bluuebunny/crossref_metadata_2025 huggingface dataset:
Design and study of ultrasound‐based automatic patient movement monitoring device for quantifying the intrafraction motion during teletherapy treatment
Authors: Senthilkumar S. , Vinothraj R.
Published: February 2017

The aim of the present study is to fabricate indigenously ultrasonic‐based automatic patient's movement monitoring device (UPMMD) that immediately halts teletherapy treatment if a patient moves, claiming accurate field treatment. The device consists of circuit board, magnetic attachment device, LED indicator, speaker, and ultrasonic emitter and receiver, which are placed on either side of the treatment table. The ultrasonic emitter produces the ultrasound waves and the receiver accepts the signal from the patient. When the patient moves, the receiver activates the circuit, an audible warning sound will be produced in the treatment console room alerting the technologist to stop treatment. Simultaneously, the electrical circuit to the teletherapy machine will be interrupted and radiation will be halted. The device and alarm system can detect patient movements with a sensitivity of about 1 mm. Our results indicate that, in spite of its low‐cost, low‐power, high‐precision, nonintrusive, light weight, reusable and simplicity features, UPMMD is highly sensitive and offers accurate measurements. Furthermore, UPMMD is patient‐friendly and requires minimal user training. This study revealed that the device can prevent the patient's normal tissues from unnecessary radiation exposure, and also it is helpful to deliver the radiation to the correct tumor location. Using this alarming system the patient can be repositioned after interrupting the treatment machine manually. It also enables the technologists to do their work more efficiently.

PACS number: 87.53.Dq
Dose variations in tumor volumes and organs at risk during IMRT for head‐and‐neck cancer
Authors: Beltran Mercè , Ramos Mónica , Rovira Juan José , Perez‐Hoyos Santiago , Sancho Marc , Puertas Enrique , Benavente Sergi , Ginjaume Mercè , Giralt Jordi
Published: February 2017

Many head‐and‐neck cancer (HNC) patients treated with radiotherapy suffer significant anatomical changes due to tumor shrinkage or weight loss. The purpose of this study was to assess dose changes over target volumes and organs at risk during intensity‐modulated radiotherapy for HNC patients. Sixteen HNC IMRT patients, all requiring bilateral neck irradiation, were enrolled in the study. A was performed and the initial dose distribution was calculated. During the treatment, two subsequent CTs at the 15th and 25th fractions were acquired. The initial plan was calculated on the and , and dose‐volume differences related to the were assessed. For target volumes, mean values of nearmaximun absorbed dose () increased at the 25th fraction, and doses covering 95% and 98% of volume decreased significantly at the 15th fraction. Contralateral and ipsilateral parotid gland mean doses increased by 6.1% (range: ‐5.4, 23.5%) and 4.7% (range: ‐9.1, 22.3%), respectively, at . The in the spinal cord increased by 1.8 Gy at . Mean absorbed dose increases at and were observed in: the lips, 3.8% and 5.3%; the oral cavity, 3.5% and 2.5%; and lower middle neck structure, 1.9% and 1.6%. Anatomical changes during treatment of HNC patients affect dose distribution and induce a loss of dose coverage to target volumes and an overdosage to critical structures. Appropriate organs at risk have to be contoured and monitored in order to know if the initial plan remains suitable during the course of the treatment. Reported dosimetric data can help to identify patients who could benefit from adaptive radiotherapy.

PACS numbers: 87.53.Kn, 87.55.Dk
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
Retrospective analysis of linear accelerator output constancy checks using process control techniques
Authors: Sanghangthum Taweap , Suriyapee Sivalee , Srisatit Somyot , Pawlicki Todd
Published: February 2017

