bluuebunny/crossref_metadata_2025_split huggingface dataset:
Accuracy of lung nodule density on HRCT: analysis by PSF‐based image simulation
Authors: Ohno Ken , Ohkubo Masaki , Marasinghe Janaka C , Murao Kohei , Matsumoto Toru , Wada Shinichi 
Published: February 2017

A computed tomography (CT) image simulation technique based on the point spread function (PSF) was applied to analyze the accuracy of CT‐based clinical evaluations of lung nodule density. The PSF of the CT system was measured and used to perform the lung nodule image simulation. Then, the simulated image was resampled at intervals equal to the pixel size and the slice interval found in clinical high‐resolution CT (HRCT) images. On those images, the nodule density was measured by placing a region of interest (ROI) commonly used for routine clinical practice, and comparing the measured value with the true value (a known density of object function used in the image simulation). It was quantitatively determined that the measured nodule density depended on the nodule diameter and the image reconstruction parameters (kernel and slice thickness). In addition, the measured density fluctuated, depending on the offset between the nodule center and the image voxel center. This fluctuation was reduced by decreasing the slice interval (i.e., with the use of overlapping reconstruction), leading to a stable density evaluation. Our proposed method of PSF‐based image simulation accompanied with resampling enables a quantitative analysis of the accuracy of CT‐based evaluations of lung nodule density. These results could potentially reveal clinical misreadings in diagnosis, and lead to more accurate and precise density evaluations. They would also be of value for determining the optimum scan and reconstruction parameters, such as image reconstruction kernels and slice thicknesses/intervals.PACS numbers: 87.57.‐s, 87.57.cf, 87.57.Q‐
Six degrees of freedom CBCT‐based positioning for intracranial targets treated with frameless stereotactic radiosurgery
Authors: Dhabaan Anees , Schreibmann Eduard , Siddiqi Arsalan , Elder Eric , Fox Tim , Ogunleye Tomi , Esiashvili Natia , Curran Walter , Crocker Ian , Shu Hui‐Kuo 
Published: February 2017

Frameless radiosurgery is an attractive alternative to the framed procedure if it can be performed with comparable precision in a reasonable time frame. Here, we present a positioning approach for frameless radiosurgery based on in‐room volumetric imaging coupled with an advanced six‐degrees‐of‐freedom (6 DOF) image registration technique which avoids use of a bite block. Patient motion is restricted with a custom thermoplastic mask. Accurate positioning is achieved by registering a cone‐beam CT to the planning CT scan and applying all translational and rotational shifts using a custom couch mount. System accuracy was initially verified on an anthropomorphic phantom. Isocenters of delineated targets in the phantom were computed and aligned by our system with an average accuracy of 0.2 mm, 0.3 mm, and 0.4 mm in the lateral, vertical, and longitudinal directions, respectively. The accuracy in the rotational directions was 0., 0., and 0. in the pitch, roll, and yaw, respectively. An additional test was performed using the phantom in which known shifts were introduced. Misalignments up to 10 mm and in all directions/rotations were introduced in our phantom and recovered to an ideal alignment within 0.2 mm, 0.3 mm, and 0.4 mm in the lateral, vertical, and longitudinal directions, respectively, and within 0. in any rotational axis. These values are less than couch motion precision. Our first 28 patients with 38 targets treated over 63 fractions are analyzed in the patient positioning phase of the study. Mean error in the shifts predicted by the system were less than 0.5 mm in any translational direction and less than 0. in any rotation, as assessed by a confirmation CBCT scan. We conclude that accurate and efficient frameless radiosurgery positioning is achievable without the need for a bite block by using our 6 DOF registration method. This system is inexpensive compared to a couch‐based 6 DOF system, improves patient comfort compared to systems that utilize a bite block, and is ideal for the treatment of pediatric patients with or without general anesthesia, as well as of patients with dental issues. From this study, it is clear that only adjusting for 4 DOF may, in some cases, lead to significant compromise in PTV coverage. Since performing the additional match with 6 DOF in our registration system only adds a relatively short amount of time to the overall process, we advocate making the precise match in all cases.PACS number: 87.55.tm; 87.55.Qr; 87.57.nj
Development and implementation of an EPID‐based method for localizing isocenter
Authors: Hyer Daniel E. , Mart Christopher J. , Nixon Earl 
Published: February 2017

