bluuebunny/crossref_metadata_2025 huggingface dataset:
SU‐DD‐A2‐01: The Utility of Depth Dose Modulation (DDM) for Electronic Brachytherapy
Authors: Hiatt J , Segala J , Cardarelli G , Sternick E
Published: April 2010

Purpose: To illustrate the utility of Depth Dose Modulation (DDM) for Ir‐192, Electronic Brachytherapy (EB) and EBDDM. Method and Materials: A numerical model was created for a miniature x‐ray source equipped with an adjustable collimator that produces a fan‐beam distribution. A general‐purpose multi‐particle transport code was used to calculate the dose distribution for multiple collimator gaps. A software program superimposed the collimated dose images at intervals to build an overall dose distribution for a simulated micro‐stepping treatment. TG‐43 data were input to the Nucletron PLATO treatment planning system. Treatment plans were generated for breast, endometrial and lung cases; doses to target volumes and normal tissues were compared for each of the planning sources. Results: For the breast case, PTV coverage for Ir‐192, EB and EBDDM plans was 96, 100 and 94% with maximum skin doses of 100, 97 and 89% respectively. For the endometrial case, PTV coverage for the Ir‐192, EB and EBDDM plans was 99, 100 and 77% with maximum rectal doses of 140, 127 and 105% and bladder doses 115, 111 and 87% respectively. For equivalent prescription point doses in lung, with Ir‐192, EB and EBDDM, the maximum rib dose was 43, 30 and 34% while V50Lung was 11, 8 and 7% respectively. Conclusions: With intracavity breast cases, DDM is a useful tool, reducing Ir‐192 skin dose by up to 11% while maintaining adequate target coverage. For endometrial treatments, however, EBDDM target coverage is inadequate; because of collimated source anisotropy, there is little dose deposition superiorly. To achieve full target coverage while maintaining significant normal tissue sparing, a treatment would require a combination of EB and EBDDM. For lung, EBDDM allows a two‐fold reduction in V50Lung. Conflict of Interest: Partial financial support provided by Xoft, Inc.
SU‐DD‐A3‐06: Fully Automated Internal Marker Tracking Algorithm for Cine EPID Images
Authors: Park S , Ionascu D , Hacker F , Mamon H , Berbeco R
Published: April 2010

Introduction: An electronic portal imaging device (EPID) in cine mode can be used for validating respiratory gating and stereotactic body radiation therapy (SBRT) by tracking implanted fiducials. Manual tracking methods are time and labor intensive, limiting the utility of the validation. We have developed a fully automated algorithm to quickly and accurately extract the markers in EPID images and reconstruct their 3D positions. Materials and Methods: The markers were detected and recognized using an image processing algorithm based on the Laplacian of Gaussian (LoG) filter. To reduce false marker detection, a marker registration technique was applied using image intensity as well as the geometric spatial transformations between the reference marker positions produced from the projection of 3D CT images and the estimated marker positions. An average marker position in 3D was reconstructed by backprojecting, towards the source, the position of each marker on the 2D image. Results: From phantom studies, spatial accuracies of <1 mm were achieved in both 2D and 3D marker locations. Using only the LoG algorithm, the marker detection success rate was 88.8%. However, adding the registration technique which utilizes prior CT information, the success rate was increased to 100%. In addition, we have examined the cases of 5 patients being treated under an SBRT protocol for hepatic metastases. The intrafractional tumor motion (3.1–11.3 mm) in the SI direction was measured using the 2D images. The interfractional patient setup errors (0.1–12.7 mm) in the SI, AP, and LR directions were obtained from the marker locations reconstructed in 3D and compared to the reference planning CT image. Conclusions: The measured intrafractional tumor motion and the interfractional daily patient setup error can be used for off‐line retrospective verification of SBRT.

This work was partially supported by a grant from Varian Medical Systems, Inc.
SU‐DD‐A4‐06: Tradeoff Between Noise and Resolution in CT Images — Comparison of Filtered Backprojection and the Penalized Alternating Minimization Algorithm
Authors: Evans J , Politte D , Whiting B , O'Sullivan J , Williamson J
Published: April 2010

Purpose: Relative to linear reconstructions, statistical image reconstruction algorithms have been shown to produce images with less error, artifacts and noise for similar high‐contrast resolution as measured with the MTF. This study compares the noise and resolution, using the edge blur, of images reconstructed using filtered backprojection (FBP) and a new statistical algorithm, Alternating Minimization (AM) [O'Sullivan IEEE TMI vol: 26, ♯3]. Method and Materials: Monoenergetic projection data were simulated for two phantoms, each with a high and low‐contrast insert. Two levels of simple Poisson noise were added to simulate low and clinical‐dose protocols. To study image noise and resolution, FBP was performed with a Gaussian blurred ramp filter of varying FWHM. The penalized AM algorithm was run with a range of penalty strengths. Reconstructed pixel size was also varied. Image noise was quantified as the percent standard deviation in the phantom background. Resolution was evaluated by measuring edge blur at contrast boundaries. Blur was quantified as the FWHM of the Gaussian that, when convolved with the known truth image, gives the highest correlation between reconstructed and convolved images for pixels surrounding the edge. Blur was calculated independently around each contrast boundary. AM and FBP image noise is compared as a function of edge blur. Results: For high resolution images (small edge blur), the AM algorithm reconstructs images with up to 50% less noise than FBP for similar resolution. For all conditions (varying pixel size, projection noise, and contrast inserts), AM exhibits an advantage. Conclusion: Edge blur is used as a metric of CT image resolution for both high and low contrast inserts. The penalized AM algorithm is shown to reduce image noise with less edge blurring than FBP. Future work will extend the use of edge blur to compare AM performance in experimentally acquired CT data.
SU‐EE‐A1‐02: In Vivo Dosimetry for HDR Brachytherapy Using a Scintillating Fiber Dosimeter
Authors: Therriault‐Proulx F , Villeneuve M , Martin A , Gingras L , Beddar S , Beaulieu L
Published: April 2010

