bluuebunny/crossref_metadata_2025 huggingface dataset:
Further evaluation of a new standard of efficacy for stored platelets
Authors: AuBuchon James P. , Herschel Louise , Roger Jill
Published: June 2005

BACKGROUND:  The proposal to assess the viability capabilities of platelets (PLTs) collected, treated, or stored in a developmental system against “fresh” PLTs from the same subject poses several important methodologic issues pertaining to the timing and manner of the collecting and separating the fresh PLTs. This study extended the previous validation of this method of comparing fresh and stored PLTs, applying it to an assessment of apheresis PLTs stored for 7 days with a newly standardized radiolabeling protocol.

STUDY DESIGN AND METHODS:  Eighteen normal subjects donated 1 unit of leukoreduced PLTs, pheresed with a standard, approved system. They received an aliquot radiolabeled with 51Cr on Day 7 simultaneously with 111In‐labeled fresh PLTs that had been separated by a manual method. Recovery and survival were compared to determine whether the stored PLTs were not inferior to the criterion of 67 percent of recovery and 50 percent of survival of fresh PLTs. Separate studies were undertaken to document the similarity of recovery and survival with 51Cr and 111In radiolabeling in PLTs stored to 8 days and to determine the importance of correcting the radioactivity in timed samples for the activity remaining in blood beyond the life span of the retransfused PLTs.

RESULTS:  PLTs stored for 7 days demonstrated 88.7 ± 35.2 percent of the recovery and 89.9 ± 21.2 percent of the survival of PLTs collected via a nonproprietary, manual system and thus met the comparative criterion. In a separate study (n = 12), labeling Day 8 PLTs with 51Cr or 111In resulted in recoveries and survivals that were not different. Radiolabel eluted from labeled PLTs in vitro was taken up by cellular blood elements in a reuptake incubation.

CONCLUSION:  Apheresis PLTs stored for 7 days met the criterion proposed for comparison with fresh PLTs. This analytic approach is feasible with PLTs collected and prepared via a manual method. A standardized protocol for radiolabeling PLTs with 51Cr and 111In and analyzing the results in a standardized fashion was employed successfully, with the two radioisotopes yielding similar results. The importance of correcting for residual activity after disappearance of injected cells was noted.
A unified framework for exact cone‐beam reconstruction formulas
Authors: Zhao Shiying , Yu Hengyong , Wang Ge
Published: June 2005

In this paper, we present concise proofs of several recently developed exact cone‐beam reconstruction methods in the Tuy inversion framework, including both filtered‐backprojection and backprojection‐filtration formulas in the cases of standard spiral, nonstandard spiral, and more general scanning loci. While a similar proof of the Katsevich formula was previously reported, we present a new proof of the Zou and Pan backprojection‐filtration formula. Our proof combines both odd and even data extensions so that only the cone‐beam transform itself is utilized in the backprojection‐filtration inversion. More importantly, our formulation is valid for general smooth scanning curves, in agreement with an earlier paper from our group [Ye, Zhao, Yu, and Wang, Proc. SPIE 5535, 293–300 (Aug. 6 2004)]. As a consequence of that proof, we obtain a new inversion formula, which is in a two‐dimensional filtering backprojection format. A possibility for generalization of the Katsevich filtered‐backprojection reconstruction method is also discussed from the viewpoint of this framework.
Investigation into dosimetric effect of a MAGNA‐SITE™ tissue expander on post‐mastectomy radiotherapy
Authors: Thompson Rosemary C. A. , Morgan Andrew M.
Published: June 2005

It is increasingly common for radiotherapy departments to encounter high density objects in patients being planned for radiotherapy. Many cases, such as artificial hip prostheses, are well documented. In our cancer center we have recently come across a new type of implant—a McGhan Style 133 Tissue Expander—implanted in patients who have undergone a mastectomy and will in future have breast reconstruction. This type of implant contains a small rare earth magnet encased in a titanium body, which induces significant perturbations in the dose distribution. These perturbations have been measured using a p‐type semiconductor diode. Attenuation of up to 30% of local dose has been observed for a single beam. However, in more realistic clinical situations using tangential parallel opposed beams, it is estimated that part of the planning target volume maybe be underdosed by approximately 10%. Comparisons have been made between measured attenuation and that calculated by a treatment planning system, which demonstrates inadequate modeling of the dose perturbation caused by the implant in this case.
Accuracy of finite element model‐based multi‐organ deformable image registration
Authors: Brock K. K. , Sharpe M. B. , Dawson L. A. , Kim S. M. , Jaffray D. A.
Published: June 2005

