bluuebunny/crossref_metadata_2025 huggingface dataset:
SU‐GG‐T‐342: Dosimetric Evaluation and Characterization of a MicroLion Liquid Ionization Chamber
Authors: Gutiérrez A , Calvo O , Stathakis S , Papanikolaou N
Published: August 2010

Purpose: To evaluate the dosimetric characteristics of the microLion liquid ionization chamber. Evaluation criteria were dose rate dependence, energy and angular dependence, spatial resolution, and suitability for narrow field dosimetry. Method and Materials: Measurements were performed using a Varian 2300 C/D linear accelerator (Varian Medical System, Inc., Palo Alto CA). The microLion ionization chamber (PTW Freiburg, Germany) has a sensitive volume of 0.002cm3 with the centroid located at 0.975 mm from the entrance window. The spatial resolution, dose rate and energy dependence measurements were performed using the BluePhantom from Scanditronix‐Wellhofer (IBA, Memphis TN). A calibrated Unidoswebline electrometer (PTW Freiburg, Germany) was used to measure the charge and current. An external high voltage supply (PTW Freiburg, Germany) was used to provide the recommended bias voltage of 800V. Angular dependence was measured using a solid water phantom. Results: Dose rate analysis showed differences of <1.5%. Electron energy dependence showed differences of up to 3.0%. Output factors for field sizes smaller than 3.0×3.0cm2 showed differences when compared to a Semiflex detector. Small differences (<1.0%) in response due to angular dependence were observed. However, a 7.0% difference in response was noted when the detector was irradiated parallel, as opposed to perpendicular, to the beam direction. The microLion detector exhibited a sharper fall off in the penumbra region as well as a larger shoulder when compared to a Semiflex detector. Good reproducibility was demonstrated in percent depth dose curves. Conclusion: The dosimetric evaluation of the microLion detector, a liquid ionization chamber, showed that the detector demonstrates good relative and absolute dosimetry characteristics. When operated at 800V bias, the detector shows good signal response in addition to good stability. The extremely small sensitive volume allows the microLion to be used for small field dosimetry.
SU‐GG‐T‐357: Initial Evaluation of a Fast Optical CT Scanner for Gel Dosimetry
Authors: Xu Y , Maryanski M , Wuu C
Published: August 2010

Purpose: To evaluate the performance of the OCTOPUS™‐10X optical CT scanner (MGS Research, Inc., Madison, CT) based on a single laser diode and a single photodiode detector. Method and Materials: Optical CT scanner using a single laser beam and a single photodiode detector does not suffer from the light scattering problem inherent in scanners using broad light sources. The OCTOPUS™‐10X optical CT scanner is an upgrade of the OCTOPUS™ research scanner with improved design for faster motion of the laser beam and faster data acquisition process. The motion of the laser beam in the new configuration is driven by the rotational motion of a scanning mirror. The center of the scanning mirror and the center of the photodiode detector are adjusted to be on the focal spots of two coaxial Fresnel lenses. A glass water tank is placed between the two Fresnel lenses to house gel phantoms and matching liquids. The laser beam scans over the water tank in parallel beam geometry for projection data as the scanning mirror rotates at the speed of less than 0.1 second per circle. Signal sampling is performed independently of the motion of the scanning mirror. Technical issues with regard to the new design of the scanner are addressed, including projection data extraction from raw samples, non‐uniform pixel averaging and reference image normalization. Results: The mechanical stability of the scanner, the accuracy of the non‐uniform pixel averaging algorithm and the effectiveness of the reference image normalization method are analyzed. Gamma analysis are performed between the 3D dose distributions from the gel measurement and the Eclipse planning system for a 12MeV, 6cm × 6cm single electron field irradiation and a 5‐field IMRT plan. Conclusion: The OCTOPUS™‐10X optical CT scanner can reconstruct 3D dose distribution from gel dosimeters with reasonable accuracy in a timely fashion.
SU‐GG‐T‐359: The Applications of MatriXX to Electron Beam Dosimetry
Authors: Zhang M , Li S , Deng H , Zhou S
Published: August 2010

Purpose: The objective of this study is to investigate the properties of I'mRT Matrixx device in electron beams, and to develop methods of electron dosimetry using Matrixx. Method and Materials: The measurements were conducted using Matrixx in electron beams from Siemens linacs. The Matrixx was placed horizontally on the linac tabletop, supported with solid water blocks. Solid water layers were used for dose buildup on top of the Matrixx. For all the measurements, the linac gantry angle was 0°, and the SSD was 100 cm from the surface of solid water buildup. The depth ionization was measured for different energies and field sizes, thus the depth of maximum ionization and the effective water equivalent depth of Matrixx could be determined. The electron cone factors and beam profiles were measured at the maximum ionization depths. The 2D dose maps and cutout factors of custom blocks were studied using Matrixx. Results: It was estimated that the intrinsic effective water equivalent depth of Matrixx is about 4.5 mm. When measuring at the respective depth of maximum electron intensity (peak of ionization), the Matrixx has slightly different dose responses for different electron energies. The cone factors measured by Matrixx are nearly identical to those derived by ionization chambers. Beam profiles (thus the flatness and symmetry) can be easily determined using Matrixx, and they are comparable to water tank results. The planar dose map of cutout blocks can be visually observed, and the cutout factors can be conveniently measured. Conclusion: The MatriXX dose response to electron beams is different from photon beams, and separate dose calibration factors should be established for electron dosimetry. The ionization chamber array in Matrixx has the ability to display planar dose map in a single measurement. Matrixx has the potentials in electron beam dosimetry and routine QA.
SU‐GG‐T‐364: Designing Custom Radiation Therapy Phantoms Using Contoured Regions‐Of‐Interest
Authors: Nelms B
Published: August 2010

