bluuebunny/crossref_metadata_2025 huggingface dataset:
SU‐E‐I‐20: Dead Time Count Loss Compensation in SPECT/CT: Projection Versus Global Correction
Authors: Siman W , Kappadath S
Published: July 2014

Purpose:

To compare projection‐based versus global correction that compensate for deadtime count loss in SPECT/CT images.

Methods:

SPECT/CT images of an IEC phantom (2.3GBq 99mTc) with ∼10% deadtime loss containing the 37mm (uptake 3), 28 and 22mm (uptake 6) spheres were acquired using a 2 detector SPECT/CT system with 64 projections/detector and 15 s/projection. The deadtime, Ti and the true count rate, Ni at each projection, i was calculated using the monitor‐source method. Deadtime corrected SPECT were reconstructed twice: (1) with projections that were individually‐corrected for deadtime‐losses; and (2) with original projections with losses and then correcting the reconstructed SPECT images using a scaling factor equal to the inverse of the average fractional loss for 5 projections/detector. For both cases, the SPECT images were reconstructed using OSEM with attenuation and scatter corrections. The two SPECT datasets were assessed by comparing line profiles in xyplane and z‐axis, evaluating the count recoveries, and comparing ROI statistics. Higher deadtime losses (up to 50%) were also simulated to the individually corrected projections by multiplying each projection i by exp(‐a*Ni*Ti), where a is a scalar. Additionally, deadtime corrections in phantoms with different geometries and deadtime losses were also explored. The same two correction methods were carried for all these data sets.

Results:

Averaging the deadtime losses in 5 projections/detector suffices to recover >99% of the loss counts in most clinical cases. The line profiles (xyplane and z‐axis) and the statistics in the ROIs drawn in the SPECT images corrected using both methods showed agreement within the statistical noise. The count‐loss recoveries in the two methods also agree within >99%.

Conclusion:

The projection‐based and the global correction yield visually indistinguishable SPECT images. The global correction based on sparse sampling of projections losses allows for accurate SPECT deadtime loss correction while keeping the study duration reasonable.
SU‐E‐I‐21: Deformation Mapping and Shape Prediction with 3D Tumor Volume Morphing
Authors: Mao S , Wu H , Fang S , Lu M
Published: July 2014

Purpose:

To compare projection‐based versus global correction that compensate for deadtime count loss in SPECT/CT images.

Methods:

SPECT/CT images of an IEC phantom (2.3GBq 99mTc) with ∼10% deadtime loss containing the 37mm (uptake 3), 28 and 22mm (uptake 6) spheres were acquired using a 2 detector SPECT/CT system with 64 projections/detector and 15 s/projection. The deadtime, Ti and the true count rate, Ni at each projection, i was calculated using the monitor‐source method. Deadtime corrected SPECT were reconstructed twice: (1) with projections that were individually‐corrected for deadtime‐losses; and (2) with original projections with losses and then correcting the reconstructed SPECT images using a scaling factor equal to the inverse of the average fractional loss for 5 projections/detector. For both cases, the SPECT images were reconstructed using OSEM with attenuation and scatter corrections. The two SPECT datasets were assessed by comparing line profiles in xyplane and z‐axis, evaluating the count recoveries, and comparing ROI statistics. Higher deadtime losses (up to 50%) were also simulated to the individually corrected projections by multiplying each projection i by exp(‐a*Ni*Ti), where a is a scalar. Additionally, deadtime corrections in phantoms with different geometries and deadtime losses were also explored. The same two correction methods were carried for all these data sets.

Results:

Averaging the deadtime losses in 5 projections/detector suffices to recover >99% of the loss counts in most clinical cases. The line profiles (xyplane and z‐axis) and the statistics in the ROIs drawn in the SPECT images corrected using both methods showed agreement within the statistical noise. The count‐loss recoveries in the two methods also agree within >99%.

Conclusion:

The projection‐based and the global correction yield visually indistinguishable SPECT images. The global correction based on sparse sampling of projections losses allows for accurate SPECT deadtime loss correction while keeping the study duration reasonable.
SU‐E‐I‐25: Determining Tube Current, Tube Voltage and Pitch Suitable for Low‐ Dose Lung Screening CT
Authors: Williams K , Matthews K
Published: July 2014

Purpose:

The quality of a computed tomography (CT) image and the dose delivered during its acquisition depend upon the acquisition parameters used. Tube current, tube voltage, and pitch are acquisition parameters that potentially affect image quality and dose. This study investigated physicians' abilities to characterize small, solid nodules in low‐dose CT images for combinations of current, voltage and pitch, for three CT scanner models.

Methods:

Lung CT images was acquired of a Data Spectrum anthropomorphic torso phantom with various combinations of pitch, tube current, and tube voltage; this phantom was used because acrylic beads of various sizes could be placed within the lung compartments to simulate nodules. The phantom was imaged on two 16‐slice scanners and a 64‐slice scanner. The acquisition parameters spanned a range of estimated CTDI levels; the CTDI estimates from the acquisition software were verified by measurement. Several experienced radiologists viewed the phantom lung CT images and noted nodule location, size and shape, as well as the acceptability of overall image quality.