As more pretreatment imaging becomes integrated into the treatment planning process and full three‐dimensional image‐guidance becomes part of the treatment delivery the need for a deformable image registration technique becomes more apparent. A novel finite element model‐based multi‐organ deformable image registration method, MORFEUS, has been developed. The basis of this method is twofold: first, individual organ deformation can be accurately modeled by deforming the surface of the organ at one instance into the surface of the organ at another instance and assigning the material properties that allow the internal structures to be accurately deformed into the secondary position and second, multi‐organ deformable alignment can be achieved by explicitly defining the deformation of a subset of organs and assigning surface interfaces between organs. The feasibility and accuracy of the method was tested on MR thoracic and abdominal images of healthy volunteers at inhale and exhale. For the thoracic cases, the lungs and external surface were explicitly deformed and the breasts were implicitly deformed based on its relation to the lung and external surface. For the abdominal cases, the liver, spleen, and external surface were explicitly deformed and the stomach and kidneys were implicitly deformed. The average accuracy (average absolute error) of the lung and liver deformation, determined by tracking visible bifurcations, was 0.19 (s.d.: 0.09), 0.28 (s.d.: 0.12) and , in the LR, AP, and IS directions, respectively. The average accuracy of implicitly deformed organs was 0.11 (s.d.: 0.11), 0.13 (s.d.: 0.12), and , in the LR, AP, and IS directions, respectively. The average vector magnitude of the accuracy was for the lung and liver deformation and for the implicitly deformed organs. The two main processes, explicit deformation of the selected organs and finite element analysis calculations, require less than 120 and , respectively. This platform can facilitate the integration of deformable image registration into online image guidance procedures, dose calculations, and tissue response monitoring as well as performing multi‐modality image registration for purposes of treatment planning.
Correspondence in texture features between two mammographic views
Authors: Gupta Shalini , Markey Mia K.
Published: June 2005

It is well established that radiologists are better able to interpret mammograms when two mammographic views are available. Consequently, two mammographic projections are standard: mediolateral oblique (MLO) and craniocaudal (CC). Computer‐aided diagnosis algorithms have been investigated for assisting in the detection and diagnosis of breast lesions in digitized/digital mammograms. A few previous studies suggest that computer‐aided systems may also benefit from combining evidence from the two views. Intuitively, we expect that there would only be value in merging data from two views if they provide complementary information. A measure of the similarity of information is the correlation coefficient between corresponding features from the MLO and CC views. The purpose of this study was to investigate the correspondence in Haralick's texture features between the MLO and CC mammographic views of breast lesions. Features were ranked on the basis of correlation values and the two‐view correlation of features for subgroups of data including masses versus calcification and benign versus malignant lesions were compared. All experiments were performed on a subset of mammography cases from the Digital Database for Screening Mammography (DDSM). It was observed that the texture features from the MLO and CC views were less strongly correlated for calcification lesions than for mass lesions. Similarly, texture features from the two views were less strongly correlated for benign lesions than for malignant lesions. These differences were statistically significant. The results suggest that the inclusion of texture features from multiple mammographic views in a CADx algorithm may impact the accuracy of diagnosis of calcification lesions and benign lesions.
Penalized‐likelihood sinogram smoothing for low‐dose CT
Authors: La Rivière Patrick J.
Published: June 2005

We have developed a sinogram smoothing approach for low‐dose computed tomography (CT) that seeks to estimate the line integrals needed for reconstruction from the noisy measurements by maximizing a penalized‐likelihood objective function. The maximization is performed by an algorithm derived by use of the separable paraboloidal surrogates framework. The approach overcomes some of the computational limitations of a previously proposed spline‐based penalized‐likelihood sinogram smoothing approach, and it is found to yield better resolution‐variance tradeoffs than this spline‐based approach as well an existing adaptive filtering approach. Such sinogram smoothing approaches could be valuable when applied to the low‐dose data acquired in CT screening exams, such as those being considered for lung‐nodule detection.
Feasibility of using ultrasound for real‐time tracking during radiotherapy
Authors: Hsu A. , Miller N. R. , Evans P. M. , Bamber J. C. , Webb S.
Published: June 2005

This study was designed to examine the feasibility of utilizing transabdominal ultrasound for real‐time monitoring of target motion during a radiotherapy fraction. A clinical Acuson 128/XP ultrasound scanner was used to image various stationary and moving phantoms while an Elekta SL25 linear accelerator radiotherapy treatment machine was operating. The ultrasound transducer was positioned to image from the outer edge of the treatment field at all times. Images were acquired to videotape and analyzed using in‐house motion tracking algorithms to determine the effect of the SL25 on the quality of the displacement measurements. To determine the effect on the dosimetry of the presence of the transducer, dose distributions were examined using thermoluminescent dosimeters loaded into an Alderson Rando phantom and exposed to a treatment field with and without the ultrasound transducer mounted outside the field edge. The ultrasound images acquired a periodic noise that was shown to occur at the pulsing frequency of the treatment machine. Images of moving tissue were analyzed and the standard deviation on the displacement estimates within the tissue was identical with the SL25 on and off. This implies that the periodic noise did not significantly degrade the precision of the tracking algorithm (which was better than ). The presence of the transducer at the surface of the phantom presented only a 2.6% change to the dose distribution to the volume of the phantom. The feasibility of ultrasonic motion tracking during radiotherapy treatment is demonstrated. This presents the possibility of developing a noninvasive, real‐time and low‐cost method of tracking target motion during a treatment fraction.
Relative output factor measurements of a 5 mm diameter radiosurgical photon beam using polymer gel dosimetry
Authors: Pappas E. , Petrokokkinos L. , Angelopoulos A. , Maris T. G. , Kozicki M. , Dalezios I. , Kouloulias V.
Published: June 2005