The aim of this study was to develop a phantom and analysis software that could be used to quickly and accurately determine the location of radiation isocenter to an accuracy of less than 1 mm using the EPID (Electronic Portal Imaging Device). The proposed solution uses a collimator setting of to acquire EPID images of a new phantom constructed from LEGO blocks. Images from a number of gantry and collimator angles are analyzed by automated analysis software to determine the position of the jaws and center of the phantom in each image. The distance between a chosen jaw and the phantom center is then compared to the same distance measured after a collimator rotation to determine if the phantom is centered in the dimension being investigated. Repeated tests show that the system is reproducibly independent of the imaging session, and calculated offsets of the phantom from radiation isocenter are a function of phantom setup only. Accuracy of the algorithm's calculated offsets were verified by imaging the LEGO phantom before and after applying the calculated offset. These measurements show that the offsets are predicted with an accuracy of approximately 0.3 mm, which is on the order of the detector's pitch. Comparison with a star‐shot analysis yielded agreement of isocenter location within 0.5 mm. Additionally, the phantom and software are completely independent of linac vendor, and this study presents results from two linac manufacturers. A Varian Optical Guidance Platform (OGP) calibration array was also integrated into the phantom to allow calibration of the OGP while the phantom is positioned at radiation isocenter to reduce setup uncertainty in the calibration. This solution offers a quick, objective method to perform isocenter localization as well as laser alignment and OGP calibration on a monthly basis.PACS number: 87.55.Qr
Gantry angle determination during arc IMRT: evaluation of a simple EPID‐based technique and two commercial inclinometers
Authors: Rowshanfarzad Pejman , Sabet Mahsheed , O'Connor Daryl J. , McCowan Peter M. , McCurdy Boyd M.C. , Greer Peter B. 
Published: February 2017

The increasing popularity of intensity‐modulated arc therapy (IMAT) treatments requires specifically designed linac quality assurance (QA) programs. Gantry angle is one of the parameters that has a major effect on the outcome of IMAT treatments since dose reconstruction for patient‐specific QA relies on the gantry angle; therefore, it is essential to ensure its accuracy for correct delivery of the prescribed dose. In this study, a simple measurement method and algorithm are presented for QA of gantry angle measurements based on integrated EPID images acquired at distinct gantry angles and cine EPID images during an entire arc. A comprehensive study was carried out to evaluate this method, as well as to evaluate two commercially available inclinometers (NG360 and IBA GAS supplied in conjunction with popular array dosimeters and , respectively) by comparing their simultaneous angle measurement results with the linac potentiometer readouts at five gantry speeds. In all tested measurement systems, the average differences with the reference angle data were less than 0. in static mode. In arc mode, at all tested gantry speeds the average difference was less than 0. for the IBA GAS and the proposed EPID‐based method, and 0. for the NG360 after correction for the inherent systematic time delay of the inclinometer. The gantry rotation speed measured by the three independent systems had an average deviation of about 0./s from the nominal gantry speed.PACS numbers: 06.30.Bp; 87.56.Fc; 87.56.‐v
Improving dose calculations on tomotherapy MVCT images
Authors: Crop F. , Bernard A. , Reynaert N. 
Published: February 2017

