bluuebunny/crossref_metadata_2025 huggingface dataset:
TH‐C‐224‐03: Medical Physicistˈs Role in Coding, Billing and Electronic Recording
Authors: Bagne F
Published: November 2011

Purpose: The presentation is intended to introduce and educate medical physicists as to the vast new opportunities that are available for advancement in their careers. This is particularly significant when considering the turbulent nationˈs economy and the shrinking available funds for health care services.

Method and Materials: Medical Physicists, through their ever‐expanding role, may now have an opportunity to considerably increase their influence in a medical setting, secure their positions and gain additional monitory rewards. It is of no dispute that the long term success of a medical practice is crucially dependent on reducing the cost of operation and increasing its revenue. In addition to providing competent, accurate and advanced medical service, a practice must utilize correct CPT coding; complete charge submission to Medicare, Medicaid and insurance carriers as well as full collection of the payments owed. Finally, an advanced Electronic Medical Recording (EMR) system is essential for the future survival of a medical practice.

First, the role of medical physicists in correct coding and optimization of billing for radiation oncology, radiology and nuclear medicine is discussed. Examples will be provided in the areas where medical physicists can maximize departmental income. Next, the process of selecting an EMR system will be presented in detail. The criteria for a complete EMR system are discussed and the available systems currently on the market are compared. Lastly, factors to consider when searching for an EMR system are outlined and the necessity of each factor is emphasized.

Conclusion: Medical physicists have the potential to expand their role in a free‐standing medical practice, hospital department or a medical physics consulting service organization by assuming the additional responsibilities for coding, billing and EMR. It is highly recommended that medical physicistsˈ training and education include knowledge and familiarity in the above areas.
TH‐C‐BRB‐03: Reconstructing Images of Prompt Gammas Emitted during Proton Radiotherapy
Authors: Peterson S , Polf J , Mackin D , Beddar S , Gillin M
Published: November 2011

Purpose: Recent studies have shown that prompt gammas emitted during proton therapy are strongly correlated to the distribution of dose and proton beam range in the patient. This has led to an increasing interest in the measurement of prompt gammas as a means of providing in‐vivo beam range verification. The purpose of this work was to investigate the feasibility of reconstructing images of prompt gamma emission from tissues irradiated during proton radiotherapy. Methods: For this study we developed an iterative image reconstruction program based on the Stochastic Origin Ensembles (SOE) technique that used data calculated using a Monte Carlo (MC) model of prompt gamma measurement by a 3‐stage Compton camera during proton irradiation. We studied the ability of the SOE technique to reconstruct 2D and 3D images that accurately reproduced the prompt gamma distribution in irradiated tissue phantoms as a function of image pixel size, number of measured prompt gammas, and number of iterations performed by the reconstruction program. Results: Using data from our MC model, we were able to reconstruct images of the prompt gamma emission profile in tissue phantoms irradiated with a clinical proton beams (pencil beam, broad beam, and spread out Bragg peak). The beam range in the reconstructed images agreed with the prompt emission range to within 1–2 mm for reconstructions with 1 mm pixel size, 10,000 iterations, and using 1.5 million measured prompt gammas. Conclusions: We conclude that it is possible to reconstruct both 2D and 3D images of prompt gamma ray emission during proton radiotherapy. Although, the reconstruction algorithm used in this study is not optimal and much more development is needed, we believe the image resolution (1–2 mm) achieved in this study shows the feasibility of prompt gamma imaging (PGI) as clinical technique for verifying in‐vivo dose range for proton radiotherapy.

This work was supported by award number R21CA137362 from the National Cancer Institute.
TH‐C‐BRB‐07: Treatment Planning with Multiple Spot Sizes to Improve Delivery Efficiency in Intensity Modulated Proton Therapy
Authors: Mo X , Westerly D , Zhang M , Mackie T
Published: November 2011

Purpose: Intensity modulated proton therapy (IMPT) has the potential to deliver highly conformal dose distributions to target volumes via the superposition of a large number of independently weighted proton pencil beam spots. While smaller proton spots offer superior dose conformity, the increase in treatment time can be significant. The purpose of this study is to develop treatment planning strategies for IMPT that employ proton spots of different sizes, and evaluate the potential reduction in total number of spots and/or improvement in dose conformity given the same treatment time. Methods: Two patient cases (prostate and lung) were analyzed by comparing three spot scanning strategies. Plans A and B use uniform spot sizes (standard deviation of the Gaussian profile) of 3mm and 6mm, respectively. Plan C uses a combination of 3mm and 9mm spots, placed close to the target surface and in the target center, respectively. Slight overlap between the two spot grids was allowed to provide adequate target coverage. The spot spacing was chosen to ensure uniform dose coverage to the target. Treatment plans were created to minimize dose to all normal structures while maintaining similar dose uniformity within the target. Results: Target uniformity was similar for all planning techniques. Plan C achieved nearly the same conformity as plan A, but resulted in spot reductions of 58% and 71% for the prostate and lung cases respectively. Plan B required about the same number of spots as Plan A; however, the D20% to normal tissues near the target increased by 59.6% and 25.6% for the two cases compared with plan C. Conclusions: Combining proton spots of various sizes in IMPT treatment planning allows for the same plan quality as with only using smaller spots. Depending on the target volume, up to a 70% reduction of number of spots can be achieved.
TH‐C‐BRB‐08: Treatment Verification Using Post‐Treatment PET Imaging and Monte Carlo Simulation
Authors: Beltran C , Jia Y
Published: November 2011

