bluuebunny/crossref_metadata_2025_split huggingface dataset:
MO‐G‐BRB‐02: Commissioning a Small Animal Irradiator Using 2D and 3D Dosimetry Techniques
Authors: Newton J , Oldham M , Li Y , Adamovics J , Das S 
Published: November 2011

Purpose: To commission and characterize a novel small animal irradiator, the XRad225cx from Precision X‐Ray Inc. This system is capable of delivering both square and circular fields ranging in size from 1mm to 40mm. The combination of very small field size and relatively low energy (225kV) represents a substantial challenge in acquiring accurate dosimetry beam data. This work reports on commissioning studies using 2 independent dosimetry systems: EBT2 radiochromic film and PRESAGETM /optical‐CT 3D dosimetry. Methods: Initial measurements were made with 6×8cm pieces of EBT2 radiochromic film. Output factors were determined at 3 depths (0, 0.5 and 2cm) from films irradiated normally resting on the surface or sandwiched in solid water. Percent‐depth‐dose (PDD) measurements were made from films also sandwiched in solid water and irradiated edge on. Independent 3D dosimetry measurements were obtained using PRESAGETM radiochromic dosimeters and imaged with the Duke Large field‐of‐view Optical‐CT Scanner (DLOS). Output factors and PDDˈs were obtained using a combination of small fields. Results: The relative output factors and PDDˈs obtained from EBT2 and PRESAGETM showed agreement below 1 cm depth. For field sizes >1cm, relative output factors were found to be stable (∼1.00) with differences between PRESAGETM and EBT2 <6%. At smaller field sizes the output relative to the 20 mm cone decreased substantially, down to ∼0.5 for the smallest 1 mm cone. A slightly greater drop was observed in the PRESAGETM measurements, which is currently being investigated. Conclusions: Output factors and PDD curves were successfully obtained for all cones using a combination of EBT2 and PRESAGETM. Consistency was observed between both independent measurements after correcting for the lack of exact water equivalence of both the solid water and PRESAGETM. The 3D dosimetry system has potential advantages in terms of convenience, efficiency and comprehensiveness when commissioning small fields.Funded by NIH R01CA100835 and NIH S10‐3034539
MO‐G‐BRB‐06: Integrating Carbon Nanotube and Micropallet Technologies for Microbeam Radiotherapy Biology Research
Authors: Wang S , Fiordalisi J , Xu W , Zhang J , Snider J , Yang G , Cox A , Allbritton N , Chang S 
Published: November 2011

Purpose: Microbeam radiotherapy (MRT) is a preclinical therapy that has been shown in animal experiments to have a selective ability to eradicate tumor cells while sparing normal tissue. However, potential MRT clinical application is hindered by the lack of understanding of the biological mechanisms involved. To study DNA damage and repair mechanisms and cell survival under MRT irradiation, our objective is to integrate a carbon nanotube field emission technology‐enabled high dose rate (100ˈs Gy/s) electron microbeam with a micropallet array technology‐enabled cell retrieval and analysis system. The focus of this presentation is a feasibility demonstration of the integrated system for MRT cellular irradiation. Methods: We have upgraded our carbon nanotube field emission‐based prototype cell irradiator system to produce a single or multiple ∼40 micron wide electron MRT beams at a dose rate range of several hundred Gy per second. Dosimetry is measured using GAFCHROMIC HD‐810 film. SW480 colon cancer cells are plated on individual square micropallets of 60 or 100 micron in size, placed in a customized culture dish. Cells can be collected from each individual micropallet while remaining adherent to their growth surface for further analysis. Results: We have demonstrated the MRT cellular irradiation using gamma‐H2AX, a nuclear histone protein that becomes phosphorylated in proximity to IR‐induced DNA double strand breaks. The MRT radiation beam profile shown by staining fixed cells post‐ IR for phospho‐H2AX was consistent with calculation. Conclusions: We have developed an integrated MRT cellular irradiation and analysis system using carbon nanotube field emission technology and micropallet array technology. We have characterized the dosimetry and demonstrated the feasibility of MRT beam irradiation in cellular irradiation for future mechanistic research on microbeam therapy.Acknowledgements: This work is partially supported by North Carolina University Cancer Research Fund.
TU‐A‐BRB‐04: Incorporating Beam‐Specific Target Volumes Into Beam Angle Selection in Proton Therapy
Authors: Park P , Zhu X , Sahoo N , Lee A , Zhang L , Cheung J , Dong L 
Published: November 2011

