bluuebunny/crossref_metadata_2025 huggingface dataset:
A quality assurance tool for helical tomotherapy using a step‐wedge phantom and the on‐board MVCT detector
Authors: Althof Vincent , van Haaren Paul , Westendorp Rik , Nuver Tonnis , Kramer Dinant , Ikink Marijke , Bel Arjen , Minken Andre
Published: February 2017

The purpose of this study was to develop and evaluate filmless quality assurance (QA) tools for helical tomotherapy by using the signals from the on‐board megavoltage computed tomography (MVCT) detector and applying a dedicated step‐wedge phantom. The step‐wedge phantom is a 15 cm long step‐like aluminum block positioned on the couch. The phantom was moved through the slit beam and MVCT detector signals were analyzed. Two QA procedures were developed, with gantry fixed at 0°: 1) step‐wedge procedure: to check beam energy consistency, field width, laser alignment with respect to the virtual isocenter, couch movement, and couch velocity; and 2) completion procedure: to check the accuracy of a field abutment made by the tomotherapy system after a treatment interruption. The procedures were designed as constancy tool and were validated by measurement of deliberately induced variations and comparison with a reference method. Two Hi‐Art II machines were monitored over a period of three years using the step‐wedge procedures. The data acquisition takes 5 minutes. The analysis is fully automated and results are available directly after acquisition. Couch speed deviations up to 2% were induced. The mean absolute difference between expected and measured couch speed was 0.2% (1 standard deviation SD). Field width was varied around the 10 mm nominal size, between 9.7 and 11.1 mm, in steps of 0.2 mm. Mean difference between the step‐wedge analysis and the reference method was (1 SD). Laser (mis)alignment relative to a reference situation was detected with 0.3 mm precision (1SD). The step‐wedge profile was fitted to a PDD in water. The PDD ratio D20/D10, measured at depths of 20 cm and 10 cm, was used to check beam energy consistency. Beam energy variations were induced. Mean difference between step‐wedge and water PDD ratios was 0.2% (1SD). The completion procedure was able to reveal abutment mismatches with a mean error of ‐0.6 mm (1SD). The trending data over a period of three years showed a mean deviation of 0.4% (1 SD) in couch speed. The spread in field width was 0.15 mm (1 SD). The sagittal and transverse lasers showed a variation of 0.5 mm (1 SD). Beam energy varied 1.0% (1 SD). A mean abutment mismatch was found of (1 SD) between interrupted treatments. The on‐board MVCT detector, in combination with the step‐wedge phantom, is a suitable tool for a QA program for helical tomotherapy. The method allowed frequent monitoring of machine behavior for the past three years.

PACS number: 87.55.Qr
Influence of acquisition parameters on MV‐CBCT image quality
Authors: Gayou Olivier
Published: February 2017

The production of high quality pretreatment images plays an increasing role in image‐guided radiotherapy (IGRT) and adaptive radiation therapy (ART). Megavoltage cone‐beam computed tomography (MV‐CBCT) is the simplest solution of all the commercially available volumetric imaging systems for localization. It also suffers the most from relatively poor contrast due to the energy range of the imaging photons. Several avenues can be investigated to improve MV‐CBCT image quality while maintaining an acceptable patient exposure: beam generation, detector technology, reconstruction parameters, and acquisition parameters. This article presents a study of the effects of the acquisition scan length and number of projections of a Siemens Artiste MV‐CBCT system on image quality within the range provided by the manufacturer. It also discusses other aspects not related to image quality one should consider when selecting an acquisition protocol. Noise and uniformity were measured on the image of a cylindrical water phantom. Spatial resolution was measured using the same phantom half filled with water to provide a sharp water/air interface to derive the modulation transfer function (MTF). Contrast‐to‐noise ratio (CNR) was measured on a pelvis‐shaped phantom with four inserts of different electron densities relative to water (1.043, 1.117, 1.513, and 0.459). Uniformity was independent of acquisition protocol. Noise decreased from 1.96% to 1.64% when the total number of projections was increased from 100 to 600 for a total exposure of 13.5 MU. The CNR showed dependence on the number of projections and 10% dependence on the scan length. However, these variations were not statistically significant. The spatial resolution was unaffected by the arc length or the sampling rate. Acquisition parameters have little to no effect on the image quality of the MV‐CBCT system within the range of parameters available on the system. Considerations other than image quality, such as memory storage, acquisition speed, and individual projection image quality, speak in favor of the use of a coarse sampling rate on the short scan.

PACS numbers: 87.57.C‐; 87.57.nf
Calculating the peak skin dose resulting from fluoroscopically‐guided interventions. Part II: Case studies
Authors: Jones A. Kyle , Pasciak Alexander S.
Published: February 2017

Part II of this review article presents four case studies for which peak skin doses are calculated following the methods outlined in Part I of this review. The data available in the cases ranges from proprietary dose reports to fluoroscopy time and number of digital acquisition frames only. Flowcharts are provided for each case. These flowcharts outline the calculation steps and data sources used to estimate the peak skin dose. The accuracy that can be achieved using these methods depends on several factors, including the calibration accuracy of dosimetric equipment, accuracy of information reported in the DICOM header and proprietary dose reports, accuracy of quantities measured by the medical physicist, and procedural factors such as rotation of the C‐arm during a fluoroscopically‐guided procedure.

