bluuebunny/crossref_metadata_2025 huggingface dataset:
SU‐FF‐T‐437: Total Skin Electron Beam Commissioning with EBT Film
Authors: Lightfoot D
Published: July 2006

Purpose: To investigate the usefulness of ebt film (a high sensitivity self‐developing radiochromic film) in the commissioning of an accelerator based electron beam for total skin irradiation. Method and Materials: Measurements were made with ebt film in both water and solid water and compared with parallel plate ionization chamber measurements made in a small rectangular water phantom to determine calibration and depth dose characteristics. The ebt film was wrapped around the outer and inner plastic surfaces of a cylindrical water filled container to study the relationship between calibration measurements in the rectangular phantom and the surface dose characteristics from simulated clinical treatment. Results: The ionization chamber measurements agreed well with the film measurements. In the rectangular phantom surface dose measured about 80% of maximum dose. In the simulated clinical treatment dose was highest at the surface of the cylinder and ranged from approximately 2.5 to 3.5 times the dose at maximum from a single cylinder orientation compared with the six orientations used for the clinical simulation. Minimum and maximum clinical dose versus depth curves merged at a depth of about 5 mm. Conclusion: The film was found to be quite easy to use and produced results with less than the anticipated effort for this type of commissioning. It was found necessary to install UV filter sleeves over room fluorescent lights to minimize UV fog to low dose areas of the film.
SU‐FF‐T‐439: Treatment Planning to Achieve Skin Sparing with Tomotherapy
Authors: Studinski R , Cherpak A , Cygler J , Gerig L , Saoudi A , Carty K , Fox G , Montgomery L
Published: July 2006

Purpose: To determine the extent to which skin dose can be reduced by defining the skin as a Region at Risk (RAR) structure to an IMRT treatment plan of a head and neck patient being delivered with a tomotherapy unit. Method and Materials: The head and neck section of a RANDO phantom was imaged in a CT scanner and two treatment plans were created for it simulating the treatment of a head and neck cancer. Both plans were identical, with the exception that for one an attempt was made to spare the skin as much as possible without compromising the tumor coverage or increasing dose to other RARs. This was accomplished by defining the skin as a RAR, for the purpose of pan optimization. In order to confirm the doses predicted by the treatment planning system the RANDO phantom was treated as per the plans, with metal oxide‐silicon semiconductor field effect transistors (MOSFETs) placed on its surface to determine the dose. Results: The DVHs created by the treatment planning system showed a substantial reduction to skin dose as a result of introducing a skin RAR. The dose coverage of the PTV and other RARs were comparable. The change in skin dose was confirmed by the readings from the MOSFET detectors which indicated that the skin dose per treatment could be reduced from ∼180 cGy to ∼150 cGy with this process. Conclusion: The dose to the skin for head and neck treatments delivered with IMRT is known to be greater than that of conventional radiation therapy. We propose a method of delivering IMRT on a tomotherapy unit with substantial skin sparing. In order to control the skin dose to the patient, treatment plans must be made treating it as an organ at risk.
SU‐FF‐T‐440: Treatment Table Induced Dose Perturbation in An IMRT Treatment
Authors: Das I , Stambaugh M
Published: July 2006

Purpose: Treatment table support bars create problems in treatment planning and delivery. It is a complex issue for the case of IMRT with multiple and varying size beamlets. Methodology to account for the dose perturbation due to the presence of the table support in IMRT treatments is presented. Method and Materials: Five patients were planned with 7‐beam IMRT using a posterior field and six other fields spaced at equal gantry angles. Treatment plans were optimized to produce suitable dose distributions for patient treatment. Plans were imported to solid phantom for dose verification. Treatment plan verification with ion chamber and film was carried out with and without bar. A mathematical weighted dose calculation is presented based on the equation: Dose = TD * [(MU‐ ΣMUij*T)/MU)], where TD is total prescribed dose, MU is total monitor unit from all beams, MUij is monitor unit in ith beam and jth beamlet that is blocked through the bar, and T is the measured transmission factor through bar. T was measured at 90 cm SSD at a depth of 10 cm for all photon energy and a film profile was taken. Results: Measured transmission through the center of the Siemens table bar for 6 MV and 18 MV was found to be 72.9% and 78.8% respectively. Even though IMRT beamlets pass through the bar, the dosimetric effect is minimal. Measured and calculated doses through bar for all clinical cases show agreement within ±4.5%, which is within the limits of the IMRT criterion. Conclusion: IMRT planning and treatment should be coordinated carefully to avoid passage of the beam through treatment table supports to avoid underdosage of the target area. However, in an accidental situation, methodology presented here provides simple and accurate dose estimates for an IMRT treatment.
SU‐FF‐T‐441: Updated Solid Water™ to Water Conversion Factors for 125I and 103Pd Brachytherapy Sources
Authors: Awan S , Meigooni A , dou k , Dini S
Published: July 2006

