bluuebunny/crossref_metadata_2025 huggingface dataset:
TU‐F‐BRE‐04: Development of a High‐Resolution EPID Based Dosimetry Strategy for Radiosurgery QA
Authors: Han B , Ding A , Xing L , Wang L
Published: July 2014

Purpose:

To systematically investigate a high spatial‐resolution (0.2mm) electronic portal imaging device (EPID) for CyberKnife (CK) based radiosurgery system quality assurance (QA).

Methods:

An EPID‐based dosimetric measurement technique is applied to CK output measurement and field size verification. A Monte Carlo (MC) simulated pixel‐to‐pixel EPID response specific to CK is used to convert a raw EPID‐measured image of a radiosurgery field into water‐based dose distribution. The output factors are measured using EPID for radiosurgery fields formed by fixed and variable aperture (Iris) cones. Circular fields of 5, 7.5, 10, 15, 30 and 60mm diameters are measured and compared with diode measurements. The equivalent diameters are determined by analyzing the area received dose greater than half maximum.

Results:

For both fixed and Iris cones, the EPID measured output factors of circular fields of 5mm to 60mm diameters are in good agreement with the radiosurgery diode measurements. The mean output differences are 1.0% and 1.5% for fixed and Iris cone respectively. The max differences are 2.2% for the 15mm fixed cone, and 1.8% for the 10mm Iris field. The equivalent diameters derived from the EPID measurements are in good agreement comparing to the water scan result with mean differences of 0.21±0.09mm and 0.02±0.22mm for fixed and Iris cone, respectively. The high detector density EPID is able to measure the whole radiation field and identify the field edge and center. Therefore, there is no need to align the detector center perfectly at field center and the setup time is greatly reduced for QA.

Conclusion:

The high spatial‐resolution EPID is proved to be an accurate and efficient dosimetric tool for radiosurgery QA and especially useful in Cyberknife QA for variable aperture collimators.
TU‐F‐BRF‐03: Effect of Radiation Therapy Planning Scan Registration On the Dose in Lung Cancer Patient CT Scans
Authors: Cunliffe A , Contee C , White B , Justusson J , Armato S , Malik R , Al‐Hallaq H
Published: July 2014

Purpose:

To characterize the effect of deformable registration of serial computed tomography (CT) scans on the radiation dose calculated from a treatment planning scan.

Methods:

Eighteen patients who received curative doses (≥60Gy, 2Gy/fraction) of photon radiation therapy for lung cancer treatment were retrospectively identified. For each patient, a diagnostic‐quality pre‐therapy (4–75 days) CT scan and a treatment planning scan with an associated dose map calculated in Pinnacle were collected. To establish baseline correspondence between scan pairs, a researcher manually identified anatomically corresponding landmark point pairs between the two scans. Pre‐therapy scans were co‐registered with planning scans (and associated dose maps) using the Plastimatch demons and Fraunhofer MEVIS deformable registration algorithms. Landmark points in each pretherapy scan were automatically mapped to the planning scan using the displacement vector field output from both registration algorithms. The absolute difference in planned dose (|ΔD|) between manually and automatically mapped landmark points was calculated. Using regression modeling, |ΔD| was modeled as a function of the distance between manually and automatically matched points (registration error, E), the dose standard deviation (SD_dose) in the eight‐pixel neighborhood, and the registration algorithm used.

Results:

52–92 landmark point pairs (median: 82) were identified in each patient's scans. Average |ΔD| across patients was 3.66Gy (range: 1.2–7.2Gy). |ΔD| was significantly reduced by 0.53Gy using Plastimatch demons compared with Fraunhofer MEVIS. |ΔD| increased significantly as a function of E (0.39Gy/mm) and SD_dose (2.23Gy/Gy).

Conclusion:

An average error of <4Gy in radiation dose was introduced when points were mapped between CT scan pairs using deformable registration. Dose differences following registration were significantly increased when the Fraunhofer MEVIS registration algorithm was used, spatial registration errors were larger, and dose gradient was higher (i.e., higher SD_dose). To our knowledge, this is the first study to directly compute dose errors following deformable registration of lung CT scans.
TU‐F‐BRF‐04: Registration of 3D Transesophageal Echocardiography and X‐Ray Fluoroscopy Using An Inverse Geometry X‐Ray System
Authors: Speidel M , Hatt C , Tomkowiak M , Funk T , Raval A
Published: July 2014

Purpose:

To develop a method for the fusion of 3D echocardiography and Scanning‐Beam Digital X‐ray (SBDX) fluoroscopy to assist with catheter device and soft tissue visualization during interventional procedures.

Methods:

SBDX is a technology for low‐dose inverse geometry x‐ray fluoroscopy that performs digital tomosynthesis at multiple planes in real time. In this study, transesophageal echocardiography (TEE) images were fused with SBDX images by estimating the 3D position and orientation (the “pose”) of the TEE probe within the x‐ray coordinate system and then spatially transforming the TEE image data to match this pose. An initial pose estimate was obtained through tomosynthesis‐based 3D localization of points along the probe perimeter. Position and angle estimates were then iteratively refined by comparing simulated projections of a 3D probe model against SBDX x‐ray images. Algorithm performance was quantified by imaging a TEE probe in different known orientations and locations within the x‐ray field (0‐30 degree tilt angle, up to 50 mm translation). Fused 3D TEE/SBDX imaging was demonstrated by imaging a tissue‐mimicking polyvinyl alcohol cylindrical cavity as a catheter was navigated along the cavity axis.

