Spatial Dose Research Articles

Dosimetry in brain tumor phantom at 15 MV 3D conformal radiation therapy

Glioblastoma multiforme (GBM) is the most common, aggressive, highly malignant and infiltrative of all brain tumors with low rate of control. The main goal of this work was to evaluate the spatial dose distribution into a GBM simulator inside a head phantom exposed to a 15 MV 3D conformal radiation therapy in order to validate internal doses. A head and neck phantom developed by the Ionizing Radiation Research Group (NRI) was used on the experiments. Such phantom holds the following synthetic structures: brain and spinal cord, skull, cervical and thoracic vertebrae, jaw, hyoid bone, laryngeal cartilages, head and neck muscles and skin. Computer tomography (CT) of the simulator was taken, capturing a set of contrasted references. Therapy Radiation planning (TPS) was performed based on those CT images, satisfying a 200 cGy prescribed dose split in three irradiation fields. The TPS assumed 97% of prescribed dose cover the prescribed treatment volume (PTV). Radiochromic films in a solid water phantom provided dose response as a function of optical density. Spatial dosimetric distribution was generated by radiochromic film samples at coronal, sagittal-anterior and sagittal-posterior positions, inserted into tumor simulator and brain. The spatial dose profiles held 70 to 120% of the prescribed dose. In spite of the stratified profile, as opposed to the smooth dose profile from TPS, the tumor internal doses were within a 5% deviation from 214.4 cGy evaluated by TPS. 83.2% of the points with a gamma value of less than 1 (3%/3mm) for TPS and experimental values, respectively. At the tumor, measured at coronal section, a few dark spots in the film caused the appearance of outlier points in 13-15% of dose deviation percentage. And, as final conclusion, such dosimeter choice and the physical anthropomorphic and anthropometric phantom provided an efficient method for validating radiotherapy protocols.

Development and validation of radiochromic film dosimetry and Monte Carlo simulation tools for acquisition of absolute, high-spatial resolution longitudinal dose distributions in ocular proton therapy

Dosimetric validation of prescribed clinical plans in ocular proton therapy requires the use of adapted instrumentation providing high accuracy and spatial resolution. The aim of this work was to develop two independent tools based on Monte Carlo (MC) and EBT3 films to perform high spatial resolution longitudinal dose maps in water for clinical Spread-Out Bragg peaks (SOBP). The first tool is based on EBT3 films, irradiated in beam alignment with a tilt angle of 7° and scanned with high resolution of 300 dpi. Dedicated software was developed to convert Pixel Values (PV) to absolute dose, which makes use of a calibration curve and a correction function of the LET based on MC. MC tool was implemented to generate dose maps in a grid plane with the same configuration (300 dpi, longitudinal alignment, tilt angle of 7°). Both tools were tested for a same SOBP and two collimators of different shapes and apertures. Validation of EBT3 and MC methods was performed by dose map comparison (gamma index test) to a silicon diode and film, respectively. Good agreement was found between diode and film (gamma index >99%) and between MC and film (gamma index >83%). At the plateau, accuracy in dose is better than 0.3% and maximum divergences are of 5% at the SOBP entrance, for both tools. Inconvenience of films is high pixel dispersion (2.3%) and uncertainty in film positioning. MCNPX overestimates angular deflection of Multiple Coulomb Scattering (MCS) and involves lateral profiles 0.5 mm wider at 20% isodose. The mesh tally size in the transversal direction has an impact on dose distributions if spherical or cylindrical beam modifiers are used due to dose convolution in a larger mesh volume, reflected in a slight underdose at lateral edges in deeper depths. The defaults of EBT3 and MC tools concern localized areas outside the Planning Target Volume (PTV) and therefore could potentially be used to perform dosimetric validation of prescribed clinical plans. Work is in progress to further explore their potential and limitations.

The use of radiochromic EBT2 film for the quality assurance and dosimetric verification of 3D conformal radiotherapy using Microtek ScanMaker 9800XL flatbed scanner