Purpose: Investigate the feasibility of using post proton therapy PET and Monte Carlo simulation as a treatment verification system for pediatric patients with localized brain tumors. Method: Under a prospective IRB approved protocol, twelve patients received proton therapy followed by a PET activation study. All patients were under the age of 3 and were under general anesthesia during treatment and post PET imaging. On the day of the PET evaluation, the patient was treated with a single beam corresponding to the activation beam under study. A separate plan was developed to ensure that using a single beam did not compromise the treatment plan. The duration between end of treatment and start of PET imaging for each of the single field treatments was recorded. The PET activation study was acquired for 30 minutes. The patient was fully immobilized for the PET in the same manner as during treatment. The Monte Carlo simulation utilized a previously verified proton dose distribution system modified to report a weighted count of positrons. Comparisons between the treatment planning dose and acquired PET image and between the acquired PET image and Monte Carlos simulated image were made. Results: On average, there were 3 treatment fields per plan and 2 per plan that met the criteria for the PET activation study. The average time between end of irradiation and start of PET acquisition was 14.5+/−1.3 minutes. Based on preliminary data, setup errors are detectable and, utilizing Monte Carlo, distal edge errors may be detectable. Conclusion: The potential exists to detect setup errors and it may be possible to determine if there is a discrepancy between the planned and delivered distal edge of a field. Out of room PET verification has limited clinical usefulness; however, in room PET may be of benefit.
TH‐C‐BRB‐10: Scanned Proton Pencil Beamˈs Lateral Profile Library to Describe the Spot Dose Characteristics
Authors: Anand A , Sahoo N , Zhu X , Titt U , Sawakuchi G , Li Y , Poenisch F , Amos R , Suzuki K , Ciangaru G , Mohan R , Gillin M
Published: November 2011

Purpose: To create a comprehensive data library of lateral dose profiles to characterize proton pencil beam spots (PPBS) with wide range of energies available for clinical use. Methods: To improve accuracy of dose modeling by the treatment planning system, a comprehensive data library of measured PPBS profiles has been created. At our institution, there are 94 energies available for spot scanned proton beams. For each energy, lateral dose profiles of PPBS in water have been measured at several depths. A pinpoint chamber with an active volume of 0.015 cm3 was used to collect relative dose profiles in water tank using a fixed SSD setup. Both in‐line and cross‐ line relative dose profiles of PPBS have been measured and analyzed. A PTW Bragg peak chamber (BPC) was used to obtain the absolute planar integral spot dose (PISD) of these PPBS at the respective depths of measurements. A structured query language based data repository has been created for query and retrieval of the details of dosimetry data of these PPBS. Results: PPBS characteristics, such as full width half maximum, the PISD (Gy‐cm2/MU) and integral spread of the PISD along the central axis have been tabulated for all available beam energies. The availability of this database allows the study of the spot size distribution as a function of energy and depth. Additionally, the measured data also provides the critical long tail dose correction factors (LTDCF) for the BPC measured PISD as a function of energy and depth. Conclusions: The lateral profiles measured for 94 different energies, has provided useful information about the effect of multiple Coulomb scattering and nuclear halo effect on the propagation of PPBS in water, and spot sizes as a function of energy and depths. The database provides a comprehensive library of lateral profiles of PPBS for clinical and research uses.

This project was partially supported by Varian Master Research Agreement, # CS2005‐00012856SP andNIH/NCI Grant 5‐P01CA021239‐30.
TH‐C‐BRC‐07: Automated Identification of Surface Marker Positions to Maximize Tumor Tracking Accuracy
Authors: Dong B , Jia X , Graves Y , Cerviño L , Jiang S
Published: November 2011

Purpose: Using markers at patient body surface to predict the tumor location is a widely used approach in lung cancer radiotherapy with respiratory gating. The purpose of this work is to identify a sparse set of locations on the patientˈs external surface, which are most correlated with the tumor motion and hence can be used for tumor location predication effectively. Methods: Thoracic 4DCT scans with 10 phases are used for the study. For each phase, points on external surface (except for patientˈs back) are segmented and the correspondence of the points between phases is established via deformable image registration of the corresponding CT images. It is assumed that there is a linear relationship between the selected surface points and the tumor locations. The selection of the sparse locations on external surface and the linear dependence of these points to internal tumor motion are represented by a prediction matrix. Such a matrix is determined by solving an optimization problem, where the objective function contains a sparsity term about the number of surface points chosen. Bregman iteration is used to solve the optimization problem. To test our algorithm on realistic patient cases, we first solve our problem using the 9 out of 10 phases of the 4DCT images to identify surface points that are most correlated with the tumor locations and the prediction matrix. The 10th phase is then used to test the accuracy of the prediction. Results: The method is tested on 6 patient data. The average prediction error is under 1 mm. The number of locations selected on patientˈs external surface is under 7 in average. Conclusions: Our method can automatically select sparse locations on patientˈs external surface and estimates a correlation matrix of these locations with internal tumor motions based on 4DCT.
TH‐C‐BRC‐08: An Innovative Tracking Device to Improve Left Breast Treatment Accuracy during the Deep Inspiration Breath Hold Technique
Authors: Urribarri J , Scholl K , Berbeco R , Lingos T
Published: November 2011

