bluuebunny/crossref_metadata_2025 huggingface dataset:
SU‐E‐J‐24: Imaging Dose Dependence On Fractionation Scheme and Tracking Method in CyberKnife Robotic Radiosurgery
Authors: Tien CJ , Dieterich S , Lee S , Curran BH , Sternick ES
Published: July 2013

Purpose: Imaging dose in robotic radiosurgery is analogous to cone‐beam computed tomography imaging for stereotactic radiosurgery: there needs to be a balance between increasing imaging to increase targeting accuracy versus reducing imaging to lower imaging dose. We study the effect of fractionation scheme and tracking method upon reducing imaging dose. Methods: The imaging system of the Accuray CyberKnife consists of two ceiling‐mounted kilovoltage x‐ray tubes and two accompanying floor‐mounted amorphous silicon flat‐panel detectors. The x‐ray tubes have 2.5 mm Al filtration and are capable of 40‐125 kV, 25‐300 mA, and 1‐500 ms. A cohort of 427 patients from two institutions using CyberKnife was retrospectively reviewed to determine the number of images taken during treatment. This database was analyzed to determine if different fractionation schemes or tracking methods affected the number of images. Results: Over all patients, the median number of images taken was approximately 400, which was an estimated entrance skin exposure of about 0.5 Gy. This number was found to be most dependent upon the fractionation scheme and tracking method. The amount of imaging increased 400% when switching between one‐fraction and three‐fraction treatments. Additionally, the amount of imaging increased 150% between skull and spinal tracking. Between the two institutions, differences were found in the absolute magnitude in images taken due to the sampling interval chosen. Dose differences were also observed as a Result of operator adjustment of kV, mAs, or exposure time. Conclusion: This study provides supplemental information to AAPM TG‐75, which did not examine imaging dose in robotic radiosurgery. The imaging dose was found to vary widely but was most strongly dependent upon fractionation scheme and tracking method. We identified three methods with the potential to decrease imaging dose by 300%.
SU‐E‐J‐25: A Quantitative Comparison of Contrast‐To‐Noise in Rib Suppressed Images
Authors: Luce J , Bray T , Roeske J
Published: July 2013

Purpose: To compare the contrast to noise ratio (CNR) of two different rib suppression methodologies ‐ dual‐energy (DE) image subtraction and blind signal separation (BSS)‐used for lung cancer patients receiving image‐guided radiotherapy. Methods: A database consisting of 28 planar radiographs obtained at 60 kVp and 120 kVp were used in this study. DE subtraction imaging was performed by taking a weighted logarithmic subtraction of the individual images. A weighting parameter of 2.1 was chosen to produce the optimal soft tissue (rib suppressed) images for each image pair. Similarly, BSS was used to extract the soft tissue and bony image components from a patient image. An open source program for performing BSS, called FastICA, was used in conjunction with the same 60 kVp and 120 kVp images. Regions of interest (ROIs) were contoured on the resultant images and the CNR from each technique was calculated and compared. Results: A paired t‐test was run on the CNR values, resulting in a p value < 0.05, indicated there was a statistically significant difference in the CNRs generated by the two methods. For 24 of the 28 image sets that were evaluated, the CNR values were found to be higher for the DE subtraction images. Of these 24 images, 9 had CNR values > 20% higher, and 4 had CNR values > 40% higher. Conclusion: Based on this study, DE image subtraction creates images with higher CNR values than those generated with FastICA. This is likely due, at least in part, to the ability to customize the weighting factor of the DE subtraction images. However, there are numerous methods for performing BSS outside of FastICA, and further study is warranted to determine if alternative BSS methods could produce better rib suppressed images. This research was supported by Varian Medical Systems.
SU‐E‐J‐29: Assessing the Dosimetric Effects of Tumor Tracking During Irregular Respiration Using a Mass‐Conserving XCAT Phantom
Authors: Williams C , Seco J , Mishra P , St. James S , Mak R , Berbeco R , Lewis J
Published: July 2013

