bluuebunny/crossref_metadata_2025 huggingface dataset:
WE‐C‐BRB‐05: Results from 1005 IMRT Irradiations of an Anthropomorphic Head and Neck Phantom
Authors: Molineu A , Hernandez N , Alvarez P , Ibbott G , Galvin J , Followill D
Published: November 2011

Purpose: To credential institutions treating clinical trial patients with intensity modulated radiation therapy Methods: The credentialing bodyˈs anthropomorphic head and neck phantom was sent to institutions wishing to participate in multi‐institutional clinical trials. The phantom contained two PTV structures and an organ at risk (OAR). TLD and film dosimeters were imbedded in the PTV. Institutions were asked to image, plan and treat the phantom as they would a patient. The treatment plan should cover at least 95% of the primary PTV with 6.6 Gy and at least 95% of the secondary PTV with 5.4 Gy. The plan should limit the dose to the OAR to less than 4.5 Gy. The passing criteria were +/−7% for the TLD in the PTVs and a distance to agreement of 4 mm in the high dose gradient area between the PTV and the OAR. Results: The phantom was irradiated 1005 times by 689 institutions from 2001 through February 2011. 804 of the irradiations passed the criteria. 145 irradiations failed only the TLD criteria, 24 failed only the film criteria and 32 failed both sets of criteria. Only 61% of the irradiations passed a narrowed TLD criterion of +/− 5%. When possible, gamma calculations were made for an area around the primary PTV in the axial plane. The average percent of pixels meeting the gamma criteria was 89%. Conclusions: The head and neck phantom is a useful credentialing tool for multi‐institutional IMRT clinical trials. Tightening the criteria would significantly reduce the number of passing irradiations. Altering the criteria to use the gamma calculation instead of the DTA would slightly reduce the number of institutions passing, but would give a more comprehensive view of the fitness of the irradiation.

The investigation was supported by PHS grants CA10953, CA81647 and CA21661 awarded by the NCI, DHHS.
WE‐C‐BRB‐11: Four Dimensional Analysis of VMAT Delivery
Authors: Yan G , Liu C , Lu B , Li J
Published: November 2011

Purpose: To develop a technique for analyzing the time dependent delivery of VMAT treatment with a 4D diode array. Method and Materials: VMAT treatment plans with two full arcs for H&N patients were generated with Pinnacle SmartArc. The plan was delivered and measured with a 4D diode array (ArcCHECK). ArcCHECK records data every 50 milliseconds and saves in a movie file for post analysis. Algorithm was designed to derive gantry angle for each signal update based on the intersection of beam edges with the cylindrical ArcCHECK phantom. Angular correction factor for each diode was interpolated and applied, with intrinsic sensitivity correction factor, to the raw data to remove diode response dependence. Based on the derived gantry angles, dose between any two control points can be integrated and written into an ArcCHECK measurement file. Measured dose distribution at any instance or integrated between any two control points can be compared with the Pinnacle calculated control point dose using the MapCHECK software. Results: Five IMRT beams were used to test the accuracy of the gantry angle derivation algorithm. The maximum mean error was 0.6o. For VMAT delivery, the derived gantry angles showed a smooth 360o clockwise gantry motion starting from 180o. Seven individual control points (#1, #15, #1∼3, #1∼5, #4∼5, #5∼15 and #1∼90) were selected for dose comparison in relative dose mode. The average passing rates with 3%/3mm and 2%/2mm were 97.1% and 90.5%, respectively. Conclusion: Control point based dose comparison showed satisfactory results indicating the accurate delivery of VMAT plans. The technique will be valuable in diagnosing VMAT delivery system errors, especially those originating from MLC and gantry motion.
WE‐C‐110‐06: Two‐Material Decomposition from a Single CT Scan Using Statistical Image Reconstruction
Authors: Long Y , Fessler J , Balter J
Published: November 2011

Purpose: Dual‐energy (DE) CT methods can separate two basis materials (e.g., soft tissue and bone) for applications such as dose calculations. However, typical DECT methods require either two scans or specialized scanners. We propose a statistical penalized weighted least‐squares (PWLS) method to reconstruct two basis material images from a single‐energy CT scan acquired with a simple split X‐ray filter. Methods: We used a pre‐patient split‐filter that contains 2mm aluminum across half the fan beam and 200 microns molybdenum for the other half. Using a 360‐degree rotation of the X‐ray source, the whole scanned object is exposed to two incident spectra with different effective energies during a single scan. We propose an optimization transfer method with a separable quadratic surrogate to monotonically decease a PWLS cost function with edge‐preserving regularization. We first reconstructed the bone‐corrected FBP images using the Joseph and Spital method, and separated the soft and bone components by a threshold to initialize the iterative algorithm. We used the ordered subsets approach to accelerate the convergence to a good local minimum. Results: The test object is a chest NCAT image with 1.0 for soft tissue, 0.5 for lungs, 1.5 for spine, and 2.0 for ribs (the units are physical density: g/cc.). The lungs and soft tissue had the “soft tissue” characteristics and the spine and ribs had the “bone” characteristics. The root‐mean‐square (RMS) errors of the soft tissue, bone and density map were 0.03, 0.02 and 0.01 for PWLS, compared to 0.06, 0.03 and 0.05 for the FBP initialization for the noiseless simulation. The PWLS method removed the beam hardening artifacts more effectively than the FBP‐JS method. Conclusions: The proposed PWLS reconstruction method was able to separate soft tissue and bone images with low RMS errors from a single CT scan using a split‐filter.