Radiochromic and radiographic films are widely used for radiation dosimetry due to the advantage of high spatial resolution and two‐dimensional dose measurement. Different types of scanners, including various models of flatbed scanners, have been used as part of the dosimetry readout procedure. This paper focuses on the characterization of the EBT2 film response in combination with a Microtek ScanMaker 9800XL scanner and the subsequent use in the dosimetric verification of a 3D conformal radiotherapy treatment. The film reproducibility and scanner uniformity of the Microtek ScanMaker 9800XL was studied. A three‐field 3D conformal radiotherapy treatment was planned on an anthropomorphic phantom and EBT2 film measurements were carried out to verify the treatment. The interfilm reproducibility was found to be 0.25%. Over a period of three months, the films darkened by 1%. The scanner reproducibility was ± 2% and a nonuniformity was ±1.9% along the direction perpendicular to the scan direction. EBT2 measurements showed an underdose of 6.2% at high‐dose region compared to TPS predicted dose. This may be due to the inability of the treatment planning system to predict the correct dose distribution in the presence of tissue inhomogeneities and the uncertainty of the scanner reproducibility and uniformity. The use of EBT2 film in conjunction with the axial CT image of the anthropomorphic phantom allows the evaluation of the anatomical location of dose discrepancies between the EBT2 measured dose distribution and TPS predicted dose distribution.PACS number: 87.55.Qr

고용량 옥소 치료 시 3차원적 공간선량률 측정 및 연구

Spatial dose rates of high dose therapy patients were Measured Three dimensional (X, Y, Z) distributions. I have constructed geometrical an aluminum support structure for spatial dose meters placed in 5 different heights, 8 different azimuthal angles, 6 different time interval and distance 100 cm from High dose therapy patients. when the height of vertical plane Spatial dose distribution is 100 cm, the Spatial dose rates is max and the error range is low. the vertical plane Spatial dose rates was found to be 71.85 on the average at a distance of 100 cm, height 100 cm, from the patients 24 hours after oral administration. I divided 12 patients into two groups. I have analysed group A (drinking 5 L water) and group B (drinking 3 L water) in order to measure decrease spatial dose rates. I have found the spatial distributions of patient dose rates is in group A and in group B by 24 after oral administration. the reduction factor was found to be approximately 54 % through drinking 5 L water during 24 hours.

A software tool for 3D dose verification and analysis

The main recent developments in radiotherapy have focused on improved treatment techniques in order to generate further significant improvements in patient prognosis. There is now an internationally recognised need to improve 3D verification of highly conformal radiotherapy treatments. This is because of the very high dose gradients used in modern treatment techniques, which can result in a small error in the spatial dose distribution leading to a serious complication. In order to gain the full benefits of using 3D dosimetric technologies (such as gel dosimetry), it is vital to use 3D evaluation methods and algorithms. We present in this paper a software solution that provides a comprehensive 3D dose evaluation and analysis. The software is applied to gel dosimetry, which is based on magnetic resonance imaging (MRI) as a read-out method. The software can also be used to compare any two dose distributions, such as two distributions planned using different methods of treatment planning systems, or different dose calculation algorithms.

Dose‐shaping using targeted sparse optimization

Dose volume histograms (DVHs) are common tools in radiation therapy treatment planning to characterize plan quality. As statistical metrics, DVHs provide a compact summary of the underlying plan at the cost of losing spatial information: the same or similar dose-volume histograms can arise from substantially different spatial dose maps. This is exactly the reason why physicians and physicists scrutinize dose maps even after they satisfy all DVH endpoints numerically. However, up to this point, little has been done to control spatial phenomena, such as the spatial distribution of hot spots, which has significant clinical implications. To this end, the authors propose a novel objective function that enables a more direct tradeoff between target coverage, organ-sparing, and planning target volume (PTV) homogeneity, and presents our findings from four prostate cases, a pancreas case, and a head-and-neck case to illustrate the advantages and general applicability of our method. In designing the energy minimization objective (E tot (sparse)), the authors utilized the following robust cost functions: (1) an asymmetric linear well function to allow differential penalties for underdose, relaxation of prescription dose, and overdose in the PTV; (2) a two-piece linear function to heavily penalize high dose and mildly penalize low and intermediate dose in organs-at risk (OARs); and (3) a total variation energy, i.e., the L1 norm applied to the first-order approximation of the dose gradient in the PTV. By minimizing a weighted sum of these robust costs, general conformity to dose prescription and dose-gradient prescription is achieved while encouraging prescription violations to follow a Laplace distribution. In contrast, conventional quadratic objectives are associated with a Gaussian distribution of violations, which is less forgiving to large violations of prescription than the Laplace distribution. As a result, the proposed objective E tot (sparse) improves tradeoff between planning goals by "sacrificing" voxels that have already been violated to improve PTV coverage, PTV homogeneity, and/or OAR-sparing. In doing so, overall plan quality is increased since these large violations only arise if a net reduction in E tot (sparse) occurs as a result. For example, large violations to dose prescription in the PTV in E tot (sparse)-optimized plans will naturally localize to voxels in and around PTV-OAR overlaps where OAR-sparing may be increased without compromising target coverage. The authors compared the results of our method and the corresponding clinical plans using analyses of DVH plots, dose maps, and two quantitative metrics that quantify PTV homogeneity and overdose. These metrics do not penalize underdose since Etot (sparse)-optimized plans were planned such that their target coverage was similar or better than that of the clinical plans. Finally, plan deliverability was assessed with the 2D modulation index. The proposed method was implemented using IBM's CPLEX optimization package (ILOG CPLEX, Sunnyvale, CA) and required 1-4 min to solve with a 12-core Intel i7 processor. In the testing procedure, the authors optimized for several points on the Pareto surface of four 7-field 6MV prostate cases that were optimized for different levels of PTV homogeneity and OAR-sparing. The generated results were compared against each other and the clinical plan by analyzing their DVH plots and dose maps. After developing intuition by planning the four prostate cases, which had relatively few tradeoffs, the authors applied our method to a 7-field 6 MV pancreas case and a 9-field 6MV head-and-neck case to test the potential impact of our method on more challenging cases. The authors found that our formulation: (1) provided excellent flexibility for balancing OAR-sparing with PTV homogeneity; and (2) permitted the dose planner more control over the evolution of the PTV's spatial dose distribution than conventional objective functions. In particular, Etot (sparse)-optimized plans for the pancreas case and head-and-neck case exhibited substantially improved sparing of the spinal cord and parotid glands, respectively, while maintaining or improving sparing for other OARs and markedly improving PTV homogeneity. Plan deliverability for E tot (sparse)-optimized plans was shown to be better than their associated clinical plans, according to the two-dimensional modulation index. These results suggest that our formulation may be used to improve dose-shaping and OAR-sparing for complicated disease sites, such as the pancreas or head and neck. Furthermore, our objective function and constraints are linear and constitute a linear program, which converges to the global minimum quickly, and can be easily implemented in treatment planning software. Thus, the authors expect fast translation of our method to the clinic where it may have a positive impact on plan quality for challenging disease sites.

