bluuebunny/crossref_metadata_2025_split huggingface dataset:
SU‐E‐T‐862: Planning and Delivery of Voxel‐Based Dose Painting Plan Using TomoTherapy
Authors: Chen Q , Chen Y , Chen M , Lu W 
Published: November 2011

Purpose: Dose painting is useful in prescribing dose based on the biological information and in correcting the hot/cold spot from previously delivered fractions in adaptive therapy. The feasibility of planning and delivering of voxel‐based dose painting plan in TomoTherapy system using a complementary dose approach is studied. Methods: The current intensity modulated radiotherapy (IMRT) treatment planning aiming at uniform target coverage, is not readily adaptable to dose painting that requires voxel‐based prescription. TomoTherapy Optimizer is modified to read a complementary dose from disk. The complementary dose converts the voxel based prescription into the uniform target coverage. Four dose painting plans are created on a phantom for evaluation. The plans are delivered to the phantom with film measurement to verify the deliverability and accuracy. Results: The conformity of plans to prescriptions is found to be exceptional. The difference between 1% volume and 99% volume for quality volume histogram (Q1‐Q99) is around 0.017 for simple plans and 0.1 for complex plans. Since the prescription become a uniform target prescription with complementary dose, the conformity index for the combined dose can be evaluated with conventional metrics. The D1‐D99 is around 1Gy for simple plan and 5.5Gy for complex plan with combined prescribed dose at 80Gy. Although the dose paint plan prescribes maximum dose of 80Gy, the delivery time for most plan is almost the same as the plan with uniform 60Gy prescription. The dose painting plans are delivered to a phantom with TomoTherapy system and the film measured dose showed excellent agreement with planned dose. Conclusions: This study shows the TomoTherapy system is capable of creating and delivery voxel based dose painting plan accurately.The authors are current and former employees of TomoTherapy Inc.
SU‐E‐T‐869: Direct Aperture Optimization Based on Multi‐Objective Evolutionary Algorithm in Intensity Modulated Radiation Therapy
Authors: Cao R , Pei X , Wang J , Wu Y 
Published: November 2011

Purpose: Direct Aperture Optimization (DAO) is an Intensity Modulated Radiation Therapy (IMRT) inverse planning technique whereby the shapes and relative weights of the apertures in the plan are optimized directly. As DAO is capable of producing treatment plans that are comparable to plans produced using the traditional inverse planning approach while using significantly fewer segments, DAO is studied more and more in recent years. Inverse planning optimization is a multi‐objective optimization problem whose solution is known as Pareto solution set. So, the multi‐objective direct aperture optimization based on Pareto solution set was studied in this paper.Method: The clinical requirements for a treatment plan were transformed into a multi‐objective optimization problem with multiple constraints, in which the parameters are the shapes and relative weights of the apertures. And then the fast and elitist multi‐objective Non‐dominated Sorting Genetic Algorithm (NSGA‐II) was introduced to optimize the problem. The aim of NSGA‐II based optimization algorithm is to provide a representative set of non‐dominated solutions for problems where many conflicting objectives and many constraints need to be considered simultaneously instead of a single solution. Results: A clinical example was tested using the method. The results showed that a set of non‐dominated solutions obtained distributed uniformly, and the corresponding dose distribution of each solution not only approached to the expected dose distribution but also met the dose‐volume constraints. Conclusions: It was indicated that the clinical requirements were better satisfied by the method and planner could select the optimal treatment plan.Supported by the National Natural Science Foundation under grant No.30900386 and the Anhui Provincial Natural Science Foundation under grant No. 090413095 and 11040606Q55.
SU‐E‐T‐882: Electron Disequilibrium Pitfalls for Small Megavoltage Photon Fields Incident on Lung Tumors
Authors: Disher B , Hajdok G , Gaede S , Battista J 
Published: November 2011

