bluuebunny/crossref_metadata_2025 huggingface dataset:
SU‐E‐J‐100: A Contour‐Guided Deformable Image Registration Algorithm for Adaptive Radiotherapy
Authors: Gu X , Jia X , Gautier Q , Dong B , Mell L , Jiang S
Published: November 2011

Purpose: To develop a contour‐guided deformable image registration algorithm to improve the accuracy of deformation image registration in adaptive radiotherapy, especially for improving the accuracy of low contrast structures deformation. Methods: We developed an efficient algorithm to accurately deform low‐contrast structures in CT images. The new DIR algorithm is based on our original developed Demons algorithm by adding constraints defined by physician drawn contour pairs on images. By iteratively increasing the intensity of ROI enclosed by contour pairs, the optimization problem defined in Demons is ensured to converge to a desirable solution. Results: The new algorithm was validated on both a numerical phantom experiment and a clinical patient case. For the digital phantom experiment, a moving image is defined as two intersected spheres embedded in a cube and the contrast between spheres and cube is low; and a target image is a low‐contrast sphere in a cubic. For the clinical case, two CT images scanned for a head and neck cancer patient in one month apart are treated as a pair of moving and target images. The left parotids with anatomical changes are defined as structures of interest (SOIs). Qualitatively, with visual inspection, the proposed algorithm yields satisfactory results in both numerical and clinical testing cases. Quantitatively, root mean squares error (RMS) and normalized correlation coefficient (NCC) were calculated between the deformed and target SOI. Compared to the original Demons algorithm, the contour‐guided Demons algorithm results the decrease of RMS and the increase of NCC for both cases. Conclusions: The proposed contour‐guided demons algorithm permits us to take advantage of the structures defined by physicians to obtain more accurate image deformations. It provides a useful clinical tool for future interactive adaptive radiotherapy.
SU‐E‐J‐101: Towards MR‐Only Simulation: A QA Phantom for Coalescing Consecutive MR Scans of the Head and Neck
Authors: Yu H , Mah K
Published: November 2011

Purpose: One strategy for reducing the amount of time required to MR scan the volume required for radiation treatment planning of the head and neck region (top of head to apex of lung) is to divide this volume into three consecutive scans using different scan volumes, fields of views, and resolutions. Unlike CT, MR image positions are reconstructed relative to the isocenter of magnetic field. Thus for different scan volumes, the MR couch moves the volume of interest to the isocenter. Couch movement error must be quantified if several consecutive MR datasets are to be coalesced accurately along the cranial‐caudal axis. A QA phantom was constructed to quantify MR couch movement error. Methods and Materials: The phantom consists of three pieces of 2mm acrylic material arranged in a figure “N” within a hollow, acrylic box filled with distilled water. The angles within the N were designed to detect longitudinal shift errors of 1mm. Geometric accuracy of the QA phantom was evaluated using CT. Using a Philips 3T Archieva MR scanner, the phantom was imaged in sections using different resolutions, field of views, couch positions and varying couch loads. Results: A couch shift error of 0.3±0.4mm and 0.8±0.3 mm was measured for 5cm and 10 cm movements, respectively with 95kg load. For no load, the corresponding values were 0.1±0.2mm and 0.3±0.4mm. Three consecutive scans of the QA phantom acquired with different sequences and FOVs (240∼360mm) and resolution (0.95×0.95×1mm3 and 1×1×2mm3) were accurately ‘stitched’ into one data set using the quantified couch shift correction. Conclusions: The QA phantom developed for this work could be used to quantify absolute MR couch shift and geometrically correct for any couch error in the coalescing of consecutive MR scans. It may be useful as a daily QA tool for MR simulation.
SU‐E‐J‐106: Interactive 4D Proton Pencil Beam Dose Calculation Using Shadie: A Fast GPU‐Based Visualization Language
Authors: Wolfgang J , Hasan M , Pfister H , Chen G
Published: November 2011