Results:

Image quality for assessment of nodules was deemed unsatisfactory for all scanners at 80 kV (any tube current) and at 35 mA (any tube voltage). Tube current of 50 mA or more at 120 kV resulted in similar assessments from all three scanners. Physician‐measured sphere diameters were closer to actual diameters for larger spheres, higher tube current, and higher kV. Pitch influenced size measurements less for larger spheres than for smaller spheres. CTDI was typically overestimated by the scanner software compared to measurement.

Conclusion:

Based on this survey of acquisition parameters, a low‐dose CT protocol of 120 kV, 50 mA, and pitch of 1.4 is recommended to balance patient dose and acceptable image quality. For three models of scanners, this protocol resulted in estimated CTDIs from 2.9–3.6 mGy.
SU‐E‐I‐29: Generalized Relative Object Detectability (G‐ROD): A Metric for Comparing X‐Ray Imaging Detector Systems
Authors: Singh V , Jain A , Bednarek D , Rudin S
Published: July 2014

Purpose:

To determine the relative task‐specific performance of two x‐ray imaging detectors including the effect of other components of the imaging chain.

Methods:

The relative object detectability (ROD) was defined as the ratio of the integral of the detective‐quantum efficiency (DQE) of a detector weighted by the square of the Fourier Transform (or frequency spectrum) of the object to the same integral for a second detector. The generalized ROD (G‐ROD) is calculated by replacing DQE by the generalized DQE (GDQE) which includes geometric unsharpness and scatter to evaluate the total imaging chain. The G‐ROD was calculated for the micro‐angiographic fluoroscope (MAF) relative to a flat‐panel detector (FPD) for low (1.05) and high (1.2) magnifications with two focal‐spot sizes, small (0.3 mm) and medium (0.5 mm), and for the same value of scatter fraction. Solid spheres from 50 to 600 microns were simulated as the objects for this evaluation. The G‐ROD results were compared with those of the ROD which considers the detectors alone.

Results:

For 50‐micron spheres, the ROD is 7.93 and, for the small [medium] focus, the G‐ROD is 6.74 [5.22] at low magnification and 3.03 [1.66] at high magnification, indicating superior performance of the MAF particularly at low magnification. Both ROD and G‐ROD decrease monotonically with size and remain around one above 400‐microns. The G‐ROD decreases more dramatically with low compared to high magnification for both focal spots.

Conclusion:

In all cases, the MAF performs better than the FPD and the decreasing trend of the G‐ROD indicates that the performance of both detectors becomes similar as the object size increases and becomes nearly equal above 400‐micron diameter sphere size. Finally, increased magnification and focal‐spot size decrease the G‐ROD, indicting that they degrade the performance of the MAF more than that of the FPD for a small‐object viewing task.

Supported by NIH Grant: 2R01EB002873 and an equipment grant from Toshiba Medical Systems Corporation
SU‐E‐I‐35: Investigation of Commercially Available Image Uniformity Filters in MRI Imaging
Authors: Zhou Y
Published: July 2014

Purpose:

To investigate and compare the performance of two types of imaging filters that are used in commercial MRI scanners to improve the image uniformity for phased array coil imaging.

Methods:

ACR QC phantom and manufacturer supplied sphere phantom were used and the axial images were acquired using the ACR standard T1 protocol and a standard clinical axial T1 protocol. The scanner platform used in the measurement is an open‐bore 3T system (GE MRI 750w). An 8 Channel HD phased array head coil was used. The image acquisition was done with no imaging filter, a calibration based filter (PURE), and an image based filter (SCIC). The Percentage Image Uniformity (PIU) was calculated according to the ACR guideline. Profile plot of the images were obtained to assess detailed performance of the filters. The ROI at the center of the sphere phantom across different slices were also recorded.

Results:

The PIU values are 74.5% (no filter), 81.6% (PURE), and 92.1 (SCIC). Only the result from the SCIC filter would pass the ACR accreditation criteria. The profile plot also shows that the PURE leaves a valley like shape towards the center of the phantom. However, due to the factor that PURE filter utilizes the information from a volumetric calibration; it yields more uniform intensity across slices.

Conclusion:

This work indicates that the SCIC filter yields the highest in‐plane uniformity value, but the PURE filter yields better cross slice uniformity. The choice of filter for clinical imaging may depend on specific applications. The result needs to be verified for consistency on multiple systems using both phantoms and patients to fully understand the impact on image quality.
SU‐E‐I‐38: Meeting the ACR QC Requirements for Mechanically Scanned Transducers
Authors: Blatnica A , Errico A
Published: July 2014

Purpose:

To investigate methods and phantoms, both commercially available and fabricated, that will comply with the Geometric Accuracy Quality Control test for mechanically scanned transducers.

Methods:

A Gammex UTED was modified to enable caliper dimension measurements by insertion of polyester thread “pins” using needles and a locating jig that allowed placement of the thread at 14mm intervals. The modified phantom was evaluated on a Philips iU22 US system with a VL13‐5 broadband linear array transducer with single sweep 3D volume acquisition. 2D (axial and lateral) caliper measurements were made on inserted pins. The transducer was rotated 90 degrees and a 3D sweep was acquired, with measurements taken on the reconstructed slices in the scanning direction. A CIRS model 054GS US phantom was then imaged using the same techniques and methods, with measurements being taken on the lateral resolution pins (3mm and 7mm spacing) at 3cm depth and the results were compared.

