bluuebunny/crossref_metadata_2025 huggingface dataset:
A method to measure PET scatter fractions for daily quality control
Authors: de Jong H. W. , Lubberink M. , Watabe H. , Iida H. , Lammertsma A. A.
Published: September 2009

Purpose:

Regular monitoring of PET scanner performance is mandatory to assure quality of acquired data. While extensive performance measurements include many scanner characteristics such as resolution, count rate, uniformity, sensitivity, and scatter fraction (SF), most daily QC protocols are limited to uniformity and sensitivity measurements. These measurements may be too insensitive to detect more subtle drifts in detector gains that could lead to reduced detection of primary and increased detection of scattered events. Current methods to measure SF, such as those prescribed by the NEMA protocols (SF‐NEMA), however, require specially designed phantoms and are too cumbersome to be performed on a daily basis.

Methods:

In this study, a simple and versatile method to determine SF is described. This method (SF‐DAILY) does not require additional measurements, making it suitable for daily QC. The method was validated for four different scanners by comparing results with those obtained with the NEMA 1994 protocol.

Results:

For all scanner types and acquisition modes, excellent agreement was found between SF‐NEMA and SF‐DAILY.

Conclusions:

The proposed method is a very practical and valuable addition to current daily QC protocols. In addition, the method can be used to accurately measure SF in phantoms with other dimensions than the NEMA phantom.
A region growing method for tumor volume segmentation on PET images for rectal and anal cancer patients
Authors: Day Ellen , Betler James , Parda David , Reitz Bodo , Kirichenko Alexander , Mohammadi Seyed , Miften Moyed
Published: September 2009

The application of automated segmentation methods for tumor delineation on‐fluorodeoxyglucose positron emission tomography (FDG‐PET) images presents an opportunity to reduce the interobserver variability in radiotherapy (RT) treatment planning. In this work, three segmentation methods were evaluated and compared for rectal and anal cancer patients: (i) Percentage of the maximum standardized uptake value, (ii) fixed SUV cutoff of 2.5, and (iii) mathematical technique based on a confidence connected region growing (CCRG) method. A phantom study was performed to determine thethreshold value and found to be 43%,. The CCRG method is an iterative scheme that relies on the use of statistics from a specified region in the tumor. The scheme is initialized by a subregion of pixels surrounding the maximum intensity pixel. The mean and standard deviation of this region are measured and the pixels connected to the region are included or not based on the criterion that they are greater than a value derived from the mean and standard deviation. The mean and standard deviation of this new region are then measured and the process repeats. FDG‐PET‐CT imaging studies for 18 patients who received RT were used to evaluate the segmentation methods. A PET avidregion was manually segmented for each patient and the volume was then used to compare the calculated volumes along with the absolute mean difference and range for all methods. For themethod, the volumes were always smaller than thevolume by a mean of 56% and a range of 21%–79%. The volumes from themethod were either smaller or larger than thevolume by a mean of 37% and a range of 2%–130%. The CCRG approach provided the best results with a mean difference of 9% and a range of 1%–27%. Results show that the CCRG technique can be used in the segmentation of tumor volumes on FDG‐PET images, thus providing treatment planners with a clinically viable starting point for tumor delineation and minimizing the interobserver variability in radiotherapy planning.
Malignant lesion segmentation in contrast‐enhanced breast MR images based on the marker‐controlled watershed
Authors: Cui Yunfeng , Tan Yongqiang , Zhao Binsheng , Liberman Laura , Parbhu Rakesh , Kaplan Jennifer , Theodoulou Maria , Hudis Clifford , Schwartz Lawrence H.
Published: September 2009

Breast tumor volume measured on MRI has been used to assess response to neoadjuvant chemotherapy. However, accurate and reproducible delineation of breast lesions can be challenging, since the lesions may have complicated topological structures and heterogeneous intensity distributions. In this article, the authors present an advanced computerized method to semiautomatically segment tumor volumes on T1‐weighted, contrast‐enhanced breast MRI. The method starts with manual selection of a region of interest (ROI) that contains the lesion to be segmented in a single image, followed by automated separation of the lesion volume from its surrounding breast parenchyma by using a unique combination of the image processing techniques including Gaussian mixture modeling and a marker‐controlled watershed transform. Explicitly, the Gaussian mixture modeling is applied to an intensity histogram of the pixels inside the ROI to distinguish the tumor class from other tissues. Based on the ROI and the intensity distribution of the tumor, internal and external markers are determined and the tumor contour is delineated using the marker‐controlled watershed transform. To obtain the tumor volume, the segmented tumor in one slice is propagated to the adjacent slice to form an ROI in that slice. The marker‐controlled watershed segmentation is then used again to obtain a tumor contour in the propagated slice. This procedure is terminated when there is no lesion in an adjacent slice. To reduce measurement variations possibly caused by the manual selection of the ROI, the segmentation result is refined based on an automatically determined ROI based on the segmented volume. The algorithm was applied to 13 patients with breast cancer, prospectively accrued prior to beginning neoadjuvant chemotherapy. Each patient had two MRI scans, a baseline MRI examination prior to commencing neoadjuvant chemotherapy and a 1 week follow‐up after receiving the first dose of neoadjuvant chemotherapy. Blinded to the computer segmentation results, two experienced radiologists manually delineated all tumors independently. The computer results were then compared with the manually generated results using the volume overlap ratio, defined as the intersection of the computer‐ and radiologist‐generated tumor volumes divided by the union of the two. The algorithm reached overall overlap ratios of and in comparison to the two manual segmentation results, respectively. The overall overlap ratio between the two radiologists’ manual segmentations was . Preliminary results suggest that the proposed algorithm is a promising method for assisting in tumor volume measurement in contrast‐enhanced breast MRI.
Noise injection for training artificial neural networks: A comparison with weight decay and early stopping
Authors: Zur Richard M. , Jiang Yulei , Pesce Lorenzo L. , Drukker Karen
Published: September 2009