Results:

Detected changes in probe tilt angle agreed with the known changes to within 1.2 degrees. For a 50 mm translation along the source‐detector axis, the detected translation was 50.3 mm. Errors for in‐plane translations ranged from 0.1 to 0.9 mm. In a fused 3D TEE/SBDX display, the catheter device was well visualized and coincident with the device shadow in the TEE images. The TEE images portrayed phantom boundaries that were not evident under x‐ray.

Conclusion:

Registration of soft tissue anatomy derived from TEE imaging and device imaging from SBDX x‐ray fluoroscopy is feasible. The simultaneous 3D visualization of these two modalities may be useful in interventional procedures involving the navigation of devices to soft tissue anatomy.
TU‐F‐BRF‐08: Intensity Modulation Expanded to Spatio‐Temporal Space; IMRT Combined with Optimal Fractionation Schedule
Authors: Kim M , Saberian F , Ghate A
Published: July 2014

Purpose:

Past efforts to improve the therapeutic ratio have focused on a spatial approach where highly conformal radiation dose is given to tumors while minimizing dose to normal tissues, e.g., IMRT, VMAT, and IGRT. However, the fractionation schedule, i.e., a temporal approach to radiotherapy, has been largely overlooked so far in maximizing the therapeutic ratio. We establish a rigorous mathematical spatio‐temporal approach to systematically investigate the feasibility and potential benefits of simultaneously optimizing radiation dose distribution in space and time.

Methods:

Stochastic control formalism is constructed to maximize the average tumor BED by choosing an optimal radiation dose distribution for an optimal number of fractions subject to normal tissue BED constraints. Three separate simulations are run on two groups of phantom cases; 5 cases with prostate cancer and 5 cases with head‐and‐neck cancer. (1) Conventional IMRT with 70Gy/35fx for head‐and‐neck, and 81Gy/45fx for prostate, (2) IMRT is done independently from the fractionation schedule optimization (S‐model), (3) integrated spatio‐temporal approach (I‐model) where radiation intensities are simultaneously optimized for the first time ever in space and time. Final tumor BEDs from the three trials are compared in prostate and head‐and‐neck cases.

Results:

Numerical simulations show that final tumor BED from I‐model is 20–90% larger than conventional IMRT, and 20‐50% larger than S‐model for head‐and‐neck cancer with α/β=10 and Tdouble=2–50 days. Final tumor BED from I‐model is also 90–140% larger than conventional IMRT, and 20–30% larger than S‐model for prostate cancer with α/β=2 and Tdouble=5–80 days.

Conclusion:

Our spatio‐temporal optimization of radiotherapy allows an expansion of search space for the optimal treatment plans to include the temporal distribution of radiation dose in addition to the spatial distribution. Such spatio‐temporal approach shows great potential to improve the therapeutic ratio, particularly with fast growing, aggressive tumors with short doubling time and/or low α/β.
TU‐F‐17A‐08: The Relative Accuracy of 4D Dose Accumulation for Lung Radiotherapy Using Rigid Dose Projection Versus Dose Recalculation On Every Breathing Phase
Authors: Lamb J , Valdes G , Lee C , Tee S , Lee P , Robinson C , Iwamoto K , Low D
Published: July 2014

Purpose:

To investigate the accuracy of 4D dose accumulation using projection of dose calculated on the end‐exhalation, mid‐ventilation, or average intensity breathing phase CT scan, versus dose accumulation performed using full Monte Carlo dose recalculation on every breathing phase.

Methods:

Radiotherapy plans were analyzed for 10 patients with stage I‐II lung cancer planned using 4D‐CT. SBRT plans were optimized using the dose calculated by a commercially‐available Monte Carlo algorithm on the end‐exhalation 4D‐CT phase. 4D dose accumulations using deformable registration were performed with a commercially available tool that projected the planned dose onto every breathing phase without recalculation, as well as with a Monte Carlo recalculation of the dose on all breathing phases. The 3D planned dose (3D‐EX), the 3D dose calculated on the average intensity image (3D‐AVE), and the 4D accumulations of the dose calculated on the end‐exhalation phase CT (4D‐PR‐EX), the mid‐ventilation phase CT (4D‐PR‐MID), and the average intensity image (4D‐PR‐AVE), respectively, were compared against the accumulation of the Monte Carlo dose recalculated on every phase. Plan evaluation metrics relating to target volumes and critical structures relevant for lung SBRT were analyzed.

Results:

Plan evaluation metrics tabulated using 4D‐PR‐EX, 4D‐PR‐MID, and 4D‐PR‐AVE differed from those tabulated using Monte Carlo recalculation on every phase by an average of 0.14±0.70 Gy, – 0.11±0.51 Gy, and 0.00±0.62 Gy, respectively. Deviations of between 8 and 13 Gy were observed between the 4D‐MC calculations and both 3D methods for the proximal bronchial trees of 3 patients.

Conclusions:

4D dose accumulation using projection without re‐calculation may be sufficiently accurate compared to 4D dose accumulated from Monte Carlo recalculation on every phase, depending on institutional protocols. Use of 4D dose accumulation should be considered when evaluating normal tissue complication probabilities as well as in clinical situations where target volumes are directly inferior to mobile critical structures.
TU‐F‐17A‐09: Four‐Dimensional Cone Beam CT Ventilation Imaging Can Detect Interfraction Lung Function Variations for Locally Advanced Lung Cancer Patients
Authors: Kipritidis J , Hugo G , Weiss E , Williamson J , Keall P
Published: July 2014

Purpose:

Four‐dimensional cone beam CT ventilation imaging (4D‐CBCT VI) is a novel functional lung imaging modality requiring validation. We hypothesize that 4D‐CBCT VI satisfies a necessary condition for validity: that intrafraction variations (e.g. due to poor 4D‐CBCT image quality) are substantially different to interfraction variations (e.g. due to changes in underlying function). We perform the first comparison of intrafraction (pre/post fraction) and interfraction (week‐to‐week) 4D‐CBCT VIs for locally advanced non small cell lung cancer (LA NSCLC) patients undergoing radiation therapy.

