bluuebunny/crossref_metadata_2025_split huggingface dataset:
SU‐E‐I‐149: Digital Breast Tomosynthesis Using 2D Source Scanning Patterns: A Simulation Study
Authors: Zhong Y , You Z , Shen Y , Liu X , Lai C , Wang T , Ge S , Yi Y , Shaw C 
Published: November 2011

Purpose: Digital tomosynthesis (DTS) imaging with 2D scanning patterns may help reduce the artifacts by more effectively blurring the off‐fulcrum objects. In this study, the effects of various source scanning patterns on the reconstructed images are studied via simulation. Methods: The X‐ray source was assumed to be movable following various scanning patterns. The source‐to‐iso‐center and source‐to‐image distances were assumed to be 500 mm and 600 mm, respectively. Projection images were computed using an improved distance‐driven algorithm. The objects studied included a Shepp‐ Logan phantom and a digital breast phantom constructed from segmented cone beam CT images. The X‐ray absorption coefficients were taken of mono‐energetic X‐ray at 19 keV. The x‐ray source was scanned with 1D (1D DTS) and 2D (2D DTS) patterns. The objects were reconstructed using the iterative expectation‐maximization algorithm. The root‐mean‐squared‐ deviation (RSMD) was calculated to indicate the deviation in terms of CT numbers of the reconstructed image to the original phantom. Results: The RMSD of the reconstructed Shepp‐Logan phantom was 243.3 for 1D DTS and 104.7 for 2D DTS. Visual inspection revealed reduced artifacts and better CT number accuracy with 2D DTS than 1D DTS. For the digital breast phantom, the accuracy of the reconstructed tissue structures was assessed using the CT number uniformity in the dense tissue and adipose tissue regions. The RMSD of the digital breast phantom was 113.1 for 1D DTS and 50.0 for 2D DTS. The comparison showed that the 2D DTS resulted in better accuracy in CT number uniformity. Conclusions: Our results demonstrated that the use of 2D source scanning patterns has the potential advantage of more effectively blurring objects in off‐fulcrum planes, thus reducing the artifacts and resulting in more accurate image reconstruction.This work was supported in part by research grants: CA104759 and CA124585, EB000117 from NIBIB, CA138502A1, and a subcontract from NIST‐ATPs.
SU‐E‐I‐150: Cone‐Beam Artifacts in Dedicated Breast CT
Authors: Vedantham S , Shi L , Noo F , Glick S , Karellas A 
Published: November 2011

Purpose: Cone‐beam CT with circular trajectory is susceptible to cone‐angle related artifacts that affect quantitative imaging. These artifacts were quantified under conditions relevant to dedicated breast CT for full and short‐scans. Methods: Three sets of numerical phantoms (0.2‐mm voxels) were used: (1) cylindrical Defrise phantom of 14‐cm diameter and 10.6‐cm length inclusive of 2‐mm skin, with alternating 4‐mm coronal layers of fixed (0.15) and variable (0 to 1, in steps of 0.1) glandular fraction breast tissue; (2) semi‐ellipsoidal Defrise phantom with dimensions matched to the cylindrical phantom for a realistic pendant‐breast geometry; (3) 20 surgical mastectomy specimens based numerical phantoms. Source‐to‐rotational axis and source‐to‐detector distances of 65‐cm and 100‐cm, respectively, were used. Noise‐free simulations were performed at 30‐keV, with the phantoms co‐aligned to rotational axis, using an ideal detector (0.4‐mm pixels), and without the confounding effects of focal spot blur (point source) and x‐ray scatter. Constant angular sampling of 1.2‐degrees was used resulting in 300 and 165 projections for full‐scan and short‐scan (198‐ degrees). Reconstructions were performed using Hamming‐windowed FDK‐algorithm with short‐scan using Parker weights. For the Defrise phantoms, the cone‐angle dependence of the artifacts was analyzed using percent difference at the rotational axis between the reconstructions and phantoms, and by visual inspection. For the mastectomy specimens, power spectral analysis was performed. Results: For Defrise phantoms, increasing attenuation difference between layers resulted in higher inaccuracies (artifacts). Cylinder resulted in higher inaccuracies compared to semi‐ ellipsoid particularly near maximum cone‐angle. Visual inspection and power spectral analysis indicate that the spatial distribution of these artifacts is different between full and short‐scans. Conclusions: Cone‐beam artifacts at breast CT relevant conditions are observed. They depend on object shape, and attenuation difference of the tissues within the object. These artifacts must be remediated as they may impact task‐specific assessment and can profoundly affect quantitative imaging.Supported by NIH/NCI R01CA128906. The contents are sole responsibility of the authors and do not represent the official views of the NIH or NCI. SG: Research contract with Toshiba Medical Research Institute.
SU‐E‐J‐54: Evaluation of a Toolkit for Automatic Deformable Registration and Segmentation of Treatment Images in Clinical Prostate Cancer IGRT Applications
Authors: Xu Z , Chaney E , Kress A , Tracton G , Foskey M , Lian J , Chang S 
Published: November 2011