Purpose: To quantitatively assess the impact of real time tumor tracking on the delivered dose during thoracic radiotherapy in the presence of realistic breathing. Methods: The 4D XCAT digital torso phantom was used in this study. The phantom was created with irregular breathing motion based on observed patient tumor motion. A locally mass‐conserving framework was applied to modify the XCAT to enable dose accumulation. The first 6 seconds of phantom data were used to simulate 4DCT acquisition. Two SBRT treatment plans were developed to assess the effects of tracking. The first plan, simulating a standard SBRT treatment, used an ITV+5mm aperture from the maximum intensity projection of the 4DCT. This plan was normalized to deliver 54 Gy to 95% of the PTV based on the 4DCT dose. The second plan simulated couch tracking by defining apertures from a single 4DCT phase (GTV+2mm), and translating the phantom during the delivery to keep the tumor centered in the aperture. Delivered dose was calculated using Monte Carlo techniques for the subsequent 60 seconds of phantom data at 1‐second time resolution, and was deformed and accumulated on to a reference phase. Results: The tumor D95 was 55.5 Gy for the ITV‐based plan and 54.6 Gy for the tracking plan. For the ITV‐based plan, the lung V5 was 22.9%, V20 was 3.6% and the mean dose was 3.9 Gy. For the tracking plan, the V5 was 14.5%, the V20 was 1.8% and the mean dose was 2.5 Gy. Conclusion: A method for assessing the dosimetric impact of tumor tracking during respiration has been demonstrated using the digital XCAT phantom. For the phantom simulated in this study, the tracking and conventional SBRT plans both delivered the prescribed dose to the tumor, and the lung dose is substantially reduced with tracking. The project described was supported, in part, by an RSNA Research Scholar Grant and Award Number R21CA156068 from the National Cancer Institute. The content is solely the responsibility of the authors and does not necessarily represent the official views of the RSNA, National Cancer Institute or the National Institutes of Health.
SU‐E‐J‐30: Intuitive Display Coordinates for Six‐Degree‐Of‐Freedom Treatment Couches
Authors: Remmes N , Whitaker T , Beltran C , Kruse J , Bues M , Herman M
Published: July 2013

Purpose: To define couch display coordinates of six‐degree‐of‐freedom treatment couches in a manner that is more intuitively linked to the position of isocenter in the patient, permits easy identification of irregularities in couch positioning, and permits the tightest possible override tolerances for all couch motions. The display coordinates should be calculated from the IEC table‐top coordinate system with no patient‐specific information. Methods: Couch display coordinates are proposed as the position of radiation isocenter in IEC table‐top coordinates. Coordinate systems are compared across multiple radiation therapy machines and then compared to the proposed display coordinates. Examples are provided showing how the proposed definition can be applied across a variety of different couch designs. Results: Consistent with IEC standards, most machines with six‐degree‐of‐freedom couches, and particularly those with robotic couches, measure rotations about a point fixed with respect to the couch and independent of all translational motions. This convention has the undesirable consequence of eliminating the one‐to‐one relationship between the translational coordinates displayed and the position of the radiation isocenter in the patient. By defining the display coordinates as the position of radiation isocenter in IEC table‐top coordinates, the one‐to‐one relationship is reestablished. Examples provided show that the proposed definition insures that a one‐to‐one relationship between the position of isocenter in the patient and the three translational display coordinates regardless of the values of the three angular degrees of motion. Conclusion: The examples illustrate how the proposed couch display coordinates lead to easier identification of irregularities in couch positioning such as identifying laterality of isocenter or shifts in multi‐isocenter treatments. The proposed display also allows tighter tolerances for couch overrides. These advantages suggest a revised IEC display standard following these conventions has the potential to reduce setup errors at the treatment machine and enhance the utility of the couch display coordinates.
SU‐E‐J‐31: MR Only Simulation for Radiation Therapy _ DRR Generation
Authors: Yang Y , Han F , Cao M , Sheng K , Selch M , Kaprealian T , Agazaryan N , Low D , Hu P
Published: July 2013

