bluuebunny/crossref_metadata_2025 huggingface dataset:
TU‐G‐134‐02: A Harmonic Field Approach to Quantifying MRI Spatial Accuracy for MRIgRT
Authors: Tadic T , Jaffray D , Stanescu T
Published: July 2013

Purpose: An outstanding problem in the clinical implementation of MRIgRT is the development of simple and efficient methods for the measurement, characterization, and monitoring of geometrical accuracy in MRI. This study presents the theory, implementation, and validation of a novel harmonic field approach to the quantification of spatial accuracy in MRI. Methods: A harmonic field description of the 3D distortion vector field in MRI is derived as the solution of a second‐order boundary value problem comprised of the Laplace equation and a limited measurement of the distortion at a sparse distribution of points. Harmonic representations of the distortion field were calculated for spherical, cylindrical, and irregular regions of interest (ROIs). These representations were then used to derive volumetric mappings of the distortion field that were compared against reference data obtained on a 3 T full‐body scanner. The effects of sampling density were explored and a statistical uncertainty analysis was performed. Results: The volumetric mappings of the distortion field derived from the harmonic analysis were found to be in excellent agreement with the reference data. For all ROI geometries and distortion vector components, the 1 mm3 voxel size of the images used to acquire the reference data was greater than at least two standard deviations in all discrepancies. The statistical uncertainty analysis demonstrated the robustness of the harmonic approach, as the uncertainties in the volumetric mappings were calculated to be less than or equal to the input reference data. Conclusion: A novel harmonic approach has been proposed for quantifying MRI spatial accuracy in large imaging volumes for MRIgRT using only limited measurement data. This technique abates the requirement to directly measure the distortion at a dense 3D array of points and thus permits the design of simple, inexpensive phantoms that may feature additional modules for supplementary imaging and dosimetry QA objectives.
TU‐G‐134‐06: Quantitative DCEMRI of the Breast at 1.5T and 3T
Authors: Pineda F , Medved M , Fan X , Ivancevic M , Newstead G , Abe H , Sennett C , Karczmar G
Published: July 2013

Purpose: To investigate whether quantitative methods reduce the variability in dynamic contrast‐enhanced MRI (DCEMRI) of the breast in patients scanned at two field strengths. Methods: We designed calibration phantoms, consisting of compartments with varying concentrations of gadodiamide solutions (0.05‐0.5mM Omniscan), that were placed into a 16‐channel bilateral breast coil during the DCEMRI. Eleven patients were scanned at both 1.5T and 3T (Philips Achieva 1.5T/3T‐TX) under an IRB approved protocol. The phantoms provide reference signals used to calibrate the signal vs. concentration relationship, leading to a time‐series displaying the concentration of contrast media. Signal enhancement and concentration curves were fit to an empirical mathematical model (EMM) which has been shown to accurately describe kinetic curves in tissue. The parameters from the EMM were compared for the signal enhancement and concentration in enhancing lesions. Results: For most of the parameters in the EMM conversion to concentration reduced the mean difference between 1.5T and 3T, however only uptake slope saw a significant reduction (54% vs. 20%, p=0.02). Overall washout rate saw an increase in variation after conversion. This could be due to increased error in the estimation of concentration at higher values, an issue currently being addressed. Parameters descriptive of contrast media uptake were more reproducible. Plots of signal enhancement versus concentration showed a single value of enhancement corresponding to a range of concentration, suggesting enhancement alone does not provide an accurate measure of concentration. Conclusions: Quantitative methods reduced the variability of dynamic parameters across two fields. Refinement of these methods may further reduce this variability, including a more accurate measurement of proton density ratio between tissue and the phantoms. Parameters descriptive of uptake were more reproducible, suggesting uptake should be a primary diagnostic variable. Quantitative methods have the potential of providing standardized information, which could be used in longitudinal or inter‐institutional studies. Funding: Philips Healthcare. Department of Defense Breast Cancer Research Program Predoctoral Traineeship Award. Illinois Department of Public Health
TU‐G‐134‐08: Short Term Reproducibility in Apparent Diffusion Coefficient for Diffusion Weighted MRI of the Prostate
Authors: Sadinski M , Medved M , Karademir I , Wang S , Peng Y , Jiang Y , Sammet S , Karczmar G , Oto A
Published: July 2013

Purpose: In this study we evaluate the short term reproducibility of Diffusion Weighted MR Imaging (DW‐MRI) of the prostate by analyzing variation in ADC maps. Methods: 14 patients with biopsy proven prostate cancer were evaluated under an IRB‐approved protocol. Each patient underwent two, identical DW‐MRI scans with the patient remaining on the table and only automatic shimming with tuning and matching between acquisitions. ADC maps were generated using a least squares fit. The prostate and ROIs within cancer lesions were delineated on each scan per patient by two radiologists using the b‐0 images and a rigid local registration was performed using multiple radiologist‐defined landmarks throughout the prostate on each of the two scans. The absolute and percentage differences in ADC per voxel were calculated. For each patient the prostate was divided into equally spaced sextants and the voxel‐based variation in each sextant was compared. Results: The absolute difference in ADC per voxel within the prostate ranged from 1.13×10−9 to 1.91×10∼−3 mm2/sec (mean and standard deviation percentage difference 10.35% ± 10.91%). The largest variation is seen in the posterior apex (mean 11.46%, median 8.02%, standard deviation 11.73%) although we were not able to demonstrate statistical significance in the difference in variation between sextants. Cancer ROIs showed a mean, median and standard deviation in ADC difference of 13.36%, 6.90% and 14.48%, respectively. Conclusion: DW‐MRI has strong potential to become a powerful quantitative imaging biomarker for prostate cancer. It is imperative to know the reproducibility of the imaging method when utilizing DW‐MRI in the clinic or developing new approaches for its use. Our data demonstrates that ADC variation within the prostate is modest, on the order of 10%, similar to other abdominal tissues, and the variation appears to be highest in the apex region of the prostate.
TU‐G‐134‐09: Human Brain GABA J‐Difference Editing Spectral Quantification with the Fast Pade Transform
Authors: Zhang J , Woods R , Alger J , Thomas A , Espinoza R , Narr K
Published: July 2013