Purpose: The goal was to develop a scintillating fiber dosimeter and verify its suitability in assessing the dose deposited during brachytherapy HDR treatments. As a first step toward in vivo dosimetry, it has been decided to conduct a full process, from planning to treatment, using a prostate phantom. Method and Materials: The scintillating fiber dosimetry system is composed of a RGB photodiode (MCS3AT) detecting light emitted from a scintillator (BCF‐60) coupled to a plastic optical fiber. Fiber is aligned on the photodiode, and its output is then amplified and acquired through a National Instruments acquisition card. Signal processing, including Cerenkov and fluorescence light subtraction, is done and dose deposited during treatment is obtained through integration. A prostate phantom (CIRS ♯053) has been used to conduct the study. An ultrasound‐guided catheter insertion procedure was performed by a radiation oncologist at our institution. A total of 13 catheters were inserted, one of those being used for the dosimeter. Following a CT scan, the prostate and urethra were contoured and treatment planning was performed according to our prostate clinical protocol on a PLATO workstation (Nucletron BV, Netherlands). The plan was delivered using a microSelectron V2 192Ir afterloader. Results: We measured dose rate as function of time. It varies with distance between the dosimeter and the dwell‐positions. Dose rate integration, once the contamination component is subtracted, determines the total dose deposited during treatment. Measurements were within 2% of the dose predicted by the planning system. Conclusion: Scintillating fiber dosimeter provides an accurate method to assess dose deposited to targets and organs at risk during HDR brachytherapy. Dose rates measured allow QA of treatment delivery for each catheter and total delivered dose. Measurements have been done in a prostate phantom, but there is a potential for a variety of clinical sites.
SU‐EE‐A1‐04: LINAC Quality Assurance and Calibration Using Electronic Portal Imaging Device
Authors: Ramirez H , Yan D , Zhang T
Published: April 2010

Purpose: Radiation treatment machine QA can be time consuming and oftentimes not accurate. The EPID on linacs can possibly be utilized for machine QA and calibration. In this study, we have developed methods to perform QA using EPID images. Method and Materials: A modified ball bearing phantom was constructed and set up according to the room laser center. Portal images were taken at different collimator, gantry, and table angles on an Elekta Synergy LINAC equiped with an a‐Si EPID. Portal images of several jaw and MLC control points were taken also. All images were analyzed using custom developed software in Matlab to calculate collimator/table angle, collimator/table/gantry runout, and jaw/MLC positions. Multiple CBCT images were also taken to verify KV‐MV coincidence and table correction accuracy. Results: Accurate quantitative results for mechanical, MLC, jaw and CBCT QA can be obtained using the developed method. Conclusions: We have developed automatic treatment machine QA methods using EPID images. This QA procedure is faster and more accurate than traditional QA methods.
SU‐EE‐A1‐06: Quality Control of External Beam Treatment Delivery: Mechanical Parameters
Authors: Able C , Bright M
Published: April 2010

Purpose: The focus of this study is to develop a methodology using statistical process control (SPC) that provides effective quality control of mechanical parameters in external beam treatment delivery. Materials and Methods: A four‐field box clinical treatment technique was used as the evaluation tool. Parameters tested were gantry angle, table height, table lateral, and collimator field size. The dosimeter, GafChromic EBT film, was placed vertically in a pelvic phantom in the transverse plane at isocenter. All films were digitized and evaluated using a Vidar film scanner and RIT, Inc. software. Dose distributions of accurate treatment delivery were measured and compared to treatment delivery with a single mechanical parameter deviated at 0.5, 1.0 and 1.5 times the TG‐40 parameter specification. Each distribution was sampled in the penumbra region using three sampling sets (SS). Each SS consisted of different (size and/or position) regions of interest (ROI). Set‐A and B were 1.5cm × 1.5cm while Set‐C was 0.8cm × 1.0cm. Set‐A and C were centered in the same locations along each beam entry 7cm from isocenter. Set‐B was positioned at the corners of the dose box in the distribution. Results: Two process behavior charts (PBC) were prepared for each SS, evaluating the mean dose and mean dose range. PBC for Set‐A were unable to distinguish between accurate and inaccurate distributions. Set‐B detected all mechanical parameters deviated at 1.0 and 1.5 times the TG‐40 specification but also indicated four false‐positives. These PBC were also effectively unable to distinguish between the accurate and inaccurate distributions. Set‐C PBC detected all mechanical parameters deviated at the 1.0 and 1.5 level and reliably indicated the inaccurate distributions. Conclusions: Small and therefore more homogeneous, strategically located ROI can be effective in SPC to detect inaccurately delivered treatments. Quality control of linac mechanical parameters can be performed using SPC‐based methodology.
SU‐EE‐A2‐02: Validation of a Grid‐Based Boltzmann Solver for 6 and 18 MV Photon Beams Impinging On a Heterogeneous Phantom
Authors: Vassiliev O , Wareing T , McGhee J , Failla G , Salehpour M , Mourtada F
Published: April 2010

