bluuebunny/crossref_metadata_2025_split huggingface dataset:
Comparative evaluation of image quality from three CT simulation scanners
Authors: McCann Claire , Alasti Hamideh 
Published: February 2007

Today, radiation therapy (RT) is moving toward increased radiation dose to the tumor as a result of 3D conformal RT (3DCRT) and intensity‐modulated RT (IMRT), which have been made possible by advances in volumetric‐based image planning with digital imaging systems such as computed tomography (CT). Treatment planning for such RT requires superior CT image quality. Our goal in this study was to evaluate and to compare the image quality of three unique CT simulation scanners available at our center for both single‐ and multiple‐slice helical scanners. These scanners included a conventional 70‐cm bore single‐slice scanner (Philips Medical Systems), a large 85‐cm bore single‐slice scanner (Philips Medical Systems), and a 70‐cm bore multislice scanner (GE Medical Systems). Image quality was evaluated in terms of image noise, low‐contrast detectability (LCD), limiting spatial resolution (modulation transfer function), and slice thickness accuracy in accordance with guidelines set out by the AAPM. A commercially available Catphan® phantom was used to characterize image quality for both axial and helical modes of scanning. We found that image quality was generally comparable for all scanners. Limiting spatial resolution and slice thickness accuracy were comparable for all three scanners for both scanning modes. The multislice unit was superior in terms of noise content, resulting in improved visualization of small, low‐contrast objects, which is of significant clinical importance, particularly for soft tissue delineation. In addition, the multislice unit optimizes volume coverage speed and longitudinal resolution without compromising image quality, a significant advantage for the radiation oncology environment.PACS numbers: 87.57.Ce, 87.59.Fm, 87.57.Nk
A dose‐volume‐based tool for evaluating and ranking IMRT treatment plans
Authors: Miften Moyed M. , Das Shiva K. , Su Min , Marks Lawrence B. 
Published: February 2007

External beam radiotherapy is commonly used for patients with cancer. While tumor shrinkage and palliation are frequently achieved, local control and cure remain elusive for many cancers. With regard to local control, the fundamental problem is that radiotherapy‐induced normal tissue injury limits the dose that can be delivered to the tumor. While intensity‐modulated radiation therapy (IMRT) allows for the delivery of higher tumor doses and the sparing of proximal critical structures, multiple competing plans can be generated based on dosimetric and/or biological constraints that need to be considered/compared. In this work, an IMRT treatment plan evaluation and ranking tool, based on dosimetric criteria, is presented. The treatment plan with the highest uncomplicated target conformity index is ranked at the top. The is a dose‐volume‐based index that considers both a target conformity index (TCI) and a normal tissue‐sparing index (NTSI). is designed to assist in the process of judging the merit of a clinical treatment plan. To demonstrate the utility of this tool, several competing lung and prostate IMRT treatment plans are compared. Results show that the plan with the highest values accomplished the competing goals of tumor coverage and critical structures sparing best, among rival treatment plans for both treatment sites. The study demonstrates, first, that dose‐volume‐based indices, which summarize complex dose distributions through a single index, can be used to automatically select the optimal plan among competing plans, and second, that this dose‐volume‐based index may be appropriate for ranking IMRT dose distributions.PACS numbers: 87.53.‐j, 87.53.Tf
MR perfusion measurements on pharyngeal tumors: Comparison of quantification strategies
Authors: Hietschold Volker , Kittner Thomas , Schreyer Michele , Appold Steffen , Beuthien‐Baumann Bettina , Laniado Michael 
Published: February 2007

