bluuebunny/crossref_metadata_2025 huggingface dataset:
MO‐D‐304A‐03: Noise Suppression in Scatter Correction for Cone‐Beam CT
Authors: Xing L , Wang J , Zhu L
Published: April 2010

Purpose: Scatter correction is crucial to the quality of reconstructed images in X‐ray cone‐beam computed tomography (CBCT). Most of existing scatter correction methods assume smooth scatter distributions. The high‐frequency scatter noise remains in the projection images even after a perfect scatter correction. To circumvent the problem and truly gain from scatter correction, an effective scatter noise suppression method must be in place. Method and Materials: We analyze the noise properties in the projections after scatter correction, and propose to use a penalized weighted least‐squares (PWLS) algorithm to reduce the noise in the reconstructed images. The method aims to estimate the ideal linear integrals by minimizing a PWLS objective function which models the first and second moments of the projection data. Results: Experimental results on an evaluation phantom (Catphan@600) show that the proposed algorithm further reduces the reconstruction error in a scatter corrected image from 10.6% to 1.7%, and increases the CNR by a factor of 3.6. Significant image quality improvement is also shown in the results on an anthropomorphic phantom, in which the global noise level is reduced and the local streaking artifacts around bones are suppressed. Conclusion: In this paper, using a clinical CBCT system and a measurement‐based scatter correction, we show that a scatter correction alone does not provide satisfactory image quality and the loss of the contrast‐to‐noise ratio (CNR) of the scatter corrected image may overwrite the benefit of scatter removal. A statistics‐based PWLS is proposed to reduce the image noise after scatter correction and the algorithm performance is demonstrated using experiments.
MO‐D‐304A‐09: Multi‐Slice CT Versus Cone Beam CT for Breast Imaging: Radiation Dose Distributions with Monte Carlo Simulation
Authors: Yi Y , Han T , Liu X , Shen Y , Chen L , Zhong Y , Lai C , Ge S , You Z , Wang T , Shaw C
Published: April 2010

Purpose: To use Monte Carlo simulation method to investigate and compare the overall radiation dose and dose distribution for breast imaging using multi‐slice CT and cone beam CT (CBCT) techniques. Method and Materials: CBCT images of a breast specimen have been combined with multi‐slice CT images of a patient chest to form a 210×206×110 model for a patient lying in prone position with both breasts freely protruding downward. Image segmentation was applied to separate the images into areas for adipose tissue, soft tissue, muscle, air and bone. Rep78 was used to compute the spectra for 120 and 80 kVp x‐rays with a HVL of 4.65 and 4.08 mm Al, respectively, for simulating multi‐slice CT and CBCT, respectively. A collimator was added to simulate the x‐ray fan beam used in multi‐slice CT and a half‐cone beam for CBCT. To simplify the simulation, the table was assumed to shift by one fan beam width after the gantry makes one full rotation. 2×107 photons were used to calculate the dose for multi‐slice CT with DOSXYZnrc and 1×109 photons for CBCT scan of the same breast phantom. The results of the dose calculations were rescaled for 240 mAs and 25 mAs, respectively. Results: The results of Monte Carlo calculations for multi‐slice CT indicated that dose levels in the heart and bone structures were about twice as high as those in the breasts. The breast dose from multi‐slice CT was from 0.8 to 2 times as high as those in cone beam breast CT. Conclusion: Results from our Monte Carlo calculations indicated that breast doses were found to be higher with a typical multi‐slice CT scan of the chest. An additional dose problem for multi‐slice CT is full exposures to the rest of the chest, incurring high radiation doses in the heart and bone structures.
MO‐D‐210A‐02: Clinical CT Applications with Photon‐Counting Detectors
Authors: Levinson R
Published: April 2010

Photon‐counting detectors are now being introduced in medical imaging systems. A major challenge for PC detectors is to enable high count rate operation required for medical imaging. High count rate operation is now available with state‐of‐the art pulse counting electronics. Pulse counting techniques can work together with direct‐conversion sensors enabling additional cost and performance benefits versus indirect‐conversion sensors.

PC detectors are easily configurable for multi‐energy acquisitions, enabling dual and triple (k‐edge) imaging techniques. The energy discrimination and binning by PC detectors competes well with the energy separation achieved with dual kVp imaging systems and provides unique performance capabilities for triple/k‐edge imaging.

PC detectors have been shown to have negligible levels on electronic noise. The low noise performance enables new scanning techniques and ultimately reduces the radiation dose the patient, an important consideration in the design of X‐ray imaging systems.

This lecture will provide an overview on the use of photon‐counting detectors in dual‐energy CT imaging and image quality on clinical CT applications.