Methods:

A total of 215 4D‐CBCT scans were acquired for 19 LA NSCLC patients over 4‐6 weeks of radiation therapy, including 75 pairs of pre‐/post‐fraction scans on the same day. 4D‐CBCT VIs were obtained by applying state‐of‐the‐art, B‐spline deformable image registration to obtain the Jacobian determinant of deformation between the end‐exhale and end‐inhale phases. All VIs were deformably registered to the corresponding first day scan, normalized between the 10th and 90th percentile values and cropped to the ipsilateral lung only. Intrafraction variations were assessed by computing the mean and standard deviation of voxel‐wise differences between all same‐day pairs of pre‐/post‐fraction VIs. Interfraction differences were computed between first‐day VIs and treatment weeks 2, 4 and 6 for all 19 patients. We tested the hypothesis by comparing cumulative distribution functions (CDFs) of intrafraction and interfraction ventilation differences using two‐sided Kolmogorov‐Smirnov goodness‐of‐fit tests.

Results:

The (mean ± std. dev.) of intrafraction differences was (−0.007 ± 0.079). Interfraction differences for weeks 2, 4 and 6 were (−0.035 ± 0.103), (−0.006 ± 0.094) and (−0.019 ± 0.127) respectively. For week 2, the changes in CDFs for intrafraction and interfraction differences approached statistical significance (p=0.099).

Conclusion:

We have shown that 4D‐CBCT VI can satisfy a necessary condition for validity; intrafraction variations do not limit the ability to measure interfraction variations in LA NSCLC patients.

This work is supported by a Cancer Institute NSW Early Career Fellowship, an NHMRC Australia Fellowship and NIH P01CA116602.
WE‐D‐BRF‐01: FEATURED PRESENTATION – Investigating Particle Track Structures Using Fluorescent Nuclear Track Detectors and Monte Carlo Simulations
Authors: Dowdell S , Greilich S , Zimmerman F , Evans C , Paganetti H , Schuemann J
Published: July 2014

Purpose:

To report on the efforts funded by the AAPM seed funding grant to develop the basis for fluorescent nuclear track detector (FNTD) based radiobiological experiments in combination with dedicated Monte Carlo simulations (MCS) on the nanometer scale.

Methods:

Two confocal microscopes were utilized in this study. Two FNTD samples were used to find the optimal microscope settings, one FNTD irradiated with 11.1 MeV/u Gold ions and one irradiated with 428.77 MeV/u Carbon ions. The first sample provided a brightly luminescent central track while the latter is used to test the capabilities to observe secondary electrons. MCS were performed using TOPAS beta9 version, layered on top of Geant4.9.6p02. Two sets of simulations were performed, one with the Geant4‐DNA physics list and approximating the FNTDs by water, a second set using the Penelope physics list in a water‐approximated FNTD and a aluminum‐oxide FNTD.

Results:

Within the first half of the funding period, we have successfully established readout capabilities of FNTDs at our institute. Due to technical limitations, our microscope setup is significantly different from the approach implemented at the DKFZ, Germany. However, we can clearly reconstruct Carbon tracks in 3D with electron track resolution of 200 nm. A second microscope with superior readout capabilities will be tested in the second half of the funding period, we expect an improvement in signal to background ratio with the same the resolution.We have successfully simulated tracks in FNTDs. The more accurate Geant4‐DNA track simulations can be used to reconstruct the track energy from the size and brightness of the observed tracks.

Conclusion:

We have achieved the goals set in the seed funding proposal: the setup of FNTD readout and simulation capabilities. We will work on improving the readout resolution to validate our MCS track structures down to the nanometer scales.
WE‐D‐BRF‐05: Quantitative Dual‐Energy CT Imaging for Proton Stopping Power Computation
Authors: Han D , Siebers J , Williamson J
Published: July 2014

Purpose:

To extend the two‐parameter separable basis‐vector model (BVM) to estimation of proton stopping power from dual‐energy CT (DECT) imaging.

Methods:

BVM assumes that the photon cross sections of any unknown material can be represented as a linear combination of the corresponding quantities for two bracketing basis materials. We show that both the electron density (ρe) and mean excitation energy (Iex) can be modeled by BVM, enabling stopping power to be estimated from the Bethe‐Bloch equation. We have implemented an idealized post‐processing dual energy imaging (pDECT) simulation consisting of monogenetic 45 keV and 80 keV scanning beams with polystyrene‐water and water‐CaCl2 solution basis pairs for soft tissues and bony tissues, respectively. The coefficients of 24 standard ICRU tissue compositions were estimated by pDECT. The corresponding ρe, Iex, and stopping power tables were evaluated via BVM and compared to tabulated ICRU 44 reference values.

Results:

BVM‐based pDECT was found to estimate ρe and Iex with average and maximum errors of 0.5% and 2%, respectively, for the 24 tissues. Proton stopping power values at 175 MeV, show average/maximum errors of 0.8%/1.4%. For adipose, muscle and bone, these errors result range prediction accuracies less than 1%.