Purpose: Proton treatment planning for thoracic and gastrointestinal targets requires sensitivity to motion issues upstream from the distal surface of the defined disease site. Variations in radiological path length due to organ motion, both inter‐ and intra‐fraction, can result in significant under‐ and over‐shoot of the defined proton dose distribution due to the high radiological range sensitivity of particle beam radiotherapy. We describe a method for interactive exploration of this range sensitivity through direct, ‘on‐the‐fly’ dose recalculation using a GPU‐based visualization language, Shadie. Methods: Based on a python‐like syntax, the GPU kernel is defined and recompiled by the Shadie language interpreter for CUDA code compilation. This kernel is evaluated directly in the rendering pipeline, coupling the display to the final, volume rendered patient anatomy. The size and/or number of spatial‐temporal volumetric datasets is limited only by available GPU memory, allowing for kernel operations against multiple data sets simultaneously. A pencil beam proton dose calculation algorithm has been re‐implemented using this shader language to allow real time recalculation of proton dose distributions. Interactivity of the volume rendered image is provided by exposing relevant treatment delivery variables to the user, including: beam range, modulation, couch and gantry angle, and source position. As these exposed variables are modified, the dose is continuously recalculated and displayed. Results: The speed of the dose calculation engine allows for 4D visualization of both anatomy and dose distribution in a volume rendered environment. The flexibility of Shadie allows for easy adaptation to multiple visualization needs, including mean and standard deviation dose distribution maps as well as a cinematic mode where the dose is recalculated as the datasets are cycled through sequentially. Conclusions: This tool may provide assistance when planning/reviewing treatment sites subject to temporal variability, allowing for deeper understanding of the dosimetric implications of organ motion.
SU‐E‐J‐107: Utilization of Hysteresis Motion as a Marker for Tumor Margin in a Free‐Breathing Lung
Authors: Zhao T , White B , Low D
Published: November 2011

Purpose: To study the feasibility of using hysteresis motion characterized by a free‐breathing lung motion model as a marker for tumor margin in lung patients. Methods: Anatomical and physiological evidences have shown that solid tumors typically have more collagen in tumor stroma and consequently are firmer than surrounding normal tissues. For patients with lung cancer, the increased firmness in tumor stroma would alter pattern of breathing motion, mostly prominent in the hysteresis component that is defined as the variation between motion trajectories during inhalation and exhalation. A free‐breathing lung motion model, x= x0+alpha*v+beta*f, where v and f denote tidal volume and air flow respectively, decomposes breathing motion into a non‐hysteresis component alpha*v, which is purely due to air filling, and a hysteresis component beta*f. Four patients acquired in Cinè mode were analyzed and beta was obtained by linear least‐square fitting registered motions to air flows measured by spirometry. Results: Hysteresis motions were found to gently change in magnitude and direction throughout whole lungs except around cancerous regions where the hysteresis motions turn sharply following the curvature of the tumors, indicating shear motions along the interface between tumors and surrounding normal tissues. Conclusions: The vector map of hysteresis motion demonstrates affinity to tumor curvature in the vicinity of the tumor, reflecting intrinsic physiological and mechanical changes at the transition from tumor stroma to surrounding normal tissue. It has the potential to be used as a marker for tumor margin.
SU‐E‐J‐108: The Novel Moving Phantom for Evaluation of Respiration‐Monitors and 4DCT Scanners
Authors: Nishijima Y
Published: November 2011

Purpose: Though the 4DRT techniques have been rapidly developed, the accuracies of these devices have not been generally discussed due to the limitation of the functions of the conventional moving phantoms. The purpose of this study is to evaluate several 4DRT devices such as respiration‐detectors and 4DCT scanners by using the newly developed moving phantom with highly accurate position control in three directions. Methods: Three commercial respiration‐detectors (AZ‐733VTM, ANZAI Medical Co., Bellows SystemTM, Philips, Inc. and Real‐time Position Management (RPM)TM, Varian Medical Systems, Inc.) were set on the 1D‐axial unit of the moving phantom, which imitates the motion of the abdominal surface that was moved along the cos2n(x) curves (n=1,2,3) with different cycle times (3,5,7 seconds). Then the input and the measured motions were compared. For the verification of the 4DCT scanners, the acryl sphere with a diameter of 6 mm was moved in three directions. The 4DCT data sets were acquired by 16‐detector row 4DCT scanners (AquilionTM, Toshiba Medical Systems, Co. and Brilliance CTTM, Philips, Inc.), and the positional errors were evaluated. Results: The averages of the positional errors of the respiration‐detectors were 5.20 % for AZ‐733VTM, 6.20 % for Bellows SystemTM and 0.96 % for RPMTM, suggesting that optical sensors could be more accurate than pressure‐sensors. The positional errors of the target measured by 4DCT scanners tended to be larger when the cycle time was shorter. The ratios of the positional errors less than 5% to all the measured phases for cycle times of 3 and 7 seconds were 37 and 59 % in LR, 59 and 74% in AP and 52 and 78% in SI direction, respectively. Conclusions: The major respiration‐detectors and 4DCT scanners were evaluated by using our novel moving phantom. This moving phantom can be used for evaluation of various 4DRT devices.
SU‐E‐J‐109: Evaluation of the Dosimetric Impact of Respiratory‐Induced Motion
Authors: St‐Pierre C , Tremblay D , Lavoie C , Archambault L
Published: November 2011