Purpose: As radiation therapy planning and delivery systems get more complex, the medical physicist must take greater care and be more thorough in the commissioning of the planning/delivery system. The system's performance must be assessed and risks understood over a wide range of clinical parameters such as target volume/shape, patient size/shape/surface, and critical structure arrangement. Currently there are commercially available 3D phantoms and solid water arrangements, but these designs are not especially customizable. This work introduces a very easy way to use contoured regions‐of‐interest (ROIs) from DICOM RT Structure Sets to make custom phantoms that can be manufactured by a 3rd party milling company. Materials and Methods: A prototype software system reads DICOM RT Structures and allows the user to select which structure(s) they would like to render and mill as a three‐dimensional object. Construction parameters include material and rescale size (to allow solids to be magnified or shrunk vs. the real size in the patient). The system will compute the optimal base plane angle which minimizes any regions on the 3D surface that would be un‐millable due to complex concavities or smallness. Results: Custom phantoms will be exhibited, each made from a patient DICOM RT Structure Set and using various materials (high melting temperature wax, acrylic, other plastics) and in various rescale sizes. Conclusions: Custom phantoms can be made very accurately to mimic three‐dimensional anatomic shapes defined by DICOM RT Structure Sets. Patient external contours can be used to generate a patient‐shaped phantom, or internal contours can be used to render solid organs. It is possible to make anatomic surfaces that can be temporarily fixed to commercial 3D dosimetry phantoms. Research sponsored by .decimal, Inc.
SU‐GG‐T‐377: Experimental Verification of Clinically‐Relevant Monte Carlo X‐Ray Simulations
Authors: Sawkey D , O'Shea T , Faddegon BA
Published: August 2010

Purpose: Verify that Monte Carlo simulations of clinically‐relevant x‐ray fields based on open‐field simulations agree with measured dose distributions. Incident beam energy and spot‐sized were determined independently, previously; the only simulation parameters varied here were the jaw/MLC positions. Methods & Materials: Monte Carlo simulations using EGSnrc/BEAMnrc of small x‐ray fields and fields modified with wedges were compared to measured dose distributions and output factors at 6 and 18 MV. Simulation parameters were derived from a match of open field simulation to measurement using independently measured energy of the electron beam in the waveguide and spot size, and measured jaw/MLC positions. Asymmetry, for example in the positioning of the flattening filter, was accounted for in the simulations. Output factors were measured with a CC13 ion chamber for large field sizes and an Exradin A14 for small field sizes. Transmission through the jaw was determined. Results: Simulated and measured dose distributions were in close agreement. Profiles and PDD curves agreed as well as the open field measurements, to within 1.5%/1.5 mm. Output factors were in agreement to within 2% down to a square field of size of 1.6 cm. Measured and simulated penumbra agreed, as expected because the spot size was measured. Conclusions: Simulations of clinically‐relevant x‐ray fields based on open field measurements were in close agreement with measurement. This validated both the simulations and the methods used to determine them, namely matching open field measurements with independently measured spot size and incident beam energy. Support from NIH R01 CA104777‐01A2.
SU‐GG‐T‐406: A Feasibility Study on Monte Carlo‐Based Organ Dose Reconstructions for Patients Treated by External Beam Radiotherapy
Authors: Lee C , Lamart S , Curtis R , Inskip P
Published: August 2010

Purpose: To develop a Monte Carlo‐based technique to reconstruct organ doses for patients treated by external beam radiotherapy Methods and Material: To explore a feasibility to use Monte Carlo simulation method for organ dose reconstructions for radiotherapy patients, five medical records of patients diagnosed as breast cancer after Hodgkin Lymphoma (HL) treated by Co‐60 therapy unit were obtained from the previous epidemiologic study of second breast cancer risk. Breast tumor site and ovarian doses were previously estimated by using measurement‐base approach. Eldorado Co‐60 machine (Best Theratronics, Ltd, Ontario, Canada) including Co‐60 source and collimation system were modeled by using MCNPX2.6 code based on the schematic diagram obtained from the manufacturer. The 15‐year and adult female hybrid computational phantoms were employed to model the five different female patients by adjusting body weight and height of the phantoms to match the sizes from medical records. Treatment settings including beam characteristics (e.g. field size, location, and direction) as well as lung blocks were accurately simulated based on the treatment records and drawings/pictures. Absorbed doses per launched photon to breast tumor site and ovaries were calculated by MCNPX2.6 and multiplied by the number of photons required to obtain prescribed dose at a certain treatment planning depth. Results: Absorbed doses to breast tumor site and ovaries were calculated for five different patients and compared with the results from measurement‐based method. Both breast tumor site and ovarian doses from the simulation were up to 40% different from the values from measurement‐base estimation. Conclusion: Breast site doses are very sensitive to the locations of lung block and breast tumor which showed research needs of dose sensitivity analysis associated with those parameters. This feasibility study opened door to improved dose reconstruction method for radiotherapy patients using Monte Carlo technique.
SU‐GG‐T‐427: Development of Monte Carlo Dose Verification System for MHI‐TM2000
Authors: Ishihara Y , Sawada A , Nakamura M , Kaneko S , Takayama K , Mizowaki T , Kokubo M , Hiraoka M
Published: August 2010