PACS numbers: 87.59.Dj, 87.53.Bn
Medical physics staffing for radiation oncology: a decade of experience in Ontario, Canada
Authors: Battista Jerry J. , Clark Brenda G. , Patterson Michael S. , Beaulieu Luc , Sharpe Michael B. , Schreiner L. John , MacPherson Miller S. , Van Dyk Jacob
Published: February 2017

The January 2010 articles in The New York Times generated intense focus on patient safety in radiation treatment, with physics staffing identified frequently as a critical factor for consistent quality assurance. The purpose of this work is to review our experience with medical physics staffing, and to propose a transparent and flexible staffing algorithm for general use. Guided by documented times required per routine procedure, we have developed a robust algorithm to estimate physics staffing needs according to center‐specific workload for medical physicists and associated support staff, in a manner we believe is adaptable to an evolving radiotherapy practice. We calculate requirements for each staffing type based on caseload, equipment inventory, quality assurance, educational programs, and administration. Average per‐case staffing ratios were also determined for larger‐scale human resource planning and used to model staffing needs for Ontario, Canada over the next 10 years. The workload specific algorithm was tested through a survey of Canadian cancer centers. For center‐specific human resource planning, we propose a grid of coefficients addressing specific workload factors for each staff group. For larger scale forecasting of human resource requirements, values of 260, 700, 300, 600, 1200, and 2000 treated cases per full‐time equivalent (FTE) were determined for medical physicists, physics assistants, dosimetrists, electronics technologists, mechanical technologists, and information technology specialists, respectively.

PACS numbers: 87.55.N‐, 87.55.Qr
Feasibility of a remote, automated daily delivery verification of volumetric‐modulated arc therapy treatments using a commercial record and verify system
Authors: Fontenot Jonas D.
Published: February 2017

Volumetric‐modulated arc therapy (VMAT) is an effective but complex technique for delivering radiation therapy. VMAT relies on precise combinations of dose rate, gantry speed, and multileaf collimator (MLC) shapes to deliver intensity‐modulated patterns. Such complexity warrants the development of correspondingly robust performance verification systems. In this work, we report on a remote, automated software system for daily delivery verification of VMAT treatments. The performance verification software system consists of three main components: (1) a query module for retrieving daily MLC, gantry, and jaw positions reported by the linear accelerator control system to the record and verify system; (2) an analysis module which reads the daily delivery report generated from the database query module, compares the reported treatment positions against the planned positions, and compiles delivery position error reports; and (3) a graphical reporting module which displays reports initiated by a user anywhere within the institutional network or which can be configured to alert authorized users when predefined tolerance values are exceeded. The utility of the system was investigated through analysis of patient data collected at our clinic. Nearly 2500 VMAT fractions have been analyzed with the delivery verification system at our institution. The average percentage of reported MLC leaf positions within 3 mm, gantry positions within 2°, and jaw positions within 3 mm of their planned positions was , and , respectively. The level of agreement between planned and reported MLC positions decreased for treatment plans requiring larger MLC leaf movements between control points. Differences in the reported MLC position error between the delivery verification system and data extracted manually from the control system were noted; however, the differences are likely systematic and, therefore, may be characterized if appropriately accounted for. Further investigation is needed to confirm the utility and accuracy of the system.

PACS numbers: 87.55.N‐, 87.55.T‐, 87.55.Qr
A semi‐empirical model for the therapeutic range shift estimation caused by inhomogeneities in proton beam therapy
Authors: Moskvin Vadim , Cheng Chee‐Wai , Fanelli Leia , Zhao Li , Das Indra J.
Published: February 2017

The purpose of this study was to devise a simple semi‐empirical model to estimate the range shift in clinical practices with high‐Z inhomogeneity in proton beam. A semi‐empirical model utilizing the logarithmic dependence on Z in stopping power from Bohr's classical approach has been developed to calculate the range shift due to the presence of inhomogeneity. Range shift from metallic plates of atomic number Z of various thicknesses were measured in water using a parallel plate ionization chamber and calculated with the FLUKA Monte Carlo code. The proton range shifts for bone and polymethyl methacrylate (PMMA) were estimated using the semi‐empirical model and compared with Monte Carlo calculation. The semi‐empirical equation to determine range shift and water equivalent thickness is presented. The model predicts a shift of the therapeutic range to within 2.5% accuracy for initial proton energies of 50 to 250 MeV and atomic numbers from 3.3 (effective Z for water) to 82. This equation is independent of beam energy, and thus provides range shift from high‐Z materials without the knowledge of proton energy. The proposed method of calculating the therapeutic range shift accurately requires only knowledge of the effective or actual atomic number of the inhomogeneity and the thickness of the inhomogeneity along the beam direction. The model generalizes the range shift calculation for any material based on its effective atomic number, and permits reliable prediction of the range shift for material combinations where no data is currently available. The proposed model can be readily implemented in routine clinical practice for proton range shift estimation and quality assurance on the treatment planning.