Purpose: The goal of the Deep Inspiration Breath Hold (DIBH) technique is to avoid direct radiation to the heart while treating the left breast tissue. Accurate and reproducible treatment setup of the patient is very important to successfully achieve the benefits of the DIBH technique. The purpose of this work is to introduce a device named the Real Time Skin Surface Distance (RTSSD) that accurately tracks the patient position during therapy. Methods: Five left‐sided breast cancer patients were used for this study. The RTSSD device consists of a laser distance meter rigidly fixed to the treatment couch. At the time of simulation, the RTSSD device measures chest position at the sternum tattooed location during free‐breathing and DIBH CT scans. Prior to each radiation treatment, free breathing and DIBH distances are measured at the sternum tattoo location using the RTSSD device and compared to the ones measured at the time of the CT scans. If a difference larger than +/− 3mm is found, the patient is repositioned. KV orthogonal images are acquired during DIBH and compared to the reference digital radiographs for internal verification. During irradiation, the therapist monitors the RTSSD measurement and interrupts the treatment if it exceeds the 3 mm tolerance. Cine EPID images, acquired during irradiation, are used retrospectively to validate the localization. Results: The RTSSD device tracked the patient accurately during the DIBH treatment as confirmed by in‐treatment imaging. The cine EPID images showed agreement with reference DRRs within the +/− 3mm tolerance. Conclusions: The RTSSD device is non‐invasive, easy to operate and well tolerated by the patients. The device tracked accurately the distance from patientˈs sternum tattooed location during DIBH simulation and delivery. Imaging results confirmed that the device measurements were reliable to use for patient positioning during DIBH treatment.
TH‐C‐BRC‐11: 3D Tracking of Interfraction and Intrafraction Head and Neck Anatomy during Radiotherapy Using Multiple Kinect Sensors
Authors: Santhanam A , Low D , Kupelian P
Published: November 2011

Purpose: The process of daily measurement and validation of tumors and normal structures with onboard imaging provides information useful for reducing patient setup uncertainty errors. However, the use of daily onboard CT imaging greatly increases the radiation dose to critical structures that lie within the CT volume. We now present a quantitative skin surface 3D imaging that when coupled with quantitative patient‐specific biomechanical models determine the tumor and normal organ deformation caused by routine patient head and neck misalignments. Incorporating such modeling and imaging could substantially decrease the number of cone‐ beam CT scans required for patient setup and ultimately the daily CT scan dose. Methods:The quantitative skin surface 3D imaging that monitors the patient anatomy are developed using multiple Kinect sensors. A set of 4 3D cameras are used for illustration purposes to track the patient anatomy externally. Of the 4 cameras, 3 of them are used to track the patientˈs anatomy contour (e.g. face, hands etc) using depth and intensity based contour tracking. Such an approach provides a set of 3D contours for each anatomical region from each camera. The 4th camera employs a marker less face recognition and tracking for delineating the region of the patientˈs face. The location of the face is then shared among the camera controllers in realtime and the anatomical contour that closely matches the face region is selected. Once selected, all the contours are then integrated to form a single 3D representation of the anatomy and overlapping contours are cleaned using Voronoi data re‐sampling. Results: The unified 3D representation presents a quantified 3D surface image within a precision range of 0.3 cm at an acquisition rate of 30 frame‐per‐second. Conclusions :Daily measurement of 3D skin surface with the proposed imaging system is feasible for reducing patient setup uncertainty errors while minimizing radiation exposure risk.
TH‐C‐BRC‐12: Correcting Drift in Target Position during Radiotherapy via Computer‐Controlled Couch Adjustments on a C‐Arm Linac
Authors: McNamara J , Lovelock D , Yorke E , Goodman K , Rimner A , Mageras G
Published: November 2011

Purpose: We investigate the feasibility of tracking and correcting respiration‐averaged drift in target position by means of couch adjustments on a radiotherapy accelerator equipped with such capability. This is particularly applicable to hypofractionated treatment where high precision is required and patients are subject to longer treatments. Our motivation is that these types of slower variations are easier to predict and correct than for full breathing motion. Methods: A breathing‐motion phantom is programmed to move according to previously recorded patient respiration signals from an external monitor. A retro‐reflective marker on the phantom is monitored by an optical tracking‐system whose signal is assumed to represent internal target motion. Use of a Kalman filter allows prediction of the respiration‐ averaged (baseline) position 5s in advance for application of couch corrections every 10s. The couch corrections are programmed into a research mode of the accelerator (Varian TrueBeam) and synchronized with the motion phantom and optically monitored to evaluate the systemˈs ability to correct for drift. We examined synthetic motion signals as well as 10 recorded patient breathing traces. In each case, root‐mean‐squared‐error (RMSE) or deviation of the baseline from the treatment planned position is computed with and without couch corrections. Results: Drift in the uncorrected baseline is evident and clearly reduced with scripted couch adjustments. In 10 patient cases, RMSE is reduced from a mean of 4.1 mm (range 2.3–8.9mm) before correction to 0.7mm (range 0.4–1.7mm) after correction. Treatment time with this scheme is increased ∼5% relative to that for no correction; mean time for a couch motion segment is 0.2s. Conclusions: This work illustrates the efficacy of using Kalman‐based couch corrections with a 5s prediction window to effectively reduce baseline target drift. We anticipate future machine upgrades will permit near realtime couch correction computation and application. Research supported by NIH award T32CA61801 and Varian.
TH‐C‐214‐01: Use of Functional and Molecular Imaging for Treatment Planning
Authors: Jeraj R
Published: November 2011

