bluuebunny/crossref_metadata_2025_split huggingface dataset:
SU‐FF‐T‐37: A Primer On Plasma Wakefields: A New Method of Particle Acceleration
Authors: Obcemea C 
Published: July 2007

Objective: We present in this paper a pedestrian, pedagogical introduction to the basic concepts, physical mechanisms and recent breakthroughs in the use of plasma wakefields as a completely new method of particle acceleration. This new method is attractive because it offers the possibility of really compact accelerators as electron, proton and ion beam sources; although here we focus on electrons. We describe the original ideas, basic equations and recent experimental results. Since the medical physics community is more familiar with RF microwave technology and concepts than those of plasma physics, we believe this primer would be useful and instructive. Summary: Finding new ways to accelerate particles has been a Holy Grail eversince it was realized 25 years ago that RF technology could only get to a theoretical limit of 100MeV/m field gradient. Past that, waveguide electrical breakdown and beam instability are insurmountable(1). The seminal work of Tajima‐Dawson (2–3) showed however that plasma, being fully ionized media can support much higher gradients, and when excited by short, high‐intensity laser pulse or similar electromagnetic pulse, can generate wakefields that can trap and accelerate the plasma electrons to fields as high as 10GeV/cm. With such high accelerating fields, particles can gain huge energy over very short distance. The 2‐mile SLAC accelerator can thus be shrunk into a few meters, a medical linac “waveguide” into about a millimeter.We describe the basic equations characterizing a plasma, its parametric instabilities, and dispersion relations as response to any incoming disturbance. We derive the ponderomotive force(fig.1–3)(exerted by the incident laser/electromagnetic pulse on the plasma), which generates the wakefields (much like a moving boat would generate wakes along its trail) and show analytically how these wakefields trap and accelerate the plasma electrons. Finally, we describe several important breakthroughs(4–6,fig.4) as proofs‐of‐principle and advances towards a real, practical accelerator device.
SU‐FF‐T‐41: A Simple Algorithm to Account for Inter‐Seed Effects in the Dose Calculation of Prostate Implant Brachytherapy
Authors: Gao M , Sethi A , Rusu I , Xu M , Ke Y , Glasgow G 
Published: July 2007

Purpose: For multi‐seed implant, dose calculation (TG‐43) is based on the superposition of doses from each source, i.e. attenuations of neighboring seeds are neglected. Monte Carlo (MC) and measurements showed that inter‐seed effects reduce dose coverage by up to 10%. However, MC is too time‐consuming for clinical practice. We developed a simple algorithm to include inter‐seed effects. Method: Seed is treated as a three‐segment line with different attenuations in the center and edge segment. Attenuation of an active source by a neighboring seed exists in the triangular shadow formed by the seed (line) and the source center (point). Effective lengths and attenuations for each segment (LC, LE, μC, μE) are obtained through best fit to published MC data.I‐125 seeds (model 6702 and 6711) are investigated. For the fit, four parallel coplanar seeds are configured 0.75cm apart, one as active source and other three as neighboring seeds. Doses at forty‐eight grid points are calculated and fitted. To test the generality of fit results, another configuration of four seeds 0.5cm apart is calculated and compared. Results: For 6711, LC=0.38cm & LE=0.11cm and μC=0.47 & μE=0.81. Total effective length (0.60cm) is slightly longer than its physical size (0.46cm) due to perturbation at edge. Averaged over all points, calculated inter‐seed factor is 0.77 as compared with 0.80 from Monte Carlo.For 6702, LC=0.12cm & LE=0.23cm and μC=0.83 & μE=0.71. In contrast to 6711, center segment is shorter and less attenuating because 6702 uses three small spheres while 6711 uses a 3mm wire. Averaged inter‐seed factor is 0.88 (algorithm) as compared with 0.87 (MC).For 0.5cm configuration, fit results lead to inter‐seed factor of 0.64 (0.61 MC) and 0.80 (0.77 MC) for 6711 and 6702 respectively. Conclusion: Neglecting inter‐seed effects may significantly overestimate dose. A simple algorithm was developed and reasonable accuracy is achieved.
SU‐FF‐T‐200: Establishment of Japanese QA Booklet in Permanent Prostate Implant Brachytherapy
Authors: Takahashi Y , Sumida I , Sato T , Oita M , Hashimoto M , Nakamura Y , Mizuno H , Okumura M , Hoshina M , Inaba M , Ebihara H , Amano K , Yamashita T , Dokiya T 
Published: July 2007