Purpose: MRI only radiation therapy has been increasingly gaining research interests. Conventionally, MRIs are fused with CT to take advantage of its superior soft tissue contrast. Such an approach has drawbacks such as additional uncertainty from fusion and extra cost. To achieve MR‐based simulation for radiation therapy, bone imaging is an important challenge that needs to be overcome. The ultra‐short T2 and T1 of cortical bone Result in low signal intensity, which presents difficulty for both dose calculation and patient setup in terms of digitally reconstructed radiograph (DRR) generation. Current solutions will either require manual bone contouring or multiple MR scans. We present a technique to generate brain DRR using bone MRI with a single Ultra Short Echo Time (UTE) sequence. Methods: Healthy volunteers were scanned at 1.5 Tesla using a radial UTE sequence. The sequence acquires two images at two different echo times (0.07ms and 3.6ms). The two images were processed using in‐house software, which performs pixel‐by‐pixel magnitude subtraction of the two images. The difference image was subsequently divided pixel‐by‐pixel to the long TE (3.6ms) image. As the cortical bone has larger percentile difference between the UTE and long TE image compared with other tissues, the bone is bright in the processed image. The resultant bone images were subsequently loaded into commercial treatment planning system to generate DRRs. Results: The majority of cranial, facial and vertebral bones are well visualized in both volunteers. The fused image of the long TE image with the processed bone image demonstrates the accuracy of automatic bone identification using our technique. The generated DRR is of acceptable quality. Conclusion: This study shows the potential of DRR generation with single MR sequence. Further work will be needed on MR sequence development and post‐processing procedure to achieve MR bone image with comparable quality to CT.
SU‐E‐J‐33: Proton Therapy Fiducial Comparison
Authors: Ramirez E , Zheng Y , Rana S
Published: July 2013

Purpose: Fiducial markers are commonly used in Image Guided Radiotherapy as landmarks to ensure patient setup accuracy and reproducibility. Good fiducials need to be radiopaque, yet not so much to create significant CT artifacts and disturb the tumor dose downstream. The latter is even more important in Proton radiotherapy to fully achieve its preciseness. The purpose of the study is to investigate several potential fiducial markers on their suitability for prostate proton therapy. Methods: In total, eight commercially available fiducial markers were compared in this study. These fiducials include: 3 types of VisiCoil (VC1‐0.5×5 mm, VC2‐0.35×5 mm, VC3‐0.35×10 mm), BiomarC, FusionCoil, PolyMark, PointCoil, and FlexiCoil. We compared them in 4 ways. First, we scanned them using a GE RT16 scanner with a clinically used scanning protocol, and evaluated the degree of CT artifacts in two different water tank geometries; second, we evaluated visibility on kV images used for patient positioning, third, we compared their visibility on MRI. In addition, we looked at the perturbance of isodose lines distal to the fiducials in our treatment planning system. Results: Our preliminary study shows that PolyMark, BiomarC, VC2, and VC3 have the least CT artifacts of the group; FusionCoil, Flexicoil, PointCoil, and VC1 are most visible and PolyMark almost invisible on kV images; Evaluation of MRI visibility and dosimetric effects for these fiducials are in progress. Conclusion: The VC1 and BiomarC seem to have the best performance in balance of CT artifacts and x‐ray visibility. Further study on MRI visibility and dosimetric effect will be conducted to determine the overall performance of each fiducial and its suitability for clinical use in proton therapy.
SU‐E‐J‐37: The Validation Tool for Compensation of Patient Positioning Error Using DRR Images
Authors: Kim M , Cho W , Jung J , Jung W , Suh T
Published: July 2013