SU-E-T-123: Development of a Methodology to Assess the Image Quality of the ExacTracTM Localization System Using the PIPSproTM Software and Unfors RaySafe Xi R/F Detector

Purpose: To develop a methodology of assessing and evaluating the consistency of the spatial resolution, dose, energy, noise, contrast, and geometrical accuracy of the BrainLab ExacTrac™ system. Methods: A device was constructed to hold the QCkV‐1 Phantom firmly and reproducibly against the face of the flat panel detectors. Two image sets per detector were acquired using the ExacTrac present console setting‐‐Cranial Standard. The two image sets were analyzed in PIPSpro™ and the following metrics were recorded: spatial resolution (f 30 , f 40 , f 50 ), noise and Contrast‐to‐Noise Ratio. Geometrical image accuracy was evaluated by assessing the length of QCkV‐1. Dose and kVp were recorded using the Unfors RaySafe Xi R/F Detector. The kVp and dose were evaluated for the following: Cranial (80kV,80mA,80ms), Thorax (120kV,160mA,160ms), Abdomen (120kV,160mA,130ms) and Pelvis(120kV,160mA,160ms). Results: With regards to spatial resolution, the mean values of the f 30 , f 40 and f 50 for the left detector were, 1.39±0.09, 1.24±0.10 and 1.15±0.07 respectively, while the right detector were 1.38±0.07, 1.22±0.08 and 1.13±0.10, respectively. Mean CNR for the left and right detectors was 114±10 and 116±13, respectively. For geometrical accuracy, both detectors had a measured image length of the QCkV‐1 of 218.8±0.3mm. The left detector showed dose measurements of 1.37±0.01 mGy (CS), 12.56±0.03 mGy (TS), 10.08±0.04 mGy (AS) and 12.58±0.05 mGy (PS) while the right detector showed 1.27±0.01 mGy (CS), 11.48±0.03 mGy (TS), 9.21±0.04 mGy (AS) and 11.50±0.04 mGy (PS), respectively. For energy, the left detector had kVp readings of 81.2±0.3 (CS), 121.1±0.4 (TS), 121.0±0.3 (AS) and 121.0±0.3 (PS) and the right detector had 79.9±0.1 (CS), 117.2±0.2 (TS), 117.2±0.2 (AS) and 117.2±0.2 (PS). Conclusion: A methodology was developed to assess the basic image quality parameters recommended by TG‐142 for the ExacTrac™ system. The ExacTrac system shows a consistent dose, kVp, spatial resolution, CNR and geometrical accuracy for each detector over the evaluated timeframe.