The purpose of this investigation was the creation of a new protocol allowing more precise dose calculations on megavoltage CT (MVCT) images for tomotherapy, both for adaptive and StatRT planning. Daily MVCT images offer, next to positioning purposes, the possibility for daily dose check and adaptive planning. Dose calculations use the image value to density table (IVDT) to calculate physical densities from Hounsfield Units (HUs). These measured HUs change over time, leading to a dose calculation error. We noticed dose calculation variations due to IVDT changes of: 0.2% dose during a day, up to 1.6% dose from long‐term variations, and up to 1.5% dose due to technical interventions. An analysis was performed applying the general methodology of a calibration problem. A model was obtained using a weighted least squares inverse prediction method (HU as function of density) taking into account the heteroscedasticity. The b parameter is the major variable and depends also on the dose rate (DR). We demonstrate the correction for DR variations and the constance of the c parameter. Instead of scanning the whole tissue characterization phantom daily, we propose a simplified daily protocol: (a) morning airscan‐like procedure with only two inserts on the table (defining b and thus the IVDT curve), (b) DR variations throughout the day can be corrected for using the DR model. A patient‐specific protocol for which two inserts next to the patient are scanned could also be used, but results in equal uncertainties and is less practical. Therefore we recommend the morning procedure with dose rate variation correction. Applying the proposed transformations and the model, the correct IVDT of the moment can be reconstructed, with a simple measurement in the morning, and corrected with DR changes during the day. This corresponds with a linear mapping in time of the proposed IVDT function. The dosimetric variation is hereby reduced from up to 3% to 0.4 % for the tested pelvic and head‐and‐neck cases. In practice, several IVDT curves corresponding to “b” values can be entered. The correct IVDT curve of that moment can then be chosen from the list. Instead of the two high‐density inserts on table, any calibrated single density phantom could be used in order to create the IVDT curve of the day, but it should have a larger size than the current inserts.PACS number: 87.55.Gh
Practical methods for improving dose distributions in Monte Carlo‐based IMRT planning of lung wall‐seated tumors treated with SBRT
Authors: Altman Michael B. , Jin Jian‐Yue , Kim Sangroh , Wen Ning , Liu Dezhi , Siddiqui M. Salim , Ajlouni Munther I. , Movsas Benjamin , Chetty Indrin J. 
Published: February 2017

Current commercially available planning systems with Monte Carlo (MC)‐based final dose calculation in IMRT planning employ pencil‐beam (PB) algorithms in the optimization process. Consequently, dose coverage for SBRT lung plans can feature cold‐spots at the interface between lung and tumor tissue. For lung wall (LW)‐seated tumors, there can also be hot spots within nearby normal organs (example: ribs). This study evaluated two different practical approaches to limiting cold spots within the target and reducing high doses to surrounding normal organs in MC‐based IMRT planning of LW‐seated tumors. First, “iterative reoptimization”, where the MC calculation (with PB‐based optimization) is initially performed. The resultant cold spot is then contoured and used as a simultaneous boost volume. The MC‐based dose is then recomputed. The second technique uses noncoplanar beam angles with limited path through lung tissue. Both techniques were evaluated against a conventional coplanar beam approach with a single MC calculation. In all techniques the prescription dose was normalized to cover 95% of the PTV. Fifteen SBRT lung cases with LW‐seated tumors were planned. The results from iterative reoptimization showed that conformity index (CI) and/or PTV dose uniformity () improved in 12/15 plans. Average improvement was 13%, and 24%, respectively. Nonimproved plans had PTVs near the skin, trachea, and/or very small lung involvement. The maximum dose to 1cc volume (D1cc) of surrounding OARs decreased in 14/15 plans (average 10%). Using noncoplanar beams showed an average improvement of 7% in 10/15 cases and 11% in 5/15 cases for CI and , respectively. The D1cc was reduced by an average of 6% in 10/15 cases to surrounding OARs. Choice of treatment planning technique did not statistically significantly change lung V5. The results showed that the proposed practical approaches enhance dose conformity in MC‐based IMRT planning of lung tumors treated with SBRT, improving target dose coverage and potentially reducing toxicities to surrounding normal organs.PACS numbers: 87.55.de, 87.55.kh
Analysis of the advantage of individual PTVs defined on axial 3D CT and 4D CT images for liver cancer
Authors: Li Fengxiang , Li Jianbin , Xing Jun , Zhang Yingjie , Fan Tingyong , Xu Min , Shang Dongping , Liu Tonghai , Song Jinlong 
Published: February 2017

