bluuebunny/crossref_metadata_2025 huggingface dataset:
A New Approach to Blade Design With Constant Rake and Relief Angles for Face-Hobbing of Bevel Gears
Authors: Habibi Mohsen , Chen Zezhong Chevy
Published: June 2015

Face-hobbing is a productive process to manufacture bevel and hypoid gears. Due to the complexity of face-hobbing, few research works have been conducted on this process. In face-hobbing, the cutting velocity along the cutting edge varies because of the intricate geometry of the cutting system and the machine tool kinematics. Due to the varying cutting velocity and the specific cutting system geometry, working relief and rake angles change along the cutting edge and have large variations at the corner which cause the local tool wear. In this paper, a new method to design cutting blades is proposed by changing the geometry of the rake and relief surfaces to avoid those large variations while the cutting edge is kept unchanged. In the proposed method, the working rake and relief angles are kept constant along the cutting edge by considering the varying cutting velocity and the machine tool kinematics. By applying the proposed method to design the blades, the tool wear characteristics are improved especially at the corner. In addition, in this paper, complete mathematical representations of the cutting system are presented. The working rake and relief angles are measured on the computer-aided design (CAD) model of the proposed and conventional blades and compared with each other. The results show that, unlike the conventional blade, in case of the proposed blade, the working rake and relief angles remain constant along the cutting edge. In addition, in order to validate the better tool wear characteristics of the proposed blade, finite element (FE) machining simulations are conducted on both the proposed and conventional blades. The results show improvements in the tool wear characteristics of the proposed blade in comparison with the conventional one.
Local Dynamic Joint Stability During Human Treadmill Walking in Response to Lower Limb Segmental Loading Perturbations
Authors: Beaudette Shawn M. , Worden Timothy A. , Kamphuis Megan , Ann Vallis Lori , Brown Stephen H. M.
Published: June 2015

Our purpose was to quantify changes in local dynamic stability (LDS) of the lumbar spine, hip, knee, and ankle in response to changes in lower limb segment mass, as well as to quantify temporal adaptations to segment loading during treadmill walking. Results demonstrate that increased mass distal to a joint yields either the maintenance of, or increased stabilization of, that particular joint relative to the unloaded condition. Increased mass proximal to a particular joint resulted in joint destabilization. The hip and ankle LDS were observed to change temporally, independent of segment loading condition, suggesting adaptation to walking on a treadmill interface.
Enhancement mode p-channel SnO thin-film transistors with dual-gate structures
Authors: Choi Yong-Jin , Han Young-Joon , Jeong Chan-Yong , Song Sang-Hun , Baek Geun Woo , Jin Sung Hun , Kwon Hyuck-In
Published: June 2015

The authors demonstrate the enhancement mode p-type SnO thin-film transistors (TFTs) using dual gate (DG) structures. The cross-linked polyvinyl alcohol dielectric with a polymethylmethacrylate buffer layer is formed as a top gate (TG) insulator of the DG SnO TFT. The fabricated DG SnO TFT exhibits better electrical performances than the bottom gate (BG) and TG SnO TFTs including higher field-effect mobility and smaller subthreshold slope. In fabricated DG TFTs, the threshold voltage (Vth) of the BG TFT is linearly modulated by the voltage applied to the TG electrode. The BG transfer curve exhibits a depletion mode operation when measured while TG is grounded, but operates in the enhancement mode with a negative Vth (=−0.9 V) when a positive bias of 10 V is applied to the TG electrode. The enhancement mode operation of p-type SnO TFTs can increase the output voltage swing range and decreases the off-stage leakage currents of the complementary logic circuits.
SU‐B‐213‐06: Development of ABR Examination Questions
Authors: Allison J.
Published: June 2015

The North American medical physics community validates the education received by medical physicists and the clinical qualifications for medical physicists through accreditation of educational programs and certification of medical physicists. Medical physics educational programs (graduate education and residency education) are accredited by the Commission on Accreditation of Medical Physics Education Programs (CAMPEP), whereas medical physicists are certified by several organizations, the most familiar of which is the American Board of Radiology (ABR). In order for an educational program to become accredited or a medical physicist to become certified, the applicant must meet certain specified standards set by the appropriate organization.

In this Symposium, representatives from both CAMPEP and the ABR will describe the process by which standards are established as well as the process by which qualifications of candidates for accreditation or certification are shown to be compliant with these standards.

The Symposium will conclude with a panel discussion.

Learning Objectives:

Recognize the difference between accreditation of an educational program and certification of an individual

Identify the two organizations primarily responsible for these tasks

Describe the development of educational standards

Describe the process by which examination questions are developed

GS is Executive Secretary of CAMPEP.
SU‐C‐213‐06: Dosimetric Verification of 3D Printed Electron Bolus
Authors: Rasmussen K , Corbett M , Pelletier C , Huang Z , Feng Y , Jung J
Published: June 2015

Purpose:

To determine the dosimetric effect of 3D printed bolus in an anthropomorphic phantom.

Methods:

Conformable bolus material was generated for an anthropomorphic phantom from a DICOM volume. The bolus generated was a uniform expansion of 5mm applied to the nose region of the phantom, as this is a difficult area to uniformly apply bolus clinically. A Printrbot metal 3D Printer using PLA plastic generated the bolus. A 9MeV anterior beam with a 5cm cone was used to deliver dose to the nose of the phantom. TLD measurements were compared to predicted values at the phantom surface. Film planes were analyzed for the printed bolus, a standard 5mm bolus sheet placed on the phantom, and the phantom with no bolus applied to determine depth and dose distributions.