Purpose: High quality IGRT is only practical when robust tools are available for accurate and fast deformable registration and segmentation of the treatment images. We have implemented such a toolkit for the male pelvis using a class of statistically trainable deformable models (SDMs) of anatomical structures, called medial representations (m‐reps). The aim of this study is to evaluate its capabilities and performance in clinical prostate cancer IGRT applications. Methods: An image collection for prostate cancer patients treated with IGRT using a CT‐on‐Rails (CTORs) system was studied retrospectively with this toolkit to determine the actual delivered dose throughout the treatment course. The patient‐specific planning models of the male pelvic organs, including the prostate, bladder, rectum, and femoral heads, were constructed via user‐guided autosegmentation of the planning CT. The planning CT was then automatically registered to the CTORs images via a rigid‐body, soft‐tissue‐based registration method. The planning models were then transformed into initialized treatment models to segment the CTORs images. The essential tissue‐voxel correspondence across treatment images was established by this model‐based segmentation process. The dose delivered to the same tissue elements can, therefore, be accumulated for adaptive planning and/or outcome assessment. Results: Preliminary results show that the m‐rep‐based planning image segmentations are clinically acceptable to the physicians and can be readily constructed from the planning CT with nominal user guidance. The automatic image registration with the treatment‐day image, occasionally followed by manual refinement, also considered acceptable by clinical staff. Treatment image segmentation with intrinsic tissue‐voxel correspondence used substantially less time (5 ± 1.3 minutes) in comparison to manual contouring. Conclusions: Our clinic‐oriented toolkit is effective in segmentation of treatment images of the male pelvis. Application for dose accumulation and adaptive IGRT is in progress.This work has been conducted in collaboration with Morphormics, Inc. with grant support from NCI R44 CA119571.
SU‐E‐J‐64: Margins for Single‐Fraction Treatments: Stereotactic Radiosurgery Brain Cases
Authors: Zhang Q , Chan M , Burman C , Amols H , Ling C , Mageras G 
Published: November 2011

Purpose: To determine the appropriate margin expansion from clinical target volume (CTV) to planning target volume (PTV) for single‐fraction stereotactic radiosurgery (SRS). Setting a proper margin is crucial for delivering the right dose to the CTV and sparing of organs at risk. Methods: Whereas in conventional fractionated treatment a Gaussian function is used to represent systemic errors, for single‐fraction treatment with a specific machine, the delta function is more appropriate. As input to the function, we measured the differences between image isocenter and radiation isocenter for a Varian Trilogy linac over a period of six weeks. To approximate the residual setup errors for a population of patients, we adopted a Gaussian function with different standard deviation. A phenomenological formula for calculating the CTV‐PTV margin for single‐fraction SRS brain cases is proposed. For 95% success (CTV received prescribed dose) of patientsˈ treatments, the margin for a single‐fraction treatment is obtained which is a function of standard deviation of the residual setup errors and system errors. Results: The differences between the image isocenter and radiation isocenter remain constant to within sub‐ millimeter during the typical treatment period of six weeks. This confirms our assumption on the system errors distribution as being a delta function and machine‐specific. This definition is especially important for a single‐fraction treatment. Our study found that human factors could also attribute to the reduction of the margin of CTV‐PTV in addition to stability of the treatment machine. Conclusions: A margin formula is proposed for the SRS brain case that attempts to help physicists determine the proper margin of CTV‐ PTV. This margin derivation could also extend for multi‐fraction cases because the system errors do not change from time to time unless system upgrades.R01‐CA126993
SU‐E‐J‐116: New RPM Amplitude Averaging Enlarges Gross Tumor Volume in 4DCT
Authors: Hunter L , Zamora D , Sun X , Pan T 
Published: November 2011