Purpose: To quantify in vivo GABA concentration levels using a novel parametric proton magnetic resonance signal quantification algorithm called the Fast Pade Transform. Methods: Single voxel MEGA‐PRESS data were collected on a Siemens 3T Tim Trio system using 12‐channel phased‐array head coil (TE=68 ms, TR=2000 ms, Voxel size=30×30×30 mm3, Vector size=1024, NEX=64). Both water reference and water suppressed spectra were obtained. A total of three phantoms (containing NAA, Cr, Cho, GABA, and Lac) were created with different GABA concentration levels of 1 mMol, 2 mMol and 3 mMol. In vivo data were collected from the anterior cingulate cortex region in 5 human volunteers. The fast Pade transform algorithm was implemented in MATLAB. Spectral data were processed with this FPT program to obtain parametric information such as frequency, line‐width, phase and amplitude. GABA concentration levels were calculated using the ratio of metabolite and water amplitude information, since signal amplitudes are directly proportional to the amount of protons present in the acquisition volume. Results: The results suggest that the Fast Pade Transform algorithm measured GABA concentrations in phantoms are very close to the actual known values. And this method is capable of quantifying in vivo MEGA‐PRESS proton spectra in 5 human brain data with a mean measurement of 2.01 mMol, which agrees with literature reported human brain in vivo GABA concentration level. Conclusion: This work demonstrates the potential of the fast Pade transform technique to quantify the GABA C‐4 doublet resonance signals with the MEGA‐PRESS acquisition. We plan to test this method with more in vivo data as well as with other MRS acquisition techniques in the future. NIH funding – R01MH092301
TU‐G‐116‐01: A Roadmap for Installing and Commissioning New Equipment
Authors: Dieterich S , Yang J , Sherouse G , Fahimian B
Published: July 2013

Learning Objectives:

1. To learn how to build a new equipment commissioning project plan using efficient project management methods

2. To identify equipment, personnel resources and commissioning time required

3. Understand how to account for commissioning new technology with small install base

4. Learn to develop a representative commissioning plan for a linac, CK, HDR unit or treatment planning system. Commissioning a large new piece of equipment or software is a core responsibility for a clinical medical physicist, yet it can be a daunting undertaking. Increasingly complex technology requires more complex, commissioning tasks to be completed. Many of these tasks originate from recently published AAPM Task Groups, but there is not yet a good sense in the community of how much time these tasks typically require. Medical Physicists are required to do all recommended tests to ensure patient safety while at the same time being conscious of revenue loss during commissioning time. Therefore, commissioning time needs to budgeted within a fairly tight tolerance.

This session will give audiences the tool to develop a commissioning plan including time required, equipment needs, staff needs, and commissioning checklist. The speakers will demonstrate how to develop a sample commissioning plan for a linac, CyberKnife, HDR unit and treatment planning system.
WE‐A‐500‐01: Quality Control of Lung SBRT: Minimizing Uncertainties From Simulation to Treatment
Authors: Yin F , Benedict S , Bradley J , Cai J , Wijesooriya K
Published: July 2013

Stringent quality control is critical to the success of lung SBRT. However, uncertainties exist in each step of the lung SBRT procedure. Characterization of organ motion using 4DCT may not present true tumor motion excursion due to its low temporal resolution and patients' breathing irregularity. In treatment planning, tumor ITV could be significantly under/over‐estimated by 4DCT. Different delivery techniques such as 3D‐conformal, IMRT/VMAT, may introduce different degrees of uncertainties. The relative pros/cons of each motion management technique are usually not patient‐specifically quantified, leading to uncertainty in finding the optimal technique for the patient. Other uncertainties include the choosing of planning CT, the determination of PTV and gating window, etc. At patient positioning, image guidance is prone to uncertainties due to technical limitations: CBCT may not present true ITV due to patient's irregular breathing. Rotational errors may not be fully corrected without six degree‐of‐freedom couch. At dose delivery, correlation between external motion and tumor motion is uncertain for respiratory‐gated treatment. Tumor motion and size during treatment may be different from those measured at simulation, and may vary between fractions. For physics QAs, uncertainties in dose measurement devices and delivery devices could be substantial with inhomogeneity tissues. Quality control of lung SBRT requires accurate quantification of target motion by using the proper 4D‐imaging technique and parameters based on patient's conditions, quantitative evaluation of different planning techniques, QA of treatment plan using 4D dosimeter and 4D phantom simulations, optimal patient positioning and motion monitoring during treatments.