Learning Objectives:

1. Understand the operation of direct‐conversion, photon‐counting detectors

2. Application of photon‐counting detectors to multi‐energy CT imaging

3. Use of photon counting CT system in a clinical setting
MO‐EE‐A1‐03: A 4D IMRT Planning Method Using Deformable Image Registration for Lung Cancer
Authors: Li X , Wang X , Li Y , Pan X , Mohan R , Zhang X
Published: April 2010

Purpose: 4D CT is increasingly used to define the ITV, the envelope of the CTV as it moves during breathing, and PTV (ITV + set up margin). IMRT plans are designed to provide uniform dose to the PTV. We propose a planning method to design true 4D IMRT plans in which the PTVs of the individual phases of the 4D CT as well as the conventional PTV may receive non‐uniform doses, but the cumulative doses to the PTVs of individual phases, computed using deformable image registration (DIR), are uniform. Methods: The non‐uniform dose prescription for conventional PTV was obtained by solving linear equations by requiring motion‐convolved 4D dose to be uniform to the PTV for the end exhale phase (PTV50%) and by constraining maximum inhomogeneity to be 30%. A plug‐in code to Pinnacle was developed to perform the IMRT optimization based on this non‐uniform PTV dose prescription. The 4D dose was obtained by summing the mapped doses from individual phases of the 4D CT using DIR. This 4D dose distribution was compared with that of the ITV method. The robustness of 4D plans over the course of radiotherapy was evaluated by computing the sum of the 4D dose distributions for each weekly CT mapped to the planning 4D CT using DIR. Results: The 4D dose distribution provided additional lung sparing by 5% for V5, V10, V20 and V30 compared to the use of the ITV method. The dose volume histograms of PTV50%, CTV, lung, spinal cord, and heart for the cumulative dose over the course of IMRT were similar to those for 4D dose at the time of original planning. Conclusion: The proposed 4D planning method may increase lung sparing compared to the ITV method used commonly in the clinics and is robust against inter fractional set‐up and anatomy changes.
MO‐EE‐A1‐04: A Comparison Study of a New Optimal Field Splitting Algorithm in IMRT
Authors: Dou X , Wu X , Kim Y , Bayouth J , Buatti J
Published: April 2010

Introduction In IMRT treatment planning, multi‐leaf collimator (MLC) with a maximum leaf spread constraint is used to deliver the prescribed intensity maps (IMs). However, the maximum leaf spread of an MLC may require splitting a large IM into several overlapping sub‐IMs that are each delivered separately. Existing approaches usually require fixed sizes of sub‐IMs. We developed a method producing sub‐IMs of flexible sizes subject to the maximum leaf spread, which may improve the delivery efficiency. In this work, we propose to optimally split an IM into sub‐IMs while minimizing the total complexity of the sub‐IMs. Method and Material The complexity measure of an intensity map we use is the total sum of positive gradients of all rows. We solve the optimal field splitting problem using dynamic programming. Our algorithm also balances minimum beam‐on times of the resulting sub‐IMs. We evaluated the performance of our algorithm by implementing it on clinical IMs obtained from the Department of Radiation Oncology, University of Iowa and comparing it to ommercial software derived solutions. 14 IMs from pelvic treatment plans on 2 patients were used for splitting resulting in 3 sub‐IMs (3‐splitting) algorithm experiments and 20 IMs from head & neck treatment plans from 3 patients were used for 2‐splitting algorithm experiments. We replaced the field splitting method in Pinnacle with our method and the results were compared. Results For 3‐splitting cases, the number of segments was reduced by 12.5%, and the number of MU's was improved by 30.0%, along with 144‐sec reduction of beam delivery time per fraction. For 2‐splitting, the number of segments was reduced by 5.3%, and the number of MU's was improved by 27.6%. The performance for 3‐splitting cases was better than for 2‐splitting. Conclusion We have developed an optimal field splitting method which appears to outperform the commercial software Pinnacle.
MO‐EE‐A1‐05: Direct Aperture Optimization of Intensity Modulated Arc Therapy
Authors: Park J , Cheong K , Cho W , Jung W , Xing L , Suh T
Published: April 2010

Purpose: Intensity modulated radiation therapy has been a very popular and effective treatment technique for the treatment of prostate, head & neck and liver etc. Meanwhile, another innovative treatment technique, intensity modulated arc therapy, was developed to complement some drawbacks of IMRT like long treatment time and low MU efficiency. Since the IMAT completes the treatment just within one or two rotations, it is not easy to get optimized leaf sequences in a deterministic way. In this study, we tried to get optimized IMAT treatment plan by genetic algorithm. Method and Materials: First, the start/end positions of MLC leaves at each rotation angle with 10° interval were selected as optimization variables and encoded into genetic chromosomes. They experience genetic operations such as generation, selection, crossover, mutation and reproduction and the most optimized solution remains in the end of iteration. The constraint of maximum leaf speed was included in these operations. And the fitness of each population was evaluated by DVH volume constraint based objective function. IMAT dose distribution was calculated as a weighted sum of MLC shape at each angle and related Dij matrix similar to IMRT dose calculation. The algorithm was implemented in our treatment planning system and the dose distributions and DVHs of single and double gantry rotation cases were compared. Results: IMAT plan gave comparable results with conventional IMRT even with single gantry rotation and there was not significant improvement in double gantry rotations. Genetic algorithm required about 3,000 generations to reach optimized value due to its stochastic nature. Conclusion: It was possible to optimize IMAT plan with genetic algorithm and the results are optimized MLC leaf sequences readily deliverable in general linear accelerators. It can be an efficient method to solve IMAT optimization problem despite of relative slow convergence.
MO‐EE‐A2‐03: Improved Monte Carlo Simulation of Small Electron Fields
Authors: O'Shea T , Faddegon B , Sawkey D , Foley M
Published: April 2010