Results:

TLDs measured within 2.5% of predicted value for the 3D bolus. Film demonstrated a more uniform dose distribution in the nostril region for the 3d printed bolus than the standard bolus. This difference is caused by the air gap created around the nostrils by the standard bolus, creating a secondary build‐up region. Both demonstrated a 50% central axis dose shift of 5mm relative to the no bolus film. HU for the bolus calculated the PLA electron density to be ∼1.1g/cc. Physical density was measured to be 1.3g/cc overall.

Conclusion:

3D printed PLA bolus demonstrates improved dosimetric performance to standard bolus for electron beams with complex phantom geometry.
SU‐C‐213‐07: Fabrication and Testing of a 3D‐Printed Small Animal Rectal Cooling Device to Evaluate Local Hypothermia as a Radioprotector During Prostate SBRT
Authors: Hrycushko B , Chopra R , Futch C , Bing C , Wodzak M , Stojadinovic S , Jiang S , Medin P
Published: June 2015

Purpose:

The protective effects of induced or even accidental hypothermia on the human body are widespread with several medical uses currently under active research. In vitro experiments using human cell lines have shown hypothermia provides a radioprotective effect that becomes more pronounced at large, single‐fraction doses common to SBRT treatments. Relevant to prostate SBRT, this work details the fabrication and testing of a 3D‐printed cooling device to facilitate the investigation of the radioprotective effect of local hypothermia on the rat rectum.

Methods:

A 3cm long, two‐channel rectal cooling device was designed in SOLIDWORKS CAD for 3D printing. The water intake nozzle is connected to a 1mm diameter brass pipe from which water flows and circulates back around to the exit nozzle. Both nozzles are connected by plastic tubing to a water chiller pump. Following leak‐proof testing, fiber optic temperature probes were used to evaluate the temperature over time when placed adjacent to the cooling device within a rat rectum. MRI thermometry characterized the relative temperature distribution in concentric ROIs surrounding the probe. CBCT images from a small‐animal irradiator were evaluated for imaging artifacts which could affect Monte Carlo dose calculations during treatment planning.

Results:

The rectal temperature adjacent to the cooling device decreased from body temperature (37°C) to 15°C in 10–20 minutes from device insertion. Rectal temperature was maintained at 15±3°C during active cooling. MRI thermometry tests revealed a steep temperature gradient with increasing distance from the cooling device, with the desired temperature range maintained within the surrounding few millimeters.

Conclusion:

A 3D printed rectal cooling device was fabricated for the purpose of inducing local hypothermia in rat rectums. Rectal cooling capabilities were characterized in‐vivo to facilitate an investigation of the radioprotective effect of hypothermia for late rectal toxicity following a single large dose of radiation.

Funding support provided by RSNA research seed grant
SU‐C‐304‐04: A Compact Modular Computational Platform for Automated On‐Board Imager Quality Assurance
Authors: Dolly S , Cai B , Chen H , Anastasio M , Tan J , Sun B , Yaddanapudi S , Noel C , Goddu S , Mutic S , Li H
Published: June 2015

Purpose:

Traditionally, the assessment of X‐ray tube output and detector positioning accuracy of on‐board imagers (OBI) has been performed manually and subjectively with rulers and dosimeters, and typically takes hours to complete. In this study, we have designed a compact modular computational platform to automatically analyze OBI images acquired with in‐house designed phantoms as an efficient and robust surrogate.

Methods:

The platform was developed as an integrated and automated image analysis‐based platform using MATLAB for easy modification and maintenance. Given a set of images acquired with the in‐house designed phantoms, the X‐ray output accuracy was examined via cross‐validation of the uniqueness and integration minimization of important image quality assessment metrics, while machine geometric and positioning accuracy were validated by utilizing pattern‐recognition based image analysis techniques.

Results:

The platform input was a set of images of an in‐house designed phantom. The total processing time is about 1–2 minutes. Based on the data acquired from three Varian Truebeam machines over the course of 3 months, the designed test validation strategy achieved higher accuracy than traditional methods. The kVp output accuracy can be verified within +/−2 kVp, the exposure accuracy within 2%, and exposure linearity with a coefficient of variation (CV) of 0.1. Sub‐millimeter position accuracy was achieved for the lateral and longitudinal positioning tests, while vertical positioning accuracy within +/−2 mm was achieved.

Conclusion:

This new platform delivers to the radiotherapy field an automated, efficient, and stable image analysis‐based procedure, for the first time, acting as a surrogate for traditional tests for LINAC OBI systems. It has great potential to facilitate OBI quality assurance (QA) with the assistance of advanced image processing techniques. In addition, it provides flexible integration of additional tests for expediting other OBI quality assurance tests, such as 2D/3D image quality, making completely automated QA possible.

Research Funding from Varian Medical Systems Inc. . Dr. Sasa Mutic receives compensation for providing patient safety training services from Varian Medical Systems, the sponsor of this study.
SU‐C‐304‐05: Use of Local Noise Power Spectrum and Wavelets in Comprehensive EPID Quality Assurance
Authors: Lee S , Gopal A , Yan G , Bassett P , Park C , Samant S
Published: June 2015

Purpose:

As EPIDs are increasingly used for IMRT QA and real‐time treatment verification, comprehensive quality assurance (QA) of EPIDs becomes critical. Current QA with phantoms such as the Las Vegas and PIPSpro™ can fail in the early detection of EPID artifacts. Beyond image quality assessment, we propose a quantitative methodology using local noise power spectrum (NPS) to characterize image noise and wavelet transform to identify bad pixels and inter‐subpanel flat‐fielding artifacts.