TH-C-108-01: Radiobiological Models in Brachytherapy Treatment Planning and Evaluation

Brachytherapy utilizes a multitude of radioactive sources and treatment techniques that often exhibit drastically different spatial and temporal dose delivery patterns from one another and from external beam radiotherapy. Typical photon energies vary from 0.02 MeV to 1 MeV and decay half-lives vary from days to years. Treatments can consist of single-fraction continuous low-dose-rate irradiations over a period of days or months to multi-fraction high-dose-rate irradiations of different dose fractionations. The clinical impact of such diverse spatial-temporal variations cannot be adequately assessed using traditional physical dose-based indices alone because these indices do not take into account the complex interplay between the dynamics of dose delivery and the biological response of the irradiated cells. Radiobiological models that capture the interacting effects of dose delivery with cellular biology can potentially provide a useful clinical tool for comparing and optimizing the relative clinical effectiveness of different brachytherapy treatment strategies. These models have been used increasingly by clinical medical physicists over the last decade in research settings. Currently, there are several different models presented in the literature with a range of applications and limitations. Information on model parameters, uncertainties, and their impact on model predictions are also scattered in the literature. The primary goal of this educational course is to provide a comprehensive review of existing radiobiological models and parameters, and their use in the evaluation of selected brachytherapy modalities. Particular emphasis will be placed on discussion of model limitations that may hinder the proper interpretation of model predictions and practical implementation. Learning Objectives: 1. To understand the rationale and basis of existing radiobiological models used in the evaluation of brachytherapy treatments. 2. To recognize the underlying assumptions and limitations of existing models and their proper application in the relative comparison of competing brachytherapy modalities. 3. To be aware of the pitfalls regarding the selection, use, and interpretation of radiobiological models in treatment planning and evaluation ZC would like to acknowledge partial support of NIH grant R01 CA134627

WE‐G‐108‐02: Oncospace: A Database Designed for Personalized Medicine in Radiation Oncology

Purpose: The Oncospace database aggregates treatment planning and clinical information about prior patients facilitating extraction of knowledge from prior courses of care. The goal is to use this knowledge to influence clinical decisions, quality and safety of care for new patients. Methods: The Oncospace website, built in C# and ASP.NET, accesses the MS SQLServer database for analysis. The data tables are designed to support patient geometry, targets and organs at risk (OAR) and their spatial relationships, dose distributions, toxicities, diagnosis and disease progression, chemotherapy and medications, laboratory values, patient histories and demographics. Data is collected directly from the treatment planning system and the oncology information system (OIS). Point of service data collection is facilitated with tablet (iPad) forms linked to the OIS. Results: Web pages have been built to answer the following: A) For a selected toxicity and OAR, display the dose volume histogram (DVH) and colorize them by the maximum toxicity grade of the patient while identifying a selected patients DVH B) For a selected OAR and percent volume (%V), find the lowest dose achieved from all patients whose %V is closer to the selected target volume? C) For a given diagnosis, toxicity and treatment, display the aggregate trend in toxicity from start of treatment (acute) through several year follow‐up (late)? Oncospace currently supports: and a full H&N database, a multi‐institutional pancreatic stereotactic trial, and shape database for automated planning pancreas cancer. Conclusion: Oncospace can provide fast access to large amounts of data through complex queries designed to answer specific clinical questions to influence the safety and quality of care for new patients. This system can be used in the clinical setting to assess both plan quality and outcome expectations for new patients based on the data of prior patients. Funding for this research was provided by the Commonwealth Foundation, Elekta/IMPAC Medical Systems, Inc., Philips Radiation Oncology Sytems, and the Johns Hopkins University.

SU-E-J-132: Lung Dose Reduction From Patient Specific 4D Motion Based Non-Uniform Dose Prescription in Lung IMRT Treatment

Purpose: Motion of the tumor target in lung can be significant in patients. Traditionally lung dose is uniformly prescribed to the entire Internal Tumor Volume (ITV) with certain setup margin. Such uniform dose prescription may deliver quite high dose to the normal tissue surrounding the target volume due to tumor motion. This study explores patient specific motion based non‐uniform dose prescription that is to deliver prescription dose to the target while maximizing the sparing of the surrounding normal tissue. Methods: Patient 4D CT images were collected during simulation. CT phases were deformably registered. The spatial tracks of the tumor and surrounding tissue voxels were extracted from the transform matrix. The voxel dose to the tumor target and the surrounding tissue was evaluated at each phase and then summed together. Simulated Annealing algorithm was used to search for the spatial dose prescription distribution that delivers sufficient tumor voxel dose while minimizing the surrounding normal tissue dose. Results: Simple phantom and patients studies were included. The optimization process generally converged within 60 seconds to obtain a solution for non‐uniform dose prescription. The Result has shown a reduction in the adjacent lung tissue as great as 18% while maintaining the tumor dose. Conclusion: This study proposed a methodology for a non‐uniform dose prescription that would deliver sufficient dose to the moving lung tumor target while maximizing the sparing of the surrounding lung tissue. The beam delivery and the interplay effect are being further studied.