Purpose: To validate the use of improved source and geometry parameters, derived from Monte Carlo simulation of a Siemens Primus accelerator at maximum field size (40 × 40 cm2), for clinically relevant small electron fields. Method and Materials: Measurements were performed on a Siemens Primus linear accelerator for electron energies 6–21 MeV with open applicators and circular cerrobend inserts ranging from 1 cm to 5 cm in diameter. For the open applicators, relative output factors (ROF), depth penetration and off‐axis profiles were measured with parallel‐plate (Roos) and small volume thimble (CC13) chambers. For the cerrobend insert collimated fields a diode (EFD) was used for high spatial resolution. Off‐axis profiles were measured at 0.5 cm, dmax, in the fall‐off and in the bremsstrahlung tail of each beam. Monte Carlo simulations were performed using the EGSnrc accelerator simulation code BEAMnrc. The source and geometry parameters used were obtained from a previous study following disassembly of the treatment head, for maximum field size and no electron applicator, which resulted in an unprecedented match to measurement. Results: Good agreement was found between measured and calculated off‐axis profiles and percentage depth dose curves, to 2 % / 1 mm or better. The normalized off‐axis profiles in the bremsstrahlung tail matched to 2 – 3 %. Calculated relative output factors were within 1 % of those measured with the Roos chamber. Conclusion: This work has shown that a recent methodology used to extract accurate details on the source and geometry of the treatment head for maximum field size, is applicable for clinically relevant small electron fields. The need for careful measurements and accurate knowledge on the source and geometry of the treatment head as a precursor to accurate fluence and dose calculation is highlighted.
MO‐EE‐A2‐04: Calculation of Water Equivalent Thicknesses of Materials of Arbitrary Densities, Elemental Compositions and Thicknesses in Proton Radiotherapy
Authors: Zhang R , Taddei P , Fitzek M , Newhauser W
Published: April 2010

Purpose: To develop simple and general analytical formulas to calculate water equivalent thickness (WET) values with an accuracy of 1 mm for materials commonly used in proton radiotherapy. Method and Materials: Based on theoretical range‐energy relationships, three formulas were derived to predict the WET of materials of arbitrary density, composition and thickness Lead, aluminum, polymethylmethacrylate, polystyrene, and lung‐equivalent slabs, which represent materials with different densities, were placed in therapeutic proton fields. Alternative approaches were developed for targets that were ‘radiologically thin’ or ‘thick’. We compared the WET values calculated by the three formulas to those of experimental measurements and iterative numerical calculations. We also compared the accuracy of approximations based on International Atomic Energy Agency (IAEA) report and stopping power ratios (SPR) with numerical calculations. Results: The differences between the values of WET calculated using the analytical formula and the measured data were less than 0.8 mm. Likewise, the WET values calculated using analytical formulas agreed well with those calculated numerically, while IAEA and SPR approximations only work well for thin targets. The comparisons revealed that simple analytical methods could be used to calculate WET values with small, known errors. Conclusion: The results of this study provide evidence that simple analytical formulas can be used to accurately calculate WET of various materials in proton fields of therapeutic energies. Therapeutic proton beams are commonly characterized by their water‐equivalent ranges; therefore, the formulas developed in this study can be used for the convenient and accurate calculation of WET values for common clinical and research applications.
MO‐EE‐A3‐01: Comparison of Prostate Rotation and Calypso Beam Rotation for Prostate Margin Evaluation
Authors: Xu Q , Li J , Shan G , Veltchev I , Emam I , Fan J , Lin T , Jin L , Chen L , Ma C
Published: April 2010

Purpose: The Beacon rotation angles reported by the Calypso system have not been utilized clinically due to the difficulties in rotating the patient. The actual prostate rotation angle is affected by Beacons' migration, prostate's shrinkage and deformation due to rectal/bladder filling. This work investigates the actual prostate rotation angles between the planning CT and the treatment CBCT and to compare those reported by the Calypso system. Method and Materials: The Calypso system reports centroid shifts and rotation angles of the 3 implanted Beacons, relative to their locations on the planning CT. CBCT scans were obtained for 9 treatment fractions of 5 patients. The same sets of the Beacons in the planning CT and post‐treatment CBCT were segmented according to their high intensities and aligned according to their centroid positions. An iterative closest point (ICP) method was developed to find the best matching iteratively between two sets of Beacons after rotation and translation. Results: The maximum inter‐Beacon distance varied from 1.1 to 4.7 mm with inter‐Beacon distances from 14.4 to 40.4 mm. The mean Beacon rotation angle reported by the Calypso system in each plane was 4.7±3.8°, which were likely caused by the inter‐Beacon distance change. After the best 3D matching of the Beacons, our method reported a mean rotation angle of 1.5±1.7° for all the fractions. If the projected inter‐Beacon distance was >9mm there was good agreement between our method and the Calypso system. As the inter‐Beacon distance decreased, the uncertainty in the reported rotation angle increased. Conclusion: The actual rotation angles for the prostate were smaller than those for the Beacons reported by the Calypso system. It is recommend to avoid small (<9mm) projected inter‐Beacon distances to reduce the uncertainty in the reported rotation angle.
MO‐EE‐A3‐02: Inferring Nodal Volume and Primary Tumor Positions From Multiple Anatomical Surrogates Using 4D CT in Stage III Lung Cancer
Authors: Malinowski K , Pantarotto J , Senan S , McAvoy T , D'Souza W
Published: April 2010