Sponsored in part by NIH P01CA59827
WE‐C‐301‐01: Overview of Accreditation Programs for Radiation Oncology: ACR and ACRO
Authors: Sibata C , Kuettel M , Mian T
Published: November 2011

There are two accreditation bodies that perform practice reviews specific for radiation oncology: ACR/ASTRO and ACRO. The history and process/procedures for accreditation of these two organizations will be presented from both a Medical Physicist and Radiation Oncologist perspective. In addition, State activities for requiring accreditation will be discussed. Finally, requirements for Medical Physics reviewers will be outlined.
WE‐D‐220‐01: Tissue Displacement Monitoring for Prostate and Liver IGRT Using a Robotically‐Controlled Ultrasound System
Authors: Schlosser J , Salisbury K , Hristov D
Published: November 2011

Purpose: We previously reported the implementation of a novel telerobotic ultrasound system capable of real‐time soft‐tissue imaging during radiotherapy beam delivery. Expanding on this capability, the aim of this work was to develop and characterize an image‐based technique for real‐time detection of prostate and liver displacements. Methods: Image processing techniques were implemented on spatially localized images to generate two tissue displacement parameters (TDPs) in real‐time. The TDPs were derived from the cross correlation similarity measure between a reference image template and the current image within the incoming stream. In five volunteers, soft‐tissue targets were continuously imaged with a customized robotic manipulator while recording the TDPs. Variations of the TDPs in the absence of tissue displacements were evaluated, as well as the sensitivity of the TDPs to prostate translations and rotations. Robustness of the method to template window selection and total time lag of the system were also investigated. The systemˈs applicability to liver respiratory gating was explored with two volunteers. Results: Prostate translations of 1.8 mm, 2.1 mm, and 2.0 mm were detectable in the M/L, A/P, and S/I directions at the 95% confidence level. Prostate pitch of 3.8° was also detectable. False positives in the absence of displacements were registered at a rate of 1 false positive event per 7 minutes of continuous imaging time. Total system time lag was 173 ms, mostly limited by ultrasound acquisition rate. Respiratory signals based on liver blood vessel monitoring differed significantly from signals based on an external marker. Conclusions: For the first time, quantitative real‐time monitoring of soft‐tissue target displacements was demonstrated in‐vivo using telerobotic ultrasound. Such monitoring has the potential to detect small clinically‐relevant intra‐fractional variations of the prostate position during radiotherapy. An internal ultrasound‐based respiratory signal could be a better predictor of liver target motion than an external surrogate.
WE‐E‐224‐02: Preparing for ABR Board Exams
Authors: Flynn R
Published: November 2011

It is easy to become overwhelmed by the pool of potentially useful study material for Part II of the ABR Board Exam in radiotherapy physics. Therefore it is difficult to extract a sufficiently broad and relevant subset of material to study. Moreover, balancing the time‐consuming exam preparation process with a full time job and family life is also challenging. In order to make best use of available study time, attendees are taught an efficient organizational framework for Part II exam preparation that maximizes high‐yield active learning study activities and minimizes low‐yield study activities. This method is then combined with a productive group‐based study technique.

The format and scope of the Part II ABR exam in radiotherapy physics is described, and the eligibility requirements are reviewed. High‐ and low‐yield study activities are defined and examples are discussed in detail. A problem‐based strategy for limiting the scope of study material is described. A method for studying in groups by distributing delegable tasks among multiple group members and ensuring their completion is described.

Educational objectives

1. Understand the scope of material covered on Part II of the ABR radiotherapy physics exam and which references to study for the exam.

2. Be able to design and execute an efficient study plan that enables an active learning approach.

3. Learn to use group study techniques to enhance efficiency.
WE‐E‐BRB‐01: Voxelized Quenching Correction for Proton Pencil Beams in a Liquid Scintillator Detector
Authors: Robertson D , Mirkovic D , Mohan R , Beddar S
Published: November 2011

Purpose: To correct for quenching on a voxel‐by‐voxel basis for proton pencil beams in a liquid scintillation dosimetry system. Methods: Scintillation light from a proton pencil beam in a tank of organic liquid scintillator (20×20×20 cm3) was measured with a CCD camera for three beam energies (100.9, 144.9, and 161.6 MeV). Three‐dimensional dose and linear energy transfer (LET) distributions were calculated for each beam energy using a validated Monte Carlo model of the proton pencil beam. The quenching for each voxel in the scintillator was calculated using the LET and material‐specific empirical factors. The empirical factors for the scintillator were obtained by a fit to the Monte Carlo LET and dose data and the intensity values measured with the CCD camera for the central energy (144.9 MeV). The empirical values and Monte Carlo calculations were then used to predict the quenched light signal for the other two proton energies. The differences between the predicted and measured light signals were quantified using a gamma index of 3% or 3mm to agreement. Results: The LET in the distal falloff region was a factor of 10 higher than in the proximal build‐up region, while the measured light peak was 75% of the Bragg peak height. The calculated light signal derived from the voxelized quenching factors provided a good approximation of the measured light signal. Conclusion: The results of this study indicate that it is possible to correct for scintillator quenching on a voxel‐by‐voxel basis in a large detection volume. This correction requires a prior knowledge of the three‐dimensional LET distribution of the beam and the material‐dependent empirical quenching factors for the scintillator. This quenching correction method will be employed in future studies using liquid scintillators to obtain three‐dimensional dosimetric information from proton pencil beams.
WE‐E‐BRB‐04: VMAT Dynamic QA for Moving Lung Tumors
Authors: Ionascu D , Tyagi N , Yang K
Published: November 2011

