bluuebunny/crossref_metadata_2025 huggingface dataset:
MO‐F‐BRC‐03: Respiratory Motion Assessment of Liver Tumor during Free‐Breathing CBCT Scans Using Continuous B‐Spline Deformation
Authors: Zhang J , Laub W
Published: November 2011

Purpose: To assess three‐dimensional liver tumor movements during free‐ breathing CBCT scans. Methods: In this study, two CBCT scans were acquired for the same treatment position: one with breath hold (BH) and the other with free breathing (FB). First, BH‐CBCT images were reconstructed. Then the BH‐CBCT images were deformed into FB‐CBCT images through a bspline deformation map estimated based on scatter‐corrected FB‐CBCT projections. The FBCBCT projections were taken as a continuous data stream. As the gantry rotated, the deformation map was updated continuously. A liver case was studied using two methods. One method is to only use projections from current breath cycle and the other one is to combine projections of same respiratory phases from three breath cycles. Both methods were implemented based on an open source software (plastimatch) and accelerated by GPU. We evaluated the performance of the proposed methods by comparing tumor centroid trajectories in 4D CT and 4D CBCT images. Results: Both methods were able to detect tumor movements along all three dimensions. In the tested case, the tumor moved 11.0, 3.7, and 4.3 mm along the longitudinal, lateral, and vertical directions, respectively. The maximum detection errors were 0.8, 1.4, and 3.2 mm for the single‐breath‐cycle method. The maximum detection errors were 1.5, 1.0, and 1.2 mm when projections from three breath cycles were combined. Conclusions: The study showed that it is feasible to detect three‐ dimensional respiratory motion of liver tumor using continuous B‐spline deformation.
MO‐F‐BRC‐06: Relative Gamma Analysis Approach Using an EPID Portal Dose‐Based to Set CBCT Imaging Decision Threshold for Lung Patients
Authors: Varfalvy N , Archambault L , Beaulieu L , Gauthier J , Cyr M , Dagnault A
Published: November 2011

Purpose: Determine decision thresholds for replanning lung tumor patients and verify the relation between volume variations and thresholds. Method and Materials:We used a relative gamma analysis approach with an EPID portal dose‐based imaging on Varian Clinac iX. After testing our preliminary thresholds against a weekly CBCT with the first patient, we followed 24 patients with lung tumor. Typically patient received 60 Gy in 30 fractions. When threshold were reached, a CBCT was done to evaluate the quality of the planning. If the target moves outside planning margin or OAR doses increased, a replanning procedure started. Only 3 patients were planned with IMRT. A target volume study, final CBCT volume over initial CT volume, was made for 17 patients to check if there is a relation between thresholds and volume variation. The effect of chemotherapy is also verified. Results: The thresholds were evaluated with the first patient using a weekly CBCT. A good correlation of 0.98 was found between %>1 and the average gamma. The thresholds of 15% and 0.60 were confirmed for %>1 and average gamma respectively. 8 patients exceeded the thresholds but only 3 were replanned due to target outside margins. 2 other patients became palliatve one. For the target volume study, 6 patients who has exceeded thresholds the mean Vf/Vi has 0.45 ± 19 and 0.80 ± 0.38 for the other 11 patients. In those 11 patients, if we remove 4 patients with a diffuse tumor, the mean Vf/Vi becomes 0.85 ± 0.08. Chemotherapy does not have an effect on this study or the relative gamma analysis. Conclusion: The utility of gamma analysis from dose EPID images was demonstrated for patients having lung tumor treatments. With this technique, CBCT scan has to be done only when EPID gamma analysis indicates significant dosimetric change.
MO‐F‐214‐04: Protoyping Compositions of Novel Radiochromic Film Types: Towards Complete Absorbed Dose Energy Independence
Authors: Singh K , Sarfehnia A , Tomic N , Liang L , Deblois F , Seuntjens J , Lewis D , Shih H , Devic S
Published: November 2011

Purpose: To develop a new generation energy‐independent radiochromic film over a wide energy range of 50 kVp to 18 MV. The films are preferably symmetric in structure and can be used for measurements in complex spectral distributions. Methods: The overall energy dependence and intrinsic energy dependence were measured for EBT2 and several prototype films of known compositions. The intrinsic energy response is quantified through a measurement of total energy response divided by the Monte Carlo calculated absorbed dose energy response. The measurements consisted of delivering an exact dose of 2 Gy to the sensitive layer of the film at both orthovoltage energies (50kVp, 120kVp, and 180kVp) and 60Co beam. Thus far, two iterations have been performed, whereby; numerical simulations are used to obtain an optimized absorbed dose energy response that will undo for the film intrinsic energy response. DOSRZnrc user‐code of the EGSnrc Monte Carlo code was used for all simulations. AAPM TG51 and TG61 were used to determine the dose‐to‐water and air‐kerma in air in megavoltage and orthovoltage beams, respectively, while Monte Carlo simulated corrections were used to convert these results to the desired dose to film. Results: For EBT2 films the overall energy dependence was found to vary by 35% over 50 kVp to Co‐60 energy range. The latest prototype measured in this work has shown a total net variation of 8% over the same range. High atomic number elements (Chlorine and bromine) were found to affect absorbed dose response drastically. The iterative optimization technique has placed a large focus in accurately determining the elemental composition. Conclusions: We have quantified the intrinsic energy dependence of radiochromic films, and have used the data to numerically optimize the composition of the active layer to produce an energy‐ independent film with an 8% energy variation over a wide energy range.