PACS numbers: 87.53.‐j, 87.55.‐x, 87.53.Bn, 87.55.D‐, 87.55.Qr, 87.55.K‐
The extent and serial pattern of interfractional variation in patients with whole pelvic irradiation: a study using a kilovoltage orthogonal on‐board imager
Authors: Yoon Won Sup , Yang Dae Sik , Lee Jung Ae , Lee Suk , Park Young Je , Kim Chul Yong
Published: February 2017

The purpose of this study is to assess the extent and serial pattern of setup error of conventional fractionated whole pelvic irradiation using a kilovoltage on‐board imager. The daily on‐board images of 69 patients were matched with the digitally reconstructed radiographs of simulation on the basis of pelvic bony structure. The shifts along x‐ (lateral), y‐ (longitudinal), and z‐ (vertical) axes, and the 3D vector, were measured. The shift between an origin of the first fraction and each fraction and the shift between an isocenter of simulation and each fraction were calculated. To evaluate serial changes, the shifts of each fraction were classified into four consecutive sessions, and an ANOVA and chi‐square test were used. The systematic error of the and were 2.72 and 1.43 mm along the x‐axis, 2.98 and 1.28 mm along the y‐axis, and 4.26 and 2.39 mm along the z‐axis, respectively. The and of the 3D vector occurred in 54.3% and 23.1%, respectively. The recommended margins to cover setup error in case of using were 3.81, 3.54, and 6.01 mm along x‐, y‐, and z‐axes, whereas those using were 6.39, 6.95, and 9.95 mm, respectively. With the passage of time, the of 3D vector and along any axis in supine setup increased from 14.1% for first session to 22.5% for fourth session and from 10.8% to 18.5% , respectively. In prone setup, first session was better than others in the of 3D vector and along any axis. It is expected that the correction using the on‐board images on the first fraction improves geometrical uncertainties and reduces the margin for target coverage. Daily continuous OBI follow‐up during conventional fractionated pelvic irradiation can increase the reproducibility and be more effective in the late period.

PACS number: 87.55.km
In vivo proton dosimetry using a MOSFET detector in an anthropomorphic phantom with tissue inhomogeneity
Authors: Kohno Ryosuke , Hotta Kenji , Matsubara Kana , Nishioka Shie , Matsuura Taeko , Kawashima Mitsuhiko
Published: February 2017

When in vivo proton dosimetry is performed with a metal‐oxide semiconductor field‐effect transistor (MOSFET) detector, the response of the detector depends strongly on the linear energy transfer. The present study reports a practical method to correct the MOSFET response for linear energy transfer dependence by using a simplified Monte Carlo dose calculation method (SMC). A depth‐output curve for a mono‐energetic proton beam in polyethylene was measured with the MOSFET detector. This curve was used to calculate MOSFET output distributions with the SMC . The output value at an arbitrary point was compared with the value obtained by the conventional , which calculates proton dose distributions by using the depth‐dose curve determined by a parallel‐plate ionization chamber (PPIC). The ratio of the two values was used to calculate the correction factor of the MOSFET response at an arbitrary point. The dose obtained by the MOSFET detector was determined from the product of the correction factor and the MOSFET raw dose. When in vivo proton dosimetry was performed with the MOSFET detector in an anthropomorphic phantom, the corrected MOSFET doses agreed with the results within the measurement error. To our knowledge, this is the first report of successful in vivo proton dosimetry with a MOSFET detector.

PACS number: 87.56.‐v
Analysis of the optimum internal margin for respiratory‐gated radiotherapy using end‐exhalation phase assessments using a motion phantom
Authors: Yaegashi Yuji , Tateoka Kunihiko , Nakazawa Takuya , Fujimoto Kazunori , Shima Katsumi , Suzuki Junji , Nakata Akihiro , Saito Yuichi , Abe Tadanori , Sakata Koichi , Hareyama Masato
Published: February 2017

We aimed to optimize internal margin (IM) determination for respiratory‐gated radiotherapy using end‐expiratory phase assessments using a motion phantom. Four‐dimensional computed tomography (4D CT) data were acquired using a GE LightSpeed RT CT scanner, a respiratory‐gating system, and a motion phantom designed to move sinusoidally. To analyze the accuracy of 4D CT temporal resolution, a 25.4 mm diameter sphere was inserted into the motion phantom, and we measured the differences in sphere diameters between static and end‐exhalation phase images. In addition, the IM obtained from the maximum intensity projection within the gating window image was compared to theoretical value. Cranial–caudal motion displacement ranged from 5.0 to 30.0 mm, and the respiratory period ranged from 2.0 to 6.0 sec. Differences in sphere diameters between static and end‐exhalation phase images ranged from 0.37 to 4.6 mm, with 5.0 ‐mm and 30 mm target displacements, respectively. Differences between the IM obtained from the and the theoretical values ranged from 1.12 to 6.23 mm with 5.0 mm and 30 mm target displacements, respectively. These differences increased in proportion to the target velocity due to a motion artifact generated during tube rotation. In this study, the IMs obtained using the image were overestimated in all cases. We therefore propose that the internal target volume (ITV) for respiratory‐gated radiotherapy should be determined by adding the calculated value to the end‐exhalation phase image. We also demonstrate a methodology for subtracting motion artifacts from the ITV using a motion phantom.

