bluuebunny/crossref_metadata_2025 huggingface dataset:
TU‐D‐I‐611‐05: Monte Carlo Investigation of Scatter Contribution to Kilovoltage Cone‐Beam Computed Tomography Images
Authors: Jarry G , Moseley D , Jaffray D , Verhaegen F
Published: June 2005

Purpose: In this work, we evaluate the scatter radiation present in projection images produced by kilovoltage (kV) cone‐beam computed tomography (CBCT) using Monte Carlo (MC) calculations. We also demonstrate that MC simulations can be used to reduce scatter in kV CBCT reconstructed images. Method and Materials: All images were acquired using a kV CBCT bench‐top system composed of an x‐ray tube, a rotation stage and a CsI flat‐panel imager. The EGSnrc MC code was used to fully model the flat‐panel imager and the x‐ray source for energies of 80, 100, and 120 kVp. The x‐ray source model was validated using first and second half‐value layer (HVL) and profile measurements. MC simulations and measured images were obtained for a cylindrical water phantom and for the head of the anthropomorphic Rando phantom. A modified version of the DOSXYZnrc program was used to score phase space files with identified scattered and non‐scattered particles after the phantoms. The cone angle and the source‐to‐detector distance (SDD) were varied during the simulations to determine their effect on scatter radiation in projection images. MC predictions of the scatter distribution were subtracted from the CBCT projection images prior to the reconstruction to improve the reconstructed image quality. Results: The simulated and measured first and second HVL agree within 2% except for the 80 kVp beam where the agreement is within 9%. The measured and simulated profiles agree within 4%. Simulated and measured projection images are in good agreement. Decreasing the cone angle and increasing the SDD decrease the amount of scatter. On the other hand, the phantom geometry has little effect on the scatter radiation distribution. Conclusion: MC simulations were used to characterize the scatter radiation from different geometries. It was shown that it is possible to use MC simulations to reduce the scatter in the reconstructed image.
TU‐D‐I‐611‐06: A Direct, Empirical Method for X‐Ray Scatter Correction in Digital Radiography and Cone‐Beam CT
Authors: Siewerdsen J , Bakhtiar B , Moseley D , Richard S , Keller H , Daly M , Jaffray D
Published: June 2005

Purpose: X‐ray scatter poses a severe physical limitation to image quality in cone‐beam CT (CBCT), resulting in contrast reduction, image artifacts, and lack of CT number accuracy. We report and demonstrate the performance of a novel scatter correction method in which scatter fluence is estimated directly in each projection from pixel values at the edge of the detector behind the collimator leaves. Method and Materials: The algorithm operates on the assumption that signal behind the collimator leaves is attributable to x‐ray scatter. The 2D scatter fluence is estimated by interpolating between pixel values measured along the top and bottom edges of the detector behind the collimator leaves. The resulting scatter fluence is subtracted from each projection to yield primary‐only images for CBCT reconstruction. Performance was investigated in phantom experiments on an experimental CBCT benchtop, and the effect on image quality was demonstrated in patient images (head, chest, and pelvis sites) obtained on a preclinical system for CBCT‐guided radiation therapy. Results: The algorithm provides significant reduction in scatter artifacts without compromise in contrast‐to‐noise ratio (CNR) — e.g., Head: cupping reduced from 10% to 2%, while breast‐to‐water CNR improved from 5.2% to 7.8%; Body: cupping reduced from 42% to 26% without change in CNR. Patient images demonstrate increased uniformity, accuracy, and contrast, with slightly increased noise (net increase in CNR) in all of the sites investigated. Qualitative evaluation illustrates that soft‐tissue structures that are otherwise undetectable are clearly delineated in scatter‐corrected reconstructions. Conclusion: The algorithm provides a robust method for x‐ray scatter fluence estimation and correction in CBCT. Operating from a single assumption without prior information, analytical modeling, or Monte Carlo, the technique is easily incorporated as a preprocessing step in CBCT reconstruction. Quantitative evaluation in phantoms and pre‐clinical evaluation in patients demonstrates significant artifact reduction without degradation in CNR.
TU‐D‐I‐611‐08: Cone Beam X‐Ray Scatter Removal Via Image Frequency Modulation and Filtering
Authors: Bani‐Hashemi A , Blanz E , Maltz J , Hristov D , Svatos M
Published: June 2005

Purpose: To develop a rapid method of patient scatter removal from cone beam (CB) projection images that requires no scatter measurement, physical modeling or strong assumptions regarding the spatial smoothness of the scatter distribution. Method and Materials: A modulator grid is placed between the imaged distribution and the detector that differentially frequency modulates primary and scattered photons. When photons travel through the grid, photons that originate directly from the CB source are modulated by a higher frequency than scattered photons that have more proximal, diffusely distributed sources. We employ non‐linear Fourier domain filtering to attenuate the contribution of scatter to the image spectrum. The theoretical validity of the method is verified using linear analysis of planar sources and its performance is evaluated using a simulator based on this analytical model. Results: Simulation experiments with an ideal modulator indicate that even unrealistically large amounts of scatter are almost entirely removed by this method. The recovered images are devoid of major artifacts and exhibit an RMS error of 10%. Conclusion: A disadvantage of the technique is that it will always produce a filtered image having at best 0.41 of the maximum detector resolution when maximum scatter rejection is desired. This is not a major issue in most medical X‐ray CB imaging applications using contemporary detector technology, especially since scatter often significantly reduces useful resolution. Conflict of Interest: Supported by Siemens Medical Solutions USA, Inc.
TU‐D‐J‐6C‐05: Investigation of the Actually Delivered Patient Dose in Lung IMRT Treatment Based On Deformable Registration of 4D CT Data and Monte Carlo Simulations
Authors: Flampouri S , Sharp G , Wolfgang J , Niemierko A , Choi N , Jiang S
Published: June 2005