Purpose: MHI‐TM2000 is an innovative image‐guided radiotherapy system with a C‐band X‐ray head on an O‐ring shaped gantry. We are developing an integrated Monte Carlo (MC) dose calculation system for four‐dimensional radiotherapy using MHI‐TM2000. The purposes of this study were to propose specific MC models of the X‐ray head and the multi‐leaf collimator (MLC) for MHI‐TM2000 and to validate their accuracy. Methods and Materials: 6 MV photon beam delivered by the MHI‐TM2000 unit was implemented by EGSnrc/BEAMnrc and EGSnrc/DOSXYZnrc. Subsequently, the X‐ray head composed of a target, a primary collimator, a flattening filter, a monitor chamber, a fixed secondary collimator, and a MLC was simulated based on the specification. Next, the central axis depth doses and the lateral doses at 15, 100, and 200 mm depth were simulated under the source to surface distance (SSD) of 900 mm. Then, Each of them was compared with the corresponding measurements using a CC06 ionization chamber and a water phantom. For the MLC model, Tongue‐and‐Groove (100 mm depth, SSD 900 mm), leaf leakage (50 mm depth, SSD 950 mm), and round leaf effects (100 mm depth, SSD 900 mm) were simulated. Meanwhile film measurements were performed using EDR2 film and a solid water phantom under similar conditions. These doses were normalized to the corresponding doses for the open field at the isocenter. The differences between simulated and measured doses were calculated. Results: For the X‐ray head, depth doses beyond the buildup region and lateral doses within the region of flatness showed agreement of within 1.3%. For each MLC test, the simulated and measured doses agreed less than 3.0%, respectively. Conclusions: We have demonstrated that the proposed MC models of the X‐ray head and the MLC for MHI‐TM2000 have reasonable accuracy.

Conflicts of Interest: Research sponsored in part by Mitsubishi Heavy Industries, Ltd.
SU‐GG‐T‐435: Novalis Tx MonteCarlo Based Linear Accelerator
Authors: Quino L Vazquez , Stathakis S , Gutiérrez A , Shi C , Papanikolaou N
Published: August 2010

Purpose: To commission a Monte Carlo model of the NovalisTX linear accelerator equipped with high definition MLC. Method and Materials: Percent depth dose curves were calculated and compared against measured ones in water. The measurement data was collected using a PTW microLion ionization chamber with sensitive volume of 0.002cc. Various field sizes were compared for a 6.0 MV photon beam in order to validate the Monte Carlo model. BEAMNRC software was used to model the NovalisTx linear accelerator. DOSXYZNRC was used to create the geometry of a virtual water phantom in order to compute the phantom dose. In‐house software using a MATLAB platform was utilized to convert the 3D dose file obtained from the Monte Carlo simulation to a file which can be read using commercially‐available software for dose visualization (RIT software). In the RIT software platform, the 3D dose of the virtual phantom was compared against the commissioning data of the NovalisTX. Results: Good agreement was observed between measured and calculated percent depth dose curves, within 2% difference with the commissioning data from the linear accelerator. Output factors were calculated within 2% when compared to the measured ones for fields sizes ranging from 2cm×2cm to 25cm×25cm. Irregular fields created with the high definition MLC were in agreement with measured ones. Conclusion: Based on the results, the Monte Carlo based NovalisTx linear accelerator model is in good agreement with measured data. The commissioned model can be used for dose verification purposes of patient plans.
SU‐GG‐T‐446: Minimizing Energy Changes in Particle Therapy Using Voronoi Partitions
Authors: Riofrio D , Cabal G , Keyes R , Holzscheiter M , DeMarco J , Jäkel O , Luan S
Published: August 2010

Purpose: To develop a treatment planning algorithm that can reduce the number of energy changes for scanning beam particle therapy. Materials and Methods: Changing beam energies in particle therapy requires a considerable amount of time; therefore, a high quality treatment plan with minimum number of energy changes is desired. In this research, we explore using Voronoi diagram to achieve this. A Voronoi diagram of a set of objects partitions a metric space into cells with one cell per object, such that each cell contains the region closest to its object. Our new planning algorithm mainly uses these steps: (1) Calculating a Voronoi partition of the target for the given beam angles, such that each Voronoi cell contains the portions of tumor “closest” to its beam. Here by “closest”, we mean to be able to hit a target from a beam angle with minimum penetration of normal tissues and no penetration of critical structures. (2) During optimization, each beam only treats the tumor region within its Voronoi cell. The final dose distribution is optimized using a combination of randomization and non‐negative least square (NNLS). The new planning algorithm has been implemented in C. The proton and antiproton kernels used for treatment planning were generated using FLUKA, and contains energy ranges from 75MeV to 175MeV at 1MeV step. Results: The new algorithm has been applied to a 3D C‐shaped tumor phantom for proton and anti‐proton therapies. Compared to not using Voronoi partition, we can reduce the number of energy changes by 70%, while maintaining similar treatment qualities. Conclusion: A particle therapy planning algorithm that can reduce energy changes by 70% has been developed. As part of our ongoing research, we are testing the algorithm for different anatomical sites.
SU‐GG‐T‐451: Scattering Factor of Energy‐Stacking Layer on Outputs of Modulated Protons Using Uniform Scanning Technique
Authors: Hsi W , Schreuder A , Zheng Y , Ding X , Zhao Q , Das I
Published: August 2010