The purpose of this study was to investigate the effect of a noise injection method on the “overfitting” problem of artificial neural networks (ANNs) in two‐class classification tasks. The authors compared ANNs trained with noise injection to ANNs trained with two other methods for avoiding overfitting: weight decay and early stopping. They also evaluated an automatic algorithm for selecting the magnitude of the noise injection. They performed simulation studies of an exclusive‐or classification task with training datasets of 50, 100, and 200 cases (half normal and half abnormal) and an independent testing dataset of 2000 cases. They also compared the methods using a breast ultrasound dataset of 1126 cases. For simulated training datasets of 50 cases, the area under the receiver operating characteristic curve (AUC) was greater (by 0.03) when training with noise injection than when training without any regularization, and the improvement was greater than those from weight decay and early stopping (both of 0.02). For training datasets of 100 cases, noise injection and weight decay yielded similar increases in the AUC (0.02), whereas early stopping produced a smaller increase (0.01). For training datasets of 200 cases, the increases in the AUC were negligibly small for all methods (0.005). For the ultrasound dataset, noise injection had a greater average AUC than ANNs trained without regularization and a slightly greater average AUC than ANNs trained with weight decay. These results indicate that training ANNs with noise injection can reduce overfitting to a greater degree than early stopping and to a similar degree as weight decay.
Ionization chamber gradient effects in nonstandard beam configurations
Authors: Bouchard Hugo , Seuntjens Jan , Carrier Jean‐Francois , Kawrakow Iwan
Published: September 2009

Purpose:

For the purpose of nonstandard beam reference dosimetry, the current concept of reporting absorbed dose at a point in water located at a representative position in the chamber volume is investigated in detail. As new nonstandard beam reference dosimetry protocols are under development, an evaluation of the role played by the definition of point of measurement could lead to conceptual improvements prior to establishing measurement procedures.

Methods:

The present study uses the current definition of reporting absorbed dose to calculate ionization chamber perturbation factors for two cylindrical chamber models (Exradin A12 and A14) using the Monte Carlo method. The EGSnrc based user‐code EGS̱chamber is used to calculate chamber dose responses of 14 IMRT beams chosen to cause considerable dose gradients over the chamber volume as previously used byBouchard and Seuntjens [“ Ionization chamber‐based reference dosimetry of intensity modulated radiation beams,” Med. Phys. 31(9), 2454–5465 (2004)].

Results:

The study shows conclusively the relative importance of each physical effect involved in the nonstandard beam correction factors of 14 IMRT beams. Of all correction factors involved in the dosimetry of the beams studied, the gradient perturbation correction factor has the highest magnitude, on average, 11% higher compared to reference conditions for the Exradin A12 chamber and about 5% higher for the Extradin A14 chamber. Other perturbation correction factors (i.e.,, , and ) are, on average, less than 0.8% different from reference conditions for the chambers and beams studied. The current approach of reporting measured absorbed dose at a point in water coinciding with the location of the centroid of the chamber is the main factor responsible for large correction factors in nonstandard beam deliveries (e.g., intensity modulated radiation therapy) reported in literature.

Conclusions:

To reduce or eliminate the magnitude of perturbation correction factors in nonstandard beam reference dosimetry, two possible ways to report absorbed dose are suggested: (1) Reporting average dose to the sensitive volume of the chamber filled with water, combined with removing the reference field implicit gradient effect when measuring output factors, and (2) reporting average dose to the chamber itself during output factor verifications. The first option could be adopted if clinical beam correction factors are negligible. The second option could simplify quality assurance procedures when correction factors are not negligible and have to be calculated using Monte Carlo simulations.
Dose prescription complexity versus tumor control probability in biologically conformal radiotherapy
Authors: South C. P. , Evans P. M. , Partridge M.
Published: September 2009