Purpose: To accurately calculate the difference between prescribed and delivered dose caused by respiratory motion and artifacts in free breathing helical CT (fbCT) for lung IMRT treatments, and to estimate the impact of this difference in clinical outcome. Method and Materials: Ten cases were studied. For all patients, fbCT and 4DCT reconstructed at 10 phases of the respiratory cycle were available. Patients were selected to have a wide range of tumor motion, size, and position. CORVUS was used to make two IMRT plans calculated on the fbCT for GTV (volume determined on fbCT) and ITV (volume determined by 4DCT) targets respectively. The prescribed dose was 60Gy. The fluence maps and beam setup parameters of the IMRT plans were used by the Monte Carlo dose calculation engine MCSIM for absolute dose calculation on free breathing and 4DCT data. CT deformable registration between the breathing phases was performed and the composite dose over the whole breathing cycle was calculated for the GTV, CTV and lungs. EUD and TCP/NTCP values were determined for the composite dose over the whole breathing cycle based on both plans. Results: For a patient with 4 cm peak to peak tumor movement, a planned CTV EUD of 58 Gy was reduced to 54Gy and 33Gy respectively for the composite 4D dose distribution of ITV and GTV plans. 3‐year control estimates for this patient, assuming that 3‐year local control after 60Gy in the GTV is 30%, were reduced to 29% and 23% for the ITV and the free breathing plans respectively. Conclusion: With the advent of 4DCT, CT data deformable registration and Monte Carlo dose calculations, it is feasible to accurately calculate in retrospect the actually delivered dose and compare it with what historically was assumed to be delivered.
TU‐D‐J‐6C‐06: 3D Respiratory Motion Estimation From Slowly Rotating 2D‐Xray Projection Views
Authors: Zeng R , Fessler J , Balter J
Published: June 2005

Purpose: To more directly model changes in patient configuration due to respiratory motion during gantry rotation for “4D” cone‐beam CT (CBCT). Method and Materials: The process takes advantage of the similarity between the patient at treatment and their model from a prior (planning) CT scan. A reference thorax volume is obtained from a conventional fast CT scanner under breath‐hold conditions. At treatment, a sequence of projection views of the same patient is acquired using a slowly rotating cone‐beam system, which takes 1 minute for a full rotation. Breathing motion over the entire acquisition period is estimated by deforming the reference volume through time to best match the measured projection views. A B‐spline based motion model is used to describe free breathing motion. Optimized parameters of this model (by minimizing a regularized square error cost function) determine the motion of each point of the object at any time within the scanning period. Performance of this approach was evaluated by simulation, in which a 128×128×40 reference thorax volume and a 3D cone‐beam geometry were used to generate 12 projection views of one breathing cycle. Results: Results showed good agreement between the estimated and true motion. A 30‐degree angular rotation during one breathing cycle (5 seconds) yielded a mean absolute estimation error (MAE) of 0.7 mm (maximum 2.1mm). A 360‐degree angular rotation yielded MAE of 0.4mm (maximum 1.3mm). Conclusion: It is feasible to estimate non‐rigid motion from a sequence of slowly rotating projections. Improved accuracy with increased angular range indicates advantages of faster rotation or limited periodicity constraints. Supported by NIHP01‐CA598
TU‐D‐T‐617‐04: Dose Rate Constant of the Cesium‐131 (model CS‐1) Interstitial Brachytherapy Seeds Measured by Thermal‐Luminescent Dosimeter (TLD) and by Gamma‐Ray Spectroscopy
Authors: Chen Z , Bongiorni P , Nath R
Published: June 2005

Purpose: To measure the dose rate constant of the model CS‐1 low‐energy interstitial brachytherapy seeds containing . Method and Materials: Eight seeds were obtained from the seed manufacture (IsoRay). The air‐kerma strength of each seed was measured by the manufacture whose dosimeter calibration is traceable to the air‐kerma strength standard established for the seeds at NIST (1σ uncertainty < 1%). The dose rate constant of each seed was measured by two independent methods: One based on the actual photon energy spectrum emitted by the seed using gamma‐ray spectroscopy and the other based on the dose‐rate measured by thermal‐luminescent dosimeter (TLD) in solid‐water phantoms. Results: The dose rate constant in water determined by the gamma‐ray spectroscopy technique and by TLD dosimetry are 1.066± 0.049 Gyh−1U−1 and 1.069 ± 0.096 cGyh−1U−1, respectively, showing excellent agreement with each other. These values, however, are approximately 15% higher than a previously reported value of 0.915 cGyh−1U−1 (Med. Phys. 31, 1529–1538, 2004). Since the average photon energy emitted by is on the order of that emitted by , the previously reported value could only be possible if the seeds had generated a significant amount of lower energy fluorescent x‐rays. Fluorescent x‐rays at 16.6 and 18.7 keV originating from Niobium in the seed construction were indeed measured in the energy spectra but their yields were not sufficient to lower the dose rate constant to 0.915 cGyh−1U−1. Conclusion: The dose rate constant of the model CS‐1 seeds was carefully determined using two independent methods. A large discrepancy (> 15%) was observed against a previously reported value. Additional determination of the dose rate constant may be needed to establish an AAPM recommended census value.
TU‐D‐T‐617‐05: TG‐43U1 Based Dosimetric Characterization of Model 67‐6520 Cs‐137 Brachytherapy Source
Authors: Wright C , Duncan R , Rachabatthula V , Koona R , Meigooni A , Baker C
Published: June 2005