Purpose: Assess the impact of respiratory motion on three‐dimensional conformal radiation therapy (3DCRT) treatment planning and IMRT treatment planning with 4DCT datasets. Methods: A clinical 3DCRT treatment plan made on clinical primary dataset (free‐breathing 3DCT) was the starting point of this planning analysis. GTV contours were manually reproduced and adapted to account for anatomy changes on each 4DCT phases. For comparison, an IMRT plan was created with the primary dataset using the same contours. The 3DCRT and IMRT plans were copied and recalculated on each phase datasets, keeping all respective beams parameters and monitor units the same. Dosimetric parameters were extracted for each phases of all plans.Results: The lung case presented is a tumor clinging to the diaphragm, chosen for its unusual position and large amplitude of movement among the pool of patients available. Considering PTV coverage for the 3DCRT plans, expiration phases are closer to the primary plan than the inspiration phases. PTV coverage for inspiration phases is best represented by the 4DCT average dataset whereas the primary dataset is better suited to represent the expiration phases. The phase‐calculated IMRT plans also showed expiration phases PTVs coverage is closer to the primary plan than for inspiration phases. In this case, the average dataset is better suited than the primary dataset to describe the shape of the DVH dose drop‐ off for the 4DCT phases. The results obtained showed that a difference of up to 12% in PTV coverage for a 3DCRT and 17% for an IMRT plan can be observed when using breathing phase anatomy to calculate a plan made on the primary dataset Conclusions: Anatomy changes caused by breathing cannot be neglected because of their influence on dosimetric parameters. Our results indicate that the choice of a plan dataset may have an impact on treatment accuracy and robustness.
SU‐E‐J‐112: Evaluation of Surface Tracking System for Respiratory Sensing in 4DCT: Commissioning of GateCT
Authors: Kauweloa K , Song W
Published: November 2011

Purpose: To analyze the consistency and accuracy of the respiratory signal tracking from the GateCT™ for 4DCT scanning. Methods: This experiment involved the use of the GateCT™ system, RPM™ system, GE CT scanner, QUASAR respiratory motion platform (Chest Wall Platform), and MATLAB. Both GateCT and RPM systems were used to collect data on the CT scanner, using 20 various‐range breathing patterns (12 simulated & 8 patients). Once data was acquired with both systems, MATLAB was used to analyze the possible frequency and amplitude discrepancies between input and recorded signals. Results: All recorded breathing patterns of both GateCT and RPM had a frequency percent error less than 4% from the ideal frequency despite some breathing patterns being irregular. Also, the correlation coefficients of GateCT and RPM, with respect to the input breathing pattern, had an average percent difference of 1.26% within the range of 0.24%–3.22%. GateCT accurately recorded the frequency of the input breathing pattern, but sometimes displayed an amplitude drift within its data. The amplitude drift within the recorded breathing pattern of GateCT has shown to be significant when the chest wall platform has amplitudes less than 0.42cm. When the chest wall platform has amplitude greater than 0.50cm, the amplitude drift has a change of less than 5%, rendering the amplitude drift insignificant. Conclusions: GateCT has shown its accuracy and consistency in recording the frequency of any breathing pattern, be it typical or irregular. Due to its accurate tracking, GateCT is trustworthy of tracking the breathing pattern of any patient, in result, producing high quality 4DCT images that will improve the patientˈs treatment plans. When a patient has breathing amplitude less than 0.42cm, RPM should be used due to GateCT displaying a significant amplitude drift. In conclusion, GateCT provides accurate data necessary for high quality 4DCT images.
SU‐E‐J‐113: Impact of 4D PET and Motion Correction in the Delineation of Gross Tumor Volume for Radiotherapy Treatment Planning in Lung Cancer
Authors: Le Maitre A , Wallach D , Hatt M , Edel S , Boussion N , Pradier O , Visvikis D
Published: November 2011