Purpose: Development of a novel QA phantom and technique designed to evaluate the accuracy of VMAT delivered dose to the GTV when tumor motion is present. Materials and Methods: We have modified the Arccheck cylindrical QA phantom for VMAT delivery by designing a dynamic insert that can be accommodated in the central cavity of the detector and dosimetrically monitored. This was achieved by the use of a custom made water equivalent sphere with 5 imbedded mosfets. This sphere was encapsulated in a lung insert that can be accommodated by both the cylindrical QA phantom AND a thorax dynamic phantom. The motion of the dynamic phantom was preprogrammed for different trajectories including prerecorded traces of lung implanted fiducials from a previous study. A 4DCT scan was performed on the static/moving target and a VMAT treatment plan was correspondingly generated. These plans were mapped and calculated on the corresponding VMAT QA phantom (static/dynamic). The mosfets and the arccheck dose measurements from the treatment delivery were compared with the expected values obtained from the TPS. Results: Arccheck absolute dose analysis between measurement and calculation using γ (3%/3mm) shows more than 98% of diodes passing for both static and dynamic phantom with and without the lung phantom insert. Mosfet static measurement showed 2% agreement with the calculated value (5450 ± 120 vs 5250 ± 20 cGy). The dynamic measurement showed a larger spread than calculated (6900 ± 140 vs 7000 ± 250 cGy) indicating an accentuated interplay effect between MLC motion and tumor motion. Conclusion: We have developed a novel device to perform VMAT QA on moving tumors and to quantitatively estimate the dosimetric difference between the treatment plan and delivery. Our method is used to investigate a large variety of dose discrepancies including interplay effect and respiratory motion variation.
WE‐E‐BRB‐06: An EPID Based Method for High Accuracy Calibration of an Optical External Marker Tracking Device with the LINAC Reference Frame
Authors: Grelewicz Z , Kang H , Wiersma R
Published: November 2011

Purpose: The accuracy of an optical camera system used for patient motion monitoring is typically limited to 1–2 mm due to use of the light field crosshair and in‐room lasers for initial camera calibration setup making it unsuitable for highly accurate patient monitoring procedures such as frameless SRS. To provide submillimeter accuracy in calibrating a 3D stereoscopic infrared optical camera with the treatment frame of a LINAC, a semi‐automated calibration method was developed based on simultaneous viewing of external markers with both the MV treatment beam and optical camera system. Methods: A phantom comprised of 9 steel BBs covered in highly IR reflective tape was placed on the LINAC treatment couch and imaged with both a 3D stereoscopic IR imager, and the on board MV EPID imager at a variety of gantry angles. Using the relative 3D BB positions given by the camera, simulated annealing was used to optimize 9 parameters including source‐to‐imager distance, detector tilt, and deviations from nominal isocenter. Singular value decomposition was then used to calculate the transformation between different reference frames. Additionally, a traditional method of calibration was used for comparison. Results: Using modeled data, the simulated annealing process was able to determine the locations of the BBs with .2 mm accuracy. Using projection images acquired with an MV imager, initial preliminary results show the ability to determine locations of BBs with a .2 mm planar standard deviation and a 1 mm axial standard deviation. Conclusions: The method can be used to provide a highly accurate spatial registration between an external 3D camera frame and the LINAC frame. The real MV imager results, while not as precise as the simulated results, exceed current standards and are expected to improve with continued refinement.
WE‐E‐BRC‐06: Comparison of Two Methods of Contouring Internal Target Volume on Multiple 4DCT Data Sets from the Same Subjects: Maximum Intensity Projection and Combination of 10 Phases
Authors: Salter B , Wang B , Sadinski M , Ruhnau S , Sarkar V , Hinkle J , Hitchcock Y , Kokeny K , Joshi S
Published: November 2011