Methods:

A total of 93 image sets including bar‐pattern images and open exposure images were collected from four iViewGT a‐Si EPID systems over three years. Quantitative metrics such as modulation transform function (MTF), NPS and detective quantum efficiency (DQE) were computed for each image set. Local 2D NPS was calculated for each subpanel. A 1D NPS was obtained by radial averaging the 2D NPS and fitted to a power‐law function. R‐square and slope of the linear regression analysis were used for panel performance assessment. Haar wavelet transformation was employed to identify pixel defects and non‐uniform gain correction across subpanels.

Results:

Overall image quality was assessed with DQE based on empirically derived area under curve (AUC) thresholds. Using linear regression analysis of 1D NPS, panels with acceptable flat fielding were indicated by r‐square between 0.8 and 1, and slopes of −0.4 to −0.7. However, for panels requiring flat fielding recalibration, r‐square values less than 0.8 and slopes from +0.2 to −0.4 were observed. The wavelet transform successfully identified pixel defects and inter‐subpanel flat fielding artifacts. Standard QA with the Las Vegas and PIPSpro phantoms failed to detect these artifacts.

Conclusion:

The proposed QA methodology is promising for the early detection of imaging and dosimetric artifacts of EPIDs. Local NPS can accurately characterize the noise level within each subpanel, while the wavelet transforms can detect bad pixels and inter‐subpanel flat fielding artifacts.
SU‐C‐304‐06: Determination of Intermediate Correction Factors for Three Dosimeters in Small Composite Photon Fields Used in Robotic Radiosurgery
Authors: Christiansen E , Belec J , Muir B , Vandervoort E
Published: June 2015

Purpose:

To calculate using Monte‐Carlo the intermediate and total correction factors (CFs) for two microchambers and a plastic scintillator for composite fields delivered by the CyberKnife system.

Methods:

A linac model was created in BEAMnrc by matching percentage depth dose (PDD) curves and output factors (OFs) measured using an A16 microchamber with Monte Carlo calculations performed in egs_chamber to explicitly model detector response. Intermediate CFs were determined for the A16 and A26 microchambers and the W1 plastic scintillator in fourteen different composite fields inside a solid water phantom. Seven of these fields used a 5 mm diameter collimator; the remaining fields employed a 7.5 mm collimator but were otherwise identical to the first seven. Intermediate CFs are reported relative to the respective CF for a 60 mm collimator (800 mm source to detector distance and 100 mm depth in water).

Results:

For microchambers in composite fields, the intermediate CFs that account for detector density and volume were the largest contributors to total CFs. The total CFs for the A26 were larger than those for the A16, especially for the 5 mm cone (1.227±0.003 to 1.144±0.004 versus 1.142±0.003 to 1.099±0.004), due to the A26's larger active volume (0.015 cc) relative to the A16 (0.007 cc), despite the A26 using similar wall and electrode material. The W1 total and intermediate CFs are closer to unity, due to its smaller active volume and near water‐equivalent composition, however, 3–4% detector volume corrections are required for 5 mm collimator fields. In fields using the 7.5 mm collimator, the correction is nearly eliminated for the W1 except for a non‐isocentric field.

Conclusion:

Large and variable CFs are required for microchambers in small composite fields primarily due to density and volume effects. Corrections are reduced but not eliminated for a plastic scintillator in the same fields.
SU‐C‐BRA‐02: Gradient Based Method of Target Delineation On PET/MR Image of Head and Neck Cancer Patients
Authors: Dance M , Chera B , Falchook A , Das S , Lian J
Published: June 2015

Purpose:

Validate the consistency of a gradient‐based segmentation tool to facilitate accurate delineation of PET/CT‐based GTVs in head and neck cancers by comparing against hybrid PET/MR‐derived GTV contours.

Materials and Methods:

A total of 18 head and neck target volumes (10 primary and 8 nodal) were retrospectively contoured using a gradient‐based segmentation tool by two observers. Each observer independently contoured each target five times. Inter‐observer variability was evaluated via absolute percent differences. Intra‐observer variability was examined by percentage uncertainty. All target volumes were also contoured using the SUV percent threshold method. The thresholds were explored case by case so its derived volume matched with the gradient‐based volume. Dice similarity coefficients (DSC) were calculated to determine overlap of PET/CT GTVs and PET/MR GTVs.

Results:

The Levene's test showed there was no statistically significant difference of the variances between the observer's gradient‐derived contours. However, the absolute difference between the observer's volumes was 10.83%, with a range from 0.39% up to 42.89%. PET‐avid regions with qualitatively non‐uniform shapes and intensity levels had a higher absolute percent difference near 25%, while regions with uniform shapes and intensity levels had an absolute percent difference of 2% between observers. The average percentage uncertainty between observers was 4.83% and 7%. As the volume of the gradient‐derived contours increased, the SUV threshold percent needed to match the volume decreased. Dice coefficients showed good agreement of the PET/CT and PET/MR GTVs with an average DSC value across all volumes at 0.69.