The purpose of this study was to compare positional and volumetric differences of planning target volumes (PTVs) defined on axial three dimensional CT (3D CT) and four dimensional CT (4D CT) for liver cancer. Fourteen patients with liver cancer underwent 3D CT and 4D CT simulation scans during free breathing. The tumor motion was measured by 4D CT. Three internal target volumes (ITVs) were produced based on the clinical target volume from 3DCT (): i) A conventional ITV () was produced by adding 10 mm in CC direction and 5 mm in LR and and AP directions to ; ii) A specific ITV () was created using a specific margin in transaxial direction; iii) was produced by adding an isotropic margin derived from the individual tumor motion vector. was defined on the fusion of CTVs on all phases of 4D CT. PTVs were generated by adding a 5 mm setup margin to ITVs. The average centroid shifts between PTVs derived from 3DCT and in left–right (LR), anterior–posterior (AP), and cranial–caudal (CC) directions were close to zero. Comparing to , , and resulted in a decrease in volume size by 33.18% , 24.95% , 48.08% , respectively. The mean degree of inclusions (DI) of in , and in , and in was 0.98, 0.97, and 0.99, which showed no significant correlation to tumor motion vector (, 0.259, and 0.244; , 0.371, and 0.401). The mean DIs of in , in , and in was 0.66, 0.73, and 0.52. The size of individual PTV from 4D CT is significantly less than that of PTVs from 3DCT. The position of targets derived from axial 3DCT images scatters around the center of 4D targets randomly. Compared to conventional PTV, the use of 3D CT‐based PTVs with individual margins cannot significantly reduce normal tissues being unnecessarily irradiated, but may contribute to reducing the risk of missing targets for tumors with large motion.PACS number: 87
The impact of continuously‐variable dose rate VMAT on beam stability, MLC positioning, and overall plan dosimetry
Authors: Boylan Christopher , McWilliam Alan , Johnstone Emily , Rowbottom Carl 
Published: February 2017

A recent control system update for Elekta linear accelerators includes the ability to deliver volumetric‐modulated arc therapy (VMAT) with continuously variable dose rate (CVDR), rather than a number of fixed binned dose rates (BDR). The capacity to select from a larger range of dose rates allows the linac to maintain higher gantry speeds, resulting in faster, smoother deliveries. The purpose of this study is to investigate two components of CVDR delivery — the increase in average dose rate and gantry speed, and a determination of their effects on beam stability, MLC positioning, and overall plan dosimetry. Initially, ten VMAT plans (5 prostate, 5 head and neck) were delivered to a dosimetric phantom using both the BDR and CVDR systems. The plans were found to be dosimetrically robust using both delivery methods, although CVDR was observed to give higher gamma pass rates at the gamma level for prostates (). For the dual arc head‐and‐neck plans, CVDR delivery resulted in improved pass rates at all gamma levels ( to ) for individual arc verifications (), but gave similar results to BDR when both arcs were combined. To investigate the impact of increased gantry speed on MLC positioning, a dynamic leaf‐tracking tool was developed using the electronic portal imaging device (EPID). Comparing the detected MLC positions to those expected from the plan, CVDR was observed to result in a larger mean error compared to BDR (0.13 cm and 0.06 cm, respectively, ). The EPID images were also used to monitor beam stability during delivery. It was found that the CVDR deliveries had a lower standard deviation of the gun‐target (GT) and transverse (AB) profiles (). This study has determined that CVDR may offer a dosimetric advantage for VMAT plans. While the higher gantry speed of CVDR appears to increase deviations in MLC positioning, the relative effect on dosimetry is lower than the positive impact of a flatter and more stable beam profile.PACS numbers: 87.56.bd; 87.55.km; 87.55.Qr
Dosimetric assessment of prostate cancer patients through principal component analysis (PCA)
Authors: Gloi Aime M , Buchanan Robert 
Published: February 2017