Purpose: To investigate the feasibility of modeling primary tumor and nodal volume positions from anatomical surrogates in order to reduce the contouring burden of planning from 4D CTs in Stage III lung cancer. Method and Materials: To localize their centroid positions at each respiratory phase, we contoured nodal volumes and primary tumors in 16 Stage III lung cancer planning 10‐equal‐phase 4D CTs. We also localized a series of anatomical respiratory surrogates (carina, xyphoid, nipples, midsternal external marker) in each image. To explore the feasibility of our proposed method, we 1) characterized the correlations between target and surrogate 3D motion, 2) applied Ordinary Least‐Squares (OLS) and Partial Least‐Squares (PLS) to a random subset (3–8) of images to predict the target positions in the remaining images, 3) determined the best set of three respiratory phase bins to contour, and 4) used them to create 3‐phase models using either all anatomical surrogates or carina alone. Results: The surrogate best‐correlated to target motion was most often the carina but varied widely. Depending on the number of phases used to build the models, mean errors ranged from 1.0mm to 1.4mm and from 0.8mm to 1.0mm for OLS and PLS, respectively. When the 0%, 40%, and 70% respiration phases were used, 3‐phase models had mean(±standard deviation) errors of 0.8±0.5mm and 2.4±9.0mm for models based on all surrogates and carina alone, respectively. For target coordinates with motion>5mm, the mean 3‐phase error was 1.3mm. Conclusion: Using only three contoured respiratory phases to train the models, the mean model error was on the order of CT resolution. Inferential modeling of the primary tumor and nodal volume positions may have the potential to decrease the time required to process 4D CT scans, thereby improving therapy by allowing for incorporation of patient‐specific margins in the planning process.
MO‐EE‐A3‐06: Comparison of Pre‐ and Post‐Implant Prostate Volume Segmentation Using Trans‐Rectal Ultrasound and Computed Tomography
Authors: Tynan P , Joyner M , Smith M , Gutiérrez A , Stathakis S , Mavroidis P , Papanikolaou N , Swanson G
Published: April 2010

Purpose: To quantitatively evaluate differences in prostate volume measurements via transrectal ultrasound (TRUS) and computed tomography (CT) used for dosimetric planning in prostate brachytherapy. Method and Materials: Prostate volume measurements were made in 83 prostate brachytherapy patients. One to two weeks prior to implantation, patients were placed in the dorsal lithotomy position, and prostate volumes were measured via TRUS. Immediately afterward, patients were rescanned using CT to allow for comparison of CT and TRUS measurements. On treatment day, patients were rescanned via TRUS before and after implantation and were rescanned by CT within an hour after procedure completion. The prostate and urethra were delineated by the same physician on all scans, and prostate volumes were calculated. Results: Substantial correlation was found between pre‐/post‐ implant prostate US volumes (R2=0.7998), pre‐/post‐ implant CT volumes (R2=0.7872), and pre‐implant US and post‐implant CT volumes (R2=0.8352). However, it was found that the difference between pre‐ and post‐implant volume measurements varied with the combination of modalities compared. For pre‐ vs post‐implant TRUS, post‐implant prostate volumes averaged 26.1% larger than those measured prior to treatment. For pre‐ vs. post‐ implant CT, post‐implant measurements averaged 58.9% greater. Post‐implant CT measurements averaged 23.8% greater than post‐implant TRUS measurements. Conclusion: While it would be ideal to use the same method to measure pre‐ and post‐implant volumes, this is not generally practiced. Prostate volumes measured using TRUS and CT show a distinct relationship, but it is important to note that this does not mean that the modalities provide the same values for the same prostate. In addition, the relationship between pre‐implant TRUS and CT is not identical to that between post‐implant TRUS and CT. Therefore, it is not possible to state that accurate comparison of pre‐ and post‐implant dosimetric plans can be accomplished when different imaging modalities are used for each.
MO‐EE‐A4‐04: Quantitative Measurement of Hypoxia in Human Brain Tumors Using QBOLD MRI
Authors: Massoumzadeh P , He X , Rich K , Garbow J , Yablonskiy D , Benzinger T
Published: April 2010

Purpose: The main objective of this study is to evaluate the feasibility of using a recently developed MR technique, quantitative blood oxygenation level‐dependent (qBOLD), to quantify the oxygen extraction fraction (OEF) of tumors metastatic to the brain. Materials & Methods: The qBOLD technique provides a regional OEF measurement based upon an MR signal model of brain that incorporates prior knowledge about brain tissue composition. A 3D version of gradient echo sampling of spin echo sequence with RF spoiling is used to obtain the MRI signal. (He, Zhu, and Yablonskiy, MRM 60:4, 882–888, 2008). To evaluate the feasibility of qBOLD quantify OEF in central nervous system tumors, six patients (47.9 y to 67.2 y, mean 55.4 y, 4 female and 2 male) with metastatic brain tumors were prospectively enrolled in a longitudinal imaging study. The primary malignancies were lung cancer (in five patients) and renal cell carcinoma (in one patient). The qBOLD procedure was performed as part of an integrated neuroimaging protocol, including conventional pre‐ and post‐contrast images and dynamic susceptibility contrast perfusion. The patients were scanned at 1.5T (Siemens TIM Espree) while wearing a stereotactic frame prior to radiation therapy. Post processing was performed offline using Matlab. Results: Supratentorial metastatic tumors (6 patients) and surrounding vasogneic edema demonstrated marked visual conspicuity and quantifiably altered OEF using the qBOLD MRI: e.g, OEF values for the area of vasogenic edema were 54.8+/−12.3 % compared to 36.6+/−6.6 % in contralateral normal white matter. Conclusions: Using a recently developed MR pulse sequence, qBOLD, we were able to quantify the OEF in humans with metastatic brain tumors. qBOLD offered excellent visual conspicuity for lesion detection for supratentorial, non‐hemorrhagic lesions. Interestingly, vasogenic edema surrounding both primary and metastatic tumors was also associated with elevated OEF, a finding which warrants further investigation.
MO‐EE‐A4‐05: Image Feature‐Based Tumor Shrinkage Modeling in Head and Neck Cancer for Adaptive Radiation Therap
Authors: Chao M , Xie Y , Xing L
Published: April 2010