Conclusion:

Gradient‐based segmentation of PET volume showed good consistency in general but can vary considerably for non‐uniform target shapes and intensity levels. PET/CT‐derived GTV contours stemming from the gradient‐based tool show good agreement with the anatomically and metabolically more accurate PET/MR‐derived GTV contours, but tumor delineation accuracy can be further improved with the use PET/MR.
SU‐C‐BRA‐04: Use of Esophageal Wall Thickness in Evaluation of the Response to Chemoradiation Therapy for Esophageal Cancer
Authors: Wang J , Kang M , Kligerman S , Lu W
Published: June 2015

Purpose:

To quantitatively evaluate the esophageal cancer response to chemoradiation therapy (CRT) by measuring the esophageal wall thickness in CT.

Method:

Two datasets were used in this study. The first dataset is composed of CT scans of 15 esophageal cancer patients and 15 normal controls. The second dataset is composed of 20 esophageal cancer patients who underwent PET/CT scans before (Pre‐CRT) and after CRT (Post‐CRT). We first segmented the esophagus using a multi‐atlas‐based algorithm. The esophageal wall thickness was then computed, on each slice, as the equivalent circle radius of the segmented esophagus excluding the lumen. To evaluate the changes of wall thickness, we computed the standard deviation (SD), coefficient of variation (COV, SD/Mean), and flatness [(Max–Min)/Mean] of wall thickness along the entire esophagus.

Results:

For the first dataset, the mean wall thickness of cancer patients and normal controls were 6.35 mm and 6.03 mm, respectively. The mean SD, COV, and flatness of the wall thickness were 2.59, 0.21, and 1.27 for the cancer patients and 1.99, 0.16, and 1.13 for normal controls. Statistically significant differences (p < 0.05) were identified in SD and flatness. For the second dataset, the mean wall thickness of pre‐CRT and post‐CRT patients was 7.13 mm and 6.84 mm, respectively. The mean SD, COV, and flatness were 1.81, 0.26, and 1.06 for pre‐CRT and 1.69, 0.26, and 1.06 for post‐CRT. Statistically significant difference was not identified for these measurements. Current results are based on the entire esophagus. We believe significant differences between pre‐ and post‐CRT scans could be obtained, if we conduct the measurements at tumor sites.

Conclusion:

Results show thicker wall thickness in pre‐CRT scans and differences in wall thickness changes between normal and abnormal esophagus. This demonstrated the potential of esophageal wall thickness as a marker in the tumor CRT response evaluation.

This work was supported in part by the National Cancer Institute Grant R01CA172638.
SU‐C‐303‐02: Correlating Metabolic Response to Radiation Therapy with HIF‐1alpha Expression
Authors: Campos D , Peeters W , Nickel K , Eliceiri K , Kimple R , Van Der Kogel A , Kissick M
Published: June 2015

Purpose:

To understand radiation induced alterations in cellular metabolism which could be used to assess treatment or normal tissue response to aid in patient‐specific adaptive radiotherapy. This work aims to compare the metabolic response of two head and neck cell lines, one malignant (UM‐SCC‐22B) and one benign (Normal Oral Keratinocyte), to ionizing radiation. Responses are compared to alterations in HIF‐1alpha expression. These dynamics can potentially serve as biomarkers in assessing treatment response allowing for patient‐specific adaptive radiotherapy.

Methods:

Measurements of metabolism and HIF‐1alpha expression were taken before and X minutes after a 10 Gy dose of radiation delivered via an orthovoltage x‐ray source. In vitro changes in metabolic activity were measured via fluorescence lifetime imaging (FLIM) to assess the mean lifetime of NADH autofluorescence following a dose of 10 Gy. HIF‐1alpha expression was measured via immunohistochemical staining of in vitro treated cells and expression was quantified using the FIJI software package.

Results:

FLIM demonstrated a decrease in the mean fluorescence lifetime of NADH by 100 ps following 10 Gy indicating a shift towards glycolytic pathways for malignant cells; whereas this benign cell line showed little change in metabolic signature. Immunohistochemical analysis showed significant changes in HIF‐1alpha expression in response to 10 Gy of radiation that correlate to metabolic profiles.

Conclusion:

Radiation induces significant changes in metabolic activity and HIF‐1alpha expression. These alterations occur on time scales approximating the duration of common radiation treatments (approximately tens of minutes). Further understanding these dynamics has important implications with regard to improvement of therapy and biomarkers of treatment response.
SU‐C‐303‐07: Influence of Image Registration Algorithms and Noise Levels On the Accuracy of Fractional Regional Ventilation
Authors: Liu Y , Badea C , Mistry N , D'souza W
Published: June 2015

Purpose:

The derivation of fractional regional lung‐ventilation (FRV) involves registering images corresponding to extreme phases of the respiratory cycle. The purpose of this work was to investigate the influence of registration algorithms and image noise on the accuracy of the mouse lung tidal volume (TV) by employing a density‐based mass‐conservation technique in the calculation of fractional regional lung ventilation (FRV).

Methods:

Three mice mechanically ventilated using a fixed volume (0.4 ml) ventilator. CT images were acquired at full‐inhale and end‐exhale breath hold. Deformable image registration between inhale and exhale images was performed using three image registration algorithms: B‐splines, Demons‐Diffusion and Demons‐Fluid model. The impact of noise was studied by adding Gaussian noise resulting in images with relative signal‐to‐noise ratio (SNR) of 1 (zero noise), 0.65 (relative to zero noise), 0.39 and 0.26. A density‐based technique for evaluation of FRV from CT images was used to calculate tidal volume. The global TV calculated from the FRV maps was benchmarked to the known ventilated mouse lung volume of 0.4 ml.

