bluuebunny/crossref_metadata_2025_split huggingface dataset:
SU‐FF‐J‐50: Dose‐Guided Radiation Therapy Strategies with Megavoltage Cone‐Beam CT
Authors: Pouliot J , Aubry J , Aubin M , Morin O , Chen J , Nunna C , Celi J 
Published: July 2007

Dose Guided Radiation Therapy (DGRT) is an extension of adaptive radiation therapy where dosimetric considerations constitute the basis of treatment modification and validation. The objective of this work is to elaborate two DGRT scenarios, treatment‐time and progressive, and gather all the required functionalities within the same workstation to use it in a clinical environment.The proposed DGRT strategies use a density‐calibrated Megavoltage Cone‐Beam CT (MVCBCT) image acquired at treatment time, the reference dose plan imported from the planning system and an independent dose calculation engine. A DGRT workstation was created to compare the initial plan with the dose distribution of the day. The beam arrangement is copied to the pre‐registered MVCBCT and dose distribution is calculated. Side by side comparison, dose difference maps and DVH differences are used to assess the clinical situation. Phantom experiments and patient data were used to test the DGRT scenarios. A Pinnacle dose calculation was performed to validate the local dose calculation engine.The DGRT workstation integrates the following steps; image registration, correction and conversion of MVCBCT images into density, dose re‐calculation, dose comparison with the reference plan and a data extraction module for statistical analysis. Dose re‐calculation on MVCBCT images is performed with a precision better than 3%, enabling the progressive DGRT scenario. When performed on a patient treated for a base of tongue tumor with IMRT, the DGRT scenario showed a mean dose increase from 26 to 42 Gy in the left parotid.DGRT brings together the knowledge of 3D imaging and the 3D dose distribution to assess the clinical situation. By making dose re‐calculation fast and accurate, the DGRT workstation allows dosimetric studies on a large scale. Results from on‐going clinical studies will determine how frequently significant dose differences occur and lead to site‐specific adaptation strategies. Research sponsored by Siemens OCS.
SU‐FF‐J‐54: A Hybrid Multiresolution Method for Automatic Registration Between Reference and On Board Digital Tomosynthesis
Authors: Ren L , Yan H , Godfrey D , Yin F 
Published: July 2007

Purpose: Automatic registration between reference and on‐board digital tomosynthesis (DTS) is a critical step for target localization using DTS. We previously developed an approximate method for automatic registration between reference and on‐board DTS, in which reference DTS was not generated iteratively to match with the anisotropic resolution of on‐board DTS. This study aims at developing an accurate method for automatic DTS registration with improved efficiency, robustness and accuracy. Method and Materials: The accurate DTS registration method was realized mainly by hardware acceleration of DRR generation, which was achieved by implementing a 3D texturemap based volume rendering process in graphic card using OpenGL language. The alpha blending mode was chosen to simulate ray casting algorithm, and three color channels of graphic card were used for data storage. With hardware acceleration, the accurate method changes the CT pose and regenerates DRR and reference DTS iteratively to match reference DTS with on‐board DTS based on mutual information. A hybrid multiresolution method was developed to combine approximate and accurate methods in a multiresolution scheme. It was tested on both anthropomorphic chest phantom and H&N patient data with simulated translations and rotations. The registration efficiency, attraction range and accuracy were recorded and compared with previous results. Results: The hybrid multiresolution method is 4 times faster than approximate method. Its registration attraction range is 2–5 times larger than that of approximate method for single‐axis translations and rotations, and 1.5–2 times larger for combined 6‐D rotations and translations. The registration accuracy is within 1.2 deg/mm for phantom data and 1.5deg/mm for patient data through the whole attraction range. Conclusions: The hybrid multiresolution method is much more efficient, robust, and accurate than approximate method. It is potentially a practical and reliable method to clinically implement DTS for target localization.Partially supported by a Varian research grant.
SU‐FF‐J‐57: A Phantom Study On the 3‐D Target Localization Accuracy Using CBCT of An On‐Board Imager
Authors: Zhang L , Yan H , Yin F 
Published: July 2007