For the case of pharyngeal carcinomas, the clinical value as well as the stability of several evaluation methods of MR tomographic perfusion measurement are compared. Eighteen patients suffering from histologically proven squamous cell carcinomas were investigated by MR tomography (1.5 T, 0.2 mmol/kg Gd‐DTPA) prior to and during radiation therapy. Perfusion measurements were performed using a double‐echo FLASH sequence. Parameters describing regional blood flow, blood volume, mean transit time, and interstitial concentration of contrast medium (CM) were calculated, applying seven different combinations of correction approaches (separating the shortening of and , arterial input function (AIF), and tumor shunts). Their correlations to MR independent tumor physiological parameters were analyzed (metabolic activity measurements using 18F‐FDG‐PET, polarographical measurement, tumor volume). Significant improvements of the correlation between perfusion‐dependent and other tumor physiological parameters could be achieved by decoupling the shortening of and and by applying of the tumor shunt model. Deconvolution from the AIF deteriorated the correlation. Therefore, the elimination of the shortening due to interstitial CM proves to be essential for MR perfusion measurements on contrast medium uptaking lesions. Depending on the measurement conditions (temporal resolution, signal‐to‐noise ratio), the consideration of the AIF can even make the results significantly worse by introducing additional measuring errors.PACS numbers: 87.61.‐c
Comparison of six phantoms for entrance skin dose evaluation in 11 standard X‐ray examinations
Authors: Compagnone Gaetano , Pagan Laura , Bergamini Carlo 
Published: February 2007

Entrance skin dose (ESD) is an important parameter for assessing the dose received by a patient in a single radiographic exposure. The most useful way to evaluate ESD is either by direct measurement on phantoms using an ionization chamber or using calculations based on a mathematical model. We compared six phantoms (three anthropomorphic, two physical, and one mathematical) in 11 standard clinical examinations (anterior‐posterior (AP) abdomen, posterior‐anterior (PA) chest, AP chest, lateral (LAT) chest, AP lumbar spine, LAT lumbar spine, LAT lumbo‐sacral joint, AP pelvis, PA skull, LAT skull, and AP urinary tract) for two reasons: to determine the conversion factors to use for ESDs measured on different phantoms and to validate the mathematical model used. First, a comparison was done between the three anthropomorphic phantoms (Alderson Rando, chest RSD‐77SPL, and 3M skull) and the two physical phantoms (Uniform and AAPM 31); for each examination we obtained “relative entrance skin dose factors.” Second, we compared these five phantoms with the mathematical phantom: the overall accuracy of the model was better than 14%. Total mathematical model and total ionization chamber uncertainties, calculated by quadratic propagation of errors of the single components, were estimated to be on the order of and , respectively. To reduce the most significant source of uncertainty, the overall accuracy of the model was recalculated using new backscatter factors. The overall accuracy of the model improved: better than 12%. For each examination an anthropomorphic phantom was considered as the gold standard relative to the physical phantoms. In this way, it was possible to analyze the variations in phantom design and characteristics. Finally, the mathematical model was validated by more than 400 measurements taken on different phantoms and using a variety of radiological equipment. We conclude that the mathematical model can be used satisfactorily in ESD evaluations because it optimizes available resources, it is based on direct measurements, and it is an easy dynamic tool.PACS number(s): 87.66.Xa
Dosimetric evaluation of GAFCHROMIC® XR type T and XR type R films
Authors: Dini Sharifeh A. , Koona Rafiq A. , Ashburn John R. , Meigooni Ali S. 
Published: February 2007

The high spatial resolution of radiochromic film makes it ideal for dosimetric measurements and dose distributions in regions of high dose gradient. Intensity‐modulated radiation therapy, intravascular brachytherapy, and eye‐plaque radiation therapy demand precise spatial dosimetric calculations. Such precision is not possible with conventional dosimeters, such as thermoluminescent dosimeters and ionization chambers. Recently, new GAFCHROMIC® XR type T and type R films have been developed for radiation dosimetry, specifically in interventional radiology procedures. Dosimetric characteristics (i.e., linearity, post‐exposure density growth, energy dependence, dose‐rate dependence, and UV light sensitivity) of these new films were investigated. To evaluate the clinical applications of these films, their characteristics were compared with other commercially available film models. GAFCHROMIC® XR type T and type R films were found to be more sensitive to low‐energy doses as compared with GAFCHROMIC® MD‐55 films.PACS numbers: 87.66‐a, 87.53‐j
A novel platform simulating irregular motion to enhance assessment of respiration‐correlated radiation therapy procedures
Authors: Fitzpatrick Mathew J. , Starkschall George , Balter Peter , Antolak John A. , Guerrero Thomas , Nelson Christopher , Keall Paul , Mohan Radhe 
Published: February 2007