Shewhart control charts have previously been suggested as a process control tool for use in routine linear accelerator (linac) output verifications. However, a comprehensive approach to process control has not been investigated for linac output verifications. The purpose of this work is to investigate a comprehensive process control approach to linac output constancy quality assurance (QA). The RBA‐3 dose constancy check was used to verify outputs of photon beams and electron beams delivered by a Varian Clinac 21EX linac. The data were collected during 2009 to 2010. Shewhart‐type control charts, exponentially weighted moving average (EWMA) charts, and capability indices were applied to these processes. The Shewhart‐type individuals chart (X‐chart) was used and the number of data points used to calculate the control limits was varied. The parameters tested for the EWMA charts (smoothing parameter (λ) and the control limit width (L)) were , ; , ; and , , as well as the number of points used to estimate the initial process mean and variation. Lastly, the number of in‐control data points used to determine process capability () and acceptability () were investigated, comparing the first in‐control run to the longest in‐control run of the process data. and values greater than 1.0 were considered acceptable. The 95% confidence intervals were reported. The X‐charts detected systematic errors (e.g., device setup errors). In‐control run lengths on the X‐charts varied from 5 to 30 output measurements (about one to seven months). EWMA charts showed in‐control runs ranging from 9 to 33 output measurements (about two to eight months). The and ratios are higher than 1.0 for all energies, except 12 and 20 MeV. However, 10 MV and 6, 9, and 16 MeV were in question when considering the 95% confidence limits. The X‐chart should be calculated using 8–12 data points. For EWMA chart, using 4 data points is sufficient to calculate the initial mean and variance of the process. The EWMA limits should be calculated with , . At least 25–30 in‐control data points should be used to calculate the and indices.

PACS number: 89
A multi‐institutional study for tolerance and action levels of IMRT dose quality assurance measurements in Korea
Authors: Kim Jung‐in , Chung Jin‐Beom , Park Yang‐Kyun , Song Ju‐Young , Kim Sung Kyu , Ahn Sung Hwan , Choi Chang Heon , Choi Won Hoon , Cho Byungchul , Ju Sang Gyu , Kim Sung Jin , Ye Sung‐Joon
Published: February 2017

The purpose of this study was to suggest tolerance levels for IMRT DQA measurements using confidence limits determined by a multi‐institutional study in Korea. Ten institutions were grouped into LINAC (seven linear accelerators) and TOMO (three tomotherapy machines). The DQA processes consisted of point (high‐ and low‐dose regions) and planar (per‐field and composite‐field) dose measurements using an ion chamber and films (or 2D detector array) inserted into a custom‐made acryl phantom (LINAC) or a cheese phantom (TOMO). The five mock structures developed by AAPM TG‐119 were employed, but the prostate as well as the H&N structures were modified according to Korean patients' anatomy. The point measurements were evaluated in a ratio of measured and planned doses, while the planar dose distributions were assessed using two gamma criteria of 2 mm/2% and 3 mm/3%. The confidence limit (|mean + 1.96 σ|) for point measurements was determined to be 3.0% in high‐dose regions and 5.0% in low‐dose regions. The average percentage of points passing the gamma criteria of 2 mm/2% and 3 mm/3% for per‐field measurements was 92.7 and 98.2 , respectively. Thus, the corresponding confidence limit was 79.1% and 92.7%, respectively. The gamma passing rate averaged over all mock tests and institutions for composite‐field measurements was 86.1 at 2 mm/2% and 95.3 at 3 mm/3%, leading to the confidence limit of 73.3% and 87.9%, respectively. There was no significant difference in the tolerance levels of point dose measurements between LINAC and TOMO groups. In spite of the differences in mock structures and dosimetry tools, our tolerance levels were comparable to those of AAPM and ESTRO guidelines.

PACS number: 87.55.Qr
Accuracy and sources of error of out‐of field dose calculations by a commercial treatment planning system for intensity‐modulated radiation therapy treatments
Authors: Huang Jessie Y. , Followill David S. , Wang Xin A. , Kry Stephen F.
Published: February 2017

Although treatment planning systems are generally thought to have poor accuracy for out‐of‐field dose calculations, little work has been done to quantify this dose calculation inaccuracy for modern treatment techniques, such as intensity‐ modulated radiation therapy (IMRT), or to understand the sources of this inaccuracy. The aim of this work is to evaluate the accuracy of out‐of‐field dose calculations by a commercial treatment planning system (TPS), v.9.0, for IMRT treatment plans. Three IMRT plans were delivered to anthropomorphic phantoms, and out‐of‐field doses were measured using thermoluminescent detectors (TLDs). The TLD‐measured dose was then compared to the TPS‐calculated dose to quantify the accuracy of TPS calculations at various distances from the field edge and out‐of‐field anatomical locations of interest (i.e., radiosensitive organs). The individual components of out‐of‐field dose (patient scatter, collimator scatter, and head leakage) were also calculated in Pinnacle and compared to Monte Carlo simulations for a field. Our results show that the treatment planning system generally underestimated the out‐of‐field dose and that this underestimation worsened (accuracy decreased) for increasing distances from the field edge. For the three IMRT treatment plans investigated, the TPS underestimated the dose by an average of 50%. Our results also showed that collimator scatter was underestimated by the TPS near the treatment field, while all components of out‐of‐field dose were severely underestimated at greater distances from the field edge. This study highlights the limitations of commercial treatment planning systems in calculating out‐of‐field dose and provides data about the level of accuracy, or rather inaccuracy, that can be expected for modern IMRT treatments. Based on our results, use of the TPS‐reported dose could lead to an underestimation of secondary cancer induction risk, as well as poor clinical decision‐making for pregnant patients or patients with implantable cardiac pacemakers and defibrillators.