Purpose: Dosimetric characteristics of a newly designed Cs‐137 source (Model 67‐6520) by Isotope Product Laboratories were determined using experimental and theoretical methods. These determinations were performed using TG‐43U1 for distances larger than the active length of the source and along‐away matrix for shorter distances. Method and Materials: Radial dose function, dose rate constant, 2D and 1D anisotropy function of the new Cs‐137 source were determined following updated AAPM Task Group 43 (TG‐43U1) recommendations. The experimental setup used for the determination of these parameters consisted of 1.0 × 1.0 × 1.0 mm3 and 3.2 × 3.2 × 0.89 mm3 TLD‐100 LiF thermoluminescent dosimeters in Solid Water™ Phantom Material (40 × 40 × 20 cm3). TLD's were read using a Harshaw model 3500 TLD reader. The experimental results were compared to theoretical data using Monte Carlo simulations in liquid and Solid Water™. A Monte Carlo N‐particle Transport Code (MCNP4C2) was used to calculate the dose rate distribution in Solid Water™ and liquid water. This code is capable of accounting for photoelectric, coherent, Compton and pair production interaction processes. The photon interaction cross section file used in this study was DLC‐200 library distributed by the Radiation Shielding Information Computing Center (RSICC). In this study, up to 20×106 photons were used for each simulation. Calculations were set up in the same design format as the TLD experiments. Results: The calculated dose rate constant in liquid water and Solid Water™ were found to be 0.961 cGyh−1U−1 and 0.962 cGyh−1U−1, respectively. In addition, there was good agreement between the measured and calculated dose rate constant, radial dose function and the anisotropy function in Solid Water™. Conclusion: The dosimetric characteristics of the IPL 67‐6520 Cs‐137 source were determined using the TG‐43U1 recommendation. The characteristics of the new Cs‐137 source are comparable to the other commercially available sources.
TU‐D‐T‐617‐06: The Optimization of Dose Delivery for Intraoperative High‐Dose‐Rate Radiation Therapy Using Curved HAM Applicators
Authors: Briere T , Krishnan S , Wang X , Crane C , Horton J , Beddar AS
Published: June 2005

Purpose: To quantify the effect of the curvature of flexible applicators on the dose distribution in high‐dose‐rate intraoperative radiation therapy (HDR‐IORT). Method and Materials: Treatment planning was performed with flat Harrison‐Anderson‐Mick applicators using as the radioactive source, and dwell times were optimized using dose‐point optimization techniques. These optimized dwell times were then used for the curved applicators, and the dose distributions that would actually be delivered to patients were determined. Shallow, moderate, and steep curvatures were considered. The discrepancies in dose distribution resulting from the applicator's curvature were quantified, and the regions receiving significant underdoses or overdoses were identified. Results: The dose directly below the central catheter was strongly dependent on the curvature of the applicator. Steep parabolic curves caused underdoses as large as 19% at the prescribed depth of 1 cm normal to the convex side of the applicator surface. The rate of dose reduction with increasing distance from the applicator surface was also greatly affected by applicator curvature. The local dose distribution was not greatly affected by the number of catheters. On the concave side of the applicator, curvature pushed the isodose curves from the applicator surface, causing overdosing. Data from these experiments could be used to create a simple library of treatment plans for curved geometries to complement existing libraries for flat applicators. Conclusion: The curvature of the applicator profoundly affects dosimetry and can be exploited to optimize coverage of the target during HDR‐IORT procedures. To ensure accurate dose delivery, these dose perturbations must be accounted for in the planning process. We recommend maintaining a dosimetry atlas of various applicator sizes and curvatures in addition to one for flat applicators.
TU‐D‐T‐6E‐01: Why, What, and How Much QA Is Necessary for IMRT?
Authors: Palta J , Mijnheer B , Sherouse G , Hevezi J
Published: June 2005