Purpose: To evaluate scattering factor of energy‐stacking‐layers (ESL) on outputs of modulated protons using uniform scanning technique. Methods: Using scanning magnet instead of scatterer requires minimal material to spread protons laterally. However, scattering induced by ESL becomes one of factors, such as beam range (Rw), modulation width (Mw) and field‐size (FS) that affect outputs of modulated protons. Outputs as functions of Rw and Mw were measured on gantries at Midwest Proton Radiotherapy Institute (MPRI) and Procure Oklahoma City (OKC) center. Using similar beam‐line configurations, the energy spread for same Rw and Mw between the two gantries were almost identical at the phantom. In addition, MU chamber and scanning magnet were placed at similar location. However, ELS was placed upstream at OKC versus downstream to the scanning magnet at MPRI. Distances from ESL to MU chamber varied largely between two gantries at different facilities. As a result, scatterings of ELS impacted outputs differently between the two gantries. Observed trends of measured outputs as a function of r, defined as (Mw ‐ Rw)/ Mw, were further utilized to examine the effect of ELS scattering factor. Results: After outputs for each individual Mw were normalized to the output of 17cm Rw with same Mw, normalized outputs of 3.5 Mw varied more than 10% to outputs of 12.5 Mw at 13 and 27 cm Rw for OKC outputs while only 5% variations were seen for MPRI outputs. Trend of output as a function of r also varied larger for OKC than MPRI. Conclusion: Larger varied trend as a function of r indicates that the scattering factor of ELS placed upstream, farther away from MU chamber, presents a larger effect on outputs in terms of Rw and Mw. The effect of ELS scattering on outputs for field‐size dependency need be further studied.
SU‐GG‐T‐551: Spinal Radiosugery: Comparison between Volumetric Modulated Arc Therapy and Static Gantry IMRT
Authors: Chow P , Agazaryan N , Tenn S , Lee C , Gorgulho A , DeSalles A , Lee P , Selch M , Steinberg M
Published: August 2010

Purpose: Image Guided Radiosurgery (IGRS) has been used successfully to treat lesions involving the spine. Treatment plans usually involve multiple static Intensity Modulated Radiotherapy (IMRT) fields. Conformality is paramount in spinal RS treatments to maximize the dose to the target while sparing the intimately associated spinal cord. To improve conformality, it is necessary to increase the number of fields, increasing the complexity of the treatment as well as time of delivery. Delivery time is crucial with this group of patients as it is difficult for them to remain on the couch without moving for long periods of time. Volumetric Modulated Arc Therapy (VMAT) can deliver treatment in a shorter time. In this study, we compared the conformality of plans created with VMAT and IMRT. Materials and Methods: Four patients were planned using both RapidArc VMAT and IMRT. The same structure sets were used for both planning methods. Plans were normalized such that prescription dose covered 95% of the planning target volume. Optimization was accomplished with comparable constraints and maximum cord dose was desired. Once acceptable plans had been achieved, the conformality index was calculated. Results: In comparing the plans for the two methods, the Paddick Conformality Index for VMAT ranged from 0.7553 to 0.8938 while for IMRT it went from 0.7315 to 0.8186. Conformality was consistently better for VMAT than for IMRT. Maximum cord dose differed by no more than 5%. Conclusion: Although planning time for VMAT was longer than for IMRT, conformality was consistently better. This study has shown that faster delivery time does not compromise quality of the dose distribution. Shorter delivery time also increases accuracy due to less patient movement during treatment. VMAT is a viable and effective tool for treating patients where spine SRS is indicated. Research supported by Varian Medical Systems
MO‐A‐204C‐01: Pulse Sequences and Acquisition Techniques for Breast MRI
Authors: Price R
Published: August 2010

Dynamic contrast enhanced MRI (DCE‐MRI) of the breast using a gadolinium contrast agent has become an important diagnostic tool for evaluating disease extent, monitoring therapy response and for screening women that are at high risk for breast cancer.

The sensitivity of DCE‐MRI for detecting cancerous lesions is primarily determined by the degree of contrast enhancement that can be achieved relative to the surrounding normal tissues. The specificity of DCE‐MRI, for distinguishing malignant from benign lesions, often relies upon the DCE‐MRI kinetic data. Malignant lesions generally exhibit rapid uptake and washout while benign lesions typically have a slower uptake that gradually increases with time.

In an effort to achieve both the high sensitivity and specifically, breast MRI pulse sequences should be optimized to achieve high gadolinium contrast enhancement, high three‐dimensional spatial resolution (< 1 mm in‐plane) as well as adequate temporal resolution. The evolution of breast MR imaging has lead to the general use of fat‐suppressed, 3D T1‐weighted gradient‐echo pulse sequences that can be acquired with a temporal resolution of approximately 60 seconds.