PACS numbers: 87.53.Bn; 7.55.D‐
Coronary calcium quantification using contrast‐enhanced dual‐energy computed tomography scans
Authors: Yamak Didem , Pavlicek William , Boltz Thomas , Panse Prasad M. , Akay Metin
Published: February 2017

The purpose of this study is to evaluate a direct measure of calcium burden by using dual‐energy computed tomography (DECT) during contrast‐enhanced coronary imaging, potentially eliminating the need for an extra noncontrast X‐ray acquisition. The ambiguity of separation of calcium from contrast material on contrast‐enhanced images was solved by using virtual noncontrast images obtained by DECT. A new threshold CT number was required to detect the calcium carrying potential risk for adverse coronary events on virtual noncontrast images. Two methods were investigated to determine the 130 HU threshold for DECT scoring. An in vitro anthropomorphic phantom with 29 excised patient calcium plaques inserted was used for both a linear and a logistic regression analysis. An IRB approved in vivo prospective study of six patients was also performed to be used for logistic regression analysis. The threshold found by logistic regression model to define the calcium burden on virtual noncontrast images detects the calcium carrying potential risk for adverse coronary events correctly (2.45% error rate). DECT calcium mass and volume scores obtained by using the threshold correlates with both conventional Agatston and volume scores . A conventional CT cardiac exam requires two scans, including a noncontrast scan for calcium quantification and a contrast‐enhanced scan for coronary angiography. With the ability to quantify calcium on DECT contrast‐enhanced images, a DECT cardiac exam could be accomplished with one contrast‐enhanced scan for both calcium quantification and coronary angiography.

PACS numbers: 87.57.Q, 87.57.N
An investigation of image guidance dose for breast radiotherapy
Authors: Alvarado Rosemerie , Booth Jeremy T. , Bromley Regina M. , Gustafsson Helen B
Published: February 2017

Cone‐beam computed tomography (CBCT) is used for external‐beam radiation therapy setup and target localization. As with all medical applications of ionizing radiation, radiation exposure should be managed safely and optimized to achieve the necessary image quality using the lowest possible dose. The present study investigates doses from standard kilovoltage kV radiographic and CBCT imaging protocol, and proposes two novel reduced dose CBCT protocols for the setup of breast cancer patients undergoing external beam radiotherapy. The standard thorax kV and low‐dose thorax CBCT protocols available on Varian's On‐Board Imaging system was chosen as the reference technique for breast imaging. Two new CBCT protocols were created by modifying the low‐dose thorax protocol, one with a reduced gantry rotation range (“Under breast” protocol) and the other with a reduced tube current‐time product setting (“Low dose thorax 10ms” protocol). The absorbed doses to lungs, heart, breasts, and skin were measured using XRQA2 radiochromic film in an anthropomorphic female phantom. The absorbed doses to lungs, heart, and breasts were also calculated using the PCXMC Monte Carlo simulation software. The effective dose was calculated using the measured doses to the included organs and the ICRP 103 tissue weighting factors. The deviation between measured and simulated organ doses was between 3% and 24%. Reducing the protocol exposure time to half of its original value resulted in a reduction in the absorbed doses of the organs of 50%, while the reduced rotation range resulted in a dose reduction of at least 60%. Absorbed doses obtained from “Low dose thorax 10ms” protocol were higher than the doses from our departments orthogonal kV‐kV imaging protocol. Doses acquired from “Under breast” protocol were comparable to the doses measured from the orthogonal kV‐kV imaging protocol. The effective dose per fraction using the CBCT for standard low‐dose thorax protocol was ; for the “Low dose thorax 10ms” protocol it was ; and for the “Under breast” protocol it was when the image isocenter was positioned at the phantom center and when the image isocenter was positioned in the middle of right breast. The effective dose per fraction using the orthogonal kV‐kV protocol was . The reduction of the scan exposure time or beam rotation range of the CBCT imaging significantly reduced the dose to the organs investigated. The doses from the “Under breast” protocol and orthogonal kV‐kV imaging protocol were comparable. Simulated organ doses correlated well with measured doses. Effective doses from imaging techniques should be considered with the increase use of kV imaging protocols in order to support the use of IGRT.

