bluuebunny/crossref_metadata_2025 huggingface dataset:
SU‐E‐J‐68: Evaluation of Non‐Rigid Registration Techniques for Region of Interest Propagation in Adaptive Radiation Therapy
Authors: Franz A , Allaire S , Mallya Y , Buerger C , Kabus S , Bijl HP , Schulz H , Bzdusek K
Published: July 2013

Purpose: Adaptive radiation therapy aims at compensating anatomical variations during a radiotherapy course by modifying the treatment plan accordingly. Therefore regions of interest (ROIs) have to be defined in the most recent imaging data. We investigated three different non‐rigid image registration algorithms to automatically propagate ROIs from an initial planning CT to a pre‐treatment CT. Methods: Clinical reference data of four patients with head and neck tumor, consisting of a planning CT and a pre‐treatment CT, were used in this study. Seven ROIs (spinal cord, glottis, left and right parotid glands, left and right submandibular glands and thyroid) were independently delineated by three head and neck radiation oncologists in the initial planning CT as well as in the pre‐treatment CT. The ROIs defined in the planning CT were automatically propagated to the pre‐treatment CT using three different non‐rigid registration algorithms: salient‐feature‐based registration, piecewise linear registration, and elastic registration, based on partial differential equations. The propagated ROIs were quantitatively compared with the expert‐drawn ROIs. As measures for comparison the Dice coefficient for the whole 3D region, the mean slicewise Dice coefficient and the mean slicewise Hausdorff distance were used. Results: All three registration algorithms were able to propagate the investigated structures such that they deviate from the hand‐segmented contours in a range comparable with the inter‐observer variability, ranging up to 15mm mean slicewise Hausdorff distance and down to a Dice coefficient of 0.5. The deviations are smaller when the propagated structures are compared with the reference structures recontoured by the same physician. Conclusion: Different image registration algorithms were compared for its use in adaptive radiation therapy. All three methods yielded acceptable results. However, automatically propagated ROIs should be thoroughly reviewed by the treating physician. The remaining deviations from the expert‐drawn ROIs can be corrected by interactive tools.
SU‐E‐J‐69: Normalization of Ventilation Data From 4D‐CT for Comparison Before and After Treatment
Authors: Latifi K , Huang T , Feygelman V , Moros E , Stevens C , Dilling T , Zhang G
Published: July 2013

Purpose: If one were to evaluate ventilation distributions before and after radiotherapy derived from 4D‐CT scans, changes in tidal volume (TV) might potentially bias the results. This is important because differences in TV were found to be large in some cases. To eliminate this uncertainty we proposed to normalize the ventilation to the TV. Methods: Absolute ventilation (AV) data were generated for 6 SBRT cases before and after treatment, using the direct geometric algorithm and diffeomorphic morphons deformable image registration (DIR). Each pair of AV distributions was converted to TV‐normalized, percentile ventilation (PV) and low‐dose well‐ventilated‐normalized ventilation (LDWV) distributions. The latter two were described in previous publications. The ventilation change was calculated in various dose regions based on the treatment plans using the DIR‐registered before and after treatment data sets. The ventilation change based on TV‐normalized ventilation was compared with the AV as well as the data normalized by PV and LDWV. Results: AV change may be misleading when the TV differs before and after treatment which was found to be up to 6.7% in the cases studied. All three normalization methods produced a similar trend in ventilation change: the higher the dose to a region of lung, the greater the degradation in ventilation. In low dose regions (<5 Gy), ventilation appears relatively improved after treatment due to the relative nature of the normalized ventilation. However, the LDWV may not be reliable when the ventilation in the low‐dose regions varies. As an example, in one case LDWV appeared degraded regardless of dose. PV exhibited a similar ventilation change trend compared to the TV‐normalized in all cases. However, by definition, the ventilation distribution in the PV is significantly different from the original distribution. Conclusion: Normalizing ventilation distributions by the TV is a simple and reliable method for evaluation of ventilation changes. This work was partially supported by a research grant from Varian Medical Systems, Inc., Palo Alto, CA.
SU‐E‐J‐70: Intra and Intermodality Validation of Registration Algorithms On a Deformable Phantom
Authors: Vincent SD , Archambault L
Published: July 2013

Purpose: Clinical use of deformable image registration algorithms (DRA) requires a thorough preliminary study of their capacity and performance. To rigorously quantify the registrations, images showing deformation of precise amplitude must be used. Deformations representative of the average anatomical variations possibly encountered during radiation treatments were used for DRA evaluation. Methods: A three‐dimensional anthropomorphic phantom representing the main pelvic structures (prostate, bladder, rectum, femoral heads) was created. Three types of deformation were studied: translation (prostate), volume variation (bladder) and deformation of contours without volume change (prostate). The design of the phantom allows a precise knowledge of deformation amplitudes. Each pairs of initial and deformed images were scanned on both CT and CBCT. This way an image database offering the same images on both modalities was available for intra and intermodality validation. The algorithm validated was an open‐source software (Elastix) that offers a large control of the registration parameters. Results: Deformation of 5 mm on the contour, translation of 0.5, 1, 2 cm and volume variation of 50, 100, 200 ml were scanned on both modalities. Registration with basic Mutual information metric succeed between 98% and 71%, these results representing the fraction of the deformation registered with success on its initial image. The worst cases were observed when a CT is registered onto a CBCT. By combining the Mutual information registration metric with manually delineated points (corresponding point metric) the worst cases (71 to 79%) were greaty improved (88 to 96%). Conclusion: By optimizing the deformation parameters in a controlled setting (i.e. an anthropomorphic phantom) we could achieve better DRA efficiency. Combining multiple registration metric lead to registration of superior quality. Deformable vector field shows that many areas free from actual deformation were altered during registration which indicate that deformation parameters optimized to improve registration of organ contours are not well suited for dose deformation.
SU‐E‐J‐71: Dosimetric Evaluation of Image Based and Anatomical/physiological Model Based Deformable Registration Methods
Authors: Guo B , Xu X , De S , Shi C
Published: July 2013