Purpose: A novel technique was developed to model the tumor shrinkage/growth in response to radiotherapy in head‐n‐neck (HN) cancer to better understand the therapeutic process and compute the cumulative dose for adaptive radiation therapy (ART). Methods and materials: Five HN patients were enrolled in the study. For each case, 8∼10 pre‐treatment cone beam computed tomography (CBCT) images were acquired using the Varian Trilogy on‐board imager. Planning CT and gross tumor volume (GTV) for each patient was used as a template. An image feature based model was employed to establish the correspondence between planning CT and CBCT. Due to the non‐conservation of the image contents, similarity based deformable model cannot be solely used. Two‐step procedure was adopted: homologous tissue features shared by the planning CT and CBCT were detected and their correspondence was matched using the Scale Invariance Feature Transformation method. This was followed by a registration of the rest points using a basis spline interpolation. A bi‐directional mapping was developed to increase the precision of tissue feature correspondence. The proposed model was tested with a number of digital phantoms with introduction of artificial volumetric changes. Results: The application of the bi‐directional feature based model to digital phantoms revealed that the artificial volumetric changes could be modeled accurately. The error of GTV boundary between the modeled and the ground truth was less than 1mm. For the clinical cases, the new algorithm worked reliably for a reasonable volume change (<35%), indicating the time span between two consequent imaging sessions should not be unreasonably far away in order for the model to function properly. Conclusions: We developed an image feature‐based model to derive the tumor change kinetics to better understand the tumor response to radiotherapy. The new model will find its wide spread application in ART for HN cancer.
MO‐FF‐A1‐05: Quantitative Radiation Therapy Dosimetry Using Reusable Storage Phosphor KCl:Eu2+
Authors: Han Zhaohui , Driewer Joseph P , Zheng Yuanshui , Low Daniel A , Li H. Harold
Published: April 2010

Purpose: To investigate the quantitative use of a novel dosimeter for radiation therapy dosimetry. Methods and Materials: Cylindrical dosimeters 7 mm in diameter and 1 mm thick were fabricated. Dosimetric properties were studied with an in‐house optical readout system after irradiation by a linear accelerator. The overall experimental uncertainty was estimated to be within ±2.5%. Results: 1) showed satisfactory radiation hardness. There was no significant change in the stimulation spectra after irradiation up to 200 Gy when compared to a fresh sample, indicating that this material could be reused at least 100 times if 2 Gy per use was assumed, e.g., for a patient‐specific IMRT QA; 2) exhibited supra‐linear response to dose after irradiation from zero cGy to 800 cGy; 3) After x‐ray irradiation the PSL signal decayed with time and eventually reached a plateau (0.1% per hour) after 12 hours, which was significantly better than a commercial CR (computed radiography) plate; 4) The sensitivity of the dosimeter was independent of the dose rate ranging from 15 cGy/min (underneath a MLC) to 1000 cGy/min; 5) The sensitivity showed no energy dependence for either open x‐ray or megavoltage electron fields; 6) Over‐response to low‐energy scattered photons was comparable to radiographic film, e.g., a Kodak EDR2 film. Reduction of dosimeter thickness to tens of microns would minimize the energy dependence. Conclusion: We have demonstrated that dosimeters have many desirable dosimetric characteristics and that has great potential to replace as the primary storage phosphor material for radiation therapy dosimetry. In the future, a large‐area based CR plate created using modern thin film techniques would provide a reusable, quantitative, high‐resolution two‐dimensional dosimeter with minimal energy dependence.

This work is supported in part by an NIH grant CA131690.
MO‐FF‐A1‐06: Quantitative Light Dosimetry in Air Using Spherical Optical Fiber Detector
Authors: Ferreira M , Austerlitz C , Sheng C , Benhabib S , Allison R , Sibata C
Published: April 2010