Intensity ‐modulated radiation therapy (IMRT) represents one of the most significant technical innovations of the modern day radiation therapy. Unlike conventional three‐dimensional conformal radiation therapy (3DCRT), both the treatment planning and delivery of IMRT are more complex and less intuitive to the users. Thus, IMRT requires much more diligence in understanding the whole planning and delivery process, associated quality assurance procedures, QA frequencies, and QA tolerance limits with action levels over and beyond what is currently understood for 3DCRT. The complexity of IMRT technology has vastly outgrown our current task group checklist system. It will now require the implementation of new and innovative paradigms of science and engineering of quality management. It is just not possible to develop a single checklist for comprehensive IMRT QA. This panel will describe the objective technical details of what should be done for IMRT QA. It will address why we do what we do and how we could do a better job of allocating our limited resources. The presenters will expound on the influence that the specific wording and interpretation of current procedural terminology (CPT) codes has on IMRT QA and how it may change in the future.
TU‐D‐W‐608‐01: Department of Transportation Hazmat Employee Training for Shippers of Radioactive Materials
Authors: Parker R
Published: June 2005

Medical Physicists are frequently involved in shipping radioactive materials or supervising those who do. Current U.S. Department of Transportation Hazardous Material Regulations, 49 CFR Parts 171 – 185, require hazmat employees to have documented training specified in 49 CFR 171 Subpart H. A hazmat employee is defined as an individual who: (1) loads, unloads or handles hazardous material; (2) manufactures, tests, reconditions, repairs, modifies, marks or otherwise represents containers, drums or packagings as qualified for use in the transportation of hazardous materials; (3) prepares hazardous materials for transportation; (4) is responsible for safety of transporting hazardous materials; or (5) operates a vehicle used to transport hazardous materials. Recurrent training is required at least once every three years. (The IATA two year training interval is not applicable and is generally misunderstood.) FAA has escalated inspection and enforcement and facilities who ship radiopharmaceuticals to other laboratories, return radiopharmaceuticals or radioactive sources to suppliers or otherwise ship radioactive materials have been cited for failure to provide and documents this training. The course will cover typical shipments by air and highway which are encountered in a medical institution. Items such as fissile materials, highway route controlled quantities, rail shipments, vessel shipments and such will be omitted, although specific questions may be addressed. A major objective of the course is to provide the process of shipping radioactive material in a sequential and logical fashion. Radioactive material shipments of excepted packages and Type A packages will be emphasized. The new exempt material activity concentrations and exempt consignment activity limits will be presented, as well as the new international proper shipping names and UN numbers which become mandatory on October 1, 2004. The program is designed to meet the DOT training requirements, but it is the hazmat employer's responsibility to ensure that each hazmat employee is properly trained. It is the hazmat employer's responsibility to determine the degree to which this course meets the employer's requirements, including contents of the course and the examination. Participants will gain sufficient knowledge to prepare training programs for others in their institutions. Handouts will summarize the course. A feature handout is a composite table which provides A1, A2, RQ, Exempt Concentration, and Exempt Consignment values in a single table in both Becquerel and Curie units. The examination at the conclusion will be self graded in the course and retained by the participant to form part of his training documentation. Certification of course attendance will be through the AAPM CEU documentation system.
TU‐E‐I‐611‐01: Comparison of Radiation Dose Using Full Field Digital and Conventional Screen‐Film Mammography in a Screening Clinic
Authors: Gingold E
Published: June 2005

Purpose: To evaluate radiation doses delivered by an amorphous selenium based full‐field digital mammography (FFDM) system, and to determine if the expected reduction in average glandular dose (AGD) resulting from the increased efficiency of the digital detector is realized in clinical practice. A secondary purpose was to determine clinical exposure parameters for digital mammography that maintain a level of image noise consistent with screen/film mammography. Method and Materials: Phantom material that approximates breast tissue (50% adipose, 50% glandular) was used for direct comparison of dose between the two clinical mammography units, one digital and one conventional. The mammographic view, compressed breast thickness, kilovoltage, milliampere‐second product, and K‐edge filter were recorded for images of randomly‐selected patients examined on each machine. Entrance skin exposure was calculated from measurements, and AGD was estimated using normalized exposure‐to‐dose conversion factors that assume 50% adipose and 50% glandular breast composition. A two‐tailed student t‐test was used to compare the patient doses. Results: No difference was observed in the mean AGD delivered by the two mammography units over a wide range of compressed breast thicknesses and compositions. For compressed breast thickness above 7 cm, the dose was significantly lower for the FFDM unit (P<0.05) due to the use of higher kilovoltage and rhodium filtration, and correspondingly lower values of mAs. Conclusion: The exposure parameter selection algorithm employed by the FFDM unit does not reduce dose compared with a conventional mammography unit for a wide range of breast thicknesses. Users wishing to reduce AGD should consider using manual techniques, and developing technique charts to achieve the desired compromise between dose and image quality. The algorithm used by the conventional mammography unit to automatically select kVp resulted in extended exposure times and unnecessarily high values of mAs and AGD because of its relatively low upper bound on kVp.
TU‐E‐I‐611‐02: The Dosimetric Effect of Unrealistic Arm Structure of Stylized Human Model
Authors: Lee C , Lee J
Published: June 2005