Purpose: The present study was designed to develop the validation tool for compensation of patient positioning error using digitally reconstructed radiograph (DRR) extracted from three‐dimensional computed tomography (3DCT) and two orthogonal kilo‐voltage x‐ray images. Methods: To generate DRR image from 3DCT, the ray casting which is most straightforward method was applied in this study. The traditional ray casting algorithm finds the intersections of a ray with all objects, voxels of the 3DCT volume in the scene, with nearest‐neighbor interpolation method. Similarity between extracted DRR and orthogonal image was measured by using normalized mutual information method. All process was done by using Matlab. Two orthogonal image was acquired from Cyber‐knife system from anterior‐posterior view and right lateral view. 3DCT and two orthogonal image of an anthropomorphic Alderson‐Rando phantom and head and neck cancer patient were applied in this study. Finally, we designed graphic user interface (GUI) for easy use. Results: Registration accuracy with average errors of 2.12 mm ± 0.5 mm for transformation and 1.23° ± 0.4° for rotation using an anthropomorphic Alderson‐Rando phantom has been acquired. Conclusion: We demonstrated that this validation tool could compensate the patient positioning error. For further study, with the developed validation GUI tool for compensation of patient positioning error, we will add the registration tool by manual/auto using cone‐beam CT and kilo‐voltage CT image to utilize clinically in heavy‐ion radiation treatment center in Korea which scheduled for completion in 2016.
SU‐E‐J‐38: Fast Patient Localization Method in Total Marrow Irradiation with Helical Tomotherapy
Authors: Takahashi Y , Chityala R , Hui S
Published: July 2013

Purpose: Reducing imaging and treatment times is a crucial issue in total marrow irradiation (TMI) with helical tomotherapy. The purpose of this study was to develop the fast patient localization method for TMI patients with helical tomotherapy. Methods: The topographic images were acquired by getting the megavoltage CT (MVCT) after running calibration procedures with the couch traversing through the gantry at static orthogonal beam angles. Geometric and detector response corrections were performed to generate a MV topogram (MVtopo). We also generated kilovoltage topogram (kVtopo) from the projection data of 3D CT images datasets to reproduce the same geometry as MVtopo. Imaging dose and the optimal image acquisition parameters including jaw size, couch velocity, and dose rate were investigated. Geometric uncertainty and image quality of MVtopo were analyzed. In‐house image registration software was developed and verified with a rando phantom. Finally, MVtopo was acquired for a TMI patient. Results: The longitudinal geometric uncertainty was 0 mm, 10.2 mm, and 23.6 mm, in the jaw size of 0.3 cm, 1 cm, and 2.5 cm, respectively. No jaw size dependency in the lateral geometric uncertainty was observed. Couch velocity did not have an effect on the geometric uncertainty. The doses of MVCT and MVtopo with the jaw size of 3 mm and the couch velocity of 0.8cm/sec were 1.5cGy, and 1.7 cGy, respectively. Contrast‐Noise‐ratio, noise, and MTF were improved by using lower dose rate (55MU/min) and smaller jaw size (3 mm). The image registration accuracy with our in‐house software was within 1 mm. In a clinical TMI case, MVtopo with couch speed of 1.0cm/s reduced imaging time by 80% compared with MVCT. The couch shifts derived from KVCT with MVCT registration, and kVtopo with MVtopo registrations agreed within 4 mm. Conclusion: The MVtopo could be useful for TMI treatment with helical tomotherapy. This work was supported by the National Institute of Health grants (1R01CA154491‐01).This work was also supported by PHS Cancer Center Support Grant P30CA77398.
SU‐E‐J‐40: Automated Estimation of Lung Tumor Locations for Tumor‐Based Patient Setup Using MV‐CBCT Images in Stereotactic Body Radiotherapy
Authors: Yoshidome S , Arimura H , Nakamura K , Shioyama Y , Atsumi K , Yoshikawa H , Nishikawa K , Hirata H
Published: July 2013