Besides the fine spatial resolution inherent in polymer gel‐magnetic resonance imaging (MRI) dosimetry, the method also features the potential for multiple measurements of varying sensitive volume in a single experiment by integrating results in MRI voxels of finite dimensions (i.e., in plane resolution by slice thickness). This work exploits this feature of polymer gel dosimetry to propose an experimental technique for relative output factor (OF) measurements of small radiosurgical beams. Two gel vials were irradiated with a 5 and 30 mm diameter 6 MV radiosurgery beam and MR scanned with the same slice thickness and three different in plane resolutions. Using this experimental data set, 5 mm OF measurements with the PinPoint ion chamber are simulated by integrating results over a sensitive volume equal to that of the chamber. Results are found in agreement within experimental uncertainties with actual PinPoint measurements verifying the validity of the proposed experimental procedure. The polymer gel data set is subsequently utilized for OF measurements of the 5 mm beam with varying sensitive volume to discuss the magnitude of detector volume averaging effects. Seeking to correct for volume averaging, results are extrapolated to zero sensitive volume yielding a 5 mm OF measurement of . This result compares reasonably with corresponding ionometric and radiographic film measurements of this work and corresponding, limited, data in the literature. Overall, results suggest that polymer gel dosimetry coupled with the proposed experimental procedure helps overcome not only tissue‐equivalence and beam perturbation implications but also volume averaging and positioning uncertainties which constitute the main drawback in small radiosurgical beam dosimetry.
An approximate short scan helical FDK cone beam algorithm based on nutating curved surfaces satisfying the Tuy's condition
Authors: Hu Jicun , Tam Kwok , Qi Jinyi
Published: June 2005

Traditionally, short scan helical FDK algorithms have been implemented based on horizontal transaxial slices. However, not every point on the horizontal transaxial slice satisfies Tuy's condition for the corresponding segment of helix, which means that some points on the horizontal slices are incompletely sampled and are impossible to be exactly reconstructed. In this paper, we propose and implement an improved but still approximate short scan helical cone beam FDK algorithm based on nutating curved surfaces satisfying the Tuy's condition. This surface is defined by averaging PI surfaces emanating the initial and final source points of a segment of helix. One of the key characteristics of the surface is that every point on it satisfies the Tuy's condition for the corresponding segment of helix, which means that we can potentially reconstruct every point on the surface exactly. This difference makes the proposed algorithm deliver a better‐reconstructed image quality while requiring a smaller detector area than that of traditional FDK methods based on horizontal transaxial slices. Another characteristic of the proposed surface is that every point within the helix belongs to one and only one such surface. Therefore, the location of the short scan segment for the reconstruction of a point in Cartesian coordinate could be precalculated and stored in a look‐up table. This enables us to perform reconstruction directly on rectangular grids. We compare the performance of the improved FDK algorithm with that of a quasi‐exact algorithm based on data combination technique. The simulation results show that the reconstructed image quality of these two methods is similar.
Fast radiographic film calibration procedure for helical tomotherapy intensity modulated radiation therapy dose verification
Authors: Yan Yulong , Papanikolaou Nikos , Weng Xuejun , Penagaricano Jose , Ratanatharathorn Vaneerat
Published: June 2005

Film dosimetry offers an advantageous in‐phantom planar dose verification tool in terms of spatial resolution and ease of handling for quality assurance (QA) of intensity modulated radiation therapy (IMRT) plans. A critical step in the success of such a technique is that the film calibration be appropriately conducted. This paper presents a fast and efficient film calibration method for a helical tomotherapy unit using a single sheet of film. Considering the unique un‐flattened cone shaped profile from a helical tomotherapy beam, a custom leaf control file (sinogram) was created, to produce a valley shaped intensity pattern. There are eleven intensity steps in the valley pattern, representing varying dose values from . This dose range covers the most commonly prescribed doses in fractionated IMRT treatments. An ion chamber in a solid water phantom was used to measure the dose in each of the eleven steps. For daily film calibration the whole procedure, including film exposure, processing, digitization and analysis, can be completed within , making it practical to use this technique routinely. This method is applicable to film calibration on a helical tomotherapy unit and is particularly useful in IMRT planar dose verification due to its efficiency and reproducibility. In this work, we characterized the dose response of the KODAK EDR2 ready‐pack film which was used to develop the step valley dose maps and the IMRT QA planar doses. A comparison between the step valley technique and multifilm based calibration showed that both calibration methods agreed with less than 0.4% deviation in the clinically useful dose ranges.
A novel dose uncertainty model and its application for dose verification
Authors: Jin Hosang , Chung Heetaek , Liu Chihray , Palta Jatinder , Suh Tae‐Suk , Kim Siyong
Published: June 2005