Respiratory motion continues to present challenges in the delivery of radiation therapy to tumors in the thorax and abdomen by causing movement of structures within those areas. Several approaches to account for this movement in the planning and delivery of treatment have been developed over the past several years. To assist in the development and assessment of various techniques for respiration‐correlated radiation therapy, a platform capable of programmable irregular longitudinal motion has been designed and fabricated to simulate intrafractional respiratory motion. A sliding platform and the base on which it was mounted were constructed from polycarbonate plastic, and a stepper motor provided platform motion. Respiratory motion data, either artificially generated on a spreadsheet or extracted from respiratory monitoring files, were converted to a format appropriate for driving the stepper motor. Various phantoms were placed on top of the platform and used in studies related to respiration‐correlated radiation therapy. Several applications of the platform were demonstrated, such as improving the quality of acquisition of time‐dependent computed tomography image datasets, comparing various methods of acquiring such datasets, and implementing feedback‐guided breath hold treatment delivery procedures. This study showed that a platform capable of programmable irregular motion is a useful tool for the development and assessment of procedures related to the effects of respiratory motion in radiation therapy.PACS number: 87.66.Xa
Experience in implementing continuous arterial spin labeling on a commercial MR scanner
Authors: Steger Theodore R. , Jackson Edward F. 
Published: February 2007

Continuous arterial spin labeling (CASL) is a technique for performing quantitative perfusion measurements without the need for exogenous contrast agent administration. This technique has seen limited use in the clinic due to problems of poor sensitivity and the potential for artifacts. In addition, CASL requires the application of long‐duration radiofrequency pulses and the acquisition of a large number of images, which can cause difficulties when implemented on commercial MR scanners. This work details our experience in implementing CASL on a commercial MR scanner for the measurement of cerebral blood flow, including pitfalls regarding hardware, radiofrequency energy deposition, and practical application in human subjects. Results of studies to determine the optimal acquisition procedures are also presented.PACS number: 87.61.‐c
Limited accuracy of dose calculation for large fields at deep depths using the BrainSCAN v5.21 treatment‐planning system
Authors: Hsi Wen C. , Zhang Yunkai , Kirk Michael C. , Bernard Damian , Chu James C.H. 
Published: February 2007

The Varian 120 multileaf collimator (MLC) has a leaf thickness of 5 mm projected at the isocenter plane and can deliver a radiation beam of large field size (up to 30 cm) to be used in intensity‐modulated radiotherapy (IMRT). Often the dose must be delivered to depths greater than 20 cm. Therefore, during the commissioning of the BrainSCAN v5.21 or any radiation treatment‐planning (RTP) systems, extensive testing of dose and monitor unit calculations must encompass the field sizes (1 cm to 30 cm) and the prescription depths (1 cm to 20 cm). Accordingly, the central‐axis percent depth doses (PDDs) and off‐axis percentage profiles must be measured at several depths for various field sizes. The data for this study were acquired with a 6‐MV X‐ray beam from a Varian 2100EX LINAC with a water phantom at a source‐to‐surface distance (SSD) of 100 cm. These measurements were also used to generate a photon beam module, based on a photon pencil beam dose‐calculation algorithm with a fast‐Fourier transform method. To commission the photon beam module used in our BrainSCAN RTP system, we performed a quantitative comparison of measured and calculated central‐axis depth doses and off‐axis profiles. Utilizing the principles of dose difference and distance‐to‐agreement introduced by Van Dyk et al. [Commissioning and quality assurance of treatment planning computers. Int J Radiat Oncol Biol Phys. 1993; 26:261—273], agreements between calculated and measured doses are and for the regions of low‐ and high‐dose gradients, respectively. However, large errors (up to and for 20‐cm and 30‐cm fields, respectively, at the depth 20 cm) were observed for monitor unit calculations. For a given field size, the disagreement increased with the depth. Similarly, for a given depth the disagreement also increased with the field size. These large systematic errors were caused by using the tissue maximum ratio (TMR) in BrainSCAN v5.21 without considering increased field size as depth increased. These errors have been reported to BrainLAB.PACS number: 87.53.‐j
Advantages of inflatable multichannel endorectal applicator in the neo‐adjuvant treatment of patients with locally advanced rectal cancer with HDR brachytherapy
Authors: Devic Slobodan , Vuong Té , Moftah Belal 
Published: February 2007