Purpose: To study the dosimetric differences of five image and anatomical/physiological model based registration methods. Methods: A lung patient with a tumor in the right middle lobe was studied. GTV and normal structures were contoured individually on ten breathing phases of 4DCT. Volume of GTV ranged from 23.3 cc on end‐inhale phase p0 to 28.0 cc on end‐exhale phase p50. The range of GTV motion was 0.37 cm in L‐R, 0.28 cm in A‐P and 0.54 cm in S‐I directions. VMAT plans were generated on ten breathing phases and 4D composite doses were calculated by registering doses to p0. Five different registration methods were compared: (1) Rigid registration aligning the center of mass of the tumor; (2) B‐spline deformable image registration; (3) Demons deformable image registration; (4) A physiological lung model based on 4DCT, measured pressure‐volume data and finite element analysis and (5) a whole body non‐uniform rational B‐spline model based on 4DCT and contours of structures. The parameters of image registration and anatomical/physiological modeling were optimized so that the volume of the GTV and the lungs and the boundary between the GTV and the lungs were preserved. Results: All image and model based deformable registration methods gave very similar dose coverage to GTV and PTV and similar doses to normal structures including lungs, spinal cord, heart and esophagus. Rigid registration has higher minimum dose to the targets due to the fact that it does not account for tumor deformation. Conclusion: All deformable registration methods with parameters chosen to preserve the volume of target and normal structures and the boundary between them will yield similar dosimetric results. For tumors whose volume changes among phases, deformable registration will give different results compared to rigid registration.
SU‐E‐J‐73: Effect of 4D‐CT Image Artifacts On the 3D Lung Registration Accuracy: A Parametric Study Using a GPU‐Accelerated Multi‐Resolution Multi‐Level Optical Flow
Authors: Santhanam A , Dou T , Min Y , Meeks S , Kupelian P
Published: July 2013

Purpose: To perform a parametric study of the effect of registration parameters on 4D‐CT image registration accuracy.Methods and Materials: A GPU based 4D‐CT image registration that registers the 4D lung anatomy using a multi‐level multi‐contrast optical flow was used for this study. A set of 14 4D‐CT datasets was employed for this study. The multi‐level lung anatomy was segmented into the surface contour, blood vessels and parenchyma regions using OsiriX. The registration started at the lowest resolution of a 3D volume. Within each resolution level, the volumes were registered using optical flow. The motion field was first computed for surface contour pairs in the lowest resolution. At this stage, all the voxels except those on the surface contour (the lowest level of anatomical representation) were not included. GPU based Thin‐Plate Splines was applied to the motion field so that voxels surrounding the surface contour had an initial displacement motion, which was closer to the actual value. The motion field was iteratively updated until the highest (original) resolution of the volume was processed. Results: The GPU implementation provided a speed‐up of >50x as compared to the CPU implementation. The registration accuracy varied non‐linearly with the kernel size. For both kernel size and smoothness factor, a non‐linear correlation was observed towards the registration accuracy with an optimal value being 5 cu.mm and 200, respectively. The accuracy improved with the number of resolution and contrast levels with 4 and 3, respectively, providing optimal registration accuracy. Finally, usage of the first 3 anatomical level representations provided the optimum registration accuracy as opposed to 4 or more levels. Conclusion: A parametric 4D image registration analyses showed its relationship to the registration accuracy to be non‐linear. A patient breathing and CT‐scanner specific study will quantitatively relate the registration errors on treatment planning and delivery.
SU‐E‐J‐74: Assessing Accuracy of Tumor Localization with Aperiodic Respiratory Breathing Using 4D‐CT and 4D‐CBCT Imaging
Authors: Lee S , Lu B , Liu C , Samant S
Published: July 2013