Purpose: The updated TG‐43U1 recommends determination of the consensus of low energy brachytherapy source parameters using experimental and Monte Carlo Simulated data. As per this recommendation, the measured parameters in Solid Water™ are converted into water data for clinical application. However, the published conversion factors may have been obtained using Monte Carlo simulations with a cross section files that may have errors for low energy photons, and also for inaccurate chemical composition of the phantom material. In this project impact of different calcium composition in Solid Water™ phantom on dose rate constant, radial dose function of 103Pd and 125I brachytherapy sources have been investigated. Method and Materials: Conversion factor of Solid water™ to water has been determined using MCNP5 Monte Carlo code. In these simulations two different calcium compositions in Solid Water™ of 2.3% (SWa) and 1.7% (SWb) were utilized. Monte Carlo simulations were performed for 125I sources, with and without silver marker, in order to investigate the impact of characteristic x‐rays (emitted by silver marker) on dosimetric parameters. However, the simulation for 103Pd was performed only on one type of the source. Each simulation was run for a total of 20M histories to keep statistical fluctuation less than 0.3%. Results: For 2.3% calcium content phantom material the calculated conversion factor was found to be 1.027 and 1.045 for 125I and 103Pd sources respectively. However, for 1.7% calcium these values were found to be 0.989 and 0.963, respectively. Conclusion: The Solid water‐to‐water conversion factors for 125I and 103Pd sources are found to be 0.989 and 0.963 respectively as compared to the published value of 1.05 and 1.048. In addition, presence of silver marker had no significant impact on conversion factor for I‐125 sources. Moreover, conversion for g(r) was also introduced for clinical application of measured data.
SU‐FF‐T‐446: Using Mini‐Verification Films in Clinical Practice
Authors: Wood R
Published: July 2006

Purpose: To present a clinical example of finding field matching errors in a supine three‐field cranial‐spinal irradiation technique utilizing miniverification films. Method and Materials: A three‐field Cranial‐Spinal Irradiation technique uses right and left lateral head fields and one or more PA spinal fields. The table and collimator are rotated in order to match the three fields at the three‐field junction. Verification simulation films are taken to verify adequate block design and field localization. Lead markers are placed on the patient's immobilization mask at the field junction. Portal images are taken and reviewed. In a darkroom, EDR2 (Kodak) film is cut into a 10cm × 20 cm rectangle, placed in an opaque paper jacket and sealed with black tape. This “mini‐verification film” is taped onto the patient's headrest and the patient is placed supine with the C2–5 vertebral‐body level over the film. An immobilization mask is then placed over the patient's head. The mini‐film is exposed by all three fields during dose delivery. The film is developed and reviewed immediately. Results: Using miniverification film, a field overlap was immediately detected on a patient. Under closer review of the port film, the spinal field was superior to the lead markers at the junction. This mismatch was subtle and not immediately obvious. However, the overlap was striking on the mini‐verification film. Conclusion: Field matching in three‐field Cranial‐Spinal irradiation is critical to avoid underdosing or overdosing the spinal cord. Numerous checks and balance systems should be in place to avoid such field mismatching. The example presented illustrates the effectiveness of the mini‐verification film to discover the overlap. The use of the mini‐film provided immediate and conclusive evidence of patient mistreatment.
SU‐FF‐T‐448: Validation of a New Photon Dose Calculation Model—Analytical Anisotropic Algorithm
Authors: Rong Y , Mubata C , Chisela W , Jaradat H , Tewatia D , Paliwal B
Published: July 2006

Purpose: To validate a new photon dose calculation model Analytical Anisotropic Algorithm (AAA) on Eclipse™ treatment planning system (TPS). Comparison of AAA dose calculation was performed with measurements and other two conventional algorithms, Pencil Beam Convolution (PBC) algorithm on Eclipse™ and Collapsed Cone Convolution/Superposition (CCC) algorithm on Pinnacle3.0 TPS.

Method and Materials: Four phantoms were CT scanned and the image set was imported into both TPS for dose computation and analysis. The four phantoms were: 1) homogenous tissue equivalent phantom, 2) tissue equivalent phantom with infinite lung heterogeneity, 3) tissue equivalent phantom with finite lung, 4) IMRT dose verification phantom. Measurements were made by exposing the phantom using Varian Linac. Point measurement and film measurements were compared with calculated results from the three algorithms. Dose responses for high and low energy photon beams were investigated for several different depths and PDD curves were compared in the phantom for various field sizes. The IMRT plans were generated by both TPS and were performed on the IMRT phantom to compare fluence maps. Results: AAA dose prediction fits the film measurements well except that there is up to ±6% discrepancy for dose profile perpendicular to the interface of tissue and lung. Point measurements support the AAA algorithm calculations. AAA also accurately predicts the decrease in PDD curves due to the lung inhomogeneity for 6MV energy. For the high energy photon beam and very small field size (2cm*2cm) in lung region, AAA prediction is up to 8% lower than the measurements. Conclusion: AAA algorithm accounts for attenuation corrections and electron transport, and models the deposited dose in the lung with greater accuracy than PBC. It is also faster than CCC algorithm. AAA algorithm can not accurately model the lateral scattering in tissue heterogeneity, but it can still give a reasonably close (within ±6%) prediction.
SU‐FF‐T‐449: Validation of a Plan‐Based Calibration Method for Relative Dosimetry of IMRT
Authors: Olch A
Published: July 2006