Purpose: To quantitatively evaluate current clinical dose calculations delivered by cylindrical diffusers used in superficial Photodynamic Therapy (PDT) treatments. Method and Materials: A setup was developed to investigate light irradiance patterns in air ranging from 2–50mm of Source to Detector Distances (SDD), distances customarily used in superficial PDT treatments. A 630 nm PDT diode laser light source was used in junction with diffusers ranging from: 10, 20, 25, and 50 mm. The detector was mounted on an optical bench along varying SDDs. The irradiance was then measured using a spherical optical fiber detector (1.8‐mm diameter), which was calibrated against a 1cm×1cm window photodiode detector (Ophir PD300‐3W traceable to NIST) connected to a power meter. Finally, sets of predicted irradiance values were calculated under typical clinical conditions by dividing the total power by the cylinder area bounded by the SDD. Results: The measured and predicted values were plotted and compared. For the 10mm diffuser, at approximately 50mm SDD, the predicted value was nearly fourteen times greater than that of the measured. For the larger diffusers, the disparity between the predicted and measured results narrowed. For example, the 50mm diffuser, at the same distance as that of the 10mm, predicted an intensity of only two times greater than that of the measured. Conclusion: Agreement between measured and predicted irradiance values is expected to occur for a hypothetical infinite length diffuser or for small SDD. The results however, revealed that at large distances from the source, with respect to the diffuser size, the theoretical results diverge from those obtained experimentally. Therefore, the current dose calculation should be reviewed for clinical PDT, as the understanding of the irradiance in air is paramount for the correct calculation of light dose delivered in PDT treatments.
MO‐FF‐A2‐05: A Novel Stereotactic Radiosurgical Device for the Treatment of Age‐Related Macular Degeneration (AMD)
Authors: Chell E , Firpo M , Bolch W , Lee C , Hanlon J
Published: April 2010

Purpose: Age‐related Macular Degeneration (AMD) is the leading cause of blindness in people over 65 in the U.S. It is caused by a proliferation of capillaries in the retina and can result in profound and rapid loss of central vision. As a neovascular disease, it has been shown to be susceptible to radiotherapy. Recently, a 100kVp tabletop stereotactic radiosurgical (SRS) device has been developed to deliver highly‐collimated beams of X‐rays to the fovea to treat AMD. This study is an evaluation of that system. Method and Materials: The device delivers a three‐port, 16Gy single fraction dose to the macula. Using a suction‐enabled contact lens assembly (“the I‐Guide”) to stabilize the eye, three 4mm diameter beams of 100kVp x‐rays are delivered to the fovea, directed by a positioning robot. The beams enter the eye through the sclera and avoid the radio‐sensitive lens. The I‐Guide includes reflective fiducials that are monitored by cameras, and the real‐time position of the beam on the retina is calculated from the fiducial positions. Because of uniformity across adult eye populations, a class‐solution treatment plan was implemented using a single parameter (eye length). Software manages treatment time and automatic gating of beam in case of excessive eye motion. A clinical trial is underway. Results: 100kVp proves an optimal energy for ophthalmic radiotherapy. A therapeutic dose to the retina can be delivered with negligible impact to the brain and the scleral entry dose is well‐tolerated. The scatter from the narrow beam is minimal to sensitive structures in the eye. Submillimeter targeting precision was demonstrated in the lab and in the clinic. Submillimeter motion‐management was also demonstrated. Conclusion: The eye‐specific SRS device shows great promise for providing a precise and non‐invasive method of treating AMD.

Research sponsored by Oraya Therapeutics.
MO‐FF‐A2‐06: Effects of Lung Tumor Motion On Rapid Arc Treatment Technique
Authors: Raghavendiran B , Sriram P , Vivekanandan N , Prakash J , Prabakar S , Jothybasu K , Lakshmanan AV
Published: April 2010

Purpose/Objective: To determine the error due to lung tumor motion on dose distribution delivered by Rapid Arc (RA) treatment technique, a procedure also known as volumetric modulated arc therapy. Materials/Methods: An indigenously developed dynamic phantom was set in linear sinusoidal motion in cranio‐caudal direction with amplitude of 2cm and at a frequency of 15 cycles/minute. A RA treatment plan was optimized for and delivered to the phantom containing a simulated target and critical organs. The treatment plan was executed for 30 fractions to the dynamic phantom, started at random initial breathing phases. GAF‐Chromic films embedded in the moving phantom in the coronal plane at the isocenter level were used to capture the dose distribution. Results: (i) ROI as PTV: When the daily dose distributions were compared against the static distribution, dose variation of 10% to 20% was observed near the field edges and 5% to 10% dose difference was observed elsewhere. Similar results were observed when comparing the dose distribution averaged for 30 fractions against the static distribution. (ii) ROI as CTV (simulated target): It is observed that on a day‐to‐day basis the standard deviation of the dose to a given pixel could be as high as 4.5% to 6.5%. Also, the mean, median, and modal dose varies inter‐fractionally with a standard deviation of 5.62%, 5.61%, and 5.73% respectively. When comparing the averaged dose distribution with the static distribution, dose variation ranging from 5% to 10% was observed. Also, the mean, median and modal doses were reduced by 6.35%, 6.45% and 6.87% respectively, compared with static distribution. Conclusion: Our study indicates that, if respiratory management techniques were not implemented, RA procedures for lung cancer treatment can result in underdosage, so this error should be measured and accounted for as part of the patient specific quality assurance.
MO‐FF‐A4‐01: Evaluation of Background Trend Correction Technique in Breast Tomosynthesis Quantitation
Authors: Shafer C , Lo J , Samei E
Published: April 2010