The technical feasibility and potential benefits of voxel‐based nonuniform dose prescriptions for biologically heterogeneous tumors have been widely demonstrated. In some cases, an “ideal” dose prescription has been generated by individualizing the dose to every voxel within the target, but often this voxel‐based prescription has been discretized into a small number of compartments. The number of dose levels utilized and the methods used for prescribing doses and assigning tumor voxels to different dose compartments have varied significantly. The authors present an investigation into the relationship between the complexity of the dose prescription and the tumor control probability (TCP) for a number of these methods. The linear quadratic model of cell killing was used in conjunction with a number of modeled tumors heterogeneous in clonogen density, oxygenation, or proliferation. Models based on simple mathematical functions, published biological data, and biological image data were investigated. Target voxels were assigned to dose compartments using (i) simple rules based on the initial biological distribution, (ii) iterative methods designed to maximize the achievable TCP, or (iii) methods based on an ideal dose prescription. The relative performance of the simple rules was found to depend on the form of heterogeneity of the tumor, while the iterative and ideal dose methods performed comparably for all models investigated. In all cases the maximum achievable TCP was approached within the first few (typically two to five) compartments. Results suggest that irrespective of the pattern of heterogeneity, the optimal dose prescription can be well approximated using only a few dose levels but only if both the compartment boundaries and prescribed dose levels are well chosen.
Dose‐calculation algorithms in the context of inhomogeneity corrections for high energy photon beams
Authors: Papanikolaou Niko , Stathakis Sotirios
Published: September 2009

Radiation therapy has witnessed a plethora of innovations and developments in the past 15 years. Since the introduction of computed tomography for treatment planning there has been a steady introduction of new methods to refine treatment delivery. Imaging continues to be an integral part of the planning, but also the delivery, of modern radiotherapy. However, all the efforts of image guided radiotherapy, intensity‐modulated planning and delivery, adaptive radiotherapy, and everything else that we pride ourselves in having in the armamentarium can fall short, unless there is an accurate dose‐calculation algorithm. The agreement between the calculated and delivered doses is of great significance in radiation therapy since the accuracy of the absorbed dose as prescribed determines the clinical outcome. Dose‐calculation algorithms have evolved greatly over the years in an effort to be more inclusive of the effects that govern the true radiation transport through the human body. In this Vision 20/20 paper, we look back to see how it all started and where things are now in terms of dose algorithms for photon beams and the inclusion of tissue heterogeneities. Convolution‐superposition algorithms have dominated the treatment planning industry for the past few years. Monte Carlo techniques have an inherent accuracy that is superior to any other algorithm and as such will continue to be the gold standard, along with measurements, and maybe one day will be the algorithm of choice for all particle treatment planning in radiation therapy.
2D‐3D registration for prostate radiation therapy based on a statistical model of transmission images
Authors: Munbodh Reshma , Tagare Hemant D. , Chen Zhe , Jaffray David A. , Moseley Douglas J. , Knisely Jonathan P. S. , Duncan James S.
Published: September 2009

Purpose:

In external beam radiation therapy of pelvic sites, patient setup errors can be quantified by registering 2D projection radiographs acquired during treatment to a 3D planning computed tomograph (CT). We present a 2D‐3D registration framework based on a statistical model of the intensity values in the two imaging modalities.

Methods:

The model assumes that intensity values in projection radiographs are independently but not identically distributed due to the nonstationary nature of photon counting noise. Two probability distributions are considered for the intensity values: Poisson and Gaussian. Using maximum likelihood estimation, two similarity measures, maximum likelihood with a Poisson (MLP) and maximum likelihood with Gaussian (MLG), distribution are derived. Further, we investigate the merit of the model‐based registration approach for data obtained with current imaging equipment and doses by comparing the performance of the similarity measures derived to that of the Pearson correlation coefficient (ICC) on accurately collected data of an anthropomorphic phantom of the pelvis and on patient data.

Results:

Registration accuracy was similar for all three similarity measures and surpassed current clinical requirements of for pelvic sites. For pose determination experiments with a kilovoltage (kV) cone‐beam CT (CBCT) and kV projection radiographs of the phantom in the anterior‐posterior (AP) view, registration accuracies were (MLP), (MLG), and (ICC). For kV CBCT and megavoltage (MV) AP portal images of the same phantom, registration accuracies were (MLP), (MLG), and (ICC). Registration of a kV CT and MV AP portal images of a patient was successful in all instances.