Purpose: Two methods to generate ITV on 4DCT images are explored: direct contouring on MIP images and combining GTV contours on individual phase images. We compared these two methods on multiple 4D data sets from the same subjects. Methods: 42 simulation and image guidance 4DCT data sets, for 9 SBRT patients treated 3–5 fractions each, were retrospectively analyzed. Two sets of ITV contours were generated from the raw 4DCT cine data for each patient scan: MIP image set [ITV(MIP)‐ direct contouring on MIP] and 10 phase‐binned image sets [ITV(10phase)‐ Boolean OR of GTVs contoured on 10 phase image sets]. A single operator segmented all ITVs using a semi‐automated approach with the ITK‐SNAP 3D segmentation tool. Results: The mean volumetric ratio of ITV(MIP) to ITV(10phase) across all patients was 1.02 (Range 0.56 – 1.77; 1 = ideal). The distance between the Center Of Mass of the two sets of ITVs, across all patients, had a median of 1.3 mm (range 0.1 – 7.5 mm), thus indicating that both volume and location of the ITVs generated by these two methods agree well on average across all patients, but can differ non‐trivially for select cases. Interestingly, we observed large variations between the two contouring methods for repeated scans of the same patient. For example, one patient demonstrated excellent agreement for the first (simulation) scan (agreement ratio=1.02), but then poor agreement for three subsequent scans (agreement ratios = 0.85, 1.11, 1.15). Conclusion: ITVs generated by the two methods of MIP, and combination of 10 phases on 4DCT, agreed well on average, but differed non‐trivially for select cases. In particular, we observed the potential for large variation within the same patient, when multiple 4D scans of the same patient were evaluated. This is likely attributable to daily breathing pattern variations.
WE‐E‐214‐01: Targeted Radionuclide Therapy
Authors: Frey E
Published: November 2011

Targeted radionuclide therapy (TRT) is becoming an increasingly important tool for therapy of some cancers including non‐Hodgkins lymphoma, thyroid cancer, and neuroendocrine tumors. The dose delivered to neoplasms and normal tissues, and thus the therapeutic response and incidence of toxicities, depends on the anatomy and physiology of the patient. Therefore, optimal treatment planning requires estimating the dose distribution for each patient. The dose distribution is estimated in two steps: measurement of the activity distribution of a planning dose at a series of time points using nuclear medicine imaging methods and calculating the dose to organs or voxels in the patient. State of the art dose estimation requires, as an input, estimates of the 3D activity distribution of the planning dose in the patient at each time point.

The 3D activity distribution of a radionuclide can be estimatedusing the tomographic nuclear medicine imaging modalities SPECT and PET. Since uptake times of TRT agents are typically on the order of several days, radionuclides such as In‐111 or I‐131 (for SPECT) or I‐124 or Y‐86 (for PET) having longer half‐lives are used for treatment planning. The SPECT radionuclides emit medium or high‐energy photons, which can make quantification of the SPECT images more difficult and requires compensating for the collimator‐detector response. The PET radionuclides have prompt gamma emissions that can result in false coincidences, once again complicating quantification. For both modalitiesattenuation and scatter compensation are essential. Compensation for partial volume effects is important for dose‐estimation in small objects such as tumors.

This lecture will review the challenges and recent advances in methods for quantifying 3D activity distributions from SPECT and PET imaging using radionuclides relevant for TRT. It will describe the impact of these advances in terms of metrics relevant to dose estimation and describe the levels of accuracy and precision that are obtainable with state‐of‐the‐art methods.

Learning Objectives:

1. Understand the applications and requirements of quantitative SPECT and PET for targeted radionuclide therapy.

2. Understand the factors that limit the quantitative reliability of SPECT images and how to compensate for them.

3. Understand the factors that limit the quantitative reliability of PET.
WE‐E‐214‐02: Dose Response Modeling for Targeted Radiotherapies
Authors: Roberson P
Published: November 2011

The efficacy of biologically targeted radionuclide therapy (TRT) is dependent on the properties of the treatment strategy, the vector (carrier) molecule, the radionuclide products, and the target and normal tissue architecture. Both dose estimation and cellular response at the lower dose rates of TRT are more complex than typical external beam or high dose brachytherapies, for both targeted and normal tissues. Estimation of TRTresponse of target and normal tissues suffers from inaccurate macroscopic dose estimation, heterogeneous microscopic dose and dose rate dependence, and confounding factors including pretreatment patient status and treatment synergy with concurrent treatment regimens. Cellular response depends on cell survival, being influenced by apoptosis, damage repair, cell division delay, cell cycle redistribution, reoxygenation, regeneration and bystander effects. Tissue response can be described using the linear‐quadratic model, including allowances forthe effects of the above modifying factors. The demand for improved therapy (dose) response modeling, a prerequisite for improved therapy dose optimization, requires more extensive and detailed imaging. Effects that can be modeled usingquantitative imaging are: 1) tissue changes over an extended therapy interval (e.g. SPECT/CT, dual energy CT);2) macro and micro structure and activity distributions of targeted and normal tissues (e.g. SPECT/CT, autoradiography); and 3) macroscopic effects of cell response to therapy (e.g. PET/CT). To help accomplish this, increased efforts are being made to perform more frequent high‐resolution imaging, along with potential correlation to biomarkers. Results point to characteristic non‐uniform micro distributions that can be used to modify therapy—response estimates based on routine macro distribution measurements. Examples of the need for improved imaging include 1) evidence that imaging‐based bone marrow doses correlate with outcome better than blood‐based methods; 2) dose estimations from 3D (SPECT/CT) methods are significantly superior to 1D (planar) methods; 3) evidence that factors other than dose affect therapy outcomes, possibly with synergistic relationships with dose and dose rate.

Learning Objectives:

1. Understand the importance of quantitative imaging and reconstruction for therapy response modeling in TRT

2. Understand the importance of modeling biological effects in TRT in comparison to external beam therapy

3. Learn some approaches to therapy response modeling of TRT
WE‐E‐110‐01: Optimization of Image Acquisition and Reconstruction in Multi‐Slice CT
Authors: Yu L , McCollough C , Leng S , Kofler J
Published: November 2011

CT scanning protocols, which specify image acquisition and reconstruction parameters, need to be optimized so that minimum radiation dose can be used to achieve sufficient image quality for specific diagnostic tasks. To achieve this goal, the relation among image acquisition parameters, image reconstruction algorithms, image quality, and radiation dose must be clearly understood. This lecture will provide an overview on how to optimize image acquisition and reconstruction parameters in multi‐slice CT.