Purpose: To investigate the dosimetric effect of unrealistic arms in stylized human models on organ doses for external irradiation geometry by comparing organ doses of ICRP74 to those from four realistic tomographic models for gamma radiation in lateral geometry. Method and Materials: By comparing the transversal images of the representative stylized model, MIRD (Medical Internal Radiation Dose) phantom to those of VHP (Visible Human Project) human, it was obviously manifested that arms of the MIRD phantom are unrealistically included in trunk region. Dose conversion coefficients of ICRP 74 were adopted as representative dosimetric data based on stylized models. Photon dose conversion coefficients of four organs (lungs, stomach, esophagus, and liver) which seemed to be sensitively affected by arms in lateral geometries were compared with those from four realistic tomographic human models: KTMAN‐1, KTMAN‐2, VIP‐man, and Zubal phantom. All models have arms except for KTMAN‐1 of which arms were upward stretched when scanned. Organ doses for lateral geometries were computed by MCNPX2.4 using KTMAN‐1, KTMAN‐2 and Zubal phantom, and those of VIP‐man were obtained from published article. KTMAN‐1 and KTMAN‐2 are Korean tomographic models under preparation for publication. Results: Absorbed dose conversion coefficients of four organs from ICRP 74 were higher up to 88% (esophagus) than tomographic models. The overestimation was caused by less shielding offered by arms‐included torso in stylized models than arms‐attached torso in tomographic models. Organ doses of armless KTMAN‐1 were higher than those of other tomographic models, and less than those from ICRP 74 as expected. Conclusion: The unrealistic arms in stylized models cause overestimation of some major organ doses for external photon beams in lateral geometry up to 88% depending on individuals. One should keep in mind the overestimation when using stylized models for dose evaluation of medical staffs.
TU‐E‐I‐611‐03: The UF Series of Tomographic Anatomic Models of Pediatric Patients
Authors: Lee C , Williams J , Bolch W
Published: June 2005

Purpose: To develop a series of detailed tomographic computational models of pediatric patients for the use in patient dose evaluation under various diagnostic and therapeutic procedures. Method and Materials: IDL‐based image manipulation tools were utilized to develop five tomographic head and torso models of different pediatric patients (9‐month male, 4‐year female, 8‐year female, 11‐year male, and 14‐year male) from CT image data of live patients. The models were created from fused images taken from head and CAP CT exams of the same individuals (9‐month and 4‐year models) or two different individuals of the same sex with close age (8‐year, 11‐year, and 14‐year models) since continuous images from head to CAP were not available. During the process, the image resolutions and slice positions were adjusted based upon their anatomy and engineered into single head‐torso image sets. Lungs, bones, and adipose tissues were automatically segmented by using window leveling of original CT numbers. The remainders were either semi‐automatically or manually segmented with the aids of both anatomical knowledge and available image processing techniques. Skin layers were created by adding voxels along the contour of the bodies. Results: Total of five high‐resolution pediatric tomographic model series were developed. More than 60 regions of interest were identified for each model to be used for the organ absorbed dose calculation and consequent effective dose assessment. Organ masses are compared to the age‐interpolated values of ICRP 89 reference data. Conclusion: This work provides the medical physics community with tomographic computational models, which are readily adaptable to general Monte Carlo codes to evaluate radiation risks of pediatric patients under various radiation procedures.
TU‐E‐I‐611‐06: A Novel Shielding System That May Eliminate the Need for Lead Apparel During Fluoroscopic Procedures
Authors: McCormick V , Goldstein J , O”Neill W , Pica M
Published: June 2005

Purpose: To demonstrate the effectiveness of a novel shielding system that completely shields the operator and attending staff during fluoroscopic procedures. Materials and Methods: The enclosure system, developed by ECLS, Inc., is composed of lead glass, leaded drapes and a steel frame. Most of the patient's body and the x‐ray unit are on one side of the enclosure. The leaded glass and leaded drapes contain 1 mm and 0.5 mm lead equivalency, respectively. All exposure measurements were taken with a Radcal 9010 survey instrument with a 60cc ion chamber. The scatter phantom was composed of 7 inches of Acrylic and 3 mm Aluminum. Measurements were taken at various positions in the room during boosted fluoroscopy. Measurements were also taken within a lead apron, with 0.5 mm lead equivalency, at 2 ft from phantom with no interposed shielding. Results: The maximum exposure rate was measured at the operator position and was 1.9 mR/h, 2.5 ft from the phantom. A corresponding measurement on the phantom side of the shield was 824 mR/h. The maximum exposure rate seen within the lead apron was 13.7 mR/h. The shielding system performed better than the 0.5 mm lead equivalency lead aprons. A staff member standing at the operator's position for all 211 hours of fluoro time last year in that lab would have receive 401 mrem, well below 10% of the legal limit of 5000 mrem whole body allowed for occupational exposure. Conclusion: This shielding system provided protection superior to that of a standard lead apron. It is hoped that the use of this shielding system may eliminate the need for lead apparel during fluoroscopic procedures. Conflicts of Interest: This research is partially funded by ECLS, Inc.
TU‐E‐I‐611‐07: Characterization of Two Optically Stimulated Luminescence (OSL) Dosimeter Systems for Monitoring Entrance Skin Dose During Interventional Procedures
Authors: Newkirk N , Rong X , Gaza R , Yukihara E , Klein D , Trent N , McKeever S
Published: June 2005