Based on statistical approach, a novel dose uncertainty model was introduced considering both nonspatial and spatial dose deviations. Non‐space‐oriented uncertainty is mainly caused by dosimetric uncertainties, and space‐oriented dose uncertainty is the uncertainty caused by all spatial displacements. Assuming these two parts are independent, dose difference between measurement and calculation is a linear combination of nonspatial and spatial dose uncertainties. Two assumptions were made: (1) the relative standard deviation of nonspatial dose uncertainty is inversely proportional to the dose standard deviation , and (2) the spatial dose uncertainty is proportional to the gradient of dose. The total dose uncertainty is a quadratic sum of the nonspatial and spatial uncertainties. The uncertainty model provides the tolerance dose bound for comparison between calculation and measurement. In the statistical uncertainty model based on a Gaussian distribution, a confidence level of theoretically confines 99.74% of measurements within the bound. By setting the confidence limit, the tolerance bound for dose comparison can be made analogous to that of existing dose comparison methods (e.g., a composite distribution analysis, a test, a evaluation, and a normalized agreement test method). However, the model considers the inherent dose uncertainty characteristics of the test points by taking into account the space‐specific history of dose accumulation, while the previous methods apply a single tolerance criterion to the points, although dose uncertainty at each point is significantly different from others. Three types of one‐dimensional test dose distributions (a single large field, a composite flat field made by two identical beams, and three‐beam intensity‐modulated fields) were made to verify the robustness of the model. For each test distribution, the dose bound predicted by the uncertainty model was compared with simulated measurements. The simulated measurements were within the tolerance bound as expected by a statistical prediction of the model. Using the dose uncertainty distributions, an uncertainty length (uncertainty area and uncertainty volume for two‐dimensional and three‐dimensional, respectively) histogram (a plot of the dose uncertainty of received by a length of field) was made. The histogram provides additional information on superiority of a treatment plan in terms of uncertainty. In summary, the uncertainty model provides the dose comparison tool as well as the evaluation tool of a treatment planning system.
Dosimetry of the source used in interstitial brachytherapy
Authors: Dauffy Lucile S. , Braby Leslie A. , Berner Barry M.
Published: June 2005

The American Association of Physicists in Medicine Task Group 43 reports, AAPM TG‐43 and its update TG‐43U1, provide an analytical model and a dosimetry protocol for brachytherapy dose calculations, as well as documentation and results for some sealed sources. The radionuclide (, ) has been used in the form of seeds for brachytherapy treatments including brain, eye, and prostate tumors. However, TG‐43 reports have no data for seeds, and none have previously been obtained. For that reason, and because of the conversion of most treatment planning systems to TG‐43 based methods, both Monte Carlo calculations (MCNP 4C2) and thermoluminescent dosimeters (TLDs) are used in this work to determine these data. The geometric variation in dose is measured using an array of TLDs in a solid water phantom, and the seed activity is determined using a high purity germanium detector (HPGe) and a well ionization chamber. The results for air kerma strength, , per unit apparent activity, are 2.063 (MCNP) and 2.089 (measured) , values close to those published in 1991 in the AAPM Task Group 32 report. The dose rate constant, , is found equal to 1.115 (MCNP) and 1.095 (measured) . The radial dose function, , anisotropy function, , and anisotropy factor, , are also given.
A preliminary study of the novel application of normoxic polymer gel dosimeters for the measurement of CTDI on diagnostic x‐ray CT scanners
Authors: Hill Brendan , Venning Anthony J. , Baldock Clive
Published: June 2005

Computer tomography dose index (CTDI) is a measurement undertaken during acceptance testing and subsequent quality assurance measurements of diagnostic x‐ray CT scanners for the determination of patient dose. Normoxic polymer gel dosimeters have been used for the first time to measure dose and subsequently CTDI during acceptance testing of a CT scanner and compared with the conventional ionization chamber measurement for a range of imaging protocols. The normoxic polymer gel dosimeter was additionally used to simultaneously determine slice‐width dose profiles and CTDI in the transaxial plane, the measurements of which are usually determined with thermoluminescent dosimetry or film. The resulting CTDI for all slice widths calculated from the normoxic polymer gel dosimeter were within corresponding ionization chamber CTDI values. Slice‐width dose‐profiles full‐width half‐maximum values from the normoxic polymer gel dosimeter were compared to the slice sensitivity profiles and were within the tolerances of the manufacturer. Normoxic polymer gel dosimeters have been shown to be a useful device for determining CTDI and dose distributions for CT equipment, and provide additional information not possible with just the use of an ionization chamber.
Application of a radiophotoluminescent glass plate dosimeter for small field dosimetry
Authors: Aaki Fujio , Ishidoya Tatsuya , Ikegami Tohru , Moribe Nobuyuki , Yamashita Yasuyuki
Published: June 2005

We have recently developed a prototypical radiophotoluminescent glass plate dosimeter (GPD) system as a device for small field dosimetry. The purpose of this study is to examine the usefulness of the GPD system for small field dosimetry. The profiles measured with the GPD were evaluated by comparing them to those from Kodak X‐Omat V and GAFCROMIC XR type R film dosimeters for 2, 5, 9, and circular collimators created by a linear accelerator‐based radiosurgery system. The GPD output factors were compared with those of various detectors including an ion chamber, a ‐type silicon diode detector, a glass rod dosimeter (GRD), and a diamond detector. The results measured with the GPD were also confirmed by comparing them to those from Monte Carlo simulations. The accuracy of a simulated beam is validated by the excellent agreement between Monte Carlo calculated and measured central axis depth‐dose curves for 9‐ and circular collimators using 4‐ and photon beams. The GPD profiles show almost the same full width at half maximum as those of film dosimeters and Monte Carlo simulations at 4‐ and photon beams, but a little narrower penumbrae than the film dosimeters and Monte Carlo simulations. The output factors measured with the GPD are in good agreement with those from a diode detector, a diamond detector, and the GRD with a small active volume and Monte Carlo simulations, except for a very small circular collimator. It was found that the GPD is a very useful detector for small field dosimetry.
SU‐AA‐P‐6B‐03: Correct Coding Guidelines for Medical Physicists: Tips and Hints For Getting It Right
Authors: Granucci S
Published: June 2005