The next significant advance in cancer therapy will occur with the paradigm shift from a population‐based to a personalized patient‐based dose prescription. The most feasible way to assess biological information necessary to migrate to personalized prescription is to utilize in vivo functional and molecular imaging. In radiation therapy this paradigm shift will not lead only to adjustment of the total dose prescribed, but also to transition from the current standard of uniform dose prescription to non‐ uniform dose prescription — the process most often termed “dose‐painting”. While current technologies enable delivery of such dose distributions through image‐guided intensity modulated radiotherapy, several questions remain, such as which biological phenotypes should be preferentially targeted, how well can we characterize them with functional and molecular imaging and how much should we modulate the dose? This symposium will review the current status of functional and molecular imaging for treatment planning, discuss its limitations and provide the clinical background of its potential use and application.

Learning objectives:

1. To learn about the potential of functional and molecular imaging in treatment planning

2. To learn about the limitations of PET and MRI imaging for treatment planning

3. To learn about the clinical aspects of functional and molecular imaging in treatment planning
TH‐C‐301‐03: Utilization of MOSFET Dosimeters for Clinical Measurements in Radiology
Authors: Hintenlang D
Published: November 2011

Purpose: MOSFET dosimeters are attractive dosimeters for a number of applications in diagnostic radiology due primarily to their small size and the ability to rapidly read the resulting x‐ray dose. It is important to understand the characteristics of these unique dosimeters in order to accurately interpret the output and successful predict patient dose.

Methods: The characteristics of MOSFET dosimeters have been evaluated for a variety of diagnostic radiology applications. Specific tests were designed to evaluate important MOSFET responses over the x‐ray energy range of interest (20–150 keV). Responses of these devices have been characterized for energy response, angular dependence, temperature, fading, dose linearity and sensitivity.

Results: MOSFET dosimeters are available in configurations having differing physical geometry, sizes, sensitivity and absorbed dose limited usefulness. These dosimeters typically exhibit good angular response around their longitudinal axis and the variation of response as a function of ambient temperature is small. Some of the parameters that need to be carefully considered include the variation in energy response and sensitivity limits inherent to MOSFET dosimeters. These dosimeters require an accurate calibration exposure (or dose) to mV calibration for the energy source corresponding to the intended application. For example, a separate calibration needs to be developed for mammography applications for different accelerating potential and target/filter combinations. The overall sensitivity of these dosimeters can be a limitation for accurate dose assessment at clinical exposure levels. Examples of MOSFET applications for clinical dosimetry, when integrated with anthropomorphic phantoms are presented for mammography, radiography and computed tomography examples.

Conclusions : MOSFET dosimeters can provide a convenient dosimetry tool capable of simultaneous measurement for multiple dosimetry points, usually up to twenty individual locations. Careful energy calibration is essential to accurate dosimetry interpretation and care should be exercised to ensure that exposures are large enough to provide consistent radiation measurement.
TH‐C‐301‐04: Optically Stimulated Luminescent Dosimeters (OSLDs) and Thermoluminescence Dosimeters (TLDs)
Authors: Lu Z , Feng W , Yahnke C
Published: November 2011

In this presentation, we will focus on two types of scintillators with trapping of excited electrons for dosimetric purposes. The conventional type is thermoluminescent dosimeter (TLDs), in which the electrons are trapped in excited status when exposed to ionizing radiation, and when later heated, the trapped electrons then fall to their ground state with light emission. By measuring the light emitted one can determine the radiation dose previously received. In recent years, optically stimulated luminescent (OSL) dosimeter has grown to be an alternative to TLDs due to the convenience of its usage. The OSL dosimeters also trap excited electrons when exposed to ionizing radiation. Instead of heat, stimulation light is used to release the stored energy in OSL dosimeters. The intensity of the emitted light depends on the dose absorbed by the OSL dosimeters and the intensity of the stimulation light. Its sensitivity, reproducibility, precision in responding to accumulative dose and its energy dependence have also been studied in order to demonstrate its potential. We will discuss both TLDs and OSLDs with regards to their dosimetric properties and applications in radiation therapy dosimetry as well as in diagnostic imaging dose monitoring.