Purpose: Due to range uncertainty and its interplay effect with setup error and internal tissue heterogeneity, proton beams usually use a large distal and proximal margin, especially when the distal margin falls in a low density tissue, such as lung. As a result, beam angle selection is very important for proton therapy. In this study, we incorporate beam‐specific planning target volumes (bsPTVs) into a beam angle optimization process to minimize required treatment volumes for each beam and combination of two beams along with other dose restrictions to the organ at risks (OARs) in the beam path. Methods: The bsPTVs were constructed for each beam angle over 10 degrees interval by taking into account both the range and setup error. Subsequently, doses from each beam angle were approximated using analytical dose model assuming uniform‐dose distribution throughout the target volume. The objectives set included the volume of bsPTV for each beam, the volume of intersection between multiple bsPTVs, and mean doses to OARs in the beam path. Results: A software tool was developed and applied to optimize two‐beam arrangement for a lung cancer patient. Objectives were plotted as figure‐of‐merits in color maps and bsPTVs were overlaid on axial CT images to assist the interpretation of results and the eventual angle selection. Conclusions: We found that the intersection of beam‐specific PTV is a convenient tool for minimizing the combined high dose volume by selecting the best combination of beam angles. Our visual tools that display trade‐offs between different objectives were found helpful for angle selection as well as the interpretation of results.Supported in part by NCI P01 CA021239
TU‐C‐220‐07: Photoacoustic and Ultrasound Imaging Using a Hemispherical Aperture
Authors: Kruger R , Lam R , Reinecke D , DelRio S 
Published: November 2011

Purpose: The aim of our research is to develop a breast cancer screening alternative to x‐ray mammography that will improve screening accuracy in women with dense breasts and young women with a predisposition to breast cancer. Methods: We have implemented 3D photoacoustic and ultrasound computed tomography using a single transducer array that samples a hemispherical aperture. Such an array samples radial projections though K space uniformly and can produce 3D images that demonstrate nearly isotropic spatial resolution for both photoacoustic and backscattered ultrasound. Data acquisition and image reconstruction strategies will be discussed. Results: We have successfully visualized hemoglobin distribution in the breast vasculature of a normal patient. Spatial resolution was better than 0.5 mm and vessels were adequately visualized to a depth of 35 – 40 mm. Microcalcifications as small as 180 microns were visualized in 3D in a breast‐tissue‐mimicking phantom. Conclusion: Hemoglobin and microcalcifications can be imaged in 3D using a single ultrasound detector array that samples a hemispherical aperture. Application of the technology for detecting two biomarkers associated with breast cancer — hemoglobin and microcalcifications ‐ will be discussed.Educational Objectives:1. Introduce the concept of photoacoustic imaging using ultrasound transducer arrays.2. Discuss data acquisition strategies and reconstruction strategies.3. Discuss photoacoustic contrast mechanisms
TU‐E‐110‐02: Multibeam X‐Ray Source Array Based on Carbon Nanotube Field Emission
Authors: Zhou O , Lu J , Calderon‐Colon X , Qian X , Yang G , Cao G , Gidcumb E , Tucker A , Shan J , Spronk D , Sprenger F 
Published: November 2011