Purpose: To determine if new RPM amplitude averaging enlarges NSCLC iGTV delineation in the 4D‐CT simulation. Methods: We selected 24 NSCLC patients with respiratory‐induced lung motion of 1 cm or greater and generated two 4D‐CTs (from one scan) for each patient using a GE 8‐slice PET/CT scanner with a Varian RPM respiratory surrogate. For each patient both 4D‐CTs used phase‐corrected phase‐binning (PC‐PB) for image selection; however, for phase determination one 4D‐CT assigned phases based on the RPM amplitude at the median time point of the image acquisition (the contemporary technique), and the other 4D‐CT assigned phases based on the average RPM amplitude recorded over the image acquisition time. We developed software to assign phase and select images as described to create maximum intensity projections (MIPs) of the 4D‐CTs. These two MIPs and the cine MIP (CMIP; generated from all acquired images before image selection in 4D‐CT) were sent to the Pinnacle 9.0 treatment planning software for auto‐contouring to obtain internal gross tumor volumes (iGTVs). Auto‐contouring was done at the lung window level with a threshold of 800 and occasional, consistent manual intervention to prune regions that included non‐tumor tissue. Results: On average, iGTVs generated using the median time point RPMs and averaged RPM amplitudes were 91.9% and 94.1% of the iGTV generated from the CMIP, respectively (a 2.2% difference). The mean increase in iGTV when switching to RPM averaging was 0.37 cc with a p‐value of 0.0402 and corresponds to a mean percent increase in iGTV of 2.40%. Conclusions: This work demonstrates that new RPM amplitude averaging enlarges NSCLC iGTVs generated from MIPs of 4D‐CT.The presenting author, Luke Hunter, received funding support as a recipient of the Hertz Foundation Applied Science Fellowship.
SU‐E‐J‐121: Assessment of Different Approaches of Treatment Plan Selection in a Multiple Plans IGRT Strategy
Authors: Octave N , Gingras L , Boutry C , Berry I , Beaulieu L 
Published: November 2011

Purpose: To assess treatment plan selection in a multiple plans adaptive IGRT strategy in routine clinical workflow. Methods: Continuous Offline Replanning (COR) is an adaptive IGRT treatment strategy where patient treatment plan is selected from a pool of offline previously calculated plans based on the patient repositioning CBCT images. A treatment sequence with n=19 fractions was simulated and, with COR strategy, different selection approaches based on numerical analysis of DVH extracted values (COR_PTVV95, COR_CF) or on qualitative human selection (COR_H) were investigated. In numerical analysis, PTV coverage and multi‐objectives cost function were investigated. Each COR strategy was compared with the standard IGRT strategy using prostate center of mass translations (IGRT_0), and an optimal online replanning strategy (IGRT_Opt). In COR_H, operators were asked to select the most appropriate plan available from a screen display, priorizing geometrical fit of prostate, rectum and bladder contours on CBCT images. Results: Cumulative average values of PTV V95 range from 92.9 to 95.5% for COR_H; 93.2 to 97.7 % for COR_PTVV95; 92.7 to 93.2% for IGRT_0 and 99.9 to 100% for IGRT_Opt, which ranks IGRT_Opt as the best treatment option and the COR_PTVV95 as second best option. Values of the multi‐objectives cost function were consistent with PTV coverage and were in the range 0.71 to 2.62; 0.36 to 2.40; 1.74 to 2.69 and 0.014 to 0.021 respectively for COR_H, COR_CF, IGRT_0 and IGRT_Opt. Operators were asked to choose preferentially among the first 10 contour sets to see if 10 plans were sufficient to represent the diversity of anatomical configurations routinely seen. They succeeded for 17/19 fractions. Conclusions: For multiple plans adaptive prostate IGRT treatment, numerical selection process of daily plan based on target dose coverage or cost function values appear to be superior to human visual selection. Further development aim to minimize time selection procedure.Part of this work was financially supported by Varian Medical Sytems France.
SU‐E‐J‐122: Planning Four‐Dimensional Intensity‐Modulated Arc Therapy for Tumor Tracking
Authors: Niu Y , Betzel G , Yang X , Gui M , Parke W , Yi B , Yu C 
Published: November 2011