Learning Objectives:

1. Understand how the CT acquisition parameters (helical pitch, collimation, detector configurations, etc.) affect the image quality.

2. Understand how the reconstruction parameters (kernel, slice thickness, etc.) affect the image quality.

3. Understand how to optimize the acquisition and reconstruction parameters for different diagnostic tasks in order to improve image quality or reduce radiation dose.
WE‐E‐220‐02: Ultrasound and Microbubble Enhancement of Radiation Response in Tumours
Authors: Czarnota G
Published: November 2011

Purpose: It is now appreciated that radiation not only damages the DNA inside tumour cells in vivo but may act by damaging the endothelial cells of the vasculature. In this study we tested the hypothesis that microbubble agents in vivo may be used apriori to cause endothelial cell perturbations thus causing “radiosensitization” of tumours. Materials and Methods: Human prostate cancer xenograft‐bearing mice (120 animals) were exposed to combinations of ultrasound (570kPa peak negative pressure with a 3kHz pulse repetition frequency for 750 milliseconds over 5 minutes), activated‐microbubbles (Definity) alone and in the presence of ultrasound at various concentrations, and radiation (160 kVp) (8 animals per group) at doses of 0, 2 and 8 Gy. In order to optimize treatments, studies undertaking the timing of the ultrasound and radiation treatments were carried out (40 animals) by introducing a time‐gap between ultrasound and radiation treatments ranging from 0 to 24 hours. In another cohort of animals (n=60) insonifying pressure and radiation dose were varied to investigate the effects of these parameters on treatment effect. In order to further demonstrate the efficacy of this type of combination treatment, multiple treatments combining radiation and ultrasound were also administered to tumour bearing mice over 3–4 weeks (40 animals). Treatment effects were monitored using staining of representative tumour sections with immunohistochemistry, clonogenic assays and growth delay studies. Results: Analyses indicated a synergistic increase in tumour cell kill due to vascular disruption caused by the combined therapies leading to endothelial cell apoptosis through the activation of the ceramide cell‐death pathway caused by microbubbles. The optimal time for combining the two treatments in order to maximize treatment synergy varied with radiation dose and appeared to be within 6 hours. Effects varied with radiation dose and insonifying ultrasound pressure. Multiple treatments indicated better therapeutic outcome compared to single treatments and caused tumour regression. Analyses indicated activation of ceramide‐mediated apoptotic cell death in endothelial cells leading to vascular disruption in tumours. Conclusions: This work forms the basis for ultrasound‐induced spatial targeting of radiotherapy enhancement. Results indicated a greater than 50‐fold increase in tumour cell death. This type of combination treatment has the potential to increase the efficacy of radiation and should permit lower radiation doses to be used with the same treatment effect as high doses of radiation when administered alone.
WE‐E‐220‐06: Histological Changes in the Mouse Prostate Tumors Treated with Non‐Thermal Pulsed Focused Ultrasound
Authors: Cvetkovic D , Chen X , Ma C , Chen L
Published: November 2011

Purpose: To date, detailed studies assessing histological changes in prostate tumors upon treatment with non‐thermal pulsed focused ultrasound (pFUS) are scarce in the literature. The purpose of our study was to evaluate the effect of non‐thermal pFUS on the morphology of mouse prostate tumor tissues by light microscopy. Methods: The orthotopic implantation of 106 LNCaP cancer cells in nude male mice resulted in prostate tumor growth that was monitored by MRI. When tumors reached approximately 100mm3 in volume, the animals were treated with non‐thermal pFUS using the following parameters: 1MHz; 25W acoustic power; 5Hz frequency and 0.1 duty cycle for 60sec with temperature kept below 42 degree C (InSightec ExAblate 2000 with a 1.5T GE MR scanner). On average 6–8 sonications were used to cover the tumor volume. Animals were sacrificed immediately after pFUS treatment and tumors were fixed in formalin, embedded in paraffin and 5 microns thick tissue sections were stained with H&E. Tumors from untreated animals were used as controls. Results: Morphological analysis of prostate tumor tissues revealed poorly differentiated cancers. The main histological findings in both pFUS‐treated and untreated tumors were coagulation necrosis and hemorrhage. The extravasation of blood cells, hemorrhage, was predominant in the periphery, while necrosis was present in the central zones of the tumor, in both pFUS‐treated and control, untreated prostate tumors. However, the main distinction between the treated and untreated tumors was the increased hemorrhage in the treated group. This finding is consistent with our previous studies. Conclusions: Our results indicated that non‐thermal pFUS increased extravasation of blood cells in prostate tumors compared to controls. We are performing more detailed histological and immunohistological analyses at different time points post pFUS treatment to look for markers of apoptosis in prostate tumors.
WE‐G‐214‐08: Interobserver Volume Variations in the Target Delineation of High‐Grade Gliomas Using Magnetic Resonance Imaging and 18F‐FDOPA Positron Emission Tomography
Authors: Kosztyla R , Hsu F , Wilson D , Zhang S , Moiseenko V , Ma R , McKenzie M , Benard F , Nichol A
Published: November 2011

