were studied through commonly used dosimetric indices (DIs). Statistical equivalence tests were further performed to establish population-based significance results. Both DVH- and energy-based plans for each case were normalized so that 95% of the planning target volume receives the prescription dose. The average differences for the rectum and bladder DIs ranged from 1.6 to 25%, where the energy-based quantities were lower. For both femoral heads, the energy-based optimization-derived doses were lower on average by 32%. The statistical tests demonstrated that the significant differences in the tallied dose indices range from 2.7% to more than 50% for rectum, bladder, and femoral heads. For majority of the clinically relevant dosimetric quantities, energy-based inverse optimization performs better than the standard of care DVH-based optimization in prostate carcinoma. The population averaged statistically significant differences range from ~3 to ~50%. Therefore, this newly proposed optimization approach, incorporating explicitly quantitative imaging information in the inverse optimization function, holds potential for further reduction of complication rates in prostate cancer.

Comparing the Effect of Human Wisdom Teeth Pulverized in Micron and Nano Particle Dimensions as Grafting Material in Healing of Tibial Bone Defect

Background: In this article, we decided to introduce an available, affordable and biocompatible material from human teeth using nanotechnology to repair bone defects. Totally impacted wisdom teeth of human, which had been removed by surgery, were prepared as powder in two particle sizes of 500 micron and nano (up to 100 nm) after sterilization. Method: Test cases were eight white rabbits of New Zealand species that were divided into 2 groups. Pores with 6 × 6 mm dimensions were created at hamstring area of tibia bone. In left leg tibia’s pore, nanoparticles powder and in the right leg tibia’s pore, micro particles powders were placed. The groups of two were sacrificed after 4, 8, 12 and 16 weeks. Samples underwent histomorphometric analysis and radiological analysis. The results showed the superiority of nano-groups in the percentage of new bone formation (26.62±10.88) over micro-groups (14.36±8.4) to (P-value = 0.015). Obtained Hounsfield number for micro-particle group was 2477±480 and for nanoparticle group was 1387±429 (p-value = 0.001). The differences in value soft bone vitality, inflammation, and foreign body reaction were not significant between the two groups of micro and nano. In micro particle group, despite suitable biocompatibility and Osseo integration, due to higher density and degree of crystalline, absorption and replacement rates by new bone and overall percentage of new bone formed were lower than nano group.