Purpose: To benchmark the accuracy of a grid‐based Boltzmann solver, Acuros, against Monte Carlo for 6 and 18MV photon beams in a tissue‐bone‐lung‐tissue slab phantom. Method and Materials: Acuros was developed specifically for radiotherapy dose calculations. It solves for both neutral and charged particle transport, and incorporates spatial adaptation to automatically increase spatial resolution in regions of sharp gradients such as beam penumbra and material heterogeneities. Comparisons were made between EGSnrc and Acuros for single field photon beams impinging on a 30×30×30cm3 slab phantom consisting of: tissue (0–3cm), bone (3–5cm), lung (5–12cm), and tissue (12–30cm). Calculations were performed for square fields of 2.5×2.5, 5.0×5.0, and 10×10cm2 for both 6MV and 18MV energies. Comparisons were made between Acuros and EGSnrc on 2×2×2mm3 voxels along the beam centerline (0–30cm), and on transverse lines at depths of Dmax, 10, and 20cm. To minimize the influence of Monte Carlo uncertainties, the EGSnrc calculations were run to a tight statistical uncertainty (σ≈0.1%) and fine resolution, up to 1 mm in the penumbra. Acuros results were output on a 2×2×2mm3 cubic grid encompassing the 30×30×30cm3 phantom. All comparisons were made in terms of absolute doses, Gy per incident particle. Results: For all 6 cases, maximum voxel‐wise differences between EGSnrc and Acuros along the beam centerline were less than 2% of Dmax or 1mm distance‐to‐agreement (DTA). Maximum voxel‐wise differences along the transverse lines were less than 2% of Dmax or 2mm DTA. Acuros calculation times were less than 5 minutes on a two processor AMD Opteron workstation. Conclusion: The results indicate an excellent agreement between both codes. Since Acuros calculation times are primarily dependent on the volume of the region being solved, and not on the number of beams, it is well suited for arc‐therapy modalities.

Conflict of Interest: Work funded by NIH Grant 2R44CA105806‐02.
SU‐EE‐A2‐04: Alternative Delivery Approach for RapidArc Using Constant Dose Rate
Authors: Tang G , Earl M , Yu C
Published: April 2010

Purpose: Varian RapidArc™ is a new treatment technique that delivers conformal dose distributions to the target in one single gantry rotation. The segments in the treatment arc are allowed to have different monitor unit (MU) weightings requiring variable dose‐rate (VDR) for delivery. An alternative delivery approach for (VDR) RapidArc plans that utilizes constant dose‐rate (CDR) was developed. Method and Materials: For four patient cases (two head‐and‐neck (HN), one brain, one prostate), RapidArc plans were generated using the Eclipse treatment planning system. The resultant VDR treatment plans were converted into CDR plans by re‐distributing the equi‐spaced segments in the VDR arc such that the segments with larger MU weighting occupy a greater angular interval. To minimize perturbation from the optimized dose distribution, the angular deviation of the segments was restricted to 5°. This restriction requires the treatment arc to be broken into multiple sectors such that the local MU fluctuation within each sector is reduced, thereby lowering the angular deviation of the segments during re‐distribution. The converted broken‐sector CDR (b‐CDR) plans were delivered with a single gantry sweep as in the VDR plans but each sector was delivered with different values of CDR. Results and Conclusion: For plans with complex angular MU distribution, the number of broken sectors may increase in the b‐CDR plans in order to maintain the original plan quality. All b‐CDR plans produced similar dose distributions to the VDR plans by dissecting the arc up to 5 sectors. On average, the delivery times of the b‐CDR plans were 1 minute longer than that in the VDR plans. Since the majority of treatment time is spent on the patient setup, these results show that VDR RapidArc plans can be delivered using CDR without significantly compromising the plan quality or treatment efficiency.

Research sponsored by Varian Medical Systems.
SU‐EE‐A2‐05: A Planning System for Dynamic Gamma Knife Radiosurgery
Authors: Luan S , Swanson N , Chen Z , Ma L
Published: April 2010

Purpose: To develop a prototype planning system for dynamic Gamma Knife radiosurgery. Method and Materials: Dynamic Gamma Knife is a new concept for implementing Gamma Knife radiosurgery. It uses the spherical high dose volume created by the Gamma Knife unit is as a 3D “paintbrush”, and treatment planning becomes routing the “paintbrush” to “paint” a 3D tumor volume. We have recently finished developing an inverse planning system for dynamic Gamma Knife radiosurgery. Our planning system is a “turn‐key” solution, where the inverse planning problem is solved as a traveling salesman problem combined with constrained least square optimizations. Its input parameters include: (1) contoured anatomy and prescriptions, (2) desired delivery time, (3) APS (advanced patient positioning system) speed, and (4) amount of system memory available. The outputs include: (1) a control point sequence for the APS system together with shot configuration and beam‐on times at each control point, and (2) dose distributions and DVH plots for each structures. Results and Conclusion: We have tested simulated cases that included a spherical tumor, a C‐shaped tumor, and a C‐shaped tumor surrounding a spherical critical structure. The results of these tests showed that: (1) dynamic Gamma Knife radiosurgery is ideally suited for inverse planning, where high quality radiosurgery plans with tight isodose distributions and sharp DVH curves can be obtained in minutes of computation; (2) dynamic radiosurgery plans are more conformal and uniform than current plans and have significantly shorter delivery times; (3) dynamic Gamma Knife radiosurgery can maintain steep dose gradient (around 13% per mm) between the target volume and the surrounding critical structures; (4) with dynamic Gamma Knife radiosurgery, one can obtain a family of plans representing a tradeoff between the delivery time and the dose distributions, thus giving the clinician flexibility in choosing a plan based on the clinical situations.
SU‐EE‐A2‐06: Dosimetric Verification of Ultra Small Fields of Image‐Guided Linac‐Based Stereotactic Radiosurgery
Authors: Jin H , Huh S , Toramatsu C , Li Z , Malyapa R
Published: April 2010