Purpose: To quantitatively assess the impact of motion correction in 4D‐PET images on the accuracy of automatic lung tumour volume delineation for radiotherapy treatment planning and the resulting dosimetry modifications.Methods: : Simulated 18F‐FDG‐PET data using the NURBS‐based Cardiac‐Torso phantom and Geant4 Application for Tomography Emission were considered. Homogeneous and heterogeneous spherical cases were designed with two tumor‐to‐background (T:B) contrasts (4 and 10) and 3 motion amplitudes (0.5, 1.5 and 2.5cm). Two more realistic cases derived from real clinical PET/CT datasets were also generated. Data were corrected for respiratory motion using two Methods: reconstruction incorporating elastic transformations and super‐resolution. The tumours were segmented with the Fuzzy Locally Adaptive Bayesian algorithm on each respiratory phase with or without correction and on the motion average image. For heterogeneous cases global and boost volumes were delineated. The union of the volumes at each phase with or without motion correction, the average PET volume and the volume with internal margins added to one respiratory phase were compared to the union of the simulated volumes (ground‐truths). For each of these target volumes, IMRT planning was used to compare the different motion management approaches in terms of impact on dosimetry.Results: The smallest and largest volumes were obtained on the average PET and the one with internal margins respectively. The best compromise between sensitivity and positive predictive value were obtained with corrected PET, with similar results for both corrections. The best compromise between ground‐truth volume coverage and organs‐at‐risk sparing was achieved by the volumes with most accurate delineation. The volume with margins always covered the ground‐truth Conclusions: 4D‐PET with motion correction leads to more accurate delineation of lung tumours and boost volumes in the presence of respiratory motion. This also leads to improved margins for treatment planning.
SU‐E‐J‐114: Real‐Time 4DCT Using Magnetic Tracking Methods and Magnetic Shielding
Authors: McGary J , Chen J , Zubiao X
Published: November 2011

Purpose: Real‐time, tumor tracking for 4DCT does not exist, which is needed for accurate gated therapy. Magnetic tracking is a possible method, however, eddy currents induced from the magnetic source create magnetic noise that is difficult to filter from the signal; the noise shares the same frequency as the signal and other characteristics have to be addressed. We present a method, based on a specialized algorithm, sensor configuration, and magnetic shielding to accurately calculate the transponder position.Method: The CT and transponder were modeled to calculate the magnetic fields within the ideal CT environment, where the gantry was a conducting cylinder. The magnetic fields were simulated using the Ansoft Maxwell electromagnetic solver. The sensors were modeled as search coils of finite dimension, with different size, number, and geometry. An innovative algorithm was developed to use magnetic gradient information to filter eddy current noise. Magnetic material applied to the gantry was modeled to optimize the signal frequency, the magnetic permeability, and thickness. Results: We found that 4 detectors, with 7 sensors, were able to locate the transponder within 2 mm over the majority of points within the CT bore; however, there were regions where the errors were in excess of 4–5 mm. After modeling the magnetic layer on the gantry surface, we found that the localization accuracy was a function of permeability and magnetic thickness. Results showed a minimum in error as a function of magnetic thickness. The localization error in that region was less than 1 mm. Conclusions: We have developed an innovative method to localize a tumor in 4DCT to within 1 mm using a specifically developed algorithm, sensor configuration, and magnetic material along the CT surface. We believe this technique may solve the problem of real‐time 4DCT.
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‐123: A Fast Finite Element Model to Predict Respiratory Lung Motion
Authors: Zehtabian M , Faghihi R , Mosleh‐Shirazi M , Baradaran M , Shakibafard A , Mohammadi M
Published: November 2011

Purpose: The aim of this study was to determine a fast and suitable approach to construct a thorax model that can be employed for simulating chest wall motion due to respiration for radiation therapy of lung cancer to help perform a more realistic treatment planning. Methods: Two data sets corresponding to two men with different thorax sizes were processed. For each patient, two sets of CT images were obtained. The chest and thorax were 3D reconstructed and then transferred to the ABAQUS software for FFE modeling. The geometry was constructed using inhale CT images. To tune the FFE model, for the first patient, the tissue mechanical properties, distension forces and boundary conditions were adjusted to find the optimum combinations of these parameters, to individually produce the best match with CT images in all stages. Then the model with the best‐matched coefficients was tested in a predictive mode, to predict chest and thorax motion and deformation following respiration for the second patient. Results: The tuned FFE model of chest wall motion matched the measurements to within 1 mm. In the predictive mode, the maximum and mean discrepancy between the landmarks and those predicted by the model were 4.7 mm, and 3.1 mm respectively. Conclusions: The developed FFE thorax model shows promise for the prediction of the chest and thorax shape changes using only one CT scan. Following further testing, this model can potentially be used in image‐guided radiotherapy of chest tumors within the time available in clinical practice.
SU‐E‐J‐125: CT Dose Survey for Simulations in Radiation Oncology
Authors: Rice R , Kim G , Wang J , Pawlicki T
Published: November 2011

