bluuebunny/crossref_metadata_2025_split huggingface dataset:
WE‐A‐BRB‐01: Accurate Dosimetric Characterization of a Fully Loaded 20 Mm COMS I‐125 Eye Plaque Using Specially Designed GAFCHROMICTM Film
Authors: Trichter S , Chiu‐Tsao S , Zaider M , Sabbas A , Kulidzhanov F , Chang J , Cohen G , Nori D , Chao K 
Published: November 2011

Purpose: The majority of eye plaques used in the U.S. are of Collaborative Ocular Melanoma Study (COMS) design with I‐125 brachytherapy seeds. Treatment planning is usually done using the TG‐43 formalism, not accounting for the gold alloy backing and Silastic insert, which significantly reduce the dose, as calculated by BrachyDose Monte Carlo (MC) (www.physics.carleton.ca/clrp/eye_plaque/). Dosimetric characterization of a fully loaded 20 mm COMS plaque using radiochromic film is reported. Methods: A 20 mm COMS eye plaque was uniformly loaded with 24 6711 I‐125 seeds at 6.75 U/seed. Measurements were performed using specially designed single layer GAFCHROMIC EBT1 film sandwiched perpendicular to the plaqueˈs central axis at depths 0 – 19 mm between inserts of a Solid Water “eye” phantom located at the center of a 30×30×30 cm3 full scatter Solid Water phantom. The films were calibrated using a 6711 I‐125 seed in Solid Water, applying the TG‐43 formalism. Results: Dose distributions in planes perpendicular to the central axis of the plaque are radially isotropic and uniform. Measured depth dose on central axis as well as off‐axis profiles, agree well with the results of MC. At 3 mm from the inner sclera, the measured dose rate is 12.5% lower than TG‐43 dose rate in homogenous water, similar to 11.9% for MC. The thin flexible film enabled measurements of the dose at the surface of the plaque. Results on duplicate films agree within 5.5%. Conclusions: GAFCHROMIC film in a Solid Water phantom is a convenient, accurate, and reproducible dosimeter for I‐125 eye plaque dosimetry. Dose measurements on the inner surface of the plaque enable precise assessment of the scleral dose and its homogeneity, and of the active area of the plaque for coverage determination. This work validates the MC simulations about the dose reduction effect by the plaqueˈs backing and insert.In‐Kind support of materials provided by Oncura, Inc., Arlington Heights, IL and by International Specialty Products, Inc., Wayne, NJ
WE‐B‐214‐01: CT Dose Reduction Strategies
Authors: Mahesh M 
Published: November 2011

The number of CT examinations performed in the United States has been growing at an annual rate of approximately 10% leading to more than 70 million procedures in 2008. The apparent increase in the number of CT procedures,new protocols and the associated radiation dose and risks has drawn considerable attention. It appears that the so‐called ‘slice wars’ with regard to the number of slices provided per CT gantry rotation may be reaching a plateau and increasing concerns about radiation dose due to CT examinations are fueling the efforts to reduce radiation dose and leading to the beginning of the so‐called ‘dose wars’.A number of radiation dose reduction strategies are been considered and many new are been developed. At the same time, efforts to optimize CT protocols, dose modulation techniques and further improvement in image quality and image quantificationsare gaining ground.There is an increasing demand for the medical physicists to assist clinicians in developing, reviewing and recommending changes to the clinical protocols. Therefore, it is critical for the medical physicists to become familiar with the various dose reduction strategies that are currently available and thenew technologies that are been developed. In this lecture, variousCT dose reduction strategies will be discussed.Educational Objectives:1. To become familiar with radiation dose reduction strategies in CT.2. To understand various image quality improvements in CT.
WE‐C(SAM)‐211‐01: Physics of MR Safety
Authors: Stafford R 
Published: November 2011