Purpose: To investigate mechanical and dosimetric accuracy of ultra small fields of a cone beam CT (CBCT)‐based stereotactic radiosurgery (SRS) system. Method and Materials: Ultra small fields (7.5 mm, 10 mm, and 12.5 mm cones) of an Elekta linac‐based SRS system were assessed using CBCT‐based setup and film dosimetry. To examine mechanical accuracy of the linac for SRS, a technique of image analysis was developed using flex maps acquired with a phantom holding a CT‐compatible sphere target at the center. The accuracy of CBCT‐based SRS setup was evaluated with sophisticatedly designed geometrical structures of the phantom in sub‐millimeter precision. For dosimetric verification, another cylindrical acrylic phantom with film inserts was developed. The film phantom has marker structures for setup verification. Radiochromic film was inserted into the phantom and 4 SRS plans of 100° arc beams using three SRS cones were delivered. Dose difference distributions and profiles between computations (Philips Pinnacle3) and the film measurements were qualitatively compared. For quantitative analysis, the computations and the measurements were generated in a resolution of 0.25 mm/pixel and a gamma test with 3%/1mm (dose difference/distance‐to‐agreement (DTA)) criteria was performed. Results: The spherical target in the flex maps (portal images of 0.5 mm/pixel) and image‐guided sphere phantom setup showed the mechanical uncertainty of the SRS system is less than 1 mm. The geometrical marker structures in the film phantom were employed to set up the phantom with sub‐millimeter accuracy using CBCT. The gamma test showed that the dose delivery matched the dose calculation within 3% dose difference or 1mm DTA. Conclusion: The comprehensive quality assurance tools using CBCT‐based SRS setup and radiochromic film dosimetry allowed us to achieve maximum 1 mm of mechanical uncertainty and 3% of dosimetric uncertainty of ultra small fields in our linac‐based SRS system.
SU‐EE‐A3‐06: Uncertainty in GTV and ITV Delineation with 4DCT Imaging
Authors: Watkins W , Lewis J , Li R , Jiang S , Song W
Published: April 2010

Purpose: To determine geometric uncertainties in GTV and ITV delineations using RPM sorted 4DCT images for radiotherapy treatment planning. Methods and Materials: Three targets have been embedded within a cork block (to simulate lung tissue) and attached to a programmable motion controller to simulate lung/tumor motion. We input several breathing patterns including ideal sine waves with varying amplitudes, and realistic patient breathing patterns. The cine slices were reconstructed using RPM signal. The three targets (of known dimensions) were contoured and their dimensions were measured in the direction of motion in the 4DCT images. We measured GTV dimensions reconstructed in the phase‐binned images (10 phases) and ITV dimensions reconstructed in the CT MIP and CT average images. Results: ITV measured in CT MIP images is superior to all other techniques used in our study, with errors < 2 mm in all cases except one, and on average 1.1 mm. The reconstruction is accurate even in cases of irregular breathing and varying amplitudes, with dimensions along the direction of motion within 9% of the expected values. For each set of phase‐binned CT images, the GTV is not consistently greater or less than the actual target dimension. The errors for individual targets were maximized at large input amplitudes with the largest uncertainties at 15 mm. At phase 0 and 50 %, the measured errors were minimum. Conclusions: We have performed a comprehensive evaluation of the limitations of 4DCT image reconstruction and its use in treatment planning for target delineation. Specifically, we observed that a general trend of increased GTV delineation uncertainty is seen in phase‐binned CT images with increasing breathing amplitude. However, CT MIP images allowed consistent ITV delineation with minimal uncertainties for all input amplitudes. This study may be useful in guiding clinical judgments in 4DCT and gating procedures.
SU‐EE‐A4‐01: Evaluation of Noise and SDNR Characteristics of Blended ASIR and FBP Images Obtained with the GE Discovery CT 750 HD Scanner
Authors: Goodsitt M , Christodoulou E
Published: April 2010

Purpose: The new GE 750 HD CT scanner utilizes adaptive statistical iterative reconstruction (ASIR), which can be blended in various proportions with the filtered back projection reconstructions. A study was performed to characterize the dependence of noise and signal‐difference‐to‐noise ratio (SDNR) on %ASIR for a range of doses.