Purpose: To assess the accuracy of tumor localization for aperiodic respiratory breathing for 4D‐CT and 4D cone‐beam CT (4D‐CBCT) imaging using a computer controlled moving phantom. Methods: We simulated an aperiodic respiratory based tumor motion using a programmable respiratory motion phantom (Quasar Modus QA). 4D‐CT scans were acquired four times at different starting points of respiratory cycle. 4D‐CT acquisitions were sorted into ten phases using time‐based binning, and the respiratory cycle reconstructed from the target motion. 4D‐CBCT scans, acquired with Elekta XVI 4DCBCT (Symmetry option), were sorted into 10 phases using amplitude‐based binning. A phased 4D‐CT dataset was selected as a reference CT image on the basis of minimum variation of tumor location over all 4 scans. This phased CT was used as reference for registration with 4D‐CBCT imaging, and the respiratory signal reconstructed. Results: For the selected aperiodic respiratory signal, phases 50% to 70% showed minimal variation amongst the four 4D‐CT scans. The 50% phase was selected as the reference for registration with 4D‐CBCT imaging. This yielded a reconstructed respiratory signal differing from the average tumor trajectory (based on the motor signal) by <2mm for the 50%‐70% region, which was similar to using the average 4D‐CT image (averaged over all phases) as the reference image. Use of other phases of 4D‐CT imaging as the reference yielded differences of up to 6mm from the average tumor motion trajectory. Conclusion: For aperiodic respiration motion considered here, this study showed that the use of phases 5 through 7 is optimal for treatment delivery, not only due to longer time of target in that position, but also because the variation in the reconstructed respiratory signals (and hence uncertainty in target position) due to different starting points in respiratory cycle in 4D‐CT imaging, is minimal.
SU‐E‐J‐75: The Clinical Evaluation of a Minimum Point Distance Histogram for Image Registration in the 4DCT Based Gastric Cancer Radiotherapy
Authors: Hu W , Ye J , Li G , Zhang Z
Published: July 2013

Purpose: The contour‐based evaluation is crucial in the radiotherapy and one popular parameter is the dice similarity coefficient (DSC). The DSC alone is insufficient in some situation and additional evaluation parameters are required. The purpose of this study is to create a minimum point distance histogram (mPDH) for contour‐based deformable image registration evaluation and to investigate the clinical dosimetric endpoints related to the mPDH in organs at risk for gastric patients with 4DCT images. Methods: The mPDH was created and tested in 4DCT images. The 0% phase (P0) and the 50% phase (P5) image data sets from 4DCT of 5 gastric cancer patients with contours delineated by a radiation oncologist were transferred to the VelocityVI image registration package. The contours on the P5 were rigidly transferred (rigid registration) and warped (deformable registration) to the P0. All contours were export to a homemade Matlab program for calculating the mPDH. The mPDHs were obtained for the rigid‐manual (RM) and the deformed‐manual (DM) contours. Furthermore, the original treatment plan was applied to the P0 for dose calculation and the dosimetry‐based investigation related to the mPDH was performed. Results: The mPDH provides a useful data for quantifying the agreement of the contours. The mean DI95%(the distance includes more than 95% of the points) and P3mm (the percent of points within 3mm distance) from mPDH show significant difference between the DM and RM (p<0.05). For dosimetric evaluation, there is no dose check point has difference larger than 3% if the DI95% is within 4mm. Conclusion: A new informative image registration evaluation tool is created. The mPDH provides a useful data for quantifying the agreement of the contours. The clinical validation of mPDH in the gastric cancer shows the feasibility of apply this tool in the radiotherapy for evaluation the clinical accuracy of deformable registration.
SU‐E‐J‐78: Deformable Registration Method by Joint Using TPS and B‐Spline for Lung Cancer in Radiotherapy
Authors: Han N , Xie Y
Published: July 2013

Purpose: To increase the accuracy of deformable registration method for lung deformation problem caused by respiratory in CT image. Methods: One issue in radiotherapy is the lung deformation during respiratory motion. Respiratory motion can lead to the changes in sizes, shape, and location of tumors, which can' t be solved by rigid registration. It becomes a vital factor for prognosis when Stereotactic Body Radiation Therapy (SBRT) is employed to treat lung cancer, because of the high dose rate and shorten treatment time. Interpolation is an essential step in deformable registration. Thin plate spline (TPS) and B‐spline are two widely used interpolation methods in radiotherapy. TPS can achieve high speed calculation, but may Result in large errors because of its global effect on the image and B‐spline takes overlong run‐time caused by the iterative calculation in the optimization process. In this work, we proposed a novel method to combine these two methods. First, TPS is used to register two CT images rapidly. Then B‐spline is used to refine the registration Result. Results: In our experiment, a couple of clinical lung images are simulated using the proposed method. The Result indicates that both of run‐time and registration quality have been obviously improved, compared with the conventional methods solely using either TPS or B‐spline. As for lung cancer in radiotherapy, when high accuracy is achieved, the results show large differences between these two methods in iteration times and computation time. The registration method using B‐spline takes 3624.5s with 66 iteration times. While the proposed method can do less work (1999.4s with 51 iteration times) to achieve the same accuracy. However, if only lower accuracy is required, the differences are not so apparent. Conclusion: The proposed method takes advantage of both of these two methods and can perform good adaptivity and robustness in registration of lung CT images. This work is supported in part by grants from National Natural Science Foundation of China (NSFC: 81171402), NSFC Joint Research Fund for Overseas Research Chinese, Hong Kong and Macao Young Scholars (30928030), National Basic Research Program 973 (2010CB732606) from Ministry of Science and Technology of China, Guangdong Innovative Research Team Program (No. 2011S013) of China, Science and Technological Program for Dongguan's Higher Education, Science and Research, and Health Care Institutions(Grant No.2011108101001), and grant Comprehensive Strategic Cooperation Project of Guangdong province and Chinese academy of sciences (Grant No.2011B090300079).
SU‐E‐J‐79: Characterizing Accuracy in 4DCT Deformable Registration Using the POPI M odel
Authors: Piper J , Duchateau M , Nelson A , Verellen D , De Ridder M Mark
Published: July 2013