Purpose: To provide attendees the essence of coding, reimbursement, coverage, rules and regulations for radiation therapy physics with a focus on new technologies such as IMRT, Accelerated Partial Breast Irradiation, Stereotactic Radiosurgery with Robotics, TomoTherapy and Stereoscopic Image Guided Radiation Therapy (IGRT). Method and Materials: Available Medicare codes and 2005 fees will be developed for both hospitals and free‐standing practices for each service category. Any billing guidelines available will be collected from ACR, Medicare National and various Local Coverage Decision policies, as well as any published commercial and a few providers and vendors to provide insight into correct coding. In addition, the Correct Coding Initiative edit tables will be accessed to determine current bundling issues. All of this information will be compiled into the handouts. A good dose of coding and billing experience will be interjected into the presentation to help provide practical application to the information. Additional references and resources on web sites, manuals and publications will be provided. Results: All of these tools are designed to help healthcare providers focus on the business aspect of physics and these newer radiation therapies. They are intended to achieve results that add to the bottom line, and at the same time, to be compliant with government program requirements. Conclusions: The materials provided can be used for financial feasibility assessments for either adoption of new technology, or changes in practice setting. They will also allow internal checkup of current practice to assure correct coding options are in place.
SU‐CC‐J‐6C‐02: A Monte Carlo Simulation of Out‐Of‐Field Radiation From An 18‐MV Beam
Authors: Kry S , Titt U , Poenisch F , Followill D , Vassiliev O , Mohan R , Salehpour M
Published: June 2005

Purpose: Patients undergoing radiation therapy are exposed to out‐of‐field radiation in the form of scattered and leakage photons, and at photon energies greater than 10‐MV, neutrons. This secondary radiation may pose a health risk to the patient by inducing secondary cancers in long‐term survivors; it is also a great concern for pregnant patients. Although estimations and measurements of out‐of‐field doses are possible, they are typically crude or time consuming and measurements may be only applicable to the particular treatment examined. A more robust tool is needed that can calculate accurately, and with relative ease, out‐of‐field photon and neutron dose equivalents. Such a tool has been developed with Monte Carlo. Method and Materials: A Varian 2100 accelerator and treatment vault, operated at 18‐MV, have been simulated in detail with MCNPX (including head shielding and structure, gantry, and couch). The out‐of‐field photon dose and neutron fluence were simulated. Simulated photon doses were compared with those measured with TLD‐700 in an acrylic phantom. Simulated neutron fluences were compared with fast neutron fluences measured with moderated gold foils in the patient plane. Neutron fluence can be converted to dose equivalent via conversion factors provided by the ICRP Report 74. Results: From a 10cm × 10cm field, the simulated out‐of‐field photon doses were found to agree, on average, within 10% of measured data over the range of 5cm to 40cm from the edge of the treatment field. Simulated neutron fluences were found to agree within 22% of measured data. Conclusion: A Monte Carlo model has been developed that is capable of calculating both the photon and neutron dose equivalent out‐of‐field. This tool is a substantial improvement on conventional calculations of the out‐of‐field dose from radiation treatments.
SU‐CC‐J‐6C‐03: Factors Affecting Remote Control Endovascular Catheter Steering for IMRI
Authors: Settecase F , Sussman MS , Roberts TPL
Published: June 2005

Purpose: Current applied to a wire solenoid wound at the tip of an endovascular catheter can be used to remotely steer a catheter in interventional MRI. In this study, we attempted to 1) optimize catheter visualization by comparing “real‐time” pulse sequences, 2) derive and verify an equation that characterizes the relationship between the number of solenoid turns, applied current, catheter stiffness, and resulting catheter tip deflections. Method and Materials: Solenoids of 50, 100, 150 turns were wound on separate 1.8 F (using 44 AWG magnet wire) and 5F catheters (using 37 AWG magnet wire). Varying currents were applied using a DC power supply in the MRI control room. Images were obtained with 1.5 T scanner with the distal catheter suspended at 90 degrees to the main magnetic field in a water bath on the scanner bed, using ssFSE, spiral SPGR, FSPGR, FIESTA, and GRE‐EPI pulse sequences. Deflection angles were measured on acquired sagittal images using eFilm. Results: ssFSE and FIESTA images had the highest SNR and the lowest sensitivity to local field inhomogeneity artifact. The deflection angleθ was predicted by the equation, θ = [nIAB/k]sin(γ‐θ), where n is solenoidal turns, I is current, A is area, B is the scanner magnetic field, k is related to the catheter elastic modulus, and γ is the initial angle between the catheter and B (R2 = 0.9671−0.9875). For a 1.8 F catheter and 60 mA applied, deflection was 31.5, 36, and 45.5 degrees from baseline for 50, 100, and 150 turns, respectively. Less flexible catheters required currents over 800 mA to cause deflection.over 20 degrees. Conclusion: SsFSE and FIESTA real‐time pulse sequences are optimal for visualization of catheter tip deflection. The number of solenoidal turns, applied current, and catheter stiffness are important considerations for remote steering of endovascular catheters in iMRI.
SU‐CC‐J‐6C‐04: Theoretical and Empirical Investigations of Flat‐Panel Imagers Incorporating Single‐ and Dual‐Stage Pixel‐Amplifiers Based On Polycrystalline Silicon Thin Film TFTs
Authors: Li Y , Antonuk LE , El‐Mohri Y , Du H , Zhao Q , Yamamoto J , Sawant A , Wang Y , Lu J , Street RA
Published: June 2005