PACS numbers: 87.53.Kn, 87.55.Gh, 87.56.jk
A comparison of three commercial IMRT treatment planning systems for selected pediatric cases
Authors: Eldesoky Ismail , Attalla Ehab M. , Elshemey Wael M. , Zaghloul Mohamed S.
Published: February 2017

This work aimed at evaluating the performance of three different intensity‐modulated radiotherapy (IMRT) treatment planning systems (TPSs) — KonRad, XiO and Prowess — for selected pediatric cases. For this study, 11 pediatric patients with different types of brain, orbit, head and neck cancer were selected. Clinical step‐and‐shoot IMRT treatment plans were designed for delivery on a Siemens ONCOR accelerator with 82‐leaf multileaf collimators (MLCs). Plans were optimized to achieve the same clinical objectives by applying the same beam energy and the same number and direction of beams. The analysis of performance was based on isodose distributions, dose‐volume histograms (DVHs) for planning target volume (PTV), the relevant organs at risk (OARs), as well as mean dose , maximum dose , 95% dose , volume of patient receiving 2 and 5 Gy, total number of segments, monitor units per segment (MU/Segment), and the number of MU/cGy. Treatment delivery time and conformation number were two other evaluation parameters that were considered in this study. Collectively, the Prowess and KonRad plans showed a significant reduction in the number of MUs that varied between 1.8% and 61.5% for the different cases, compared to XiO. This was reflected in shorter treatment delivery times. The percentage volumes of each patient receiving 2 Gy and 5 Gy were compared for the three TPSs. The general trend was that KonRad had the highest percentage volume, Prowess showed the lowest . The KonRad achieved better conformality than both of XiO and Prowess. Based on the present results, the three treatment planning systems were efficient in IMRT, yet XiO showed the lowest performance. The three TPSs achieved the treatment goals according to the internationally approved standards.
Comparison of 16 mm OSU‐Nag and COMS eye plaques
Authors: Zhang Hualin , Davidorf Frederick , Qi Yujin
Published: February 2017

OSU‐NAG eye plaques use fewer sources than COMS‐plaques of comparable size, and do not employ a Silastic seed carrier insert. Monte Carlo modeling was used to calculate 3D dose distributions for a 16 mm OSU‐NAG eye plaque and a 16 mm COMS eye plaque loaded with either Iodine‐125 or Cesium‐131 brachytherapy sources. The OSU‐NAG eye plaque was loaded with eight sources forming two squares, whereas the COMS eye plaque was loaded with thirteen sources approximating three isocentric circles. A spherical eyeball 24.6 mm in diameter and an ellipsoid‐like tumor 6 mm in height and 12 mm in the major and minor axes were used to evaluate the doses delivered. To establish a fair comparison, a water seed carrier was used instead of the Silastic seed carrier designed for the traditional COMS eye plaque. Calculations were performed on the dose distributions along the eye plaque axis and the DVHs of the tumor, as well as the 3D distribution. Our results indicated that, to achieve a prescription dose of 85 Gy at 6 mm from the inner sclera edge for a six‐day treatment, the OSU‐NAG eye plaque will need 6.16 U/source and 6.82 U/source for and , respectively. The COMS eye plaque will require 4.02 U/source and 4.43 U/source for the same source types. The dose profiles of the two types of eye plaques on their central axes are within 9% difference for all applicable distances. The OSU‐NAG plaque delivers about 10% and 12% more dose than the COMS for and sources, respectively, at the inner sclera edge, but 6% and 3% less dose at the opposite retina. The DVHs of the tumor for two types of plaques were within 6% difference. In conclusion, the dosimetric quality of the OSU‐NAG eye plaque used in eye plaque brachytherapy is comparable to the COMS eye plaque.

PACS number: 87.56B, 87.55k, 87.55kh
Immobilization precision of a modified GTC frame
Authors: Winey Brian , Daartz Juliane , Dankers Frank , Bussière Marc
Published: February 2017

The purpose of this study was to evaluate and quantify the interfraction reproducibility and intrafraction immobilization precision of a modified GTC frame. The error of the patient alignment and imaging systems were measured using a cranial skull phantom, with simulated, predetermined shifts. The kV setup images were acquired with a room‐mounted set of kV sources and panels. Calculated translations and rotations provided by the computer alignment software relying upon three implanted fiducials were compared to the known shifts, and the accuracy of the imaging and positioning systems was calculated. Orthogonal kV setup images for 45 proton SRT patients and 1002 fractions (average 22.3 fractions/patient) were analyzed for interfraction and intrafraction immobilization precision using a modified GTC frame. The modified frame employs a radiotransparent carbon cup and molded pillow to allow for more treatment angles from posterior directions for cranial lesions. Patients and the phantom were aligned with three 1.5 mm stainless steel fiducials implanted into the skull. The accuracy and variance of the patient positioning and imaging systems were measured to be , with the maximum uncertainty of rotation being pairs of interfraction image sets and 974 intrafraction image sets were analyzed. 3D translations and rotations were recorded. The 3D vector interfraction setup reproducibility was 0.13 mm for translations and the largest uncertainty of for rotations. The intrafraction immobilization efficacy was 0.19 mm for translations and the largest uncertainty of for rotations. The modified GTC frame provides reproducible setup and effective intrafraction immobilization, while allowing for the complete range of entrance angles from the posterior direction.