Method and Materials: Scans of the low contrast resolution module in the ACR CT accreditation phantom were acquired using “full‐dose”, 2/3 dose, ½ dose, and ¼ dose techniques. Scans were obtained in normal resolution mode with the STD, edge, and soft kernels, and in high resolution mode using the STD, HD STD, and edge kernels. ROIs were placed in the 25 mm cylinder and adjacent background region in this module. Images were reconstructed with %ASIR ranging from 0 –100 in steps of 10. For each condition, mean and standard deviations in the ROIs were obtained for 5 central slices in the module. Noise and SDNR were computed and the %ASIR that yielded the same noise and SDNR as in the full‐dose cases were determined for the lower doses. Results: %ASIR and dose had no effect on the mean CT♯s in the cylinder and background. Noise was found to linearly decrease with %ASIR, (R2>0.997). SDNR increased quadratically with %ASIR (R2>0.996) . For normal resolution, STD kernel, the noise and SDNR at full dose were achieved at 2/3 dose, ½ dose and ¼ dose, using 30%, 50% and 84% ASIR, respectively. Corresponding %ASIR for high resolution, HD STD were 23%, 42% and 68%. Values for other kernels will be presented. Conclusion: ASIR reduces noise and improves SDNR. By applying appropriate %ASIR, one can achieve similar image quality at reduced dose. The frequency content of the noise is different which can affect the %ASIR that is acceptable in the clinic.
SU‐EE‐A4‐03: Metal Artifact Reduction Algorithm for X‐Ray CT Using a Three‐Pass Approach
Authors: Mazin S , Pelc N
Published: April 2010

Purpose: To investigate a three‐pass reconstruction approach for metal artifact reduction in x‐ray CT. Method and Materials: The algorithm consists of: 1) Initial reconstruction from the original sinogram data; 2) Simple thresholding to identify high‐density regions (e.g. metal) that can cause artifacts; 3) Delineation of corresponding regions in the original sinogram that are replaced using linear interpolation; 4) Second reconstruction after the interpolation; 5) All pixels in the second image that lie between −500 and +500 HU are replaced with the mean of these pixels; 6) Rays in the sinogram through the metal are estimated a second time through forward projection of the segmented second image; 7) Third and final reconstruction. To avoid the need for forward projection across the entire native field‐of‐view (FOV) during step 6 above, a double‐wedge filter is applied in the 2DFT space of the sinogram so that objects outside of the reconstruction FOV are filtered out of the original sinogram. If k and p are the view‐angle and fan‐angle frequency variables, respectively, the double‐wedge filter consists of setting to zero all frequencies in the 2DFT of the sinogram for which |k/(k+p)|>R/L, where R is the reconstruction FOV and L is the source‐to‐isocenter distance. Results: The algorithm substantially reduces streak and blooming artifacts that are present in the original reconstruction for three scans with dental fillings, and performs better than linear interpolation across missing regions in the sinogram. The double‐wedge filter is effective in removing contributions to the sinogram from objects outside of the reconstruction FOV. Conclusion: The algorithm is effective for reducing metal artifacts as well as computationally practical. Conflicts of Interest: Funding was provided by GE Healthcare.
SU‐EE‐A4‐06: Impact of KVp and Bowtie Compensator On Cone‐Beam CT Image Quality: An Elekta Synergy XVI Experience
Authors: Liu Z , Chan P , Chau E , Miyamoto C , Micaily B , Li S
Published: April 2010

Purpose: To evaluate the impact of kVp and Bowtie compensator on cone‐beam CT image quality using Elekta Synergy XVI system. Materials and Methods: An XVI system was customarily calibrated at 80, 100, 120, and 138 kVp for various collimation settings. For each kVp, the beam quality and output of the x‐ray tube was measured using a 6‐cm3 ionchamber with a series of tube current (mA) with and without Bowtie filter. Catphan 500 phantom was used for CBCT imaging. For the small FOV and 20‐cm length collimation (S20), high‐resolution CBCT images were reconstructed with voxel size of .5×0.5×0.5 mm3. Spatial resolution, uniformity, CT‐number accuracy and linearity were measured on the Catphan images. Contrast‐to‐noise‐ratio (CNR) was measured using the means (S) and standard deviations (s) in 6‐mm diameter circular region‐of‐interest (ROI) within the polystyrene (PS) and LDPE by the formula of ( ) / (2 2) / 2 LDPE PS LDPE PS CNR = S − S s +s. Results: The exposure rate with Bowtie filter is linearly proportional to the mAs, increases at a rate of (kVp)2.85, and decreased to 73% of that without Bowtie at equivalent kVp and mAs settings. Without Bowtie, the spatial uniformity improves but the CNR deteriorates when increasing kVp at equivalent exposure rates. Application of Bowtie compensator improves the spatial uniformity by more than 11% and increases the accuracy of CT number for soft‐tissue materials at all tested kVps. Bowtie compensator also increases the CNR from 1.64 to 1.94 at 100 kVp, but reduces the CNR by ∼20% at 120kVp and 138kVp. Conclusion: Through this clinical investigation, we have found that Bowtie compensator improves the uniformity and CT‐number accuracy for soft‐tissue materials and may increase the CNR at the low kVp but decrease CNR at the high kVp. In image‐guided radiotherapy, using Bowtie with low kVp for small‐body and no Bowtie with high kVp for large‐body imaging appeared to be optimal settings.
SU‐FF‐P‐02: Regulatory Compliance Without Quality Assurance ‐ Problems
Authors: Shepherd J
Published: April 2010

This presentation shall cover the major problems that resulted from the purchase and use of a Radioactive Material Transport Package. Purchase of these containers does not require a fully implemented Quality Assurance program. Use and inspection requires adherence to a USNRC qualified Part 71 Quality Assurance program. The ‘old school’ thought process is that you get what you pay for, and you believe what people tell you, especially if you have paperwork to back it up. This is a model that is no longer viable. The consequences of trusting others without an internal confirmation has been significant.