Conclusion:

A new two‐parameter separable DECT model (BVM) for estimating proton stopping power was developed. Compared to competing parametric fit DECT models, BVM has the comparable prediction accuracy without necessitating iterative solution of nonlinear equations or a sample‐dependent empirical relationship between effective atomic number and Iex. Based on the proton BVM, an efficient iterative statistical DECT reconstruction model is under development.
WE‐D‐17A‐02: Evaluation of a Two‐Dimensional Optical Dosimeter On Measuring Lateral Profiles of Proton Pencil Beams
Authors: Hsi W , Lee T , Gao M , Boyer S , Pillainayagam M , Schultz T , Arjomandy B , Park S , Pankuch M , Schreuder A , Mah D
Published: July 2014

Purpose:

To evaluate the accuracy of a two‐dimensional optical dosimeter on measuring lateral profiles for spots and scanned fields of proton pencil beams.

Methods:

A digital camera with a color image senor was utilized to image proton‐induced scintillations on Gadolinium‐oxysulfide phosphor reflected by a stainless‐steel mirror. Intensities of three colors were summed for each pixel with proper spatial‐resolution calibration. To benchmark this dosimeter, the field size and penumbra for 100mm square fields of singleenergy pencil‐scan protons were measured and compared between this optical dosimeter and an ionization‐chamber profiler. Sigma widths of proton spots in air were measured and compared between this dosimeter and a commercial optical dosimeter. Clinical proton beams with ranges between 80 mm and 300 mm at CDH proton center were used for this benchmark.

Results:

Pixel resolutions vary 1.5% between two perpendicular axes. For a pencil‐scan field with 302 mm range, measured field sizes and penumbras between two detection systems agreed to 0.5 mm and 0.3 mm, respectively. Sigma widths agree to 0.3 mm between two optical dosimeters for a proton spot with 158 mm range; having widths of 5.76 mm and 5.92 mm for X and Y axes, respectively. Similar agreements were obtained for others beam ranges. This dosimeter was successfully utilizing on mapping the shapes and sizes of proton spots at the technical acceptance of McLaren proton therapy system. Snow‐flake spots seen on images indicated the image sensor having pixels damaged by radiations. Minor variations in intensity between different colors were observed.

Conclusions:

The accuracy of our dosimeter was in good agreement with other established devices in measuring lateral profiles of pencil‐scan fields and proton spots. A precise docking mechanism for camera was designed to keep aligned optical path while replacing damaged image senor. Causes for minor variations between emitted color lights will be investigated.
WE‐D‐17A‐04: Magnetically Focused Proton Irradiation of Small Volume Targets
Authors: McAuley G , Slater J , Wroe A
Published: July 2014

Purpose:

To explore the advantages of magnetic focusing for small volume proton irradiations and the potential clinical benefits for radiosurgery targets. The primary goal is to create narrow elongated proton beams of elliptical cross section with superior dose delivery characteristics compared to current delivery modalities (eg, collimated beams). In addition, more general beam shapes are also under investigation.

Methods:

Two prototype magnets consisting of 24 segments of samarium‐cobalt (Sm2Co17) permanent magnetic material adhered into hollow cylinders were manufactured for testing. A single focusing magnet was placed on a positioning track on our Gantry 1 treatment table and 15 mm diameter proton beams with energies and modulation relevant to clinical radiosurgery applications (127 to 186 MeV, and 0 to 30 mm modulation) were delivered to a terminal water tank. Beam dose distributions were measured using a PTW diode detector and Gafchromic EBT2 film. Longitudinal and transverse dose profiles were analyzed and compared to data from Monte Carlo simulations analogous to the experimental setup.

Results:

The narrow elongated focused beam spots showed high elliptical symmetry indicating high magnet quality. In addition, when compared to unfocused beams, peak‐to‐entrance depth dose ratios were 11 to 14% larger (depending on presence or extent of modulation), and minor axis penumbras were 11 to 20% smaller (again depending on modulation) for focused beams. These results suggest that the use of rare earth magnet assemblies is practical and could improve dose‐sparing of normal tissue and organs at risk while delivering enhanced dose to small proton radiosurgery targets.

Conclusion:

Quadrapole rare earth magnetic assemblies are a promising and inexpensive method to counteract particle out scatter that tends to degrade the peak to entrance performance of small field proton beams. Knowledge gained from current experiments will inform the design of a prototype treatment nozzle that incorporates similar focusing magnets.

This project was sponsored in part by funding from the Department of Defense (DOD# W81XWH‐BAA‐10‐1).
WE‐D‐17A‐06: Optically Stimulated Luminescence Detectors as ‘LET‐Meters’ in Proton Beams
Authors: Granville D , Sahoo N , Sawakuchi GO
Published: July 2014

Purpose:

To demonstrate and evaluate the potential of optically stimulated luminescence (OSL) detectors (OSLDs) for measurements of linear energy transfer (LET) in therapeutic proton beams.