Purpose: Stereotactic body radiation therapy (SBRT) of lung uses sub‐centimeter MV x‐ray fields. Under these conditions, lateral electron disequilibrium (LED) can occur in lung tissue, which causes perturbations of the dose distribution near the tumor. This purpose of this work is to characterize the LED effect in lung for clinically relevant ranges of beam energies, field sizes, and lung densities. Methods: The MC code DOSXYZnrc (National Research Council of Canada, Ottawa, ON) was employed to simulate two 20×20×25cm3 water‐lung‐water slab phantoms. The two phantoms were identical in composition except that the second phantom also included a 3×3×3cm3 centrally located water cube to mimic a small lung tumor. To characterize LED, dose calculations were performed using combinations of beam energy (Co‐60 up to 18MV), field sizes (1×1cm2 up to 15×15cm2), and lung densities (0.001g/cm3 up to 1g/cm3) for both phantoms. Results: MC lung slab phantom simulations revealed that for each combination of beam energy and field size, a critical lung density (CLD) could be defined to establish LED. For example, a 6MV 5×5cm2 photon field was subject to LED for lung densities of 0.2g/cm3 or lower. On the contrary, employing an 18MV 5×5cm2 photon field increased the CLD to 0.5g/cm3. With regard to the second lung tumor phantom, the LED effect caused major reductions in the calculated dose near to the tumor. For instance, dose reductions of 24% and 16% were found within the distal and proximal tumor surfaces, respectively. Conclusion: We have fully characterized the LED effect and shown that it causes dose reductions in both lung and tumor tissues. To avoid these dose perturbations, SBRT of lung cancer patients should be optimized to select radiation therapy parameters carefully in accordance with patient lung density.Financial support from the Natural Sciences and Engineering Research Council of Canada (NSERC), and the Canadian Institutes of Health Research (CIHR) are gratefully acknowledged.
MO‐D‐BRC‐02: Image Guidance in Video‐Assisted Thoracoscopic Surgery (VATS) Using a Mobile C‐Arm for Cone‐Beam CT: Image Quality, Dose, and First Experience in Visualizing the Fully Deflated Lung
Authors: Schafer S , Uneri A , Mirota D , Nithiananthan S , Stayman J , Zbijewski W , Kleinszig G , Schmidgunst C , Sussman M , Siewerdsen J 
Published: November 2011

Purpose: A growing number of early‐stage lung malignancies identified in low‐dose CT raises a challenge for thoracic surgeons to accurately localize subpalpable nodules, increasing the potential for erroneous resection or unnecessarily large margins. We investigate combining minimally invasive video‐assisted thoracic surgery (VATS) with intraoperative image guidance using a mobile C‐arm for cone‐beam CT (CBCT). Method and Materials:Studies were performed on a C‐arm prototype equipped with a flat‐panel detector enabling high‐quality CBCT. Lung nodule detectability was assessed in three pig models using solid lung nodules (∼50 HU) simulated by ∼6 mm polyethylene spheres inserted into the lung. Scans were performed at inhale, exhale, and complete deflation to assess visualization of tumors within the deflated lung and identify minimum‐dose limits. A cadaveric torso provided first experience in CBCT guidance of VATS in cooperation with a thoracic surgeon. Experiments employed an in‐house guidance system combining pre‐ and intraoperative images, surgical planning, trackers, and thoracoscope video augmentation. Results: Simulated lung nodules were conspicuous in low‐dose scans (0.41 mSv) for the inhale and exhale states by virtue of high contrast within the air‐filled parenchyma. Nodule visibility in the deflated lung required higher dose (1.63 mSv) for confident visualization and suggested a valuable means of intraoperative localization. For the cadaveric torso, preoperative CT and planning were registered to CBCT using deformable registration methods, with error ∼3–10 mm in soft‐tissue registration error. Real‐time tracking of thoracoscopy allowed valuable augmentation of the video stream with image and planning data. Conclusion: C‐arm CBCT integrated with tracking, registration, and video augmentation promises to advance the safety and precision of VATS, showing potential for improved tumor targeting and normal tissue sparing. CBCT image quality was sufficient for direct visualization of solid nodules in the inflated and collapsed lung, and registration with thoracoscopic video provided significant improvement to visualization and workflow.Research supported by National Institutes of Health R01‐CA‐127444 and collaboration with Siemens Healthcare (Erlangen Germany).
MO‐D‐BRC‐03: Concomitant RapidArc® and Acquisition of KV‐CBCT with Minimal MV Scatter
Authors: Ling C , Zhang P , Sun M , Hunt M 
Published: November 2011