Learning Objectives:

1. To understand the basic principles of optically stimulated luminescent (OSL) and thermoluminescence (TLD) dosimeters.

2. To learn their physical properties and characteristics as dosimeters.

3. To compare the applications of OSL and TLD dosimeters in radiation therapy dosimetery as well as in diagnostic imaging dose monitoring.
TH‐C‐220‐01: Pilot Study for the Development of Clinical Microbeam Radiation Therapy Using a Carbon Nanotube Field Emission Micro‐CT Scanner
Authors: Hadsell M , Zhang J , Cao G , Schreiber E , Lu J , Chang S , Zhou O
Published: November 2011

Purpose: The possibilities of microbeam radiation therapy (MRT) up until now have mainly been studied using synchrotron sources due to their high flux (100s Gy/sec) and approximately parallel X‐ray paths. We wish to show that both of these advantages are also attainable with the use of carbon nanotube (CNT) field emission based X‐ray source arrays, and that by using this type of source a compact MRT system may be possible. Methods: The study was performed with our CNT micro‐CT scanner (100μm focal spot). A microbeam collimator alignment assembly with the capability to collimate and superimpose beams coming from different gantry positions was fabricated and attached to the scanner. Two orthogonal dosimetric films (Gafchromic EBT2) were embedded inside a cylindrical phantom to record the MRT dose distribution. Microbeams were fired at this target from 44 different entry angles to simulate an array of sources. In a separate experiment, phantom translation was used to simulate multiple parallel beams. Results: Forty‐four beams were superimposed in the phantom to produce a single microbeam dose profile with a FWHM of 310m (expected value was 280μm) indicating proper collimator alignment. A new MRT‐ specific tube was proposed and commissioned based on the preliminary experimental results and the corresponding Monte Carlo simulations. The estimated dose rate for this proposed tube was calculated to be over 100 Gy/sec from these initial measurements. Also, during the multiple beam simulation, a reasonable peak to valley dose ratio (∼12) was found when the translation distance was roughly 4x the beam width. Conclusions: We have shown that it will not only be possible to create microbeams with our CNT sources, but that the flexibility of these field emission sources will open the field of MRT study to the larger research community and possibly bring effective and compact MRT devices to the clinical environment.
TH‐C‐220‐02: Development of Binary Micro MLCs for an Open Source Small Animal Imaging and Therapy System with IMRT Capability
Authors: Prajapati S , Seaton J , Sekhon J , Mackie T , Jeraj R
Published: November 2011

Purpose: Current micro‐RT systems use either stationary collimators or dynamic hexagonal collimators. Even though dynamic multileaf collimators (MLCs) offer superior target conformity and beam modulation, no such system is currently available for small animal systems. This study aims to develop binary micro MLCs (bmMLCs) to be incorporated into an open source combined micro‐PET/CT/RT system with IMRT capability. Methods: A bmMLC system was designed using Flexinol actuator wire which features muscle‐like contraction when electrically driven. An assembly was constructed by attaching brass leaves to supporting steel tubes with springs which can translate within larger concentric steel tubes on a customized collimator support structure. The actuator wires were connected to the inner steel rods. When electricity was passed through the wire, it contracted pulling the assembly against the spring on supporting rod to open the leaves. Individual collimator leaves were arranged to move in opposing directions and stacked in an interleaved position. Results: A proof of concept prototype has been successfully tested using a two leaf‐system. In order to get a treatment width of 0.25cm at isocenter, brass leaves that are 2cm long, 0.05cm wide and 2.4cm thick (for 99.99% attenuation of 250kVp X‐ray) were used. The full scale collimation system was designed using 20 leaves on each side. Leaves were designed to translate 1cm producing a maximum field size of 5×10cm2 at the isocenter of the RT system. Opening and closing time of collimator leaves was less than a second which is sufficient for the expected low dose rate from the X‐ray source. Conclusions: The first dynamic bmMLC system for a micro‐RT system is being developed to enable IMRT applications. The mechanical characteristics of the bmMLC system are currently being evaluated and optimized. Future work will include development of software to drive the collimator movement for use in treatment planning.
TH‐C‐220‐05: Development of GE EXplore CT 120 Micro‐CT for Small Animal Radiotherapy with an In‐Bore Collimator
Authors: Jensen M , Chen J , Holdsworth D , Drangova M , Van Sas F , Wong E
Published: November 2011

Purpose: To extend the capabilities of a micro‐CT to perform conformal image‐guided small animal radiotherapy with minimal system modifications. Methods: A GE eXplore CT 120 preclinical imaging system, with an upgraded x‐ray generator (140kVp, 50 kW), was recently installed at our institution. We have constructed an in‐bore collimator that allows delivery of off‐axis rectangular fields, equivalent to a pair of independent orthogonal jaws. All measurements were performed using the large focal spot (1.0 mm) at 140 kVp, 50 mA, 25 ms pulse duration, with 220 ms between pulses. The half value layer (HVL) was determined in aluminum. The dose rate at isocenter of an un‐collimated field was measured in a 20 mm diameter PMMA phantom with 0.6 cc ion chamber. EBT2 radiochromic film was calibrated against the ion chamber up to 8 Gy. Square beam profiles (5 × 5, 10 × 10, 20 × 20 and 30 × 30 mm) were measured using EBT2 film on the surface of a 40 × 40 × 19 mm polystyrene block, with the surface placed at isocenter. Films were scanned on a flatbed scanner (Epson 1000XL) and converted to dose using a fitted calibration curve. Results: The first and second HVL was determined to be 7.1±0.3 and 10.2±0.2 mmAl respectively. The dose rate of an un‐collimated field was measured at 29.4±0.1 cGy/min, including beam off time. The beam profiles showed the fields were reasonably flat and symmetric, with flatness values ranging from 1.4% to 5.0% and symmetry from 0.4% to 6.5%. The beam penumbra was very sharp, with values from 0.4 to 0.7 mm, due to the in‐bore collimation. Conclusion: The initial performance of this micro‐CT scanner and in‐bore collimator shows potential for conformal radiotherapy for small animals including rats without significant structural modification of the micro‐CT.
TH‐C‐220‐06: Optimization of a Retrospective Respiratory‐Gated Micro‐Computed Tomography Technique for Free‐Breathing Rats
Authors: Ford N , Yip K , Yohan D , Holdsworth D , Drangova M
Published: November 2011