Methods:

Batches of Al2O2:C OSLDs were irradiated with an absorbed dose of 0.2 Gy in un‐modulated proton beams of varying LET (0.67 keV/μm to 2.58 keV/μm). The OSLDs were read using continuous wave (CW‐OSL) and pulsed (P‐OSL) stimulation modes. We parameterized and calibrated three characteristics of the OSL signals as functions of LET: CW‐OSL curve shape, P‐OSL curve shape and the ratio of the two OSL emission band intensities (ultraviolet/blue ratio). Calibration curves were created for each of these characteristics to describe their behaviors as functions of LET. The true LET values were determined using a validated Monte Carlo model of the proton therapy nozzle used to irradiate the OSLDs. We then irradiated batches of OSLDs with an absorbed dose of 0.2 Gy at various depths in two modulated proton beams (140 MeV, 4 cm wide spread‐out Bragg peak (SOBP) and 250 MeV, 10 cm wide SOBP). The LET values were calculated using the OSL response and the calibration curves. Finally, measured LET values were compared to the true values determined using Monte Carlo simulations.

Results:

The CW‐OSL curve shape, P‐OSL curve shape and the ultraviolet/blue‐ratio provided proton LET estimates within 12.4%, 5.7% and 30.9% of the true values, respectively.

Conclusion:

We have demonstrated that LET can be measured within 5.7% using Al2O3:C OSLDs in the therapeutic proton beams used in this investigation. From a single OSLD readout, it is possible to measure both the absorbed dose and LET. This has potential future applications in proton therapy quality assurance, particularly for treatment plans based on optimization of LET distributions.

This research was partially supported by the Natural Sciences and Engineering Research Council of Canada.
WE‐D‐18A‐02: Performance Evaluation of Automatic Exposure Control (AEC) Across 12 Clinical CT Systems
Authors: Winslow J , Wilson J , Christianson O , Samei E
Published: July 2014

Purpose:

Automatic exposure control (AEC) is not typically evaluated or monitored in CT quality assurance programs. The purpose of this study was to develop/evaluate a new AEC testing platform for the clinical physics program at our institution, and characterize AEC performance across different CT systems.

Methods:

The Mercury Phantom comprises three tapered and four uniform regions of polyethylene(16, 23, 30, and 37 cm in diameter); each region includes four inserts: air, Polystyrene, Acrylic, and Teflon. The phantom was imaged using AEC and a fixed tube current technique across 12 clinical CT scanners. Those included five Siemens Somatom Definition Flash, four GE Discovery CT750HD, and three GE Lightspeed VCT systems. A custom MATLAB software package provided MTF, NPS, and detectability indices for each diameter section of the phantom. Detectability indices were used to evaluate the relationship between AEC setting, patient size, and image quality. The magnitude of the power of a best fit exponential curve to the detectability indices and phantom diameter was used as a measure of AEC strength. Results were compared within/across scanner models, and as baseline values for comparison with future system performance testing.

Results:

For each scanner model, the percent difference in expected image quality and AEC setting was under 3%(+/−2%). The average decrease in detectability between the small and large diameter phantom sections for the Siemens Flash, GE CT750, and GE VCT was 99%(+/−10%), 42%(+/−25%), and 33%(+/−41%), respectively. The value signifying AEC strength was 0.051(+/−13%), 0.019(+/−18%), and 0.018(+/−26%), for the Siemens Flash, GE CT750, and GE VCT models, respectively.

Conclusion:

This study demonstrated a practical approach to test the AEC performance of clinical CT systems at a large academic medical center. The quantification and evaluation of AEC performance should be included in acceptance testing and in annual physics testing of clinical CT systems.
WE‐D‐18A‐03: BEST IN PHYSICS (IMAGING) – Statistical Model Based Iterative Reconstruction (MBIR) in Clinical CT Systems: Experimental Assessment of Z‐ and Axial Spatial Resolution
Authors: Li Ke , Garrett John , Ge Yongshuai , Chen G.‐H.
Published: July 2014

Purpose:

The purpose of this work was to experimentally assess the unique spatial resolution characteristics of statistical model based iterative reconstruction (MBIR) along both axial and z directions and to examine the impact of spatial resolution on the task‐based diagnostic detection performance.

Methods:

An anthropomorphic chest phantom was repeatedly scanned 100 times using a clinical CT scanner at four dose levels (25%, 50%, 75%, 100%). Both FBP and MBIR (Veo™) were used for reconstruction. Nine objects with contrasts ranging from 13 to 1710 HU were used to assess spatial resolution. The axial and z resolutions were quantified locally in the image domain by point spread functions (PSF) and slice sensitivity profiles (SSP) respectively. The tradeoff between local image noise and resolution and their joint impact on the channelized Hotelling observer (CHO) detectabilities (d ') was investigated.

Results:

The axial resolution of MBIR improved monotonically with increasing dose and contrast level (FWHM_PSF=2.0 mm at 13 HU/25% dose and was 0.8 mm 1710 HU/100% dose). In comparison, axial resolution of FBP was independent of dose and contrast (FWHM_PSF=1.2 mm). The z resolution of MBIR demonstrated similar contrast dependence but only negligible dose dependence. The spatial resolution of MBIR and FBP became equivalent at some transitional contrast levels (280 HU for 25% dose and 90 HU for 100% dose), above which MBIR demonstrated superior resolution than FBP (and vice versa). Spatial resolution and noise assessed at the same location demonstrated a strong tradeoff in MBIR, and CHO detectability index d' was improved by MBIR for all contrast and dose levels.

Conclusion:

MBIR produces images with unique spatial resolution characteristics and introduces new challenges to its clinical use and evaluation. One potential solution, as suggested by this work, is to perform rigorous spatial resolution and noise measurements at different dose levels for each specific task.

