bluuebunny/crossref_metadata_2025_split huggingface dataset:
Wide field array calibration dependence on the stability of measured dose distributions
Authors: Simon Thomas A. , Simon William E. , Kahler Darren , Li Jonathan , Liu Chihray 
Published: July 2010

PurposeThe aim of this work was to simulate the effect of dose distribution changes on detector array calibrations and to explore compensatory methods that are used during calibration measurements.MethodsThe array calibration technique that was investigated is known as wide field (WF) calibration. Using this method, a linear array [‐axis (65 detectors) of the IC PROFILER™ (Sun Nuclear Corporation, Melbourne, FL)] is calibrated with three measurements (, , and ); each measurement uses the same radiation field, which is larger than the array. For measurement configuration , the array is rotated by 180° from its position in ; for , the array is shifted by one detector from its position in . The relative detector sensitivities are then determined through ratios of detector readings at the same field locations (using and ). This method results in error propagation that is proportional to the number of detectors in the array. During the procedure, the calibration protocol operates under three postulates, which state that (a) the beam shape does not change between measurements; (b) the relative sensitivities of the detectors do not change; and (c) the scatter to the array does not change as the array is moved. The WF calibration's sensitivity to a postulate (a) violation was quantified by applying a sine shaped perturbation (of up to 0.1%) to , , or , and then determining the change relative to a baseline calibration. Postulate (a) violations were minimized by using a continuous beam and mechanized array movement during and . A continuously on beam demonstrated more stable beam symmetry as compared to cycling the beam on and off between measurements. Additional side‐scatter was also used to satisfy postulate (c).ResultsSimulated symmetry perturbations of 0.1% to or resulted in calibration errors of up to 2%; was relatively immune to perturbation ( error). Wide field calibration error on a linear accelerator with similar symmetry variations was ±1.6%. Using a continuous beam during and with additional side‐scatter reduced the calibration error from ±1.6% to ±0.48%.ConclusionsThis work increased the reproducibility of WF calibrations by limiting the effect of measurement perturbations primarily due to linear accelerator symmetry variations. The same technique would work for any array using WF calibration.
Total skin electron therapy (TSET): A reimplementation using radiochromic films and IAEA TRS‐398 code of practice
Authors: Schiapparelli P. , Zefiro D. , Massone F. , Taccini G. 
Published: July 2010

PurposeThe aim of this work is to present an updated implementation of total skin electron therapy (TSET) using IAEA TRS‐398 code of practice for absolute dosimetry and taking advantage of the use of radiochromic films. The optimization of quality control tests is also included.MethodsA Varian 2100 C/D linear accelerator equipped with the special procedure (high dose rate total skin electron mode, ) was employed to perform TSET irradiations using the modified Stanford technique. The commissioning was performed following the AAPM report 23 recommendations. In particular, for dual‐field beams irradiation, the optimal tilt angle was investigated and the dose distribution in the treatment plane was measured. For a complete six dual‐field beams irradiation, the treatment skin dose on the surface of a cylindrical phantom was evaluated by radiochromic films and the factor which relates the single dual‐field skin dose to the six dual‐field skin dose was assessed. Since the TRS‐398 reference conditions do not meet the requirements of TSET absolute dosimetry, GafChromic EBT films were also employed to check and validate the application of the protocol. Simplified procedures were studied to verify beam constancy in PMMA phantoms without the more difficult setup of total skin irradiation.ResultsThe optimized geometrical setup for dual‐field beams was: Tilt , , and the beam degrader placed at 320 cm from the source. As regards to dose homogeneity in the treatment plane, for dual‐field beams irradiation, the mean relative dose value was (normalizing to 100% at the calibration point level). For six dual‐field beams irradiation, the multiplication factor was 2.63. In addition, beam quality, dose rate, and bremsstrahlung contribution were also suitable for TSET treatments. The TRS‐398 code of practice was used for TSET dosimetry, as dose measurements performed by ionization chamber and radiochromic film agreed within 2.5%. Simplified quality control tests and baseline values were presented in order to check flatness, symmetry, and field size with radiochromic films and output and beam quality constancy with ionization chamber. Short‐term reproducibility and MU linearity tests were also included.ConclusionsCommissioning parameters met the requirements of TSET treatments and the matching of AAPM guidelines with the IAEA code of practice was successful. Frequent beam performance controls can be easily performed through the presented quality assurance tests. Radiochromic dosimetry facilitated the TSET commissioning and played a major role to validate the application of TRS‐398.
A symmetric nonrigid registration method to handle large organ deformations in cervical cancer patients
Authors: Bondar Luiza , Hoogeman Mischa S. , Vásquez Osorio Eliana M. , Heijmen Ben J. M. 
Published: July 2010