PACS number: 87.53.Ly, 87.55.Qr
Target localization using scanner‐acquired SPECT data
Authors: Roper Justin R. , Bowsher James E. , Wilson Joshua M. , Turkington Timothy G. , Yin Fang‐Fang
Published: February 2017

Target localization using single photon emission computed tomography (SPECT) and planar imaging is being investigated for guiding radiation therapy delivery. Previous studies on SPECT‐based localization have used computer‐simulated or hybrid images with simulated tumors embedded in disease‐free patient images where the tumor position is known and localization can be calculated directly. In the current study, localization was studied using scanner‐acquired images. Five fillable spheres were placed in a whole body phantom. Sphere‐to‐background radioactivity was 6:1. Ten independent SPECT scans were acquired with a Trionix Triad scanner using three detector trajectories: left lateral 180°, 360°, and right lateral 180°. Scan time was equivalent to 4.5 min. Images were reconstructed with and without attenuation correction. True target locations were estimated from 12 hr SPECT and CT images. From the 12 hr SPECT scan, 45 sets of orthogonal planar images were used to assess target localization; total acquisition time per set was equivalent to 4.5 min. A numerical observer localized the center of the targets in the 4.5 min SPECT and planar images. SPECT‐based localization errors were compared for the different detector trajectories. Across the four peripheral spheres, and using optimal iteration numbers and postreconstruction smoothing, means and standard deviations in localization errors were for proximal 180° trajectories, for 360° orbits, and for distal 180° trajectories. This rank order in localization performance is predicted by target attenuation and distance from the target to the collimator. For the targets with mean localization errors , attenuation correction reduced localization errors by 0.15 mm on average. The improvement from attenuation correction was 1.0 mm on average for the more poorly localized targets. Attenuation correction typically reduced localization errors, but for well‐localized targets, the detector trajectory generally had a larger effect. Localization performance was found to be robust to iteration number and smoothing. Localization was generally worse using planar images as compared with proximal 180° and 360° SPECT scans. Using a proximal detector trajectory and attenuation correction, localization errors were within 2 mm for the three superficial targets, thus supporting the current role in biopsy and surgery, and demonstrating the potential for SPECT imaging inside radiation therapy treatment rooms.

PACS numbers: 87.55.Gh, 87.57.qp, 87.57.uh
Study of ExacTrac X‐ray 6D IGRT setup uncertainty for marker‐based prostate IMRT treatment
Authors: Shi Chengyu , Tazi Adam , Fang Deborah Xiangdong , Iannuzzi Christopher
Published: February 2017

Novalis Tx ExacTrac X‐ray system has the 6D adjustment ability for patient setup. Limited studies exist about the setup uncertainty with ExacTrac X‐ray system for IMRT prostate treatment with fiducial markers implanted. The purpose of this study is to investigate the marker‐based prostate IMRT treatment setup uncertainty using ExacTrac 6D IGRT ability for patient setup. Forty‐three patients with prostate cancers and markers implanted have been treated on the Novalis Tx machine. The ExacTrac X‐ray system has been used for the patient pretreatment setup and intratreatment verification. In total, the shifts data for 1261 fractions and 3504 correction times (the numbers of X‐ray images were taken from tube 1 and tube 2) have been analyzed. The setup uncertainty has been separated into uncertainties in 6D. Marker matching uncertainty was also analyzed. Correction frequency probability density function was plotted, and the radiation dose for imaging was calculated. The minimum, average, and maximum translation shifts were: , , and , respectively, in the lateral direction; , , and , respectively, in the longitudinal direction; and , , and , respectively, in the vertical direction. The minimum, average, and maximum rotation shifts were: , , and , respectively, along lateral direction; , , and , respectively, along longitudinal direction; and , , and , respectively, along vertical direction. On average, each patient had three correction times during one fraction treatment. The radiation dose is about 3 mSv per fraction. With the ExacTrac 6D X‐ray system, the prostate IMRT treatment with marker implanted can achieve less than 2 mm setup uncertainty in translations, and less than 0.25° in rotations as overall interfraction mean error. The imaging dose is less than kV (CBCT) for setup verification.

PACS number: 87.55.km, 87.55.Qr, 87.56.bd
Mechanisms and prevention of thermal injury from gamma radiosurgery headframes during 3T MR imaging
Authors: Bennett Marcus C. , Wiant David B. , Gersh Jacob A. , Dolesh Wendy , Ding X. , Best Ryan C. M. , Bourland J. D.
Published: February 2017

Magnetic resonance imaging (MRI) is regularly used for stereotactic imaging of Gamma Knife (GK) radiosurgery patients for GK treatment planning. MRI‐induced thermal injuries have occurred and been reported for GK patients with attached metallic headframes. Depending on the specific MR imaging and headframe conditions, a skin injury from MRI‐induced heating can potentially occur where the four headframe screws contact the skin surface of the patient's head. Higher MR field strength has a greater heating potential. Two primary heating mechanisms, electromagnetic induction and the antenna effect, are possible. In this study, MRI‐induced heating from a 3T clinical MRI scanner was investigated for stereotactic headframes used in gamma radiosurgery and neurosurgery. Using melons as head phantoms, optical thermometers were used to characterize the temperature profile at various points of the melon headframe composite as a function of two 3T MR pulse sequence protocols. Different combinations of GK radiosurgery headframe post and screw designs were tested to determine best and worst combinations for MRI‐induced heating. Temperature increases were measured for all pulse sequences tested, indicating that the potential exists for MRI‐induced skin heating and burns at the headframe attachment site. This heating originates with electromagnetic induction caused by the RF fields inducing current in a loop formed by the headframe, mounting screws, and the region of the patient's head located between any of the two screws. This induced current is then resistively dissipated, with the regions of highest resistance, located at the headframe screw–patient head interface, experiencing the most heating. Significant heating can be prevented by replacing the metallic threads holding the screw with electrically insulated nuts, which is the heating prevention and patient safety recommendation of the GK manufacturer. Our results confirm that the manufacturer's recommendation to use insulating nuts reduces the induced currents in the headframe nearly to zero, effectively preventing heating and minimizing the likelihood of thermal injury.