Purpose: Validation of a new “plan‐based” image calibration method for IMRT relative dosimetry comparisons. Method and Materials: Radiological Imaging Technology image analysis software (version 4.2) contains a new calibration routine called plan‐based calibration (patent pending). After registration of a 2‐D dose image from the planning system with a measured but uncalibrated dose image, the routine then maps the planning system doses to each film or CR image pixel value and constructs a calibration curve. This calibration curve is then applied throughout measurement image to convert all pixels to dose. Because it does not use an independent dose vs. pixel calibration, it can be used for relative dosimetry only. Ten IMRT cases were studied for which both conventional dose calibration using parallel irradiation of film and the plan‐based calibration were used. The Gamma value was used as a measure of agreement where 3% dose and 3 mm distance to agreement were set as tolerances. For these same cases, a 5 mm registration error was introduced and the comparison repeated. Results: In all properly registered cases, the plan‐based calibration had fewer pixels with Gamma >1 than did the conventional calibration. Overall, the plan‐based method gave 50% fewer pixels with Gamma > 1 than did the film‐based calibration. This may be due to additional errors of the film calibration process convolving with intrinsic planning system, phantom setup, and film processing and scanning errors. The plan‐based calibration was equally able to detect the registration error by giving a similarly large increase in percentage of pixels with Gamma >1.

Conclusion: These data suggest that the plan‐based calibration method provides a more accurate comparison of the measured vs. calculated dose distribution than conventional calibration methods using less time and materials. Conflict of Interest: This research was supported by Radiological Imaging Technology.
SU‐FF‐T‐452: Verification of Cell Irradiation Dose Deposition Using Radiochromic Film
Authors: Tomic N , Gosselin M , Wan J , Saragovi U , Evans M , Podgorsak E , Devic S
Published: July 2006

Purpose: A standard technique for cell survival curve determination is based on the cell culture technique. Survival curve is reconstructed by plotting the fraction of surviving cells as a function of delivered dose. We describe a technique that irradiates all cells at once by using two wedges (static and dynamic wedge concurrently) on a linear accelerator whereby we irradiate the multi‐compartmental dish to a desired dose range from 1 – 5 Gy. We also employed EBT model GAFCHROMIC™ film to verify the dose delivered in each of the compartments within the dish. Our technique overcomes the problem of possible contamination during the re‐plating after irradiation and all cells are kept under the same conditions.

Method and Materials: Cells, plated within a multi‐compartmental (8 × 12) dish were irradiated using a 6 MV photon beam employing a combination of 60° physical (“static”) wedge and 60° Enhanced Dynamic Wedge. A 10 cm by 12.5 cm piece of EBT film was positioned below cells. Spatial dosimetry was performed using the AGFA Arcus II document scanner. The change in optical density of the unexposed film piece was subtracted from the exposed film piece to obtain the final netOD that was converted to dose using previously determined calibration curve for the reference type dosimetry. Results: Technique described delivers a dose gradient ranging from 1 Gy within the first compartment to 5 Gy within the last compartment. Maximum relative uncertainty of 2% was observed at 5 Gy. Conclusions: In this work, we describe a technique using a combination of static and dynamic wedge to obtain doses necessary to reliably perform MTT Assay in a dose range from 1 Gy to 5 Gy within a multi compartmental dish. We have also described a method to verify the dose delivered using the EBT model radiochromic film.
SU‐FF‐T‐456: What Is the Optimal Source‐To‐Collimator Distance for An Extendible MLC Designed for Energy‐ and Intensity‐Modulated Electron Radiation Therapy of Superficial Tumors
Authors: Deng J , Chen Z , Roberts K , Nath R
Published: July 2006

Purpose: To determine an optimal source‐to‐collimator distance (SCD) for an extendible multi‐leaf collimator (exMLC) designed for energy‐ and intensity‐modulated electron radiotherapy for superficial tumors. Method and Materials: To implement an extendible Modulated Electron Radiation Therapy (exMERT) technique for optimized radiotherapy of superficial tumors, we designed a virtual exMLC and investigated the effect of SCD on the characteristics of resulting electron beams. An exMLC made of tungsten leaves of 15 mm thickness and 5 mm width and with straight leaf ends was modeled as a MLC component module in EGS4/BEAM simulations. Phase space files were scored at the back surface of the exMLC and at 100 cm SSD for 6 to 20 MeV electron beams emerging from a Varian Clinac 21EX treatment head equipped with exMLC located at SCDs of 85, 90 and 95 cm. These phase space files were then analyzed using BEAMDP and used as beam input for further dose calculations in water. Results: At shorter SCD (85 cm), the in‐air scatter and dose overlapping at depth were the worst compared to other SCDs. The 80–20 penumbra of 1 cm × 1 cm beamlet was 0.92 cm at 100 cm SSD and 1.35 cm at 2 cm depth in water for 6 MeV beam. On the other hand, the leaf scatter and leakage from the exMLC located at 95 cm SCD resulted in larger bremsstrahlung photon dose (∼4% of maximum dose for 20 MeV electrons). Overall, the exMLC at 90 cm SCD yielded modest leaf scatter and leakage as well as dose overlapping at depths, acceptable to clinical applications of exMERT with good clearance for patient setups. Conclusions: Based on the consideration of beam penumbra, photon contamination, and patient clearance, the SCD of 90 cm was determined to be the best compromise for exMLC to be used in exMERT.
SU‐FF‐T‐458: MC Simulations in Support of Developing and Testing An Analytical Dose Algorithm in Ocular Proton Therapy
Authors: Koch N , Newhauser W
Published: July 2006