Learning Objectives:

1. Review protocols and pulse sequences used for breast MR imaging.

2. Review the MRI timing diagram used for T1‐weighted, fat‐suppressed, 3D gradient echo‐pulse sequences.

3. Understand how k‐space sampling affects temporal resolution.

4. Review how parallel imaging can be used to help achieve the temporal resolution needed for breast DCE‐MRI.

5. Discuss issues related to data acquisition and post‐acquisition image processing.
MO‐B‐204C‐01: Practical Aspects of Medical Physics Surveys of Mammography Equipment and Facilities
Authors: Martin M
Published: August 2010

Some of the practical aspects of performing the required medical physics evaluations of both digital and film/screen mammography equipment and facilities will be presented and discussed based on the experience of surveying all brands of mammography equipment for the past 15 years. A complete list of the required tests for both digital and film/screen systems will be covered with tips for completing these tests in an efficient and practical manner to minimize the time required for the facility to be without access to their equipment. Facility evaluation not only includes the mammography equipment but also the viewing conditions for the radiologists and technologists workstations for digital systems as well as the viewboxes in clinical use for film/screen systems. A review process of the printers and processors as appropriate is required for a complete facility evaluation. The mammography physicist must be familiar with all of the tests required to be performed by the mammography technologist as part of the MQSA required Quality Control Program. At each annual review, the physicist must perform a complete review of the QC program and should make any suggestions appropriate to improve the images obtained at the facility.

Learning Objectives:

1. Attendees will know the Annual Tests required to be performed by the medical physicist to meet MQSA and ACR accreditation requirements for both Digital and Film/Screen Mammography Equipment.

2. Attendees will be aware of efficient methods to be used to perform the required tests to meet accreditation requirements.

3. Attendees will made familiar with the required tests for laser printers and monitors for digital systems and for film processors and viewboxes for film/screen systems.
MO‐EE‐A2‐01: On the Dosimetric/DVH Impact of Variation in Organ Delineation: A Multi‐Institutional Study and Proposed Quality System
Authors: Nelms B , Robinson G , Magliari J , Roeske J
Published: August 2010

Purpose: Anatomy contouring is an early and critical step in the workflow of per‐patient customization of modern radiation therapy. Accurate and consistent delineation of regions of interest (ROIs) is vital, as inaccuracies will affect everything downstream in the workflow: the optimized dose, the DVH metrics, and in some instances the ROI‐based guidance used in IGRT. However, despite the importance of ROI accuracy, there is, as yet, no industry‐wide QA system for “anatomy engineering.” This study examines this problem objectively. Methods and Materials: Source data were generated by submitting a common head/neck CT dataset (with targets already defined) to over 100 institutions for them to contour and produce an IMRT Plan. The received data (Plans, Structures, Dose) were filtered by plan quality to pare down to a collection of the 32 best plans, each contoured and planned by a different dosimetrist. We quantify: 1) the ROI variation, and 2) the impact that the ROI variation has on important dosimetry/DVH endpoints. New technologies are employed, including a volumetric ROI comparison tool and a cross‐platform 3D Dose/DVH tool allowing flexible association between DICOM RT structures and 3D dose grids. Results: There is significant inter‐dosimetrist variation in critical ROIs, with the degree of variation being organ‐dependent. For the patient/plan we studied, there was a corresponding range of dose errors caused by the ROI variation (errors ranged from −289% to +56% for mean ROI dose; −22% to 35% for max dose). Based on our analysis, there appears to be an obvious ROI comparison metric cutoff beyond which the associated dose errors become minimal. Conclusions: Given these results, we propose a practical “Quality System” that could quantify the performance of anatomy engineering systems (dosimetry staff, autosegmentation algorithms, physicians, etc.) and provide feedback for continual quality improvement.
MO‐E‐BRA‐02: Computer Aided Design and Monte Carlo Validation of a Patient‐Specific Co‐60 TBI Treatment Unit
Authors: Serban M , Seuntjens J , Roussin E , Tremblay J , Chevrier M , Khaouam N , Wierzbicki W
Published: August 2010

Purpose: To modify and characterize a teletherapy 60Co unit for total body irradiation (TBI) treatments at extended SSD using experiments and a Monte Carlo (MC) model and to propose the design of custom compensators based on MC dose in the patient. Methods and Materials: An existing Eldorado T78 60Co teletherapy unit was stripped from its original collimator and equipped with beam‐defining cerrobend blocks for extended SSD TBI treatments. An acrylic flattening filter was numerically designed based on detailed mapping of the dose distribution of the large open field at 10 cm depth in water and using a primary radiation attenuation calculation. An EGSnrc MC model of the resulting unit was developed and validated. Dose distributions measured using ionization chambers were compared to MC dose distribution in air and phantom. The validated model was used to calculate dose in a whole‐body patient CT image. A compensator, designed to make the patient mid‐plane dose uniform was proposed. Results: The designed filter flattens the beam to within ±2% over an area of 200 × 70 cm2 at patient mid‐plane. The agreement between measured and calculated dose profiles in the open and the filtered beams is at the sub 2% and sub 1% level, respectively. Surface dose in the filtered beam is 78.5% and mean photon energy of the primary fluence is 0.94 MeV independent of position in the field. Patient‐specific calculations show excess dose in lung and the area of neck and extremities relative to prescription dose, by up to 20% and 30%, respectively. These excess doses can be reduced by introducing compensators, designed from the mid‐plane dose distribution, following similar techniques as for the design of the filter. Conclusions: This work shows that extended SSD 60Co irradiation equipment and patient‐specific compensators designed based on realistic dose distributions, can improve TBI delivery.
MO‐E‐BRA‐06: Dose Response of MD‐55, EBT and EBT‐2 Radiochromic Films: A Monte Carlo Study
Authors: Chibani O
Published: August 2010