WE‐C‐103‐01: Attenuation‐Based Dynamic CT Bowtie Filtration: Evaluation of Signal Homogenization and Dose Reduction by Monte‐Carlo Simulation

Purpose: CT bowtie filters modulate X‐ray intensity across the fan beam, compensating for decreasing absorption due to shorter X‐ray path lengths through patient body periphery. The effect of replacing static CT beam‐shaping filter geometry by a filter geometry dynamically adapted to the attenuation of objects of elliptic cross‐section has been evaluated with regard to its potential for signal homogenization and radiation exposure reduction. Methods: A theoretical model of a beam‐shaping filter that adapts its attenuation profile to subjects of elliptic cross‐section as a function of fan‐and projection‐angle has been developed. For comparison, the static geometrical shape of the bowtie filter of a real CT system has been measured at different fan angles (0°–21°) using Compton spectroscopy. Both bowtie models were implemented in a Geant4 Monte‐Carlo simulation of MDCT, and attenuation profiles of a water phantom of elliptic cross‐section (16.0 cm semimajor, 12.5 cm semiminor axes) and maps of dose absorbed within the phantom were simulated for projections a.p. to lateral in steps of 10° (2×108 photons/projection). Exploiting phantom symmetry, total spatial dose distributions within the phantom were reconstructed and used to evaluate relative radiation exposure reduction achievable by replacing static with dynamic bowtie filtration in CT. Results: With dynamic filtration, attenuation profiles of the elliptical phantom become constant, i.e. independent of fan‐and projection‐angle, whereas the measured static filter produces asymmetric profiles. Compared to a CT acquisition without any beam‐shaping filter, measured static and proposed dynamic beam‐shaping filter allow reducing total deposited dose by 33% and 48%, respectively. Thus, an additional radiation exposure reduction by about 15% can be achieved with a filter dynamically adapted to subject shape. Conclusion: Homogenization of the signal and a significant additional reduction of radiation exposure could be achieved by replacing static with dynamic beam‐shaping filtration for CT examinations of subjects of elliptic cross‐section. This research project was funded by the German Federal Ministry of Education and Research (BMBF) within the collaboration project: Innovative Methods for the Optimization of Radiological Applications in Biomedical Imaging, grant numbers 02NUK008G/B

TH‐F‐105‐01: BEST IN PHYSICS (THERAPY) — The Emergence of Non‐Uniform Spatio‐Temporal Fractionation Schemes Within the Standard BED Model

Purpose: We consider the fractionation problem in intensity‐modulated proton therapy (IMPT). It is known that a low α/β ratio in the normal tissue favors a hyperfractionated regimen. In contrast, a low α/β ratio in the tumor gives rise to hypofractionation. However, in current clinical practice, the patient is treated with the same dose distribution in each fraction. We demonstrate that the standard biologically equivalent dose (BED) model gives rise to non‐uniform fractionation schemes, i.e. for an intermediate range of α/β ratios, it can be optimal to deliver distinct dose distributions in different fractions. Methods: We consider the simultaneous optimization of IMPT dose distributions and the fractionation scheme. This is achieved by simultaneously optimizing multiple (possibly distinct) IMPT plans for different fractions. To that end, we consider an objective function based on the cumulative BED distribution delivered over all fractions. Results: It is shown that the optimal treatment regimen may consist of distinct IMPT plans. For proton therapy this has an intuitive explanation: The dose in the entrance region of the proton beam is mostly independent of the range. Thus, an incident proton beam can primarily irradiate the distal part of the tumor in one fraction, and the proximal part in the subsequent fraction ‐ without significantly changing the dose in the normal tissue. This can be interpreted as the possibility of hypofractionating subregions of the tumor while continuing to hyperfractionate in the normal tissue. Conclusion: To date, the determination of the fractionation scheme and the optimization of the spatial dose distribution in IMRT and IMPT are considered independently. Here, we demonstrate that both problems are interdependent. In particular, the therapeutic ratio can potentially be improved by delivering distinct dose distributions in different fractions.