Purpose: There is a great concern of patient skin injury and a demand for an effective technique for direct measurement of patient dose in real‐time. We have characterized two dosimeter systems for possible future development of a clinically feasible dosimetry system. Success of this investigation may lead to significant reduction of patient radiation dose and skin injury. Method and Materials: High‐sensitivity, fiber‐optic dosimetry systems based on OSL from and KBr:Eu single crystals (detectors) were developed at Oklahoma State University. The physical characteristics of the detector systems were investigated using clinical fluoroscopic machines. The detector's dependence on x‐ray energy, exposure rate, and the angle of x‐ray incidence were evaluated. The data from the dosimetry systems are normalized to ion chamber readings under the same conditions. The detectors were attached to an anthropomorphic chest phantom for physicians to evaluate the visibility of the detectors in the fluoroscopic image. A mathematical model was developed to simulate data sampling of the KBr:Eu system when used with pulsed fluoroscopic equipment. Results: Both types of detectors were nearly invisible under various kVp conditions for typical fluoroscopic procedures. Across the energy range of 60 to 120 kVp, energy dependence was less than 23% for system and less than 8% for the KBr:Eu system. Dose rate dependence was less than 2.1% for the KBr:Eu system, but the system responded too slowly. Angular dependence was less than 6% for the system and 3.5% for the KBr:Eu system. The mathematical model shows that the KBr:Eu system should function consistently under various pulsed fluoroscopic operations. Conclusion: The OSL detectors are of small size, yet sensitive to low exposure, and exhibit practically invisible in fluoroscopic images. Response to variation of fluoroscopic x‐ray parameters is acceptable. Both systems show promise for a clinically feasible skin dose dosimetry system.
TU‐E‐W‐608‐01: Department of Transportation Hazmat Employee Training for Shippers of Radioactive Materials
Authors: Parker R
Published: June 2005

(see abstract: TU‐D‐W‐608‐01)
TU‐E‐T‐6E‐01: The ASTRO Physics Curriculum
Authors: Klein E
Published: June 2005

In 2002, the American Society of Therapeutic Radiology and Oncology (ASTRO)'s Radiation Physics Committee appointed an Ad‐hoc Committee on Physics Teaching To Medical Residents. The main initiative of the committee was to develop a core curriculum for physics education. The document resulted in a recommended 54‐hour course. Some of the subjects were based on American College of Graduate Medical Education (ACGME) requirements (particles, hyperthermia), while the majority of the subjects along with the appropriated hours per subject were devised and agree upon by the committee. For each subject there are learning objectives and for each hour there is a detailed outline of material to be covered. Some of the required subjects/hours are being taught in most institutions (i.e. Radiation Measurement and Calibration for 4 hours), while some may be new subjects (4 hours of Imaging for Radiation Oncology). To ensure that the subject matter and emphasis remain current and relevant, the curriculum will be updated every two years.
TU‐EE‐A3‐04: Cone Beam CT Imaging Versus Digital Tomosynthesis: A Computer Simulation Study for Comparisons
Authors: Tu S , Shaw C , Chen L
Published: June 2005

Purpose: We used a general‐purpose PC cluster to develop a parallel computer simulation model for comparisons between the cone beam CT imaging and digital tomosynthesis with the same image acquisition geometry. Method and Materials: Our model incorporates quantum noise, detector blurring, and additive system noise into the computer simulation. Radon transforms formalism was applied to analytically calculate the phantom image projection data which were then used to reconstruct the volumetric images for low contrast performance and image quality studies. Feldkamp algorithm was used in the cone beam CT imaging, while the shift‐and‐add, filtered backprojection, and optimization based algorithms were used in digital tomosynthesis. We implemented a parallel random number generator based on the Weyl sequence to simulate both quantum and system noise. For digital tomosynthesis, we used blurring profiles and the artifact spread function (ASF) to quantify the magnitude of the out‐of‐plane artifacts. We also calculated the noise power spectra to characterize the image quality for cone beam CT imaging and digital tomosynthesis. Some artifacts removal methods and programming optimization techniques were also investigated in this study. Results: The test results showed that our parallel random number generator had good randomness quality and can be used in the noise study. The images reconstructed from using the digital tomosynthesis algorithms were worse than the Feldkamp algorithm in the cone beam CT imaging. However, it was possible to remove the out‐of‐plane blurring in digital tomosynthesis by using some special techniques. Conclusion: We had successfully developed a parallel computing technique to simulate quantum noise, detector blurring, and system noise for both cone beam CT imaging and digital tomosynthesis. Several quantification methodologies were used to compare these two 3D imaging techniques. Supported in part by a research grant EB000117 from the NIBIB and a research grant CA104759 from the NCI.
TU‐EE‐A3‐05: Scatter Radiation in Digital Tomosynthesis
Authors: Liu B , Glick S , Gong X
Published: June 2005