Purpose: To calculate the film dose response using Monte Carlo simulation of photon/electron transport. The film dose response (dose in film versus dose in water) is calculated for brachytherapy sources (103Pd, 125I, 192Ir and 137Cs) and megavoltage photons beams (60Co, 6 MV and 18 MV). Effects of the film composition and source‐film distance on the film response are also investigated. Material and Methods: The GEPTS code is used for dose calculations in radiochromic films. The detailed film structure including the film base, the adhesive, the surface layer, and the active layer is simulated. The elemental compositions of these layers are provided by the manufacturer. Photons and electrons are transported down to 1 keV. The GEPTS photoionization and atomic relaxation processes are based on the latest EPDL97 cross section database. Results: The film response is very sensitive to variations of the elemental composition of the active layer. Up to 100% differences are seen between MD‐55, EBT and EBT‐2. For a given film, variations in Cl, K and Br (which contents are normally below 0.3%) can have major effects on the film response for barchytherapy sources (e.g. 103Pd, 125I and 192Ir). Increased source‐film distance can lead to non‐negligible variations of the dose response because of energy spectrum hardening (e.g. 3% for 103Pd at 8 cm versus 2 cm from the film). For 60Co, 6 MV and 18 MV beams, the film dose response is very close to unity even in the buildup region. Conclusion: Although the energy deposited in film is not simply related to the measured optical density, it is nevertheless important to understand how it compares with the dose in water for different energies and irradiation setups. Present calculations are the first step towards a more comprehensive study involving the chemistry and physics of radiochromic films (e.g. percolation theory).
MO‐E‐204C‐09: Quantitation of Nanoparticle Concentrations in Microscopic Bound States
Authors: Weaver J , Rauwerdink A
Published: August 2010

Purpose: To measure the distribution of nanoparticles into microscopic bound states. Antibody targeting has had varying success primarily due to competing mechanisms of uptake, including nonspecific binding and phagocytic activity, and the inability of nanoparticles to penetrate the vascular barrier. Methods of estimating the number of nanoparticles in each bound state will allow us to understand the mechanisms that deprive nanoparticles of their ability to bind targeted antigens and allow us to design methods to enhancing the antigen binding. Method and Materials: When a pure sinusoidal magnetic field is applied to magnetic nanoparticles, the signal at the harmonics of the applied field can be detected at very low concentrations of nanoparticles because there are no other sources of signal and the bandwidth of the measurement can be very narrow. Identical iron oxide nanoparticles (25nm) were a) in aqueous solution and b) bound to two‐micron polystyrene beads. The phase and amplitude of the third and fifth harmonics were measured using applied fields with different frequencies and amplitudes. The signals from the two pure solutions were fit the signals from known combinations of the two solutions using a linear mixture model. Results: The harmonics as a function of frequency and amplitude of the applied field from the two samples were linearly independent. The condition number was 31.8 when the amplitude was varied from 10mT to 24mT and 14.8 when frequency was changed over the range 300Hz to 2700Hz. For two frequencies, 570, 2100 Hz, the average measured error from a linear least squares fit of the data for three mixtures was 4.7% and the maximum was 28%. Conclusion: MSB can be used to monitor the concentrations of nanoparticles in at least two bound states remotely with reasonable accuracy. The system is nonlinear so a nonlinear model would reduce the errors significantly.
MO‐E‐204B‐06: Comparative Study of Dose Calculations Using the BrainLAB Pencil Beam and Monte Carlo Dose Algorithms
Authors: Ali I , Algan O , Thompson S , Herman T , Ahmad S
Published: August 2010

Purpose: To compare and assess accuracy of the doses calculated using the BrainLAB pencil beam (PB) and Monte Carlo (MC) algorithms for lung, prostate, brain, head and neck and paraspinal tumors. Methods and Material: Dose was calculated using PB convolution and MC algorithms in the IPLAN treatment planning system from BrainLAB for 5 lungs, 3 brains, 5 prostates, 2 head and neck and 2 paraspinal tumors. Dose was calculated using a combination of three‐dimensional conformai and IMRT plans. The leaf sequences from IMRT plans or beam shapes from conformai plan and monitor units (MUs) calculated by the PB were used to calculate dose with MC. Results: The DVH's calculated by PB and MC in the brain, prostate, paraspinal and head and neck are in good agreement within 5%. However, the DVH's of the lung patients have large discrepancies and while PB shows good coverage, MC shows lack of dose coverage. For maintaining similar dose coverage, higher MUs up to 30% are needed for MC compared to that predicted by PB calculations. Despite large discrepancies in DVH coverage of the PTV between PB and MC, the point dose at isocenter for lung calculated by both algorithms were within 5%. Further, the dose measured at isocenter using ionization chamber agrees well with pencil beam within 5% for several selected plans. Conclusions: The calculated dose by MC and PB agrees within 5% for prostate, brain, head and neck and paraspinal tumors. However, considerable discrepancies up to 30% are observed in dose‐volume coverage between MC and PB in lung tumors. Point dose measurements at isocenter are not representative of the discrepancies in dose coverage between PB and MC and verification with two‐ and three‐dimensional dose measurements are required.
TU‐A‐204B‐04: A Technique to Correct Crescent Artifacts in On‐Board CBCT
Authors: Giles W , Bowsher J , Yin F
Published: August 2010