Purpose: We propose a practical four‐dimensional (4D) planning scheme of intensity‐modulated arc therapy (IMAT) for tumor tracking using dynamic multileaf collimators (MLC). Methods: We contour the target and critical structures on each image set of 4DCT associated with each breathing phase. Transformation vectors of the target from a reference phase to other phases are derived. A 3D‐IMAT plan is first optimized on the reference phase without motion‐induced margin. Assuming delivery starts at a predetermined breathing phase and the patient breathes the same way as during 4DCT imaging, we know the phases at which each planned segment will be delivered. Then, we transform the optimized segments from the reference phase to the phases of their delivery based on projections of transformation vectors of the target in the beamˈs eye‐view. The connectivity of the transformed segments between adjacent beam angles is enforced. The dose for each phase is calculated using segments delivered at that phase, and transformed to the reference phase to obtain cumulative dose. The resulting 4D plan is compared with the 3D plan without considering respiratory motion and with motion‐induced margins. Effects of enforcing connectivity on the plan quality are also evaluated. Results: Compared to the PTV dose of 3D plan without tumor tracking, the 4D PTV dose is more conformal and uniform, and it approaches the ideal situation of the patient being static. The 4D plan also showed better critical organ sparing than the 3D plan with motion‐induced margins. Adding MLC motion required for tracking to the planned motion rarely causes physical constraints to be exceeded, and enforcing connectivity thus has little effect on plan quality. Conclusions: The proposed scheme of 4D‐IMAT planning for tumor tracking is a feasible and practical approach under the current clinical planning environment. Dosimetric benefits of 4D planning have been clearly demonstrated.This stusy is supported in part by NIH R01 grant 1R01CA133539‐01A2
SU‐E‐J‐150: Applicability of a Point Fiducial‐Based Model for the Prostatic Bed in Post‐Prostatectomy Radiation Therapy Patients: An Expedited Dosimetric Analysis Using New Functionality in Philipsˈ Pinnacle3 Treatment Planning Systemˈs Research Version
Authors: Bharat S , Zhu M , Gay H , Michalski J , Santanam L , Noel C , Parikh P 
Published: November 2011

Purpose: The shape of the post‐prostatectomy volume, fiducial placement and isodose coverage is more complex than prostate radiation therapy; but to date, there have been no commercial tools to estimate the delivered dose in patients aligned with fiducials. A fiducial‐based algorithm to determine the dosimetric effects of fiducial localization has been implemented as ˈDelivered Dose Investigational Toolˈ (DiDIT), in Philipsˈ Pinnacle TPSˈ research version (Philips Medical Systems, Fitchburg, WI).Methods: 17 post‐prostatectomy patients were treated with SMLC IMRT, electromagnetic (Calypso Medical Technologies, Seattle, WA) tracking, 5mm CTV‐PTV expansions and 3mm tracking tolerances. The DiDIT tool implemented convolution of the static plan dose distribution with rigid motion (rotations and translations) calculated from the ∼150,000 fiducial tracking points, to generate estimates of the delivered dose. This analysis takes into account fiducial placement eccentricity, rotations, translations and the individual patient anatomy and treatment plan. Treatment adequacy was defined as the delivered minimum dose to the prostatic bed (CTV) >= 98% of planned minimum dose. Tracking data from subsets of the treatment course (first 3, 5 and 10 fractions) were utilized to determine the ability to predict treatment adequacy.Results: Each patient had fiducial motion of less than 2mm. Each DiDIT evaluation took 5 – 15 minutes. Treatment was adequate in 11 of 17 patients, with the CTV having cold spots of 4 to 32%. DiDIT analysis of the initial fractions was not predictive of inadequate dose delivery. Patients with inadequate dosimetry seemed to have more eccentrically placed transponders and/or more rotation though no cut‐off values were noted Conclusions: The DiDIT tool was used to quickly model delivered dose from fiducial localization. Results show that even with continuous fiducial tracking, there may be residual errors in the localization of the prostatic bed. Further work comparing these results with daily volumetric imaging is warranted.Work sponsored by NIH R01 CA134541‐01.
SU‐E‐J‐151: Geometric Accuracy of the X‐Ray Image‐Based Dynamic Tracking for a Four‐Dimensional Image‐Guided Radiotherapy System with Gimbals Mechanism of MHI‐TM2000 (Vero)
Authors: Mukumoto N , Nakamura M , Sawada A , Takahashi K , Miyabe Y , Takayama K , Mizowaki T , Kokubo M , Hiraoka M 
Published: November 2011