Purpose: Deformable image registration can aid in fully utilizing 4DCT data without significantly increasing workload. In this study, we characterize the accuracy of a commercially available free‐form intensity‐based DIR algorithm on 4DCT using both successive registration through intermediate phases (SERIAL) and direct registration between the phases of interest (DIRECT). Methods: Two real‐patient 4DCT phantom datasets from the POPI model were used to test the SERIAL and DIRECT registration methods. One POPI model (patient1) displayed typical respiratory motion, 6.3mm +/− 3.0mm while the other (patient2) displayed significant respiratory motion, 14.0mm +/− 7.2mm, between end‐expiration and end‐inspiration. The phantoms were also used to study the relationship between initial rigid registration error and residual registration error after deformation. Results: For patient1, the residual errors after DIRECT and SERIAL deformation were 0.8mm +/− 0.4mm and 1.8mm +/− 1.4mm, respectively. For patient2, the errors after DIRECT and SERIAL were 5.1mm +/− 7.5mm and 1.6mm +/− 1.6mm, respectively. The correlation between initial and residual error was significant for both DIRECT (r = 0.72: linear, r = 0.80: second order polynomial) and SERIAL (r = 0.32: linear). The mean residual errors for points of interest with <5mm, 5–10mm, 10–15mm, 15–20mm, 20–25mm, and 25+mm initial error were 0.9mm, 0.9mm, 1.4mm, 4.7mm, 9.7mm, and 20.2mm after DIRECT and 1.3mm, 1.4mm, 2.1mm, 2.3mm, 1.9mm, and 3.1mm after SERIAL, respectively. Conclusion: DIRECT was more accurate for typical respiratory motion while SERIAL was more accurate when significant respiratory motion was present. There was flat correlation between residual and initial error for SERIAL as compared to a very steep correlation for DIRECT. Results show that the DIRECT approach delivers excellent results when the movement is limited to 15mm but when the movement increases, the SERIAL approach is favorable. Aaron Nelson and Jon Piper are both employees and owners of MIM Software Inc.
SU‐E‐J‐80: Analysis of Morphology of Normal Liver and Tumor by Breathing Motion Using Deformable Registration Method
Authors: Gong G , Wang H , Yin Y
Published: July 2013

Purpose: Through combining the free form deformable registration algorithm and four‐dimensional computed tomography (4D‐CT) to discuss morphology of normal liver and tumor by breathing motion of hepatocellular carcinoma patients. Methods: 8 hepatocellular carcinoma patients accepted radiotherapy was selected, then acquire 4D‐CT simulate positioning images and 4D CT images were segmented into 10‐series CT images which were named CT0, CT10 to CT80, CT90 according to the respiratory phases with CT0 at end inspiration and CT50 at end expiration. We chose the CT50 as the reference image. we used the free form deformable (FFD) model based on B‐spline grid registration method to deform the other 9 set‐image to CT50, this paper also utilized limited‐memory Broyden Fletcher Goldfarb Shannon minimization (L‐BFGS) to enhance the registration accuracy and speed. Then the subtractions,hausdroff distance and multi‐information are used to analyze the influnce of normal liver and tumor targets from breathing motion. Results: (1)The breathing movement for deformation of normal liver and tumor targets is obvious, and the difference between CT0 and CT50 is biggest. (2)The FFD model based on B‐spline grid registration method can deform 4D‐CT images effectively. The hausdroff distance between CT0 and CT50 of normal liver and tumors was from 0.0914 to 0.0432 after registered, the average improvement proportion was 54.1%, and the multi‐information was from 0.789 to 0.814, the average improvement proportion was 3.17%. Conclusion: The breathing movement for deformation of normal liver and tumor targets is not ignored, and the FFD model based on B‐spline grid registration method can deform 4D‐CT images effectively.
SU‐E‐J‐82: Ground‐Truth Tests of Deformable Image Registration Using Matched PET‐CT Image Pairs
Authors: Lamb J , Jani S , White B , Thomas D , Gaudio S , Robinson C , Low D
Published: July 2013

Purpose: To investigate the possibility of using tracer activity density measured in matched PET/CT scan pairs as a ground‐truth test of deformable image registration and dose accumulation software. Methods: Respiratory‐correlated (4D) PET/CT was used for this proof‐of‐concept study. Amplitude‐gated 4D‐CT scans of 2 lung cancer patients acquired as part of an IRB‐approved protocol were studied. List‐mode FDG‐PET data was acquired in the same sessions and gated into 4D images (i.e., activity distributions) matched in phase to the 4D‐CT. End‐inhale phase 4D‐CT images were deformably registered to the end‐exhale phase images using a free‐form intensity based algorithm provided by a commercial software package. The corresponding 4D‐PET activity distributions at the same inhale breathing phase were deformed using the deformation vector fields from the 4D‐CT registration. CT registration accuracy was then assessed by visually inspecting the deformed inhale‐phase PET activity distributions against the exhale‐phase activity distributions. Errors in registration were identified when the deformed inhale‐phase activity distribution failed to match the exhale phase distribution. Results: To test the utility of this methodology deformed PET activity distributions were used to identify CT‐CT registration failure in the region of the mediastinum. The registration failure could not be seen by inspection of the deformed CT itself, due to lack of contrast inside the mediastinum, but was clearly visible from the deformation of the activity distribution of a tracer‐avid lymph node. Control cases were used for validation, consisting of correct and incorrect registrations of lung tumors near the chest wall, where the performance of the registration was visible from CT deformation alone. Conclusion: PET‐measured tracer activity in combined PET/CT scans can be used as a ground truth to qualitatively assess the accuracy of deformable image registration of CT images and deformable dose accumulation. Further work is needed to understand the limits of quantitative assessment. This work is supported in part by NIH R01CA096679 and R01CA116712.
SU‐E‐J‐84: Use of Deformation Error Histogram as An Accuracy Indicator for Deformable Image Registration
Authors: Kim H , Monroe J , Yao M , Lo S , Ellis R , Machtay M , Sohn J
Published: July 2013