Purpose: Large dark and bright crescents are commonly seen in cone‐beam (CB) CT images acquired onboard radiation therapy machines. The purpose of this project is to develop a technique for removing this artifact. Method and Materials: We propose that crescent artifacts are caused by small angle‐dependent shifts of the bowtie filter and that they can be avoided by using angle‐dependent blank projections when reconstructing CBCT images. Blank projections are those acquired without an attenuating object in the field of view. Bowtie motion as a function of angle was quantified by tracking the center of mass of pixel intensity in blank projections. Computer simulations were used to demonstrate that crescent artifacts arise under that quantified level of bowtie motion. Clinical onboard scanner studies with a Catphan® 504 phantom were used to demonstrate that crescent artifacts are removed by incorporating angle‐dependent, rather than fixed, blank projections into image reconstruction. Results: The center of mass study indicated that crescent artifacts result from shifts in the bowtie filter of much less than 1 mm. The computer‐simulation studies demonstrated crescent artifacts when the same blank image was used for all projection angles. These crescent artifacts matched the positions, widths, and amplitudes of those seen clinically. In the computer‐simulation studies and with data acquired on clinical CBCT systems, the artifacts were removed when angle‐dependent blank images were utilized. Conclusion: Crescent artifacts are shown to arise from unaccounted motion of the bowtie filter during the acquisition of CBCT projections. Correction of this artifact, through use of angle‐dependent blank images, is proposed and demonstrated. This technique could be effectively implemented into clinical practice. Conflict of Interest: This research is partly supported by Varian Medical Systems.
TU‐B‐BRA‐01: Total Body Irradiation (TBI): Looking from Differrent Angles
Authors: Zhuang T , Wu Q
Published: August 2010

Purpose: To explore the new degree of freedom of VMAT to design a novel technique for TBI, in which patient is positioned supine/prone on the floor and an arc field is delivered with variable dose rate and/or dynamic collimators. Method and Materials: A formalism of designing an arc field with variable dose rate and/or dynamic jaw/MLC to deliver an arbitrary one‐dimensional dose profile is developed. The dose rate and/or jaw/MLC position are obtained by minimizing the difference between prescribed and calculated dose at each spatial point. The formalism is applied to design TBI treatment plan to achieve (1) a uniform dose over the entire body, and (2) a reduced dose in the lung region. MATLab codes were developed to solve the optimization problem using gradient decent method. Three types of treatment plans were generated: (1) variable dose rate (VDR) only, (2) VDR with dynamic MLC (DMLC), and (3) DMLC only. The optimized treatment plans were converted into DICOM‐RT format and delivered in a Varian 21‐EX machine capable of Rapidarc in DICOM‐RT mode. Measurements with farmer chamber in air with buildup cap were performed and compared with the optimization results. Results: For a patient with 200cm height placed at 100cm below the linac iso‐center, the differences between measured profile from plans with VDR only for uniform/lung sparing case are (−1.4±1.9)% and (−0.2±2.4)%, respectively. They improved to (−0.4±1.0)% and (−0.5±2.2)% with VDR+DMLC. The latter also had 40% higher efficiency. The results for DMLC only were less desirable with reduced range of (−85cm, 85cm) and slightly higher discrepancies. Conclusion: It is feasible to deliver TBI using VMAT, thereby eliminating the need for large treatment room size or hand‐made compensators. Regular linac operating in arc therapy with dynamic MLC alone can be also used, although with less efficiency.
TU‐B‐201C‐01: Gamma Camera and SPECT Routine Quality Assurance Testing
Authors: White S
Published: August 2010

Routine quality control, calibration and performance testing of gamma cameras are necessary in order to consistently acquire good quality images without artifacts. This lecture will briefly cover the basics of gamma camera image formation and performance characteristics. The lecture will primarily focus on routine quality assurance tests for gamma cameras.

It is increasingly common for providers of nuclear medicine imaging services to seek accreditation, either from the American College of Radiology (ACR) or the Intersocietal Commission for Accreditation of Nuclear Medicine Laboratories (ICANL). Both accrediting bodies recommend routine quality control tests and these tests will be discussed.

Common problems and image artifacts will be discussed as well as how to correct these problems. Calibration procedures such as center of rotation and uniformity calibration will be discussed.