Purpose: To establish baseline values and ranges for CTDIvol and DLP as a function of treatment site to be used to monitor CT simulation protocols and scan techniques for inadvertent changes and patient specific anomalies. Methods: We have collected CTDIvol (mGy) and DLP (mGy cm) values reported for all CT simulations performed on two large bore GE lightspeed RT scanners and one GE PET/CT scanner located in the Radiation Oncology facilities of the University of California San Diego for the calendar year 2010. Additional acquired data included patient identifier, scan date, scan type, intended treatment site and scanner location. Data was analyzed to calculate averages and standard deviations of CTDIvol and DLP as a function of intended treatment site and scan type. Results: The average CTDIvol for all helical scans was 32.3 with a standard deviation of 16.3 while the average DLP was 1095 with a standard deviation of 570. The average CTDIvol for all CINE scans was 115.6 with a standard deviation of 40.3. while the average DLP was 2064 with a standard deviation of 1625. As a function of treatment site for the helical scans, average values for CTDIvol ranged from 16.7 for TBI to 49.1 for brain while DLP ranged from 755 for breast to 1888 for TBI. For the CINE scans, average values for CTDIvol ranged from 113 for lung to 155 for liver while DLP ranged from 1630 for lung to 3929 for liver. Conclusions: The collected data provides expected ranges for CTDIvol and DLP for technologists to use in evaluating CT scans to look for anomalies which may be caused by changes in scan protocols or incorrect protocol or scan parameter selection. This will allow us to set up a quality assurance program to detect, report and correct such errors as they occur.
SU‐E‐J‐130: Hyperpolarized 13C Biomarkers of Response to Prostate Cancer Radiation Therapy
Authors: Zhang V , Cunha J , Bok R , Hsu I , Scott K , Sukumar S , Kurhanewicz J , Pouliot J
Published: November 2011

Purpose: Prior 13C MR imaging studies of hyperpolarized (HP) [1‐13C]pyruvate and 13C urea in the TRAMP murine model of prostate cancer have demonstrated the ability to monitor changes in metabolism and perfusion. Radiation therapy represents a common treatment of prostate cancer that could clinically benefit from an early assessment of therapeutic efficacy. The goal of this work was to investigate serial changes in perfusion (HP urea) and HP pyruvate metabolism in TRAMP tumors following exposure to increasing doses of radiation therapy in order to better understand the potential clinical value of HP 13C MR for predicting prostate cancer radiation therapy. Methods: Three TRAMP tumors (mean tumor size = 4.3 ± 1 cc) were exposed to varying doses of radiation by placing a single radioactive seed source using a Nucletron microSelectron‐HDR applicator on the surface of the tumor for ∼10 min. dwell periods. This resulted in doses of 14 Gy (close to the seed) to 5 Gy (deeper within the tumor). MR imaging studies were acquired serially at baseline, 1 day, 4 days and 8 days following therapy using a 14T, 600WB micro‐imaging spectrometer. Results: There are visually clear dose dependent changes in the lactate/pyruvate ratio over time. HP urea and total HP carbon significantly decreased in tumor regions receiving both high (p < 0.01; and 0.05, respectively) and intermediate doses (p< 0.01, for both) by 1 day after treatment. Whereas HP urea initially increased in the low dose regions and then decreased. For all three doses, the lactate/pyruvate ratios significantly decreased (p < 0.01 for all doses) by 8 days following treatment. Conclusions: Significant, dose‐dependent decreases in perfusion and pyruvate‐to‐lactate flux were observed after radiation therapy. Ongoing serial radiation studies of TRAMP tumors are investigating the relationship between perfusion and metabolic changes and therapeutic efficacy.
SU‐E‐J‐132: Inter‐Fractional Setup Accuracy of the Body Pro‐Lok™ System for Hypo‐Fractionated Liver Radiotherapy Using Novalis Tx™
Authors: Gutierrez A , Stathakis S , Crownover R , Esquivel C , Papanikolaou N
Published: November 2011

Purpose: To assess the inter‐fractional set‐up uncertainty of the Body Pro‐Lok™ System used in combination with the cone beam kVCT (CBCT) onboard imaging of the Novalis Tx™ during hypo‐fractionated liver radiotherapy. Methods: Thirty‐two patients (n=32) treated with 3 to 10 fractions were prospectively analyzed. The Body Pro‐Lok™ system was used in both CT simulation and during patient treatment setup. Patients were immobilized with a vacuum cushion placed posteriorly over the thoracic region, an abdominal compression plate, and a knee and foot sponge. Pretreatment CBCT scans of the Novalis Tx™ unit were fused with the planning kVCT prior to delivery of each fraction to determine the inter‐ fractional set‐up error. A total of 229 shifts were analyzed to assess the inter‐fractional set‐up accuracy. Results: Results showed that the mean inter‐fractional set‐up errors and standard deviations were 0.1 ± 4.5 mm, −1.3 ± 4.3mm, and 0.5 ± 3.6mm for lateral (IEC‐X), longitudinal (IEC—Y), and vertical (IEC—Z) variations, respectively. Maximum motion was 14.0, 15.0 and 17.0mm in the lateral, longitudinal, and vertical direction, respectively. When all three translational coordinates were analyzed, a mean composite displacement vector of 4.8 ± 2.1mm (range: 1.7–9.4mm) was obtained for all patients. Additionally, no differences were noted in setup accuracy between the first and second fractions (mean vector displacement 5.7 vs. 5.9mm, p=0.49) and between the first and last fraction (mean vector displacement 5.7 vs. 6.7mm, p=0.24). Conclusions: Based on the findings, image‐guided hypo‐fractionated radiotherapy to the liver using the Body Pro‐Lok™ system in conjunction with the CBCT of Novalis Tx™ is capable of minimizing inter‐fractional set‐up error.
SU‐E‐J‐138: The Effect of Shoulder Variation on IMRT and SmartArc Plans for Head and Neck Cancer
Authors: Neubauer Emily , Dong Lei , Followill David , Garden Adam , Court Laurence , White R. Allen , Kry Stephen F.
Published: November 2011