Purpose: The main shortcoming of breast tomosynthesis (tomo) imaging when compared to CT is poor resolution in the depth direction and the associated difficulty in quantifying tissue density. This study will assess the quantitative potential of breast tomo using a clinical prototype and relatively simple reconstruction and the proposed background trend correction scheme. Tomo quantitation would allow improved characterization of lesions as well as proper image processing of tomo images (analogous to that of mammography). Method and Materials: Studies were based on a Siemens prototype breast tomo system with a 45° total angular span. First, Monte Carlo simulations were conducted using geometry to mimic the aforementioned prototype and voxelized breast tissue‐equivalent phantoms embedded with eleven small cuboid lesions of varying density. The material surrounding the lesions was either fat or glandular equivalent plastic. From the simulations, the effects of scatter, lesion depth, and background material density were studied. Empirical studies were then conducted with the prototype system and tissue‐equivalent phantoms similar to those of the simulations to allow investigation of the effects of lesion depth and background material density. All image reconstruction was performed using filtered backprojection incorporating a filter designed to emulate some grayscale characteristics of iterative reconstruction. Results: Resulting images displayed a visible difference in lesion brightness for both empirical and simulated experiments. After applying our background trend correction technique, the lesion voxel values varied linearly with glandular fraction (all R2 ⩾ 0.90) under all simulated and empirical conditions. Significant differences were encountered only for different background materials (in all scatter‐included paradigms). Conclusions: These high R2 values suggest that breast tomo image voxel values corrected by our outlined methods are highly positively correlated with true tissue density, implying that breast tomo imaging has definite quantitative potential.
MO‐FF‐A4‐03: Testing of the High‐Resolution ROI Micro‐Angio Fluoroscope (MAF) Detector Using a Modified NEMA XR‐21 Phantom
Authors: Ionita C , Keleshis C , Jain A , Bednarek D , Rudin S
Published: April 2010

Purpose: To test the MAF in conditions and tasks specific to minimally invasive neurovascular procedures. Materials and Methods: A high‐sensitivity, high‐resolution MAF detector was built and incorporated into a standard angiographic C‐Arm system. This detector consists of a 300μm CsI input phosphor coupled to a dual stage GEN2 micro‐channel‐plate light image intensifier, followed by minifying fiber‐optic taper coupled to a CCD chip. The detector is attached to a very stable detector‐changer onto a Flat‐Panel (FP) C‐arm angiographic unit to allow facile placement of the detector into the field‐of‐view whenever high resolution is needed. A NEMA XR21‐2000 phantom was modified to evaluate neurovascular x‐ray imaging systems. The phantom was restructured to be head‐equivalent; two aluminum plates shaped to fit into the NEMA phantom geometry were added to a 15cm thick section. Digital subtraction angiography (DSA) testing was enabled by adding a removable central section with a hollow slot which allows insertion of various angiographic test blocks. DSA and DA were tested using a standard removable insert having simulated arteries with thicknesses of 4, 2 and 1 mm and 15mg/cm3 iodine contrast and with stenoses and aneurysms (AAPM Report 15). Features on the central plates of the NEMA XR21 phantom such as bar pattern and iodine‐detail‐contrast‐targets were also imaged. The results of the evaluation of the MAF with the modified phantom were compared with the images obtained with a standard flat panel. Results: The phantom imaging results presented as (MAF‐detected‐features/Flat‐Panel‐detected‐features) are: bar pattern — (5.0/3.1) lines/mm; smallest iodine‐contrast target group detectable — (10/10) mg/cm2, details of smallest simulated vessel in DSA — (1/2) mm. Conclusions: The MAF detector performs at least as well as a standard FP in detection of low‐contrast objects, and is superior in the visualization and identification of the small details. (Support: NIH grant R01‐EB002873, R01EB0008425).
MO‐FF‐A4‐05: Comparison of Detectability of a Simple Object with Low Contrast Displayed On a High‐Brightness Color LCD Monitor and a Monochrome LCD Monitor
Authors: Takahashi K , Morishita J , Sakai S , Toyofuku F , Higashida Y , Ohki M
Published: April 2010

Purpose: To examine the potential usefulness of a high‐brightness color liquid crystal display (LCD) monitor, the detectability of the color monitor was compared with the detectability of a monochrome LCD monitor by using receiver operating characteristic (ROC) analysis. Materials and Method: Two LCD monitors were used in this study: a two‐megapixel high‐brightness color monitor (RX‐211, 750 cd/m2 (maximum), Nanao, Japan), and a two‐megapixel monochrome monitor (GS‐220, 1,000 cd/m2 (maximum), Nanao, Japan). Both monitors were calibrated to grayscale standard display function. We examined the detectability of a color LCD monitor with different luminance settings (500 and 170 cd/m2) and a monochrome LCD monitor (500 cd/m2). Totally, 40 images were taken — including 20 images with a ball (8 mm in diameter), which was used as a signal and put on the surface of a 15.5 cm acrylic plate. All images were acquired by use of a computed radiographic system (CR9000, Fuji Film, Japan). All images were displayed on the LCD monitors with 8‐bit gray scale without any ambient lighting. Finally, the confidence data obtained by thirteen observers were analyzed by use of software (DBM MRMC, The University of Chicago) for ROC analysis, and the statistically significant differences between the areas under the ROC curve (AUC) were determined with the jackknife method. Results: The AUCs of color the LCD monitor with a maximum luminance of 500 cd/m2, 170 cd/m2 and monochrome LCD monitor with a maximum luminance of 500 cd/m2 were 0.937, 0.924, and 0.915, respectively. There were no statistically significant differences between the monochrome LCD monitor and the color LCD monitor with different luminance settings. Conclusion: The detectability of a high‐brightness color LCD monitor indicated comparable performances obtained with a monochrome LCD monitor.
TU‐A‐BRD‐01: KV and MV Cone‐Beam CT Imaging for Daily Localization: Commissioning, QA, Clinical Use, and Limitations
Authors: Hammoud R , Miften M , Moseley D , Pouliot J
Published: April 2010