PACS numbers: 87.55.Qr, 87.55.ne, 87.53Bn, 87.55.kh
Performance evaluation of respiratory motion‐synchronized dynamic IMRT delivery
Authors: Yoganathan S.A. , Das K.J. Maria , Agarwal Arpita , Kumar Shaleen
Published: February 2017

The purpose of this study was to evaluate the capabilities of DMLC to deliver the respiratory motion‐synchronized dynamic IMRT (MS‐IMRT) treatments under various dose rates. In order to create MS‐IMRT plans, the DMLC leaf motions in dynamic IMRT plans of eight lung patients were synchronized with the respiratory motion of breathing period 4 sec and amplitude 2 cm (peak to peak) using an in‐house developed leaf position modification program. The MS‐IMRT plans were generated for the dose rates of 100 MU/min, 400 MU/min, and 600 MU/min. All the MS‐IMRT plans were delivered in a medical linear accelerator, and the fluences were measured using a 2D ion chamber array, placed over a moving platform. The accuracy of MS‐IMRT deliveries was evaluated with respect to static deliveries (no compensation for target motion) using gamma test. In addition, the fluences of gated delivery of 30% duty cycle and non‐MS‐IMRT deliveries were also measured and compared with static deliveries. The MS‐IMRT was better in terms of dosimetric accuracy, compared to gated and non‐MS‐IMRT deliveries. The dosimetric accuracy was observed to be significantly better for 100 MU/min MS‐IMRT. However, the use of high‐dose rate in a MS‐IMRT delivery introduced dose‐rate modulation/beam hold‐offs that affected the synchronization between the DMLC leaf motion and target motion. This resulted in more dose deviations in MS‐IMRT deliveries at the dose rate of 600 MU/min.

PACS numbers: 87.53.kn, 87.56.N‐
Assessing the role of volumetric‐modulated arc therapy in hepatocellular carcinoma
Authors: Xi Mian , Zhang Li , Li Qiao‐Qiao , Zhao Lei , Zhang Rui , Liu Meng‐Zhong
Published: February 2017

The role of volumetric‐modulated arc therapy (VMAT) in hepatocellular carcinoma (HCC) remains controversial. The purpose of this study was to determine the potential clinical role of VMAT compared with three‐dimensional conformal radiotherapy (3D CRT) for liver irradiation. Four‐dimensional CT scans of 24 patients with unresectable HCC were included and divided into two groups: (1) adjacent group (), with planning target volumes overlapping or within 1 cm adjacent to the alimentary tract; (2) nonadjacent group (), in which the normal liver itself was the dose‐limiting structure. Target coverage, organs‐at‐risk (OARs) doses, delivery parameters, and treatment accuracy were evaluated. Superior target coverage, conformity, and homogeneity were achieved with VMAT compared with 3D CRT. In the adjacent group, VMAT provided superior sparing of serial functioning OARs including the stomach, small intestine, and spinal cord. In the nonadjacent group, VMAT provided inferior sparing of most OARs including the liver, stomach, and small intestine. For the whole group, the effective treatment time was min for 3D CRT and min for VMAT. For liver lesions adjacent to the alimentary tract, this study indicates that VMAT should be selected due to the plan quality, delivery efficiency, and superior sparing of stomach and small intestine. However, for liver lesions away from the alimentary tract, VMAT is not superior to 3D CRT for normal tissue protection.

PACS number: 87.55‐x.
Fast Monte Carlo simulation for total body irradiation using a teletherapy unit
Authors: Liu Xiaodong , Lack Danielle , Rakowski Joseph T. , Knill Cory , Snyder Michael
Published: February 2017