Purpose: First, to determine an average and maximum displacement of the shoulder relative to isocenter over the course of treatment. Second, to establish the dosimetric effect of shoulder displacements relative to correct isocenter alignment on the dose delivered to the target and the surrounding structures for head and neck cancer patients. Methods: The frequency of shoulder shifts of various magnitudes relative to isocenter was assessed for 4 patients using image registration software. The location of the center of the right and left humeral head relative to isocenter (usually C2) was found daily from CT on rails scans, and was compared to the location of the humeral heads relative to isocenter on the initial simulation CT. Three Baseline head and neck IMRT and SmartArc plans were generated in Pinnacle based on simulation CTs. The CT datasets (external contour and boney structures) were then modified to represent shifts of the shoulder (relative to isocenter) between 3 mm and 15 mm in the SI, AP, and LR directions. The initial plans were recalculated on the image sets with shifted shoulders. Results: On average, shoulder motion was 2‐5 mm in each direction, although displacements of over 1 cm in the inferior and posterior directions occurred. Shoulder shifts induced perturbations in the dose distribution, although generally only for large shifts. Most substantially, superior shifts resulted in coverage loss of up to 152 cc for targets in the lower neck. Inferior shifts elevated the dose to the brachial plexus by 0.6–4.1 Gy. SmartArc plans showed similar loss of target coverage as IMRT plans. Conclusions: The position of the shoulder can have an impact on target coverage and critical structure dose. Shoulder position may need to be considered for setup of head and neck patients depending on target location.
SU‐E‐J‐140: Motion Analysis of Target during Stereotactic Radiotherapy of Lung Tumors Using Volumetric Modulated Arc Therapy
Authors: Imae T , Haga A , Onoe T , Nakagawa K , Ino K , Okano Y , Tanaka K , Sasaki K , Saegusa S , Shiraki T , Oritate T , Yano K , Shinohara H
Published: November 2011

Purpose: Volumetric modulated arc therapy (VMAT) is a rotational intensity‐modulated radiotherapy (IMRT) technique capable of acquiring projection images for cone‐beam computed tomography (CBCT). Respiratory‐correlated cone‐beam computed tomography, namely 4D‐CBCT, serves to assess the displacement of a tumor position between planning and treatment due to organ motion and respiration, and is important for more accurate radiation therapy. On the other hand, recently a 320‐detector row CT scanner, namely 4D‐CT, has become available that allows axial volumetric scanning of a 16‐cm‐long range in a patient without table movement. The goal of our research is to establish a new method of verification during treatment in stereotactic body radiotherapy. In this study, we compare the movement of the tumor between “before treatment” using 4D‐CT and “in treatment” using 4D‐CBCT. Methods: Three patients (55–68 years of age) with lung tumors underwent CT scans for radiotherapy planning, 4D‐CT scans to analyze the movement of the tumor before treatment. After planning and verification, the patients were treated by VMAT while acquiring projection images. The respiratory phase from the projection images was recognized by normalized cross correlation (NCC) and divided into four phases; peak‐exhale, peak‐inhale, and two intermediate phases. 4D‐CBCT datasets were reconstructed from the projection images using in‐house programs. Results and Discussion: The tumor positions in 4D‐CT and 4D‐CBCT were detected and the movement of the tumor between “before treatment” and “in treatment” was similar. The movement of the tumors during treatment was predictable from 4D‐CT before treatment. Furthermore, 4D‐CBCT clarified the tumor position during treatment and could reevaluate the actual tumor position and dose distribution. Conclusions: We have successfully shown that the movement of the tumor between “before treatment” using 4D‐CT and “in treatment” using 4D‐CBCT.
SU‐E‐J‐142: A Comparison of TomoTherapy and Respiratory‐Gated IG‐IMRT for the Treatment of Pancreatic Cancer
Authors: Prah D , Erickson B , Li X
Published: November 2011