Purpose: To create a Monte Carlo (MC) model of an ocular proton therapy device, or ocular nozzle, that can predict relative doses to within 3% or 0.5 mm, D/MU values, and be used to develop and commission an analytical algorithm to predict doses and D/MU values to within similar criteria. Methods and Materials: Depth dose profiles and D/MU values were measured in eight ocular proton therapy fields including four unmodulated and four modulated beams using a parallel‐plane ionization chamber in water. Crossfield profiles were measured at three or more depths for each of the modulated beams using film. A MC model of the ocular nozzle was constructed using the MCNPX radiation transport code. After benchmark tests against the measurements, the MC model was used to provide dosimetric data needed to develop a broad‐beam algorithm capable of predicting relative and absolute doses and to test the algorithm's predictions more comprehensively than could be afforded with measured data. Specifically, MC and analytical predictions were calculated and compared in two‐dimensions in a water phantom and in an anthropomorphic model of the eye. Results: Relative depth dose profiles between MC and measurements agreed to within 3% or 0.5 mm. MC predicted D/MU values agreed to within 1% of the measured values. Similarly, the analytical algorithm accurately predicted dose distributions where the predictions were generally within 3% or 0.5 mm of measured and simulated values at water depth > 6 mm. At shallower depths, the analytical model underestimated the dose by approximately 3% to 6%, which MC simulations revealed was due to edge‐scattered protons from the nozzle's collimators. Conclusion: The MC model accurately predicted dose distributions and D/MU values in ocular proton therapy beams. Furthermore, the present work demonstrates the value of the MC method for developing and testing contemporary analytical dose algorithms.
SU‐FF‐T‐465: Relating Changes in Pulmonary Functin Tests (PFTs) to Changes in Radiation‐Induced Regional Lung Perfusion
Authors: Mao J , Zhang J , Zhou S , Folz R , Wong T , Marks L
Published: July 2006

Purpose: To further assess if RT‐induced changes in pulmonary function tests (PFTs) can be prospectively predicted based on the sum of predicted RT‐induced changes in regional lung perfusion. Method and Materials: Between 1991 and 2005, 123 evaluable patients with lung cancer underwent pre‐ and post‐RT PFTs (forced volume capacity [FVC], forced expiratory volume in one second [FEV1] and diffusion capacity for carbon monoxide [DLCO]) as part of a prospective trial. Patients with recurrence or death within 6‐month post‐RT were excluded. The maximal declines in PFTs were noted. The anticipated decline in PFTs was computed by summing the predicted reductions in regional perfusion, throughout the lung, based on a previously‐defined population dose‐response model [DRC] and the patient's pre‐RT SPECT (single photon emission computed tomography) lung perfusion scan. This “integrated response” is also termed the overall response parameter (ORP):
urn:x-wiley:0094-2405:media:mp1379:mp1379-math-0001 where Vd is the percentage volume of lung irradiated to dose d, and Rd is the predicted reduction in regional perfusion at dose d based on a population DRC. Correlations between predicted and measured changes in PFTs were evaluated using 2‐tailed Pearson test. Results: There was a statistically‐significant association between the reduction in PFTs (i.e. FVC and DLCO) and ORP, p<0.01; however, correlation coefficients were low (range: 0.24–0.35). Correlations were better in the subgroup of patients without large central tumors (i.e. those often with associated hypoperfusion of adjacent lung on the pre‐RT SPECT) and with more than 2 follow‐up PFTs post‐RT (range: 0.41–0.62). Conclusion: The sum of predicted RT‐induced changes in regional perfusion is related to RT‐induced changes in PFTs, however, correlations are relatively weak. These findings are consistent with our prior analysis involving fewer patients and continue to illustrate that predicting changes in PFTs is extremely challenging.

Supported partly, by NIH grant R01‐CA69579. Thanks to UNC for PLUNC planning software.
SU‐FF‐P‐01: Management Issues in Implementing IGRT
Authors: Kota C , Craig S
Published: July 2006

Purpose: To investigate and develop an appropriate framework for establishing and monitoring staff competency for IGRT procedures in the community setting. To evaluate existing resources to establish and monitor staff competency. Method and Materials: The full benefit of IGRT can only be realized through the proper deployment of appropriate technology coupled with staff expertise in technical and clinical aspects of IGRT. All of the three main technical processes comprising the treatment chain in IGRT: CT simulation, treatment planning and delivery are greatly increased in complexity compared to 3D CRT. This necessitates the acquisition and monitoring of additional competencies among staff in their technical and clinical skill sets. Management is faced with the challenges of 1. providing competency training for staff and monitoring performance, 2. developing and implementing appropriate policies, procedures and oversight, to ensure the accuracy of IGRT treatments. Anecdotal evidence suggests an accelerating pace of IGRT technology diffusion among community radiation therapy centers. However, there seem to be inadequate formal resources for staff training and competency certification in IGRT procedures, which can hinder the optimal use of the technology in the community setting. In this work, existing frameworks for staff and quality management are examined along with a review of available resources. Experiences of a medium sized community hospital in implementing IGRT are discussed.
SU‐FF‐P‐02: Live Webcast and Video Archiving of Physics Seminars
Authors: Woo M
Published: July 2006