Magnetic resonance imaging (MRI) is a non‐invasive and non‐ionizing imaging modality that has an excellent track record for safety in its capacity as a diagnostic imaging device for over 20 years. MRI devices utilize a strong static magnetic field to polarize a sample, radiofrequency pulsed magnetic fields to excite the sample, and rapidly switched magnetic field gradients to spatially and temporally modulate the magnetization in the sample for image encoding. Because of their potential interaction with biological tissue as well as with medical implants or ancillary objects in the room, each of these fields presents a unique potential risk to the patient, staff or family members in the MRI environment that must be mitigated via education and constant vigilance.Additionally, innovations in MRI design and use can significantly impact safety considerations in and around the suite. MRI is no longer exclusively confined to a diagnostic imaging environment as its use as a treatment planning, interventional or intra‐operative imaging device expands. In addition to the safety challenges associated with performing procedures in these unique environments, technological advancements also constantly engage a re‐evaluation of MRI safety principles as they apply to monitoring of patients and objects in the MR suite. The use of higher field strengths as well as innovative bore designs which impact the spatial magnetic field gradients, such as wide or short bore magnets, may interact more strongly with implants or objects previously regarded as safe for use in the MRI environment. More powerful gradient systems invite much more rapid or higher resolution imaging acquisitions, which can increase the energy imparted to the patient or implant as well as push the limits of acoustic noise and peripheral nerve stimulation.The purpose of this continuing education review is to provide an overview for the Medical Physicist of the underlying physics which motivate many of the safety concerns associated with operating in the MRI environment. The primary intent is to provide additional perspective to, and promote a better understanding of, the current safety guidelines and recommendations as well as aid in addressing safety questions and concerns related to developing, operating and working in an MRI suite.Learning Objectives:1. Understand the major safety risks associated with MRI from a physics perspective2. Understand the potential impact MRI technology may have on safety considerations3. Review current FDA MR safety guidelines
WE‐C‐BRB‐01: Does IMRT Treatment Plan Complexity or Mismatched Dosimetry Data Contribute to Dose Delivery Errors Detected Using an IMRT H&N Quality Assurance Phantom?
Authors: Tonigan J , Kry S , Dong L , Purdie T , White R , Ibbott G , Followill D 
Published: November 2011

Purpose: Investigate whether increased intensity modulated radiation therapy (IMRT) treatment plan complexity or mismatched accelerator dosimetry data are responsible for or contribute to failures with the Radiological Physics Centerˈs IMRT H&N QA phantom. Methods: Eight H&N IMRT plans with a range of total MU (1460–3466), number of segments (54–225), and modulation complexity scores (MCS) (0.181–0.609) were created in Pinnacle v.8 and delivered to the RPCˈs H&N phantom on a single Varian Clinac. One of the IMRT plans (1851 MU, 88 segments, and MCS=0.469) was equivalent to the median H&N plan from ∼1000 RPC H&N phantom irradiations. This average IMRT plan was also delivered on four matched Varian Clinac machines and the dose distribution calculated using a different 6MV beam model. Radiochromic film and TLD within the phantom were used to analyze the dose profiles and absolute doses. Results: Increasing the treatment plan complexity by varying the MU, number of segments, or the MCS resulted in no clear trend toward an increase in dosimetric error using either ±7%/4mm or ±5%/3mm gamma index criteria. Varying the delivery machines as well as the beam model (use of a Clinac 6EX 6MV beam model vs. Clinac 21EX 6MV model), also did not show any clear trend towards an increased dosimetric error using the criteria indicated above. Conclusions: Accurate IMRT dose delivery requires a complicated chain of events involving numerous steps, each of which might contribute to dose delivery errors. IMRT modulation complexity and mismatched dosimetry data have been postulated as contributing to IMRT dose delivery errors but our results indicate otherwise. Other components of the IMRT delivery chain such as MLC performance and modeling uncertainty in setup, machine mechanical integrity, etc. should be investigated to determine whether they contribute significantly to IMRT dose delivery errors.Work supported by PHS CA010953 and CA081647, awarded by NCI, DHHS.
WE‐C‐BRB‐05: Results from 1005 IMRT Irradiations of an Anthropomorphic Head and Neck Phantom
Authors: Molineu A , Hernandez N , Alvarez P , Ibbott G , Galvin J , Followill D 
Published: November 2011

Purpose: To credential institutions treating clinical trial patients with intensity modulated radiation therapy Methods: The credentialing bodyˈs anthropomorphic head and neck phantom was sent to institutions wishing to participate in multi‐institutional clinical trials. The phantom contained two PTV structures and an organ at risk (OAR). TLD and film dosimeters were imbedded in the PTV. Institutions were asked to image, plan and treat the phantom as they would a patient. The treatment plan should cover at least 95% of the primary PTV with 6.6 Gy and at least 95% of the secondary PTV with 5.4 Gy. The plan should limit the dose to the OAR to less than 4.5 Gy. The passing criteria were +/−7% for the TLD in the PTVs and a distance to agreement of 4 mm in the high dose gradient area between the PTV and the OAR. Results: The phantom was irradiated 1005 times by 689 institutions from 2001 through February 2011. 804 of the irradiations passed the criteria. 145 irradiations failed only the TLD criteria, 24 failed only the film criteria and 32 failed both sets of criteria. Only 61% of the irradiations passed a narrowed TLD criterion of +/− 5%. When possible, gamma calculations were made for an area around the primary PTV in the axial plane. The average percent of pixels meeting the gamma criteria was 89%. Conclusions: The head and neck phantom is a useful credentialing tool for multi‐institutional IMRT clinical trials. Tightening the criteria would significantly reduce the number of passing irradiations. Altering the criteria to use the gamma calculation instead of the DTA would slightly reduce the number of institutions passing, but would give a more comprehensive view of the fitness of the irradiation.The investigation was supported by PHS grants CA10953, CA81647 and CA21661 awarded by the NCI, DHHS.
WE‐C‐110‐06: Two‐Material Decomposition from a Single CT Scan Using Statistical Image Reconstruction
Authors: Long Y , Fessler J , Balter J 
Published: November 2011