Conclusions:

The results indicate that high registration accuracy is achievable with multiple methods including methods that are based on a statistical model of a 3D CT and 2D projection images.
An on‐line replanning method for head and neck adaptive radiotherapya)
Authors: Ahunbay Ergun E. , Peng Cheng , Godley Andrew , Schultz Christopher , Li X. Allen
Published: September 2009

Daily setup for head and neck (HN) radiotherapy (RT) can vary randomly due to neck rotation and anatomy change. These differences cannot be totally corrected by the current practice of image guided RT with translational repositioning. The authors present a novel rapid correction scheme that can be used on‐line to correct both interfractional setup variation and anatomy change for HN RT. The scheme consists of two major steps: (1) Segment aperture morphing (SAM) and (2) segment weight optimization (SWO). SAM is accomplished by applying the spatial relationship between the apertures and the contours of the planning target and organs at risk (OARs) to the new target and OAR contours. The new target contours are transferred from planning target contours to the CT of the day by means of deformable registration (MIMVISTA). The dose distribution for each new aperture was generated using a planning system with a fast dose engine and hardware and was input into a newly developed SWO package using fast sequential quadratic programming. The entire scheme was tested based on the daily CT images acquired for representative HN IMRT cases treated with a linac and CT‐on‐Rails combo. It was found that the target coverage and/or OAR sparing was degraded based on the CT of the day with the current standard repositioning from rigid registration. This degradation can be corrected by the SAM/SWO scheme. The target coverage and OAR sparing for the SAM/SWO plans were found to be equivalent to the original plan. The SAM/SWO process took 5–8 min for the head and neck cases studied. The proposed aperture morphing with weight optimization is an effective on‐line approach for correcting interfractional patient setup and anatomic changes for head and neck cancer radiotherapy.
Modeling of plasmonic heating from individual gold nanoshells for near‐infrared laser‐induced thermal therapy
Authors: Cheong Seong‐Kyun , Krishnan Sunil , Cho Sang Hyun
Published: September 2009

Gold nanoparticles can be engineered to target cancerous cells and at the same time designed to absorb specific wavelengths of light. Consequently, with the presence of optically tunable gold nanoparticles such as gold nanoshells, light can be effectively converted to heat via photothermal effect well enough to raise the temperature of medium surrounding gold nanoshells for thermal ablation or hyperthermia treatments of cancers. In this study, the authors proposed a new computational method to estimate thermal response of gold nanoshells embedded in a tissue‐like medium when illuminated by a near‐infrared (NIR) laser. Specifically, the light transport theory with diffusion approximation was initially applied to model the temperature rise within a medium without gold nanoshells as a result of the dissipation of the NIR laser power throughout the medium. After then, the heat generated by individual gold nanoshells due to photothermal effect was calculated and combined with the results for the medium without gold nanoshells to estimate the global elevation of temperature within the gold nanoshell‐laden medium. The current computational model was tested for its validity using two different phantom examples, one of which was similar to a previously reported phantom experiment. The test demonstrated the capability of the current model in terms of producing qualitatively reasonable results, while it also revealed a number of potential differences in the assumptions for the current model and previous experiment. After an adjustment in the model parameters to properly take into account such differences, the computational results and the experimental data matched reasonably well within the average percentage difference of 10%.
Treatment head disassembly to improve the accuracy of large electron field simulation
Authors: Faddegon Bruce A. , Sawkey Daren , O’Shea Tuathan , McEwen Malcolm , Ross Carl
Published: September 2009

Purpose:

The purposes of this study are to improve the accuracy of source and geometry parameters used in the simulation of large electron fields from a clinical linear accelerator and to evaluate improvement in the accuracy of the calculated dose distributions.

Methods:

The monitor chamber and scattering foils of a clinical machine not in clinical service were removed for direct measurement of component geometry. Dose distributions were measured at various stages of reassembly, reducing the number of geometry variables in the simulation. The measured spot position and beam angle were found to vary with the beam energy. A magnetic field from the bending magnet was found between the exit window and the secondary collimators of sufficient strength to deflect electrons 1 cm off the beam axis at 100 cm from the exit window. The exit window was 0.05 cm thicker than manufacturer's specification, with over half of the increased thickness due to water pressure in the channel used to cool the window. Dose distributions were calculated with Monte Carlo simulation of the treatment head and water phantom using EGSnrc, a code benchmarked at radiotherapy energies for electron scatter and bremsstrahlung production, both critical to the simulation. The secondary scattering foil and monitor chamber offset from the collimator rotation axis were allowed to vary with the beam energy in the simulation to accommodate the deflection of the beam by the magnetic field, which was not simulated.

Results:

The energy varied linearly with bending magnet current to within 1.4% from 6.7 to 19.6 MeV, the bending magnet beginning to saturate at the highest beam energy. The range in secondary foil offset used to account for the magnetic field was 0.09 cm crossplane and 0.15 cm inplane, the range in monitor chamber offset was 0.14 cm crossplane and 0.07 cm inplane. A 1.5%/0.09 cm match or better was obtained to measured depth dose curves. Profiles measured at the depth of maximum dose matched the simulated profiles to 2.6% or better at doses of 80% or more of the dose on the central axis. The profiles along the direction of MLC motion agreed to within 0.16 cm at the edge of the field. There remained a mismatch for the lower beam energies at the edge of the profile that ran parallel to the direction of jaw motion of up to 1.4 cm for the 6 MeV beam, attributed to the MLC support block at the periphery of the field left out of the simulation and to beam deflection by the magnetic field. The possibility of using these results to perform accurate simulation without disassembly is discussed. Phase‐space files were made available for benchmarking beam models and other purposes.