Funding: This work was supported by the Natural Sciences and Engineering Research Council of Canada contract No. 386009.

Conflict of interest: ISP is a manufacturing company of GAFCHROMICTM films.
MO‐F‐214‐06: Linear Energy Transfer Response of Polymer Gel Dosimeters in Therapeutic Proton Beams
Authors: Maryanski M , Lopatiuk‐Tirpak O , Su Z , Li Z , Zeidan O , Meeks S
Published: November 2011

Purpose: preliminary investigation of the new unique formulation of BANG3‐Pro polymer gels for detecting and mapping local variations of LET in proton beam deliveries. Methods: Four polymer gel dosimeters — labeled A through D and employing four different systems of free‐radical chain‐termination and chain‐transfer—were irradiated by a 230 MeV proton beam in a spread‐out Bragg peak modulation (SOBP, 10 cm water‐ equivalent range, 6 cm width). The dosimeters were read out using an optical laser CT scanner OCTOPUS‐IQ, yielding three‐dimensional optical density distributions. All polymer gels and the laser CT scanner were developed and made by MGS Research, Inc. To illustrate the LET‐ dependent response variations, the residual signal was isolated by subtracting the PDD curve obtained by ion chamber measurements from the measured depth profiles of optical density, normalized to the proximal end of the SOBP. The residual signal was then spatially correlated to the analytically calculated depth profile of LET. Results: Three of the four dosimeters showed an over‐response (as compared with IC measurements) at the distal end of the SOBP consistent with their formulation. The peak magnitude of over‐response was 0%, 2%, 12%, and 17% for gels A, B, C, and D, respectively. Spatial correlation with calculated LET depth profiles revealed that gels A and B had no measurable dependence on LET and that gel C responded nearly linearly in the limited range from 1.5 to 2.3 keV/micrometer. The correlation between LET and optical response was most pronounced in gel D, where it was linear up to at least 3 keV/micrometer, with the response threshold at about 1.3 keV/micrometer. Conclusions: The free‐radical chain‐transfer and chain‐termination system in BANG3‐Pro type polymer gel dosimeters can be tailored to map distributions of LET, which may be used to better estimate the relative biological effectiveness of heavy‐ion radiotherapy treatments.

This work was supported by the Bankhead‐Coley Florida Biomedical Research Program under Grant No. 1BD10‐34212.
MO‐F‐110‐03: Reference Dosimetry of New GafChromic XR‐QA2 Model for Kilovoltage Imaging Dose Using Ion Chamber and Flat‐Bed Document Scanner
Authors: Cui Y , Giaddui T , Galvin J , Chen W , Yu Y , Xiao Y
Published: November 2011

Purpose: To study the process of generating dose calibration curve for a new radiochromic film model (GafChromic XR‐QA2) using ion chamber and flat‐bed document scanner. To investigate the effectiveness of both scanning modes (reflection and transmission) for film dosimetry. To investigate the impact of scanning spatial resolution on the uncertainty of dose calibration. Methods: The reference dosimetry system included GafChromic XR‐QA2 (ISP, Wayne, NJ) films designed for low dose measurement of low energy photon beam, a Farmer‐type ion chamber calibrated for absolute dosimetry for photon energies of 100kVp and 120kVp, and an Epson Expression 10000 flat‐bed document scanner (Epson, Nagano, Japan). A kilovoltage cone‐beam CT system mounted on Elekta linac (Elekta, Crawley, UK) was used to irradiate the films. Film response (pixel value change in reflection scanning mode or optical density change in transmission mode) was correlated to air kerma using ion chamber measurements. Fifteen dose points ranging from 0 to 9cGy were used to generate calibration curves with optimal fitting function selection. Calculation of uncertainty included experimental and curve fitting uncertainties. Several different scanning spatial resolutions were tested to study its impact on the experimental uncertainty of dose calibration curve. Results: Both scanning modes generated repeatable and smooth calibration curves with small curve fitting uncertainty (<2%). Transmission scanning mode provided comparable result with reflection mode despite a semi‐opaque white polyester layer in this model of film. The experimental uncertainty was lower than 4% for doses above 1cGy with 50 dots‐per‐inch (DPI) scanning spatial resolution, but went up to about 7% for 300 DPI spatial resolution in both scanning modes. Conclusions: Dose calibration curves for XR‐QA2 film were successfully generated coupling with uncertainty analysis. Transmission scanning mode was capable of doing reference dosimetry with this model of film. Low DPI setting of the scanner reduced the experimental uncertainty with sacrifice of spatial resolution.
MO‐F‐110‐05: Automation of PCXMC and ImPACT for NASA Astronaut Medical Imaging Dose and Risk Tracking
Authors: Bahadori A , Picco C , Flores‐McLaughlin J , Shavers M , Semones E
Published: November 2011