Purpose: To develop a novel method to simultaneously deliver RapidArc® and acquire kV CBCT with minimal MV scatter using the TrueBeam®. Methods and Materials: A standard RapidArc® plan consists of hundreds of control points (CP) for dose delivery with designed MLC aperture, dose rate, and gantry rotation. In our design concept each original CP is converted into two: one for MV dose delivery, and the other for kV imaging. Gantry intervals of each CP and gantry speed are chosen to acquire sufficient CBCT projections in the imaging CP, while minimizing the process time. kV projections with minimal‐MV scatter are selected, based on the recorded gantry angle, and sCBCT (s: without MV‐scatter) is reconstructed. For comparison, a reference rCBCT image is acquired without MV dose delivery, and a cCBCT (c: with MV‐Scatter) acquired by running the same RapidArc®/CBCT plan but without the imaging CP. CBCT are acquired in both full‐fan and half‐fan modes. Results: The image quality of sCBCT and rCBCT are comparable, whereas MV scatter significantly degrades the cCBCT image and contributes artifacts. Image analysis results show that the contrast‐to‐noise ratio of the sCBCT and rCBCT are comparable, and is twice that of the cCBCT. Likewise, the image homogeneity (defined as the normalized standard deviation) of the sCBCT and rCBCT are also superior to cCBCT. Visually, an object of ∼2% density difference from the background can be discerned in the sCBCT and rCBCT image, but not in the cCBCT image. In this proof‐of‐principle study, a 350 MU RapidArc®/CBCT plan was delivered in 2.2 minutes. With further optimization, it should be possible to shorten this to ∼1.5 minutes. Conclusion: Our method truly integrates imaging and dose delivery. kV‐CBCT with minimal MV scatter can be acquired concomitantly with the RapidArc® with little overhead. Engineering development is needed to further improve the process.Research agreement with Varian Medical Systems.
MO‐D‐214‐01: 4D‐MRI for Radiation Therapy of Moving Tumors
Authors: Yin F , Biederer J , Cai J , Parikh P 
Published: November 2011

Four‐dimensional computed tomography (4D‐CT) has been widely used in radiation therapy for imaging moving tumors, especially in the thoracic regions. In other body sites such as the abdominal, 4D‐CT is limited due to its intrinsic low soft‐tissue contrast. Additional concern for 4D‐CT includes increased radiation dose to the patient since a 4D‐CT scan typically generates 10 times more data than a regular CT scan.On the other hand, magnetic resonance imaging (MRI) has excellent soft‐ tissue contrast and implies no known radiation hazard. 4D‐MRI can be used to improve the determination of patient specific tumor motion margin for radiation therapy, especially for the tumors in the abdominal regions where non‐contrast enhanced 4D‐CT has limitations. It can be applied for repeated or prolonged measurements covering multiple respiratory cycles to monitor individual changes in respiration frequency and depth. It is therefore desirable to develop 4D‐MRI techniques to address the problems associated with 4D‐CT.There are different approaches to develop the 4D‐MRI technique. The more frequently applied approach is based on repeated fast 3D MR pulse sequences and requires sophisticated hardware. Another approach is to retrospectively sort slice MR images acquired continuously throughout the volume based on respiratory phases. While both approaches have the promise of becoming useful imaging tools for tumor motion management in radiation therapy, they have their own pros and cons. For the first approach, its temporal resolution (∼0.7 frame/s) and spatial resolution (3–4 mm) are limited resulting in an overestimation of tumor size as the mass is volume averaged into many voxels during motion and an underestimation of lesion displacement. The second approach will require some type of respiratory surrogate (either external or internal) and is therefore subject to similar limitations as 4D‐CT.However, a simple but most robust approach for the delineation of tumor positions and trajectories during respiration is the averaging of multiple single slice MR acquisitions over time within a MIP‐display. This largely reduces the complexity of the technique and still provides sufficient information for the definition of motion adapted target volume definition which enhances the probability of its clinical application.Learning Objectives:1. To discuss the need of 4D‐MRI technique for improving patient care in radiation therapy2. To present the latest development of 4D‐MRI imaging techniques and their differences.3. To discuss the application of 4D‐MRI in tumor motion management and treatment planning in radiation therapy
MO‐D‐110‐03: Calculating Organ Dose from Fluoroscopy
Authors: Alaei P 
Published: November 2011