Our institution delivers TBI using a modified Theratron 780 unit. Due to limitations of our treatment planning system in calculating dose for this treatment, we have developed a fast Monte Carlo code to calculate dose distributions within the patient. The algorithm is written in C and uses voxel density information from CT images to calculate dose in heterogeneous media. To test the algorithm, film‐based dose measurements were made separately in a simple water phantom with a high‐density insert and a RANDO phantom and then compared to doses calculated by the Monte Carlo algorithm. In addition, a separate simulation in GEANT4 was run for the RANDO phantom and compared to both film and the in‐house simulation. All results were analyzed using RIT113 film analysis software. Simulations in the water phantom accurately predict the depth of maximum dose in the phantom at 0.5 cm. The measured PDD along the central axis of the beam closely matches the PDD generated from the Monte Carlo code, deviating on average by only 3% along the depth of the water phantom. Dose measured at planes inside the high‐density insert had a mean difference of 4.9% on cross‐profile measurement. In the RANDO phantom, gamma pass rates vary between 91% and 99% at 3 mm, 3%, and were at 5 mm, 5% for the four film planes measured. Profiles taken across the film and both simulations resulted in mean relative differences of for all profiles in each slice measured. The Monte Carlo algorithm presented here is potentially a viable method for calculating dose distributions delivered in TBI treatments at our center. While not yet refined enough to be the primary method of treatment planning, the algorithm at its current resolution determines the dose distribution for one patient within a few hours, and provides clinically useful information in planning TBI. With appropriate optimization, the Monte Carlo method presented here could potentially be implemented as a first‐line treatment planning option for TBI.

PACS number: 87.10.Rt
Accurate determination of CT point‐spread‐function with high precision
Authors: Kayugawa Akihiro , Ohkubo Masaki , Wada Shinichi
Published: February 2017

The measurement of modulation transfer functions (MTFs) in computed tomography (CT) is often performed by scanning a point source phantom such as a thin wire or a microbead. In these methods the region of interest (ROI) is generally placed on the scanned image to crop the point source response. The aim of the present study was to examine the effect of ROI size on MTF measurement, and to optimize the ROI size. Using a 4 multidetector‐row CT, MTFs were measured by the wire and bead methods for three types of reconstruction kernels designated as ‘smooth', ‘standard', and ‘edge‐enhancement’ kernels. The size of a square ROI was changed from 30 to 50 pixels (approximately 2.9 to 4.9 mm). The accuracies of the MTFs were evaluated using the verification method. The MTFs measured by the wire and bead methods were dependent on ROI size, particularly in MTF measurement for the ‘edge‐enhancement’ kernel. MTF accuracy evaluated by the verification method changed with ROI size, and we were able to determine the optimum ROI size for each method (wire/bead) and for each kernel. Using these optimal ROI sizes, the MTF obtained by the wire method was in strong agreement with the MTF obtained by the bead method in each kernel. Our data demonstrate that the difficulties in obtaining accurate MTFs for some kernels such as edge‐enhancement can be overcome by incorporating the verification method into the wire and bead methods, allowing optimization of the ROI size to accurately determine the MTF.

PACS numbers: 87.57.‐s, 87.57.cf, 87.57.Q‐
Lung SBRT: dosimetric and delivery comparison of RapidArc, TomoTherapy, and IMRT
Authors: Weyh Ashleigh , Konski Andre , Nalichowski Adrian , Maier Jordan , Lack Danielle
Published: February 2017

This study seeks to compare fixed‐field intensity‐modulated radiation therapy (FF IMRT), RapidArc (RA), and helical tomotherapy (HT) to discover the optimal treatment modality to deliver SBRT to the peripheral lung. Eight patients with peripheral primary lung cancer were reviewed. Plans were prescribed a dose of 48 Gy and optimized similarly with heterogeneity corrections. Plan quality was assessed using conformality index (), homogeneity index (HI), the ratio of the 50% isodose volume to PTV () to assess intermediate dose spillage, and normal tissue constraints. Delivery efficiency was evaluated using treatment time and MUs. Dosimetric accuracy was assessed using gamma index (3% dose difference, 3 mm DTA, 10% threshold), and measured with a PTW ARRAY seven29 and OCTAVIUS phantom. , and were lowest for HT compared to seven‐field coplanar IMRT and two‐arc coplanar RA (). Normal tissue constraints were met for all modalities, except maximum rib dose due to close proximity to the PTV. RA reduced delivery time by 60% compared to HT, and 40% when compared to FF IMRT. RA also reduced the mean MUs by 77% when compared to HT, and by 22% compared to FF IMRT. All modalities can be delivered accurately, with mean QA pass rates over 97%. For peripheral lung SBRT treatments, HT performed better dosimetrically, reducing maximum rib dose, as well as improving dose conformity and uniformity. RA and FF IMRT plan quality was equivalent to HT for patients with minimal or no overlap of the PTV with the chest wall, but was reduced for patients with a larger overlap. RA and IMRT were equivalent, but the reduced treatment times of RA make it a more efficient modality.

PACS numbers: 87.53.Ly87.55.N‐, 87.55.D‐, 87.56.bd