K. Li, J. Garrett, Y. Ge: Nothing to disclose; G.‐H. Chen: Research funded, General Electric Company Research funded, Siemens AG Research funded, Varian Medical Systems, Research funded, Hologic, Inc.
WE‐D‐18A‐04: How Iterative Reconstruction Algorithms Affect the MTFs of Variable‐Contrast Targets in CT Images
Authors: Dodge C.T. , Rong J. , Dodge C.W.
Published: July 2014

Purpose:

To determine how filtered back‐projection (FBP), adaptive statistical (ASiR), and model based (MBIR) iterative reconstruction algorithms affect the measured modulation transfer functions (MTFs) of variable‐contrast targets over a wide range of clinically applicable dose levels.

Methods:

The Catphan 600 CTP401 module, surrounded by an oval, fat‐equivalent ring to mimic patient size/shape, was scanned on a GE HD750 CT scanner at 1, 2, 3, 6, 12 and 24 mGy CTDIvol levels with typical patient scan parameters: 120kVp, 0.8s, 40mm beam width, large SFOV, 2.5mm thickness, 0.984 pitch. The images were reconstructed using GE's Standard kernel with FBP; 20%, 40% and 70% ASiR; and MBIR. A task‐based MTF (MTFtask) was computed for six cylindrical targets: 2 low‐contrast (Polystyrene, LDPE), 2 medium‐contrast (Delrin, PMP), and 2 high‐contrast (Teflon, air). MTFtask was used to compare the performance of reconstruction algorithms with decreasing CTDIvol from 24mGy, which is currently used in the clinic.

Results:

For the air target and 75% dose savings (6 mGy), MBIR MTFtask at 5 lp/cm measured 0.24, compared to 0.20 for 70% ASiR and 0.11 for FBP. Overall, for both high‐contrast targets, MBIR MTFtask improved with increasing CTDIvol and consistently outperformed ASiR and FBP near the system's Nyquist frequency. Conversely, for Polystyrene at 6 mGy, MBIR (0.10) and 70% ASiR (0.07) MTFtask was lower than for FBP (0.18). For medium and low‐contrast targets, FBP remains the best overall algorithm for improved resolution at low CTDIvol (1–6 mGy) levels, whereas MBIR is comparable at higher dose levels (12–24 mGy).

Conclusion:

MBIR improved the MTF of small, high‐contrast targets compared to FBP and ASiR at doses of 50%–12.5% of those currently used in the clinic. However, for imaging low‐ and mediumcontrast targets, FBP performed the best across all dose levels. For assessing MTF from different reconstruction algorithms, task‐based MTF measurements are necessary.
WE‐D‐18A‐05: Construction of Realistic Liver Phantoms From Patient Images and a Commercial 3D Printer
Authors: Leng S , Vrieze T , Kuhlmann J , Yu L , Matsumoto J , Morris J , McCollough C
Published: July 2014

Purpose:

To assess image quality and radiation dose reduction in abdominal CT imaging, physical phantoms having realistic background textures and lesions are highly desirable. The purpose of this work was to construct a liver phantom with realistic background and lesions using patient CT images and a 3D printer.

Methods:

Patient CT images containing liver lesions were segmented into liver tissue, contrast‐enhanced vessels, and liver lesions using commercial software (Mimics, Materialise, Belgium). Stereolithography (STL) files of each segmented object were created and imported to a 3D printer (Object350 Connex, Stratasys, MN). After test scans were performed to map the eight available printing materials into CT numbers, printing materials were assigned to each object and a physical liver phantom printed. The printed phantom was scanned on a clinical CT scanner and resulting images were compared with the original patient CT images.

Results:

The eight available materials used to print the liver phantom had CT number ranging from 62 to 117 HU. In scans of the liver phantom, the liver lesions and veins represented in the STL files were all visible. Although the absolute value of the CT number in the background liver material (approx. 85 HU) was higher than in patients (approx. 40 HU), the difference in CT numbers between lesions and background were representative of the low contrast values needed for optimization tasks. Future work will investigate materials with contrast sufficient to emulate contrast‐enhanced arteries.

Conclusion:

Realistic liver phantoms can be constructed from patient CT images using a commercial 3D printer. This technique may provide phantoms able to determine the effect of radiation dose reduction and noise reduction techniques on the ability to detect subtle liver lesions in the context of realistic background textures.
WE‐D‐9A‐01: A Novel Mesh‐Based Deformable Surface‐Contour Registration
Authors: Zhong Z , Cai Y , Guo X , Jia X , Chiu T , Kearney V , Liu H , Jiang L , Chen S , Yordy J , Nedzi L , Mao W
Published: July 2014

Purpose:

Initial guess is vital for 3D‐2D deformable image registration (DIR) while dealing with large deformations for adaptive radiation therapy. A fast procedure has been developed to deform body surface to match 2D body contour on projections. This surface‐contour DIR will provide an initial deformation for further complete 3D DIR or image reconstruction.

Methods:

Both planning CT images and come‐beam CT (CBCT) projections are preprocessed to create 0–1 binary mask. Then the body surface and CBCT projection body contours are extracted by Canny edge detector. A finite element modeling system was developed to automatically generate adaptive meshes based on the image surface. After that, the projections of the CT surface voxels are computed and compared with corresponding 2D projection contours from CBCT scans. As a result, the displacement vector field (DVF) on mesh vertices around the surface was optimized iteratively until the shortest Euclidean distance between the pixels on the projections of the deformed CT surface and the corresponding CBCT projection contour is minimized. With the help of the tetrahedral meshes, we can smoothly diffuse the deformation from the surface into the interior of the volume. Finally, the deformed CT images are obtained by the optimal DVF applied on the original planning CT images.