Results:

3D measurements in the lateral direction for the CIRS phantom showed an average difference (over multiple scanning techniques) of 9.7% at 4mm spacing and 7.9% at 7mm spacing. The modified UTED produced an average difference of 6.7% at 14mm spacing. Corresponding 2D caliper measurements resulted in a 3.0% difference for the CIRS and −3.7% for the UTED. Lateral resolution decreased from 2D to 3D scanning by 207% for the CIRS (0.53mm to 1.625mm) and 82% for the UTED (1.080mm to 1.970mm).

Conclusion:

The modified UTED phantom compares favorably with the CIRS phantom. Issues with lateral resolution blurring in the 3D sweeps can cause inconsistencies in caliper measurements, therefore yearly consistency should be the standard, not an absolute measurement. It is possible for a facility to modify a less expensive phantom that will allow them to meet the QC requirements for Geometric Accuracy set forth by the ACR.
SU‐E‐I‐42: Normalized Embryo/fetus Doses for Fluoroscopically Guided Pacemaker Implantation Procedures Calculated Using a Monte Carlo Technique
Authors: Damilakis J , Stratakis J , Solomou G
Published: July 2014

Purpose:

It is well known that pacemaker implantation is sometimes needed in pregnant patients with symptomatic bradycardia. To our knowledge, there is no reported experience regarding radiation doses to the unborn child resulting from fluoroscopy during pacemaker implantation. The purpose of the current study was to develop a method for estimating embryo/fetus dose from fluoroscopically guided pacemaker implantation procedures performed on pregnant patients during all trimesters of gestation.

Methods:

The Monte Carlo N‐Particle (MCNP) radiation transport code was employed in this study. Three mathematical anthropomorphic phantoms representing the average pregnant patient at the first, second and third trimesters of gestation were generated using Bodybuilder software (White Rock science, White Rock, NM). The normalized embryo/fetus dose from the posteroanterior (PA), the 30° left‐anterior oblique (LAO) and the 30° right‐anterior oblique (RAO) projections were calculated for a wide range of kVp (50–120 kVp) and total filtration values (2.5–9.0 mm Al).

Results:

The results consist of radiation doses normalized to a) entrance skin dose (ESD) and b) dose area product (DAP) so that the dose to the unborn child from any fluoroscopic technique and x‐ray device used can be calculated. ESD normalized doses ranged from 0.008 (PA, first trimester) to 2.519 μGy/mGy (RAO, third trimester). DAP normalized doses ranged from 0.051 (PA, first trimester) to 12.852 μGy/Gycm2 (RAO, third trimester).

Conclusion:

Embryo/fetus doses from fluoroscopically guided pacemaker implantation procedures performed on pregnant patients during all stages of gestation can be estimated using the method developed in this study.

This study was supported by the Greek Ministry of Education and Religious Affairs, General Secretariat for Research and Technology, Operational Program ‘Education and Lifelong Learning’, ARISTIA (Research project: CONCERT)
SU‐E‐I‐44: Physics of MR Imaging to Study Whole Brain Atrophy in Ischemic Stroke Patients
Authors: Konduru R , Konduru S , Kasam M
Published: July 2014

Purpose:

Studies on Whole brain atrophy (WBA) in ischemic stroke (IS) patients using MRI physics after the onset of stroke symptoms were sporadic in nature. The current work depicts the measurement of atrophy in untreated IS patients using advanced MR Imaging/ processing techniques.

Methods:

We have retrospectively (with approved IRB protocol) collected serial 19 MRI scans of 9 IS patients of age and gender matched with comparable stroke size (30 + 10 cc) admitted in Mayo Clinic from the past five years and have their MRIs between 1 month + 15 days, 6+1 month and 1 year + 1 month after the occurrence of IS. Two MRI exams were also retrospectively collected for 10 healthy subjects (who were not diagnosed with IS symptoms) with a time interval of 1 year + 1 month. The MR follow‐up exams were collected on a 3‐Tesla GE or Siemens MRI scanner using a matched MRI protocol which consists of T1 imaging sequence for anatomical volume extraction purposes. The images were post‐processed using Analyze 11.0 software to calculate whole brain volumes. The T1/T2 images were processed using Analyze 11.0 software (Biomedical Imaging Resource, Mayo Clinic, Rochester, MN) and volumes were computed in a semi‐automated method. For each patient, atrophy is computed at the second data point which is a ratio of change in volume to the original volume.

Results and Conclusion:

Compared to the healthy subjects, an increase of 18+10% of whole brain atrophy was observed in IS patients. This may be attributed to the fact that IS patients may suffer increase of atrophy or loss of brain volume compared to the healthy subjects. Additional data is needed to investigate further.
SU‐E‐I‐46: Sample‐Size Dependence of Model Observers for Estimating Low‐Contrast Detection Performance From CT Images
Authors: Reiser I , Lu Z
Published: July 2014

Purpose:

Recently, task‐based assessment of diagnostic CT systems has attracted much attention. Detection task performance can be estimated using human observers, or mathematical observer models. While most models are well established, considerable bias can be introduced when performance is estimated from a limited number of image samples. Thus, the purpose of this work was to assess the effect of sample size on bias and uncertainty of two channelized Hotelling observers and a template‐matching observer.