This presentation is to report and promote a webcasting and video archiving project at our cancer centre. We use a commercial system that requires special hardware to be installed in the presentation room, although a portable system is also available to videotape lectures but not for live webcast. The process begins with an email to the invited speaker, explaining the process and requesting his or her permission for the videotaping. Once the speaker agrees to it, the hospital's IS department is notified. All that is required of the IS staff is to enter the basic information on their computer, and then, at the actual time of the seminar, observe the speaker remotely on their TV monitor and adjust the video camera. The speaker image, the audio, together with the screen image of the speaker's presentation computer, will then be broadcast live on the web. To view the broadcast, intended audience will be sent a link in advance. The same link can be used to view the archived seminar afterwards. The archiving is done automatically, with no extra step for the IS staff. For the live webcast, some electronic form of remote audience participation, such as polling and sending questions by email, is available. We have decided that a speaker phone for audience to phone in would be most effective. The whole process is extremely easy to implement and also transparent to speakers, and the feedback has been highly positive. We are in the process of setting up an announcement for upcoming talks, as well as a catalog of archived talks. We encourage the Medical Physics community to participate in the project as audience. We would also like to promote this concept for other centres to set up similar facilities so that information and knowledge could be shared widely.
SU‐FF‐P‐03: Combined Role Of Physicist And Technologist In Optimizing CR, DR Techniques To Meet The Regulations And ALARA!
Authors: Venkataramanan N , Koehler V , Gregorius D
Published: July 2006

With advancement of CR and DR, many facilities are switching from regular FILM‐Screen combination to these new technologies. While manufacturers suggest basic techniques for different projections to be used in the radiography rooms, it is our experience, to notice that, some of the prescriptions may not meet the need. Adjusting to a different technique may make the entrance skin exposures for different projections exceed the regulatory limits. It is the responsibility of the Medical Physicist to make sure that ALARA is met in these situations while making sure that image quality is not compromised. Role of the technologist is very important to optimize the exposures. This paper will discuss the failure part and the necessary problem solving steps. Tables for entrance exposures for Filmscreen, CR and DR will be discussed with optimum techniques used in our institution as a model.
MO‐A‐ValA‐01: The Role of the Physicist in the Planning and Design of Digital Image Management Systems (PACS)
Authors: Langer S
Published: July 2006

The classically trained medical physicist strives to yield maximum diagnostic information from an exam with minimal impact on patient health (i.e. by minimizing dose). This simple objective means that in practice the physicist must: become expert on following the latest technological developments across modalities to assist in equipment purchases, monitor and oversee the imaging protocols used at an institution, and monitor the equipment performance over its lifetime.

As the department transitions to filmless radiology, the mission remains the same, but the scope of implementation increases. The DICOM services that an imager supports are analogous to the filming options supported of yesteryear. The H&D curve of film days maps to the DQE and JND of today's detectors and displays. Quality Control encompasses not only median film density of a laser camera and MTF of a CT, but how those image properties propagate from acquisition to final display device. The key point to realize is the medical physicist is uniquely empowered to have a holistic systems view of the imagers, PACS, RIS and the needs to QC the entire chain.

In this lecture, we will discuss the value add that the medical physicist provides due to the unique collection of training and skills we possess.

Educational Objectives:

1. Compare and contrast the classic role of a medical physicist in the film based department verses the filmless radiology department.

2. Identify the areas of technology and practice where the Medical Physicist adds value.

3. Case studies of cost savings made possible by the practice knowledge that a medical physicist brings to the table that IT staff may not have.
MO‐A‐230A‐01: Monte Carlo I: Source Modeling and Beam Commissioning for Treatment Planning
Authors: Ma C
Published: July 2006

In this presentation, we will discuss source modeling and beam commissioning for Monte Carlo treatment planning. We will review the current status of Monte Carlo simulations of clinical photon and electron beams and the theories and methodologies used in particle phase space representation and reconstruction for Monte Carlo dose calculation. We will discuss the sensitivity of beam characterization to simulation details, such as beam energy, angle, intensity, and details of the treatment head design. We will review different source models for photon and electron beam characterization and discuss the accuracy and efficiency tradeoffs between full phase space and simplified source models. We will describe the methods and software that have been developed for source modeling and beam commissioning for the clinical implementation of the Monte Carlo method for treatment planning and beam delivery verification. We will present different methods for source parameterization based on simulated phase space data and a standard set of measured beam data including in‐air and in‐phantom output factors and in‐phantom dose distributions.