Purpose: We recently demonstrated the feasibility of generating high current and high energy x‐ray radiation using field emitted electrons from the carbon nanotubes (CNTs). The purpose of the present work is to develop a spatially distributed multiple beam x‐ray array technology for stationary tomography imaging, including digital breast tomosynthesis, with the goal of increasing the spatial resolution and scanning speed. Method and Materials: CNT cathodes fabricated by patterned electrophoretic deposition were used as the field emission electron source for x‐ray generation. Computer simulations and experimental measurements were carried out to design the electrostatic lens to focus the field emitted electrons to the predetermined area on the metal anode. Finite element analysis was performed to determine the anode heat load under the desired operation conditions. Spatially distributed x‐ray source arrays with one‐ and two‐dimensionally distributed focal spots were constructed using matrix addressable multi‐pixel CNT cathode, and corresponding focusing and anode structures. By varying the extraction electrical field, x‐ray radiation with programmable waveform was readily generated which can be gated with external triggers such as physiological signals with sub‐microsecond response time. Dedicated control electronics were designed and manufactured to switch, scan, and regulate the x‐ray beams. Results: Several spatially distributed field emission x‐ray source arrays with different configurations and performance parameters have been fabricated and characterized for different imaging systems. Stable operation at anode voltage up to 160kVp has been achieved. Through improvement of the CNT cathode and electronic regulation beam‐to‐beam consistency in intensity and focal spot size has been demonstrated. A dedicated x‐ray source array has been designed and fabricated for stationary digital breast tomosynthesis. The source comprises 31 individually controllable x‐ray beams covering 30 degrees viewing angle, allowing collection of the all the projection images from different angles without any mechanical motion blur. It is operated up to 50KVp anode voltage at an effective focal size comparable to that of the traditional mammography tube. Tomosynthesis images of a breast phantom were obtained using the new source array and a flat‐panel x‐ray detector. Conclusion: The distributed field emission x‐ray source array technology offers unique capabilities that are attractive for tomography imaging and potentially for radiotherapy. The flexibility in source configuration opens up new possibilities in system design.Conflict of Interest: Zhou is a board director of XinRay Systems which develops and commercializes the CNT X‐Ray source technology.
TU‐G‐BRA‐01: Clinical Significance of RBE Variations in Proton and Carbon Ion Therapy (an Overview/introduction to the Problem)
Authors: Paganetti H , Grassberger C , Carabe‐Fernandez A 
Published: November 2011

The relative biological effectiveness (RBE) is defined as the ratio of the doses required by two radiations to cause the same level of effect. Thus, the RBE needs to be considered if dose constraints from photon therapy are to be adopted.Proton therapy has been based on the use of a generic RBE of 1.1, which is applied to all treatments independent of dose/fraction, position in the irradiated volume, beam energy or the tissue. Quantitative dependencies of the RBE on various physical and biological properties are disregarded. The variability of RBE in clinical situations is believed to be within 10%. Elevated RBE values might be expected particularly near the edges of the high‐dose volume because doses may be deposited by high‐LET particles. Furthermore, the increase in RBE as a function of depth in the patient results in an extension of the bio‐effective range of the beam, which is being considered in treatment planning.The magnitude of RBE values and their variations is significantly larger in Carbon ion therapy than in proton therapy. Heavy ions have a potential advantage compared to protons when it comes to their therapeutic ratio due to an elevated RBE in the tumor (based on the oxygen enhancement ratio and higher average LET values) compared to the surrounding tissue. However, there are considerable variations in RBE within the irradiated volume that have to be considered in treatment planning and delivery.At present there are still considerable uncertainties in RBE values and their dependencies on dose, LET, and alpha/beta ratio. This presentation will illustrate the magnitude of RBE variations in proton and Carbon beams. Furthermore, it will demonstrate the clinical significance for proton therapy treatments involving tissues with low alpha/beta ratio and show a method for biologically optimized treatment planning in proton therapy.
TU‐G‐BRA‐05: Optimization of Normal Tissue Sparing through Ion Selection
Authors: Remmes N , Herman M , Kruse J 
Published: November 2011

The variable radiobiological effect (RBE) of heavier ions like carbon make it challenging to compare dose distributions across different ions. Comparisons must be made between the isoeffective dose, the product of the dose with the RBE, requiring the use of a model that can predict how RBE changes across different ions. This presentation will discuss Geant4 simulations of parallel opposed beams of protons, helium, lithium, beryllium, carbon, and neon ions incorporating a microdosimetric model of RBE. The beams are constructed to give a homogeneous isoeffective dose to a treatment volume in the center of a water phantom for tissues covering a range of cobalt equivalent alpha/beta ratios from 1 to 20 Gy. Normal tissue isoeffective doses are then compared for different ions across the range of normal tissue and target tissue radiosensitivities. The ion type yielding the optimal normal tissue sparing is found to be highly dependent on the alpha/beta ratio of both the normal and target tissue. For instance, the calculated isoeffective dose to normal tissue at a 5 cm depth varies by almost a factor of 5 for carbon ions, ranging from a factor of 2 less than the isoeffective dose of a similar proton treatment to a factor of 2 greater. The heavier ions such as carbon are superior in cases where the alpha/beta of the target tissue is low and the alpha/beta normal tissue is high. However, lighter ions such as lithium and beryllium appear to offer dose advantages similar to carbon but with considerably less normal tissue dose when the alpha/beta in the target tissue is high and the alpha/beta in the normal tissue is low.Learning objectives1. To understand the variation of isoeffective doses to normal tissues across ion types for a simple parallel opposed treatment.2. To understand the dependency of isoeffective doses to normal tissues on the combination of both normal tissue radiosensitivity and target tissue radiosensitivity.
TU‐G‐BRB‐02: Comprehensive Handling of Time‐Dependent Quantities in Scanning Beam Simulation
Authors: Shin J , Perl J , Schümann J , Paganetti H , Faddegon B 
Published: November 2011