Methods:

The image data used for this study consisted of 100 signal‐present and 100 signal‐absent regions‐of‐interest, which were extracted from CT slices. The experimental conditions included two signal sizes and five different x‐ray beam current settings (mAs). Human observer performance for these images was determined in 2‐alternative forced choice experiments. These data were provided by the Mayo clinic in Rochester, MN. Detection performance was estimated from three observer models, including channelized Hotelling observers (CHO) with Gabor or Laguerre‐Gauss (LG) channels, and a template‐matching observer (TM). Different sample sizes were generated by randomly selecting a subset of image pairs, (N=20,40,60,80). Observer performance was quantified as proportion of correct responses (PC). Bias was quantified as the relative difference of PC for 20 and 80 image pairs.

Results:

For n=100, all observer models predicted human performance across mAs and signal sizes. Bias was 23% for CHO (Gabor), 7% for CHO (LG), and 3% for TM. The relative standard deviation, σ(PC)/PC at N=20 was highest for the TM observer (11%) and lowest for the CHO (Gabor) observer (5%).

Conclusion:

In order to make image quality assessment feasible in the clinical practice, a statistically efficient observer model, that can predict performance from few samples, is needed. Our results identified two observer models that may be suited for this task.
SU‐E‐I‐49: The Evaluation of Usability of Multileaf Collimator for Diagnostic Radiation in Cephalometric Exposure
Authors: Han S , Park S , Kim K , Choi S , Jung H , Kim M , Ji Y
Published: July 2014

Purpose:

This study evaluated usability of Multileaf collimator (MLC) for diagnostic radiation in cephalometric exposure using optical stimulated luminance dosimeters (OSLDs)

Methods:

The MLC material was made alloy tool steel (SKD‐11) and the density of it is 7.89g/m3 that is similar to it of steel (Fe, 7.85 g/m3) and the MLC was attached to general radiography unit (Rex‐650R, Listem Inc, Korea) for cephalometric exposure. The OSLDs that used were nanoDotTM Dosimeter (Landauer Inc, Glenwood, USA) and we read out OSLDs with micro star system (Landauer Inc, Glenwood, USA). The Optical annealing system contained fluorescent lamps (Osram lumilux, 24 W, 280 ∼780 nm). To measure absorbed dose using OSLDs, was carried out dosimetric characteristics of OSLDs. Based on these, we evaluated dose reduction of critical organ (Eyes, Thyroids) with MLC in cephalometric exposure

Results:

The dosimetric characteristics were following that batch homogeneity was 1.21% and reproducibility was 0.96% of the coefficient of variation The linearity was that the correlation of between dose and count was fitted by linear function (dose,mGy = 0.00029 × Count, R2 =0.997). The range of angular dependence was from −3.6% to 3.7% variation when each degree was normalized by zero degree. The organ dose of Rt. eye, Lt eye, thyroids were 77.8 μGy, 337.0 μGy, 323.1μGy, respectively in open field and the dose reduction of organ dose was 10.6%(8.3μGy), 12.4 %(42 μGy), 87.1%(281.4μGy) with MLC

Conclusion:

We certified dose reduction of organ dose in cephalometric exposure. The dose reduction of Eye was 11% because of reduction of field size and it of thyroids was 87% by primary beam shielding
SU‐E‐I‐56: Scan Angle Reduction for a Limited‐Angle Intrafraction Verification (LIVE) System
Authors: Ren L , Zhang Y , Yin F
Published: July 2014

Purpose:

To develop a novel adaptive reconstruction strategy to further reduce the scanning angle required by the limited‐angle intrafraction verification (LIVE) system for intrafraction verification.

Methods:

LIVE acquires limited angle MV projections from the exit fluence of the arc treatment beam or during gantry rotation between static beams. Orthogonal limited‐angle kV projections are also acquired simultaneously to provide additional information. LIVE considers the on‐board 4D‐CBCT images as a deformation of the prior 4D‐CT images, and solves the deformation field based on deformation models and data fidelity constraint. LIVE reaches a checkpoint after a limited‐angle scan, and reconstructs 4D‐CBCT for intrafraction verification at the checkpoint. In adaptive reconstruction strategy, a larger scanning angle of 30° is used for the first checkpoint, and smaller scanning angles of 15° are used for subsequent checkpoints. The onboard images reconstructed at the previous adjacent checkpoint are used as the prior images for reconstruction at the current checkpoint. As the algorithm only needs to reconstruct the small deformation occurred between adjacent checkpoints, projections from a smaller scan angle provide enough information for the reconstruction. XCAT was used to simulate tumor motion baseline drift of 2mm along sup‐inf direction at every subsequent checkpoint, which are 15° apart. Adaptive reconstruction strategy was used to reconstruct the images at each checkpoint using orthogonal 15° kV and MV projections.

Results:

Results showed that LIVE reconstructed the tumor volumes accurately using orthogonal 15° kV‐MV projections. Volume percentage differences (VPDs) were within 5% and center of mass shifts (COMS) were within 1mm for reconstruction at all checkpoints.

Conclusion:

It's feasible to use an adaptive reconstruction strategy to further reduce the scan angle needed by LIVE to allow faster and more frequent intrafraction verification to minimize the treatment errors in lung cancer treatments.