Purpose: Dual‐energy (DE) CT methods can separate two basis materials (e.g., soft tissue and bone) for applications such as dose calculations. However, typical DECT methods require either two scans or specialized scanners. We propose a statistical penalized weighted least‐squares (PWLS) method to reconstruct two basis material images from a single‐energy CT scan acquired with a simple split X‐ray filter. Methods: We used a pre‐patient split‐filter that contains 2mm aluminum across half the fan beam and 200 microns molybdenum for the other half. Using a 360‐degree rotation of the X‐ray source, the whole scanned object is exposed to two incident spectra with different effective energies during a single scan. We propose an optimization transfer method with a separable quadratic surrogate to monotonically decease a PWLS cost function with edge‐preserving regularization. We first reconstructed the bone‐corrected FBP images using the Joseph and Spital method, and separated the soft and bone components by a threshold to initialize the iterative algorithm. We used the ordered subsets approach to accelerate the convergence to a good local minimum. Results: The test object is a chest NCAT image with 1.0 for soft tissue, 0.5 for lungs, 1.5 for spine, and 2.0 for ribs (the units are physical density: g/cc.). The lungs and soft tissue had the “soft tissue” characteristics and the spine and ribs had the “bone” characteristics. The root‐mean‐square (RMS) errors of the soft tissue, bone and density map were 0.03, 0.02 and 0.01 for PWLS, compared to 0.06, 0.03 and 0.05 for the FBP initialization for the noiseless simulation. The PWLS method removed the beam hardening artifacts more effectively than the FBP‐JS method. Conclusions: The proposed PWLS reconstruction method was able to separate soft tissue and bone images with low RMS errors from a single CT scan using a split‐filter.Sponsored in part by NIH P01CA59827
WE‐E‐224‐02: Preparing for ABR Board Exams
Authors: Flynn R 
Published: November 2011

It is easy to become overwhelmed by the pool of potentially useful study material for Part II of the ABR Board Exam in radiotherapy physics. Therefore it is difficult to extract a sufficiently broad and relevant subset of material to study. Moreover, balancing the time‐consuming exam preparation process with a full time job and family life is also challenging. In order to make best use of available study time, attendees are taught an efficient organizational framework for Part II exam preparation that maximizes high‐yield active learning study activities and minimizes low‐yield study activities. This method is then combined with a productive group‐based study technique.The format and scope of the Part II ABR exam in radiotherapy physics is described, and the eligibility requirements are reviewed. High‐ and low‐yield study activities are defined and examples are discussed in detail. A problem‐based strategy for limiting the scope of study material is described. A method for studying in groups by distributing delegable tasks among multiple group members and ensuring their completion is described.Educational objectives1. Understand the scope of material covered on Part II of the ABR radiotherapy physics exam and which references to study for the exam.2. Be able to design and execute an efficient study plan that enables an active learning approach.3. Learn to use group study techniques to enhance efficiency.
WE‐E‐214‐01: Targeted Radionuclide Therapy
Authors: Frey E 
Published: November 2011