Purpose: To automate astronaut organ and effective dose calculations from occupational X‐ray and computed tomography (CT) examinations incorporating PCXMC and ImPACT tools and to estimate the associated lifetime cancer risk per the National Council on Radiation Protection & Measurements (NCRP) using MATLAB®. Methods: NASA follows guidance from the NCRP on its operational radiation safety program for astronauts. NCRP Report 142 recommends astronauts be informed of the cancer risks from reported exposures to ionizing radiation from medical imaging. MATLAB® code was written to retrieve exam parameters for medical imaging procedures from a NASA database, calculate associated dose and risk, and return results to the database, using the Microsoft .NET Framework. This code interfaces with the PCXMC executable and emulates the ImPACT Excel spreadsheet to calculate organ doses from X‐rays and CTs, respectively, eliminating the need to utilize the PCXMC graphical user interface (except for a few special cases) and the ImPACT spreadsheet. Results: Using MATLAB® code to interface with PCXMC and replicate ImPACT dose calculation allowed for rapid evaluation of multiple medical imaging exams. The user inputs the exam parameter data into the database and runs the code. Based on the imaging modality and input parameters, the organ doses are calculated. Output files are created for record, and organ doses, effective dose, and cancer risks associated with each exam are written to the database. Annual and post‐flight exposure reports, which are used by the flight surgeon to brief the astronaut, are generated from the database. Conclusions: Automating PCXMC and ImPACT for evaluation of NASA astronaut medical imaging radiation procedures allowed for a traceable and rapid method for tracking projected cancer risks associated with over 12,000 exposures. This code will be used to evaluate future medical radiation exposures, and can easily be modified to accommodate changes to the risk calculation procedure.

This research was supported by NASA Bioastronautics Contract NAS9‐ 02078.
MO‐F‐211‐03: A Practical Approach for Liver Iron Measurement in Clinical Setting
Authors: Hou P , Popat U , Lindsay R , Jackson E , Choi H
Published: November 2011

Purpose: To quantitatively and noninvasively determine a wide range of hepatic iron concentration (HIC) for hematologic oncology patients in a routine clinical setting. Methods: A total of 28 consecutive patients who underwent a bone marrow stem cell transplant at our institution within last five years were included in this study. A breath‐hold multiecho gradient‐echo sequence was used to acquire T2*‐weighted images using a 1.5‐T MRI scanner. To cover a wide range of clinically relevant T2* values, we used three HIC measurement protocols with different temporal resolutions to acquire data for each patient in three breath‐holds. Of the three measurement protocols, the one that provided the most reliable T2* values was selected for clinical use. An in‐house image post‐processing software tool was developed to generate T2*, R2*, and HIC maps for each patient. To validate the repeatability and reproducibility, a Ferri phantom consisting with different T2* tubes was used to measure T2* values with the same protocol for patients in every three to four months over a period of one year. Results: This technique is successfully used to measure a wide range of liver T2* values from 1.0 msec to 25.0 msec. Those T2* values correspond to HIC values ranging from 1.3 mg/g to 26.0 mg/g (dry weight). Phantom test for T2* tubes (range from 4.0 msec to 32.0 msec) demonstrated very good repeatability and reproducibility, with standard deviation error less than 2.0%. Conclusions: Although it is well known that T2* is proportional iron deposition in liver, clinical iron measurements using MRI are still far from routine. With the technique developed in this work, a wide range of clinically relevant HIC values can be accurately and noninvasively quantified in routine clinical settings by carefully combining breath‐holding protocols and using in‐house image post‐processing software.
MO‐F‐301‐01: Writing and Reviewing Papers for Medical Physics
Authors: Hendee W , Rogers D , Karellas A , Slattery P
Published: November 2011

There is an art to writing a scientific paper so that it communicates accurately, succinctly, and comprehensively. Developing this art comes with experience, and sharing that experience with younger physicists is an obligation of senior scientists, especially those with editorial responsibilities for the journal. In this workshop, the preparation of a scientific manuscript will be dissected so participants can appreciate how each part is developed and then assembled into a complete paper. Then the review process for the paper will be discussed, including how to examine a paper and write an insightful and constructive review. Finally, we will consider the challenge of accommodating the concerns and recommendations of a reviewer in preparing a revision of the paper.

A second feature of the workshop will be a discussion of the process of electronic submission of a paper for consideration by Medical Physics. The web‐based PeerX‐Press engine for manuscript submission and management will be examined, with attention to special features such as epaps and line‐ referencing. Finally, new features of Medical Physics will be explained, such as Vision 20/20 manuscripts, Physics Letters and the standardized formatting of book reviews.

Education Objectives:

1. Improve the participantsˈ abilities to write a scientific manuscript.

2. Understand the review process for Medical Physics manuscripts and how to participate in and benefit from it.

3. Appreciate the many features of the PeerX‐Press electronic management process for Medical Physics manuscripts.

4. Develop a knowledge of new features of Medical Physics.
MO‐F‐220‐03: Has Elasticity Reached Clinical Maturity?
Authors: Milkowski A
Published: November 2011

Elasticity is an ultrasound mode that provides mechanical stiffness information. Elasticity has been shown to provide an additional dimension of diagnostic information to anatomical (B‐mode) as well as vascular (Doppler) information.