Purpose: To investigate the characteristics of scattered radiation and its effects on image quality in digital breast tomosynthesis. Method and Materials: A GEANT 4 based Monte Carlo package was used to simulate a rotating target/detector tomosynthesis system. The compressed breast was modeled as a cubic block imbedded with 24 small cylinders of different radii and heights in the central layer. An 11cm air gap between the breast and detector was modeled. The incident photon energy was set to 20 keV to avoid the complexity of beam hardening effects. A primary image and a scatter image were generated for each projection. The gantry was rotated around the breast from −25 degree to 25 degree with a 5 degree increment. Reconstructions of the 3D breast were computed from the 11 projection images using primary x‐rays only, and primary plus scattered x‐rays. Results: The magnitude of scatter radiation does not change very much from one projection to another because the scatter volume does not change. However, the primary radiation detected can be significantly different in different projections due to different path length. As a result, scatter to primary ratio is very different for different projection. Even with the 11 cm air gap, scatter to primary ratio was observed to be as high as 0.4 for a 5 cm thick breast. 3D breast images reconstructed from projections with only primary x‐rays showed higher contrast than those reconstructed from projections with both primary and scatter. Further evaluation is needed to determine if this reduced contrast can affect tumor detectability. Conclusion: Scatter to primary ratio changed significantly from one projection to another and was observed to be as high as 0.4 for a 5 cm thick breast. Tomosynthesis slices showed a moderate decrease in contrast due to scatter.
TU‐EE‐A3‐06: Sub‐Millimeter Three Dimensional Ventilation Imaging of Rodent Lungs
Authors: Sanders K , Guerrero T , Zhang Y , Tapia R , Cody D , Zhang G , Huang T , Komaki R , Price R
Published: June 2005

Purpose: To develop a technique capable of generating a high resolution 3D ventilation image in a rat model from a series of CT images. This technique will be invaluable in developing strategies for radiation treatment optimization and characterization of pulmonary disease states. Method and Materials: A series of three 150gram Fischer 344 rats were euthanized and intubated. The lungs were equilibrated to ambient pressure, then serially inflated and imaged at approximately 1ml increments. A GE flat panel CT scanner capable of 0.15mm resolution was utilized for image acquisition. A deformable image registration algorithm, utilizing 3D optical flow, was applied to each pair of CT images to map, on a voxel by voxel basis, corresponding tissue elements. The difference in average CT number of a nine voxel region surrounding each pair of mapped voxels was then utilized to compute the change in fraction air per voxel (i.e. regional ventilation). This local ventilation measurement was then superimposed onto each voxel of the CT image to generate a 3D ventilation image. The sum of each voxel's ventilation (i.e. total lung ventilation) was then compared to the change in manually segmented lung volumes between each of a series of twenty‐two pair of CT images. Results: Visualization of the 3D ventilation images revealed regional heterogeneity of ventilation throughout the lung fields. The images required smoothing by averaging over a 0.75mm cube surrounding each voxel to minimize artifacts. The calculated total lung ventilation compared favorably with the change in manually segmented lung volumes, with a slope of unity, as expected, and a correlation coefficient of R=0.99. Conclusion: We have demonstrated a unique method of quantifying regional lung ventilation with sub‐millimeter accuracy in a rat model. This model has been developed in order to study lung function and radiation injury.
TU‐EE‐A4‐03: Daily Localization of Post‐Prostatectomy Patients with Combined CT and US Image Guidance
Authors: Paskalev K , Feigenberg S , McNeeley S , Horwitz E , Price R , Ma C , Pollack A
Published: June 2005

Purpose: Daily localization of post‐prostatectomy patients receiving radiation treatment to the surgical bed is a very challenging task. The anatomy bounding the prostate bed can significantly change from day to day due to rectal and bladder filling. Target localization based on bony anatomy may be inaccurate. Ultrasound (US) localization has potential, but since there is not a well‐defined target (i.e., prostate), reliability may be inadequate. In a previously presented study, we compared US alignments with CT alignments, and based on the results we developed a clinical procedure that incorporated the two imaging modalities. The results presented in this work are for the first 30 patients (183 alignments) that underwent IMRT treatment to the prostate bed after the initial study was completed. Method and Materials: Prior to the first treatment, each patient was aligned based on a pre‐treatment CT scan acquired with the Primatom CT‐on‐rails (Siemens). US images were then immediately acquired with the BAT system (Nomos) and these images were stored as templates. During subsequent treatments the US template images were used to assist the therapists when performing daily US alignment. The accuracy of the alignments was controlled by CT scans taken once every week. Results: The systematic differences between US and CT alignments were: 0.8 mm (lateral), 0.4 mm (AP) and 0.5 mm (longitudinal). Some of these values were statistically significant, but their clinical significance is low. The random differences between the two modalities (one standard deviation) were: 2.9 mm (lateral), 3.3 mm (AP) and 3.0 mm (longitudinal), and average absolute differences were: 2.3 mm (lateral), 2.6 mm (AP) and 2.5 mm (longitudinal). Conclusion: These results suggest that: (i) the systematic error of the every‐day US alignments is minimized; (ii) the target is fully covered by the PTV margin (8 mm) used at our institution in almost all cases.
TU‐EE‐A4‐04: Inter‐Fraction Shape Change When Using An Endorectal Balloon for Radiation Therapy of the Prostate
Authors: Court L , D'Amico A , Kadam D , Cormack R
Published: June 2005