Purpose: To investigate the potential for achieving significant improvements in DQE at low fluoroscopic exposures and high spatial frequencies, as well as at substantially higher frame rates, through the incorporation of novel pixel architectures based on polycrystalline silicon thin‐film transistors (poly‐Si TFTs). Method and Materials: Detailed studies were performed on the signal and noise characteristics of a series of arrays incorporating poly‐Si TFTs. These indirect detection designs involved three pixel architectures with a standard circuit, with a single‐stage amplifier, and with a dual‐stage amplifier — along with a continuous photodiode structure. Determinations of MTF, NPS, and DQE, as well as of individual pixel properties (sensitivity, linearity, trapping, noise) were performed under fluoroscopic and radiographic conditions. Detailed studies of these and other hypothetical array designs were also performed using circuit simulation tools. Results: These studies indicate that the high mobilities of poly‐Si lead to potential frame rates at least an order of magnitude greater than those of conventional arrays with a‐Si:H TFTs. In addition, the single‐stage and dual‐stage pixel‐amplifier arrays exhibit signal gain (∼×11 and ∼×25, respectively) very close to that expected for these designs. Furthermore, while a net increase in the signal‐to‐noise performance was beyond the objective of these initial designs, analysis of the empirical data along with theoretical modeling strongly suggests that there are no intrinsic reasons precluding such performance enhancements. Finally, the non‐destructive nature of the readout for pixel‐amplifier designs enables repeated‐signal‐sampling, thereby creating new possibilities for noise reduction. Conclusion: These results encourage the hypothesis that substantial improvements in DQE performance and readout speed are possible through the incorporation of poly‐Si circuits into flat‐panel pixel designs. Factors limiting the performance of present designs will be described and future steps in the development of this technology will be discussed. This work is supported by NIH grant R01 EB000558.
SU‐CC‐J‐6C‐05: Intra‐Fractional Variations of Anatomy During IMRT Treatment of Prostate Cancer
Authors: Melancon A , de Crevoisier R , Zhang L , O'Daniel J , Kuban D , Cheung R , Lee A , Mohan R , Dong L
Published: June 2005

Purpose: The main goals of this study are to quantify the variations of pelvic anatomy during a single treatment fraction and to analyze the relationship of prostate and seminal vesicle (SV) motion relative to the bladder and rectum. Method and Materials: Twenty‐six patients with locally advanced prostate cancer elected to participate in an IRB‐approved intra‐fractional motion study. Each patient received two CT scans with an integrated CT‐linac system, one before and one immediately after a daily IMRT fraction including an ultrasound alignment. The pair of CT images was registered based on bony structure in the pelvic region using an in‐house CT‐to‐CT 3D image registration software. The center of volume for both the prostate and SVs was used to assess the displacement of the same structure after the treatment fraction. Results: Over the duration of one treatment fraction (20 ± 3 minutes) both the prostate and SVs showed statistically significant systematic trends in the superior and anterior directions of the patient's anatomy. The net change in bladder volume was huge (133 ± 78 cm3), yet this increase did not directly coincide with large target shifts. Although the mean shifts in either direction were fairly small (1.8 mm and 1.3 mm for the prostate and SVs in the anterior direction), a few patients had shifts as large as 8.4 mm and 15.6 mm for the prostate and SVs respectively. These large shifts were highly correlated (p=0.002 and p<0.001) with large rectal volume increases caused from gaseous build‐up in the rectum. Conclusion: Although the mean intra‐fractional motion may not be clinically significant during an IMRT fraction, some treatment fractions could potentially miss portions of the target structures and/or include a larger volume of the anterior rectal wall for a small subset of patients (∼20%) with large gaseous build‐up.
SU‐CC‐J‐6C‐07: Helical Cone‐Beam CT for Radiation Therapy
Authors: Yu LF , Pan XC , Pelizzari CA , Zou Y , Munro P , Riem H. , Kaissl W.
Published: June 2005