Grant from Varian Medical System
SU‐E‐I‐58: Detecting Tumors with Extremely Low Contrast in CT Images
Authors: Sheng K , Gou S , Kupelian P , Steiberg M , Low D
Published: July 2014

Purpose:

Tumors such as the prostate focal lesions and the brain metastases have extremely low CT contrast and MRI is usually used for target delineation. The target contours are propagated to the CT for treatment planning and patient positioning. We have employed an advanced denoising method eliminating the noise and allow magnification of subtle contrast of these focal lesions on CT.

Methods:

Five prostate and two brain metastasis patients with MRI T2, diffusion or dynamic contrast enhanced (DCE) images confirmed focal lesions were included. One brain patients had 5 metastases. A block matching 3D (BM3D) algorithm was adapted to reduce the noise of kVCT images used for treatment planning. The gray‐level range of the resultant images was narrowed to magnify the tumor‐normal tissue contrast.

Results:

For the prostate patients, denoised kVCT images showed focal regions at 5, 8,11‐1, 2, and 8–10 oclock for the 5 patients, this is highly consistent to the radiologist confirmed focal lesions based on MRI at 5, 7, 11‐1, 2 and 8–10 oclock in the axial plane. These CT focal regions matched well with the MRI focal lesions in the cranio‐caudal position. The average increase in density compared to background prostate glands was 0.86%, which corresponds to ∼50% increase in cellularity and is lower than the average CT noise level of 2.4%. For the brain patients, denoised kVCT showed 5/6 metastases. The high CT‐density region of a metastasis is 2‐mm off from its corresponding elevated MRI perfusion center. Overall the detecting sensitivity was 91%.

Conclusion:

It has been preliminarily demonstrated that the higher tumor cellularity can be detected using kVCT. The low contrast‐to‐noise information requires advanced denoising to reveal. The finding is significant to radiotherapy by providing an additional tool to locate focal lesions for confirming MRI‐CT registration and providing a highly accessible outcome assessment tool.
SU‐E‐I‐60: The Correct Selection of Pitch and Rotation Time for Optimal CT Scanning : The Big Misconception
Authors: Ranallo F , Szczykutowicz T
Published: July 2014

Purpose:

To provide correct guidance in the proper selection of pitch and rotation time for optimal CT imaging with multi‐slice scanners.

Methods:

There exists a widespread misconception concerning the role of pitch in patient dose with modern multi‐slice scanners, particularly with the use of mA modulation techniques. We investigated the relationship of pitch and rotation time to image quality, dose, and scan duration, with CT scanners from different manufacturers in a way that clarifies this misconception. This source of this misconception may concern the role of pitch in single slice CT scanners.

Results:

We found that the image noise and dose are generally independent of the selected effective mAs (mA*time/ pitch) with manual mA technique settings and are generally independent of the selected pitch and /or rotation time with automatic mA modulation techniques. However we did find that on certain scanners the use of a pitch just above 0.5 provided images of equal image noise at a lower dose compared to the use of a pitch just below 1.0.

Conclusion:

The misconception that the use of a lower pitch over‐irradiates patients by wasting dose is clearly false. The use of a lower pitch provides images of equal or better image quality at the same patient dose, whether using manual mA or automatic mA modulation techniques. By decreasing the pitch and the rotation times by equal amounts, both helical and patient motion artifacts can be reduced without affecting the exam time. The use of lower helical pitch also allows better scanning of larger patients by allowing a greater scan effective mAs, if the exam time can be extended. The one caution with the use of low pitch is not related to patient dose, but to the length of the scan time if the rotation time is not set short enough.

Partial Research funding from GE HealthCare
SU‐E‐I‐61: The Role of Interpolation Method in Computing Dose‐Volume Histograms
Authors: Pickup L C , Aznar M , Kadir T
Published: July 2014

Purpose:

To study the effects of dose interpolation method on DVH computation, in order to make recommendations for quality assurance and consistency of treatment.

Methods:

We defined two IMRT plans (maximum doses: 84/79Gy) on a physical phantom using a commercial TPS, and exported four dose volumes with different spatial resolutions (2–5mm in‐plane; 2.5–5mm thickness). Contours for fifteen structures were defined on the CT. Using two different voxel counting schemes (partial volume weighting or centre inside) and four different interpolation methods (structures mapped to dose resolution, or nearest neighbour, linear or cubic interpolation of dose to the CT grid), we computed 960 DVHs, each with 1024 bins. Ground truth was taken to be the partial‐volume‐weighted DVHs on the highest‐resolution dose. These were compared to the suboptimal DVHs using the percentage of failing gammas (PFG) distance (doi:10.1088/0031‐9155/55/11/N04) at nine different comparison points (dose differences 1,2,3Gy, volume changes 1,2,3%), giving 8640 PFG measurements. The effects were analysed via multi‐way ANOVA.

Results:

DVH accuracy depended significantly on dose resolution and interpolation type (p<1e‐15 in both cases). As expected, the plan, contour and PFG parameterization were also significant sources of variation. The least significant source was voxel counting method (p=0.0030). Using the etasquared measure to examine effect size, the interpolation type (eta^2=0.0209) was marginally more important than the dose resolution (eta^2=0.0312). These importances rose to eta^2=0.130 and eta^2=0.0903 respectively if comparisons used the PVW‐DVHs from fine‐grained doses interpolated onto the CT as ground truth instead.