Purpose: The objective of this study is to optimize a retrospective respiratory‐gated micro‐CT protocol for free‐breathing rats to maintain image quality while reducing scan time and x‐ray dose. Methods: Five male Sprague‐Dawley rats were anaesthetized with ketamine and xylazine. Micro‐CT images were acquired with a GE Locus Ultra scanner at 80 kVp, 50 mA, 10 gantry‐rotations, with a scan time of 50 s and 0.28 Gy entrance dose. The respiratory traces of the free‐breathing rats were recorded throughout the scans and used to retrospectively sort the projection views that were acquired during peak inspiration and end expiration. 3D images were reconstructed with an isotropic voxel spacing of 0.15 mm. To assess the impact of missing projection views, we reconstructed images using all 10 gantry‐rotations and progressively fewer rotations (down to 3). We reconstructed a second set of images where the missing views were filled with the projection that was closest to the desired phase. Image‐based analysis of the image noise and missing view artefacts were indicators of the image quality. The physiological data (lung volume, CT density, functional residual capacity and tidal volume) were also computed. Results: By adding nearly in‐phase projections, the missing view artefacts were completely eliminated and the image noise was reduced. Measured values of lung volume, lung density and airway volume were stable for 5 or more gantry‐ rotations. Filling the projections using nearly in‐phase views resulted in lower measured values for tidal volume (1.26 mL +/− 0.22 mL in‐phase, 0.89+/− 0.17 mL nearly in‐phase). Conclusions: A 25 s imaging protocol would provide adequate physiological measurements at both respiratory phases for in‐phase reconstructions with reduced image quality. An image containing 50% of in‐phase views (remaining views are nearly in‐phase) is required to measure lung volume, 90% for airway volume and >65% for tidal volume.
TH‐C‐220‐07: Multi‐Compartmental Tumor Control Probability (TCP) Modeling Based on the Microenvironmental Conditions of a Tumor Sub‐Volume
Authors: Jeong J , Deasy J O
Published: November 2011

Purpose: The microenvironment varies throughout a tumor and is known to affect radiotherapy treatment response. In this study, impact of various microenvironmental conditions (currently thought to be critical to treatment response) was evaluated, based on the development of a compartmental TCP model. Methods: The model has three theoretical compartments based on two main microenvironmental factors, proliferation and hypoxia. The model focuses on small ‘tumorlets’ that are assumed to respond independently. The basic assumption is that each tumorlet has a limited capacity to supply cells with oxygen or glucose. The treatment response to the RT was estimated for head and neck cancer using relevant parameter values based on published sources. The tumor dose required for a TCP of 50% (TD50) was numerically derived for various growth fractions (GFˈs), and the effect of alternating fractionation was also evaluated. Results: Generally, the TD50 decreased as the GF increased, with fewer cells in the hypoxic compartments. Due to the tradeoff between repopulation and reoxygenation, there typically exists an optimal fraction size having the lowest TD50 for a given GF. Smaller conventional fraction sizes (2∼3 Gy/fx) were shown to be more effective for GFˈs in the range of 5∼15%, which is thought to be the biologically relevant range. The effective reoxygenation time was evaluated for a given GF and showed decreasing tendency as GF increases. The effect of overall treatment time on the TD50 was also evaluated and the extra dose required to overcome the longer schedule was estimated to be 0.43 Gy/day using published parameters. Conclusions: In spite of the simplicity of the model, the model reproduces the loss of local control with prolonged treatment time. The model suggests the optimal fractionation schedules may exist which have not been explored.
TH‐C‐220‐08: Simulating the Effects of Molecular Targeted Drugs on Tumor and Vasculature Development Using An Imaging‐Based, Computational Model
Authors: Adhikarla V , Titz B , Jeraj R
Published: November 2011