PurposeModern radiotherapy requires assessment of patient anatomical changes. By using unidirectional registration methods, the quantified anatomical changes are asymmetric, i.e., depend on the direction of the registration. Moreover, the registration is challenged by the large and complex organ deformations that can occur in, e.g., cervical cancer patients. The aim of this work was to develop, test, and validate a symmetric feature‐based nonrigid registration method that can handle organs with large‐scale deformations.MethodsA symmetric version of the unidirectional thin plate spline robust point matching (TPS‐RPM) algorithm was developed, implemented, tested, and validated. Tests were performed by using the delineated cervix and uterus and bladder in CT scans of five cervical cancer patients. For each patient, five CT scans with a large variability in organ shape, volume, and deformations were acquired. Both the symmetric and the unidirectional algorithm were employed to calculate the registration geometric accuracy (surface distance and surface coverage errors), the inverse consistency, the residual distances after transforming anatomical landmarks, and the registration time. Additionally, to facilitate the further use of our symmetric method, a large set of input parameters was tested.ResultsThe developed symmetric algorithm handled successfully the registration of bladders with extreme volume change for which TPS‐RPM failed. Compared to the unidirectional algorithm the symmetric algorithm improved, for the registration of organs with large volume change, the inverse consistency by 78% and the surface coverage by 46%. Similarly, for organs with small volume change, the symmetric algorithm improved the inverse consistency by 69% and the surface coverage by 13%. The method allowed for anatomically coherent registration in only 35 s for cervix‐uterus and 151 s for bladder, while keeping the inverse consistency errors around 1 mm and the surface matching errors below 1 mm. Compared to rigid alignment the symmetric method reduced the residual distances between anatomical landmarks from a range of to a range of .ConclusionsThe developed symmetric method could be employed to perform fast, accurate, consistent, and anatomically coherent registration of organs with large and complex deformations. Therefore, the method is a useful tool that could support further developments in high precision image guided radiotherapy.
Contrast detection in fluid‐saturated media with magnetic resonance poroelastography
Authors: Perriñez Phillip R. , Pattison Adam J. , Kennedy Francis E. , Weaver John B. , Paulsen Keith D. 
Published: July 2010

PurposeRecent interest in the poroelastic behavior of tissues has led to the development of magnetic resonance poroelastography (MRPE) as an alternative to single‐phase MR elastographic image reconstruction. In addition to the elastic parameters (i.e., Lamé's constants) commonly associated with magnetic resonance elastography (MRE), MRPE enables estimation of the time‐harmonic pore‐pressure field induced by external mechanical vibration.MethodsThis study presents numerical simulations that demonstrate the sensitivity of the computed displacement and pore‐pressure fields toa priori estimates of the experimentally derived model parameters. In addition, experimental data collected in three poroelastic phantoms are used to assess the quantitative accuracy of MR poroelastographic imaging through comparisons with both quasistatic and dynamic mechanical tests.ResultsThe results indicate hydraulic conductivity to be the dominant parameter influencing the deformation behavior of poroelastic media under conditions applied during MRE. MRPE estimation of the matrix shear modulus was bracketed by the values determined from independent quasistatic and dynamic mechanical measurements as expected, whereas the contrast ratios for embedded inclusions were quantitatively similar (10%–15% difference between the reconstructed images and the mechanical tests).ConclusionsThe findings suggest that the addition of hydraulic conductivity and a viscoelastic solid component as parameters in the reconstruction may be warranted.
Automatic image guidance for prostate IMRT using low dose CBCT
Authors: Wierzbicki Marcin , Schaly Bryan , Peters Terry , Barnett Rob 
Published: July 2010