Conclusion:

For applications where DVH comparability between clinical sites with different TPS is imperative (e.g. multi‐centre studies), the dose resolution and interpolation method should be strictly identical in order for DVHs to be truly comparable. For doses sampled at a lower spatial resolution, using linear — or even better, cubic — interpolation can reduce errors over nearest neighbour.
SU‐E‐I‐62: Assessing Radiation Dose Reduction and CT Image Optimization Through the Measurement and Analysis of the Detector Quantum Efficiency (DQE) of CT Images Using Different Beam Hardening Filters
Authors: Collier J , Aldoohan S , Gill K
Published: July 2014

Purpose:

Reducing patient dose while maintaining (or even improving) image quality is one of the foremost goals in CT imaging. To this end, we consider the feasibility of optimizing CT scan protocols in conjunction with the application of different beam‐hardening filtrations and assess this augmentation through noise‐power spectrum (NPS) and detector quantum efficiency (DQE) analysis.

Methods:

American College of Radiology (ACR) and Catphan phantoms (The Phantom Laboratory) were scanned with a 64 slice CT scanner when additional filtration of thickness and composition (e.g., copper, nickel, tantalum, titanium, and tungsten) had been applied. A MATLAB‐based code was employed to calculate the image of noise NPS. The Catphan Image Owl software suite was then used to compute the modulated transfer function (MTF) responses of the scanner. The DQE for each additional filter, including the inherent filtration, was then computed from these values. Finally, CT dose index (CTDIvol) values were obtained for each applied filtration through the use of a 100 mm pencil ionization chamber and CT dose phantom.

Results:

NPS, MTF, and DQE values were computed for each applied filtration and compared to the reference case of inherent beam‐hardening filtration only. Results showed that the NPS values were reduced between 5 and 12% compared to inherent filtration case. Additionally, CTDIvol values were reduced between 15 and 27% depending on the composition of filtration applied. However, no noticeable changes in image contrast‐to‐noise ratios were noted.

Conclusion:

The reduction in the quanta noise section of the NPS profile found in this phantom‐based study is encouraging. The reduction in both noise and dose through the application of beam‐hardening filters is reflected in our phantom image quality. However, further investigation is needed to ascertain the applicability of this approach to reducing patient dose while maintaining diagnostically acceptable image qualities in a clinical setting.
SU‐E‐I‐68: Practical Considerations On Implementation of the Image Gently Pediatric CT Protocols
Authors: Zhang J , Woods E , Adams C , Lumby C , Richer E , Dillon J
Published: July 2014

Purpose:

One limitation associated with the Image Gently pediatric CT protocols is practical implementation of the recommended manual techniques. Inconsistency as a result of different practice is a possibility among technologist. An additional concern is the added risk of data error that would result in over or underexposure. The Automatic Exposure Control (AEC) features automatically reduce radiation for children. However, they do not work efficiently for the patients of very small size and relative large size. This study aims to implement the Image Gently pediatric CT protocols in the practical setting while maintaining the use of AEC features for pediatric patients of varying size.

Methods:

Anthropomorphological abdomen phantoms were scanned in a CT scanner using the Image Gently pediatric protocols, the AEC technique with a fixed adult baseline, and automatic protocols with various baselines. The baselines were adjusted corresponding to patient age, weight and posterioranterior thickness to match the Image Gently pediatric CT manual techniques. CTDIvol was recorded for each examination. Image noise was measured and recorded for image quality comparison. Clinical images were evaluated by pediatric radiologists.

Results:

By adjusting vendor default baselines used in the automatic techniques, radiation dose and image quality can match those of the Image Gently manual techniques. In practice, this can be achieved by dividing pediatric patients into three major groups for technologist reference: infant, small child, and large child. Further division can be done but will increase the number of CT protocols. For each group, AEC can efficiently adjust acquisition techniques for children. This implementation significantly overcomes the limitation of the Image Gently manual techniques.

Conclusion:

Considering the effectiveness in clinical practice, Image Gently Pediatric CT protocols can be implemented in accordance with AEC techniques, with adjusted baselines, to achieve the goal of providing the most appropriate radiation dose for pediatric patients of varying sizes.
SU‐E‐I‐74: Quantitative Instrumentation for Subject Workload From Exercise During 31‐Phosphorus MR Spectroscopy to Monitor Phosophocreatine Recovery as An Index for Mitochondrial Metabolism
Authors: Settles F , Clarke G
Published: July 2014

Purpose:

Measurement of mitochondrial function is relevant to aging and diabetes. Phosphorus‐31 magnetic resonance spectroscopy (31P‐MRS) can be used to evaluate the rate of phosphocreatine (PCr) recovery following exercise. The project's aim is to develop a reproducible measurement technique using an exercise apparatus to quantify PCr recovery in the vastus lateralis muscle (VL). A workload instrument was developed to quantify work output of each subject.

Methods:

An apparatus was designed to exercise the VL with subjects in the prone position with an 1H‐31P surface coil against the thigh. Since subjects exercise at different rates and intensities, a strain gage instrument was developed to quantify the amount of work done. During a 5 minute exercise period, PCr depletion levels were measured using MRS. Coincidentally, the force exerted on the articulating arm of the apparatus appears as a voltage from the instrument on a strip recorder sampling at 1 mS and is captured as numerical values.