Calculating organ dose from fluoroscopy procedures has been of interest to radiology and cardiology communities for many years. Published work in this area includes those that employed Monte Carlo methods to calculate organ doses from fluoroscopy procedures in phantom and those that extrapolated the organ doses from skin dose or exposure measurements.Another tool which could potentially be used to compute organ doses from fluoroscopy is a treatment planning system routinely used for creating radiation therapy treatment plans. Although a treatment planning system is designed to compute dose distribution in the megavoltage energy range, its use in the diagnostic energy range is a possibility, at least for one commercial system. This requires knowledge of certain fluoroscopic beam data which can be obtained by measurements or by relying on available published data, and a CT scan of the patient. This tool, once validated, can provide detailed dose distribution within any organ exposed to radiation.This lecture provides details of the use of a radiation therapy treatment planning system for dose calculation in diagnostic energies with examples of dose distribution from fluoroscopic procedures in adults and children.Learning Objectives:1. Learn about the methods of organ dose computation from fluoroscopy2. Learn the details of using a treatment planning system for fluoroscopic dose calculation3. Learn the magnitude of typical organ doses encountered in fluoroscopy
MO‐D‐211‐01: Low Dose Molecular Breast Imaging
Authors: OˈConnor M 
Published: November 2011

Background: Several new nuclear medicine‐based breast imaging techniques have emerged over the last few years. These include Positron Emission Mammography (PEM), Breast Specific Gamma Imaging (BSGI) and Molecular Breast Imaging (MBI). These techniques usually employ doses of ∼ 10 mCi F‐18 FDG in the case of PEM, or 20–30 mCi Tc‐99m sestamibi in the cases of BSGI or MBI. In addition to their potential value as adjunct diagnostic tools, these techniques hold promise as potential adjuncts to screening mammography particularly for women with dense breast tissue where the sensitivity of mammography is known to be reduced. A previous study has shown MBI to have 2–3 times the sensitivity and equivalent specificity to screening mammography in women with dense breasts. However, the current administered doses employed in these techniques deliver effective radiation doses that are ∼10 times higher than mammography.From the BEIR VII tables, the lifetime associated risks from PEM, BSGI and MBI can be calculated and compared to that of screening mammography. These estimates indicate that in order to achieve a comparable radiation burden to mammography, the administered doses of F‐ 18 FDG and Tc‐99m sestamibi need to be reduced to less than 2 mCi F‐18 FDG and 4 mCi Tc‐99m sestamibi.This presentation will briefly review the clinical literature demonstrating the value of these new techniques in both diagnostic and screening applications, and will review the dosimetry and estimated lifetime associated risks from these technologies. It will then focus on one of these technologies — MBI, and will illustrate how we can optimize the physics of the collimation and detector to achieve a 5‐fold reduction in the required dose of Tc‐99m sestamibi for clinical studies. We will also review possible post‐acquisition processing techniques that may enable further reduction in dose, along with alternative radiopharmaceuticals that deliver low doses due to their biodistribution.A total of 4 dose reduction schemes will be discussed — a) development of optimized collimation for single‐photon imaging, b) improved utilization of the energy spectral characteristics of the gamma cameras, c) implementation of noise reduction and resolution recovery algorithms, and d) use of adaptive geometric mean algorithms for combination of images from opposing detectors. In addition we will consider alternative radiopharmaceuticals, such as Tc‐99m MDP that deliver a lower radiation burden than Tc‐99m sestamibi.We will demonstrate that image quality obtained with low‐dose MBI performed with 4 mCi Tc‐99m sestamibi matches that of standard MBI performed with 20 mCi dose. Low‐dose MBI presents radiation risks to the patient comparable to that of digital screening mammography, allowing its safe implementation as a screening technique.
MO‐D‐220‐01: In Vivo Quantitative Vascular Imaging of Tumors Using 3D Photoacoustic Imaging
Authors: Thornton M , Stantz K , Kruger R 
Published: November 2011