PurposeVarian's On‐Board Imager is a linac‐integrated cone‐beam CT (CBCT) system used at the authors’ institution to acquire images prior to delivering each fraction of prostate intensity modulated radiotherapy. The images are used to determine a couch shift that realigns the tumor with the position obtained in the planning CT. However, this manual image‐guided radiotherapy (IGRT) technique is operator dependent, time consuming, offers limited degrees of freedom, and requires significant imaging dose over the course of treatment. To overcome these problems, the authors propose two fully automatic IGRT techniques that require significantly less imaging dose.MethodsDose is reduced by lowering the x‐ray tube mA s during CBCT acquisition at the cost of increasing image noise. In “forward” IGRT, the CBCT image is automatically registered to the planning CT to obtain the necessary couch shift. The “reverse” technique offers additional degrees of freedom as it involves nonrigid registration of the planning CT to the CBCT. Both techniques were evaluated using images of an anthropomorphic phantom with simulated motion and by retrospectively analyzing data from ten prostate cancer patients.ResultsIGRT error for the phantom data at 100% relative imaging dose was , , and for setup only, forward, and reverse techniques, respectively. For patient images acquired at 100% relative imaging dose, the errors were , , , and for setup only, manual forward (performed clinically), automatic forward, and reverse IGRT, respectively. Furthermore, imaging dose could be reduced to 20% without a significant loss in image guidance accuracy.ConclusionsThe presented image guidance methods are accurate while requiring only 20% of the standard imaging dose. The combination of low dose, automation, and accuracy enables frequent corrections during treatment, possibly leading to reduced margins and improved treatment outcomes.
Multibeam field emission x‐ray system with half‐scan reconstruction algorithm
Authors: Lu Yang , Yu Hengyong , Cao Guohua , Zhao Jun , Wang Ge , Zhou Otto 
Published: July 2010

PurposeIn this article, the authors propose a multibeam field emission x‐ray (MBFEX) system along with a half‐scan fan‐beam reconstruction algorithm.MethodsThe proposed system consists of a linear CNT‐based MBFEX source array, a single large area detector that is divided into same number of segments as the number of x‐ray beams, a multihole collimator that aligns each beam with a corresponding detector segment, and a sample rotation stage. The collimator is placed between the source and the object to restrict the x‐ray radiations through the target object only. In this design, all the x‐ray beams are activated simultaneously to provide multiple projection views of the object. The detector is virtually segmented and synchronized with the x‐ray exposure and the physiological signals when gating is involved. The transmitted x‐ray intensity from each beam is collected by the corresponding segment on the detector. After each exposure, the object is rotated by a step angle until sufficient data set is collected. The half‐scan reconstruction formula for MBFEX system is derived from the conventional filtered backprojection algorithm. To demonstrate the advantages of the system and method in reducing motion artifacts, the authors performed simulations with both standard and dynamic Shepp–Logan phantoms.ResultsThe numerical results indicate that the proposed multibeam system and the associated half‐scan algorithm can effectively reduce the scanning time and improve the image quality for a time‐varying object.ConclusionsThe MBFEX technique offers an opportunity for the innovation of multisource imaging system.
Efficient generation of a magnetic field‐free line
Authors: Knopp Tobias , Erbe Marlitt , Biederer Sven , Sattel Timo F. , Buzug Thorsten M. 
Published: July 2010