High‐dose rate endorectal brachytherapy (HDR‐EBT) is mainly used as a palliative treatment modality. In this paper, we compare dosimetry distributions for a single‐channel catheter (Miami) applicator with distributions of the inflatable multichannel (Novi Sad) endorectal applicator. The comparisons were made with respect to dose coverage to the clinical tumor volume as well as to the bladder, rectal wall, prostate, and bone marrow. Our results suggest that a multichannel applicator provides better sparing of the bone marrow by 50%, clinically uninvolved parts of the rectal wall by 70%, and bladder and prostate (in the case of male patients) by 100% in terms of ratio of median doses to critical organ volume for single‐ and multichannel endorectal applicators. Our results justify the advantage of using a multichannel endorectal brachytherapy applicator as a neo‐adjuvant treatment of patients with locally advanced rectal cancer.PACS numbers: 87.53.Jw, 87.53.Tf
Virtual micro MLC commissioning
Authors: Drever Laura , Dickof Peter 
Published: February 2007

The resolution of multileaf collimators (MLCs) is limited by their finite leaf width. A commercial package (HD‐270™) uses 3D couch translation and leaf adjustments to emulate smaller leaf widths. In this paper, we report on the commissioning of this feature using software testing, dial gauge measurements, and film dosimetry. We also identify a variety of limitations: software bugs and truncation artifacts, MLC leaf positioning uncertainties (random variations, systematic gantry dependence and backlash), and uncertainties in couch positioning. These reduce the capabilities of this implementation below that achievable theoretically.PACS numbers: 87.53.Kn, 87.53.Uv, 87.53.Xd
Maximum MLC opening effect in dynamic delivery of IMRT: leaf‐positional analysis
Authors: Zygmanski Piotr , Hacker Fred , Friesen Scott , Rodenbush Robin , Lu Hsiao‐Ming , Chin Lee 
Published: February 2007

The analysis of dynamic multileaf collimator (MLC) positions for the delivered intensity‐modulated radiotherapy (IMRT) plans is crucial in that it may capture dose delivery problems otherwise difficult to observe and quantify in the conventional dosimetric measurements with film or with an ionization chamber. In some IMRT systems, delivery of IMRT fields starts with a maximum MLC opening (roughly the shape of the target in the beam's‐eye view) and then proceeds to the subsequent dynamic MLC subfields. No irradiation is required in going from the initial segment (maximum opening) to the next one, and theoretically, no dose should be delivered in that initial moment. However, due to a finite sampling time of the MLC controller, the finite speed of the MLC, and a finite leaf tolerance, there may be some dose delivered between the first and the second segment. The amount of the excess dose is higher for larger dose rates and for a smaller number of the total monitor units per IMRT field. The magnitude of the dose errors could be in the order of a few percent. Effects similar to the maximum MLC opening may occur in other situations as well, for instance, when leaves are forced to move over large distances in a short time. Confounding this are dose errors due to the uncertainty in the MLC transmission. The analysis of the actual leaf positions recorded in the dynamic MLC log file is helpful in differentiating between the two types of errors and in determining the optimal dynamic MLC delivery parameters.PACS numbers: 87.53.‐j, 87.90.+y
A feasibility study of the Dynamic Phantom scanner for quality assurance of beam profiles at various gantry angles
Authors: Zhang Yunkai , Hsi Wen C. , Chu James C.H. , Bernard Damian B. , Abrams Ross A. 
Published: February 2007