SU‐E‐T‐502: In Search of the Optimum Ion for Radiotherapy

Purpose: To investigate the physical and biological properties and the clinical potential of several different ions through computer simulations. Methods: Using the Geant4 Monte Carlo toolkit, we calculated spatial dose and LET distributions in a water phantom for monoenergetic beams for four candidate ions with the same range (28 cm in water): 207 MeV/u protons, 244 MeV/u 3He ions, 206 MeV/u 4He ions, and 400 MeV/u 12C ions. An ideal broad beam of 6 cm in diameter was used in the simulations. The scoring voxel volume was set to 1 cubic millimeter. We also recorded the dose contributions from several major nuclear fragments. Furthermore, data for a 5‐cm RBE‐weighted dose SOBP for 12C ions with a range of 30 cm were analyzed. Results: Simulation results showed advantages and disadvantages of each ion. For instance, a 12C ion beam produces the sharpest and narrowest Bragg peak, and the smallest penumbra, but it has the highest entrance to peak dose ratio, and highest and longest nuclear fragmentation tail. Furthermore, the lateral dose halo effect of 12C is substantially greater than other ions. For the same range in water, 3He and 4He ions show very similar features. They have smaller lateral penumbrae than protons, and much smaller fragmentation tails compared with 12C ions. Although protons have the largest lateral penumbra and widest Bragg peak, they do not have an observable fragmentation tail. For a pristine beam of 400 MeV/u 12C ions, the fragmentation tail dose is 15% of the peak dose. In the case of 5‐cm SOBP with 30‐cm range of 12C ions, the fragmentation tail dose can be as high as 30% of the maximum dose. Conclusion: Each type of ion has special advantages and disadvantages. Further research is needed to consider additional factors such as energy dependence, cost effectiveness and RBE. NCI grant P01CA021239

Spatial resolution improvement and dose reduction potential for inner ear CT imaging using a z‐axis deconvolution technique

To assess the z-axis resolution improvement and dose reduction potential achieved using a z-axis deconvolution technique with iterative reconstruction (IR) relative to filtered backprojection (FBP) images created with the use of a z-axis comb filter. Each of three phantoms were scanned with two different acquisition modes: (1) an ultrahigh resolution (UHR) scan mode that uses a comb filter in the fan angle direction to increase in-plane spatial resolution and (2) a z-axis ultrahigh spatial resolution (zUHR) scan mode that uses comb filters in both the fan and cone angle directions to improve both in-plane and z-axis spatial resolution. All other scanning parameters were identical. First, the ACR CT Accreditation phantom, rotated by 90° so that the high-contrast spatial resolution targets were parallel to the coronal plane, was scanned to assess limiting spatial resolution and image noise. Second, section sensitivity profiles (SSPs) were measured using a copper foil embedded in an acrylic cylinder and the full-width-at-half-maximum (FWHM) and full-width-at-tenth-maximum (FWTM) of the SSPs were calculated. Third, an anthropomorphic head phantom containing a human skull was scanned to assess clinical acceptability for imaging of the temporal bone. For each scan, FBP images were reconstructed for the zUHR scan using the narrowest image thickness available. For the CT accreditation phantom, zUHR images were also reconstructed using an IR algorithm (SAFIRE, Siemens Healthcare, Forchheim, Germany) to assess the influence of the IR algorithm on image noise. A z-axis deconvolution technique combined with the IR algorithm was used to reconstruct images at the narrowest image thickness possible from the UHR scan data. Images of the ACR and head phantoms were reformatted into the coronal plane. The head phantom images were evaluated by a neuroradiologist to assess acceptability for use in patients undergoing clinically indicated CT imaging of the temporal bone. The limiting spatial resolution was 12 lp/cm for the FBP-zUHR images and the IR-UHR images, although visual assessment indicated a slight improvement for the IR-UHR images. Image noise was 213.0, 181.8, and 153.5 for the FBP-zUHR, IR-zUHR, and IR-UHR images, respectively. While the FWHM was essentially the same for the FBP-zUHR and IR-UHR images, the FWTM of the IR-UHR images was almost 50% smaller compared to the FBP-zUHR images (0.83 vs 1.25 mm, respectively). Images of the anthropomorphic head phantom were judged to be of higher quality for the IR-UHR images compared to the FBP-zUHR images. With use of a z-axis deconvolution technique, z-axis spatial resolution was improved for scans acquired using a comb filter only in the fan angle direction relative to FBP images acquired with a comb filter in both the fan and cone angle directions. By avoiding use of the comb filter in the cone angle direction and use of an IR algorithm, image noise was substantially reduced for the same scanner output (CTDIvol). Thus, overall image quality (spatial resolution and image noise) can be maintained relative to the FBP-zUHR technique at a lower radiation dose.