Purpose: Molecular targeted therapies affecting tumor and vasculature are currently used as anti‐cancer strategies. However, their effect on the tumor‐ vasculature system is currently poorly understood and quantified. We developed an imaging‐based computational model to simulate tumor and vasculature development, and investigated the effects of Sunitinib, an anti‐ angiogenic receptor tyrosine kinase inhibitor, in silico. Methods: PET scans of tumor hypoxia ([61Cu]Cu‐ATSM) and proliferation ([18F]FLT) were taken as model input. The hypoxia scan reflecting tumor oxygenation (pO2) was used to simulate initial tumor vasculature. Vessel growth rate and tumor cell division probability were hypoxia dependent. The proliferation scan determined the tumor cell division rate. Vascular regression was Sunitinib dependent and tumor cell death hypoxia dependent. Tumor volume and oxygenation were temporally evaluated for drug dosage of 0, 10 and 40 mg/kg/day and therapy discontinuation. Results: Dose dependent changes in tumor pO2 and volume could be observed by day 2 and 5 respectively, indicating a 3 day lag between micro‐environmental and physical characteristic changes. As compared to an untreated tumor, 40 mg/kg/day dosage was twice as effective in decreasing tumor pO2 as compared to 10 mg/kg/day dosage. Discontinuation of therapy on day 5 lead to increase in the tumor pO2, with both regimen pO2 tending to the pO2 of an untreated tumor. The rebound rate of pO2 for the 40 mg/kg/day regimen was four times that of the 10 mg/kg/day dosage. Conclusions: Discontinuation of more aggressive therapy leads to a faster rebound of tumor pO2 due to increased vessel recruitment rate which eventually increases in tumor volume. The model being a part of a more comprehensive tumor‐vascular model will be useful for providing insight into the effects of therapy on the tumor‐vasculature system. Incorporation of patient specific parameters enables the model to be used as a potential tool for tailoring therapy in future.
TH‐C‐220‐09: High Resolution Image‐Guided Irradiation of Murine Brain Tumors Using the Gamma Knife Perfexion Treatment Unit
Authors: Drzymala R , Cates J , Engelbach J , Garbow J
Published: November 2011

Purpose: To provide a method of accurate, submillimeter image‐guidance for the targeting of small brain tumors in an array of 5 mice when irradiating with the Gamma Knife Perfexion treatment unit. Small‐animal models provide a useful platform for studying the effects of radioprotectors and radiosensitizers on normal brain tissue and tumors. Efficient irradiation of an array of up to 5 mice in a single programmed sequence, using the Leksell Gamma Knife Perfexion (GKPfx) treatment unit, is an ongoing technique at our institution. One challenge in the process is to accurately guide the 4‐ mm‐diameter radiation beamsˈ focus of the GKPfx treatment unit to irradiate only a small region of interest (ROI) that includes the hippocampus. This can be accomplished through image guidance using a high‐field, high‐resolution small‐animal MR imager and transforming the ROI image coordinates to Leksell stereotactic treatment coordinates. Materials and Methods: Uniquely‐tagged mice were individually‐scanned using a small‐animal MR imager. Prior to scanning, each mouse was carefully positioned and immobilized with ear bars and a bite bar using a specially designed mouse holder module, which has three, CT‐ and MR‐ viewable, fiducials embedded within it. The fiducials provide a 3‐D frame of reference to transform ROI image coordinates to Leksell stereotactic coordinates. A Matlab script displays the image set, provides a tool to locate fiducials and other ROIs in image coordinates, computes the coordinate system transforms and saves results in an Excel worksheet. Transform computation uses Hornˈs quaternion‐based method. Results: The previously described method shows accuracy of less than 1.0 mm, when imaging resolution is 0.3 mm in X and Y and 1.0mm in Z. Computation for one mouse holder position takes less than 2 s on 1.8GHz Centrino Duo PC.Conclusions: This image‐guided technique provides for fast and accurate MR/CT localized radiation targeting of mouse brain.
TH‐C‐220‐11: Interplay of Radiobiological Parameters in BED Calculations for a Linear‐Quadratic‐Linear Model
Authors: Guerrero M
Published: November 2011

Purpose: In the framework of stereotactic body radiation therapy (SBRT), dose per fraction larger than 2Gy have become more common, challenging the applicability of the linear‐quadratic (LQ) model. Several authors have proposed ways to modify the LQ model to make it linear at large doses per fraction. Qualitatively, the modification implies a reduction of biological effect with respect of the standard LQ model for large doses. The purpose of this work is to quantitatively study the effect of the survival curve linearization at high doses for BED calculation relevant to prostate and lung SBRT. Method: We use a previously published linear‐quadratic‐linear model (LQL) to calculate BEDLQL and the equivalent dose in 2Gy fractions EQD2 for several clinically used fractionation schemes of prostate and lung cancer. The LQL model adds a parameter delta that makes the survival curve linear at high doses and is estimated to be 0.05–0.2Gy‐1. We compare BED and EQD2 for the LQ and LQL models. Results: For prostate cancer if alpha/beta=1.5–3Gy the difference in EQD2 between the LQ and LQL is 5 to 10% for cases with delta=0.2Gy‐1 and moderate dose per fraction d=3–4.3Gy. For extreme hypofractionation the effect is more pronounced with differences of up to 35% in EQD2. For the lung cancer SBRT, the BEDLQL for doses of 10‐12Gy is 3–25% smaller than BEDLQ with alpha/beta=10Gy while even bigger differences ranging from 10 to 40% are possible for normal tissues alpha/beta=3Gy. Conclusions: There is a clear interplay of the alpha/beta ratio and the parameter delta in terms of BED and EQD2 calculations for different fractionations. The impact of the parameter delta is significantly higher for low alpha/beta ratios. This is particularly important for the case of prostate cancer where a large value of delta (0.2Gy‐1 or so) could bring EQD2 below acceptable therapeutic.
TH‐E‐224‐01: Role of Medical Physics in Federal and State Government
Authors: Fletcher D , Rodgers R , Suleiman O , Keith S , Gilley D
Published: November 2011

This session is designed be used as a forum to discuss the role medical physics has within the federal and state governments. Medical Physicists are involved with everything from clinical practice to regulatory jobs in state and federal agencies. There are also many jobs to include support of the Indian Health Service, program management jobs, and federal and state emergency preparedness groups as well as a variety of others. This session is designed to be an effective venue to identify specific concerns and challenges within the public sector. Speakers from DoD, FDA, CDC, and the State of Florida will provide short presentations followed by an open forum session.