Purpose: To investigate inter‐fraction shape change when using an air‐filled endorectal balloon (ERB) to localize and immobilize the prostate. Method and Materials: Under an IRB‐approved treatment protocol to evaluate the use of endorectal balloons, patients have port films acquired before delivery of the treatment fields. Position adjustments in the AP direction are made based on the comparison of lateral portal images with planning DRRs. After treatment, a left lateral portal image is taken to evaluate setup. Currently an ERB is used for 15 fractions (27Gy) of the total treatment. The anterior wall of the ERB in the left lateral portal images for five patients was contoured, and the results used to estimate inter‐fraction shape change. Results: The mean position of the ERB wall was within 2mm of its position in the treatment plan for all patients, with a standard deviation of 1.2 – 2.3mm at central axis (CAX). Since the ERB minimizes intrafraction rectum/prostate motion, most of this can be attributed to setup uncertainties or patient motion. The standard deviation of the ERB wall at a point 3cm superior to CAX, corresponding to the superior end of the prostate, was larger at 2.1 – 4.3mm. The total range in the position of the ERB wall (i.e. difference in most anterior and most posterior positions) at CAX and 3cm superior to CAX was 4–6mm and 6–13mm, respectively. These differences indicate some significant inter‐fraction shape change. Conclusions: Interfraction shape change of the ERB appears to be negligible (s.d. 3cm superior of CAX<3mm) for three patients, but more important (>3mm) for two patients, indicating that some form of image‐guided or adaptive radiation therapy may be useful for some patients. Results for more patients will be presented at the meeting.
TU‐EE‐A4‐06: Accuracy and Precision of Implantable Radiofrequency Transponder Localization Measurements Conducted Using Multislice CT
Authors: Zhang L , Mutic S , Parikh P , Riley J , Willoughby T , Hubenschmidt J , Low D
Published: June 2005

Purpose: Accurate localization and monitoring of prostate position during radiation therapy is critical for the precise and safe delivery of dose‐escalated treatments, but is challenging due to substantial internal‐organ motion. A novel method for tracking prostate position using implantable radiofrequency markers has been developed by Calypso® Medical. An important consideration for these transponders is localization accuracy using computed‐tomography (CT) imaging. We evaluated the accuracy and precision of transponder localization using multislice CT scanning. Method and Materials: A tissue‐equivalent pelvis phantom with three implanted transponders and external alignment markers was used. The relative transponder positional accuracy was 0.1mm, while the positional accuracy of the transponders relative to the phantom surface was 0.5mm. The phantom was placed on a computer‐controlled linear stage and multiple scans were acquired using a Philips Brilliance 16‐slice CT scanner, varying the detector size, slice thickness, and pitch. Scans were repeated with the phantom moved 0.5mm longitudinally between scan acquisitions to assess position‐measurement accuracy at different locations within a reconstructed CT slice thickness. The transponders were identified and localized on the reconstructed CT images automatically using in‐house image processing software. Results: The mean error of the transponder localization was less than 0.4 mm in anterior‐posterior and lateral‐medial directions, and increased to 0.8mm in longitudinal direction primarily due to the uncertainty introduced in the initial slice identification. The predicted longitudinal shift between each consecutive scan followed the actual shift amount accurately with a mean error of 0.014mm and a standard deviation of 0.08mm. Conclusion: Our investigations have demonstrated the high accuracy of the transponder localization using a multislice CT scanner. The initial results indicate that the accuracy of such a system is sufficient for prostate localization and position monitoring in clinics. Conflict of Interest: This work is supported in part by Calypso® Medical.
TU‐EE‐A1‐01: Accuracy of Clinical Dose Delivery in IOHDR Brachytherapy
Authors: Oh M , Avadhani J , Malhotra H , Cunningham B , Tripp P , Jaggernauth W , Podgorsak M
Published: June 2005

Purpose: To investigate the accuracy of clinical dose delivery in intra‐operative high dose rate (IOHDR) brachytherapy. Method and Materials: The IOHDR brachytherapy treatments of 10 patients recently treated at our facility were reconstructed. Treatment geometries reflecting each clinical scenario were simulated by a phantom assembly with no added buildup on top of the applicator. EDR2 radiographic film placed at the prescription depth recorded dose distributions for each clinical case. The treatment planning geometry (full scatter surrounding the applicator) was subsequently simulated for each case by adding bolus on top of the applicator and radiographic film was again exposed at the treatment depth. After careful determination of the film's H&D curve, absolute dose distributions in the plane of the prescription depth were evaluated for both scatter environments in each clinical case. Results: For the geometries simulating the treatment planning conditions of full scatter, the average dose measured at the treatment depths was within 2% of the prescription and dose distributions were in excellent agreement with the respective treatment plan. However, for the geometry simulating treatment conditions (no added scattering material above the applicator), the dose at the prescription depth was on average 11% lower (range 8–14%) than prescribed. An analysis of the delivered dose distributions and treatment plans shows a resulting average decrease of 2 mm (range 1.2–2.4 mm) in prescription depth. Conclusion: Dosimetry calculations for IOHDR brachytherapy are typically done with treatment planning systems with dose calculation algorithms that assume an infinite scatter environment around the applicator and target volume. We have shown that this assumption leads to dose delivery errors which result in significant foreshortening of the prescription depth. It may be clinically relevant to correct for these errors by augmenting the scatter environment or, preferably, by appropriately modifying the prescription dose entered into the treatment planning system.