The effect of gantry rotation on beam profiles of photon and electron beams is an important issue in quality assurance for radiotherapy. To address variations in the profiles of photon and electron beams at different gantry angles, a Dynamic Phantom scanner composed of a scanning Lucite block was designed as a cross‐beam‐profile scanner. To our knowledge, differences between scanned profiles acquired at different gantry angles with a small size Lucite block and those acquired a full‐size water phantom have not been previously investigated. We therefore performed a feasibility study for a first prototype Dynamic Phantom scanner without a gantry attachment mount. Radiation beams from a Varian LINAC 21EX and 2100C were used. Photon beams (6 MV and 18 MV) were shaped by either collimator jaws or a Varian 120 Multileaf (MLC) collimator, and electron beams (6 MeV, 12 MeV, and 20 MeV) were shaped by a treatment cone. To investigate the effect on profiles by using a Lucite block, a quantitative comparison of scanned profiles with the Dynamic Phantom and a full‐size water phantom was first performed at a 0° gantry angle for both photon and electron beams. For photon beam profiles defined by jaws at 1.0 cm and 5.0 cm depths of Lucite (i.e., at 1.1 cm and 5.7 cm depth of water), a good agreement (less than 1% variation) inside the field edge was observed between profiles scanned with the Dynamic Phantom and with a water phantom. The use of Lucite in the Dynamic Phantom resulted in reduced penumbra width (about 0.5 mm out of 5 mm to 8 mm) and reduced (1% to 2%) scatter dose beyond the field edges for both 6 MV and 18 MV beams, compared with the water phantom scanner. For profiles of the MLC‐shaped 6 MV photon beam, a similar agreement was observed. For profiles of electron beams scanned at 2.9 cm depth of Lucite (i.e., at 3.3 cm depth of water), larger disagreements in profiles (3% to 4%) and penumbra width (3 mm to 4 mm out of 12 mm) were observed. Additional profiles with the gantry at 90° and 270° were performed for both MLC‐ and jaw‐shaped photon beams and electron beams to evaluate the effect of gantry rotation. General good agreement is seen (less than 1 % variation) at all field sizes for collimator‐shaped 6 MV and 18 MV photon beams. Similar variations observed for MLC‐shaped photon beams indicate that the uncertainty in MLC position is similar to that for the collimator jaws. We conclude that the Dynamic Phantom scanner is a useful device for the routine quality assurance on beam profiles of photon beams and for constancy check on electron beams at various gantry angles. Caution should be taken when using this device to acquire basic electron dosimetry data.PACS number: 87.53.‐j
Image processing for IMRT QA dosimetry
Authors: Zaini Mehran R. , Forest Gary J. , Loshek David D. 
Published: February 2007

We have automated the determination of the placement location of the dosimetry ion chamber within intensity‐modulated radiotherapy (IMRT) fields, as part of streamlining the entire IMRT quality assurance process. This paper describes the mathematical image‐processing techniques to arrive at the appropriate measurement locations within the planar dose maps of the IMRT fields. A specific spot within the found region is identified based on its flatness, radiation magnitude, location, area, and the avoidance of the interleaf spaces. The techniques used include applying a Laplacian, dilation, erosion, region identification, and measurement point selection based on three parameters: the size of the erosion operator, the gradient, and the importance of the area of a region versus its magnitude. These three parameters are adjustable by the user. However, the first one requires tweaking in extremely rare occasions, the gradient requires rare adjustments, and the last parameter needs occasional fine‐tuning. This algorithm has been tested in over 50 cases. In about 5% of cases, the algorithm does not find a measurement point due to the extremely steep and narrow regions within the fluence maps. In such cases, manual selection of a point is allowed by our code, which is also difficult to ascertain, since the fluence map does not yield itself to an appropriate measurement point selection.PACS numbers: 87.53.Xd, 87.66.Cd, 87.57.Nk
A method for deconvolution of integrated electronic portal images to obtain incident fluence for dose reconstruction
Authors: Renner Wendel Dean , Norton Kevin , Holmes Timothy 
Published: February 2007

A method to convert integrated electronic portal imaging device (EPID) images to fluence for the purpose of reconstructing the dose to a phantom is investigated here for simple open fields. Ultimately, the goal is to develop a method to reconstruct the dose to patients. The EPID images are transformed into incident intensity fluence by spatial filtering with a deconvolution kernel. The kernel uses a general mathematical form derived from a Monte Carlo calculation of the point spread function of an EPID. The deconvolution kernel is fitted using a downhill search algorithm that minimizes the difference between the reconstructed dose and the dose measured in water. The beam profile “horns” that are removed by the EPID calibration procedure are restored to the resulting images by direct multiplication using the measured in‐air off‐axis ratio. Applying the fitted kernel to an EPID image provides the incident fluence for that beam. This beam fluence is then entered into an independent dose calculation algorithm for phantom or patient dose reconstruction. The phantom dose was computed to an accuracy of 2.0% of the dose at one standard deviation. The method is general and can possibly be applied to any EPID equipped with an integration mode. We demonstrate the application of the fitted kernel in two clinical IMRT cases.PACS numbers: 87.52.Df, 87.53.Bn, 87.53.Dq, 87.56.Fc, 87.66.Pm