Purpose: To verify the geometric accuracy of the X‐ray image‐based dynamic tracking for a four‐dimensional (4D) image‐guided radiotherapy system with gimbals mechanism of MHI‐TM2000 (VERO). Methods: This study was performed employing a 3D moving phantom with a steel‐ball target of 9.5‐mm‐diameter; a laser displacement gauge; orthogonal kV x‐ray imaging subsystem, a gimbaled X‐ray head, and a system controller of MHI‐TM2000. The moving phantom was driven based on the programmed motion patterns (seven periodic [Motion range: 20–40 mm, Breathing cycle: 2‐5 s] and 15 of 3D patientˈs respiratory patterns). Subsequently, the displacements of the target were measured in real time by the laser‐displacement gauge and the orthogonal kV x‐ray imaging subsystem. Meanwhile, the system predicted the future target position, and then the orthogonal gimbals were transferred to the corresponding orientation. The transferred and the current orientation of the gimbals were recorded. Predicted target positional errors (EP), mechanical errors (EM) of the gimbals, and total tracking system errors (ET) derived from EP and EM were computed. Results: Root mean square of ET (RMSET) was up to 0.68 mm for the periodic patterns. As for the entire patientˈs respiratory patterns, average RMS of EP, EM, and ET were 1.28, 0.12, and 1.24 mm, respectively. The principal component score which was computed from the patientˈs respiratory motion under the conditions of free breathing decreased with large amplitude, long breathing cycle and high breathing stability. A strong positive correlation was observed between the ratio of the RMSET to the amplitude and the principal component score of the respiratory motion (R2 = 0.76). Conclusions: This study showed that MHI‐TM2000 has the capability for high tracking accuracy. The prediction error mainly caused the total tracking system error while the mechanical error was negligible. In addition, tracking error can be predicted from the principal component analyses.This research was in part sponsored by Mitsubishi Heavy Industries, Ltd., Japan.
SU‐E‐J‐154: Free Breathing Motion Tracking in Emission Guided Radiation Therapy
Authors: Mazin S , Yang J , Yamamoto T , Nanduri A 
Published: November 2011

Purpose: To evaluate an emission guided radiation therapy (EGRT) systemˈs ability to deliver dose to a moving PET‐avid target. Methods: We are developing a treatment system that will simultaneously deliver radiation during PET acquisition. Due to PETˈs slow imaging time, a method to compensate for motion will be to deliver radiation beam‐lets along individual PET lines‐of‐response (LORˈs) as they are detected. The EGRT system involves rotating a linac and PET detectors on a closed ring gantry while dynamically controlling a binary multi‐leaf collimator for helical delivery. A cylindrical phantom and six spherical inserts were filled with FDG to achieve an 8:1 target‐to‐background ratio. The phantom was mounted onto a motion stage programmed with a free breathing trajectory acquired from a human subject using an external marker. This trajectory was translated into a purely superior/inferior (z) motion path for the stage and used as ground truth. A planning target volume (PTV) was defined around the largest sphereˈs motion path. LOR data were acquired in list‐mode from a GE Discovery system and used as input to a voxel monte carlo simulation of radiation dose delivered by the EGRT system with an average lag time of 250 ms. The EGRT method was compared to uniform irradiation of the PTV. Results: The EGRT approach exhibited a non‐uniform dose distribution to the tumor. However, for this specific case there was a 30% relative increase in dose to 50% of the tumor volume for the EGRT approach with both methods normalized to have the same integral dose to the phantom. Conclusions: We have shown that a target exhibiting free breathing motion can be tracked and treated using individual PET emissions to guide delivery. There is dose peaking at the center of a uniform PET‐avid volume. This is the first EGRT feasibility demonstration with experimental data.SRM and ASN are stockholders of RefleXion Medical.