Purpose: To quantify interobserver variations in the delineation of high‐grade gliomas for magnetic resonance imaging (MRI) with gadolinium (Gd) contrast and positron emission tomography (PET) with 3,4‐dihydroxy‐6‐, 18F‐fluoro‐L‐phenylalanine (,18F‐FDOPA) imaging modalities. Methods: Twenty patients with histologically confirmed high‐grade gliomas underwent radiotherapy treatment planning with computed tomography, Gd‐enhanced MRI and, 18F‐FDOPA PET. The images were fused and two trained observers delineated the Gd enhancement and, 18F‐FDOPA uptake. The MRI‐based gross tumor volume (GTV) was defined as the volume of Gd enhancement excluding the surgical cavity. The PET‐based GTV was defined as the union of the, 18F‐FDOPA uptake and Gd enhancement excluding the surgical cavity. For each GTV, a clinical target volume (CTV) was defined as the union of the GTV and the surgical cavity, plus a 2‐cm three dimensional (3D) margin. A planning target volume (PTV) was defined as a 0.5‐cm 3D margin on the CTV. Interobserver and intermodality variability of the GTV, CTV and PTV were quantified by differences in the volume and percent volume overlap (PVO) of the structures. Results: The MRI‐based and PET‐based GTV volumes delineated by the second observer were on average 0.65 and 0.98 times the volumes delineated by the first observer. The root mean square error (RMSE) of the linear regression of the interobserver volumes was 10.7 cm,3 and 16.0 cm,3 for MRI‐based and PET‐based volumes. The interobserver GTV PVO for MRI‐based and PET‐based delineations was similar (49.6% vs. 59.1%, p=0.132). PET‐based GTV volumes were 1.6 times larger than MRI‐based volumes, with a RMSE of 27.6 cm,3. The mean intermodalily GTV PVO was 41.6%. Conclusions: There was less interobserver variability for GTV volumes delineated with combined MRI and, 18F‐FDOPA PET compared to volumes delineated with MRI only. GTV volumes delineated with both MRI and PET were 1.6 times larger than volumes delineated using only MRI.
WE‐G‐110‐03: Directional MTF Measurement of Tomosynthesis Images Using a Cone‐Based Technique
Authors: Murphy S , Richard S , Samei E
Published: November 2011

Purpose: To develop a cone‐based modulation transfer function (MTF) measurement technique for tomosynthesis using a sphere phantom. Methods: Projections were simulated for a voxelized breast phantom with 12 mm sphere inserts using a fluence modeled from 28 kVp beam and incident upon an indirect flat‐panel detector with 200 um pixel size. Characteristic noise and blurring for each projection were added using cascaded systems analysis. The projections were reconstructed using standard filtered backprojection techniques, producing a 3D volume with an isotropic voxel size of 200 um. ROIs that completely encompassed single spheres were extracted, and conical regions were prescribed along the three axes extending from the centroids. Pixels within the cones were used to form edge spread functions (ESF), from which directional “raw” MTFs were calculated. Binning size and conical range were considered for maximizing accuracy and minimizing noise of the MTF. A method for removing out‐of‐plane artifacts of the ESFs in x and y directions was investigated and yielded an “effective” MTF. Results: Comparisons of the cone‐based MTF along the different axes and the true 3D MTF yielded good agreement. A 30 degree angle was found to provide ideal trade‐off between measurement noise and accuracy. Drop‐off frequencies in the x‐ and y‐directional “raw” MTFs were 1.5 cycles/mm and 2.5 cycles/mm, respectively. As expected, the z‐directional MTF had a much lower drop‐off due to the lack of angular sampling. The removal of artifacts in ESF yielded a “modified” MTFs which enabled a novel characterization of in‐slice resolution for tomosynthesis. Conclusion: The directional MTF of tomosynthesis reconstruction with FBP was determined by using the cone‐based MTF technique. The presented method of separating the effective resolution and artifacts from the measured ESF is expected to facilitate the interpretation of MTF measurements in tomosynthesis.
WE‐G‐110‐06: Introduction to the AAPM Task Group No. 195 ‐ Monte Carlo Reference Data Sets for Imaging Research
Authors: Sechopoulos I , Abboud S , Ali E , Badal A , Badano A , Feng SSJ , Kyprianou I , McNitt‐Gray M , Samei E , Turner A
Published: November 2011