This presentation will start with a discussion of Elastography, defined as a manual palpation method, in which stiffness or strain images of soft tissue, particularly the breast, can be used to help detect or classify lesions.

The presentation will continue with newer quantitative elasticity method called acoustic radiation force impulse imaging (ARFI). This method utilizes shear waves to provide quantitative and reproducible mechanical stiffness tissue properties.

Lastly, a review of published clinical literature will show the developing consensus on the utilization of quantitative elasticity.
MO‐G‐BRA‐02: Microdosimetry of Simulated Heterogeneous 177Lu and 90Y Activity Distributions
Authors: Grimes J , Celler A
Published: November 2011

Purpose: The aim of this study was to determine the dosimetric impact of heterogeneous cellular uptake of Lu‐177 and Y‐90 labelled compounds in targeted radionuclide therapy (TRT). Methods: Fine resolution voxel S values (VSVs) were generated for Lu‐177 and Y‐90 using Monte Carlo simulation with the EGSnrc user‐code DOSXYZnrc. The VSVs were generated to be 20 microns on edge for Lu‐177 and 100 microns for Y‐90. To simulate varying degrees of heterogeneous uptake, activity was randomly assigned to percentages ranging from 1% to 80% of voxels in cubic volumes chosen to be large enough so that a central region, 30×30×30 voxels in size could receive a cross dose from the maximum beta range of Lu‐177 and Y‐ 90. The resulting dose distributions were determined using the VSV approach where each target voxel dose is calculated by summing the product of the activity and corresponding voxel‐to‐voxel S value from each source voxel. Results: For the simulated Y‐90 activity distribution, when 80% of the 100 micron voxels were labelled, the minimum and maximum voxel doses in the central region of interest were within 2.2% and 1.3% of the mean voxel dose, respectively. A percent difference of less than 10% was maintained between the minimum/maximum and mean voxel dose all the way down to 20% labelling. At 80% labelling of Lu‐177, the minimum and maximum voxel doses were within 11.1% and 5.4% of the mean voxel dose, respectively, and at 20% labelling these values increased to 21% and 40%. Conclusions: This study indicates the impact of nonuniform activity distributions of two commonly used radionuclides in TRT. Even with low percentage labelling, the relatively long range of Y‐90 emissions helps to significantly smooth out the dose. The calculated dose distributions were not as uniform for Lu‐177 due to the shorter range of its emitted betas.
MO‐G‐BRB‐01: A Combined Dose Delivery and Transmission Dose Verification Model for a Small Animal Precision Irradiator for Pre‐Clinical Studies
Authors: Granton P V , van Hoof S , Podesta M , Nijsten S , van Elmpt W , Verhaegen F
Published: November 2011

Purpose: Novel small animal micro‐irradiators are becoming available for pre‐clinical research but they lack dedicated treatment planning systems. The purpose of this study is to develop both a Monte Carlo (MC) model and a portal dose prediction model of a small animal micro‐IR to enable forward dose calculations and compare the planned against the delivered treatment. Methods: A MC model of a small animal micro‐IR from the x‐ray tube assembly to the detector was developed. The model was compared to radiochromic film and portal images for validation. A portal dose calibration model was also developed and portal dose images were compared to film measurements. A rodent was irradiated with 1 Gy at 225 kVp (0.32 mm Cu) while portal images were acquired. A simulated portal image from the MC model was compared to the portal image acquired during irradiation. Results: Simulations of the MC modelˈs x‐ray spectra, beam profile, and half value layer thicknesses agreement within 2 % against measurements or external calculations. The portal dose prediction model resulted with 63% of pixels with a gamma value less than 1 for a gamma criterion of 5% 0.8 mm. A visual comparison between the simulated portal image and acquired portal image during irradiation of a rodent show good agreement but intensity values around regions of bone deviate from the acquired portal image. Conclusion: We have demonstrated that we can simulate the entire irradiation process of a small animal micro‐irradiator and generate comparable predicted portal images compared to acquired portal images. We believe that further refinement to the tissue and density assignment in the MC model will improve our results.
MO‐G‐BRB‐03: On the Increased RBE of Proton Clusters
Authors: Veltchev I , Fourkal E , Ma C
Published: November 2011