Conclusions:

The match to measured large field dose distributions from clinical electron beams with Monte Carlo simulation was improved with more accurate source details and geometry details closer to manufacturer's specification than previously achieved.
An MLC calibration method using a detector array
Authors: Simon Thomas A. , Kahler Darren , Simon William E. , Fox Christopher , Li Jonathan , Palta Jatinder , Liu Chihray
Published: September 2009

Purpose:

The authors have developed a quantitative calibration method for a multileaf collimator (MLC) which measures individual leaf positions relative to the MLC backup jaw on an Elekta Synergy linear accelerator.

Methods:

The method utilizes a commercially available two‐axis detector array (Profiler 2; Sun Nuclear Corporation, Melbourne, FL). To calibrate the MLC bank, its backup jaw is positioned at the central axis and the opposing jaw is retracted to create a half‐beam configuration. The position of the backup jaws field edge is then measured with the array to obtain what is termed the radiation defined reference line. The positions of the individual leaf ends relative to this reference line are then inferred by the detector response in the leaf end penumbra. Iteratively adjusting and remeasuring the leaf end positions to within specifications completes the calibration. Using the backup jaw as a reference for the leaf end positions is based on three assumptions: (1) The leading edge of an MLC leaf bank is parallel to its backup jaw's leading edge, (2) the backup jaw position is reproducible, and (3) the measured radiation field edge created by each leaf end is representative of that leaf's position. Data from an electronic portal imaging device (EPID) were used in a similar analysis to check the results obtained with the array.

Results:

The relative leaf end positions measured with the array differed from those measured with the EPID by an average of 0.11 ±0.09 mm per leaf. The maximum leaf positional change measured with the Profiler 2 over a 3 month period was 0.51 mm. A leaf positional accuracy of ±0.4 mm is easily attainable through the iterative calibration process. The method requires an average of 40 min to measure both leaf banks.

Conclusions:

This work demonstrates that the Profiler 2 is an effective tool for efficient and quantitative MLC quality assurance and calibration.
Automatic marker detection and 3D position reconstruction using cine EPID images for SBRT verification
Authors: Park Sang‐June , Ionascu Dan , Hacker Fred , Mamon Harvey , Berbeco Ross
Published: September 2009

In previous studies, an electronic portal imaging device (EPID) in cine mode was used for validating respiratory gating and stereotactic body radiation therapy (SBRT) by tracking implanted fiducials. The manual marker tracking methods that were used were time and labor intensive, limiting the utility of the validation. The authors have developed an automatic algorithm to quickly and accurately extract the markers in EPID images and reconstruct their 3D positions. Studies have been performed with gold fiducials placed in solid water and dynamic thorax phantoms. In addition, the authors have examined the cases of five patients being treated under an SBRT protocol for hepatic metastases. For each case, a sequence of images was created by collecting the exit radiation using the EPID. The markers were detected and recognized using an image processing algorithm based on the Laplacian of Gaussian function. To reduce false marker detection, a marker registration technique was applied using image intensity as well as the geometric spatial transformations between the reference marker positions produced from the projection of 3D CT images and the estimated marker positions. An average marker position in 3D was reconstructed by backprojecting, towards the source, the position of each marker on the 2D image plane. From the static phantom study, spatial accuracies of were achieved in both 2D and 3D marker locations. From the dynamic phantom study, using only the Laplacian of the Gaussian algorithm, the marker detection success rate was 88.8%. However, adding a marker registration technique which utilizes prior CT information, the detection success rate was increased to 100%. From the SBRT patient study, intrafractional tumor motion (3.1–11.3 mm) in the SI direction was measured using the 2D images. The interfractional patient setup errors (0.1–12.7 mm) in the SI, AP, and LR directions were obtained from the average marker locations reconstructed in 3D and compared to the reference planning CT image. The authors have developed an automatic algorithm to extract marker locations from MV images and have evaluated its performance. The measured intrafractional tumor motion and the interfractional daily patient setup error can be used for off‐line retrospective verification of SBRT.
Monte Carlo study on secondary neutrons in passive carbon‐ion radiotherapy: Identification of the main source and reduction in the secondary neutron dose
Authors: Yonai Shunsuke , Matsufuji Naruhiro , Kanai Tatsuaki
Published: September 2009

Purpose:

Recent successful results in passive carbon‐ion radiotherapy allow the patient to live for a longer time and allow younger patients to receive the radiotherapy. Undesired radiation exposure in normal tissues far from the target volume is considerably lower than that close to the treatment target, but it is considered to be non‐negligible in the estimation of the secondary cancer risk. Therefore, it is very important to reduce the undesired secondary neutron exposure in passive carbon‐ion radiotherapy without influencing the clinical beam. In this study, the source components in which the secondary neutrons are produced during passive carbon‐ion radiotherapy were identified and the method to reduce the secondary neutron dose effectively based on the identification of the main sources without influencing the clinical beam was investigated.