Purpose: To introduce an indicator which can show the deformable image registration (DIR) accuracy, and be used for commissioning DIR systems. Methods: Inaccurate DIR can produce inaccurate composite dose when we add doses from multiple treatment plans. Deformation Error Histogram(DEH) and QA procedure were proposed to overcome the shortfall of landmark approach. Our method conducted a DVM comparison approach instead of using the significant visible feature points of the landmark approach. To show the feasibility of using DEH, we used a Lung and a Liver cancer patient. Each patient has two CT image sets (Reference and Test image sets). We generated a truth DVM by performing DIR using R and T sets, and by applying the DVM to T, R' is generated. To quantifies the systematic error of our in‐house DIR system, we calculated a test DVM by performing DIR using R' and T image sets. Then, we calculated a difference vector in millimeter between the test DVM and the truth DVM. Finally, a DEH was made from the difference vector for showing the cumulative distribution of error per Structure‐Of‐Interest (SOI). Results: Both clinical cases, we visualized errors by displaying the calculated difference vectors. Relatively larger systematic errors are observed where large deformation occurs, such as skin, mobile joints, shoulders, diaphragm, and inferior Lung region. The DEH can show the measured confidence range in DIR for the selected SOI. For Liver patient, [Average error, Standard deviation, 95% Confidence] for SOIs were GTV [6.69,2.07, 2.94], R Kidney [4.13,1.65,1.76], Spinal Cord [3.77,0.30,3.27], and Liver [3.03,1.67,0.78] in millimeter. For Lung patient, the Result were GTV [3.24,1.37,1.12], Heart [3.16,1.63,1.02], Lung [4.93,1.95,2.00], and Spinal Cord [4.39,1.67,2.39]. Conclusion: DEH provides quantitative systematic error during DIR. DEH and our data can be a tool for estimating magnitude of errors per anatomical sites and commissioning DIR systems.
SU‐E‐J‐141: A Patient Specific Anthropomorphic Breathing Phantom for Clinically Realistic Imaging and Dosimetry Studies
Authors: Wagar M , Mannarino E , Williams C , Hacker F , Berbeco R , Lewis J
Published: July 2013

Purpose: This project sought to create a patient specific dynamic phantom setup utilizing 3D printing to fabricate realistic target volumes derived from planning CTs.Materials/Methods: The anthropomorphic phantom is a modified Alderson Phantom (The Dynamic Breathing Phantom by Radiology Support Devices). The original lung system was removed and replaced with a new foam rubber structure having lung‐equivalent density. Using patient CT data, tumor models were manufactured using a 3D printer. With the planning image set as a guide, the tumor was positioned within the anthropomorphic phantom to match the relative tumor positioning within the patient. The patient‐specific phantom setup was then imaged under both CT and MV fluoroscopy and compared to the previously acquired patient imaging. Results: These patient‐specific phantom configurations accurately reflect their respective patient's treatment planning CTs. MV fluoroscopy of the phantom demonstrated both accurate positioning when compared to patient DRRs and accurate recreation of respiratory motion as compared to 4DCT data. Conclusion: This patient‐specific anthropomorphic breathing phantom will allow for further realistic motion management studies with applications in both imaging and dose delivery.
SU‐E‐J‐145: Dosimetric Impact of Patients Set‐Up Effect in Radiation Therapy Planning System for Breast Cancer Patients with Conventional Wedge and Field‐In‐Field Techniques
Authors: Lee S , Suh T , Kim J , Park J , Kim D
Published: July 2013

Purpose: To evaluate the dosimetric effects of patients setup errors and breathing movement on whole breast irradiation with conventional hard wedge (HW) and field‐in‐field (FIF) techniques. Methods: A total of 10 patients who received whole breast irradiation were chosen for this study. We performed radiation treatment planning for whole breast irradiation with two techniques; conventional hard wedge (HW) and field‐in‐field (FIF). On the subject of each patients, ‐ original plan‐was created using the general clinical planning technique and then we generated ‐ isocenter shift plan‐and ‐ gantry angle shift plan‐to evaluate dose variation according to change of isocenter and gantry angle. In our study, the isocenter was shifted by 0.6 cm for the right‐left, 0.5 cm for superior‐inferior, and 1.4 cm for anterior‐posterior direction refer to Kinoshita et al. study. Assuming that breast shape changes subtly, the gantry angle was shifted from 1° to 5° each tangential fields. To analysis the plan quality this study calculated a dose‐volume histogram (DVH) and the dose indices that are mean dose of CTV, CTV D95, CTV V95, lung V20, heart V40 and PTV dose improvement (PDI) index. Results: When isocenter of lung and heart shifted in the right‐left and superior‐inferior direction, ‐ isocenter shift plan‐showed no significant variation from ‐ original plan‐for most of the indices. However, a significant difference was found in V95 of CTV with isocenter shift in anterior‐posterior direction by assuming the patient shifted in the posterior direction. Shifts in gantry angle slightly affected lung and heart, and smaller changes were seen in PTV. Conclusions: This study evaluated the dosimetric effects of gantry angle and isocenter shift for simulating patients setup errors and breathing motion. The effects of patient and breast changes during treatment could have influence on dose distribution of OARs as well as that of PTV.
SU‐E‐J‐159: The Investigation of OAR Dose Associated by KV‐CBCT Imaging in IGRT: A Dosimetric Study
Authors: Catan I , Canbolat A
Published: July 2013