Purpose: To develop reference data sets of common Monte Carlo simulations in medical imaging research for use by researchers who are learning how to implement Monte Carlo simulations or needing to validate their own Monte Carlo simulations. Methods: Complete implementation specifications and results for different Monte Carlo simulations reflecting common medical imaging research conditions were developed. The specifications include: full geometry details, material compositions, particle energies, spectral definitions and scoring details. The specifications for each of these simulations will be implemented in five different Monte Carlo software packages: EGSnrc, Geant4, MCNP, Penelope and Sierra. Results: A total of eight commonly performed Monte Carlo simulations for five different imaging applications were developed: (i) production of x‐rays, (ii) half‐value layer estimation, (iii) radiographic dosimetry, (iv) x‐ray scatter in radiography, (v) mammographic dosimetry, (vi) x‐ray scatter in mammography, (vii) CT dosimetry of simple volumes and (viii) CT dosimetry of voxelized volumes. The simulation conditions and the results for all five implementations will be published, in detail, in the Task Group report and will be made available online in the AAPM website. Once published, we will invite scientists to submit their results when simulating these conditions. Conclusion: The publication of reference data sets for common Monte Carlo simulations will be a useful tool for imaging researchers new to the field of computer simulations or seeking to validate their newly‐developed simulations before performing new experiments. Upon successful completion of this initial data set, we envision the extension of this work to include other modalities, such as nuclear medicine imaging.
WE‐G‐211‐03: Multiple Projection Compton Scatter Tomography
Authors: Chighvinadze T , Pistorius S
Published: November 2011

Purpose: To evaluate the use of multiple projections in spectroscopic x‐ray tomography techniques for electron density reconstruction using backprojection over isogonic curves at realistic energy resolutions. Method and Materials: Matlab was used to simulate a clinical breast CT geometry and 55 keV fan‐beam. The system design includes a point source producing an x‐ray fan‐beam, which passes through the object to be imaged, before interacting with the primary detector. The scattered x‐rays, are measured using energy sensitive photon counting detectors aligned with the source and placed outside of the periphery of the primary fan beam. We consider a 2D case where reconstructions are carried out in the fan‐beam plane. We assume no multiple scatter or attenuation of the scattered photons. Image reconstruction was performed using backprojection over isogonic curves passing through the source and detector points. Single projection reconstruction results in an image that varies in resolution and noise throughout the image. The image reconstructed at realistic energy resolutions is not of sufficient quality. For a given energy resolution, images obtained from different projection angles were fused. Results: Results demonstrate the improvement in electron density image quality of a modified Shepp‐Logan phantom as a function of projection number and the energy resolution of the detector. Conclusions: This work has shown that it is possible to improve the image quality in a spectroscopic approach for electron density image reconstruction by combining multiple projections. It appears that it may be feasible to create clinical quality images with current detector technology.
WE‐G‐211‐07: Quasi‐Monochromatization of 110 KVp X‐Rays for Bench‐Top X‐Ray Fluorescence Computed Tomography (XFCT) Imaging of Gold Nanoparticle‐Loaded Objects
Authors: Manohar N , Jones B , Cho S
Published: November 2011

Purpose: To assess the impact of adopting a quasi‐monochromatic x‐ray source for bench‐top x‐ray fluorescence computed tomography (XFCT) imaging of gold nanoparticle‐loaded objects. Methods: A Monte Carlo (MC) model of an experimental XFCT system was created using the MCNP5 code. This model was used to simulate irradiation of a small animal‐sized plastic phantom containing water columns loaded with gold nanoparticles (GNPs) at various concentrations (2% or less by weight) with a Pb‐filtered polychromatic x‐ray source. MC results were verified with measurements to validate the model. Subsequently, MC simulations were repeated with monochromatic x‐ray sources (85, 90, and 95 keV) to determine the most ideal x‐ray energy to discriminate between gold K‐shell fluorescence peaks and the Compton scatter background. As a practical alternative to monochromatic x‐rays, a quasi‐monochromatic x‐ray spectrum was experimentally created from a polychromatic x‐ray spectrum (110 kVp) by using a highly oriented pyrolitic graphite (HOPG) crystal. This spectrum was used for further MC simulations to assess the effect of a quasi‐ monochromatic x‐ray spectrum on the detection of gold K—shell fluorescence x‐rays. Results: Monochromatic x‐ray energy needed to exceed 95 keV in order for the gold K‐shell fluorescence peaks (67 and 69 keV) to be discernible over the Compton scatter background at the detector position (90 degrees with respect to the beam axis). At the same GNP concentration, there was at least a three‐fold increase in the gold fluorescence peak‐to‐scatter background ratio from using the HOPG‐ generated quasi‐monochromatic source spectrum, compared to that from using the Pb‐filtered polychromatic source spectrum. Conclusions: Since a monochromatic synchrotron x‐ray beam, although ideal, is not readily available for a bench‐top XFCT system, quasi‐monochromatization of a polychromatic x‐ray source spectrum to peak at certain energies appears to help dramatically improve the detection efficiency of K‐shell fluorescence x‐rays from GNPs.
WE‐G‐220‐03: Evaluating Image‐Similarity Metrics to Detect Prostate Motion during 3D TRUS‐Guided Prostate Biopsy
Authors: De Silva T , Fenster A , Samarabandu J , Ward A
Published: November 2011