Three‐dimensional conformal radiotherapy (3D‐CRT), intensity‐modulated radiotherapy (IMRT), and stereotactic body radiotherapy (SBRT) allow for the generation of highly conformal dose distributions for patients with tumor volumes wrapped around or adjacent to critical structures. As a consequence of steep dose gradients between the target and organs‐at‐risk, precise localization of the target volume and surrounding normal tissue is essential. However, variations in patient setup and organ motion are limiting factors in the accurate delivery of radiation treatment with a high degree of precision. Recent online image‐guided RT techniques using kilo‐Voltage cone‐beam CT (kV‐CBCT) and Mega‐Voltage CBCT (MV‐CBCT) are now offering the opportunity to overcome these limitations and greatly improve treatment localization accuracy. These IGRT techniques using the latest imaging technologies represent an improvement over traditional techniques such as 2D portal imaging. It allows for the use of volumetric online imaging to account for organ motion and setup variation by providing multiple anatomical views of the patient during the full course of RT treatment. The selection of imaging modality and system to use in support of a treatment protocol is often a compromise between image quality, efficiency, availability, and dose. The objective of this educational session is to review the current kV‐CBCT and MV‐CBCT imaging systems and their evolution for daily localization including

1. Commissioning, image quality, dose, registration process, and acquisition modes

2. Clinical integration

3. QA, stability over time, and downtime

4. Standard clinical applications

5. Novel clinical applications

6. Technology evolution and future directions
TU‐A‐303A‐01: C‐Arm Cone‐Beam CT: Principles and Applications
Authors: Siewerdsen J , Chen G
Published: April 2010

This Continuing Education session surveys the principles of 3D reconstruction, image quality, radiation dose, and applications of C‐arm cone‐beam CT. The availability of such systems has grown over the past several years, with applications including neurovascular and cardiovascular imaging in image‐guided interventions and surgery. Some systems employ conventional x‐ray image intensifiers, with corresponding limitations in image quality (i.e., imaging of high‐contrast structures only). More recent systems incorporating a flat‐panel detector in the imaging chain demonstrate increased field of view, higher 3D spatial resolution, improved noise characteristics, and the capability to visualize soft‐tissue structures. The basic principles of cone‐beam CT image reconstruction are reviewed (Feldkamp algorithm) in comparison to conventional fan‐beam filtered backprojection. The influence of image artifacts most relevant to C‐arm cone‐beam CT are reviewed — in particular, x‐ray scatter, object truncation, and the “cone‐beam” artifact. The factors governing 3D image quality are explained, with emphasis on the ability to image soft‐tissue structures, and issues of radiation dose characterization are discussed. The spectrum of various C‐arm cone‐beam CT systems is discussed in relation to primary applications in image‐guided interventions. Emphasis throughout is in regard to factors most relevant to the practicing medical physicists.

Learning Objectives: Attendees will gain practical understanding of:

1. Basic principles of 3D cone‐beam CT reconstruction

2. Image quality and artifacts most relevant to cone‐beam CT

3. Spectrum of systems and applications of C‐arm cone‐beam CTI
TU‐A‐213A‐01: CT Clinical Perspective: Challenges and the Impact of Future Technology Developments
Authors: Vannier M
Published: April 2010

Computed tomography is not the most frequent radiologic imaging procedure, but is arguably the most important in terms of clinical impact. CT is used extensively for emergencies, cardiovascular, pulmonary, gastrointestinal, endocrine, neurological, orthopedic and other applications — often as the first and only imaging procedure needed for diagnosis. The chances are very high that a patient will have a CT scan in the emergency department, as an outpatient or as an inpatient for a multitude of indications — pain, trauma, suspected infection or malignancy, and frequently to investigate symptoms such as pain, or to answer a question raised by another abnormal test, such as an EKG abnormality or ultrasound finding.

Despite the universality of CT in hospitals and clinics as well as free‐standing imaging centers, the technology continues to evolve with greater coverage, faster acquisition and multienergy sources or detectors. Multimodality scanners based on CT incorporate PET/SPECT and in the future, MRI to combine morphologic and functional imaging.

The most demanding imaging applications are cardiovascular, where complex motion and small morphologic features coexist, so imaging methods that are very satisfactory elsewhere in the body may not be successful. Clinical CT scanning consists of administering toxic materials, e.g., contrast media, often monitoring the EKG and illuminating the body with high brightness x‐rays. Larger area detectors and higher acquisition rates are welcome improvements, but don't solve all of the problems encountered with scan variability due to respiratory, random body, and cardiac motion, especially in a spectrum of patients from infant to massively obese adult sizes (< 1 kg to 250 kg or more). The challenges and pitfalls in CT and multimodality imaging will be delineated and evaluated relative to current and future technology.

Learning Objectives:

1. The role of x‐ray computed tomography (CT) in clinical medicine is central to diagnostic radiology and its functions as a hospital‐based department and service to outpatients.

2. CT technology developments, including wide area coverage multirow detector scanners, dual energy acquisition systems, visualization and post‐processing introduce changes in CT applications and utilization.

3. The limitations of a single modality, such as CT, can be overcome by integrating complementary instrumentation, especially PET/SPECT, MRI and others (such as ultrasound and fluoroscopy) to provide simultaneous morphologic and functional imaging capabilities.