Learning Objectives:

1. Provide an evidence‐based systematic review of uncertainties during lung SBRT

2. Discuss the root causes of the uncertainties and corresponding quality control strategies

3. Present data‐driven practical and effective solutions to minimize the uncertainties
WE‐A‐137‐01: Small Field Dosimetry
Authors: Das I , Sauer O , Ahnesjo A
Published: July 2013

Specialized radiation treatments such as IMRT, VAT, SRS, Tomotherapy, CyberKnife and Gammaknife use small fields or combination of small fields on the order of few millimeters. Small‐field dosimetry is challenging due to source size obstruction, lack of electronic equilibrium and size of detectors. Source size is dependent on the design of the accelerator and could be obstructed by the collimating system with decreasing field sizes. Electronic equilibrium is a phenomenon associated with the range of secondary particles and hence dependent on the beam energy, spectrum and the composition of the medium. Detectors could be inherently large compared to beam size and may produce volume averaging and perturbations. Recommendations of a good working practice for relative dosimetry measurements (PDD, TMR, output factor etc.) and dose calculations based on formulation of the new IAEA/AAPM non‐compliant dosimetry1 is discussed in the context of small field dosimetry that is adopted in the AAPM TG‐155.2 This course provides insight of TG‐155 that defines small field, provides suitability of a detector and associated correction factor to convert reading to dose. It also provides beam modeling and dose calculations as a critical step in clinical utilization of small field radiotherapy. Small errors in beam data, approximations in dose algorithms, or misaligned field settings can propagate into large errors in planned and delivered dose. The modeling and treatment planning aspects of small field dosimetry is reviewed with emphasis on the most critical parts for ensuring accurate and safe radiation therapy. Please enter your abstract text here.1P. Alfonso, P. Andreo, R. Capote, M. S. Huq, W. Kilby, P. Kjall, T. R. Mackie, H. Palmans, K. Rosser, J. Seuntjens, W. Ullrich and S. Vatnitsky, “A new formalism for refeence dosimetry of small and nonstandard fields,” Med Phys 35, 5179–5186 (2008).2I. J. Das, P. Francescon, A. Ahnesjo, M. M. Aspradakis, C. W. Cheng, G. X. Ding, G. S. Ibbott, M. Oldham, M. S. Huq, C. S. Reft and S. O.A., “Task Group 155 report: Small fields and non‐equilibrium condition photon beam dosimetry,” Med Phys (under review).

Learning Objectives:

1. Devices that deal with small fields

2. Definition of small fields

3. Description of absolute and relative dosimetry

4. Choice of detector in small field dosimetry

5. Correction factors for converting reading to dose

6. Understanding the implication of small fields in clinical practice
WE‐A‐108‐02: Radiotherapy Enhancement for Prostate Cancer Using Platinum‐Based Nanoparticles
Authors: Cifter G , Sajo E , Makrigiorgos G , Ngwa W
Published: July 2013

Purpose: In this work, the nucleus dose enhancement (nDEF) due to photoelectric interactions with cisplatin/oxaliplatin nanoparticles (CNPs/ONPs) is investigated in comparison to the nDEF due to gold nanoparticles (AuNPs) during prostate brachytherapy. CNPs/ONPs are particularly attractive since they may provide a more cost‐effective alternative to AuNPs, but could also provide additional chemotherapy effect for prostate tumors. Methods: As in previous studies, the dose enhancement to the PCa endothelial cells (EC) was determined using analytic microdosimetry calculations to determine the energy deposited in the EC nucleus due to radiation‐induced photoelectrons emitted by the nanoparticles. Dividing the energy deposited by the mass of the nucleus yields the dose. The nDEF defined as the ratio of the overall dose to the nucleus with and without nanoparticles, was determined for a range of CNP and ONP concentrations up to the FDA approved limit, which is 1–34 mg/g and 1–50 mg/g for oxaliplatin and cisplatin, respectively. Results: For Pd‐103, the calculated nDEF due to photoelectrons alone was up to 2.4, and 2.3 for oxaliplatin, and cisplatin respectively, compared to over 3 for comparable concentrations of AuNPs. For I–125, the calculated nDEF was up to 1.95, and 1.8 for oxaliplatin, and cisplatin, respectively in comparison to 2.5 for comparable concentrations of AuNP. Conclusion: The results predict that major localized dose enhancement to PCa cells can be achieved using targeted CNPs/ONPs. A potential application strategy for this Result is to load routinely used brachytherapy spacers with such nanoparticles, which can then be sustainably released from within the tumor volume for photon‐induced dose enhancement combined to the chemotherapy effect, with no increased toxicity to healthy tissue. Overall, the results motivate further work including: Monte Carlo work incorporating dose enhancement from Auger electrons, as well as corroborative experimental work towards development of this new application strategy.
WE‐A‐108‐03: Design of a New Yb‐169 Source Optimized for Gold Nanoparticle‐Aided Radiation Therapy
Authors: Reynoso F , Cho S
Published: July 2013