Purpose: Patient setup procedure in stereotactic radiation therapy should be performed based on a tumor region, not bone structures. The goal of this study was to develop an automated method of estimation of lung tumor locations for tumor‐based patient setup using megavoltage cone‐beam computed tomography (MV‐CBCT) images in stereotactic body radiotherapy (SBRT). Methods: Planning CT, treatment MV‐CBCT images (4.125 MV‐CBCT images/patient), and DICOM‐RT structure sets for 8 patients were employed for this study. The patients had solitary lung tumors smaller than 25 mm (range of effective diameter: 23 – 8.8 mm and median: 17.7 mm) and received SBRT. In the proposed method, the lung tumor locations were estimated in MV‐CBCT images by using tumor templates obtained from corresponding planning CT images. First, a MV‐CBCT image was globally aligned with a planning CT image by finding the location with the maximum cross‐correlation coefficient, and then a gross target volume (GTV) region in the structure set was placed in the planning CT and MV‐CBCT images. Second, a tumor template was produced by cropping the dilated GTV region in the planning CT image. Finally, a tumor location was estimated within the dilated GTV region in the MV‐CBCT image by using the tumor template matching and calculating the centroid of the dilated GTV region. Gold standards of tumor locations were determined by a radiation oncologist and two radiological technologists in the clinical practice. Results: A mean error between the gold standard and the tumor location estimated by the proposed method was 4.1 and standard deviation was 2.3 mm for 8 patients.. Conclusion: The results suggest that the proposed method using the MV‐CBCT may be one of useful tools for tumor‐based patient setup in SBRT.
SU‐E‐J‐42: Patient Dependent Options for Image Guidance Procedures in Radiotherapy: Prostate Cancer
Authors: Piotrowski T , Kaczmarek K , Jodda A , Ryczkowski A , Bajon T , Rodrigues G , Yartsev S
Published: July 2013

Purpose: Retrospective analysis of image guidance data in radiation treatments of prostate cancer patients allows for simulation of imaging scenarios with less frequent or modified procedures. The correlation of patient specific features with inter‐fraction prostate variations can be explained using patient cohorts with large amounts of daily image data. Methods: The 6,085 setup correction shifts performed during radiotherapy of 216 prostate cancer patients on helical tomotherapy units in two cancer centers were analyzed with respect to automatic and manual matching procedures in co‐registration of planning kV and pre‐treatment MVCT studies. Margins needed to account for inter‐fraction target motion for a daily automatic corrections scheme and three schemes with limited imaging based on one, three and five first fractions as a reference were calculated. The body mass index (BMI) was calculated for all patients and the times required for different steps in the co‐registration process were evaluated. Results: The margin calculated for the daily automatic shift scheme was significantly lower than any of the margins calculated for the limited imaging schemes. The average time needed for management of the daily automatic correction shift during the whole course of the treatment was equal to 5 minutes, and was 30 times shorter than time needed for the daily registration based on automatic and manual correction shifts. Larger setup correction shifts were observed for the patients with higher BMI values. Conclusion: The patients with normal BMI values (BMI<25) require a significantly smaller setup correction and may be treated with a limited number of imaging sessions followed by treatment without imaging using external marks that take into account average systematic shift and personalized margins obtained from the data of the first several fractions. The overweight (25<BMI<30) and obese (BMI>30) patients may be treated with daily automatic co‐registration and reduced personalized margins.
SU‐E‐J‐43: Scatter and Beam Hardening Corrections for MV‐CBCT Using a Few MLC Leaf‐Pairs and a Cylindrical Water Equivalent Phantom
Authors: Guan H , Jin J
Published: July 2013