Neural network modelling of dose distribution and dose uniformity in the Tunisian Gamma Irradiator

In this paper an approach to model dose distributions, isodose curves and dose uniformity in the Tunisian Gamma Irradiation Facility using artificial neural networks (ANNs) are described. For this purpose, measurements were carried out at different points in the irradiation cell using polymethyl methacrylate dosemeters. The calculated and experimental results are compared and good agreement is observed showing that ANNs can be used as an efficient tool for modelling dose distribution in the gamma irradiation facility. Monte Carlo (MC) photon-transport simulation techniques have been used to evaluate the spatial dose distribution for extensive benchmarking. ANN approach appears to be a significant advance over the time-consuming MC or the less accurate regression methods for dose mapping. As a second application, a detailed dose mapping using two different product densities was carried out. The minimum and maximum dose locations and dose uniformity as a function of the irradiated volume for each product density were determined. Good agreement between ANN modelling and experimental results was achieved.

변형근치유방절제술 환자의 Ion chamber 변화에 따른 디지털 흉부 영상의 화질 평가

변형근치유방절제술을 시행한 환자는 일반 여성에 비해 수술로 인한 양측 유방의 두께 차이가 나타나게 되고 이에 따른 감약 차가 생기게 된다. 이에 본 연구는 디지털 영상 특성평가의 객관적인 기준이 되는 MTF를 측정하여 변형근치유방절제술을 시행한 환자들의 흉부촬영에서 적합한 Ion chamber 조합의 기준을 제시하고자 하였다. 디텍터에 위치한 chamber에 좌측 1, 우측 2, 가운데 3으로 번호를 지정하고 엣지팬텀을 부착하여 실험 영상을 획득하였다. 획득한 영상의 해상력 특성 평가는 Matlab(R2007a)를 이용하여 50% MTF 공간주파수의 해상력 평가와 흡수선량을 측정하였다. 실험결과에서 1+3과 2+3조합의 평균 노출조건, 공간주파수, 흡수선량은 각각 2.745 mAs, 1.925 lp/mm, 0.668 mGy로 다른 조합과 비교하여 적은 선량으로 높은 해상력 특성과 높은 DQE를 나타내었다. 따라서 변형근치유방절제술을 시행한 환자의 디지털 흉부영상의 촬영에서는 본 연구에서 제시하는 chamber 조합은 피폭선량 감소와 영상 화질의 향상에 대한 보상이 가능하여 향후 임상에서 적용 및 활용 가능한 chamber 기준이 될 것으로 사료된다. The patients who had been operated total mastectomy are different from general women in their breasts thickness due to breast surgery. As a result, digital chest image from total mastectomy patients will be different attenuation. The main objective for this study is to show that a proper Ion chamber standard combination measuring MTF which is objective basis for Digital image, when be x-ray for total mastectomy patient. We have designed the unique number that shown Left is 1, Right is 2, Center is 3 and have put the edge phantom on detector ion chamber. Lastly, we have obtained experiment images. The evaluations of all image quality have measured by 50% MTF of spatial resolution and absorption dose using Matlab(R2007a). The result showed that average exposure condition, MTF value, absorption dose for 1+3 and 2+3 combinations were 2.745 mAs, 1.925 lp/mm, 0.688 mGy. Consequently, that showed high MTF, DQE and low dose than other combinations. Therefore, a proper changes of ion chambers are able to improve image quality and to reduce radiation exposure when be X-ray for total mastectomy patients. Also, it will be possible to standard for application chamber combination and utilization on clinical detection.

Evaluation of spatial and seasonal radioactivity dose fluctuations in a Wierzchowska Górna limestone cave

Measurements of the dose rate changes were carried out in order to assess seasonal and spatial radioactivity variations in the largest limestone cave of the Polish Jura Wierzchowska Górna. Thermoluminescence detectors, which were annealed, calibrated and protected against humidity were used. Measurements were repeated four times in 13 locations to observe possible changes. The external dose rate was in the range of 0.004–0.106 mGy/quarter. The results were influenced by the detector locations – lower doses were estimated closer to the cave entrance and the highest doses were in the so-called ‘primitive man room’. Doses measured in four periods were statistically significantly different. The external dose level as well as seasonal and spatial dose changes measured in the cave were low. In other caves where external doses are higher, seasonal and spatial dose changes may have a stronger impact on radiological hazard.