PACS numbers: 87.57.‐s, 87.61.‐c, 87.61.Tg, 87.57.c‐
Coplanar versus noncoplanar intensity‐modulated radiation therapy (IMRT) and volumetric‐modulated arc therapy (VMAT) treatment planning for fronto‐temporal high‐grade glioma
Authors: Panet‐Raymond Valerie , Ansbacher Will , Zavgorodni Sergei , Bendorffe Bill , Nichol Alan , Truong Pauline T. , Beckham Wayne , Vlachaki Maria
Published: February 2017

The purpose of this study was to compare dosimetric and radiobiological parameters of treatment plans using coplanar and noncoplanar beam arrangements in patients with fronto‐temporal high‐grade glioma (HGG) generated for intensity‐modulated radiotherapy (IMRT) or volumetric‐modulated arc therapy (VMAT). Ten cases of HGG overlapping the optic apparatus were selected. Four separate plans were created for each case: coplanar IMRT, noncoplanar IMRT (ncIMRT), VMAT, and noncoplanar VMAT (ncVMAT). The prescription dose was 60 Gy in 30 fractions. Dose‐volume histograms and equivalent uniform doses (EUD) for planning target volumes (PTVs) and organs at risk (OARs) were generated. The four techniques resulted in comparable mean, minimum, maximum PTV doses, and PTV EUDs (). The mean PTV dose and EUD averaged for all techniques were 59.98 Gy (Standard Deviation ) and 59.86 Gy (). Noncoplanar IMRT significantly reduced contralateral anterior globe EUDs (6.7 Gy versus 8.2 Gy, ), while both ncIMRT and ncVMAT reduced contralateral retina EUDs (16 Gy versus 18.8 Gy, ). Noncoplanar techniques resulted in lower contralateral temporal lobe dose (22.2 Gy versus 24.7 Gy). Compared to IMRT, VMAT techniques required fewer monitor units (755 vs. 478, ) but longer optimization times. Treatment delivery times were 6.1 and 10.5 minutes for coplanar and ncIMRT versus 2.9 and 5.0 minutes for coplanar and ncVMAT. In this study, all techniques achieved comparable target coverage. Superior sparing of contralateral optic structures was seen with ncIMRT. The VMAT techniques reduced treatment delivery duration but prolonged plan optimization times, compared to IMRT techniques. Technique selection should be individualized, based on patient‐specific clinical and dosimetric parameters.

PACS number: 87
An investigation into factors affecting electron density calibration for a megavoltage cone‐beam CT system
Authors: Hughes Jessica , Holloway Lois C. , Quinn Alexandra , Fielding Andrew
Published: February 2017

There is a growing interest in the use of megavoltage cone‐beam computed tomography (MV CBCT) data for radiotherapy treatment planning. To calculate accurate dose distributions, knowledge of the electron density (ED) of the tissues being irradiated is required. In the case of MV CBCT, it is necessary to determine a calibration‐relating CT number to ED, utilizing the photon beam produced for MV CBCT. A number of different parameters can affect this calibration. This study was undertaken on the Siemens MV CBCT system, MVision, to evaluate the effect of the following parameters on the reconstructed CT pixel value to ED calibration: the number of monitor units (MUs) used (5, 8, 15 and 60 MUs), the image reconstruction filter (head and neck, and pelvis), reconstruction matrix size (256 by 256 and 512 by 512), and the addition of extra solid water surrounding the ED phantom. A Gammex electron density CT phantom containing EDs from 0.292 to 1.707 was imaged under each of these conditions. The linear relationship between MV CBCT pixel value and ED was demonstrated for all MU settings and over the range of EDs. Changes in MU number did not dramatically alter the MV CBCT ED calibration. The use of different reconstruction filters was found to affect the MV CBCT ED calibration, as was the addition of solid water surrounding the phantom. Dose distributions from treatment plans calculated with simulated image data from a 15 MU head and neck reconstruction filter MV CBCT image and a MV CBCT ED calibration curve from the image data parameters and a 15 MU pelvis reconstruction filter showed small and clinically insignificant differences. Thus, the use of a single MV CBCT ED calibration curve is unlikely to result in any clinical differences. However, to ensure minimal uncertainties in dose reporting, MV CBCT ED calibration measurements could be carried out using parameter‐specific calibration measurements.

PACS number: 87.59.bd
Impact of different CBCT imaging monitor units, reconstruction slice thicknesses, and planning CT slice thicknesses on the positioning accuracy of a MV‐CBCT system in head‐and‐neck patients
Authors: Jia Ming X. , Zhang Xu , Li Na , Han Cheng B.
Published: February 2017