Methods:

A Monte Carlo study with the PHITS code was performed by assuming the beamline at the Heavy‐Ion Medical Accelerator in Chiba (HIMAC). At first, the authors investigated the main sources of secondary neutrons in passive carbon‐ion radiotherapy. Next, they investigated the reduction in the neutron dose with various modifications of the beamline device that is the most dominant in the neutron production. Finally, they investigated the use of an additional shield for the patient.

Results:

It was shown that the main source is the secondary neutrons produced in the four‐leaf collimator (FLC) used as a precollimator at HIAMC, of which contribution in the total neutron ambient dose equivalent is more than 70%. The investigations showed that the modification of the FLC can reduce the neutron dose at positions close to the beam axis by 70% and the FLC is very useful not only for the collimation of the primary beam but also the reduction in the secondary neutrons. Also, an additional shield for the patient is very effective to reduce the neutron dose at positions farther than 50 cm from the beam axis. Finally, they showed that the neutron dose can be reduced by approximately 70% at any position without influencing the primary beam used in treatment.

Conclusions:

This study was performed by assuming the HIMAC beamline; however, this study provides important information for reoptimizing the arrangement and the materials of beamline devices and designing a new facility for passive carbon‐ion radiotherapy and probably passive proton radiotherapy.
Automated segmentation of lungs with severe interstitial lung disease in CT
Authors: Wang Jiahui , Li Feng , Li Qiang
Published: September 2009

Purpose:

Accurate segmentation of lungs with severe interstitial lung disease (ILD) in thoracic computed tomography (CT) is an important and difficult task in the development of computer‐aided diagnosis (CAD) systems. Therefore, we developed in this study a texture analysis‐based method for accurate segmentation of lungs with severe ILD in multidetector CT scans.

Methods:

Our database consisted of 76 CT scans, including 31 normal cases and 45 abnormal cases with moderate or severe ILD. The lungs in three selected slices for each CT scan were first manually delineated by a medical physicist, and then confirmed or revised by an expert chest radiologist, and they were used as the reference standard for lung segmentation. To segment the lungs, we first employed a CT value thresholding technique to obtain an initial lung estimate, including normal and mild ILD lung parenchyma. We then used texture‐feature images derived from the co‐occurrence matrix to further identify abnormal lung regions with severe ILD. Finally, we combined the identified abnormal lung regions with the initial lungs to generate the final lung segmentation result. The overlap rate, volume agreement, mean absolute distance (MAD), and maximum absolute distance between the automatically segmented lungs and the reference lungs were employed to evaluate the performance of the segmentation method.

Results:

Our segmentation method achieved a mean overlap rate of 96.7%, a mean volume agreement of 98.5%, a mean MAD of, and a mean of for all the cases in our database; a mean overlap rate of 97.7%, a mean volume agreement of 99.0%, a mean MAD of , and a mean of for the 31 normal cases; and a mean overlap rate of 96.1%, a mean volume agreement of 98.1%, a mean MAD of , and a mean of for the 45 abnormal cases with ILD.

Conclusions:

Our lung segmentation method provided accurate segmentation results for abnormal CT scans with severe ILD and would be useful for developing CAD systems for quantification, detection, and diagnosis of ILD.
Optimization of radiography applications using x‐ray beams emitted by compact accelerators. Part I. Monte Carlo study of the hard x‐ray spectrum
Authors: Marziani M. , Taibi A. , Di Domenico G. , Gambaccini M.
Published: September 2009

Purpose:

A 3‐year project called LABSYNC has been recently funded by the European Commission, with the aim of designing a radiation facility based on a compact light source, i.e., a laboratory‐sized commercial synchrotron, capable of accelerating electrons up to 6 or 20 MeV. An accurate spectral description of hard x rays emitted from thin targets, irradiated by electron beams circulating in the storage ring, is of primary interest for the design and the characterization of a beamline. This article, Part I, aims at optimizing some of the parameters which are critical for the design of medical applications based on the above compact light source. The goal was to evaluate the dependence of photon fluence and beam monochromaticity on electron‐beam energy, target material, and thickness.

Methods:

The transport of 6 and 20 MeV electrons in a thin molybdenum, rhodium, and tungsten target is studied by means of Monte Carlo simulations usingMCNPX. Configurations of the x‐ray output port, different from the default forward‐directed emission of the beam, are also investigated. A comparison with reference spectra for general diagnostic radiology and mammography is carried out.

Results:

It is shown that the emitted x‐ray beams can be far more intense than those generated by conventional x‐ray tubes for radiography applications. The profiles of the calculated polychromatic spectra resemble those generated by conventional x‐ray tubes, with x‐ray energies up to the energy of the incident‐electron beam. An appreciable improvement in the monochromaticity of the beams can be obtained by viewing the x‐ray emission from an output port antiparallel to the direction of the incident‐electron beam.