Purpose: To find an optimum design of a high‐dose rate Yb‐169 brachytherapy source for gold nanoparticle‐aided radiation therapy (GNRT). Previous studies suggested that the gamma‐ray energy spectrum of Yb‐169 could be almost ideal for a brachytherapy implementation of GNRT. The current study was aimed to design a new Yb‐169 source that would maximize dose enhancement during GNRT while meeting practical constraints for manufacturing a clinically‐relevant brachytherapy source. Methods: Monte Carlo simulations were conducted using the MCNP5 code to determine spectral changes caused by four different Yb‐169 source designs and associated variations in macroscopic dose enhancement across the tumor/ICRU tissue loaded with gold nanoparticles at 0.7% by weight. The first three source models had a single encapsulation made of aluminum, titanium, or stainless steel, while the last source model adopted a dual encapsulation design with an inner aluminum capsule and an outer titanium capsule. Results: The results showed spectral changes dependent on source design and their correlation with dose enhancement. The aluminum‐encapsulated source showed the lowest intensity‐weighted average energy of 108.9 keV, and the greatest dose enhancement of 51.0% at 1 cm away from the source center. The sources encapsulated by titanium and aluminum/titanium combination showed similar levels of dose enhancement, 49.2% and 49.3%, and average energies of 113.3 keV and 112.5 keV respectively. The source encapsulated with stainless steel exhibited the smallest dose enhancement, 43.8%, and the highest average energy of 126.6 keV. Conclusion: The current investigation suggests that the attainable macroscopic dose enhancement during GNRT with an Yb‐169 source can be further increased by encapsulating the Yb‐core with aluminum, titanium or aluminum/titanium combination, instead of stainless steel. Due to its structural integrity and improved safety during manufacturing and clinical uses, the dual encapsulation design would be preferred. Supported by DOD/PCRP grant W81XWH‐12‐1‐0198; DOD/PCRP grant W81XWH‐12‐1‐0198
WE‐A‐108‐06: Dynamic Modulated Brachytherapy for Cervical Cancer
Authors: Han D , Webster M , Scanderbeg D , Yashar C , Song W
Published: July 2013

Purpose: We propose two new intra‐uterine tandem designs that are capable of creating non‐isotropic 192‐Ir dose distributions and give unprecedented dose conformality for treatment of cervical cancer. Methods: The first tandem design, MC6, has 6 peripheral holes of 1‐mm diameter, and the in‐between‐space filled with tungsten (18.0 g/cc), wrapped in delrin (1.41 g/cc). The second design, DMBT, has 19 holes of 1‐mm diameter, each occupied by gold wires (19.3 g/cc) that can slide in and out (with motors), and the in‐between‐space filled with silicon (1.14 g/cc). MCNPX Monte Carlo was used to simulate the resulting non‐isotropic dose distributions. An in‐house developed HDR brachytherapy planning platform, with intensity modulated planning capability using Simulated Annealing and Constrained‐Gradient Optimization algorithms, was used to plan 36 patient cases and compare with the clinically treated, conventional T&O applicator‐based plans. For the proposed tandem designs, the plans were optimized with the same ovoids in place, as the conventional T&O plans. Results: All 36 plans were prescribed 6Gy and normalized to D90=6Gy and V100=95%. Generally, the plan qualities were markedly better using MC6 and DMBT, with DMBT usually performing the best overall. Mean 2cc/0.1cc doses to the bladder were 9.14±0.78/9.32± 0.80Gy, 6.87±0.57/7.05±0.59Gy, and 6.61±0.51/6.74±0.52Gy, for T&O, MC6, and DMBT, respectively. For the rectum, they were 5.78± 0.69/5.92±0.70Gy, 5.17±0.52/5.30±0.52Gy, and 4.92±0.50/5.04± 0.50Gy. For the sigmoid, they were 5.23±0.58/5.34±0.59Gy, 5.04± 0.56/5.21±0.57Gy, and 4.86±0.51/5.03±0.52Gy. The most improvement was in the bladder dose and this was due to the horseshoe‐like wrapping of the bladder around the CTV, thus benefitting the most with the dose conformation enhancements achieved by the proposed designs. The CTV dose heterogeneity index (DHI) was 2.43±0.01, 2.30±0.01, and 2.26±0.01, respectively. Conclusions: We have shown two tandem designs that advance the conformality of image‐guided cervix HDR, in congruence with the current trend of 3D image based planning to maximize the therapeutic ratio.
WE‐A‐108‐07: Dynamic Modulated Brachytherapy for Accelerated Partial Breast Irradiation
Authors: Webster M , Scanderbeg D , Yashar C , Han D , Song W
Published: July 2013