The purpose of this study was to investigate the impact of different CBCT imaging monitor units (MUs), reconstruction slice thicknesses, and planning CT slice thicknesses on the positioning accuracy of a megavoltage cone‐beam computed tomography (MV‐CBCT) system in image‐guided radiation therapy (IGRT) in head‐and‐neck patients. The MV‐CBCT system was a Siemens MVision, a commercial system integrated into the Siemens ONCOR linear accelerator. The positioning accuracy of the MV‐CBCT system was determined using an anthropomorphic phantom while varying the MV‐CBCT imaging MU, reconstruction slice thickness, and planning CT slice thickness. A total of 240 CBCT images from six head‐and‐neck patients who underwent intensity‐modulated radiotherapy (IMRT) treatment were acquired and reconstructed using different MV‐CBCT scanning protocols. The interfractional setup errors of the patients were retrospectively analyzed for different imaging MUs, reconstruction slice thicknesses, and planning CT slice thicknesses. Using the anthropomorphic phantom, the largest measured mean deviation component and standard deviation of the MVision in 3D directions were 1.3 and 1.0 mm, respectively, for different CBCT imaging MUs, reconstruction slice thicknesses, and planning CT slice thicknesses. The largest setup group system error (M), system error (∑), and random error (σ) from six head‐and‐neck patients were 0.6, 1.2, and 1.7 mm, respectively. No significant difference was found in the positioning accuracy of the MV‐CBCT system between the 5 and 8 MUs, and between the 1 and 3 mm reconstruction slice thicknesses. A thin planning CT slice thickness may achieve higher positioning precision using the phantom measurement, but no significant difference was found in clinical setup precision between the 1 and 3 mm planning CT slice thicknesses.

PACS number: 87.55 ne
Effects of titanium mesh implant on dosimetry during Gamma Knife radiosurgery
Authors: Rakowski Joseph T. , Chin Karen , Mittal Sandeep
Published: February 2017

Calvarial reconstruction following resection of tumors involving the skull is often followed by stereotactic radiosurgery. Prior studies have addressed the effects of various cranioplasty materials on dose distributions in linac‐based radiosurgery. We aim to determine the effects of titanium mesh implants on Gamma Knife dose. Radiation backscatter and transmission were measured for eight types of titanium mesh using film, ion chamber, and Theratron Co‐60 teletherapy device. A single mesh was selected for Gamma Knife irradiation using a skull filled with ballistics gel. Dose profiles for reconstructed and intact skulls were compared with the planning system prediction at 2.5 and 5.5 cm depth. Titanium contact backscatter and transmission dose perturbations ranged from ‐18% to 23%. Radiation dose measured at 1.5 cm below the calvarial implant increased by 0.5% to 3.3% relative to bone. Measured Gamma Knife dose profile diameters agreed with expected profiles. Maximum dose within the intact phantom was 3% less than planned due to skull attenuation. Maximum dose within the reconstructed phantom was between the intact phantom and planned doses. Titanium mesh implants and hydroxyapatite cranioplasty result in minimal alteration () in the delivered Gamma Knife dose.

PACS number: 87.00
Evaluation of the efficiency and effectiveness of independent dose calculation followed by machine log file analysis against conventional measurement based IMRT QA
Authors: Sun Baozhou , Rangaraj Dharanipathy , Boddu Sunita , Goddu Murty , Yang Deshan , Palaniswaamy Geethpriya , Yaddanapudi Sridhar , Wooten Omar , Mutic Sasa
Published: February 2017

Experimental methods are commonly used for patient‐specific IMRT delivery verification. There are a variety of IMRT QA techniques which have been proposed and clinically used with a common understanding that not one single method can detect all possible errors. The aim of this work was to compare the efficiency and effectiveness of independent dose calculation followed by machine log file analysis to conventional measurement‐based methods in detecting errors in IMRT delivery. Sixteen IMRT treatment plans (5 head‐and‐neck, 3 rectum, 3 breast, and 5 prostate plans) created with a commercial treatment planning system (TPS) were recalculated on a QA phantom. All treatment plans underwent ion chamber (IC) and 2D diode array measurements. The same set of plans was also recomputed with another commercial treatment planning system and the two sets of calculations were compared. The deviations between dosimetric measurements and independent dose calculation were evaluated. The comparisons included evaluations of DVHs and point doses calculated by the two TPS systems. Machine log files were captured during pretreatment composite point dose measurements and analyzed to verify data transfer and performance of the delivery machine. Average deviation between IC measurements and point dose calculations with the two TPSs for head‐and‐neck plans were and , respectively. For 2D diode array measurements, the mean gamma value with 3% dose difference and 3 mm distance‐to‐agreement was within 1.5% for 13 of 16 plans. The mean 3D dose differences calculated from two TPSs were within 3% for head‐and‐neck cases and within 2% for other plans. The machine log file analysis showed that the gantry angle, jaw position, collimator angle, and MUs were consistent as planned, and maximal MLC position error was less than 0.5 mm. The independent dose calculation followed by the machine log analysis takes an average , while the experimental approach (using IC and 2D diode array measurements) takes an average about 2 hours in our clinic. Independent dose calculation followed by machine log file analysis can be a reliable tool to verify IMRT treatments. Additionally, independent dose calculations have the potential to identify several problems (heterogeneity calculations, data corruptions, system failures) with the primary TPS, which generally are not identifiable with a measurement‐based approach. Additionally, machine log file analysis can identify many problems (gantry, collimator, jaw setting) which also may not be detected with a measurement‐based approach. Machine log file analysis could also detect performance problems for individual MLC leaves which could be masked in the analysis of a measured fluence.