Results:

The exercise apparatus is a compact, single‐piece PVC assembly with little mass (<3 kg), and provides resistance of up to 13.5 kg within the confines of the bore. The instrument outputs a voltage relative to the force applied against the resistance. A subject's performance and level of fatigue is visualized in real time and captured for post processing. The summation of force applied (strain level) vs. time is the work output. Brisk exercise produced a rapid drop in PCr and concomitant increase in inorganic phosphate.

Conclusion:

The exercise apparatus immobilizes the thigh and surface coil during dynamic flexion exercise and recovery phases of the protocol. Spectral data acquired demonstrated PCr depletion and recovery in VL correlated to the subject workload.Clinical Relevance/Application:Noninvasive, reproducible measures of mitochondrial function by a well‐characterized in‐vivo biomarker can provide insights for the characterization and treatment of metabolic diseases.
SU‐E‐J‐15: A Patient‐Centered Scheme to Mitigate Impacts of Treatment Setup Error
Authors: Yang L , Tian Z , Gu X , Jia X , Jiang S
Published: July 2014

Purpose:

Current Intensity Modulated Radiation Therapy (IMRT) is plan‐centered. At each treatment fraction, we position the patient to match the setup in treatment plan. Inaccurate setup can compromise delivered dose distribution, and hence leading to suboptimal treatments. Moreover, current setup approach via couch shift under image guidance can correct translational errors, while rotational and deformation errors are hard to address. To overcome these problems, we propose in this abstract a patient‐centered scheme to mitigate impacts of treatment setup errors.

Methods:

In the patient‐centered scheme, we first position the patient on the couch approximately matching the planned‐setup. Our Supercomputing Online Replanning Environment (SCORE) is then employed to design an optimal treatment plan based on the daily patient geometry. It hence mitigates the impacts of treatment setup error and reduces the requirements on setup accuracy. We have conducted simulations studies in 10 head‐and‐neck (HN) patients to investigate the feasibility of this scheme. Rotational and deformation setup errors were simulated. Specifically, 1, 3, 5, 7 degrees of rotations were put on pitch, roll, and yaw directions; deformation errors were simulated by splitting neck movements into four basic types: rotation, lateral bending, flexion and extension. Setup variation ranges are based on observed numbers in previous studies. Dosimetric impacts of our scheme were evaluated on PTVs and OARs in comparison with original plan dose with original geometry and original plan recalculated dose with new setup geometries.

Results:

With conventional plan‐centered approach, setup error could lead to significant PTV D99 decrease (−0.25∼+32.42%) and contralateral‐parotid Dmean increase (−35.09∼+42.90%). The patientcentered approach is effective in mitigating such impacts to 0∼+0.20% and −0.03∼+5.01%, respectively. Computation time is <128 s.

Conclusion:

Patient‐centered scheme is proposed to mitigate setup error impacts using replanning. Its superiority in terms of dosimetric impacts and feasibility has been shown through simulation studies on HN cases.
SU‐E‐J‐36: Combining CBCT Dose Into IMRT Treatment Planning
Authors: Grelewicz Z , Wiersma R
Published: July 2014

Purpose:

Cone beam CT (CBCT) is increasingly used in patient setup for IMRT. Daily CBCT may provide effective localization, however, it introduces concern over excessive imaging dose. Previous studies investigated the calculation of excess CBCT dose, however, no study has yet treated this dose as a source of therapeutic radiation, optimized in consideration of PTV and OARs constrains. Here we present a novel combined MV+kV inverse optimization engine to weave the CBCT and MV dose together such that CBCT dose is used for both imaging and therapeutic purposes. This may mitigate some of the excess imaging dose effects of daily CBCT and allow complete evaluation of the CBCT dose prior to treatment.

Methods:

The EGSnrc Monte Carlo system was used to model a Varian Trilogy CBCT system and 6 MV treatment beam. Using the model, the dose to patient from treatment beam and imaging beam was calculated for ten patients. The standard IMRT objective function was modified to include CBCT dose. Treatment plan optimization using the MOSEK optimization tool was performed retrospectively with and without assuming kV radiation dose from CBCT, assuming one CBCT per fraction.

Results:

Across ten patients, the CBCT delivered peaks of between .4% and 3.0% of the prescription dose to the PTV, with average CBCT dose to the PTV between .3% and .8%. By including CBCT dose to skin as a constraint during optimization, peak skin dose is reduced by between 1.9% and 7.4%, and average skin dose is reduced by .2% to 3.3%.

Conclusions:

Pre‐treatment CBCT may deliver a substantial amount of radiation dose to the target volume. By considering CBCT dose to skin at the point of treatment planning, it is possible to reduce patient skin dose from current clinical levels, and to provide patient treatment with the improved accuracy that daily CBCT provides.
SU‐E‐J‐37: Combining Proton Radiography and X‐Ray CT Information to Better Estimate Relative Proton Stopping Power in a Clinical Environment
Authors: CollinsFekete C , Dias M , Doolan P , Hansen David C , Beaulieu L , Seco J
Published: July 2014

Purpose:

In standard proton therapy clinical practice, proton stopping power uncertainties are in the order of 3.5%, which affects the ability of placing the proton Bragg peak at the edge of the tumor. The innovating idea of this project is to approach the uncertainty problem in RSP by using combined information from X‐ray CT and proton radiography along a few beam angles. In addition, this project aims to quantify the systematic error introduced by the theoretical models (Janni, ICRU49, Bischel) for proton stopping power in media.