Assessment and characterization of the total geometric uncertainty in Gamma Knife radiosurgery using polymer gels

This work proposes and implements an experimental methodology, based on polymer gels, for assessing the total geometric uncertainty and characterizing its contributors in Gamma Knife (GK) radiosurgery. A treatment plan consisting of 26, 4-mm GK single shot dose distributions, covering an extended region of the Leksell stereotactic space, was prepared and delivered to a polymer gel filled polymethyl methacrylate (PMMA) head phantom (16 cm diameter) used to accurately reproduce every link in the GK treatment chain. The center of each shot served as a "control point" in the assessment of the GK total geometric uncertainty, which depends on (a) the spatial dose delivery uncertainty of the PERFEXION GK unit used in this work, (b) the spatial distortions inherent in MR images commonly used for target delineation, and (c) the geometric uncertainty contributor associated with the image registration procedure performed by the Leksell GammaPlan (LGP) treatment planning system (TPS), in the case that registration is directly based on the apparent fiducial locations depicted in each MR image by the N-shaped rods on the Leksell localization box. The irradiated phantom was MR imaged at 1.5 T employing a T2-weighted pulse sequence. Four image series were acquired by alternating the frequency encoding axis and reversing the read gradient polarity, thus allowing the characterization of the MR-related spatial distortions. MR spatial distortions stemming from main field (B0) inhomogeneity as well as from susceptibility and chemical shift phenomena (also known as sequence dependent distortions) were found to be of the order of 0.5 mm, while those owing to gradient nonlinearities (also known as sequence independent distortions) were found to increase with distance from the MR scanner isocenter extending up to 0.47 mm at an Euclidean distance of 69.6 mm. Regarding the LGP image registration procedure, the corresponding average contribution to the total geometric uncertainty ranged from 0.34 to 0.80 mm. The average total geometric uncertainty, which also includes the GK spatial dose delivery uncertainty, was found equal to (0.88 ± 0.16), (0.88 ± 0.26), (1.02 ± 0.09), and (1.15 ± 0.24) mm for the MR image series acquired with the read gradient polarity (direction) set toward right, left, posterior, and anterior, respectively. The implemented methodology seems capable of assessing the total geometric uncertainty, as well as of characterizing its contributors, ascribed to the entire GK treatment delivery (i.e., from MR imaging to GK dose delivery) for an extended region of the Leksell stereotactic space. Results obtained indicate that the selection of both the frequency encoding axis and the read gradient polarity during MRI acquisition may affect the magnitude as well as the spatial components of the total geometric uncertainty.

Samarium-doped oxyfluoride borophosphate glasses for x-ray dosimetry in Microbeam Radiation Therapy

One of the key parameters and most difficult challenges related to Microbeam Radiation Therapy (MRT) is the exact measurement of radiation dose delivered. The approach presented here is based on the conversion of the oxidation state of samarium ions (embedded in a suitable glass host) upon exposure to high energy radiation. The conversion from Sm3+ to Sm2+ under the effect of high x-ray irradiation doses has been studied in four oxyfluoride glasses based on Ca, Mg, Sr and Ba. These glasses can easily be prepared in air, contrary to pure fluoride glasses. They provide good transparency in the visible range, essential for analysis by confocal microscopy. Only the Mg-based glasses exhibited a clear conversion of Sm3+ to Sm2+ under x-ray exposure; and hence show potential for use as MRT dosimetry. The conversion did not saturate even up to ~20kGy (dose in air at the sample surface) under a 50keV synchrotron beam. Further, we were able to determine the spatial dose profile of the x-ray beam through confocal fluoroscopic microscopy; and the dose profile matched closely that from the Monte Carlo simulation.

User needs elicitation via analytic hierarchy process (AHP). A case study on a Computed Tomography (CT) scanner

BackgroundThe rigorous elicitation of user needs is a crucial step for both medical device design and purchasing. However, user needs elicitation is often based on qualitative methods whose findings can be difficult to integrate into medical decision-making. This paper describes the application of AHP to elicit user needs for a new CT scanner for use in a public hospital.MethodsAHP was used to design a hierarchy of 12 needs for a new CT scanner, grouped into 4 homogenous categories, and to prepare a paper questionnaire to investigate the relative priorities of these. The questionnaire was completed by 5 senior clinicians working in a variety of clinical specialisations and departments in the same Italian public hospital.ResultsAlthough safety and performance were considered the most important issues, user needs changed according to clinical scenario. For elective surgery, the five most important needs were: spatial resolution, processing software, radiation dose, patient monitoring, and contrast medium. For emergency, the top five most important needs were: patient monitoring, radiation dose, contrast medium control, speed run, spatial resolution.ConclusionsAHP effectively supported user need elicitation, helping to develop an analytic and intelligible framework of decision-making. User needs varied according to working scenario (elective versus emergency medicine) more than clinical specialization. This method should be considered by practitioners involved in decisions about new medical technology, whether that be during device design or before deciding whether to allocate budgets for new medical devices according to clinical functions or according to hospital department.