Purpose: I‐125 permanent implant brachytherapy for prostate cancer was approved in Japan in 2003, and is now offered by an increasing number of hospitals. Although existing QA guidelines (AAPM or ESTRO) in this therapy are well documented, many Japanese hospitals required more detail procedures, because of the shortage of medical physicists. In addition, it is important to supply reliability on clinical evidence in the future clinical trial in Japan. The purpose of this study is to establish new Japanese QA booklet which dedicates clinical practice. Materials and Methods: We first investigated several brachytherapy QA guidelines in western countries including AAPM reports or ESTRO booklet. Then we confirmed the procedures one by one by performing QA in our hospitals and made the resulting problems clear. After that, we determined QA items. To support QA, we developed the software for commissioning of brachytherapy treatment planning system (TPS). Results: The feature of this booklet is that (1) Much easier to understand by using many figures or examples. (2) For QA which requires expert knowledge including point dose calculation check in the commissioning of TPS, we developed software to support users. (3) The QA items were classified into two categories. Namely, category ‘Must’ indicates a recommendation that is necessary to be executed at least as a prevention of accidents, and category ‘Recommend’ indicates an advisory recommendation to keep quality of implant. (4) Items of acceptance testing and the detail procedures were described in detail to promote vendor acceptance test in the Japanese agencies. (5) Each sentence 2447_2was itemized so that users can easily read and understand. Conclusion: We established very practical Japanese QA booklet for permanent implant brachytherapy. This booklet can be helpful worldwide.This study was supported by a Grant‐in‐Aid for Cancer Research (17‐10) of Ministry of Health, Labor and Welfare.
SU‐FF‐T‐213: Evaluation of Dose From TomoTherapy Irradiation of Superficial PTVs
Authors: Cheek D , Hogstrom K , Gibbons J , Rosen I 
Published: July 2007

Purpose: To evaluate the accuracy of dose calculated by the TomoTherapy HI⋅ART treatment planning system for superficial planning target volumes (PTVs). Methods and Materials: TomoTherapy treatment plans were developed for three superficial PTVs (2−, 4−, and 6−cm deep radially by 90° azimuthally by 4−cm longitudinally) contoured on a 27−cm diameter cylindrical white opaque, high‐impact polystyrene phantom. The phantom included removable transverse and sagittal film cassettes. Kodak EDR2 films were cut using templates to match the phantom surface (±0.5mm). The phantom was aligned to the machine's isocenter (±0.5mm), and films were irradiated according to the treatment plans. Films were then scanned with a Vidar film digitizer and converted to dose using a calibration determined from a 6 MV perpendicular film exposure. Hence, axial film doses were scaled by 1.027 so that mid‐arc depth doses matched those measured in the sagittal plane. All film readings were scaled by 0.934 to correct for over response due to phantom Cerenkov light. Measured dose distributions were registered to calculated ones and compared. Results: For all PTVs, at depths less than 10mm calculated overestimated measured doses by as much as 8%. At depths greater than 10mm, the calculated and measured doses agreed to within 5%. In the dose falloff region, measured and calculated dose distributions agreed to within ±2mm. The calculated dose in the low dose region distal to the PTV was lower by as much as 2%. Each of these differences is related to an assumption in the dose model. Conclusion: Calculated dose distributions showed good agreement with measurement for depths greater than 10mm. For more superficial depths, the dose model should be carefully evaluated or one should use bolus of at least 10mm to ensure accurate calculated dose to superficial PTVs.Supported in part by a research agreement with TomoTherapy, Inc.
SU‐FF‐T‐217: Evaluation of the Dosimetric Accuracy of a Commercial Adaptive Radiotherapy Process
Authors: Hesston R , Gibbons J , Cheek D 
Published: July 2007

Purpose: To evaluate the dosimetric accuracy and reproducibility of the TomoTherapy Planned Adaptive system using MVCT datasets. Method and Materials: Comparisons were made between reference dose distributions computed with the TomoTherapy treatment planning system (TPS) and verification dose distributions computed on the TomoTherapy Planned Adaptive (PA) system. Both calculations were performed on TomoTherapy megavoltage CT (MVCT) datasets to eliminate differences associated with variations in CT‐density tables. Simulated PTVs drawn on an MVCT of an anthropomorphic radiosurgery head phantom (CIRS, Inc.) were used as input to calculate doses on the TomoTherapy TPS. After plan optimization, a post‐plan MVCT image was taken and used to calculate dose on the TomoTherapy PA system. Initially, calculations were made using the same MVCT dataset as input to both programs to investigate the agreement between the algorithms. Next, calculations were made using registered pre‐ and post‐plan MVCT images to investigate the variation with MVCT datasets. Comparisons were made using the tools available on the PA system and in‐house software to compare doses outside of contoured structures. Results: For calculations on identical datasets, isodose and DVH comparisons between the TomoTherapy TPS and PA systems showed insignificant dose differences (< 0.2%) to all contoured structures. Dose discrepancies within the phantom but outside of contoured structures showed slightly larger variations, although well within 0.5%. Similar results were found for dose calculations using different MVCT datasets. In both cases, the doses computed in air outside the phantom showed the largest differences (up to 21%). Conclusion: Comparisons between TomoTherapy's TPS and PA system MVCT dose calculations showed clinically acceptable agreement everywhere within the phantom. Differences between doses calculated in air are due to differences in the way the algorithms mask low density voxels.Research sponsored by TomoTherapy, Inc.
SU‐FF‐T‐257: IMRT Optimization Using a Shifted CTV‐Based Objective Function
Authors: Nguyen TB , Thomas SJ , Hoole ACF , Burnet NG 
Published: July 2007