PurposeSignal encoding in magnetic particle imaging (MPI) is achieved by moving a field‐free point (FFP) through the region of interest. One way to increase the sensitivity of the method is to scan the region of interest with a field‐free line (FFL) instead of the FFP. Recently, the first feasible FFL coil setup was introduced. The purpose of this article is to improve the efficiency of the FFL coil geometry even further.MethodsIn order to reduce the electrical power loss of the setup, an additional Maxwell coil pair is introduced that is tailored to generate the static part of the FFL field.ResultsUsing the proposed coil assembly, the electrical power loss for the generation of a rotating FFL is considerably reduced compared to previously known coil setups. Furthermore, the quality of the generated FFL is significantly increased.ConclusionsThe proposed coil assembly is almost as efficient as an equivalent FFP scanner. Furthermore, the assembly cannot only be used for FFL imaging but for FFP imaging as well. Hence, the findings of this article denote an important step toward the first practical implementation of the FFL coil geometry.
Light emission efficiency and imaging performance of powder scintillator under x‐ray radiography conditions
Authors: Michail C. M. , Fountos G. P. , Liaparinos P. F. , Kalyvas N. E. , Valais I. , Kandarakis I. S. , Panayiotakis G. S. 
Published: July 2010

PurposeTo evaluate powder phosphor as a radiographic image receptor and to compare it to phosphors often used in radiography. is nonhygroscopic, emitting red light with decay time close to that of .MethodsThe light intensity emitted per unit of x‐ray exposure rate (absolute luminescence efficiency) was measured for laboratory prepared screens with coating thicknesses of 33.1, 46.4, 63.1, 78.3, and and tube voltages ranging from 50 to 140 kVp. Parameters related to image quality such as the modulation transfer function (MTF) and the detective quantum efficiency (DQE) were also experimentally examined. In addition, a previously validated Monte Carlo code was used to estimate intrinsic x‐ray absorption and optical properties, as well as the MTF and the Swank factor of the scintillators.Results light intensity was found higher than that of single CsI:Tl crystal for tube voltages up to 100 kVp. The MTF and the DQE were found to be comparable with those of and CsI:Tl screens. MTF estimated by the Monte Carlo code was found very close to the experimental MTF values. showed peak emission in the wavelength range 620–630 nm. Its emission spectrum was excellently matched to various optical detectors (photodiodes, photocathodes, CCDs, and CMOS) employed in flat panel detectors.Conclusions is an efficient phosphor potentially well suited to radiography and especially to some digital detectors sensitive to red light.
Dosimetric characterization of the iBEAM evo carbon fiber couch for radiotherapy
Authors: Smith David W. , Christophides Damianos , Dean Christopher , Naisbit Mitchell , Mason Joshua , Morgan Andrew 
Published: July 2010

PurposeThis study characterizes the dosimetric properties of the iBEAM evo carbon fiber couch manufactured by Medical Intelligence and examines the accuracy of the CMS XiO and Nucletron Oncentra Masterplan (OMP) treatment planning systems for calculating beam attenuation due to the presence of the couch.MethodsTo assess the homogeneity of the couch, it was CT scanned at isocentric height and a number of signal intensity profiles were generated and analyzed. To simplify experimental procedures, surface dose and central axis depth dose measurements were performed in a solid water slab phantom using Gafchromic film for 6 and 10 MV photon beams at gantry angles of 0° (normal incidence), 30°, and 60° with an inverted iBEAM couch placed on top of the phantom. Attenuation measurements were performed in a cylindrical solid water phantom with an ionization chamber positioned at the isocenter. Measurements were taken for gantry angles from 0° to 90° in 10° increments for both 6 and 10 MV photon beams. This setup was replicated in the XiO and OMP treatment planning systems. Dose was calculated using the pencil beam, collapsed cone, convolution, and superposition algorithms.ResultsThe CT scan of the couch showed that it was uniformly constructed. Surface dose increased by for a 6 MV beam and for a 10 MV beam passing through the couch at normal incidence. Obliquely incident beams resulted in a higher surface dose compared to normally incident beams for both open fields and fields with the couch present. Depth dose curves showed that the presence of the couch resulted in an increase in dose in the build up region. For 6 and 10 MV beams incident at 60°, nearly all skin sparing was lost. Attenuation measurements derived using the ionization chamber varied from 2.7% (0°) to a maximum of 4.6% (50°) for a 6 MV beam and from 1.9% (0°) to a maximum of 4.0% (50°) for a 10 MV beam. The pencil beam and convolution algorithms failed to accurately calculate couch attenuation. The collapsed cone and superposition algorithms calculated attenuation within an absolute error of ±1.2% for 6 MV and ±0.8% for 10 MV for gantry angles from 0° to 40°. Some differences in attenuation were observed dependent on how the couch was contoured.ConclusionsThese results demonstrate that the presence of the iBEAM evo carbon fiber couch increases the surface dose and dose in the build up region. The inclusion of the couch in the planning scan is limited by the field of view employed and the couch height at the time of CT scanning.
Evaluating Auger electrons for targeted tumor radiotherapy by computational methods
Authors: Tavares Adriana Alexandre S. , Tavares João Manuel R. S. 
Published: July 2010