Purpose: To develop the helical cone‐beam scanning capability on a simulator CT system and apply a recently developed backprojection‐filtration (BPF) algorithm to reconstruct exact 3D images from data obtained in this system. Method and Materials: Helical cone‐beam CT is an emerging technology with many advantages over conventional CT scans, such as fast volume coverage speed, efficient use of x‐ray power, and sufficient data for exact 3D image reconstruction. We developed the helical cone‐beam capability on a simulator CT device (Acuity, Varian Medical Systems), which includes a kV x‐ray source, a patient couch, and an amorphous silicon flat‐panel detector (Varian PaxScan 4030CB). We fabricated a small motorized leadscrew mechanism on the couch of the Acuity, which allows for longitudinal translation of the patient couch at a constant speed as the gantry rotates. We applied the BPF algorithm to reconstruct exact 3D images from data obtained in this system. Results: A CatPhan phantom was used for data acquisition. 683 projection data were collected during a one‐turn gantry rotation while the couch was translated longitudinally with a helical pitch of 187.2 mm. The x‐ray source was operated at 125 kVp and 560 mAs. Before projection data were used for reconstruction, a number of corrections were performed, such as bad pixel, dark field, flood field, detector sag. We also applied simple corrections for beam hardening and scattering. 3D images were reconstructed from the corrected data by use of the BPF algorithm. Conclusion: We have developed for the first time the helical scanning capability on a simulator cone‐beam CT system and performed a preliminary phantom study. The BPF algorithm was used to reconstruct exact 3D images from the helical cone‐beam data. Such approach can readily be extended to cone‐beam CT components on a LINAC to provide more accurate image representations of the patient.
SU‐CC‐J‐6C‐09: Calculated Pwall Values in Clinical Electron Beams
Authors: Buckley L , Rogers D
Published: June 2005

Purpose: Dosimetry of high‐energy electrons beams is based upon absorbed dose to water standards and requires the use of ionization chambers with several correction factors. There is little information regarding the details of many of these correction factors for electron beam dosimetry. This study investigates the wall correction factor, Pwall, in high‐energy electron beams for both cylindrical and parallel‐plate chambers using Monte Carlo calculations. Dosimetry protocols use a wall correction factor of unity in high energy electron beams, despite some evidence that there may be an effect greater than 1%. Method and Materials: Monte Carlo calculations are carried out using the EGSnrc system. In particular, the user‐code CSnrc is used to calculate the wall correction factor for a series of ion chambers using a correlated sampling variance reduction technique. The wall correction is computed as the ratio of doses to the air cavity for a chamber having a wall made entirely of water to that having a realistic chamber geometry. Calculations of the wall correction are performed for a variety of chambers at the reference depth in electron beams, using realistic electron beam spectra from clinical accelerators, ranging in nominal energy from 5 MeV to 25 MeV. Results: For parallel‐plate chambers, the wall correction is between 1.5% and 1.8% at the lower energies and varies from 0.5% to 1% at the highest energies. For cylindrical chambers, the wall corrections are up to 0.7% for the energy range investigated. Conclusion: EGSnrc calculations of the wall correction factors for ion chambers in high energy electron beams show that this effect is, in many cases, greater than 1%. This differs significantly from dosimetry protocols, which assume a correction of unity in these beams. Chamber‐specific values of the wall correction for parallel‐plate chambers are parametrized as a function of the beam quality.
SU‐CC‐J‐6C‐11: Verification of IMRT Dose Distributions Using a Tissue Equivalent Plastic Scintillator Based Dosimetry System
Authors: Petric MP , Robar JL , Clark BG
Published: June 2005

Purpose: Intensity modulated radiation therapy (IMRT) offers the potential for improved target coverage and increased normal tissue sparing compared with conformal radiotherapy. The complex fluence maps used in IMRT, however, lead to more challenging quality assurance with dose verification being labor‐intensive and time consuming. An IMRT dose verification system has been developed using tissue equivalent plastic scintillator that provides easy to acquire, rapid electronic and directly digital dose measurements of a 2D plane perpendicular to the beam. Method and Materials: The prototype system consists of a water‐filled Lucite phantom with a scintillator screen built into the top surface. The phantom contains a plastic mirror to reflect scintillation light towards a viewing window where it is captured using a CCD camera and a personal computer. Optical photon spread is removed using a micro‐louvre optical collimator and by deconvolving a glare kernel from the raw images. System calibration is performed using radiation fields of known dose distributions. The system was evaluated by verifying a 5‐field IMRT plan and comparing the results to a 2‐D film dosimetry verification of the same plan. Resultant distributions were compared using 1‐D dose profiles, 2‐D dose difference maps and gamma factor analysis. A comparison of the time requirements for verification with each system was also performed. Results: Preliminary results acquired with the new verification system indicate agreement within 5% of 2‐D film dosimetry. Gamma factor analysis shows excellent agreement over most of the distributions. The timing comparison of the verification systems highlights the efficiency of the new scintillator system for IMRT verification with a 50% reduction in time. Conclusion: Results from a 5‐field IMRT plan verification using the new scintillator based system are very promising. With further development this system promises to provide a fast, directly digital, and tissue equivalent alternative to current IMRT verification systems.
SU‐DD‐A2‐02: Investigation of Patient Doses Using a Tomographic Model for Diagnostic Radiology
Authors: Park S , Lee J , Lee C
Published: June 2005