Purpose: To develop the theoretical framework for the increased LET of proton clusters and to explain the recently measured elevated RBE value of laser‐accelerated protons. When protons are generated in a laser‐plasma interaction the initial inter‐particle distances are small enough in order to facilitate the observation of the effects of proton clustering. Methods: Applying the dynamic linear response theory we investigate the increased LET of a group of closely separated protons and find how the experimentally obtained RBE(LET) curves are modified as a result. Analysis of the dependence of RBE on residual range of closely separated protons offers insight into the increased RBE of the whole cluster. Results: The theoretical model suggests that the LET of a cluster of protons depends on the velocity and inter‐particle distance through an interference term. Closely separated fast particles exhibit larger deviation from the well known stopping power of a single proton. The residual range of particles with elevated RBE is therefore extended, offering explanation of the recent experimental observations. When the inter particle distance is 0.5 microns and the velocity of the cluster is 0.1c, the traveling range of protons with RBE=1.25 is extended such that 30% more cells are being damaged. Based on the theoretical predictions of this study we suggest modified experiment in which the RBE increase due to proton clustering will be better observed. Conclusions: In this study the experimentally observed enhanced RBE of laser accelerated protons is explained in terms of proton clustering. Closely separated projectiles (cluster of protons) experience modified LET dependence on velocity and as a result travel longer distances with an elevated RBE as compared to single protons. Proton clustering is an efficient way of increasing the RBE of protons and can be explored in the future clinical applications of laser‐particle accelerators.
MO‐G‐BRB‐04: Feasibility Study of a Nanotechnology‐Enabled Desktop Image‐Guided Microbeam Radiation Therapy System
Authors: Zhang J , Hadsell M , Cao G , Laganis P , Sprenger F , Schreiber E , Tracton G , Chang S , Lu J , Zhou O
Published: November 2011

Purpose: Microbeam radiation therapy (MRT) is a preclinical and radical radiotherapy treatment that has significant potentials for clinical applications. Animal studies have shown that, although only a small fraction of the tumor volume is within the paths of the microbeams, the entire tumor can be eradicated with no damage to the function of normal tissues. However the lack of MRT delivery systems prevents most cancer researchers from MRT laboratory research and hinders the translation to clinical application. We propose to develop the world first desktop image‐ guided MRT system for cancer research now and potential clinical treatment in the future. Methods: The key challenge for a desktop MRT system is dose rate and the enabling technology is the recently emerged carbon nanotube (CNT) based spatially distributed x‐ray source technology. We have performed the corresponding simulations on the x‐ray tube electron optics and the anode heat dissipation. Monte Carlo simulation was used to evaluate the dosimetric characteristics of the system. A prototype MRT device was also constructed to validate the system design and the simulation results. Results: We have already carried out initial feasibility studies and the results indicate that this novel nanotechnology‐enabled desktop MRT system is capable of producing characteristic MRT radiation comparable to the MRT radiation produced by the synchrotron facilities. Conclusions: We strongly believe that there is a great potential to translate this promising MRT treatment from animal research to widespread clinical application. Because of the relative low cost and compactness of the proposed MRT system, once developed, the MRT treatment technology can be made readily available and affordable for widespread research and clinical application in US and beyond to benefit all cancer patients.
MO‐G‐BRC‐03: The Effects of Tissue Inhomogeneities and Biological Effectiveness on the Outcome Prediction of Electronic Brachytherapy for Accelerator Partial Breast Irradiation
Authors: Guo B , Cheng C , Shi C , Papanikolaou N
Published: November 2011

Purpose: To study the influence of tissue inhomogeneities and biological effectiveness on the outcome prediction of electronic brachytherapy (eBx) for accelerator partial breast irradiation (APBI). Methods: The dosimetric influence of tissue heterogeneities was studied by Monte Carlo method and heterogeneous “virtual patient” phantoms created from the CT images and structure contours. The enhancement of the relative biological effectiveness (RBE) of the low‐energy X‐rays was modeled using biological effective dose (BED) distributions. 10 eBx APBI cases were involved in the study. For each case, the actual BED distribution, calculated with consideration of tissue inhomogeneities and RBE enhancement, was compared with the planned BED distribution without consideration of these two factors. Results: On average, actual BED PTV V100 was 89.9% as compared to 95.2% of planned value. Actual BED PTV V200 was 0.67 times of the planned value, indicating that the high dose region in the target was overestimated in planning. Actual mean BED to the ipsilateral breast, the ipsilateral lung and the heart was 0.91, 1.78 and 1.28 times of the planned values, indicating that the toxicity to the normal organs was overestimated for the breast but underestimated for the lung and heart. Actual maximum BED to the skin was 16% lower than the planned value, but actual maximum BED to the ribs was 12.7 times higher, which indicates that toxicity to the skin was overestimated in planning but toxicity to the ribs was significantly underestimated. Conclusion: Tissue inhomogeneities and RBE enhancement of low‐energy X‐rays will affect the plan quality of eBx APBI. This case study revealed that actual target coverage was lower than planned. The toxicity to the ipsilateral breast and the skin was overestimated in treatment planning but the toxicity to the ipsilateral lung, the heart and the ribs was underestimated.
TU‐A‐BRB‐03: Simultaneous Optimization of Dose and LET in Proton Therapy Using Voronoi Partitions
Authors: Riofrio D , Keyes R , Maes D. , Luan S
Published: November 2011

Purpose: Linear energy transfer (LET) is a measure of local energy deposition along the particle track. There is a positive correlation between relative biological effectiveness (RBE) and LET. As a result, LET painting has become a recent focus in particle therapy planning. The goal of this research is to develop a planning algorithm that can simultaneously optimize dose and LET distributions for particle therapy. Methods: It is well known that the high‐LET region of a charged particle beam is located at the distal edge of the Bragg peak. Therefore if a beam stops at the center of the target, its high LET region is also likely inside the target. This makes lower energy beams more preferable than high energy beams. Intuitively, this means each target voxel should be treated using its “closet” beam, or lowest possible energy beam. This observation makes Voronoi partition a natural choice for simultaneously optimizing dose and LET distributions, which given a set of objects partitions a metric space into cells, where each cell corresponds to a region closest to an object. A planning algorithm based on Voronoi partition has been implemented in C. Given a set of particle beams, the algorithm first partitions the target into a set of Voronoi cell, each corresponding to the region of the tumor closest to a beam. Then a constrained least square solver is used to determine the optimal plan with minimized beam energies, which simultaneously optimizes the LET distributions. Results: The planning algorithm has been tested on a skull base tumor using protons. A desired LET is observed inside the target, and dose and LET distributions are simultaneously optimized. Conclusions: Voronoi partition can guide the optimization to simultaneously optimize dose and LET distributions.