Purpose: To provide a comprehensive and flexible method for handling time dependent quantities including interplay effects in proton beam scanning. Methods: The time feature was devised to handle time‐dependent quantities in the Monte Carlo simulation. Each time‐dependent quantity corresponds to one time feature. A time feature can be expressed as a simple mathematical function or composed of more complex, pre‐defined functions. The functions may be combined concurrently and/or consecutively so that users can customize complex time features. During simulation, time is set in one of two manners: 1. Randomly chosen time, suitable for handling continuous behaviors, or 2. sequentially‐generated time, where time interval is equally divided. This time feature has been incorporated in TOPAS, a tool for particle simulation with Geant4, under development to make Monte Carlo simulation more accessible to both clinical and research physicists. Results: The time feature has been deployed to simulate various proton beam scanning patterns in clinical proton beam nozzle. The patterns include parallel, raster, circular, saw‐tooth, and Lissajous figure scans. Through the parameter management in TOPAS, time features for those scanning patterns were easily implemented. Dynamics of the beam including pulse shape, spot size, and movement were concurrently simulated. Randomly set time gave more accurate results when fewer histories were simulated, resulting in under‐sampling when time was set sequentially, while the simulation time with the 2 methods was similar for the same number of histories. Conclusions: Methodology has been developed to comprehensively describe time dependent behaviors in the Monte Carlo simulation and was assessed by applying to clinical proton beam scanning. A novel aspect of the method of separation of the time generators and time receivers has made it straightforward to handle multi time‐ dependent quantities and is therefore relevant to fully simulate interplay effects.The project described was supported by Award Number R01CA140735 (“PBeam: A Fast and Easy to Use Monte Carlo System for Proton Therapy”) from the National Cancer Institute.
TU‐G‐BRB‐04: Optimal Frequency of CT Imaging for Monitoring Target Volume and Estimating Delivered Dose in Standard and Hypofractionated Prostate Proton Therapy
Authors: Wang Yi , Efstathiou Jason A. , Lu Hsiao‐Ming , Sharp Gregory C. , Trofimov Alexei V. 
Published: November 2011

Purpose: To evaluate the uncertainty in dose delivery resulted from inter‐fractional organ motion in standard and hypofractionated prostate proton therapy, to assess the need for motion reduction to limit dose deviations in hypofractionated delivery, and to estimate optimal CT imaging frequency for target volume monitoring and accurate dose verification. Methods: We used serial CT images acquired at simulation and daily treatment for ten prostate patients. For each patient, a 3D conformal proton plan (78 Gy, 39 fractions) was created and renormalized for hypofractionated delivery (28, 20, 12 and 5 fractions). The plan was computed on each daily CT. The fractional dose was mapped to the simulation anatomy via deformable registration, with the mapped coverage validated against manual contours. The accurately registered fractions were used to examine whether the target and organ dose accumulated in the various deliveries remained within tolerance, and to evaluate the maximum deviations in dose estimation as a function of imaging frequency. Results: Three patients had more than 33 accurate fractions, and the other seven had at least ten. Without large rectal gas (causing inaccurate registration and large dose deviations), the accumulated target and organ dose remained within limit for delivery in 39 and 28 fractions. For delivery in 20 and fewer fractions, motion reduction would be needed to maintain target coverage and organ sparing. Ten CT scans were sufficient to detect large, systematic changes of prostate volume. To limit the uncertainty in estimated target coverage (V78Gy) to 3%, and rectal dose (both V75Gy and V70Gy) to 5%, ten scans were also sufficient, unless a significant change of prostate volume was observed. Conclusions: For delivery in 39, 28 and 20 fractions, the minimum recommended imaging frequency is one for every four, three and two fractions, respectively. Daily imaging is needed for delivery in 12 and 5 fractions.This study was supported by the Federal Share of program income earned by Massachusetts General Hospital on C06‐CA059267, Proton Therapy Research and Treatment Center.
TU‐G‐BRC‐02: Predictive Tracking for Real‐Time Deformable Motion Using a Dynamic Virtual Patient Model
Authors: Guo B , Xu X , Shi C 
Published: November 2011