Results:

The TV obtained using the B‐splines, Demons‐Diffusion and Demons‐Fluid registration algorithms with zero noise (relative SNR=1) were 0.28±0.03 ml, 0.22±0.04 ml and 0.41±0.01 ml, respectively. We observed a decline in the calculated tidal volume as SNR decreased. The greatest decline (27%) was observed with the Demons‐Fluid algorithm. However, the absolute value of the calculated TV with a relative SNR=0.26 was 0.30±0.05 ml, still the most accurate TV of the three registration algorithms investigated. The B‐splines and Demons‐Diffusion algorithm were less sensitive to noise and resulted in TV declines of 18% with a relative SNR=0.26.

Conclusion:

The Demons‐Fluid image registration algorithm consistently provided the most accurate calculated absolute TV. Although it was the most sensitive to image noise, the calculated absolute TV was more accurate than the B‐splines and Demons Diffusion algorithms.
SU‐C‐204‐05: Simulations of a Portal Imaging System for Conformal and Intensity Modulated Fast Neutron Therapy
Authors: James S St. , Argento D , Stewart R
Published: June 2015

Purpose:

The University of Washington Medical Center offers neutron therapy for the palliative and definitive treatment of selected cancers. In vivo field verification has the potential to improve the safe and effective delivery of neutron therapy. We propose a portal imaging method that relies on the creation of positron emitting isotopes (11C and 15O) through (n, 2n) reactions with a PMMA plate placed below the patient. After field delivery, the plate is retrieved from the vault and imaged using a reader that detects annihilation photons. The spatial pattern of activity produced in the PMMA plate provides information to reconstruct the neutron fluence map needed to confirm treatment delivery.

Methods:

We used MCNP to simulate the accumulation of 11C activity in a slab of PMMA 2 mm thick, and GATE was used to simulate the sensitivity and spatial resolution of a prototype imaging system. BGO crystal thicknesses of 1 cm, 2 cm and 3 cm were simulated with detector separations of 2 cm. Crystal pitches of 2 mm and 4 mm were evaluated. Back‐projection of the events was used to create a planar image. The spatial resolution was taken to be the FWHM of the reconstructed point source image.

Results:

The system sensitivity for a point source in the center of the field of view was found to range from 58% for 1 cm thick BGO with 2 mm crystal pitch to 74% for the 3 cm thick BGO crystals with 4 mm crystal pitch. The spatial resolution at the center of the field of view was found to be 1.5 mm for the system with 2 mm crystal pitch and 2.8 mm for the system with the 4 mm crystal pitch.

Conclusion:

BGO crystals with 4 mm crystal pitch and 3 cm length would offer the best sensitivity reader.
SU‐C‐204‐06: Surface Imaging for the Set‐Up of Proton Post‐Mastectomy Chestwall Irradiation: Gated Images Vs Non Gated Images
Authors: Batin E , Depauw N , MacDonald S , Lu H
Published: June 2015

Purpose:

Historically, the set‐up for proton post‐mastectomy chestwall irradiation at our institution started with positioning the patient using tattoos and lasers. One or more rounds of orthogonal X‐rays at gantry 0° and beamline X‐ray at treatment gantry angle were then taken to finalize the set‐up position. As chestwall targets are shallow and superficial, surface imaging is a promising tool for set‐up and needs to be investigated

Methods:

The orthogonal imaging was entirely replaced by AlignRT™ (ART) images. The beamline X‐Ray image is kept as a confirmation, based primarily on three opaque markers placed on skin surface instead of bony anatomy. In the first phase of the process, ART gated images were used to set‐up the patient and the same specific point of the breathing curve was used every day. The moves (translations and rotations) computed for each point of the breathing curve during the first five fractions were analyzed for ten patients. During a second phase of the study, ART gated images were replaced by ART non‐gated images combined with real‐time monitoring. In both cases, ART images were acquired just before treatment to access the patient position compare to the non‐gated CT.

Results:

The average difference between the maximum move and the minimum move depending on the chosen breathing curve point was less than 1.7 mm for all translations and less than 0.7° for all rotations. The average position discrepancy over the course of treatment obtained by ART non gated images combined to real‐time monitoring taken before treatment to the planning CT were smaller than the average position discrepancy obtained using ART gated images. The X‐Ray validation images show similar results with both ART imaging process.

Conclusion:

The use of ART non gated images combined with real time imaging allows positioning post‐mastectomy chestwall patients in less than 3 mm / 1°.
SU‐C‐207‐02: A Method to Estimate the Average Planar Dose From a C‐Arm CBCT Acquisition
Authors: Supanich MP
Published: June 2015

Purpose:

The planar average dose in a C‐arm Cone Beam CT (CBCT) acquisition had been estimated in the past by averaging the four peripheral dose measurements in a CTDI phantom and then using the standard 2/3rds peripheral and 1/3 central CTDIw method (hereafter referred to as Dw). The accuracy of this assumption has not been investigated and the purpose of this work is to test the presumed relationship.