Purpose: Employ volumetric photoacoustic computed tomography (PA‐CT) imaging to monitor key indices of tumor biology in tumor bearing mice without the use of exogenous contrast. In this study we describe the scanning system and its use in tracking in vivo tumor vasculature and tumor volume, through tumor growth and following treatment by anti‐angiogenic therapy, in both control and treated animals. Methods: A PA‐CT scanner, specifically designed for mouse imaging, employs a sparse array of 128 discrete transducer elements (3mm in diameter, 5MHz center frequency) arranged on a hemispherical surface, a tunable NIR pulsed laser (680– 950nm), and a digital acquisition system with 128 channels. The tissue being imaged is illuminated directly by pulses of laser light and the resulting photoacoustic signals are recorded. The photoacoustic data is reconstructed using a modified 3‐D Radon transform to produce a spherical volume 25mm in diameter. EGFR+ MCF‐7 breast cancer cells were injected into two groups (control and treatment) of mice (n=6). The tumors were allowed to grow to approx. 10mm in size at which point the treatment group was injected with a single dose of Avastin (40mg/kg). The mice were scanned at 17, 27, and 34 days post‐implantation. Results: The tumor vascularity was quantified by measurement of hemoglobin (Hb) content in the tumor. The Avastin treated mice showed an average decrease of 65% in hemoglobin content following treatment while the control group had an average increase in tumor Hb content of 33%. Conclusions: The strong absorption of NIR light by oxy‐hemoglobin and deoxy‐hemoglobin provides a useful contrast mechanism for photoacoustic imaging without the use of exogenous contrast agents. Photoacoustic imaging is well suited to in vivo studies of cancer therapies where the tumor vasculature is a marker of the efficacy of the therapy or intervention.Funding Support, Disclosures, and Conflict of Interest: M. Thornton is an employee of Endra Inc.
MO‐D‐220‐03: Thermoacoustic Imaging of Porcine Kidneys
Authors: Catenacci J , Roggenbuck M , Patch S 
Published: November 2011

Purpose: To demonstrate the feasibility of thermoacoustic (TA) imaging to detect microvasculature surrounding tumors embedded 6+ centimeters deep. Methods: Ex vivo imaging of porcine kidneys in a custom TA testbed demonstrates 6cm depth penetration. Chilled glycine solution serves as acoustic couplant. Submicrosecond radiofrequency pulses with carrier frequency 108 MHz and peak power of 40kW generate TA pressures. Step‐ and‐shoot volumetric scanning is performed by rotating and translating the kidney while the transducer remains stationary. Translation increment is 3.6mm between slices. Focused single‐element videoscan transducers with center frequencies of 1 MHz and 2.25 MHz collect signals, which are amplified by a 54dB preamp. Lightly filtered single‐slice sinograms are backprojected in‐plane to reconstruct images. TA signal generated by vials of blood product and pure anticoagulant are compared with TA signal from pure water. Vials are manually positioned, diminishing repeatability of these experiments, so multiple realizations of each are presented. Results: Reconstructions of the kidneys clearly track progression of calyces from one slice to the next. In vivo, calyces are filled with urine, which can have widely varying electrical conductivity. TA signal strength is directly proportional to electrical conductivity but is also a function of other tissue parameters: bulk modulus, thermal expansion coefficient, and specific heat capacity. In our testbed, the calyces fill with glycine, which has low conductivity, causing signal dropout in the calyces. TA pressures generated by both blood product and pure anticoagulant generate orders of magnitude stronger signal than pure water. Conclusions: We demonstrate whole organ TA imaging is possible with 108 MHz RF irradiation. Furthermore, at 108 MHz, blood is highly conductive and generates strong signal, supporting the hypothesis that TA may be able to detect microvasculature surrounding aggressive tumors.This work was supported by NIH grant 5 R21 CA137364‐02.