Methods:

A 3D phantom of 36 cm3 composed of 9 materials randomly placed is created. Measured RSP values are obtained using a Gammex phantom with a proton beam. Theoretical RSP values are calculated with Beth‐Block equation in combination with three databases (Janni, ICRU49 and Bischel). Clinical RSP errors are simulated by introducing a systematic (1.5%, 2.5%, 3.5%) and a random error (+/−0.5%) to the theoretical RSP. A ray‐tracing algorithm uses each of these RSP tables to calculate energy loss for proton crossing the phantom through various directions. For each direction, gradient descent (GD) method is done on the clinical RSP table to minimize the residual energy difference between the simulation with clinical RSP and with theoretical RSP. The possibility of a systematic material dependent error is investigated by comparing measured RSP to theoretical RSP as calculated from the three models.

Results:

Using 10,000 iterations on GD algorithm, RSP differences between theoretical values and clinical RSP have converged (<1%) for each error introduced. Results produced with ICRU49 have the smallest average difference (0.021%) to the measured RSP. Janni (1.168%) and Bischel (−0.372%) database shows larger systematic errors.

Conclusion:

Based on these results, ray‐tracing optimisation using information from proton radiography and X‐ray CT demonstrates a potential to improve the proton range accuracy in a clinical environment.
SU‐E‐J‐41: Computational and Experimental Analysis of Cancer Cell Mechanics in 3D: Intracellular Viscoelasticity and Internal Stresses
Authors: Mak M , Zaman M , Kamm R
Published: July 2014

Purpose:

We develop an integrated multiscale experimental and computational system to bridge the mechanics and kinetics of motors in crosslinked actin‐networks at the molecular scale with cell‐scaled tensional dynamics in 3D. We investigate the intracellular viscoelastic properties of invasive breast cancer cells in a 3D‐matrix with a tunable microfluidic device that enables the generation of flow and gradients as well as co‐culture conditions.

Methods:

For computational analyses, we use a custom Brownian dynamics model of F‐actin networks with dynamic crosslinking proteins and active myosin motors to simulate internal stress generation and motor‐induced cytoskeletal remodeling. For experimentation, we develop a system that integrates a highly customizable microfluidic device for 3D cell culture with intracellular particle‐tracking microrheology to study intracellular viscoelasticity of cells in 3D.

Results:

Our results demonstrate that a balance between crosslinker density, actin polymerization and nucleation dynamics, and motor kinetics and density control intracellular morphology and tension. Experimentally, we show that intracellular viscoelasticity appears to be anisotropic and heterogeneous, and we compare the shear moduli of cells in 2D and 3D. Additionally, we show that altered polymerization dynamics lead to altered cytoskeletal morphologies that appear more aggregated, consistent with our simulations that show motorinduced cytoskeletal remodeling when actin assembly and disassembly rates are not sufficiently high.

Conclusion:

A multiscale approach that bridges molecular‐scaled dynamics with single and multicellular networks in 3D physiological environments can be an enabling method for understanding the physical and mechanical phenomena that govern cell force generation, migration, and cancer invasion and dissemination. By understanding how molecular mechanical mechanisms translate into metastatic behavior of cells, we can then begin to identify in a rigorous manner new therapeutics that target the functional and physical properties of cancer cells. Specifically, our approach allows for the fundamental elements that give rise to intracellular structure and tension to be investigated.
SU‐E‐J‐44: Design a Platform and Phantom Model for Photoacoustic Imaging in Combination with CT
Authors: Sick J , Alsanea F , Rancilio N , Stantz K
Published: July 2014

Purpose:

Our (long‐term) objective is to develop a US manipulator that will provide in situ radiation response and image‐guided therapy for bladder cancer based on photoacoustic molecular imaging.

Methods:

A platform was devised to provide a reproducible positional frame of reference for targeting anatomic structure between MDCT and US scans, in lieu of CBCT, and to fuse photoacoustic molecular imaging. US and photoacoustic scans are taken of a patient while in the CT scanner and IRMT. Through co‐registration, based on anatomical positions, we identified a common coordinate system to be used in Eclipse. A bladder phantom was constructed to validate anatomical tracking via US and photoacoustic imaging. We tested the platform using phantom model to demonstrate validity once moved from the CT couch to the linear accelerator couch.

Results:

This platform interlocks with Varian exact couch index points for reproducibility of positioning. Construction from low Z material and sized appropriately to fit in CT/IMRT gantry. Error in conversion from cylindrical coordinates of the manipulator to X, Y, Z coordinates of the treatment couch was less than 1mm. We measured the bladder size in 3 different directions in both Eclipse from the CT and Acuson from US. The error was less than 2mm in all directions. CT and US images were co‐registered in MATLAB. Co‐registration of photoacoustic images is still being developed.

Conclusion:

For Linear Accelerators without on board imaging, MV portal images are not a viable option for the localization of soft tissue anatomy. We believe our manipulator provides an alternative using US imaging, which will be examined in an upcoming clinical trial. We plan to examine the value of hypoxia guided treatment through photoacoustic imaging during this trial.