Purpose: For 3D transrectal ultrasound (TRUS) guided prostate biopsy, we evaluate the utility of image‐similarity metrics for comparing real‐time 2D‐ TRUS video frames to pre‐acquired 3D‐TRUS images in order to detect misalignment due to prostate motion and deformation. Methods: The experiments were conducted on retrospective data of 3D TRUS images from 3 subjects at the start of the biopsy procedure using a mechanically assisted 3D TRUS‐guided biopsy system. For each subject, 2D TRUS images were acquired immediately prior to biopsy needle insertion. In this work, simulation and real human studies were performed to explore the utility of two image similarity metrics (normalized cross correlation and mutual information) for the detection of prostate motion during the biopsy procedure. Rigid prostate motion was simulated by translating the 3D volume in the direction orthogonal to the ground truth image, and by rotating the 3D volume around the long axis of the TRUS probe. We calculated similarity metrics for each of these simulated motion images and its corresponding ground truth image. In the human study, we performed preliminary testing of a 2D‐to‐3D rigid intensity‐based registration method and measured its error by calculating its target registration error (TRE), based on identified anatomically homologous intrinsic fiducial pairs. Results: The registration gave an overall TRE of 2.1 mm, and both the mutual information and normalized cross correlation metrics have a convex shape near the optimal plane. Conclusions: The convex metric profiles encourage the use of intensity‐based registration to compensate for motion and deformation of the prostate during TRUS‐guided biopsy. The gradient of the mutual information curves are generally higher, making this metric more sensitive to the detection of small misalignments. The normalized cross correlation has a higher capture range, making it more suitable to be used in an image registration where the initialization may be less than ideal.
WE‐G‐220‐05: Modeling of Cellular Ca2+ Influx Effects Induced by Low‐Intensity Ultrasound
Authors: Yang C , Sa Y , Hu X , Lu J , Wang P , Yuan Z , Wang Y , Feng Y
Published: November 2011

Purpose: To model the ultrasound effects on cellular calcium ion (Ca2+) influx for exploring its potential impact on Ca2+ regulated cellular responses to ionizing radiation. Methods: Based on Silvaˈs membrane electrophysiology model and for the ultrasound (30 ∼ 1000mW/cm2) considered, we adopted a linear relation between ultrasound induced cellular membrane strain deltaA/A0 and ultrasound wave amplitude p as deltaA/A0 ∼ p/((Rho*C)* (Rho*C)) (A0 ‐ undisturbed membrane area, deltaA ‐ stress induced area increase, Rho ‐ liquid density, C ‐ sound velocity). The energy density W associated with membrane strain is proportional (deltaA)*(deltaA) while the ultrasound intensity I is proportional to p*p to yield W(I) = kw*I with a linearity coefficient kw. Open channel fraction f0 and rate of exogenous calcium influx qin can be expressed as the following. f0 = 1/(1+a*exp(−fe*kw*I/(kTN))) qin = 4f0*Pmax*VmF*F/(RT)(Caex‐ Cac*exp(2FVm/(RT)))/(1−exp(2FVm /(RT))) (a ‐ probability that a channel is in open state without load, fe ‐ fraction of strain energy used to gate the channel, k ‐ Boltzmann constant, T ‐ temperature, N ‐ area channel density, Pmax — membraneˈs ionic permeability when all channels are open, Vm ‐ membrane potential, F ‐ Faradayˈs constant, R ‐ gas constant, Caex ‐ extracellular calcium concentration, Cac ‐ cytosolic free calcium concentration) Results: A sigmoid relationship between qin and I is obtained, which is due to the Boltzmann character of the mechanosensitive channels. Itˈs shown that a transient rise of qin can be induced at intensities higher than 40 mW/cm2 and stimulation over 1200 mW/cm2 would lead to unphysiological level of intracellular Ca2+. Conclusions: The calcium transient induced by low‐intensity ultrasound has been shown to be comparable to that induced by ionizing radiation reported in literatures. Further investigation is thus needed to examine the potential impact of ultrasound on cellular responses to ionizing radiation, such as bystander effect.
WE‐G‐220‐06: Using MR‐Guided Focused Ultrasound to Study Heating Pattern Variations Due to Reflections from Interfaces in Both Thermal and Tissue Phantoms
Authors: Hipp E , Fan X , Partanen A , Karczmar G
Published: November 2011

Purpose:To investigate the impact of ultrasound wave reflections from distal surfaces on aimed treatment center shifts and dose distributions during MR‐ guided‐FUS (focused ultrasound) to provide important information for treatment planning. Methods: An integrated Philips Sonalleve system on a 1.5T was used for this study. FUS waves reflected from four different reflectors (air, acrylic (modeling bone), rubber, and a gel pad) after propagation through a thermal phantom and an ex vivo tissue phantom were investigated. FUS was aimed at positions 1 cm, 2 cm and 4 cm below the distal interface surface. Volumetric sonications were 20 seconds, at 50 watts for all cases. Proton resonance frequency shift imaging was used to measure temperature during and after FUS. Target location shifts toward the distal interface are reported, along with the maximum temperature at both the center of the treatment area and at the interface. Results: Surface heating was greatest at the acrylic‐thermal phantom interface. The greatest shifts from planned treatment position were beneath acrylic and rubber interfaces at an aimed depth of 2cm in the thermal phantom. Shifts in position observed in the tissue phantom were less extreme. Conclusions: In both the thermal and tissue phantoms, the gel pad interface causes the least increase in temperature at the surface, and minimal displacement from the target. For translational research utilizing animal cancer models, this work demonstrates the benefit of placing a gel pad on the distal surface of small volumes to reduce the shift that would occur if that surface was left open to the air. Future work will compare experimental data with simulations and investigate the effect of reflections from distal surfaces using in vivo animal studies.

This work was supported by grants from the Focused Ultrasound Surgery Foundation and Philips Healthcare.