Supported in part by Grants NSF CBET‐0755054 and NSF CBET‐0853157
TU‐A‐BRB‐05: Beam Controlled Arc Therapy: A Novel Delivery Concept for Stationary Targets
Authors: Zhang H , Betzel G , Yi B , DˈSouza W
Published: November 2011

Purpose: To challenge the notion that the radiation beam must be held on as the gantry rotates around the patient and to describe a new approach for delivering intensity modulated arc therapy, beam‐controlled arc therapy (BCAT), during which the radiation beam is controlled on or off and the dose rate is modulated.Methods: Conventional IMAT presupposes that it is beneficial to delivery radiation from all beam angles as the gantry rotates, requiring the MLC to maintain continuity in shape from one angle to another. In turn, radiation from undesirable beam angles compromises the dose distribution. We propose a new approach to IMAT, BCAT, in which the radiation beam is held on or off and the dose rate is modulated while the gantry rotates around the patient. We employ linear‐programming‐based dose optimization to each aperture weight, resulting in some zero weight apertures. During delivery, the radiation beam is held off at control points with zero weights as the MLC shape transits to the next non‐zero weight shape. This was tested on 10 head and neck cases. Plan quality and delivery efficiency were compared with conventional IMAT.Results: Improvements in OAR sparing and target dose uniformity at dose/volume constraint levels were up to 18% (p‐value 0.002) and 67% (p‐value 0.04) respectively. Comparing to 180 and 360 apertures used in single‐arc and double‐arc IMAT plans, BCAT used 98 and 170 apertures on average respectively. The difference of total MUs used for IMAT and BCAT plans was less than 4%. Although BCAT resulted in a significant number of control points having zero MUs associated with them, the delivery times were comparable. Conclusions: Our results demonstrate that the BCAT approach, which allows the radiation beam to be controlled on and off, yields superior dosimetric results relative to the conventional IMAT while maintaining the delivery efficiency.

NIH grant CA130814
TU‐A‐BRB‐10: Using Beam Angle Optimization to Improve Treatment Plan Quality of Intensity Modulated Proton Therapy (IMPT) for Prostate Cancer
Authors: Cao W , Lim G , Li Y , Zhang X
Published: November 2011

Purpose: To investigate the impact of optimized beam angle selections on plan quality in intensity modulated proton therapy (IMPT) treatment planning for prostate cancer. Methods: In this study, we test a beam angle optimization (BAO) algorithm to find optimized beam numbers and configurations in IMPT treatment planning. Dose distributions on PTV and OARs for all treatment plans with two to four optimized beam angles are compared with ones with two lateral opposed beam angles in current practice. The sensitivity of weighting factors for the optimization objective is also investigated. Results: For three prostate cases, a unique set of two optimized beam angles was obtained for each case. Those optimized angle sets demonstrated advantages compared with the two lateral opposed angles currently used at our facility. Moreover, plans with three optimized beam angles significantly improved rectum sparing compared with two‐beam plans, while optimized four beam angles only achieved minor improvement of plan quality based on optimized three beam angles. Our algorithm then suggests a classic three‐beam configuration based on analyzing the optimal set of three beam angles. In addition, results shown that the proposed BAO algorithm is flexible enough to yield various angle plans based on the treatment plannersˈ preferences for different objectives. Conclusions: This study shows that using optimized beam angles may improve IMPT treatment plan quality compared with current practice. In future research, by testing other cancer sites and incorporating uncertainties into the BAO algorithm, the automatic selection of optimal beam angles for IMPT treatment planning will become possible.
TU‐A‐BRC‐05: Imaging to Monitor the Efficacy of Novel Molecular Targeted Radiation Protecting Drugs
Authors: Garbow J , Thotala D , Drzymala R , Hallahan D
Published: November 2011