PurposeTechnetium‐99m has been widely used as an imaging agent but only recently has been considered for therapeutic applications. This study aims to analyze the potential use of Auger electrons for targeted tumor radiotherapy by evaluating the DNA damage and its probability of correct repair and by studying the cellular kinetics, following Auger electron irradiation in comparison to iodine‐131 beta minus particles and astatine‐211 alpha particle irradiation.MethodsComputational models were used to estimate the yield of DNA damage (fast Monte Carlo damage algorithm), the probability of correct repair (Monte Carlo excision repair algorithm), and cell kinetic effects (virtual cell radiobiology algorithm) after irradiation with the selected particles.ResultsThe results obtained with the algorithms used suggested that CKMMX (all M‐shell Coster–Kroning—CK—and super‐CK transitions) electrons and Auger MXY (all M‐shell Auger transitions) have a therapeutic potential comparable to high linear energy transfer alpha particles and higher than beta minus particles. All the other electrons had a therapeutic potential similar to beta minus particles.Conclusions CKMMX electrons and Auger MXY presented a higher probability to induce apoptosis than beta minus particles and a probability similar to alpha particles. Based on the results here, CKMMX electrons and Auger MXY are useful electrons for targeted tumor radiotherapy.
The sensitivity of patient specific IMRT QC to systematic MLC leaf bank offset errors
Authors: Rangel Alejandra , Palte Gesa , Dunscombe Peter 
Published: July 2010

PurposePatient specific IMRT QC is performed routinely in many clinics as a safeguard against errors and inaccuracies which may be introduced during the complex planning, data transfer, and delivery phases of this type of treatment. The purpose of this work is to evaluate the feasibility of detecting systematic errors in MLC leaf bank position with patient specific checks.Methods9 head and neck (H&N) and 14 prostate IMRT beams were delivered using MLC files containing systematic offsets (±1 mm in two banks, ±0.5 mm in two banks, and 1 mm in one bank of leaves). The beams were measured using bothMAPCHECK™ (Sun Nuclear Corp., Melbourne, FL) and the aS1000 electronic portal imaging device (Varian Medical Systems, Palo Alto, CA). Comparisons with calculated fields, without offsets, were made using commonly adopted criteria including absolute dose (AD) difference, relative dose difference, distance to agreement (DTA), and the gamma index.ResultsThe criteria most sensitive to systematic leaf bank offsets were the 3% AD, 3 mm DTA forMAPCHECK™ and the gamma index with 2% AD and 2 mm DTA for the EPID. The criterion based on the relative dose measurements was the least sensitive to MLC offsets. More highly modulated fields, i.e., H&N, showed greater changes in the percentage of passing points due to systematic MLC inaccuracy than prostate fields.ConclusionsNone of the techniques or criteria tested is sufficiently sensitive, with the population of IMRT fields, to detect a systematic MLC offset at a clinically significant level on an individual field. Patient specific QC cannot, therefore, substitute for routine QC of the MLC itself.