A chronological sequence of events shall be presented with sidebars detailing how problems could have been avoided at each step. The necessity of an independent and fully implemented Quality Assurance program will be discussed. A recap of the penalties and consequences which resulted from these issues will be provided at the end.
SU‐FF‐E‐01: Management of a CAMPEP‐Accredited Physics Residency Program Using a Commercial Software and Database Tool and Utilizing Its Potential to Facilitate Formation of Distributed & Affiliated Residency Programs
Authors: Zacarias A , Mills M
Published: April 2010

Purpose: A review of commercially available allied health educational management software tools led to a decision to purchase the Typhon Group Allied Health Student Tracking Module for the CAMPEP‐accredited Therapy Program at the University of Louisville. Advantages of the Typhon Group software include a) didactic course reporting and organization, b) competency reporting by topic, category and didactic course, c) student time management and reporting, d) student patient case reporting by topic, category and course. Method and Materials: The software includes the facility for recording school administrative information, setting up lists of courses, faculty, clinical sites, categories, competencies, time logs, and the inclusion of standardized external documents. There are facilities for creating evaluation and survey instruments for completion both by residents (of mentors and program) and by faculty (of students). Competency documentation includes the time spent on the problem (or with the patient), time spent with the mentor, date of the competency, and approval by the mentor and program director. Course documentation includes course and lecture title, lecturer, topic information, date of lecture and approval by the Program Director. Results: The software has been used to document 520 hours of clinical conference logs and over 70 completed competencies by one resident over the course of one year. The software has the facility to include multiple clinical sites, with local sub‐administrators having the ability to approve competencies and attendance at clinical conferences. The Typhon Group Software therefore has the capability to manage CAMPEP‐accredited residency programs or the residency portion of a CAMPEP‐accredited DMP Program. Conclusion: The Web‐based database lends the software to the support of distributed or affiliated clinical sites within a single residency program. Such tools are a critical and necessary component if the medical physics profession is to meet the projected needs for qualified medical physicists in future years.
SU‐FF‐I‐02: Assessment of the Relation Between Absorbed Dose and Image Quality in CT Examination of Children
Authors: Hosseinabad M Tavakoli , Shokrani P , Fazlolahi S
Published: April 2010

Introduction: Cancer risk associated with ionizing radiation is more important in children. Reducing radiation dose to this age group is much more vital. The aim of this research is to evaluate the effects of kVp and mAs on image quality to find out suitable conditions and ways of reducing dose to this groups of patients when attending for CT examination. Materials and Methods: To evaluate radiation dose to the patients the index of CTDI (Computed Tomography Dose Index) which is recommended by FDA is used. The CTDI were measured in three different phantoms using a pensile ionization chamber (with 10cm active length 3009 PTW‐Friburg) in two different types of spiral CT scanner (Shimadzo SCT 7800TE and Philips Tomoscan AVPF). The phantoms were made of Plexiglas with diameters of 8cm for head and body of newborn and 16cm and 24cm for head and body of 5 to 12 years old children (AAPM, 1993). At the center and periphery of the phantoms 5 axial holes were made to fit the chamber during irradiation (one at the center and the other of four one centimeter form the edge of the phantom at equal distances). The effective dose were calculated for every routine CT examination protocol. Results: Maximum effective dose obtained was for newborn chest examination with Shimadzo scanner, when mAs was 80. It was reduced by 56% when mAs was reduced to 50. In this case noise was increased only by 19%. Effective dose in 12 years children was 315% compared with newborn for chest image. For Philips scanner with reduction of kVp form 120 to 100 effective dose reduce by 54% while noise increase only by 7%and contrast reduced by 4%. Conclusions: It is fund that changing the scanner factor reduce effective dose markedly while image quality dose not change.
SU‐FF‐I‐11: Inter‐Observer Variability of Mesothelioma Area Measurements On CT Scans
Authors: Labby Z , Armato S , Sensakovic W , Starkey A , Roberts R , Straus C , Caligiuri P
Published: April 2010

Purpose: The measurement of mesothelioma is a crucial component of the assessment of disease response to therapy. Current standards for response assessment utilize summed linear measurements acquired on three CT sections. The purpose of this work was to evaluate area measurements as a metric for response assessment, specifically through the study of the inter‐observer variability of such measurements. Method/Materials: One CT scan from each of 21 mesothelioma patients was collected. Using a computer interface, three radiologists contoured the visible disease on three CT sections containing visible disease. The radiologists were able to inspect the full CT scan, but were only able to contour specified sections. The resulting 189 area measurements (three radiologists, three sections per patient, 21 patients) were compared using a random‐effects analysis of variance model to assess relative inter‐observer variability. The 63 sums of three section measurements per patient were also analyzed, since these sums of areas are more clinically relevant for response assessment. Results: When each radiologist's measurements were compared with the average of the other two radiologists' measurements, moderate correlation was observed (r‐values of 0.64 to 0.94). The 95% confidence interval for relative inter‐observer variability of section area measurements was [−81.3%, +433.7%], spanning a range of 515.0%. For the summed area measurements (three sections per patient), the 95% confidence interval for relative inter‐observer variability was [−68.8%, +220.7%], spanning a range of 289.3%. Conclusion: The inter‐observer variability in area measurements of mesothelioma tumor spans a range that encompasses the response categories of the original WHO bi‐dimensional response criteria, as well as extrapolations of the RECIST response categories to two dimensions. Manual area measurements may not be a robust means of response assessment in mesothelioma patients, thus motivating future research in more precise semi‐automated segmentation methods.
SU‐FF‐I‐14: Investigation of Metallic Filters On the Detectability of Soft Tissues in Cone Beam Computed Tomography Using Flat Panel Detector of Acuity Simulator
Authors: Kohli K , Harrop S , Kwan W , Thomas S , Ramaseshan R
Published: April 2010