Purpose: kV‐CBCT can provide an accurate target placement and patient positioning with reducing OARs doses. However some OARs such as testis and lenses which are not in the field of treatment may have an addtional doses due to being in imaging field. In this study, additional doses Result from kV‐CBCT were examined for these OARs. Methods: Rando phantom was used. Particular holes were created for placing TLDs. For this purpose three slices of phantom were replaced with the home‐made designed molded paraffin slices, one; in the head, the others; in the pelvic region. TLDs were calibrated with kV‐CBCT at Elekta Synergy. Correction factors were applied to readings. Commonly used imaging protocols of pelvic region M10/M20 and for head&neck S10/S20. M10/M20 contain a 360° rotation, 120kV, 40ms‐25mA, with 650 frames per scan. S10/S20 contain a 200°, 100kV, 10ms‐10mA, with 334 frames. The changes in OAR doses were investigated using various exposure parameters, i.e. mAs. For this purpose, M10/M20 were measured with 40mA and S10/S20 with 25mA. These values are in the available range of the X‐ray tube. Three TLDs were used in each measurement points and exposed 10 times to be able to have reliable single imaging doses. Results: Testis average doses in M10/M20 were 33.2±0.3/32.8±0.4mGy respectively. As the mA decreased to 25, the doses were reduced to 22.5±0.5/21.8±0.4mGy. Reduction of mA caused approximately %32 lower dose. Similar situation was observed for lenses (Table. 1). S20/M20 had lower dose than S10/M10 due to window of FOV is located with off‐axis and the spectrum has less effective high energy photons. Conclusion: The kV‐CBCT is known an accurate guidance technique, but a high level of dose per fraction is given to the OARs. TPS cannot take into account this additional doses. Due to biological dose effects, these should be monitored more carefully.
SU‐E‐J‐165: Shielding Design for An MR Guided Radiotherapy (MRgRT) Suite
Authors: Alasti H , Islam M , Rink A , Carlone M , Breen S , Jaffray D
Published: July 2013

Purpose: An MRI on rails is being installed at our institution to provide MR‐guided brachytherapy and teletherapy (MRgRT). The facility is comprised of collinear brachytherapy, MR‐Sim, and linac suites. The MR‐on‐rails translates into the adjacent suites for imaging. An existing bunker and adjacent space were renovated to permit the MR to be moved away from the linac during irradiation. This work describes the design and radiation shielding characteristics of the linac suite within the MRgRT facility. Methods: The original linac vault was designed with a two‐corner maze design to operate at 18 MV. The maze was removed and replaced with three direct‐shielded doors: a sliding console door allow for personnel and gurney access to the bunker; and two double sliding doors through which the MRI translates. The double doors employ an S‐shaped coupling surface to minimize radiation leakage when they are closed. These doors are also RF‐shielded as part of the MR RF cage. The shielding was designed for a workload of 5 × 106 cGy per year; 6 MV beam; maximum dose rate: 1400 MU/min; shielding level 0.05 mSv/year for members of the public and 1 mSv/year for nuclear energy workers. Results: The total thickness of the linac‐MRI sliding doors was 7 inches of lead and 2 inches of stainless steel, producing an equivalent thickness of 8 inches (20.3 cm) of lead. The dose rate at the distal surface of the linac‐MR door is 0.08 mSv/year or 10.9 μSv/hr. The final design includes a copper RF shield and bladder to provide RF shielding. Conclusion: A facility comprising three collinear brachytherapy, MR‐Sim, and linac facility has been designed to meet radiation and radiofrequency shielding limits.
SU‐E‐J‐166: Combining Dynamic Wave Arc and Tangential Arc for Breast Boost Irradiation with the Vero System
Authors: Buleteanu M , Reynders T , Verellen D , Depuydt T , Gevaert T , Poels K , Duchateau M , Van Parijs H , Simon V , De Ridder M Mark
Published: July 2013