Purpose: To develop a novel brachytherapy applicator for HDR‐based accelerated partial breast irradiation (APBI) that significantly improves upon those commercially available, thereby reducing acute and late side effects seen with current APBI techniques. Methods: First, the limitations of adjusting the channel placements or placing more channels in a balloon‐like multi‐catheter ABPI device were explored. Then, a novel tungsten‐shielded applicator design was evaluated. The applicator design consists of a 9‐mm diameter tungsten rod, density=19.0gm/cm3, with 8 sunken grooves along the edge to allow passage of the 192Ir source. Using dose distributions calculated with Monte Carlo (MCNPX), optimized plans were simulated for our devices, as well as the MammoSite and SAVI, for a set of realistic phantom geometries. These geometries, based on patient cases, were ellipsoids of varying sizes with different PTV orientations and a surrounding rind of healthy tissue to be spared. Results: The benefits of adding more channels become insignificant after about 7 channels. Calculations were done for up to 361 channels, but it was found that this was insufficient to create any noticeable improvement. However, the novel shielded design significantly decreased the V150 and V200, while maintaining the target coverage (V90). All planning variables were superior for this design, except for a modest increase in the total dwell time. Conclusions: The introduction of additional channels did little to aid the performance of a balloon‐like design. There was a very slight benefit to the dose distributions, but not nearly enough to warrant further investigations. Based on these findings, any device based on open isotropic radiation source modulation cannot be improved much further. Therefore, it is necessary to consider designs with directional radiation profiles, which we have shown to give superior coverage. Our new tungsten shielded applicators are a large step forward along the path of brachytherapy applicator development.
WE‐A‐108‐08: Development of Shape Memory Alloy Actuated Flexible Needle Control System for Prostate Brachytherapy
Authors: Ruiz B , Hutapea P , Darvish K , Dicker A , Yu Y , Podder T
Published: July 2013

Purpose: To develop and evaluate a controller system capable of accurately guiding a shape memory alloy (SMA) actuated flexible needle to deliver therapeutic agents using a curvilinear approach for prostate brachytherapy for improved geometrical and dosimetric conformity. Methods: An experimental needling system was developed using flexible cannula of a 17‐gauge HDR needle actuated by Nitinol SMA. Experiments were performed in air at room temperature (22‐degC) and in controlled warm water‐bath (38‐degC, which is close to human body temperature). A silicone‐based coating was applied to the SMA wire‐actuator for electrical insulation in water. Two closed‐loop control algorithms, proportional‐derivative‐integral (PID) and PID‐P3 (with cubic term of positional errors), were implemented and tested using LabVIEW (National Instruments, version‐4.3.3). The needle and SMA actuator were integrated with a 5‐DOF Aurora (NDI, Ontario, Canada) electromagnetic (EM) sensor embedded at the tip of the needle for trajectory tracking. Performance was evaluated in terms of EM‐sensor feedback sampling intervals of 100ms, 500ms, and 1000ms, and needle‐tip displacements of 0.5mm, 2mm, and 2.5mm. Controller gains were experimentally determined. Results: PID‐P3 controller outperformed PID controller in all measured domains. Sampling time of 100ms yielded unstable performance for all displacements in water. Sampling time of 500ms with needle‐tip displacement of 2mm yielded the optimal performance with smaller overshoot and higher stability. In‐water results were comparable to in‐air measurements for the optimum performance at 500ms sampling time and 2mm displacement. Conclusions: PID‐P3 based SMA‐actuated needle appears to be adequate for conforming to the radius of curvature of a prostate gland, as well as operating effectively in human body. For small displacements (<0.5mm), fast rise‐time was observed, however, stability suffered. For larger displacements (>=2mm), stability increased but was hampered by slower rise‐time. Further investigation of PID‐P3 and other control algorithms (neuro‐fuzzy and adaptive) may offset slow rise‐time and increase stability. This study was funded by the U.S. Army Medical Research and Materiel Command(Garnt #W81XWH‐11‐1‐0399).
WE‐A‐108‐11: Patient Specific Quality Assurance Tool in Rectal Brachytherapy
Authors: Asgharizadeh S , Syme A , Deblois F , Seuntjens J , El Naqa I , Bekerat H , Devic S
Published: July 2013

Purpose: To design and evaluate a patient‐specific quality assurance program for HDR Brachytherapy of rectal cancer. Methods: A solid water phantom with a rectal applicator positioned in the center was designed. Dose distributions were measured with two sheets of EBT3 model GAFCHROMIC™ film placed at 2 cm above and 5 cm below the center of the applicator. Treatment plans of 12 patients were studied, with each plan recalculated for the phantom geometry. FilmQA software was used to compare calculated and measured doses using the Gamma function. The region of interest (ROI) for analysis was defined as doses in excess of 20%, 30% or 40% of the maximum film dose. The average percentage of passing pixels (APP) over the 12 patients was scored for analysis. Sensitivity to source positional errors was evaluated by introducing errors of 1, 3, and 5 mm in one channel and quantifying the resultant change in APP. Results: The patient‐averaged data showed that an APP greater than 95% was achieved for the 2 cm film using criteria of 2%/3 mm with ROI=30%. For the 5 cm film an APP greater than 95% was achieved with criteria of 3%/3 mm with ROI =40%. Introducing positional errors greater than 1 mm resulted in drastic fall off in APP for all chosen ROIs and all DD/DTA criteria. For film at 2 cm and 2%/3 mm criteria, 2 mm shift error resulted in as much as 50% decrease in APP. Conclusion: The patient plans in this study were used to establish the use of 2%/3mm for gamma analysis in the 2 cm film plane on an ROI that incorporates doses in excess of 30% of the max film dose. In the 5 cm film plane, 3%/3mm for doses in excess of 40% of the max film dose is appropriate. Natural Sciences and Engineering; Research Council of Canada Contract No. 386009.
WE‐A‐WAB‐01: New Technologies Addressing the Range Uncertainty of Proton Therapy
Authors: Parodi K , Polf J , Paganetti H , Schulte R
Published: July 2013