Purpose: In this study, the patient's doses from diagnostic radiology were calculated using the tomographic model and Monte Carlo simulation. The tomographic model offers a realistic replication of human anatomy, and more accurate dosimetric results Method and Materials: The tomographic model Korean Typical Man 2 (KTMAN‐2) was segmented from PET/CT images and has 2×2×5mm3 voxel resolution. Three diagnostic x‐ray examination procedures, abdomen AP, chest PA, and pelvis PA were considered in this study. Energy deposition within organs and entrance air kerma (EAK) were calculated using KTMAN‐2 and Monte Carlo simulation. Also, organ dose comparisons were made for procedures of both a stylized and a tomographic model Results: For the chest PA examination, the lung dose assessed for the KTMAN‐2 is 0.08mGy. The absorbed doses to the stomach, liver and thyroid in the KTMAN‐2 exceed those within the stylized model by 279%, 161% and 90%, respectively. In the case of the abdomen AP examination, gut region and bladder receive a larger absorbed dose than other organs in KTMAN‐2. The absorbed doses to upper large intestine and small intestine are higher than in the stylized model. But conversely, the absorbed doses to lower large intestine and bladder in stylized model are higher than in the KTMAN‐2. For the pelvis PA examination, absorbed doses to gut region in stylized model are higher than in the KTMAN‐2 Conclusion: The model's exterior trunk shape, shape and position of organs and shielding of bone are leading factors contributing to differences in organ dose. Due to the supine position during tomographic images acquisition, back of KTMAN‐2 was pressed down and the abdominal organs are slightly shifted towards the thorax and the lungs are compressed. Thus the organ location difference between lying and upright posture should be corrected.
SU‐DD‐A2‐04: Direct Measurement of Pediatric CT Radiation Dose with a New Solid State Detector System
Authors: Nickoloff E , Dutta A , Lu Z , So J , Ruzal‐Shapiro C
Published: June 2005

Purpose: Because of potential risks, the determination of CT radiation doses is important for young children. Direct patient measurements are usually not practical. Many CT scanners provide a calculation of the CTDIvolume. A unique, tiny solid state dosimeter system (which has recently been developed) permits the instantaneous measurement of cumulative patient entrance radiation doses during clinical CT procedures. This study compared the calculated CTDIvolume to direct measurements with this new detector in pediatric patients. Method and Materials: The new dosimeter system utilizes three tiny silicon detector chips 1cm × 0.5cm in size coupled to a small readout with thin cables. The system digitally displays the total accumulated dose. The energy response is +/−10% between 60 and 120 kVp. Radiation dose measurements during routine clinical head and body CT scans with a GE CT/i scanner were gathered for pediatric patients from newborns upto 18 years old. Results: Head and body data were separated and plotted in mGy per 100 mAs. The CT scanner calculated data showed no variation with patient size or anatomical location. The measured data, however, indicated radiation doses that were 2–3 times greater in small children and matched the calculated data for larger sizes. At the lower mAs values utilized for pediatric body scans, the measured radiation doses ranged from 2 to 5 mGy per procedure. At the higher mAs values for pediatric head CT scans, the radiation doses were 5–10 times greater than the body doses. Conclusion: This solid state integrating detector system provides a new tool for the accurate and instantaneous measurement of CT radiation dose that was previously unavailable. Moreover, the data demonstrate that the scanner calculated CT radiation doses can be in error by a factor of 2 to 3 times due to patient size variations and non‐homogeneity of patient anatomy.
SU‐DD‐A2‐05: Quality Assurance Methodology to Monitor Patient Dose in Interventional Radiography
Authors: Kanal K , Stewart B , Willis P
Published: June 2005

Purpose: The purpose of this preliminary quality assurance project is to use thermoluminescent dosimeters (TLD) to monitor the equivalent dose patients receive while undergoing interventional radiology procedures at our institution. Method and Materials: A TLD is placed centrally on the collimator face of two AP tubes in the angiography department for each patient exam. The TLDs are sent out weekly to be read by Landauer, Inc. Inverse square correction is applied to yield patient equivalent dose at the minimum and maximum possible distances to the patient entrance surface (source‐to‐skin distance, SSD). The inverse square corrected results are entered into a database and analyzed according to exam type and radiation dose threshold categories. All exams having an equivalent dose of greater than 2 Gy (skin erythema threshold) are red‐flagged in the database. These red‐flagged exams are then shared with the angiography section chief radiologist and technologist for feedback and corrective action with the attending physician. Results: Of the 1852 exams surveyed (from July 2003 through the present time), the equivalent dose for minimum SSD was less than 1 Gy for 94.0% of the exams and between 1 and 2 Gy for 2.6% of the exams. The skin erythema threshold dose of 2 Gy was exceeded for 3.1% of exams throughout this time period. It is encouraging that over 96% of measured equivalent dose are below the skin erythema threshold. The remaining 4% of measured equivalent dose were red‐flagged for follow‐up with the physicians responsible for the exam. Conclusions: This preliminary quality assurance and feedback mechanism is a quick and practical way to increase physician awareness of administered patient dose and whether skin injury dose thresholds have been exceeded. It is expected that this monitoring methodology will encourage physicians to practice ALARA.