Methods:

Dose measurements were made in the central plane of two consecutively placed 16cm CTDI phantoms using a 0.6cc ionization chamber at each of the 4 peripheral dose bores and in the central dose bore for a C‐arm CBCT protocol. The same setup was scanned with a circular cut‐out of radiosensitive gafchromic film positioned between the two phantoms to capture the planar dose distribution. Calibration curves for color pixel value after scanning were generated from film strips irradiated at different known dose levels. The planar average dose for red and green pixel values was calculated by summing the dose values in the irradiated circular film cut out. Dw was calculated using the ionization chamber measurements and film dose values at the location of each of the dose bores.

Results:

The planar average dose using both the red and green pixel color calibration curves were within 10% agreement of the planar average dose estimated using the Dw method of film dose values at the bore locations. Additionally, an average of the planar average doses calculated using the red and green calibration curves differed from the ionization chamber Dw estimate by only 5%.

Conclusion:

The method of calculating the planar average dose at the central plane of a C‐arm CBCT non‐360 rotation by calculating Dw from peripheral and central dose bore measurements is a reasonable approach to estimating the planar average dose.

Research Grant, Siemens AG
SU‐C‐207‐03: Optimization of a Collimator‐Based Sparse Sampling Technique for Low‐Dose Cone‐Beam CT
Authors: Lee T , Kim I , Han B , Cho S
Published: June 2015

Purpose:

In computed tomography (CT) imaging, radiation dose delivered to the patient is one of the major concerns. Sparse‐view CT takes projections at sparser view angles and provides a viable option to reducing dose. However, a fast power switching of an X‐ray tube, which is needed for the sparse‐view sampling, can be challenging in many CT systems. We have earlier proposed a many‐view under‐sampling (MVUS) technique as an alternative to sparse‐view CT. In this study, we investigated the effects of collimator parameters on the image quality and aimed to optimize the collimator design.

Methods:

We used a bench‐top circular cone‐beam CT system together with a CatPhan600 phantom, and took 1440 projections from a single rotation. The multi‐slit collimator made of tungsten was mounted on the X‐ray source for beam blocking. For image reconstruction, we used a total‐variation minimization (TV) algorithm and modified the backprojection step so that only the measured data through the collimator slits are to be used in the computation. The number of slits and the reciprocation frequency have been varied and the effects of them on the image quality were investigated. We also analyzed the sampling efficiency: the sampling density and data incoherence in each case. We tested three sets of slits with their number of 6, 12 and 18, each at reciprocation frequencies of 10, 30, 50 and 70 Hz/ro.

Results:

Consistent results in the image quality have been produced with the sampling efficiency, and the optimum condition was found to be using 12 slits at 30 Hz/ro. As image quality indices, we used the CNR and the detectability.

Conclusion:

We conducted an experiment with a moving multi‐slit collimator to realize a sparse‐sampled cone‐beam CT. Effects of collimator parameters on the image quality have been systematically investigated, and the optimum condition has been reached.
SU‐C‐207‐06: In Vivo Quantification of Gold Nanoparticles Using K‐Edge Imaging Via Spectrum Shaping by Gold Filter
Authors: Chen H , Cormack R , Bhagwat M , Berbeco R
Published: June 2015

Purpose:

Gold nanoparticles (AuNP) are multifunctional platforms ideal for drug delivery, targeted imaging and radiosensitization. We have investigated quantitative imaging of AuNPs using on board imager (OBI) cone beam computed tomography (CBCT). To this end, we also present, for the first time, a novel method for k‐edge imaging of AuNP by filter‐based spectral shaping.

Methods:

We used a digital 25 cm diameter water phantom, embedded with 3 cm spheres filled with AuNPs of different concentrations (0 mg/ml – 16 mg/ml). A poly‐energetic X‐ray spectrum of 140 kVp from a conventional X‐ray tube is shaped by balanced K‐edge filters to create an excess of photons right above the K‐edge of gold at 80.7 keV. The filters consist of gold, tin, copper and aluminum foils. The phantom with appropriately assigned attenuation coefficients is forward projected onto a detector for each energy bin and then integrated. FKD reconstruction is performed on the integrated projections. Scatter, detector efficiency and noise are included.

Results:

We found that subtracting the results of two filter sets (Filter A:127 µm gold foil with 254 µm tin, 330 µm copper and 1 mm aluminum, and Filter B: 635 µm tin with 264 µm copper and 1 mm aluminum), provides substantial image contrast. The resulting filtered spectra match well below 80.7 keV, while maintaining sufficient X‐ray quanta just above that. Voxel intensities of AuNP containing spheres increase linearly with AuNP concentration. K‐edge imaging provides 18% more sensitivity than the tin filter alone, and 38% more sensitivity than the gold filter alone.

Conclusion:

We have shown that it is feasible to quantitatively detect AuNP distributions in a patient‐sized phantom using clinical CBCT and K‐edge spectral shaping.
SU‐D‐207‐02: Automated Respiratory Motion Tracking with Machine Vision
Authors: Armstrong H , Miften M
Published: June 2015

Purpose:

Current systems for obtaining respiratory information at time of treatment typically require the use of additional equipment and add to patient setup time. In this study, we develop a fully automated method to track respiratory motion by tracking the motion of the diaphragm surface, making use of only current imaging technology and without the need for additional mechanical, pneumatic, or optical devices.