Purpose: To develop a novel tracking technique for intensity modulated radiation therapy (IMRT) based on dynamic virtual patient modeling. Method and Materials: Predictive tracking uses a dynamic virtual patient model to account for the three‐dimensional deformable motion of the target during realistic IMRT deliveries. The virtual patient model was developed based on the 4DCT images and the structure contours delineated on different respiratory phases. With a real‐time breathing curve, the virtual patient model could be updated to a real‐time model which would then be used to predict the motion of the target, to modify the IMRT leaf sequence on‐line to account for the target motion, and to calculate the delivery dose of the IMRT plan with consideration of the interplay effect. A lung case was chosen to demonstrate predictive tracking. The quality of the predictive tracking plan was compared with two commonly used 4D IMRT treatment planning techniques: maximum intensity projection (MIP) and planning on individual phases (IP). Results: For a realistic breathing motion, predictive tracking offered better plan quality than MIP and IP. PTV V97 was 90.4% for a MIP plan, 88.6% for an IP plan and 94.1% for a predictive tracking plan. Lung V20 was 20.1% for the MIP plan, 17.8% for the IP plan and 17.5% for the predictive tracking plan. Conclusion: Predictive tracking based on dynamic virtual patient modeling is a novel 4D planning/delivery technique which is capable of managing the real time 3D deformable motion of target without increasing the workload of treatment planning or time of delivery. For a realistic breathing motion with consideration of the interplay effect in beam delivery, predictive tracking gave better plan quality than IP and MIP.Conflict of interest: Research supported by grant R01 LM009362.
TU‐G‐BRC‐07: Multileaf Collimator Tracking of Respiratory Motion Using a Novel X‐Ray Monitoring System
Authors: Krauss A , Fast M , Nill S , Oelfke U 
Published: November 2011

Purpose: To demonstrate for the first time MLC tracking of respiratory motion based solely on x‐ray motion monitoring in the unique in‐line geometry. Methods: A Siemens Artiste linac was equipped with two flat‐panel imagers (FPI), one directly underneath the linac head, the other underneath the patient couch. The kV x‐ray beam pointed towards the linac head and was tilted by 5.4deg from the MV treatment beam axis, such that the two beams were spatially separated on both FPIs. A programmable phantom with an embedded metal marker reproduced a 3D lung tumor motion trace. The marker position was automatically detected in the kV images, which were acquired on the upper FPI at a frame‐rate of 7.1Hz. The marker coordinates were sent to our tumor tracking system, which adapted the aperture of a Siemens 160 MLC in real‐time. System latency was compensated through a linear regression predictor, which was trained on a 40s breathing data window. The lower FPI was used to assess both the system latency and the geometric tracking accuracy by identifying MV field and marker position. System latency was determined by tracking a sinusoidal motion trace without prediction and calculating the phase difference from least squares fits to the phantom and treatment field trajectories. Radiochromic films were used to assess dosimetric tracking accuracy. A static radiation delivery to the non‐moving target served as reference for the delivery to the moving phantom with and without tracking. Results: The total system latency was 740ms. Respiratory motion tracking yielded root mean squared deviations between phantom and MV field positions of 1.71mm (1.26mm) parallel (perpendicular) to the leaf travel direction. 2%/2mm gamma failure rates were decreased from 42% to 20%. Conclusions: We achieved accurate MLC tracking of irregular breathing motion (perpendicular to the treatment beam) based solely on x‐ray imagery.Supported by Siemens Healthcare/CR.