The role of proton therapy in radiation therapy is currently expanding. In the U.S., there are at present 11 clinical proton treatment facilities, with 10 centers operating proton gantries and 6 additional facilities under construction. One of the main challenges in proton therapy is the uncertainty in predicting proton range. Range uncertainties in proton therapy are related to ambiguity in converting x‐ray CT attenuation data to proton relative stopping power and are further compounded by organ deformation and internal motion as well as increasing relative biological effectiveness in the distal part of proton beams. Closely related to this issue is the continued development of image guidance technology in the treatment room that ideally will provide feedback for in‐room treatment plan modifications (adaptive proton therapy). Proton therapy treatment planning applies quite substantial range uncertainty margins, negating, in part, some of the advantages of the finite range. The problem of range uncertainty in proton therapy has been addressed in many ways, the ultimate goal being to reduce this uncertainty to ∼1 mm. Approaches to address this problem include Monte Carlo simulations to study the effects of different sources on proton range uncertainty, studies showing the amount of range uncertainties in patients, robust planning techniques, and various technological and calibration methods that attempt to improve the accuracy of relative proton stopping power and to detect and minimize range errors at the time of treatment, e.g., dual energy CT scanners, proton CT and radiography, prompt gamma registration and monitoring of proton radiation therapy with PET imaging. This symposium will present a broad overview of the current status of modern computational and imaging approaches to addressing the range‐uncertainty problem of proton beams in radiation therapy.

Learning Objectives:

1. Understand the prevailing range uncertainties in proton therapy and how they can affect clinical practice.

2. Learn how the magnitude of range uncertainties has been studied with Monte Carlo simulations and in patients.

3. Get an overview of new technologies addressing the range uncertainty problem in proton therapy.

4. Learn about principles of proton computed tomography and radiography and how these techniques may be used for better range definition and pre‐treatment quality assurance.

5. Learn about the use of prompt gamma emission for proton therapy range verification.

6. Learn about the different implementations and initial clinical experience of PET verification of treatment delivery in proton and ion therapy.
WE‐A‐134‐01: Integration of X‐Ray and Optical Tomography for Precision Radiation Guidance and Real‐Time Treatment Evaluation
Authors: Yang Y , Wang K , Eslami S , Iordachita I , Patterson M , Wong J
Published: July 2013

Purpose: We are integrating cone beam CT (CBCT) and bioluminescence tomography (BLT) onto a small animal radiation research platform (SARRP) to guide focal irradiation and online evaluate tumor response. Methods: X‐ray source provides up to 225kVp X‐ray for both CBCT imaging and radiation beam delivery. Imaging is performed in the order of CBCT, Diffuse Optical Tomography (DOT) and BLT. The CBCT provides anatomical information and DOT reconstructs the tissue optical properties, both of which serve as priori information for the BLT reconstruction. The CBCT system employs 65–100kVp x‐ray, a rotating animal stage and a CMOS detector panel with 200um pixel pitch enabling image resolution of 100um at the isocenter. A low‐noise CCD camera with an f/1.4 lens is used to capture light for optical imaging. DOT is conducted with a halogen lamp providing illumination through 9 fibers placed against the anterior surface of prone positioned animals. A novel rotating mirror system reflects light emitted from the animal to the stationary CCD camera enabling multi‐view acquisition. Four band‐pass filters with the selection of central wavelengths from 590nm–650nm are mounted in front of the lens allowing multi‐spectral BLT reconstruction. Results: The mouse CBCT showed clear differentiation of bone, lung, muscle and adipose tissue. BLT studies using tissue‐like phantoms indicate that the center of mass of an optical source can be localized to within 1 mm accuracy and source power can be restored with <10% error, even in the case of using only one single view/projection. The precision of image guidance will be validated in both phantoms and animals. Conclusion: The SARRP integrated with x‐ray and optical tomography provides accurate and precise image guidance for focal irradiation. With the capability of quantitative imaging, the system can be used to monitor tumor growth and treatment response online. The research is supported by the NCI grant R01CA158100‐01.
WE‐A‐134‐04: Comprehensive Evaluation of a Respiration‐Phase‐Matched Digital Tomosynthesis (DTS) Imaging Technique for Monitoring Moving Targets
Authors: Zhang Y , Ren L , Ling C , Yin F
Published: July 2013