Purpose: Respiratory gating and high‐quality image guidance allow for use of smaller PTV margin, while non‐gated RT, such as TomoTherapy, must account for respiratory motion by increasing PTV margin. It is not clear whether this increased margin can be compensated by the fact that Tomotherapy usually offers improved normal tissues sparing. The purpose of this study is to compare the dosimetric differences between these two RT methods for pancreas irradiation. Methods: 4DCT datasets of 6 patients with pancreas irradiated previously were analyzed. The PTV for Tomotherapy was the ITV of all respiration phases plus 10 mm margin, while the PTV for the gated IG‐IMRT was the ITV for the 2 gating phases plus a 5 mm margin. This smaller margin is because a high quality CT, such as in‐room CT, is used for daily repositioning. Plans were generated for two PTVs with a prescription dose of 50.4Gy using the Tomotherapy and Prowess treatment planning systems. Results: The gated IG‐IMRT reduced the duodenum V45Gy by 15.8% (p<0.05) and the mean dose by 7.4 Gy (p<0.05) compared to the Tomotherapy. However, since the TomoTherapy generally has a more homogeneous dose distribution and since the duodenum often overlaps the PTV, the duodenum V52Gy for the gated IG‐IMRT plans was 0.9 ± 0.7 cc (p<0.05) while the TomoTherapy plans all had maximum doses below 52Gy. The mean dose to the liver was found to be 3.2 Gy less for the gated IG‐IMRT plan (p<0.05). The right kidney V45Gy for the gated IG‐IMRT plan was found to irradiate 9.2% less kidney volume (p<0.05) compared to the TomoTherapy plan. Conclusions: For pancreas irradiation with significant respiration motion, the combined effect of respiration gating and daily high‐quality CT guidance for IMRT leads to reduced doses to duodenum, liver, and right kidney as compared to Tomotherapy.
SU‐E‐J‐143: Respiratory‐Correlated Cone‐Beam CT for Potential Use in Measuring Lung Tumor Trajectory
Authors: Cropp R , Bergman A
Published: November 2011

Purpose: Respiratory‐correlated (4D) CT scans produce a set of images corresponding to different phases of the breathing cycle. In lung cancer treatment, a potential application of 4D cone‐beam CT (CBCT) scans taken on the treatment unit is to measure the tumor trajectory before each treatment, to verify whether the motion remains stable over the course of treatment. This presentation describes techniques we are developing for tumor trajectory measurement with 4D CBCT on our Varian linacs. Methods: A CBCT scan of a phantom placed on a periodically moving platform is taken on a Varian iX unit. The Varian RPM system is used to record the “breathing” phase vs time, and this information is used to sort the projection images into phase bins. For each phase bin an image is reconstructed using conventional Feldkamp‐Davis‐Kress filtered backprojection. The “tumor” region is contoured manually on one phase image, and a deformable registration algorithm is used to calculate the shift in points on the regionˈs surface from this phase to each other phase. The centroid of these surface points is used as a measure of the tumor position. Results: The deformable registration algorithm succeeds on test data consisting of clinical 4DCT scans of lung cancer patients taken on a CT simulator. Tumor motions of a few mm are measured. Preliminary 4D CBCT phantom images taken at the normal gantry rotation speed of 6 degrees/second show significant streak artifacts since the angular spacing between projections is large (>10 degrees); this low image quality is not suitable for the registration algorithm. Conclusions: Deformable image registration between phases is a practical method to measure lung tumor trajectory. In a 4D CBCT scan, reducing the gantry rotation speed is necessary to improve image quality: we plan to investigate this on a Varian TrueBeam unit.
SU‐E‐J‐144: Analysis of Intra‐Fraction Chest Wall Motion during Breath Hold Treatment for Left Sided Breast Cancer
Authors: Nelson C , Gifford K , Kirsner S , Shah S , Bloom E , Mason B , Arzu I
Published: November 2011