Results:

The accuracy of the surface‐contour registration is evaluated by 3D normalized cross correlation increased from 0.9176 to 0.9957 (sphere‐ellipsoid phantom) and from 0.7627 to 0.7919 (H&N cancer patient data). Under the GPU‐based implementation, our surface‐contour‐guided method on H&N cancer patient data takes 8 seconds/iteration, about 7.5 times faster than direct 3D method (60 seconds/iteration), and it needs fewer optimization iterations (30 iterations vs 50 iterations).

Conclusion:

The proposed surface‐contour DIR method can substantially improve both the accuracy and the speed of reconstructing volumetric images, which is helpful for applying in adaptive radiotherapy.

This research is supported by CPRIT individual investigator award RP110329.
WE‐D‐12A‐01: Stereotactic Breast Biopsy
Authors: Pizzutiello R , Patel V
Published: July 2014

This presentation will begin by comparing the image quality and dose characteristics of Stereotactic Breast Biopsy (SBB) with those of screen‐film and full field digital mammography. Part 2 of the presentation will explore several practical aspects of the ACR SBB Accreditation Program. When SBB was introduced as a commercial product in the 1990' s, x‐ray breast imaging was limited to screen‐film mammography. By the time SBB became common, all SBB systems utilized digital imaging technology. These small field of view SBB image receptors were the first common examples of digital imaging for the breast. The ACR is the only accrediting body that accredits SBB facilities. The ACR SBB QC Manual was published in 1999. Current methods of maintaining a QC program for SBB, current SBB equipment will be discussed. In addition, the process of an ACR Scheduled On‐Site Survey (for facilities that have failed to meet ACR accreditation standards) will be presented.

Learning Objectives:

Understand the image quality and dose characteristics of SBB, Screenfilm and full field digital mammography

Understand the current QC requirements for SBB facilities accredited by ACR

Understand the ACR process for Scheduled On‐Site Surveys of facilities that have failed to meet the accreditation standards
WE‐PIS‐Exhibit Hall‐01: Tools for TG‐142 Linac Imaging QA II
Authors: Childress N , Murray B
Published: July 2014

Partners in Solutions is an exciting new program in which AAPM partners with our vendors to present practical “hands‐on” information about the equipment and software systems that we use in our clinics. The therapy topic this year is solutions for TG‐142 recommendations for linear accelerator imaging QA. Note that the sessions are being held in a special purpose room built on the Exhibit Hall Floor, to encourage further interaction with the vendors.

Using DoseLab to Perform TG‐142 Imaging QA

The goals of this session will be to present a clinical overview of acquiring images for TG‐142 Imaging QA, as well as analyzing and evaluating results using DoseLab software. DoseLab supports planar imaging QA analysis using almost any QA phantom provided by numerous vendors. General advantages and disadvantages of selecting each of these phantoms will be briefly summarized. Best practices for selecting image acquisition parameters will be presented. A demonstration of using DoseLab software to perform a series of TG‐142 tests will be performed. We will disuss why DoseLab uses its own set of imaging QA formulas, and why imaging QA measurement values of the same nominal properties will vary between TG‐ 142 software packages. Because TG‐142 does not specify baseline and tolerance values for imaging QA, the presentation will recommend performing the manufacturer's acceptance test procedure to validate the equipment is functioning correctly. Afterwards, results can be obtained using the clinic's selected set of phantoms, image acquisition parameters, and TG‐142 software to set proper baseline values. This presentation will highlight the reasons why comparing imaging QA results can be trickier than comparing linear accelerator treatment results and what physicists should keep in mind when comparing imaging QA results for different machines. Physicists are often unsure of the next step when there is an issue discovered during Imaging QA. Therefore, a few common examples of imaging issues and recommended solutions will be discussed.

TG‐142 Imaging QA Simplified: Lessons From Diagnostic Physics Collaboration

There are many commercial options for the performance of imaging quality assurance tests for the linear accelerator imaging systems as required by the AAPM TG‐142 report. Imaging quality assurance testing is largely performed by the diagnostic physicist so routine performance of these tests by the practicing oncology physicist can be complicated and confusing given all of the commercially available options. This presentation focuses on the performance of imaging quality assurance testing for linear accelerators using methods similar to that of diagnostic physicists. This presentation will address the ability to perform the required testing without complicated software and explores solutions for the performance of these tests in an efficient manner while still maintaining the ability to ascertain image quality changes that may ultimately affect clinical decisions.
WE‐E‐19A‐01: Globalization of Medical Physics
Authors: Rehani M , Meghzifene A , Tsapaki V , Padovani R , Pipman Y , Lief E
Published: July 2014

Following successful 2012–2013 International Professional Symposiums as a part of Annual AAPM meetings, representatives of AAPM and International Organization of Medical Physics (IOMP) suggested to make this tradiational Symposium a permanent part of Annual AAPM meetings in future. Following the tradition, this session includes presentations of representatives of AAPM, IOMP, European Federation of Medical Physics (EFOMP), International Atomic Energy Agency (IAEA) and International Center for Theoretical Physics (ICTP). The speakers will cover various aspects of International collaboration such as educational, professional, and scientific issues, as well as help to developing countries.

With further developments of medicine and technology and increased communication with our colleagues overseas, Medical Physics becomes more and more global profession. Use of the same technology, significant progress in medical physics research and developing practical regulations worldwide makes it increasingly useful to organize global collaboration of medical physicists. Several international organizations are tasked to promote such collaboration and provide help to developing countries. Not all AAPM members are fully aware of these international efforts. It is very useful for medical physicists to know about success of our profession in other countries. Different schools present different approaches to the same problem, which allows to find the best solution. By communicating with colleagues overseas, one can learn more than from just reading scientific publications. At this session the attendees will receive a glimpse of International Medical Physics activities.