Methods:

A statistical algorithm, RANdom SAmple Consensus (RANSAC), was used for direct tracking of the diaphragm surface through kV CBCT projection images. A third order polynomial was used to model the shape of the diaphragm. Model constraints based on the diaphragm shape as well as a small motion assumption (between adjacent projections) were incorporated to constrain the model. The changing position of the diaphragm along the Superior‐Inferior direction as the patient respires then gives the respiratory trace.

Results:

On the patients studied, the respiratory trace can be obtained with between 5,000 and 1,000,000 iterations of the RANSAC algorithm, per projection. Visual comparison with the projection images in a cine like mode shows the computed respiratory trace matches well with the true respiratory cycle. With a low number of iterations (<10,000 per projection), the diaphragm location computation time is similar to projection image acquisition and therefore the trace can be computed in real time.

Conclusion:

The RANSAC algorithm is a viable method for obtaining a respiratory trace with the patient on the treatment couch. Implementing the RANSAC algorithm on a GPU should allow for a significantly larger number of iterations while maintaining the ability to acquire the respiratory trace in real time. This method of obtaining a respiratory trace should reduce costs for technology such as 4DCBCT as well as reduce patient setup times and improve patient comfort.
SU‐D‐207‐06: Clinical Validations of Shading Correction for Cone‐Beam CT Using Planning CT as a Prior
Authors: Tsui T , Wei J , Zhu L
Published: June 2015

Purpose:

Current cone‐beam CT (CBCT) images contain severe shading artifacts mainly due to scatter, hindering their quantitative use in current radiation therapy. We have previously proposed an effective shading correction method for CBCT using planning CT (pCT) as prior knowledge. In this work, we investigate the method robustness via statistical analyses on studies of a large patient group and compare the performance with that of a state‐of‐the‐art method implemented on the current commercial radiation therapy machine ‐‐ the Varian Truebeam system.

Methods:

Since radiotherapy patients routinely undergo multiple‐detector CT (MDCT) scans in the planning procedure, we use the high‐quality pCT as “free” prior knowledge for CBCT image improvement. The CBCT image with no correction is first spatially registered with the pCT. Primary CBCT projections are estimated via forward projections of the registered image. The low frequency errors in the projections, which stem from mainly scatter, are estimated by filtering the difference between original line integral and the estimated scatter projections. The corrected CBCT image is then reconstructed from the scatter corrected projections. The proposed method is evaluated on 40 cancer patients.

Results:

On all patient images, we compare errors on CT number, spatial non‐uniformity (SNU) and image contrast, using pCT as the ground truth. T‐tests show that our algorithm improves over the Varian method on CBCT accuracies of CT number and SNU with 90% confident. The average CT number error is reduced from 54.8 HU on the Varian method to 40.9 HU, and the SNU error is reduced from 7.7% to 3.8%. There is no obvious improvement on image contrast.

Conclusion:

Large‐group patient studies show that the proposed pCT‐based algorithm outperforms the Varian method of the Truebeam system on CBCT shading correction, by providing CBCT images with higher CT number accuracy and greater image uniformity.
SU‐D‐201‐01: Attenuation of PET/CT Gantries with 511 KeV Photons
Authors: Busse N
Published: June 2015

Purpose:

PET shielding requires the use of large amounts of lead because of the penetrating nature of 511 keV photons. While the uptake rooms generally require the thickest lead, the scan room often requires substantial shielding. Attenuation by the PET/CT gantry is normally assumed to be zero, but may be significant in directions perpendicular to the scanner axis.

Methods:

A 5 mL tube was filled with between 14.7 and 20.5 mCi of F‐18 and inserted into a phantom (70 cm NEMA PET Scatter Phantom). Exposure rates were recorded at several distances and 15° intervals with a pressurized ionization chamber (Ludlum 9DP) both with the phantom outside the gantry and centered in the CT and PET acquisition positions. These measurements were repeated with three scanners: Siemens Biograph TruePoint 6, GE Optima 560, and Philips Gemini 64. Measurements were decay corrected and normalized to exposure rates outside the gantry to calculate percent transmission.

Results:

Between 45° to 135° (measured from the patient bed at 0°), average transmission was about 20% for GE, 35% for Philips, and 30% for Siemens. The CT gantry was roughly twice as attenuating as the PET gantry at 90° for all three manufacturers, with about 10% transmission through the CT gantry and 20% through the PET gantry.

Conclusion:

The Philips system is a split‐gantry and therefore has a narrower angle of substantial attenuation. For the GE and Siemens systems, which are single‐gantry design, transmission was relatively constant once the angle was sufficient to block line‐of‐sight from the phantom. While the patient may spend a greater fraction of time at the PET position of the scanner, transmission characteristics of the two components are similar enough to be treated collectively. For shielding angles between 45° and 135°, a reasonably conservative assumption would be to assume gantry transmission of 50%.
SU‐D‐201‐07: Exploring the Utility of 4D FDG‐PET/CT Scans in Design of Radiation Therapy Planning Compared with 3D PET/CT: A Prospective Study
Authors: Ma C , Yin Y
Published: June 2015

Purpose:

A method using four‐dimensional(4D) PET/CT in design of radiation treatment planning was proposed and the target volume and radiation dose distribution changes relative to standard three‐dimensional (3D) PET/CT were examined.