Purpose: To present two novel treatment planning techniques developed for breast boost irradiation on the Vero system and investigate possible dosimetric advantages. Methods: The Vero system consists of a 6MV LINAC mounted on an O‐ring gantry that rotates around the patients by +/− 185°. Unlike C‐arm gantries it can also rotate around the vertical axis (+/− 60°). A preliminary version iPlan RT (Brainlab AG, Feldkirchen, Germany) was used to plan, optimize and investigate two arc‐based approaches. The Dynamic Wave Arc (DWA) combines simultaneously gantry and ring rotation, offering additional range of treatment orientation without involving patient/couch motion. The Tangential Arc (TGA), static gantry position with continuous ring rotation makes the most of the tangential benefits within the non‐coplanar delivery. Ten patients previously treated for breast boost (7–10 non‐coplanar static beams on Vero) were selected for breast boost comparison. All patients were replanned using two TGA combined with a DWA to achieve a sculpted dose around the thorax wall. The dosimetric parameters were calculated to evaluate the plan quality. Results: The combination of 2TGA and DWA proved to be a feasible technique for breast boost irradiation. In contrast with 3D‐CRT, it presented a better low dose reduction for the V5% and V15% ipsilateral lung. For the left side localizations, the TGA&DWA significantly reduced the heart doses (0.19+/− 0.5 vs. 8.4+/−17.73), the V5% being outside the heart in all cases. A better conformity index was also achieved (0.74 +/−0.03 for TGA&DWA versus 0.67 +/−0.04 for 3D‐CRT). The mean total number of Monitor Units was comparable for both planning approaches. Conclusion: TGA and DWA are two promising techniques that highlight the advantages of the unique design of the Vero system. Combining TGA&DWA already presented good results for breast boost. The dosimetric and clinical gains are to be further investigated for other sites. M. Buleteanu is a PhD student financially supported by Brainlab AG (Feldkirchen, Germany) during the entire period of the doctoral thesis. The other authors have no conflict of interest.
SU‐E‐J‐167: Iterative Reconstruction Techniques for Radiation Therapy CT Simulations: A Phantom Study
Authors: Li H , Lee D , Low D , Gay H , Michalski J , Mutic S
Published: July 2013

Purpose: To compare the Philips iDose4 iterative reconstruction techniques with filtered back‐projection techniques (FBP) in Radiation Therapy and provide clinical practice insights. Methods: An anthropomorphic pelvis phantom with added‐bolus layers was used to mimic patients with 38–58 cm lateral diameters. For each phantom size, a set of CT scans were acquired on a Philips Brilliance 64‐slice CT simulator with the mAs spanning the minimum to maximum dose. Images were reconstructed using FBP and iDose4 with noise reduction levels 1–6 for each scan, and evaluated on noise levels, contrast‐to‐noise ratios (CNR), CT number variations, and manual prostate contouring accuracy. Simulated prostate IMRT treatment plans based on these reconstructions were compared. Results: In general, greater‐dose scans yielded greater CNR and lower noise, iDose4 reduced noise up to 66.1% and increased the CNR up to 53.2% compared to FBP. Only changing iDose4 noise reduction levels induced minor noise variations (0.21–4.83HU) and CT Number variations (<1 HU). Without changing reconstruction filters, the spatial resolution (represented by MTF), was similar on images reconstructed by FBP and iDose4 . Very‐low‐dose scans yielded severe photon starvation artifacts, which decreased target visualization and could not be eliminated by iDose4, especially for the 58 cm phantom size. The gamma pass rates of the IMRT prostate treatment plans conducted using FBP or iDose4 based simulations were greater than 99.9% using 3%/3 mm criteria once they provide same segmentations as the ground truth. Conclusion: Compared against FBP, iDose4 reduced noise, increased CNR and CT number consistency, produced pleasant images without losing structure details, but the improvements of target delineation confidence varied based on patient sizes and radiation output. Especially, very‐low‐dose scans (causing severe photon starvation artifacts) should be avoided when using iDose4 for obese patients. The iDose4 usage should be driven by target contour conspicuity and CT# accuracy instead of noise/CNR considerations.
SU‐E‐J‐188: Deconvolution of Free‐Breathing Y90 PET Images for the Calculation of Y90 Dose Distribution for Radioembolization of Liver Cancer
Authors: Yu N , Qu H , Xia P
Published: July 2013

Purpose: Recent progress in the use of post treatment Y90 PET (post‐PET) imaging has made possible to quantitatively analyze the delivered tumor dose distribution for radioembolization of liver cancer with Y90 microspheres. Patient breathing may affect the calculated dose in clinically meaningful ways. The purpose of this work is to present a method to deconvolve post‐PET to obtain dose and to validate the results. Methods: Eleven patients were chosen for this retrospective study. Patient breathing patterns were obtained from fluoroscopy images acquired during treatment. The probability density functions that characterized the breathing patterns in the superior‐posterior direction were developed and used to deconvolute the post‐PET to generate the deconvoluted PET images (dec‐PET), which minimizes the breath motion effect into dose calculation. The Van‐Cittert algorithm was used for the deconvolution. To validate our method, we re‐convolved the dec‐PET with the same breathing kernel to generate post‐PET‐Ver. The delivered Y90 dose distributions were calculated with these three PET images using a previously published dose kernel. Selected isodose lines and dose volume histograms were analyzed. In particular, the dose to 95% volume encompassing 120 Gy isodose line from the post‐PET for the three sets of PET images, D95,pet were compared. Results: The motion amplitude in the superior/inferior direction for all the patients was 0.62–2.0 cm. The DVHs for the dec‐PET dose deviated significantly from the DVHs of the post‐PET dose whereas the DVHs from the dec‐PET ‐ ver nearly overlapped with the DVHs of post‐PET dose. For the 120 Gy dose line from the post‐PET, D95,dec/D95,post was 0.89 ±0.08, D95,post2/D95,post was 0.98±0.01 Conclusion: We demonstrated that the deconvolution was reversible and we can use this method to remove breathing motion effect. Using this deconvolution algorithm, Y90 dose can be accurately calculated from deconvoluted post‐PET with the breathing motion effect minimized.
SU‐E‐J‐215: A Two‐Dimensional Deformable Head and Neck Phantom With In‐Vivo Dosimetry for Adaptive Radiotherapy Verification
Authors: Graves Y , Mcilvena D , Smith A , Manilay Z , Lai Y , Rice R , Mell L , Jia X , Jiang S , Cervino L
Published: July 2013