Purpose: The purpose of this work is to investigate the image quality with metallic filters partially or completely covering the CBCT detector. Materials and methods: Aluminum metallic filters of various thicknesses were placed on top of the detector covering them either completely or partially. The influence of these filters on the detectability of soft tissue was evaluated quantitatively. The parameters investigated included signal to noise ratio (SNR), contrast to noise ratio (CNR), image uniformity and CT number accuracy. The studies were carried out using the Catphan phantom imaged in the half fan configuration mode. Assessment was carried using a 36mm2 region of interest (ROI). CNR was determined with ROIs within the insert and adjacent to the insert of the low contrast object. SNR was assessed in the uniform water region. CT numbers were measured for air, PMP, LDPE, polystyrene, acrylic, delrin, Teflon and water. All the measurements were carried out at 125kVp and 80mA with slice thickness of 2.5mm. Results: The SNR for half fan mode improved by 31% for the 0.6mm filter covering the detector uniformly while the 1.5mm filter partially covering the detector (on the non bowtie side) improved SNR by 34%. For the similar setup the CNR improved by 33% and 10% respectively. These improvements could be due to metallic filter selectively absorbing low energy scattered photons. No noticeable improvement in image uniformity was observed. The CT number accuracy was not compromised by the use of filter. Conclusion: The results of our current investigation suggest use of metallic aluminum filter on flat panel detector can improve the ability to detect low contrast objects. A series of experiments are currently underway to evaluate the effect of different filters under different geometries for both full and half fan image acquisitions.
SU‐FF‐I‐15: An Algorithm for Metal Streaking Artifact Reduction in Cone Beam CT
Authors: Bazalova M , Landry G , Beaulieu L , Reniers B , Verhaegen F
Published: April 2010

Purpose: To develop a metal streaking artifact correction for cone beam CT (CBCT) and to evaluate its effect on image quality. Method and Materials: A small water phantom with steel cylinders, a large solid water phantom with contrast inserts and steel cylinders and a GYN patient with a metallic vaginal cylinder were scanned on a CBCT scanner with an amorphous silicon flat panel detector. CBCT images were reconstructed in three different ways: using the CBCT scanner reconstruction algorithm, using an in‐house reconstruction algorithm, both on the basis of the original projections and using our reconstruction algorithm with based on modification of projection data. First, metal traces were identified in either the projection space or the image space. The projection areas corresponding to the metals were deleted and replaced by interpolated data from the neighboring projections. Results: Identification of metal traces worked very well for the phantoms and the patient. In the case of the small phantom, the scanner reconstructed images suffered from severe artifacts that were reduced when the CBCT images were reconstructed by the in‐house reconstruction algorithm. CBCT images using the interpolated projections were nearly artifact free in both phantoms. The corrected image of the large phantom closely resembled the CBCT image without metals. The original patient CBCT images showed streaking artifacts in the proximity of the vaginal cylinder that were significantly reduced after the correction algorithm was applied. A coronal slice at the position of the cylinder clearly demonstrated the improvement in image quality. Conclusions: The quality of CBCT images was greatly improved using the projection interpolation algorithm in both the phantoms and the patient. The successful test of the correction algorithm applied on CBCT images of the large phantom and in the complex patient anatomy offers the possibility to use the correction for patients with hip prostheses.
SU‐FF‐I‐16: GATE Simulations of CTDI100c for Various Phantom Shapes, Sizes, and Compositions
Authors: Lee C , Kim H , Cho H , Kim D , Park H , Yu A , Lee Y , Jung J
Published: April 2010

Purpose: The purpose of this study was to investigate CTDI100c (computed tomography dose indice at center) for various phantom shapes, sizes, and compositions by using GATE (geant4 application for tomographic emission) simulations. Method and Materials: GATE simulations were performed for various phantom shapes (cylinder, cylindroid, and hexagonal prism PMMA phantoms) and phantom compositions (water, PMMA, polyethylene, polyoxymethylene) with various diameters (1–50 cm) at various kVp (80, 100, 120, 140 kVp) and mAs (100, 200, 300, 400 mAs) levels. Results: The CTDI100c values of cylinder, cylindroid, and hexagonal prism phantom at 140 kVp, 200 mAs resulted in 20.1, 24.3, and 22.1 mGy, respectively. The cylindroid phantom may be needed to estimate CTdose, because it.s shape is closer to that of human body than cylinder and hexagonal prism PMMA phantom. The effect of phantom composition to CTDI100c was studied for water, PMMA, polyethylene, polyoxymethylene. For all phantom compositions, CTDI100c values were nonlinearly increased, linearly increased, and nonlinearly decreased as a function of kVp, mAs, and diameter, respectively. Among those compositions, CTDI100c values for water as a function of kVp, mAs, and diameter were changed most rapidly which indicating that CTDI100c values using PMMA could be underestimated and overestimated compared to those measured with water. Conclusion: In conclusion, the results of GATE simulations demonstrated that CTDI100c was able to be characterized for various phantom shapes, sizes, and compositions so that we may be able to investigate for estimating CTDIs in realistic applications.
SU‐FF‐I‐26: Automatic Detection of Calcifications in Cone Beam Breast CT Images
Authors: Han T , Chen L , Zhong Y , Lai C , Liu X , Shen Y , Yi Y , Ge S , You Z , Wang T , Shaw C
Published: April 2010