Purpose: To develop a respiration‐phase‐matched DTS technique to monitor moving targets, and to evaluate its accuracy for various imaging parameters and anatomical characteristics Methods: Conventional methods, registering on‐board DTS(OB‐DTS, reconstructed from on‐board projections) to reference DTS(R‐DTS, reconstructed from DRRs of 3D‐planning‐CT), are inadequate to monitor moving targets. Our proposed technique registers OB‐DTS to R‐DTS reconstructed from DRRs generated by the same phase images of 4D‐planning‐CT as the corresponding on‐board projections. To evaluate the improved accuracy of our technique, we performed thoracic phantom studies using (1)simulation with the 4D Digital Extended‐cardiac‐torso(XCAT) phantom, and (2)experiments with an anthropomorphic motion phantom. The studies were performed for various: respiratory‐cycle(RC), scan angle and fraction of RC contained therein. Also, we assessed the accuracy of our technique relative to target size/location, and respiration changes from the planning‐CT scan to on‐board volume. Results: In both simulation and experimental studies the respiration‐phase‐matched DTS technique is significantly more accurate in determining moving target positions. For 324 different scenarios simulated by XCAT, the respiration‐phase‐matched DTS technique localizes the 3D target position to within 1.07±0.57mm(mean±S.D.), as compared to (a)2.58±1.37mm and (b)7.37±4.18mm, for traditional DTS using 3D‐planning‐CT of (a)average‐intensity‐projection(AIP) and (b)free‐breathing‐CT(FB‐CT). For the 60 scenarios evaluated through experimental study, the uncertainties corresponding to those above are 1.24±0.87mm, 2.42±1.80mm, and 5.77±6.45mm, respectively. For a given scan angle, the accuracy of respiration‐phase‐matched DTS technique is less dependent on RC and the fraction of RC included in the scan. Increasing scan angle improves its accuracy. Its accuracy is also minimally dependent on different tumor size/location combinations, or different respiratory cycle changes from planning‐CT to on‐board volume. Increasing the respiratory amplitude change will decrease its accuracy. Conclusion: The respiration‐phase‐matched DTS is more accurate and robust in determining moving target positions than traditional DTS. It has potential application in pre‐treatment setup, post‐treatment analysis and intra‐fractional target verification. Research partially supported by grant from Varian Medical Systems
WE‐A‐134‐06: Performance Characterization of Kilovoltage Intrafraction Monitoring; a Novel Real‐Time Tumor Localization Modality
Authors: Ng J , O' Brien R , Poulsen P , Fledelius W , Kuncic Z , Keall P
Published: July 2013

Purpose: Kilovoltage Intrafraction Monitoring (KIM) is a novel real‐time tumor localization modality. Previously, KIM was used to determine the prostate trajectories during treatment retrospectively. We have recently further developed KIM for real‐time tumor localization. This study aims to characterize the performance of KIM in a real‐time clinical environment as a necessary condition for a prospective clinical trial. Methods: Intrafraction kilovoltage images acquired during Intensity Modulated Arc Therapy (IMAT) delivery from 9 prostate cancer patients (244 fractions) with implanted fiducial gold markers were used to simulate real‐time acquisition with the real‐time KIM software. The images were passed to the software in an exact replica of the clinical workflow. The software estimates the 3D positions in real‐time from the 2D projection images by maximum likelihood estimation of a 3D probability density function. The root‐mean‐square‐errors (RMSE) between the real‐time and retrospective KIM data from a previous study were computed to evaluate the 3D position determination accuracy. The average processing time per image was computed to determine the real‐time operability. Results: For the 9 patient dataset, the RMSEs between real‐time and retrospective KIM are: 0.98 mm (left‐right), 0.35 mm (superior‐inferior), 0.99 mm (anterior‐posterior) and 1.49 mm (3D). The average processing time per image is 0.24 s. Conclusion: The feasibility and accuracy of real‐time KIM has been demonstrated. With additional quality assurance tests, this work enables a clinical trial of real‐time KIM involving 30 prostate cancer patients, for which ethics approval has been sought. Funding support was received from the Australian National Health and Medical Research Council Australia Fellowship and US National Institutes of Health/National Cancer Institute grant CI R01CA93626. Drs Keall and Poulsen are inventors of the kilovoltage intrafraction motion monitoring method investigated clinically in this study. Stanford University has filed a US patent application (no. 20100172469) and has licensed the method to Varian Medical Systems. No commercial support was received for this study.
WE‐A‐134‐07: RapidTrack: A Versatile Tool for Template‐Based Target Tracking During Radiotherapy
Authors: Mostafavi H , Jeung A , Sloutsky A
Published: July 2013

Purpose: To investigate the accuracy that can be obtained by using various template‐based methods to track target motion from radiographic projections during radiation therapy dose delivery. Methods: We have developed a non‐clinical software suite (RapidTrack) in two parts to accomplish template‐based tracking. RapidTrack‐Planning is an application used to generate templates from plan CT. These templates are oriented to correspond with the imaging angle of the online images to which they will be matched. Templates may be derived from the actual voxel values of the plan CT (using MIP or tomosynthesis) or may be generated from the plan contours without reference to the voxel values. The RapidTrack‐Lung application performs the actual matching with online projections using a cross‐correlation method. The match locations can be used to derive a 3D position of the target. Quality of the match is measured using a peak‐to‐sidelobe ratio (PSR) metric, which reduces the incidence of false detection. Results: The RapidTrack suite was shown to be quite versatile for tracking of radiotherapy targets. The generated templates are not dependent on any particular shape or structure of target; hence they are applicable to a variety of fiducial shapes as well as to fiducial‐less scenarios. RapidTrack was used on intra‐fraction images of seeds in pancreas; quality of the match was visually illustrated by overlaying the planning contour on the image at the match location. PSR of the match was consistently over 2.2 at all angles. Tracking of embolization coils in lung produced similar results. Breathing motion of a lung tumor was successfully tracked using a markerless algorithm based on synthetic contour template. Conclusion: The template‐based algorithm demonstrated shows promise for tracking radiotherapy targets during treatment, both in fiducial and fiducial‐less scenarios. The PSR metric is an effective means of measuring the quality of tracking. Varian Medical Systems
WE‐A‐134‐09: Real‐Time Volumetric Imaging Based On PCA Lung Motion Model and Vision RT
Authors: Xu Y , Yan H , Zhou L , Cervino L , Jiang S , Jia X
Published: July 2013