Purpose: To design and construct a deformable head and neck (HN) phantom with in‐vivo dosimetry for adaptive radiotherapy (ART) verification purposes. Methods: The two‐dimensional deformable phantom recreates a single CT slice of a HN patient. It consists of two parallel acrylic plates with deformable material sandwiched in between. Gypsum plaster is used for bony anatomy and is rigidly attached to the plates. Soft tissue is mimicked with TX151 solidifying powder mixed with water. Areas of denser tissue are obtained by adding plaster powder into the mixture of TX151 and water. Parotids are represented with properties in between less dense and denser tissue. Tissue is distributed around the bony anatomy and constrained by an elastic rubber band around it. The pharynx is created with a hollow nylon tube. An inflatable silicone balloon filled with diluted barium sulfate acts as tumor. Thin plastic markers are glued on the phantom surfaces adjacent to the clear acrylic plates, providing quantifiable visual information of the deformation. Fixed detector holders are placed inside the cord and near the mandible while holders on rails that move with phantom deformation are placed close to the tumor and inside one parotid. Results: The deformable phantom has been tested for the validation of ART. We have studied the symmetric property and the response of an SRS diode that is used for dose measurements. The four point doses are obtained before and after deformation with the original plan and the re‐plan irradiated. The deformable image registration (DIR) algorithm accuracy is also verified by the deformation ground truth provided by surface markers. Conclusion: We have designed and constructed a deformable and durable HN phantom. This phantom can be used for DIR algorithm accuracy tests as well as ART verification.
SU‐E‐T‐27: Evaluation of Long‐Term Stability of KV Image Panel Position for Proton Gantry‐Based Treatment Systems
Authors: Zhu M , Botticello T , Winey B
Published: July 2013

Purpose: To quantify the long‐term digital image panel position variation and gantry angle dependence for gantry‐based proton treatment machines. Methods: In proton gantry machines, fixed mechanical crosshairs are currently used to define beam isocenter in kV X‐ray images. We developed an algorithm to automatically detect the crosshair center positions in the dual orthogonal kV images and analyzed 2651 images acquired with four image panels in the two treatment rooms within 12 months. The long‐term stability of the crosshair positions in the images at four gantry angles (0, 90, 180, and 270) and the positional dependence on gantry angle were investigated. Crosshair isocentricity is analyzed bi‐weekly during routine mechanical QA. Results: The standard deviations of the crosshair positions were 0.28 mm in X‐Z plane and 0.38 mm in Y axis. The 95 percentiles of the crosshair positions were −0.54 mm to 0.61 mm in X‐Z plane and −0.95 mm to 0.59 mm in Y axis. The relative large variation in Y axis is caused by a systematic crosshair projection position shifts after X‐ray tube and panel replacements. The crosshair position variation along gantry angles was within ±4mms, and different for each panel. The long‐term crosshair position is stable and its variation is consistent to the beam isocenter QA tests, and the crosshair position variation with gantry angle is in the same pattern as measured in routine QA procedures. Conclusion: This work revealed that the kV image panel positions in our proton treatment system is stable at the cardinal angles over 12 months and the panel positions can be correlated to gantry angles. This Result indicates that the image panel position is most likely predictable and, with adequate QA flexmap procedures, the crosshair may not be necessary for all kV images. The project was supported by the Federal Share of program income earned by Massachusetts General Hospital on C06 CA059267, Proton Therapy Research and Treatment Center.
SU‐E‐T‐37: Revisiting Stanford Technique for Treatment of Mycosis Fungoid Patient with a Cardiac Pacemaker
Authors: Deore S , Xu X , Luo L , Kwiatkowski T , Atanas M
Published: July 2013

Purpose: Implement a dual six field electron beam treatment technique for treatment of Mycosis Fungoid patient with a cardiac pacemaker.Introduction: Total skin electron beam therapy for treatment of mycosis fungoids requires large size of treatment fields obtained at 4 to 5 meters distance (TG 30). A large field treatment with a cardiac pacemaker presents significant challenge for mycosis fungoid treatment. The Stanford technique with adequate shielding for pacemaker was implemented.Materials and Methods: A 82 year old gentleman with mycosis fungoid stage IB was planned for treatment with large field electron beams at extended distance. The standard Stanford technique of six dual fields was implemented on Varian Clinac iX. A custom made stand was designed to reproduce & support patient for daily treatment. A treatment distance of 4.8 meters using 6 MeV electrons was implemented. To achieve uniform dose delivery along patient height, a gantry angle of ±15° was finalized. A P‐11 parallel plate chamber was used for TG‐51 and profile measurements. The B factor concept from Stanford technique was used for absolute dose calculations. For the pacemaker 6 mm thick lead shield was used to reduce maximum dose < 2Gy during entire course of the treatment. Results: Patient received 20 Gy to entire skin surface in 20 fractions, followed by additional boost dose of 10 Gy to localized active lesions. During entire course of treatment nail bed and eyes were shielded. Patient tolerated entire course of treatment very well. Conclusions: The early response was promising. The functional evaluation by cardiologist did not indicate any radiation damage to the pacemaker.