Learning objectives:

1. To provide a venue in which physicists working in the public sector can interface and discuss specific issues related to supporting the federal and state governments.

2. To provide a venue to for educating medical physicists of additional resources available within the federal and state systems.

3. To provide a venue for medical physicists to voice specific concerns with federal or state programs where medical physics should be involved and/or be more effective.
TH‐E‐BRB‐02: Automated Optimization of Treatment Plans for a Dedicated Stereotactic Radiotherapy Device Using Intelligent Isocenter Selection and Penalty‐Based Weight Optimization
Authors: Ghaffari H , Ghobadi K , Aleman D , Ruschin M , Jaffray D
Published: November 2011

Purpose: The purpose of this work is to develop and evaluate an inverse planning approach for automatic generation of treatment plans for Gamma Knife Perfexion using intelligent isocenter placement and penalty‐based optimization for beam‐weights. Methods: The optimization is a two‐step process. First, a grassfire and sphere‐packing hybrid algorithm determines the desired number of isocentre locations based on the shape and size of the target structures. Next, the selected isocentres are used in a penalty‐based optimization model to minimize the deviation of the dose delivered to each structure from its objective dose. For fast computation time and solution optimality, a constraint generation algorithm is used. This model was tested on four clinical cases: two acoustic neuromas impinging upon the brainstem, and two large brain metastases. Two sets of treatment plans were created for each case: radiosurgery (target conformality optimized) and radiotherapy (additional planning target volume, plus dose homogeneity is emphasized). Results: The mean optimization time for 30 isocentres was 15min. Multiple plans were generated for each target, with varying emphasis on minimizing beam‐on time versus maximizing target coverage and conformality. In radiosurgery (12Gy prescription dose), with a beam‐on time of 62min, 100% of the target received 98% of the prescription (V100=98%) with a maximum brainstem dose of 14.0Gy. Increasing beam‐on time up to 147min, resulted in V100=100% with a maximum brainstem dose of 13.2Gy. Similar tradeoffs were observed in radiotherapy with 50Gy prescription dose in 25 fractions. For the PTV, V100=78% and V100=85% for 17min and 46 min beam‐on time per‐fraction, respectively, while the max brainstem dose was kept at 52.5Gy. Conclusions: Our approach is capable of fast, efficient treatment plan design. Our results indicate a tradeoff between beam‐on time and dose objectives, the balance of which can ultimately be chosen by the radiation oncologist for any particular case.
TH‐E‐BRB‐05: Modeling the Correlation Between OAR Dose Sparing and Patientˈs Anatomy in Head and Neck IMRT
Authors: Yuan L , Ge Y , Li T , Zhu X , Yin F , Wu Q
Published: November 2011

Purpose: To summarize the knowledge of the dependence of organ‐at‐risk (OAR) dose‐volume distribution on patientˈs anatomy by machine learning techniques from a database of previous expert plans. Methods: 35 head‐and‐ neck IMRT plans were studied retrospectively. The OAR‐PTV geometry was modeled by the distance‐to‐target histogram (DTH). Principal Component Analysis (PCA) was applied to DVH and DTH to capture their salient features. The PCs of the DVH and DTH were then mapped to the parameter space of patient anatomy and dose distribution using correlation analysis. A polynomial model of the correlation between OAR DVH and patient anatomy was constructed and trained by a stepwise regression method. Two major OARs, the right/left parotids, were modeled in the regression analysis. Results: (1) PCA characterizes two salient features of the DTH and DVH, the first as the mean of the histogram, the second as the average gradient of the histogram within a range. (2) The regression analysis shows that the main factors contributing to the first component of the principal component score (PC1) of OAR DVH are the PC1 of DTH and the fractional volume in the overlap region, and the main factor affecting the PC2 of OAR DVH is the PC2 of DTH. (3) In terms of patient anatomy and dose‐volume distribution parameters, these correlations indicate the influences of the mean and gradient of DTH on the mean and gradient of DVH by the patient plan. In addition, the fractional volume outside treatment field with co‐planar beam setting also plays a role in determining OAR DVH. The determination coefficients by the polynomial models are: R,2=0.89 and R,2=0.47 for PC1 and PC2 of right parotid, respectively; R,2=0.64 and R,2=0.41 for PC1 and PC2 of left parotid, respectively. Conclusions: The model learned from the database quantifies the influence of geometrical complexity on the OAR dose sparing.

Duke University has a master reaserch agreement with VARIAN Medical Systems, Inc..