Purpose: Real‐time volumetric imaging is highly desirable to provide instantaneous image guidance for lung radiation therapy. This study proposes a scheme to achieve this goal by using Vision RT surface camera and a principal component analysis (PCA) based lung motion model. Methods: A patient‐specific PCA‐based lung motion model is first constructed by analyzing deformable registration vector fields between a reference image and 4DCT images at each phase. In the volumetric image reconstruction stage, we only use the first 2–3 principal components, which can capture the major component of the lung motion. Specifically, we solve the reconstruction problem from an optimization approach, where the PCA coefficients are optimized to minimize the distance between the deformed patient surface and the one captured by the Vision RT camera. The optimization problem is solved by a particle swarm simulated annealing algorithm. The resulting PCA coefficients are used to generate a deformation vector field that is applied to the reference image, yielding a volumetric image corresponding to the surface measured by the Vision RT camera. We have validated our method through simulation studies on a NCAT phantom. Results: The 4DCT image at the end‐of‐exhale phase is set as reference. We have successfully reconstructed a volumetric image based on a captured surface image in an area of size 16cm×16cm. The average relative pixel intensity difference between the reference and the ground truth image is 1.3%, whereas that between the reconstructed image and the ground truth is 0.5%. We have also compared anatomical feature location, e.g. diaphragm, and satisfactory results have been observed. Conclusion: The proposed method is capable of generating a volumetric image based on the instantaneous surface image offered by the vision RT camera. This scheme will potentially offer real‐time volumetric image guidance to facilitate lung radiotherapy.
WE‐A‐134‐10: Non‐Ionizing, Non‐Invasive, Non‐Contact, and Real‐Time Tumor Detection Using Ultra‐Wideband (UWB) Radar: A Feasibility Study
Authors: Han‐Oh S , Oh E , Tryggestad E , DeWeese T
Published: July 2013

Purpose: We introduce a revolutionary tumor‐detection technology using the Ultra‐Wideband (UWB) radar. The UWB is electromagnetic pulses with around nanosecond width encompassing 3.1‐10.6 GHz. The UWB is well known in radar world as a through‐the‐wall imaging technology. We investigate penetration capability of the UWB through biological tissues to detect tumors. Methods: To experimentally demonstrate UWB penetration, our setup consists of transmitter/receiver radar system to measure the reflected signal off from the aluminum plate behind the biological tissues (pig skins, cow muscles, bones, fat, and wet‐sponges (lung‐substitute)). We perform a series of two complementary measurements: 1) a tissue sample with an aluminum plate under the tissue, 2) tissue only. The two measurements are subtracted to extract only the reflected signal from the aluminum back through the tissue to the receiver. Additionally, a phantom consisting of 0.2‐cm skin, 2.0‐cm fat, 0.5‐cm muscle, and 2.4‐cm wet sponge stacked in series was used as a miniature version of a human thorax. Instead of an aluminum plate, a 20‐ml water balloon (diameter=5 cm) was placed under the phantom to mimic lung‐tumor. Results: We confirm that the UWB can penetrate through all biological tissues with varying transmission. Specifically, the 1/e (36.7%) transmission depths from air to bone, fat, skin, muscle, and wet sponge are 1.52, 1.24, 0.09, 0.24, and 1.74cm, respectively. For the phantom‐tumor experiment, the reflected signal from the water balloon was detected with a SNR of ∼2 and its amplitude was reduced to 11.1% compared to the reflected signal measured without the phantom. Conclusion: The UWB is a revolutionary technology for tumor detection with multiple advantages including non‐contact, non‐invasive, non‐ionizing, real‐time, and low cost. This technology shows great promise as a real‐time sensing and imaging technique for radiation oncology.
WE‐A‐116‐01: MRI Safety
Authors: Och J , Jordan D
Published: July 2013

Medical physicists are accustomed to dealing with the possibility of biological harm to patients from procedures involving ionizing radiation, whether this is the possibility of erythema in a week or so, or an increased in the relative risk of cancer developing in a decade or two. Accidents in MRI are more concrete. Their impact is immediate and catastrophic. Still, the concept of safety in the MRI facility is not always well addressed or understood. There is confusion about staffing, screening, construction, to name a few concerns. In addition, there is a proliferation in the number of patients presenting for MRI who require clearance based on the presence of one or more implanted devices that may be relative contraindications for MRI. Management of these patients has historically been very conservative, based on limited information about the interactions of these devices with the MR environment. More recently, testing and characterization of both medical devices and MR magnets have improved, but in many cases, there remains a gap in understanding which devices are likely safe to scan in particular MR environments. This session will review MRI safety considerations, with special emphasis on the recent ACR guidance document as well as the current state of MR safety labeling for conditional devices and common conditions of operation for commercially‐available MR scanners. The physicist should gain an understanding of the hazards which must be assessed and available resources.

Learning Objectives:

1. Read and understand MRI conditional safety labeling for a typical medical device

2. Assess the specific physical conditions created by a given MRI scanner for comparison with the safety conditions

3. Advise physicians performing MRI of specific risks or concerns for patients with conditional implants that do not meet the safety conditions for a given scanner or study4. Understand the

4. Zone concept and how to implement them.

5. Staffing concerns, including training and dealing with emergent situations.

6. Auditing of the MRI safety program.