Learning Objectives:

Understand the globalization of Medical Physics profession and advantages of collaboration with foreign colleagues.

See what role AAPM is playing in establishing contacts with colleagues overseas.

Understand the role of IOMP and main directions of its activity.

Learn about IAEA and how it helps developing countries.

Learn about activity of EFOMP and how can help the global development of Medical Physics.

Find out about ICTP and its educational programs.
WE‐E‐BRE‐10: Level of Breast Cancer Stem Cell Correlated with Tumor Radioresistence: An Indication for Individualized Breast Cancer Therapy Adapted to Cancer Stem Cell Fractions
Authors: Qi S , Pajonk F , McCloskey S , Low D , Kupelian P , Steinberg M , Sheng K
Published: July 2014

Purposes:

The presence of cancer stem cells (CSCs) in a solid tumor could result in poor tumor control probability. The purposes are to study CSC radiosensitivity parameters α and β and their correlation to CSC levels to understand the underlying radioresistance mechanisms and enable individualized treatment design.

Methods:

Four established breast cancer cell lines (MCF‐7, T47D, MDA‐MB‐231, and SUM159PT) were irradiated in vitro using single radiation doses of 0, 2, 4, 6, 8 or 10 Gy. The fractions of CSCs in each cell lines were determined using cancer stem cell markers. Mammosphere assays were also performed to better estimate the number of CSCs and represent the CSC repopulation in a human solid tumor. The measured cell surviving fractions were fitted using the Linear‐quadratic (LQ) model with independent fitting parameters: α_TC, β_TC (TCs), α_CSC, β_CSC (CSCs), and fs (the percentage of CSCs in each sample).

Results:

The measured fs increased following the irradiation by MCF‐7 (0.1%), T47D (0.9%), MDA‐MB‐231 (1.18%) and SUM159T (2.46%), while decreasing surviving curve slopes were observed, indicating greater radioresistance, in the opposite order. The fitting yielded the radiosensitive parameters for the MCF‐7: α_TC=0.1±0.2Gy−1, β_TC= 0.08 ±0.14Gy−2, α_CSC=0.04±0.07Gy−1, β_CSC =0.02±0.3Gy−2; for the SUM159PT, α_TC=0.08±0.25 Gy−1, β_TC=0.02±0.02Gy−2, α_CSC=0.04±0.18Gy−1, β_CSC =0.004±0.24Gy−2. In the mammosphere assay, where fs were higher than the corresponding cell line assays, there was almost no shoulder found in the surviving curves (more radioresistant in mammosphere assays) yielding β_CSC of approximately 0.

Conclusion:

Breast cancer stem cells were more radioresistant characterized by smaller α and β values compared to differentiated breast cancer cells. Percentage of breast cancer stem cells strongly correlated to overall tumor radioresistance. This observation suggested the feasibility of individualized radiotherapy prescription based on the fractions of cancer stem cells found in biopsy.
WE‐E‐18A‐02: Enhancement of Lung Tumor Visibility by Dual‐Energy X‐Ray Imaging in An Anthropomorphic Chest Phantom Study
Authors: Menten MJ , Fast MF , Nill S , Oelfke U
Published: July 2014

Purpose:

Intrafractional lung tumor motion during radiotherapy can be compensated for by tracking the tumor position using x‐ray imaging and adapting the treatment in real‐time. However, locating the tumor with an automated template‐matching algorithm is often challenging if the tumor is obscured by ribs. This study investigates the feasibility of creating dual‐energy (DE) images of the chest with increased tumor visibility on an Elekta XVI system.

Methods:

An anthropomorphic chest phantom was imaged at two different energies. Low‐energy images were obtained at 80 kVp (0.8 mAs); high‐energy images at 129 kVp (0.6 mAs, additional 1.26 mm tin filter). A Geant4 Monte‐Carlo framework was developed allowing simulation of the x‐ray tube, flat‐panel detector and phantom in order to optimize the beam energies, filtration and the weighting factor used to subtract the individual images into a synthetic DE image. The weighting factor was selected to minimize the visibility of bones while maintaining a sufficient tumor visibility. We scored the bone visibility as the contrast of tumor (with bone) to tumor (without bone), and similarly of lung tissue (with bone) to lung tissue (without bone). Tumor visibility was quantified as the contrast between tumor and lung tissue (both without bone).

Results:

In the experimentally obtained DE image the bone visibility was reduced by 79.2% in tumor and by 96.8% in lung tissue while the overall tumor visibility only decreased by 69.5%. The Monte‐Carlo simulation yielded similar results reducing the scores by 90.0%, 85.3% and only 71.9%, respectively.

Conclusion:

This work demonstrates the feasibility of DE imaging to enhance lung tumor detectability. In the future, we hope to further refine the Monte‐Carlo simulation to more accurately predict the weighting factors which would aid real‐time implementation. Furthermore, we plan to use the Monte‐Carlo framework to simulate DE images of actual lung tumors.

The authors would like to thank Paul‐Scherrer‐Institut and Centre Suisse d' Electronique et Microtechnique for lending us the anthropomorphic phantom. We acknowledge support from Elekta AB under a research agreement. Research at The Institute of Cancer Research is also supported by Cancer Research UK under Programme C46/A10588.