Purpose: This research addresses apoptosis within stem cells and necrosis as two common mechanisms of radiation induced tissue injury. Inhibitors of enzyme GSK3β markedly attenuate radiation induced apoptosis in normal tissues but not in cancer. These drugs prevented radiation induced injury in brain, intestine, bone marrow and skin. Here we develop noninvasive imaging as a means to monitor radioprotection by GSK3 inhibitors. Methods: Specific inhibitors of GSK3, SB2 and SB4, were administered to mice by IP injection prior to irradiation. Single‐treatment Gamma Knife doses of 15–60Gy were given to the 50% isodose volume (33.5mm3) in one mouse brain hemisphere. T2‐weighted, microMRI of the brain was performed weekly. Whole abdominal doses of 7–8Gy were used to treat intestine. F18‐labeled apoptosis radiotracer was manufactured in the radiochemistry laboratory and was injected by tail vein in mice at 24 hours after irradiation. MicroPET imaging was performed to monitor uptake of the apoptosis detector following irradiation. Results: Radiation induced apoptosis in the brain and intestine occurred after 24 hours in a dose dependent manner with doses as low as 2Gy. Brain necrosis was compared histologically with imaging following 15‐60Gy and was first detected 3–7 weeks after irradiation. GSK3 inhibition prevented radiation induced apoptosis and preserved organ function in irradiated mice. MRI detected brain necrosis in mice treated with Gamma Knife. The apoptosis radiotracer has a short half life which is sufficient because apoptosis is transiently detected at 24 hours after irradiation. Renal excretion of the radiotracer allows imaging of radiation induced apoptosis in intestinal crypts after abdominal irradiation. Conclusions: Radioprotection of the brain and intestine by GSK3β inhibitors can be monitored by MRI and PET imaging. Radiotracers with a high sensitivity for apoptosis are needed to monitor apoptosis. These imaging modalities are needed for the planned clinical trials of GSK3 inhibitors as radioprotectors.
TU‐C‐214‐12: On‐Board PET with Tomotherapy Using Open Dual Ring Geometry with Consideration to DOI Effect
Authors: Darwish N , Darwish N , Mackie T , Kao C , Thomadsen B
Published: November 2011

Purpose: Positron emission tomography (PET) using open dual ring geometry was investigated as an on‐board system for functional imaging and PET marker tracking, specifically with tomotherapy. The open dual ring PET would allow measurement of both inter and intra‐fractional variation, improving the delineation of tumor volume at any stage in the radiation treatment delivery process. We compare results from data obtained with ray tracing to data from Monte Carlo simulations. This study demonstrates that depth of information (DOI) along the z axis of the crystal is required to reduce artifact from DOI blurring due to long axial PET geometry. Methods: PET design was accomplished via Monte Carlo simulations with GATE, the Geant4 Application for Emission Tomography. Images were reconstructed using Software for Image Reconstruction (STIR) with a fully 3D OSEM. Investigation of whether the image blurring is the result of DOI was carried out by scaling axially the PET design to one half and one forth the original proposed open PET. Image reconstruction with varying the ring difference or level of obliqueness of the accepted lines of response (LORs) for reconstruction also indicates the role of the DOI blurring. Results: Monte Carlo simulations of the open PET geometry indicate that the prominent physical factor that degrades image quality is the DOI. When comparing the Monte Carlo simulation for a phantom with four hot sources and cold background in air (reducing the effect of attenuation, randoms, and scatter) to that of the ray tracing simulations, we can visualize the degradation in the image quality. The reason is that GATE simulates the depth information but does not correct for DOI blurring, but STIR generated data assumes all LORs interact at the crystal surface. Conclusions: Onboard open PET with Tomotherapy must include DOI detectors to correct for the observed blurring.
TU‐C‐211‐11: Thoracic and Abdominal Atlas Segmentation with Diffeomorphic Multi‐Modality Registration
Authors: Schreibmann E , Fox T , Crocker I
Published: November 2011

Purpose: Anatomical segmentation remains the most time‐consuming task in radiotherapy planning. Atlas‐based segmentation methods using deformable registration emerged as a practical approach to automate the process for head and neck anatomy, but it poses significant challenges in thoracic and pelvic regions where large inter‐patient variations are present. We present an approach combining diffeomorphic inter‐modality deformable registration with level‐set based refinement for an accurate atlas‐ based segmentation of CT scans. Methods: Our automated approach involves a multi‐atlas matching stage followed by a per‐organ refinement. At the atlas matching stage, multiple atlases are matched to the patient anatomy to determine a rough segmentation using a new non‐parametric multi‐modality diffeomorphic deformable registration algorithm able to cope with differences in contrast, bowel filling, and artifacts. A probabilistic map of organ shape and locations is constructed from each atlas mapping using the STAPLE algorithm, followed by a refinement procedure using variants of level‐set algorithms customized for each organ. Validation was performed by comparing results against clinical manual segmentations using the Dice coefficientResults: Dice comparison with manual segmentation measured on 20 clinical cases ranged 0.89–0.92 for liver, 0.91–0.93 for kidneys, 0.94–0.96 for spleen 0.87–0.92 for heart and 0.87–0.92 for the spinal cord. The algorithm is fully automated, running as a software service in the background without any user interaction Conclusions: Automated segmentation accuracy for abdominal and thoracic regions is affected without a multi‐atlas and per‐structure refinement strategy. The process significantly decreases segmentation times improving clinical workflow and efficiency as segmentations of normal tissue are automatically performed immediately after image acquisition.
TU‐C‐301‐02: Going Paperless in a Radiation Oncology Clinic
Authors: Nurushev T , Cormier A , Chetty I
Published: November 2011

Utilization of paperless recordkeeping process is becoming mandatory under new and existing government regulations. While it is possible to implement the transition from paper and film based recordkeeping to paperless and filmless using a “head on” approach, it may be proven costly and inefficient. It is very beneficial to approach this transition in a systematic and thoughtful way to assure that the quality and accessibility of patient information is not compromised, but improved during such transition.