Purpose: To quantify chest wall motion during treatment while the patient executes a breath hold (BH) maneuver for left sided breast cancer patients. Methods: Three breast cancer patients (left side) who were to receive radiation utilizing the BH technique were prospectively chosen to take part in this study. Treatment plans were generated according to standard clinical treatment planning guidelines. Images were acquired in cine mode using the EPID (Varian Medical Systems, Palo Alto, CA) on a per fraction basis for non step and shoot fields. The chest wall was defined in each image using a logarithmic edge detection algorithm. The distance of the chest wall orthogonal to the reference axis (collimator jaw parallel to chestwall) was determined in 1 cm intervals along this axis. Motion was assessed by the standard deviation of chest wall position and the maximum distance traveled, for each field, each treatment day. The root mean square (RMS) of the standard deviations was computed as well as the average and standard deviations of maximum motion for each 1 cm interval. Results: 420, 205, and 360 images were acquired respectively for patients 1, 2, and 3 for both medial and lateral tangential fields. The total RMS of the motion computed over the entire length of the chestwall was 0.7mm, 0.8mm, and 0.6mm for patients 1–3 respectively. The maximum motion over the entire chest wall for each treatment day was 1.4+1.6mm, 1.9+1.4mm, 1.1+1.3mm on average for the course of treatment. Conclusions: Chest wall motion during a breath hold treatment was analyzed for three patients and was found to be less than 2mm on average. When using the deep inspiration BH technique to displace the heart from the posterior tangential field border, our study suggests that delivery can be executed with minimal intra‐fractional motion.
SU‐E‐J‐145: Complete Study to Characterize the Effectiveness of Daily Endorectal Balloon (ERB) for Prostate Intrafraction Motion Management
Authors: Wang K , Vapiwala N , Deville C , Plastaras J , Scheuermann R , Lin H , Ad V Bar , Tochner Z , Both S
Published: November 2011

Purpose: To quantify intrafraction prostate motion between patient groups treated with and without daily endorectal balloon (ERB) employed during prostate radiotherapy and establish the effectiveness of the ERB. Methods: Real time intrafraction prostate motion from 29 non‐ERB (1061 sessions) and 30 ERB (1008 sessions) patients was evaluated based on three‐dimensional (3D), left, right, cranial, caudal, anterior and posterior displacements. The average percentage of time with 3D and unidirectional prostate displacements > 2, 3, 4, 5, 6, 7, 8, 9, and 10mm in 1 minute intervals was calculated for up to 6 minutes of treatment time. The Kolmogorov‐Smirnov method was used to evaluate the intrafraction prostate motion pattern between both groups. Results: 3D motion >=1 cm was observed for the non‐ERB group only. The motion increased as a function of elapsed time for displacements > 2 to 8mm for the non‐ERB group and > 2 to 4 mm for the ERB group (p < 0.05). The percentage time distributions between the two groups were significantly different for motion > 5 mm (p < 0.05). The 3D internal margin (IM) covering 95% treatment time can be reduced from 5 to 3 mm (40% reduction) while the asymmetrical IM can be reduced from 3 to 2 mm (33% reduction) in cranial, caudal, anterior, and posterior for 6 minutes treatment, when ERB is employed. Beyond 6 minutes, the 3D and cranial, caudal, anterior, and posterior IMs can be reduced from 9, 4, 7, 7, and 8 to 5, 2, 5, 3, and 4 mm, respectively (up to 57% reduction). The calculated IMs apply to the worst case scenario patient as well. Conclusions: The ERB effectively reduces prostate motion and allows for smaller IMs. Therefore, daily ERB has the potential to further improve toxicity profiles in prostate radiotherapy.
SU‐E‐J‐148: Correlation of Respiratory Motion between External Patient Surface and Internal Anatomical Landmarks
Authors: Fayad H , Wentz T , Pan T , Visvikis D
Published: November 2011

Purpose: Current respiratory motion monitoring devices used for motion synchronization in radiotherapy provide only 1D respiratory signals over a specific region. Newer technology offers the possibility to monitor the entire patient skin 3D surface in real time. The main objective of this work was to study the correlation between external patient surface and internal anatomical landmarks. Methods: Ten patients with full 4D‐CT datasets were included. In addition, synchronized surfaces acquired by a Time of Flight (TOF) camera were acquired during these 4D‐CT acquisitions. Two experts manually identified anatomical landmarks in the thoracic region in each of the 4D‐CT volumes. These landmarks include tumour location as well as surrounding normal tissues. Finally, the correlation between the internal landmarks motion and external surface motion was calculated and evaluated for different regions (placement and size) of the patientˈs surface. Results: The best correlation was observed between the motion of the central regions of the abdominal (0.8 ±0.18) and the thoracic area (0.72 ± 0.12) and especially with internal landmarks such as the diaphragm and mediastinum structures, as well as the tumour location landmarks. The worse correlation was found for internal landmarks that are not significantly affected by the respiratory motion such as the apex or the sternum (0.2 ± 0.18). Conclusions: Large correlation variability was observed when considering different patientsˈ external surface regions of interest and internal anatomical landmarks. The positioning of current devices used for respiratory motion synchronization may reduce such correlation by averaging the motion over correlated and poorly correlated external regions. The potential of capturing in real‐time the motion of the complete patient surface as well as choosing the surface area that best correlates with the internal motion will allow reducing such variability and associated errors in both respiratory motion synchronization and subsequent motion modeling processes.