Methods:

A target deformable registration method was used by which the whole patient's respiration process was considered and the effect of respiration motion was minimized when designing radiotherapy planning. The gross tumor volume of a non‐small‐cell lung cancer was contoured on the 4D FDG‐PET/CT and 3D PET/CT scans by use of two different techniques: manual contouring by an experienced radiation oncologist using a predetermined protocol; another technique using a constant threshold of standardized uptake value (SUV) greater than 2.5. The target volume and radiotherapy dose distribution between VOL3D and VOL4D were analyzed.

Results:

For all phases, the average automatic and manually GTV volume was 18.61 cm3 (range, 16.39–22.03 cm3) and 31.29 cm3 (range, 30.11–35.55 cm3), respectively. The automatic and manually volume of merged IGTV were 27.82 cm3 and 49.37 cm3, respectively. For the manual contour, compared to 3D plan the mean dose for the left, right, and total lung of 4D plan have an average decrease 21.55%, 15.17% and 15.86%, respectively. The maximum dose of spinal cord has an average decrease 2.35%. For the automatic contour, the mean dose for the left, right, and total lung have an average decrease 23.48%, 16.84% and 17.44%, respectively. The maximum dose of spinal cord has an average decrease 1.68%.

Conclusion:

In comparison to 3D PET/CT, 4D PET/CT may better define the extent of moving tumors and reduce the contouring tumor volume thereby optimize radiation treatment planning for lung tumors.
SU‐E‐E‐04: Assessment of Medical Physics Students and Trainees Interest and Awareness of Non‐Clinical Careers
Authors: Tanny S , Roth A , Peeler C , Rodrigues A , Ready J
Published: June 2015

Purpose:

The majority of medical physics education programs focus on preparing aspiring physicists for a career in the clinic, which could under‐represent non‐clinical opportunities in medical physics. Non‐clinical careers offer an opportunity to affect patient care on a worldwide scale, and increase the number of career options for graduating students. Our purpose is to evaluate the knowledge within the medical physics community of the opportunities available to aspiring physicists outside of the clinic.

Methods:

We have conducted a survey of current students and trainees’ and of physicists who joined the AAPM within the past 5 years. Respondents were asked to complete questions related to their knowledge and interest in non‐clinical careers. Practicing physicists were asked about the impact of non‐clinical careers in medical physics.

Results:

Over 150 students and 135 new physicists responded to our survey requests. 60% of students expressed that they did not feel knowledgeable concerning their non‐clinical options, whereas only 32% of recent graduates stated that they were unaware of non‐clinical opportunities. 68% of students expressed at least an intermediate interest in non‐clinical options. Of those interested, 54% of them did not feel knowledgeable of non‐clinical opportunities. Of the 110 respondents with intermediate or greater interest, 72%, 66%, 24% and 20% expressed interest to pursue opportunities in industry, academic research, health physics, and regulation, respectively. This was not reflected by the recent graduates, where only 43% of respondents considered a non‐clinical career path.

Conclusions:

A majority of current medical physics students surveyed expressed that they are under‐informed about non‐clinical career opportunities. Recent graduates indicated a higher level of awareness of non‐clinical options, but many chose not to consider them for their initial career placement. More work is needed from medical physics education programs to better inform students of non‐clinical options and how to prepare them.
SU‐E‐E‐09: The Novel Investigation of the Accuracy of Image Position for Liver During Respiration in Helical CT
Authors: Tsai Y , Yu P , Chang H , Chang C , Fu P , Lin C , Chiu Y , Chi S
Published: June 2015

Purpose:

To assess the image position of liver along the Z‐axis in helical CT compared to 4D CT and to evaluate the imaging similarity of helical CT and different phases of 4D CT for liver during respiration.

Methods:

Eleven patients with whole liver scanning during free breath in both helical CT and 4D CT were investigated. Eleven representative points ₍in liver segment 1, 2, 3, 4a, 4b, 5, 6, 7, 8, main portal vein, liver dome₎ were drew in helical CT image and adaptive deformed to 4D CT image, including the phase of end‐inspiration ₍phase 0₎ and end‐expiration ₍phase 50₎, using SmartAdapt in Eclipse™ version 11.5. Distances along the Z‐axis of the 11 points from helical CT to phase 0 CT, helical CT to phase 50 CT were measured, which represented the similarity of helical CT and end‐inspiration CT, helical CT and end‐expiration CT, respectively, for liver.

Results:

Mean distance along the Z‐axis from helical CT to phase 0 CT is ‐2.4±1.3 ₍mean±SD₎₍mm₎, which is the average of the 11 points ₍S1:‐2.5±4.6, S2:‐2.5±5.1, S3:‐4.0±3.2, S4a:‐0.9±4.4, S4b:‐2.9±4.1, S5:‐2.0±2.5, S6:‐3.6±3.3, S7:‐3.6±4.3, S8:‐1.8±3.9, main portal vein:‐3.4±4.1, liver dome:0.3±4.1₎. Mean distance from helical CT to phase 50 CT is 3.9±1.6 ₍S1:3.0±4.2, S2:3.2±3.8, S3:2.1±1.9, S4a:1.4±3.6, S4b:3.7±3.9, S5:3.7±2.7, S6:3.9±3.3, S7:6.0±5.0, S8:3.7±3.8, main portal vein:4.8±4.8, liver dome:7.1±5.9₎.

Conclusion:

Surprisingly, the image of helical CT scanning at random during free breath is more similar to the image at end‐inspiration, which is not corresponding to human physiology. Moreover, the helical CT image at liver dome is even beyond the image at end‐inspiration.