Educational Objectives:

1. Describe the Monte Carlo method for clinical photon and electron beam simulations.

2. Review theories and methodologies for phase space representation and reconstruction.

3. Present different source models for Monte Carlo dose calculation.

4. Describe different methods for source parameterization and beam commissioning.
MO‐B‐330A‐01: Patient Radiation Doses in Diagnostic Imaging
Authors: Nickoloff E , Lu Z
Published: July 2006

The main goal of this presentation is to discuss factors which affect patient radiation dose delivered during various diagnostic radiology imaging examinations and to relate these radiation doses to potential biological risks. Measurement methods to estimate patient radiation doses and some examples of dose reduction for radiography, mammography, fluoroscopy, angiography and CT will be reviewed. Applications of these measurements to patient dose estimation will be shown. Procedures to obtain quick computational estimates of patient doses for IRB submissions, patient inquiries and fetal dose estimations will be provided. Approaches to convert entrance skin doses, dose area products and dose length products to effective doses and risks will be discussed. Typical patient radiation dose values for common diagnostic imaging procedures will be given. Limitations, uncertainties and ranges for patient radiation dose estimates will be examined. The utilization of “reference values” for patient radiation doses will be reviewed. Some guidelines to aid physicists with relating radiation dose issues to the public and informational media will also be included. The material is intended to provide a brief overview of one crucial aspect of the responsibilities with which diagnostic medical physicists and medical health physicists must routinely handle in their jobs. Our expectation is to stimulate introspective assessments and to expand the manner in which patient radiation dose determinations are viewed and performed.

Educational Objectives:

1. To review fundamental X‐ray dosimetry quantities.

2. To identify important factors that affect patient dose delivered by various X‐ray imaging modalities.

3. To describe common methods to measure patient dose and review strategies in developing patient dose charts for routine diagnostic imaging procedures.

4. To examine the limitations of some current dosimetry methodologies.

5. To present a practical guidance to physicists in providing day‐to‐day clinical support service such as IRB submissions, patient inquiries and fetal dose estimations.
MO‐B‐ValB‐01: Advances in MRI Equipment Design, Software, and Imaging Procedures
Authors: Steckner M
Published: July 2006

The advances in MRI technology are relentless. Virtually every aspect of MR scanners is being modified and optimized. There are a myriad number of factors that drive these advances. Clinical requirements are the most obvious and important driver, but are significantly influenced by the clinical setting and/or business model. Is the scanner for a large hospital radiology department, or dedicated interventional procedures scanner, or for an orthopedic, cardiac, pediatric or breast practice or a walk‐in radiological clinic? Each of these market segments places a different relative importance on the various MR system performance specifications. Consequently, the commercially available MR scanners have their own unique operating characteristics as the various MRI vendors seek to satisfy their customers' needs. This lecture will examine some of the various subsystems and discuss selected development trends, such as:

1) Utilization of novel spatial encoding mechanisms to accelerate image acquisition: parallel imaging and the coil spatial response mechanism.

2) Magnet field strength is increasing and physical magnet size is changing: shorter magnets and larger apertures.

3) Increase the effective imaging volume with advances in moving couch methods: the couch becomes another spatial encoding mechanism.

4) Demands on the reconstruction engine are constantly growing: commercial consumer electronic technology advances help provide cost effective, faster solutions.

5) Parallel receive concepts are adapted to the transmit side: transmit‐SENSE. It is not commercially available, yet.

6) More than pretty pictures: numbers. The growth in quantitative MRI and CAD.

While these technology advances are increasing system complexity, flexibility, sequence capabilities, image quality, throughput efficiencies etc, associated technology advances are also mitigating the package footprint and costs.

Educational Objectives:

1. Recognizing the advances in MRI.

2. Understand the technology underlying these advances.

3. Understand the scientific/medical reasons for these advances.

4. Recognize that the commercial implementations are targeted at specific customer segments/requirements.

Conflict of Interest: The author is employed by Hitachi Medical Systems America, Inc.
MO‐B‐224A‐01: Shielding I: New NCRP Report: General Report Background and Formulation
Authors: Deye J
Published: July 2006

This Report was prepared through a joint effort of the AAPM Task Group 57 and the NCRP Scientific Committee 46‐13. It addresses the structural shielding design and evaluation for medical use of megavoltage x rays and gamma rays for radiotherapy and supersedes related material in NCRP Report No. 49, which was issued in 1976.

This first presentation will review the general formalisms used for primary and secondary barrier designs at energies below and above the 10MeV maximum energy that was considered by the old Report 49. While most of the formalisms and data can be found in the published literature, the goal of the report was to bring together in one work all the required methods for shielding modern radiotherapy accelerators. This overview will be followed on the second day by a review of the methods and equipment that are necessary to survey the final facility and then the equations and data presented will be used extensively in the third day's presentation to work a number of detailed example calculations.