Purpose: To evaluate the three‐dimensional target localization accuracy using CBCT of an On‐Board Imager (OBI) system by determining the detection error and residual error associated with image registration and patient repositioning. Method and Materials: An anthropomorphic pelvis phantom was used to simulate a range of shifts in the three translational directions and rotations around each of the three axes. First a simulated shift or rotation was applied. Then a CBCT scan was followed by 3D3D matching between the CBCT 3D volumetric image with the planning CT image. The detected shift vector was compared to the actual shift vector to calculate the detection error. Next the phantom was automatically realigned to the planned position by the OBI system. Subsequently, a second CBCT scan and 3D3D matching was performed to verify the re‐positioning accuracy (residual error). In each of the three translational direction, simulated shifts of 1, 2, 5 and 10 mm were evaluated. In the longitudinal direction large shifts of 20 and 50 mm were evaluated to see whether accuracy was dependant on shift magnitude. Simulated rotations of 1, 3 and 5 degrees around the three axes were also evaluated. Results: On the average, the detection error for translational shifts is 0.4+/−0.3 mm. The average of the corresponding residual error is 0.6+/−0.4 mm. For simulated rotations the average detection error is 0.2+/−0.1 degrees. The average of the corresponding residual error is 0.4+/−0.5 mm. Conclusion: The results indicate that CBCT is capable of detecting target shifts and patient rotation to within 1 mm and 0.5 degree respectively. The shifted target could be realigned to the planned isocenter to within 1mm accuracy when correcting for translational shifts and within 1.8 mm when correcting for rotations.This study is partially supported by a Varian research grant.
SU‐FF‐J‐64: The Role of Seminal Vesicle Motion in Target Margin Assessment for Online Image Guided Prostate Cancer Radiotherapy
Authors: Liang J , Wu Q , Yan D 
Published: July 2007

Purpose:. For intermediate and high risk prostate cancer, both prostate gland and seminal vesicle (SV) should be included in CTV. However, motion patterns of prostate and SV could be different resulting in different margin requirement. Our purposes are to investigate motion of SV and its role at the proper margins requirement on two online image guided correction methods. Method and Materials: Twenty‐five patients with at least 16 daily CTs per‐patient were included in this study. Contour to contour based image auto‐registrations were performed to obtain organ daily motions.Two online image guided correction methods were simulated by using conventional 4‐field treatment plan. Margins were designed to ensure that the minimal CTV cumulative dose after correction was within 2% dose reduction for at least 95% of patients. The first guidance used prostate daily translational displacement for patient online correction. In this case, two margin designs were analyzed. Margin‐A was designed as uniform margin for whole CTV. Margin‐B was designed for SV only meanwhile a fixing 3 mm uniform margin for prostate. The second guidance used the whole CTV translational displacement to determine the online correction. In this case, a uniform margin‐C was designed for whole CTV. The cumulative dose was constructed based on deformable organ registration. Results: The motion of SV was (0.1±1.7, 0.0±6.6, 0.1±3.7) mm, which was significantly larger than the prostate motion of (−0.2±1.0, −1.2±4.4, −0.1±3.1) mm. The margin‐A, margin‐B and margin‐C produced similar PTVs which were PTV=CTV+4mm, (Prostate+3mm)+(SV+4mm) and CTV+3mm. The corresponding PTV volumes were 129±30, 121±28 and 116±28cc accordingly. Conclusion: SV can move significantly larger than prostate, additional margins are needed but less essential in online correction with conformal dose delivery of prostate cancer treatment mainly due to the shallower dose gradient in the SV region.Partially supported by NIH grants CA118037 and CA091020.
SU‐FF‐T‐21: A Method to Determine the Gantry Isocentricity with a Portal Imager
Authors: Easterling S , Ting J , Scarbrough T 
Published: July 2007