The aims of this study were twofold: first, to determine the impact of variance in dose‐volume histograms (DVH) on patient‐specific toxicity after 2 high‐dose fractions in a sample of 22 men with prostate cancer; and second, to compare the effectiveness of traditional DVH analysis and principal component analysis (PCA) in predicting rectum and urethra toxicity. A series of 22 patients diagnosed with prostate adenocarcinoma was treated with 45 Gy external beam and 20 Gy dose rate brachytherapy. Principal component analysis was applied to model the shapes of the rectum and urethra dose‐volume histograms. We used logistic regression to measure the correlations between the principal components and the incidence of rectal bleeding and urethra stricture. We also calculated the equivalent uniform dose (EUD) and normal tissue complication probability (NTCP) for the urethra and rectum, and tumor control probability (TCP) for the prostate using BioSuite software. We evaluated their correlations with rectal and urethra toxicity. The rectum DVHs are well described by one principal component (PC1), which accounts for 93.5% of the variance in their shapes. The urethra DVHs are described by two principal components, PC1 and PC2, which account for 94.98% and 3.15% of the variance, respectively. Multivariate exact logistic regression suggests that urethra PC2 is a good predictor of stricture, with Nagelkerke's estimated at 0.798 and a Wald criterion of 5.421 (). The average NTCPs were and for the rectum and urethra, respectively. The average TCP was . This study suggests that principal component analysis can be used to identify the shape variation in dose‐volume histograms, and that the principal components can be correlated with the toxicity of a treatment plan based on multivariate analysis. The principal components are also correlated with traditional dosimetric parameters.PACS number: 3.6.96.0
Patient‐specific independent 3D GammaPlan quality assurance for Gamma Knife Perfexion radiosurgery
Authors: Mamalui‐Hunter Maria , Yaddanapudi Sridhar , Zhao Tianyu , Mutic Sasa , Low Daniel A. , Drzymala Robert E. 
Published: February 2017

One of the most important aspects of quality assurance (QA) in radiation therapy is redundancy of patient treatment dose calculation. This work is focused on the patient‐specific time and 3D dose treatment plan verification for stereotactic radiosurgery using Leksell Gamma Knife Perfexion (LGK PFX). The virtual model of LGK PFX was developed in MATLAB, based on the physical dimensions provided by the manufacturer. The ring‐specific linear attenuation coefficients (LAC) and output factors (OFs) reported by the manufacturer were replaced by the measurement‐based collimator size‐specific OFs and a single . Calculation depths for each LGK PFX shot were obtained by ray‐tracing technique, and the dose calculation formalism was similar to the one used by GammaPlan treatment planning software versions 8 and 9. The architecture of the QA process was based on the in‐house online database search of the LGK PFX database search for plan‐specific information. A series of QA phantom plans was examined to verify geometric and dosimetric accuracy of the software. The accuracy of the QA process was further evaluated through evaluation of a series of patient plans. The shot time/focus point dose verification for each shot took less than 1 sec/shot with full 3D isodose verification taking about 30 sec/shot on a desktop PC. GammaPlan database access time took less than 0.05 sec. The geometric accuracy (location of the point of maximum dose) of the phantom and patient plan was dependent on the resolution of the original dose matrix and was of the order of 1 dose element. Dosimetric accuracy of the independently calculated phantom and patient point (focus) doses was within 3.5% from the GammaPlan, with the and . The process for independent pretreatment patient‐specific Gamma Knife Perfexion time and dose verification was created and validated.PACS numbers: 87.53.Bn; 87.55.‐x; 87.56.Bg
Dosimetric assessment of a novel metal artifact reduction method in CT images
Authors: Spadea Maria F. , Verburg Joost , Baroni Guido , Seco Joao 
Published: February 2017

The aim of this study was to assess the ability of metal artifact reduction (MAR) algorithm in restoring the CT image quality while correcting the tissue density information for the accurate estimation of the absorbed dose. A phantom filled with titanium (low‐Z metal) and Cerrobend (high‐Z metal) inserts was used for this purpose. The MAR algorithm was applied to phantom's CT dataset. Static intensity‐modulated radiation therapy (IMRT) plans, including five beam angles, were designed and optimized on the uncorrected images to deliver 10 Gy on the simulated target. Monte Carlo dose calculation was computed on uncorrected, corrected, and ground truth image datasets. It was firstly verified that MAR methodology was able to correct HU errors due to the metal presence. In the worst situation (high‐Z phantom), the image difference, uncorrected ground truth and corrected ground truth, went from HU to HU, respectively. Secondly, it was observed that the impact of dose errors estimation depends on the atomic number of the metal: low‐Z inserts do not produce significant dose inaccuracies, while high‐Z implants substantially influence the computation of the absorbed dose. In this latter case, dose errors in the PTV region were up to 23.56% (9.72% mean value) when comparing the uncorrected vs. the ground truth dataset. After MAR correction, errors dropped to 0.11% (0.10% mean value). In conclusion, it was assessed that the new MAR algorithm is able to restore image quality without distorting mass density information, thus producing a more accurate dose estimation.PACS numbers: 87.53.Bn, 87.55.K, 87.57.cp