PACS numbers: 87.53.Bn, 87.55.Qr, 87.55.km, 87.57.Uq
Preclinical assessment of comfort and secure fit of thermobrachytherapy surface applicator (TBSA) on volunteer subjects
Authors: Arunachalam Kavitha , Craciunescu Oana I. , Markewitz Edward J. , Maccarini Paolo F. , Schlorff Jaime L. , Stauffer Paul R.
Published: February 2017

A thermobrachytherapy surface applicator (TBSA) was developed for simultaneous heat and brachytherapy treatment of chest wall (CW) recurrence of breast cancer. The ability to comfortably secure the applicator over the upper torso relative to the CW target throughout treatment is assessed on volunteers. Male and postmastectomy female volunteers were enrolled to evaluate applicator secure fit to CW. Female subjects with intact breast were also enrolled to assess the ability to treat challenging cases. Magnetic resonance (MR) images of volunteers wearing a TBSA over the upper torso were acquired once every 15 minutes for 90 minutes. Applicator displacement over this time period required for treatment preplanning and delivery was assessed using MR visible markers. Applicator comfort and tolerability were assessed using a questionnaire. Probability estimates of applicator displacements were used to investigate dosimetric impact for the worst‐case variation in radiation source‐to‐skin distance for 5 and 10 mm deep targets spreadon a torso phantom. Average and median displacements along lateral and radial directions were less than 1.2 mm over 90 minutes for all volunteers. Maximum lateral and radial displacements were measured to be less than 1 and 1.5 mm, respectively, for all CW volunteers and less than 2 mm for intact breast volunteers, excluding outliers. No complaint of pain or discomfort was reported. Phantom treatment planning for the maximum displacement of 2 mm indicatedincrease in skin dose withloss of homogeneity index (HI) for ‐2 mm uniform HDR source displacement. For +2 mm uniform displacement, skin dose decreased and HI increased by 20%. The volunteer study demonstrated that such large and uniform displacements should be rare for CW subjects, and the measured variation is expected to be low for multifraction conformal brachytherapy treatment.

PACS numbers: 41.20.Jb, 41.75.‐i, 44.
Angular dependence correction of MatriXX and its application to composite dose verification
Authors: Shimohigashi Yoshinobu , Araki Fujio , Tominaga Hirofumi , Sakata Junichi , Kawasaki Keiichi , Kanetake Nagisa , Iwashita Yuki , Yoshimura Saori , Kawakami Tamami , Ishihara Terunobu , Okuda Tomoko , Kogo Kasei
Published: February 2017

We measured the angular dependence of central and off‐axis detectors in a 2D ionization chamber array, MatriXX, and applied correction factors (CFs) to improve the accuracy of composite dose verification of IMRT and VMAT. The MatriXX doses were measured with a 10° step for gantry angles (θ) of 0°–180°, and a 1° step for lateral angles of 90°–110° in a phantom, with a field for 6 MV and 10 MV photons. The MatriXX doses were also calculated under the same conditions by the Monte Carlo (MC) algorithm. The CFs for the angular dependence of MatriXX were obtained as a function of θ from the ratios of MatriXX‐measured doses to MC‐calculated doses, and normalized at . The corrected MatriXX were validated with different fields, various simple plans, and clinical treatment plans. The dose distributions were compared with those of MC calculations and film. The absolute doses were also compared with ionization chamber and MC‐calculated doses. The angular dependence of MatriXX showed over‐responses of up to 6% and 4% at and under‐responses of up to 15% and 11% at 92°, and 8% and 5% at 180° for 6 MV and 10 MV photons, respectively. At 92°, the CFs for the off‐axis detectors were larger by up to 7% and 6% than those for the central detectors for 6 MV and 10 MV photons, respectively, and were within 2.5% at other gantry angles. For simple plans, MatriXX doses with angular correction were within 2% of those measured with the ionization chamber at the central axis and off‐axis. For clinical treatment plans, MatriXX with angular correction agreed well with dose distributions calculated by the treatment planning system (TPS) for gamma evaluation at 3% and 3 mm. The angular dependence corrections of MatriXX were useful in improving the measurement accuracy of composite dose verification of IMRT and VMAT.

PACS number: 87.55.Qr, 87.56.Fc
New strategy for automatic tumor segmentation by adaptive thresholding on PET/CT images
Authors: Moussallem Mazen , Valette Pierre‐Jean , Traverse‐Glehen Alexandra , Houzard Claire , Jegou Christophe , Giammarile Francesco
Published: February 2017

Tumor delineation is a critical aspect in radiotherapy treatment planning and is usually performed with the anatomical images of a computed tomography (CT) scan. For non‐small cell lung cancer, it has been recommended to use functional positron emission tomography (PET) images to take into account the biological target characteristics. However, today, there is no satisfactory segmentation technique for PET images in clinical applications. In the present study, a solution to this problem is proposed. The development of the segmentation technique is based on the threshold's adjustment directly from patients, rather than from phantoms. To this end, two references were chosen: measurements performed on CT images of the selected lesions, and histological measurements of surgically removed tumors. The inclusion and exclusion criteria were chosen to produce references that are assumed to have measured tumor sizes equal to the true in vivo tumor sizes. In total, for the two references, 65 lung lesions of 54 patients referred for FDG‐PET/CT exams were selected. For validation, measurements of segmented lesions on PET images using this technique were also compared to CT and histological measurements. For lesions greater than 20 mm, our segmentation technique showed a good estimation of histological measurements (mean difference between measured and calculated data equal to ) and an acceptable estimation of CT measurements. For lesions smaller than or equal to 20 mm, the method showed disagreement with the measurements derived from histological or CT data. This novel segmentation technique shows high accuracy for the lesions with largest axes between 2 and 4.5 cm. However, it does not correctly evaluate smaller lesions, likely due to the partial volume effect and/or respiratory motions.

PACS numbers: 87.53.Bn, 87.53.Kn, 87.55.D, 87.57.nm, 87.57.U