Introduction: Historical method of verifying the linear accelerator gantry isocenter depended on the use of “star shots” with film. This method is subjective and its accuracy is in doubt when the expected results are in the range of 1.0 mm or less. In addition, collimator jaw symmetry and movements affect the measurement accuracy of the gantry isocentricity.Modern linear accelerators are capable of isocentricity less than 1.0 mm radius and modern radiation therapy departments are film‐less.The purpose of this investigation is to establish a different method to verify the isocenter accuracy during the initial acceptance testing and routine physics QA. Because modern linear accelerators are equipped with electronic portal imagers, this investigation uses the portal imager to determine the gantry isocenter accuracy. Methods and Materials:Out‐line of the procedure:(1) Check the cross‐hair mechanical rotational isocentricity.(2) Setup a metallic object at the isocenter using the light‐field and the collimator cross‐hair.(3) Take a static portal image of this metallic object with gantry pointing vertically down.(4) Without moving the portal imager, take a portal image of this object while the gantry makes a 360‐degree arc rotation with the same monitor unit as the static exposure.(5) Analyze the full‐width‐half maximum (FWHM) of each or subtracting these two images. Results and Discussions: If the gantry isocentricity is perfect, the two images would be identical and the FWHM will be identical. But, if the gantry isocentricity is a 2.0 mm diameter, the FWHM will reflect that as well. Advantages of this method are:(1) Less subjective and less dependent on observers.(2) Able to detect isocentricity less than 1.0 mm diameter.(3) Results are immediately available for analysis.(4) No films.(5) Results are electronic and can be analyzed by using readily available tools and methods.
SU‐FF‐T‐31: A New Table‐Top System for Extended Characterization of Brachytherapy Radioactive Seed Batches
Authors: Douysset G , Roy H 
Published: July 2007

Purpose: To improve the quality control of brachytherapy radioactive seeds. Method and Materials: It is estimated that almost 10 million brachytherapy sources for implants (125‐I, 103‐Pd, 131‐Cs) are produced every year all over the world. Source manufacturing is a complex process due to the combination of the small size of the sources and their sophisticated design. Quality control of the seeds is therefore an important issue. The control should first include calibration but several other tests such as a check of the actual internal structure of the seed is relevant.An innovative system (patents pending) has been developed in order to fully characterize a batch of sources. It is a compact table‐top device which is able to perform the following tests for each source: visual inspection, source calibration (through low energy x‐ray spectrometry), monitoring of radiochemical impurities (e.g. 126‐I or 137‐Cs) by γ spectrometry, control of the internal structure of the seed (dimensions, presence of high‐Z markers) by micro‐radiography, control of the distribution of radioactive material by autoradiography and possible control of materials purity by XRF analysis. Results: A prototype instrument has been built. A source can be fully characterized within 30–40 s and sorted according to the results delivered by the various instruments. All tests are performed without any user's radiation exposure. Conclusion: This automated system allows a better characterization of large batches of sources and can possibly lead to improvement of the manufacturing processes. A simplified version of the instrument could be implemented at the end‐user's level allowing therefore a fast automated 100% assay of sources prior to implantation.
SU‐FF‐T‐36: A Preliminary Comparison of a New Fluence Benchmark for Clinical Electron Beams with Fluence Calculated with a Commercial Planning System
Authors: Faddegon B , Traneus E , Chen J 
Published: July 2007