Learning Objectives:

1. Understand the history and rationale behind this report.

2. Understand the appropriate use of the equations and data for calculating shielding for medical accelerators.

3. Understand the limitations of the proposed methods.
MO‐B‐224C‐01: Action Levels for IMRT QA
Authors: Palta J , Kim S
Published: July 2006

Each intensity‐modulated radiation therapy (IMRT) field includes many small, irregular, and asymmetric fields that completely obscure the relationship between monitor unit (MU) setting and radiation dose. Uncertainty and inaccuracy of dose delivery with IMRT is primarily attributed to the leaf positioning accuracy, modeling of radiation output for small field sizes, modeling of beam penumbra, and the dose outside the IMRT field. Dose‐difference distribution, distance‐to‐agreement (DTA), and a numerical gamma index are often used to evaluate the quality of agreement between measured and calculated dose distributions for the IMRT fields. The tolerance limits based on these indices for IMRT QA are often not adequate because all these methodologies do not account for space‐specific dose uncertainty information. In other words, single tolerance criterion is applied to all test points even when dose uncertainty is significantly different from point to point. At any given point, the dose uncertainty depends on different levels of dose and gradients from multiple small beams rather than that of the overall dose profile. Therefore, new methodologies are needed that determine dose uncertainties based on the dose level and gradient information of each small field. In IMRT, it is sometimes difficult to have agreement between calculation and measurement of dose at all points in a 3‐D dose distribution. A disagreement at a few points does not necessarily lead to negative overall result if other comparable points are well within the established tolerance limits. We will describe a new approach in establishing tolerance limits and action levels for IMRT QA that will ensure delivery of prescribed radiation dose within an acceptable limit of 5%.

Educational Objectives:

1. To describe the uncertainties in IMRT planning and delivery.

2. To describe the impact of spatial and dosimetric uncertainties on the IMRT dose distribution.

3. To describe the limitations of current methodologies of establishing tolerance limits for IMRT QA.

4. To describe new methodologies for establishing tolerance limits for IMRT QA.
MO‐D‐330A‐05: Cone‐Helical CT Imaging Using the 256‐Row (Cone Beam) CT Scanner
Authors: Mori S , Endo M , Obata T , Tanada S
Published: July 2006

We evaluated Feldkamp artifacts, which are specific to cone‐beam CT, in phantom and clinical studies using the 256 multi‐detector‐row CT (256MDCT), and compared the reconstruction accuracy of axial and helical scans.

Image noise, slice sensitivity profile (SSP) and artifacts with the 256MDCT were evaluated using a phantom and the results were compared to those with a 64MDCT. We also examined chest and abdomen scans produced with the 256MDCT in volunteers.

For the axial scan, Feldkamp artifacts were visualized as high‐frequency streak‐like artifacts that are oriented horizontally at the edge of the scan region in the phantom study. Similar results were obtained with the volunteers in soft‐tissue regions near either bony structures or air pockets. Feldkamp artifacts with the 256MDCT can lead to misdiagnosis if not correctly identified and minimized via helical scanning. Image noise was less for axial than helical scans, while SSP was better with helical than axial scans.

Feldkamp artifacts observed in the 256MDCT images, however, did not generally affect the interpretation of images. The 256MDCT promises more accurate diagnosis, and will provide volumetric cine images of wider cranio‐caudal coverage, enabling new applications of CT.
MO‐D‐330A‐06: Development of the X‐Ray Detector with Sequential Readout Circuits for Multidetector‐Row Computed Tomography
Authors: Konno Y , Okajima K , Ishizuka D , Ueki H
Published: July 2006

Purpose: To develop a low‐cost X‐ray detector with sequential readout circuits, to realize enough low noise for multidetector‐row computed tomography(MDCT), and to evaluate image quality. Method and Materials: We have developed an X‐ray detector that has a MOS‐switch for each pixel, connects many pixels of a common column with the electric readout circuit, and outputs the signals of these pixels from one circuit by turning on lines of switches in order. It has fewer readout circuits than a conventional MDCT detector, but new design is necessary to realize enough low noise for MDCT. First, to make the required noise specific, we simulated the relation of the detector noise and image noise (simulation(A)). Second, to consider how to realize it, we simulated the detector noise with the circuit noise model (simulation(B)). Third, we constructed the detector in order to evaluate its noise. Last, we developed a test CT system with these detectors to evaluate image noise with phantoms. Results: The result of the simulation(A) indicated that detector noise had to be less than about 10‐k rms electrons, and we found to be able to achieve it by optimizing the circuit parameters of the low pass filter and the data line as a result of the simulation(B). We constructed the detectors with these parameters to evaluate these noise, and it turned out that it was about 10.5‐k rms electrons and the required noise was achieved. Moreover, the result to evaluate the noise from images with phantoms indicated that the main was X‐ray quantum noise and the detector noise was low enough to be ignored when the object was a cylindrical water‐filled phantom less than about 30 cm in diameter and the slice thickness of the images was 0.625 mm. Conclusion: We developed a low‐noise X‐ray detector with sequential readout circuits for MDCT.
MO‐D‐330A‐08: Implementing Quantitative Computed Tomography On Multi‐Slice Scanners
Authors: Bligh M , Bidaut L , White R , Murphy W , Stevens D , Cody D
Published: July 2006