Conclusions:

The optimum target thickness for tungsten target spectra is practically constrained by a trade‐off between bremsstrahlung efficiency and focal‐spot size requirements. A larger margin for optimization of target thickness is probably available for mammographic spectra. The constraint of a backward‐directed (or, to a lesser extent, orthogonal) output port is to be considered mandatory for minimizing the high‐energy tail of the spectral distribution and keeping the radiation dose to a reasonable level. It is also fundamental to evaluate the impact of the high‐energy tail of the emitted spectra in x‐ray imaging applications, since the energy range involved is significantly beyond the diagnostic range. This topic will be dealt with in Part II of the article.
Commissioning Varian enhanced dynamic wedge in the PINNACLE treatment planning system using Gafchromic™ EBT film
Authors: Fontanarosa Davide , Orlandini Lucia Clara , Andriani Italo , Bernardi Luca
Published: September 2009

In external photon beam therapies, the technique of dynamic wedge is a well established method for dose inhomogeneity compensation. The introduction of the enhanced dynamic wedge (EDW) on Varian LINACs considerably improved the pre‐existing techniques. In the process of commissioning a Varian LINAC into a treatment planning system (TPS), the user is required to import quite a few measurements of EDW profiles and percentage depth doses (PDDs). Standard measurement devices like ionization chambers in a water phantom are not the most indicated ones for this situation where each measurement point is obtained by integrating during the entire exposure: Measurements would result to be a very laborious and time consuming operation, most of the times not practically possible. The goal of the present work is to introduce an alternative and hands‐on procedure to perform the measurements using a combination of Gafchromic™ EBT films, irradiated sideways in one single shot for both profiles and PDDs, and a single standard ionization chamber. The scanned profiles obtained at different depths have easily been imported in the TPS; for the PDD measurements, a correction was proven necessary to account for a “self‐shielding” effect introduced by the presence of the films themselves, when irradiated sideways, resulting in an underestimation of the dose at deeper depths. A correction curve was derived comparing TPS open field validated measurements with the curves extracted from Gafchromic™ EBT films. Finally, the curve was applied to all the wedged fields PDD measurements and could minimize the errors. The comparison for the photon beam between the measured and the calculated 48 profiles and 12 PDDs (field sizes from , wedge angles ranging from 15° to 60°) was acceptable. The confidence limit (CL) was used as fit indicator, as suggested by the ESTRO Booklet No. 7: For the investigated PDDs the maximum value was 6.40 in the build up region and 2.83 beyond the maximum dose point; regarding cross beam profiles, the CLs were below 3 for 85% of the points within the field and for 96% of the points outside the field; in the penumbra region, a more appropriate parameter to evaluate the agreement between calculated and measured doses is the distance to agreement; only 73% of the profiles had CLs below 15, but for the remaining ones, distance‐to‐agreement values were within . A hundred ionization chamber point dose measurements (for square and elongated fields at different depth and for points in field and out of field) were performed in a water phantom and 98 of them confirmed the TPS calculations with differences lower than 3% and considerably lower in most of the cases. This article gives valuable guidance and insight to other physicists attempting to approach EDW commissioning in the PINNACLE TPS software using Gafchromic™ EBT films.
Comparison of arc‐modulated cone beam therapy and helical tomotherapy for three different types of cancer
Authors: Ulrich Silke , Sterzing Florian , Nill Simeon , Schubert Kai , Herfarth Klaus K. , Debus Jürgen , Oelfke Uwe
Published: September 2009

Purpose:

Arc‐modulated cone beam therapy (AMCBT) is a fast treatment technique deliverable in a single rotation with a conventional C‐arm shaped linac. In this planning study, the authors assess the dosimetric properties of single‐arc therapy in comparison to helical tomotherapy for three different tumor types.

Methods:

Treatment plans for three patients with prostate carcinoma, three patients with anal cancer, and three patients with head and neck cancer were optimized for helical tomotherapy and AMCBT. The dosimetric comparison of the two techniques is based on physical quantities derived from dose‐volume histograms.

Results:

For prostate cancer, the quality of dose distributions calculated for AMCBT was of equal quality as that generated for tomotherapy with the additional benefits of a faster delivery and a lower integral dose. For highly complex geometries, the plan quality achievable with helical tomotherapy could not be achieved with arc‐modulated cone beam therapy.

Conclusions:

Rotation therapy with a conventional linac in a single arc is capable to deliver a high and homogeneous dose to the target and spare organs at risk. Advantages of this technique are a fast treatment time and a lower integral dose in comparison to helical tomotherapy. For highly complex cases, e.g., with several target regions, the dose shaping capabilities of AMCBT are inferior to those of tomotherapy. However, treatment plans for AMCBT were also clinically acceptable.
Dose spread functions in computed tomography: A Monte Carlo study
Authors: Boone John M.
Published: September 2009

Purpose:

Current CT dosimetry employing CTDI methodology has come under fire in recent years, partially in response to the increasing width of collimated x‐ray fields in modern CT scanners. This study was conducted to provide a better understanding of the radiation dose distributions in CT.