Objective: To compare a newly developed benchmark of electron fluence in clinical electron beams with fluence calculated with a commercially available treatment planning system. Materials and Method: An accurate and detailed benchmark of fluence for clinical electron beams is under development. The benchmark is based on detailed measurements of the source, geometry, relative output factors and dose distributions of clinical electron beams of a single clinical linear accelerator, including the largest available field with no applicator, along with a precision Monte Carlo simulation of the treatment head. Fluence is divided into direct electrons and those scattered from collimators, including the applicator and insert. This benchmark is used to determine the accuracy of fluence calculated with a beam model in a commercial treatment planning system commissioned with measurements done on the same accelerator used to develop the clinical benchmark. Results: Energy and spatial distributions of fluence for direct and indirect electrons are generally in good agreement between the benchmark data sets and the commercial beam model. Differences include lower resolution in the beam model than in the actual beam in the penumbra and differences in the relative contribution of direct and indirect electrons to the total fluence. Conclusion: The new benchmark is very useful in determining the accuracy of models of clinical electron beams. The benchmark is not only an excellent benchmark for the large, open field, which is seldom used for treatment. It is useful for any applicator and SSD, assuming Monte Carlo can accurately account for the jaws, applicator and insert in the somewhat simplified geometry used in the simulation. The work, currently limited to the linac from a single vendor, is to be expanded to included linacs from other vendors.Support from NIH R01 CA104777‐01A2 and Nucletron.
SU‐FF‐T‐57: Accelerating IMRT Optimization by Voxel Sampling
Authors: Martin B , Bortfeld T , Castanon D 
Published: July 2007

Purpose: To develop a new algorithm to accelerate IMRT optimization by voxel sampling. Methods and Materials: We note that standard gradient descent is fairly slow due to the time spent calculating the dose to the patient. We realized that a reasonable estimate of the objective function and gradient could be obtained by calculating the dose to only a fraction of the voxels in the patient. To avoid adding a systematic error, we randomly sample the voxels at each step to create an unbiased estimate of the gradient. Supposing sufficient samples are chosen, the errors in the gradient will tend to cancel each other out as the algorithm progresses.Uniform sampling is inefficient, however, since small, important organs tend to need a higher sampling rate while large, less critical organs could use a lower rate. We developed an algorithm to tune the sampling rates for each objective by minimizing the variance of the estimate of the objective for a fixed overall sampling rate.With the errors in the estimated gradient, we could not use techniques like conjugate gradient to further accelerate performance. However, we found that the delta‐bar‐delta algorithm provided an additional speed boost. Results: For our example case of a lung patient with 384,979 voxels and 1460 beamlets we were able to achieve a speed improvement of approximately three times using uniform sampling, 14 times using automatically tuned sampling, and 20 times using delta‐bar‐delta with automatically tuned sampling. While the algorithms are randomized, the results were very reliable and stable in our experience. Conclusions: Voxel sampling proves to be a viable way to dramatically improve the speed of IMRT optimization. It could be particularly helpful for applications such as temporo‐spatial optimization and multi‐criteria optimization, where a great many variants of a problem are optimized.
SU‐FF‐T‐71: An Interactive Software Tool for Modifying Outcome Models and Predicting Patient Specific Outcomes in Treatment Planning
Authors: Apte A , El Naqa I , Deasy J 
Published: July 2007

Purpose: For patient‐specific radiotherapy outcomes predictions (i.e., NTCP predictions), the choice of model and its parameters is of utmost importance. Our goal is to develop a software tool which will let clinicians conveniently select the model, understand the effects of the model parameter values, and thereafter predict plan specific outcomes. Method: This module has been developed within CERR (Computational Environment for Radiotherapy Research), an open source Matlab‐based software system. Two commonly used NTCP analytical models implemented are the Lyman‐Kutcher‐Burman (LKB) and the Critical volume (CV). The parameters of LKB model include: the exponent for calculating EUD, D50, and the slope parameter m; whereas the parameters of the CV model include the mean relative damaged volume, critical fraction of FSUs, and interpatient variability. Our interactive outcomes estimation module lets the user change the model and parameters and observe the change in predicted outcome simultaneously. We have also implemented a new model to predict radiation lung injury, which is a logistic regression model with two predictors — mean dose to lung (MDL) and the GTV location (GTV‐superior‐inferior position). We developed an interactive nomogram to let users look at the variation in outcome with respect to MDL and GTV‐SI position. Results: The interactive outcomes‐prediction module within CERR was tested on sample plans. The user is presented with slider bars to change the parameter values, or the user can input their own values, and the estimated outcome is simultaneously updated. The interface is simple, user‐friendly, and easily extensible to include other outcomes models. Conclusion: This outcomes prediction module, along with other graphical visualization and analysis capabilities within CERR, may aid clinicians in understanding and using NTCP models for radiation treatment planning.This research was partially supported by NIH grant R01CA85181 as well as a grant from TomoTherapy, Inc.
SU‐FF‐T‐76: Analysis of a Novel Method of IMRT QA Using EPID‐Acquired QA Planes
Authors: Rasmussen K , Nelms B , Tome W 
Published: July 2007