Clinical flow in a typical department of Radiation Oncology includes processing and storing multitude of data related to patient health, treatment plan parameters, diagnostic and planning images, treatment records, including localization imaging. In addition to that extensive follow‐up data is stored. All this data has to be stored indefinitely, yet be readily available for access. A complete record should also include and patient‐specific QA tests.

This lecture will provide a general overview of a typical data flow in a department of radiation oncology, and application of paperless tools available in Aria (Varian Medical Systems, Palo Alto, CA).

Learning Objectives:

1. Understand the documentation requirements for the clinical flow in a Radiation Oncology Department

2. Understand the tools available within the vendor provided electronic patient record keeping system

3. Understand the need to modify and adjust the paper‐based clinical flow when switching to paperless, to increase efficiency and convenience of accessing evidence data.
TU‐C‐220‐01: Three‐Dimensional Optoacoustic Tomography: Preclinical Research and Clinical Applications
Authors: Oraevsky A
Published: November 2011

We developed a 3D optoacoustic tomography (OAT) system* combining advantages of pulsed optical spectroscopy and high‐resolution ultrasonic detection, characterized the system and demonstrated that it produces high‐ contrast 3D maps of optical absorbance through the large volume of tissue from 20 to 500 mL with resolution better than 0.5 mm. Applications of this technology range from the whole body imaging of a small animal for purposes of preclinical research in oncology to the diagnostic imaging of breast cancer and angiography. An ultrawide‐band of ultrasonic frequencies present in optoacoustic signals contains wealth of information, which can be revealed through proper filtering and post‐processing. The excellent contrast of hemoglobin and oxyhemoglobin in tissue allows one not only to see the circulatory system, but also to visualize the internal organs. Application of exogenous contrast agents permits imaging of microvasculature of tumors, spine, bones and joints. We demonstrated that either larger anatomy, such as organs or major vessels, or the smaller structures (kidney medullas, ovarian arteries) and even microvasculature can be visualized in case of sufficient contrast depending on methods of signal and image processing.

The most significant value of 3D tomography employing a rigorous solution for the image reconstruction is to provide quantitative information of the absorption coefficient that can be translated into concentrations of tissue chromophores while imaging at several laser wavelengths. This system was employed to generate functional images of blood distribution and molecular images of malignancy‐related protein receptors in the cells of cancerous tumors in vivo. The most important parameter that enables clinical application is the depth of imaging. We demonstrated that the depth of optoacoustic imaging in tissues exceeds 50 mm for small blood vessel structures. Based on the experimental evidence, translation of the developed preclinical system to clinical applications will be discussed.
TU‐C‐220‐06: Photoacoustic Imaging of Deep Targets in the Breast Using a Multi‐Channel 2D Array Transducer
Authors: Wang X , Xie Z , Padilla F , LeCarpentier G , Carson P
Published: November 2011

Purpose: To pave the road toward successful application of photoacoustic imaging (PAI) to breast cancer, an initial evaluation of a home fabricated PAI system designed deliberately to achieve high sensitivity for the detection and characterization of vascular anomalies in the breast in the mammographic geometry was completed. Method and Materials: Signal detection from deep breast was achieved by a broadband 2D PVDF planar array that has a round shape with one side trimmed straight to improve fit near the chest wall. This array has 572 active elements and a −6dB bandwidth of 0.6–1.7 MHz. The low frequency of the array enhances imaging depth and increases the size of vascular collections displayed without edge enhancement. The photoacoustic signals from all the elements go through low noise preamplifiers in the probe that are very close to the array elements for optimized noise control. Driven by 20 independent on‐probe signal processing channels, imaging with both high sensitivity and good speed was achieved. Results: According to our measurements, the end of cable sensitivity was 2.5mV/Pa. Without averaging, the minimum detectable pressure was 80 Pa. Based on the measurements of a point object at different distances from the surface of the array, the lateral resolution of the system ranges from 2.9 mm to 4.2mm and axial resolution ranges from 1.9 mm to 3.7 mm within the distance of 60 mm. To evaluate the imaging depth of this system, artificial vessels embedded deeply in ex vivo breasts harvested from fresh cadavers were imaged. Using near‐infrared laser light with incident energy density within the ANSI safety limit, imaging depth of up to 49 mm in human breasts was achieved. To validate the multi‐modality imaging possibility, PAI images of a compressed breast containing a catheter balloon filled with blood was coregistered with ultrasound images acquired from the same specimen. PAI, based on the intrinsic tissue optical contrast, successfully presented some breast tissue features, including the interfaces on both sides of the skin, the connective tissue sheet in subcutaneous fat, and the lobar capsule. Conclusions: The current imaging speed of this system is adequate for laboratory research and in vivo human studies with small numbers of cooperative volunteers. With a high power tunable laser working on multiple wavelengths, this system might contribute to 3D noninvasive imaging of morphological and physiological tissue features throughout the breast.