Purpose: Microcalcifications (MCs) play an important role in early detection of breast cancer. This study is to describe a technique to automatically identify and segment the calcifications from the breast anatomy in cone beam CT (CBCT) images. Method and Materials: Projection images of mastectomy breast specimens were acquired with a bench‐top experimental CBCT system and reconstructed using FDK algorithm with a regular ramp filter. The reconstructed images were first corrected for the non‐uniform cupping artifacts due to x‐ray scatter and beam hardening. The corrected CBCT images had more uniform background but were still too noisy for threshold segmentation. To reduce the noise level, the images were processed with a noise averaging filter in z direction followed by a total variation filter to reduce the noise level while keeping the edge sharpness and contrast of calcifications. To automatically detect the calcifications with proper threshold level, a Gaussian curve fitting was used to fit the histogram of the CBCT image. Since the CT numbers of calcifications are usually significantly above those for breast tissue, cutoff point of the Gaussian curve was used as the threshold value to segment the calcifications. Results: With this method, the calcifications in the entire breast were successfully segmented from the breast tissue background. The results agreed well with those identified by visualization. Conclusion: The calcifications in CBCT breast images can be automatically detected by threshold based segmentation method with the nonuniform cupping artifacts corrected for and the noise level properly reduced.
SU‐FF‐I‐30: Generating Attenuation‐Based Tube Current Modulation (TCM) Schema Based On Voxelized Patient Models to Be Used in Simulations Estimating Organ Dose From CT
Authors: Angel E , DeMarco J , Cagnon C , McNitt‐Gray M
Published: April 2010

Purpose: There are several TCM algorithms in CT acquisition currently used including x‐y plane modulation, z‐axis only modulation and combined (x,y,z) modulation techniques. While these have been used to reduce radiation dose in general, methods do not yet exist to assess their impact on reducing organ dose. This study establishes a generalizable process to generate TCM schema from various attenuation‐based algorithms for use in Monte Carlo simulation methods to assess organ dose from voxelized patient models. Methods and Materials: A previously validated scanner‐specific Monte Carlo‐based CT scanner model was altered to allow simulation of a topogram with the x‐ray tube held at an assigned gantry angle. An Anterior‐Posterior (AP) and a Lateral topogram were simulated on a voxelized patient model. A cylindrical mesh tally was used to calculate attenuation for every slice location along the cranial‐caudal direction of the patient and for angular increments around the gantry of the patient. A plot of patient attenuation versus table position was obtained for both topograms. The ideal TCM was calculated for each table position and the entire three‐dimensional TCM schema was generated by interpolating between the ideal TCM plots to maintain smooth tube current transitions for the remainder of the gantry rotation. Results: Using this generalizable model, we were able to generate the attenuation‐based TCM schema for a voxelized patient model. Conclusion: The results of this study demonstrate the ideal TCM schema for a specific TCM algorithm, but this generalizable model can be used to generate the ideal TCM schema for any combination of gantry angle, table location, and width of detector data. Therefore, this generalizable model can be used to generate TCM schema based on all types of attenuation‐based TCM algorithms and for any voxelized patient model.
SU‐FF‐I‐43: Iterative Methods of Cone‐Beam CT Image Reconstruction for Under‐Sampled and Truncated Projection Data
Authors: Yeung I , Dawson L , Cho Y , Moseley D , Case R , Tang Q
Published: April 2010

Purpose: In this work, iterative method with total variation (TV) minimization was proposed to reconstruct cone beam CT (CBCT) image from under sampled and truncated projection data. Method and Materials: Respiratory motion is a significant source of error in CBCT image reconstruction for the thorax and upper abdomen. To reduce motion artifacts in reconstructed image, four‐dimensional (4D) CT imaging has been studied. One category of 4D CT imaging is gated image reconstruction in which projection data acquired when free breathing were retrospective sorted into several subsets of projections that each corresponds to a certain breathing phase. The projection subsets are reconstructed into CBCT volume at different phases. Normally, CBCT scanning system acquires about 330 projections over half rotation. After sorting these 330 projections into 10 subsets, each subset is under sampled and only has 33 projections. Image reconstructed with this under sampled subset has severe streaking artifacts. In addition, the detector panel does not cover the extent of the body causing truncation of the projection data along axle and transaxle directions. The maximum likelihood expectation maximization was used with TV constraint and the results were compared with those of filtered backprojection (FBP) using computer simulations and patient data. Results: The MLEM‐TV method produced a larger reconstructed region‐of‐interest (ROI) than that of FBP in computer simulation. Also, the images of the proposed method appear to have better noise removal and streaking artifact suppression induced by under‐sampling in computer simulation and patient data. Signal to noise ratio (SNR) of three typical regions on a patient image of the FBP method are 5.4, 7.5 and 8, while those of MLEM‐TV are 9.7, 20.2 and 24.8 respectively. Conclusion: Iterative method is feasible in CBCT imaging and has an advantage over FBP method when the projection data are under sampled and truncated.