Targeted radionuclide therapy (TRT) is becoming an increasingly important tool for therapy of some cancers including non‐Hodgkins lymphoma, thyroid cancer, and neuroendocrine tumors. The dose delivered to neoplasms and normal tissues, and thus the therapeutic response and incidence of toxicities, depends on the anatomy and physiology of the patient. Therefore, optimal treatment planning requires estimating the dose distribution for each patient. The dose distribution is estimated in two steps: measurement of the activity distribution of a planning dose at a series of time points using nuclear medicine imaging methods and calculating the dose to organs or voxels in the patient. State of the art dose estimation requires, as an input, estimates of the 3D activity distribution of the planning dose in the patient at each time point.The 3D activity distribution of a radionuclide can be estimatedusing the tomographic nuclear medicine imaging modalities SPECT and PET. Since uptake times of TRT agents are typically on the order of several days, radionuclides such as In‐111 or I‐131 (for SPECT) or I‐124 or Y‐86 (for PET) having longer half‐lives are used for treatment planning. The SPECT radionuclides emit medium or high‐energy photons, which can make quantification of the SPECT images more difficult and requires compensating for the collimator‐detector response. The PET radionuclides have prompt gamma emissions that can result in false coincidences, once again complicating quantification. For both modalitiesattenuation and scatter compensation are essential. Compensation for partial volume effects is important for dose‐estimation in small objects such as tumors.This lecture will review the challenges and recent advances in methods for quantifying 3D activity distributions from SPECT and PET imaging using radionuclides relevant for TRT. It will describe the impact of these advances in terms of metrics relevant to dose estimation and describe the levels of accuracy and precision that are obtainable with state‐of‐the‐art methods.Learning Objectives:1. Understand the applications and requirements of quantitative SPECT and PET for targeted radionuclide therapy.2. Understand the factors that limit the quantitative reliability of SPECT images and how to compensate for them.3. Understand the factors that limit the quantitative reliability of PET.
WE‐E‐214‐02: Dose Response Modeling for Targeted Radiotherapies
Authors: Roberson P 
Published: November 2011

The efficacy of biologically targeted radionuclide therapy (TRT) is dependent on the properties of the treatment strategy, the vector (carrier) molecule, the radionuclide products, and the target and normal tissue architecture. Both dose estimation and cellular response at the lower dose rates of TRT are more complex than typical external beam or high dose brachytherapies, for both targeted and normal tissues. Estimation of TRTresponse of target and normal tissues suffers from inaccurate macroscopic dose estimation, heterogeneous microscopic dose and dose rate dependence, and confounding factors including pretreatment patient status and treatment synergy with concurrent treatment regimens. Cellular response depends on cell survival, being influenced by apoptosis, damage repair, cell division delay, cell cycle redistribution, reoxygenation, regeneration and bystander effects. Tissue response can be described using the linear‐quadratic model, including allowances forthe effects of the above modifying factors. The demand for improved therapy (dose) response modeling, a prerequisite for improved therapy dose optimization, requires more extensive and detailed imaging. Effects that can be modeled usingquantitative imaging are: 1) tissue changes over an extended therapy interval (e.g. SPECT/CT, dual energy CT);2) macro and micro structure and activity distributions of targeted and normal tissues (e.g. SPECT/CT, autoradiography); and 3) macroscopic effects of cell response to therapy (e.g. PET/CT). To help accomplish this, increased efforts are being made to perform more frequent high‐resolution imaging, along with potential correlation to biomarkers. Results point to characteristic non‐uniform micro distributions that can be used to modify therapy—response estimates based on routine macro distribution measurements. Examples of the need for improved imaging include 1) evidence that imaging‐based bone marrow doses correlate with outcome better than blood‐based methods; 2) dose estimations from 3D (SPECT/CT) methods are significantly superior to 1D (planar) methods; 3) evidence that factors other than dose affect therapy outcomes, possibly with synergistic relationships with dose and dose rate.Learning Objectives:1. Understand the importance of quantitative imaging and reconstruction for therapy response modeling in TRT2. Understand the importance of modeling biological effects in TRT in comparison to external beam therapy3. Learn some approaches to therapy response modeling of TRT
WE‐E‐110‐01: Optimization of Image Acquisition and Reconstruction in Multi‐Slice CT
Authors: Yu L , McCollough C , Leng S , Kofler J 
Published: November 2011

CT scanning protocols, which specify image acquisition and reconstruction parameters, need to be optimized so that minimum radiation dose can be used to achieve sufficient image quality for specific diagnostic tasks. To achieve this goal, the relation among image acquisition parameters, image reconstruction algorithms, image quality, and radiation dose must be clearly understood. This lecture will provide an overview on how to optimize image acquisition and reconstruction parameters in multi‐slice CT.Learning Objectives:1. Understand how the CT acquisition parameters (helical pitch, collimation, detector configurations, etc.) affect the image quality.2. Understand how the reconstruction parameters (kernel, slice thickness, etc.) affect the image quality.3. Understand how to optimize the acquisition and reconstruction parameters for different diagnostic tasks in order to improve image quality or reduce radiation dose.
WE‐G‐220‐06: Using MR‐Guided Focused Ultrasound to Study Heating Pattern Variations Due to Reflections from Interfaces in Both Thermal and Tissue Phantoms
Authors: Hipp E , Fan X , Partanen A , Karczmar G 
Published: November 2011

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