Purpose: To assess the efficacy and quantify the accuracy of a novel method for IMRT QA in which the measured dose plane is derived from an EPID image. Method and Materials: aSi EPID data was acquired and converted using a novel method based on a machine‐specific beam model to estimate QA dose planes from mega voltage (MV) EPID images. Dose planes were calculated in a homogeneous, water‐equivalent QA phantom using the model and an acquired MV EPID image with no additional buildup required on the EPID.Specific parameters, such as field size output dependency, dose redistribution kernel, potential off‐axis corrections and absolute dose calibration, were measured to create the model that is based on the raw EPID files.QA dose planes were compared to ion chamber measurements, MapCHECK® measurements, and planar fluences generated by ADAC Pinnacle3® TPS. MapCHECK® and ion chamber (IC) measurements were taken at multiple depths at a source to detector distance (SDD) of 100cm. Dose planes in homogenous media were estimated using EPID images acquired at a distance of 140cm SDD. Data was collected for both 6 MV and 10 MV energies to determine the accuracy of the model for these two energies. Results: Preliminary sample analysis demonstrates that the dose planes estimated by the model using EPID images of complex IMRT fields result in >98% pass rate of all point measurements from MapCHECK®, employing a 3% dose or a 2mm distance to agreement criterion. Agreement between MapCHECK® and IC measurements were within 1%. Conclusion: This novel method shows promise as a tool for IMRT QA with reasonable accuracy. Setup, acquisition and analysis can be performed in a more time efficient manner than is possible with current methods of IMRT QA. Conflict of Interest: This work was partially funded by Sun‐Nuclear Co.® and Canis Lupus LLC.
SU‐FF‐T‐79: Analysis of the Virtual Wedge Implementation by the AAA Algorithm in the Varian Eclipse TPS
Authors: Both S , Bieda M , Dimofte A , Zhu T 
Published: July 2007

Purpose: To evaluate accuracy of VW implementation by the Varian Eclipse AAA Calculation Algorithm Material and Methods: A 6MV Siemens Oncor Linac beam was used to deliver symmetric and asymmetric VW (15, 30, 45, 60) profiles for a range of field sizes (5×5cm2 to 15×15cm2). All measurements were performed in absolute dose mode using a 2D diode array (Mapcheck, SunNuclear FL), at 100cm SAD and depth of 5cm under water equivalent conditions.The Varian Eclipse TPS software v.8, AAA calculation algorithm was used to determine the VW fluence maps in a water equivalent phantom. All measured and calculated Linac central axis values were analyzed. A relative and absolute comparison was conducted for all calculated and measured fluence maps using the Mapcheck Software v.3.01.08.00. Theoretical calculations of the VW factors were performed and compared with the ones calculated based one measured data. The measured output factors were compared with the calculated ones using our PennMU software and the Eclipse TPS AAA calculation algorithm. Results and discussions: All measured and theoretical symmetric VW wedge factors and output factors were in agreement. Differences up to 82% were found for asymmetric VW output comparison between the Eclipse AAA algorithm calculated output factors and the measured ones. The differences increase with the degree of asymmetry of the field and the VW angle. The data analysis suggest that the Eclipse AAA TPS defines the wedge factor to the central axis of the beam rather then to the central of the machine (VW factor definition). The relative fluence map analysis showed that over 95% of the VW measured profile are within 3%/3mm (%Diff/DTA). Conclusion: We found that the VW clinical implementation for the Eclipse TPS AAA algorithm, v.8, is valid for symmetric fields only and large errors can result for asymmetrical fields.