Purpose: Implementing Quantitative Computed Tomography (QCT) on Multi‐Slice Computed Tomography (MSCT) scanners requires investigating the effects of axial vs. helical scan modes and protocol parameter variations on quantitative data. While previous work in this area focused on single‐slice axial techniques, technological developments in Computed Tomography (CT) justify more complex assessment. Method and Materials: All scans were obtained using two phantoms designed for bone mineral (BM) densitometry: a reference phantom (three different density cores) and a QA torso phantom. Both phantoms have known properties and are required for long‐term quantitative BM density assessment. The scan acquisition parameters that were varied included kV, mA, rotation speed, pitch, image thickness, detector configuration, reconstruction algorithm, table height, and tube temperature. To assess long‐term scanner drift, the QA Torso phantom was scanned multiple times over three months on each of seven MSCT scanners (five GE Lightspeed‐ 16s, one GE Lightspeed Qx/i, and one GE Lightspeed‐Plus). The daily variability of the individual MSCT scanners and scanner‐to‐scanner variability was determined by coefficient of variation (mean/variance) from the QA Torso phantom data sets over time. All data were collected and analyzed in Hounsfield Units (HU) to provide insight about variations upstream of the actual BM density analysis through commercial software. Results: This study found no significant difference (p > 0.05) in mean HU between phantom images obtained using axial and helical scan mode, or when varying most of the other scan acquisition parameters. However, varying kV and reconstruction algorithm did result in significant (p<0.0001) quantitative shifts. Preliminary data indicated daily variability of 0.8% – 1.9% and scanner‐to‐scanner variability of 1.4%.Conclusion: MSCT systems can be optimized for use in determining the BM density of a vertebral body, provided very careful control of scan acquisition protocol is observed.
MO‐D‐330D‐01: Molecular Imaging I: The Physics of Molecular Imaging
Authors: Cody D , Stickel J , Johnson G , Boone J
Published: July 2006

The first day of the Molecular Imaging Symposium (MI‐1) will focus on the technology aspects of molecular, functional, and small animal imaging. Modalities which will be discussed include micro‐CT, micro‐PET, and high resolution MRI for small animal imaging. The presentation on micro‐CT technology will include an introduction to the basic requirements of the scanner hardware, examples of the images and biological applications in which micro‐CT is useful, and the radiation dose to the small animal undergoing micro‐CT will also be discussed. Micro‐CT techniques require longer acquisition times than human scanners, and thus maintaining the animal in a viable but motionless state is of clear importance. Therefore, issues surrounding animal support including anesthesia and respiratory gating will also be presented.

Micro‐PET systems are widely used in small animal imaging for genome research, and represent probably the mainstay of truly molecular imaging modalities at this point in time. The presentation on micro‐PET will include a description of micro‐PET scanner hardware, a discussion of PET‐radiotracers, and an overview of current small animal PET systems. The limitation of current micro‐PET system design will be discussed, and ideas for overcoming some of these limitations will be presented.

High resolution MRI systems have the benefit of delivering exquisite contrast with excellent spatial resolution, with no ionizing radiation. The presentation on micro‐MRI techniques for phenotype imaging will describe the integration of physics, biology, chemistry, engineering, and computer science which is necessary to achieve state‐of‐the‐art small animal MRI imaging. The use of hyperpolarized gases for lung imaging and MR histology will be discussed as well.

The availability of small animal imaging systems across a number of modalities has proved essential for a large number of research applications. The primary goal of MI‐1 is to help familiarize medical physicists with the technical design and capabilities of these high resolution small animal imaging systems, and to highlight research applications of their use. Different modalities are used to address different research questions, and this symposium will emphasize the strengths and weaknesses of each modality in regards to various research applications. Differences between animal imaging and human scanners will also be discussed.
MO‐D‐ValB‐02: OpenGL Based 2D‐3D Registration of a CT Image Dataset With OBI Images
Authors: Choi B , Balter P , Dong L , Mohan R , Starkschall G
Published: July 2006

Introduction. A limiting factor in registration of a three‐dimensional (3D) computed tomography (CT) dataset with two‐dimensional (2D) x‐ray images has been the time‐consuming generation of digitally reconstructed radiographs (DRRs). This can be overcome using a commercial graphics card for DRR generation enabling fast, robust, and accurate automatic image‐based 2D‐3D registration. Methods and Materials. For the iterative registration process hundreds of DRRs are created using hardware rendering in OpenGL. Each DRR from a 512×512×100 CT volume is rendered in less than 0.1 seconds using an nVidia 7800GT graphics card. The registration is based on a publicly available implementation of Mattes Mutual Information (ITK, U.S. National Library of Medicine, Bethesda, MD). To improve speed, the registration is performed on a sub‐image. A two‐step registration strategy is adopted for robustness with the first pass using a larger margin around the sub‐image and a down‐sampled resolution. A thoracic phantom (Model 602, CIRS, Norfolk, VA) was imaged and setup according to our clinical protocol and then shifted from 0–1.5 cm along each of the major axes. Anterior‐Posterior and Lateral kV x‐ray images were acquired using a commercial patient imaging system (OBI, Varian Medical System, Palo Alto, CA). Results: The mean registration times were 8 and 16 seconds without and with rotations respectively. We observed a systematic 1.1 mm offset in the longitudinal direction that we believe results from 2.5 mm CT slice spacing and OBI calibration. With this removed the mean three‐dimensional distance of the registered positions from the phantom positions was 0.4 mm with the largest disagreement being 0.75 mm. The systems ability to calculate rotations was only tested numerically.

Conclusions. The speed and accuracy of this system demonstrate that it could be a viable tool for reducing daily setup uncertainty by automating the analysis of setup images.

Research sponsored by Phillips Medical Systems.