Purpose: The Planning Target Volume (PTV) is used to ensure that the CTV is adequately covered with the prescribed dose despite geometric uncertainties. Clinically, a plan is acceptable if the 95% isodose surface covers the PTV; therefore the objective function is currently formulated based on PTV for IMRT optimization. This study investigates the feasibility of using a CTV‐based objective function for IMRT optimization in shallow tumors where the PTV extends into build‐up region. Method and Materials: For a selected shallow tumor (Head & Neck) case, a conventional IMRT plan was optimized with a PTV‐based objective function using Newton's algorithm. The CTV‐PTV margin was 10mm. Additionally, a CTV‐based objective function calculated from 6 different isocenter shifts (10mm positive and negative on each axis) was used for optimization to generate another plan. To ensure that the treatment plan is acceptable for the whole range of possible movements, the resultant objective function is formulated so that the worst plan among shifted plans is acceptable:
urn:x-wiley:00942405:media:mp0918:mp0918-math-0001The PTV DVH and CTV DVHs were analyzed for both plans. Results: Using PTV‐based optimization results in better PTV coverage than that of CTV‐based optimization: V95=93.4 % in comparison with V95=80.9%. However, in the case of CTV‐based optimization, the maximum dose of the CTV for all isocenter shifts is less than 108% in contrast with 136% using PTV‐based optimization. Furthermore, the intensity patterns from the CTV based optimization plan are less complex than those from the PTV‐based optimization.Conclusion:The current method of optimization using a PTV‐objective function might lead to an overdosage of the CTV for shallow tumors due to the build‐up region. The CTV‐based objective function has been shown to be a possible solution in reducing the skin dose with IMRT optimization for shallow tumors where the PTV extends into the build up region.
MO‐A‐M100J‐03: Performance Evaluation for New‐Technology CT Systems: Cone Beam C‐Arm CT
Authors: Fahrig R 
Published: July 2007

Conebeam CT using C‐arm mounted large area flat panels (FPs) is becoming more commonly used in neuro‐ and body‐interventional suites. The ability to visualize vascular geometry in 3D along with soft tissue during an intervention is providing information that may increase accuracy, shorten procedure time and may even change the course of treatment. However, acquisition of the projection data required for volume imaging requires dose to the patient, and understanding the trade‐offs between acquisition parameters, dose and image quality is critical to the appropriate adoption of this imaging technique.Unlike conventional CT, the beam length in conebeam CT can cover the entire length of the object to be imaged or can be varied with the use of collimation, and the concept of CTDI is not, therefore, the metric of choice for measurement of dose. In addition, most C‐arm conebeam CT systems use a short‐scan (pi plus fan‐angle) acquisition, and the dose distribution within the object is not cylindrically symmetric. Finally, since FP design has been optimized for fluoroscopy, image quality when used for CT must be carefully evaluated.This lecture will describe a dose metric that is appropriate for conebeam CT and allows direct comparison with the CTDIw of conventional CT. A perception study using the CATPHAN 600 phantom for a range of acquisition parameters will be described, and the relationships between kVp, image noise, dose and contrast perception will be discussed.Research sponsored by Siemens Medical Solutions AG, AX Division, by NIH grant R01 EB003524 and by the Lucas Foundation.Educational Objectives:1. Understand how differences in acquisition geometry between conebeam and conventional CT affect dose distribution and dose measurement.2. Understand how contrast perception in conebeam CT images depends on acquisition parameters.
MO‐A‐BRA‐01: New NCRP Report: General Report Background and Formulation
Authors: Deye J 
Published: July 2007

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‐L100E: Magnitude of Medical Radiation Exposures to US population: Preliminary results from NCRP Scientific Committee 6‐2
Authors: Mahesh M 
Published: July 2007