Methods:

Monte Carlo simulations were used to evaluate radiation dose distributions along the axis arising from CT imaging in cylindrical phantoms. Mathematical cylinders were simulated with compositions of water, polymethyl methacrylate (PMMA), and polyethylene. Cylinder diameters from were studied. X‐ray spectra typical of several CT manufacturers (80, 100, 120, and ) were used. In addition to no bow tie filter, the head and body bow tie filters from modern General Electric and Siemens CT scanners were evaluated. Each cylinder was divided into three concentric regions of equal volume such that the energy deposited is proportional to dose for each region. Two additional dose assessment regions, central and edge locations in diameter, were included for comparisons to measurements. Dose spread functions (DSFs) were computed for a wide number of imaging parameters.

Results:

DSFs generally exhibit a biexponential falloff from the position. For a very narrow primary beam input , DSFs demonstrated significant low amplitude long range scatter dose tails. For body imaging conditions ( diameter in water), the DSF at the center showed at full width at tenth maximum (FWTM), while at the edge the FWTM was . Polyethylene phantoms exhibited wider DSFs than PMMA or water, as did higher tube voltages in any material. The FWTM were 80, 180, and for 10, 30, and phantom diameters, respectively, at the center in water at with a typical body bow tie filter. Scatter to primary dose ratios (SPRs) increased with phantom diameter from 4 at the center ( diameter) for a diameter cylinder to for a diameter cylinder. The SPRs increased dramatically at the center of the phantom compared to the edge. For the three equal area regions, the edge to center SPRs for a diameter phantom were , 3.5, and 6.3, respectively.

Conclusions:

DSFs demonstrate low amplitude long ranging tails which reach considerable distances in cylindrical phantoms. The buildup that results from these long‐ranged tails increases at the center of the field (at) with increasing scan length. The DSF distributions lend a better understanding of the trends in CT dose deposition over a range of relevant imaging parameters. The DSFs as well as other related data are available to interested parties using EPAPS at http://www.aip.org/pubservs/epaps.html.
Near real-time water vapor distribution surface rendering using Ordinary KrigingThis article is one of a series of papers published in this Special Issue on the theme GEODESY.
Authors: Tao Wenyou , Gao Yang
Published: September 2009

Based on the near real-time Global Positioning System (GPS) precise pointing positioning (PPP)-inferred water vapor system recently developed at the University of Calgary, Calgary, Alberta, an Ordinary Kriging procedure has been developed to predict the local and regional precipitable water vapor (PWV) and describe its distribution over Canada using limited available data. The Ordinary Kriging procedure includes five steps: (1) quantifying PWV spatial structure by calculating an experimental semivariogram; (2) fitting semivariogram models (spherical, exponential, and Gaussian) with nonlinear, weighted least squares; (3) determining the best-fitted model with cross-validation analysis; (4) estimating whole PWV maps by Ordinary Kriging interpolation; and (5) outputting kriging standard error maps. The 24 h variogram analysis shows that the correctly calculated experimental semivariogram is essential to the accuracy of the kriged maps, which depends on the configuration of the sites, lag step, and lag tolerance. The optimal lag step and lag tolerance for the current Canadian GPS network configuration are 5° and 2.5°, respectively. Among the three semivariogram models, the spherical model fails in its performance most of the time, and the best hourly fitted semivariogram model is either the exponential (90%) or the Gaussian (10%) model. The Gaussian-model-based Ordinary Kriging process produces more detailed maps. The surface maps of the kriging standard errors indicate that the area between longitudes –125° and –60° and latitudes 44° and 54° has higher accuracy due to higher availability of data.
Assessment of wavelets analysis for carrier-phase multipath mitigationThis article is one of a series of papers published in this Special Issue on the theme GEODESY.
Authors: El-Ghazouly Ahmed A. , Elhabiby Mohamed , El-Sheimy Naser
Published: September 2009

In carrier-phase measurements, which are the most precise observations for Global Positioning System (GPS) relative positioning, multipath error is still a factor that interferes with achieving the desired accuracy. Various improvements in receiver and antenna technologies, as well as modeling strategies, have resulted in better ways of coping with this error source. However, errors caused by multipath can be as large as 5 cm, which is not an acceptable accuracy, especially in precise surveying applications like deformation monitoring. In this paper, a full assessment of different wavelets techniques that can be used in multipath mitigation is made to evaluate the optimum way of using wavelets to reduce or remove this type of error. Also, a new approach based on the wavelet detrending technique is introduced to remove carrier-phase multipath error in the measurement domain. To mitigate multipath, GPS double-difference observables are fed to an adaptive wavelet analysis procedure based on high- and low-pass filter decomposition with different levels of resolution. Consequently, the observable sequences are corrected; these corrected observables can then be used to reduce the ambiguity search volume during the initial float solution stage. Meanwhile, double-difference observations with multipath mitigation offer an efficient method for obtaining a better baseline solution.