Learning Objectives:

1. Learn the basics of gamma camera and SPECT performance measurements and quality assurance test procedures.

2. Become familiar with routine quality control tests recommended by accreditation programs.

3. Be able to identify and correct common problems and image artifacts in gamma camera and SPECT imaging.
TU‐C‐BRA‐09: High‐Performance Dose Calculation for Proton Radiotherapy Using GPU
Authors: Mo X , Westerly D , Mackie T
Published: August 2010

Purpose: To investigate the feasibility and the potential speed gain of GPU accelerated dose calculation for proton pencil beam algorithms with heterogeneity correction and to offer solutions to obstacles in implementing our algorithm. Method and Materials: We implemented our in‐house proton dose calculation system on an NVIDIA GTX 280 graphic card and an Intel Xeon 2.83 GHz processor using the Compute Unified Device Architecture environment. Several key techniques and strategies were employed in order to optimize the performance of the GPU code. (1) Modified the scaling algorithm used to calculate lateral spreading of the proton beam in the presence of tissue inhomogeneities. (2) Used an incremental ray tracing algorithm to reduce the memory requirement for each ray allowing for better parallelization. (3) The penalty of massive non‐coalesced memory reads required for convolution/superposition was alleviated by texture fetching. (4) Parallel algorithms such as reduction and prefix sum were implemented on GPU to help avoid data transfer between the CPU and GPU memory. The performance of both implementations was evaluated on a prostate clinical case. Results: With no loss in accuracy, the dose calculation time per beamlet with our GPU implementation ranges from 200 – 500 ms compared to 15 – 40 s on CPU. Approximately 80 times speed gain is achieved for various number of convolution/superposition steps. Conclusions: GPU‐based proton dose calculation is feasible with adapted algorithms and proper implementation techniques. Close to two magnitude of performance gain can be achieved with typical hardware. We believe GPU‐based fast dose calculation can reduce the routine treatment planning workload as well as provide a feasible solution to the realization of online adaptive intensity modulated proton therapy.
TU‐C‐204B‐04: Monte Carlo Characterization of Skin Doses in MRI‐Guided‐Radiotherapy
Authors: Oborn B , Metcalfe P , Butson M , Rosenfeld A
Published: August 2010

Purpose: The main focus of this work is to continue investigations into the Monte Carlo predicted skin doses seen in MRI‐guided radiotherapy (MRIgRT). In particular we aim to characterise the 70 micron skin doses. The effect of surface orientation on both the entry and exit sides is also investigated, as well as the use of exit bolus. Materials and Methods: High resolution Geant4 Monte Carlo simulations of a water phantom exposed to a 6 MV X‐ray beam (Varian 2100C) have been performed. Transverse magnetic fields of strengths between 0 and 3 T have been applied to a 30×30×20 cm3 phantom. This phantom is also altered to have variable entry and exit surfaces with respect to the beam central axis and they range from −75 to +75 deg. The exit bolus simulated is a 1 cm thick (water equivalent) slab located on the beam exit side. Results: On the entry side significant skin doses at the beam central axis are reported for large positive surface angles and strong magnetic fields. Over the entry surface angle range of −30 to −45 deg the entry skin dose is comparable with zero magnetic field skin dose, regardless of magnetic field strength and field size. On the exit side moderate skin dose increases are expected except for large positve angles at the higher magnetic fields. For exit bolus of 1 cm thick the central axis exit skin dose becomes an almost consistant value at around 35–38% of Dmax. This is due to the almost complete absorption of the ERE electrons by the bolus. Conclusion: There are many combinations in MRIgRT where skin dose may become excessive. Results from this study can be used to determine arrangements where skin dose is comparable to B = 0 T.
TU‐D‐204B‐02: Tumor Motion Assessment with 4D Cone Beam CT Using Prior Image Constrained Compressed Sensing (PICCS)
Authors: Qi Z , Chen G
Published: August 2010

Purpose: 4D‐CBCT provides capability of in‐room measurement of breathing induced tumor motion before the treatment. However, to ensure sufficient image quality for motion assessment, investigators have proposed to prolong the data acquisition from 1 minute to 4 minutes or more. In this paper, we present a method which could generate high quality 4D‐CBCT images and support tumor motion extraction using the standard 1‐minute protocol with an on‐board imager. Method and Materials: The enabling technique is Prior Image Constrained Compressing Sensing (PICCS) reconstruction method. PICCS maintains high temporal resolution for each phase‐bin image after resorting the projection data. Within each phase bin, although the number of projections is vastly undersampled, PICCS reconstruction ensures high SNR characteristics since the SNR is primarily determined by the prior image reconstructed from all cone‐beam projection data without gating. Patient studies were conducted for validation. The first case was a 1‐minute CBCT scan; the second case, although originally a 4‐minute scan, was used to simulate a 1‐minute scan by down‐sampling the projection data by 4 times. For both cases, both FBP and PICCS algorithms were performed to reconstruct 4DCBCT images; a deformable registration method was also applied to extract the tumor motion. For the second case, a comparison was also made between 4‐minute FBP images and 1‐min PICCS images. Results: For 1‐minutes scans from both studies, PICCS images showed superior image quality to FBP ones; as a result, PICCS images generated physically acceptable tumor motion profiles which agree well with direct observation. Compared with FBP images from the 4‐minute scan, PICCS images from the simulated 1‐minute scan showed higher SNR and more physically accurate motion profile. Conclusion: Clinical feasibility of 1‐minute PICCS‐4DCBCT was demonstrated. The proposed method is able to reconstruct high SNR 4D images for tumor motion assessment, without slowing down the data acquisition.