National Council of Radiation of Protection formed Scientific Committee 6.2 to work on the estimation of radiation exposure to the US population from all sources. The intended goal of the Committee is to update the NCRP report 93 published in 1987. One sub group of the sub committee was assigned with the medical exposure. The medical sub committee comprised of medical physicists, physicians, and other health physics experts.The subcommittee examined variety of data sources including commercial surveys, Medicare, Veterans Administration and insurance carrier data. Radiation exposure to the US population from medical exposures was then estimated based on the number of medical procedures grouped by modality and body parts and the radiation doses associated with each procedure. The modality groups were CT, nuclear medicine, radiography, general and interventional fluoroscopy, dental radiography, bone‐densitometry and radiation therapy.According to the preliminary results, the medical radiation exposure to US population has increased by nearly 6 times compared to the previous NCRP publication (NCRP 93). The conventional pie‐chart indicating 3 mSv from background radiation and 0.6 mSv from man‐made (medical) exposure will undergo major shape change as these preliminary results are finalized. The largest contributor to the collective dose to US population is seen with CT and Nuclear Medicine. CT scanning has increased nearly 10–11% annually in the US in the past two decade. The number of CT procedures has increased from 3 million CT scans in 1980 to more than 62 million CT scans in 2006. Similarly, the nuclear cardiac procedures have increased significantly in the last two decades.The purpose of this talk is to provide an update on the results from the medical patient exposure subcommittee and to discuss the details on how the results were derived.Learning Objectives:1. To learn about the magnitude of medical radiation exposure to US population.2. To familiarize with the types and distribution of medical imaging procedures in US.3. To understand methods used in computing the radiation exposures to US population.
MO‐D‐L100J‐01: True 3D Contouring Via Efficient Spline Representation of Anatomy
Authors: Hibbard L , Han X , Brame S 
Published: July 2007

Purpose: To make anatomy contouring more efficient by integrating contours drawn in any combination of transverse/sagittal/coronal (T/S/C) views and reconstructing the T contours from the surface defined by the drawn contours so that the user may draw/edit until the object is completed. Method and Materials: Our program performs the surface reconstruction by thin‐plate spline interpolation of points in the drawn contours. The surface is reconstructed as a variational implicit function, and runs in real‐time because we abstract the most shape‐informative points from the input contours. These points correspond to maxima in one of several functions of the second derivatives of the contour functions. We demonstrate contouring results for one of these methods—the scalar second derivative of the curve function. Before abstracting the shape salient points, contours are re‐computed to have consistent rotational directions, and to have origins placed consistently in the patient coordinate system. Since the contours' points are non‐uniform samples of the curve, each contour is reconstructed, using all input points, by B‐spline interpolation to resample the curve uniformly along the its length to compute the derivatives by finite differences. Results: We demonstrate in the supporting document: 1) the operation of the shape abstraction algorithm, and 2) the production of contours approximating the prostate from a single S and C contours, and 3) the production of contours in 270 T sections of a spinal canal from a single S and 4 C contours. Conclusion: We have developed a contouring program that integrates drawn contours in any combination of T/S/C views to create a coherent surface that is clipped to produce T contours at the appropriate image planes, so the user can and assess how much more drawing or editing is needed to make a satisfactory match to object boundaries visible in the image.Sponsored by CMS, Inc.
MO‐D‐BRB‐02: Challenges of Introducing New Technology Into the Clinic
Authors: Klein E 
Published: July 2007

Implementing new technologies into the clinic is challenging on many levels. Besides the obvious manpower issues, physicists are challenged with; unreasonable timelines driven by market competition, technical staff acceptance, incompatibilities of devices provided by multiple vendors, and the lack of opportunities for proper education. Vendors have capitalized on the open purse‐strings hospitals provide due to the healthy reimbursement for IMRT and IGRT (daily localization). Physicist must use tools such as the Abt studies to negotiate proper staffing before the technologies arrive. During this talk we will review some simple methods to justify staffing. Physicists should set realistic timelines that depend on the agreed on staffing levels including IT assistance, and on compatibility of all systems involved. We will review timelines that have been suggested for given technologies, along with time efforts from Washington University, including, MLC‐IMRT, Tomotherapy, OBI, CBCT, video surface imaging, gating, US localization, etc. Physicists must be the key decision makers in choosing a team of technical staff personal to be the initial implementers. We have found the initiation of a new technology is smoothest if the dosimetrists and therapists first involved are pro‐active and capable of implementing a new technology. Procedure writing should be a team effort to ensure there is ownership. Ongoing continuing education and scheduled migration of other support staff to operating the new technology should be the responsibility of the physicist in charge of the device or technique. This includes re‐education of all involved for new software releases or new processes. As daily localization empowers therapists to make decisions on shifting patients, physicists should work with clinicians to decide; what is the minimum shift required for a shift to take place, when is the shift too much, and whether re‐evaluation is required. Our protocols will be discussed. And finally, physicists should ensure they receive proper training beyond what the vendor provides. This may be in the form of legitimate courses and workshops, or visits to institutions using the new technology. To this end, the physics and radiotherapy community should address how new physicists (residencies), dosimetrists (MDCB), and therapists (testing out) are being trained and evaluated, and how experienced personal are being re‐trained for our new environments.Learning Objectives: From this lecture, the physicists will learn how to:1) estimate manpower needs,2) formulate implementation timelines and tasks,3) obtain the education necessary for the new technology.