Purpose: MV‐CBCT has multiple advantages over KV‐CBCT for online IGRT, but its imaging contrast is lower than that of KV‐CBCT, partly because of the scatter and the beam hardening effects. 1. To correct the scatter artifacts in megavoltage CBCT using a few MLC leaf‐pairs as beam stoppers and after that; 2. To correct the beam hardening effect using fan beam projections acquired from a water equivalent cylindrical phantom. Methods: Two or three evenly spaced MLC leaf pairs were used as beam stoppers when acquiring the MV CBCT projections, and then the pixel readings under the leaf‐blocked area was largely due to scatter. These pixel readings, plus the pixel readings just outside the field edges, can help to estimate the 2D scatter map by interpolation, which can then be subtracted from the original projections. After the scatter correction, the beam hardening correction was made by using the fan beam projections taken from a water equivalent cylindrical phantom with little scatter. In this study, 180 full MV‐projections for a Catphan500 phantom with a bone equivalent annulus were acquired over 360 degree using 6 MV photon beams, with 0–180 and 180‐360 degree scans using different leaf‐pair as beam stoppers. The fan beam projections for beam hardening correction were acquired from a phantom of uniform density with a diameter of 25 cm. Results: Scatter and beam hardening induced cupping and shading artifacts were substantially reduced in MV‐CBCT. Also, the reconstructed Catphan images were complete because we used different leaf‐pairs as beam stoppers for 0‐180 and 180‐360 degree scans. Conclusion: An efficient and effective scatter correction scheme was proposed and applied for MV‐CBCT. After the scatter correction, the MV‐CBCT image quality matched that from fan‐beam MVCT. Beam hardening correction further improved the imaging contrast of MV‐CBCT.
SU‐E‐J‐44: Imaging and Radiation Therapy: GATE Monte Carlo Simulation of a MV‐CBCT Flat Panel with Specific Application in Head and Neck Cancer
Authors: Benhalouche S , Bert J , Visvikis D , Pradier O , Nicolas B
Published: July 2013

Purpose: In radiotherapy treatment, it is necessary to position the patient before each session to ensure that the beams target the tumor while sparing the surrounding healthy tissue. This step is made possible via different imaging techniques like the “electronic portal imaging device” (EPID) which is the most common approach. In this configuration, the imaging source is the same as the treatment source, while a flat panel detector is automatically placed under the patient via an articulated arm. In this context, our study was focused on the Monte Carlo modeling of such an EPID in order to simulate both planar and 3D CBCT images. Methods: The work presented here follows a preliminary study in which the treatment part of a clinical LINAC (Siemens Oncor) was modeled in GATE v6.2. The objective was to calculate the dose delivered by complex treatments like IMRT. The objective of the study is to extend this model by incorporating the imaging part of the LINAC, which consists of a flat panel detector (Perkin Elmer XRD1640). For this purpose, geometrical and physical data provided by the manufacturer were first accurately modeled in GATE. As a second step, 2D and 3D images simulations were performed according to clinical protocols: projections over a 200° arc, 1° increments, and 41cm square field of view. IMRT QA and, RANDO anthropomorphic phantom and head‐and‐neck patient CT were used as input objects for simulations. Results: From the obtained series of 2D projections a 3D reconstruction was performed in each case, and the dimensions of the reconstructed structures were compared with actual objects. Conclusion: We have developed within the GATE platform a complete and detailed model of a 160MLC LINAC with its MVCBCT flat panel. Future work will consist in simulating epid‐based transit dosimetry.
SU‐E‐J‐48: A New High Energy X‐Ray Imaging Mode for Position Verification in Radiotherapy
Authors: Quanshi Z , Xiwen W , Qiyin S , Yuehui J , Yun L , Pengcheng Z
Published: July 2013

Purpose: To bring forward a new imaging mode for position verification in radiotherapy called as HMV which the energy of X Ray is greater than 15MeV or the nominal accelerating potential is greater than 25MV. To prove it is superior to the traditional kV and MV level imaging mode for position verification in radiotherapy. Methods: According to the basic principles of photon interaction with medium, we firstly discuss the theoretical basis and advantages of HMV imaging mode over than MV imaging mode. Then we test them with Catpan 500 phantom under 10MV, 25MV and 45 MV bremsstrahlung generated by the LA45 accelerator (Top Grade Healthcare, Beijing, China). Finally we check images of HMV and MV imaging mode with a real patient.The X Ray panel imager and soft package are XRD 1640 AN19 CS and XIS3.2.0.67 from PekinElmer.The X Ray panel is a shielding Integrates with shielding cassette for high energy applications. Results: Both theoretic and results of testing with phantom and patients are show that the quality and contrast or resolving power of HMV imaging mode is superior to the traditional MV level imaging mode. Conclusion: The theoretical and experimental results show that HMV image mode, which the X ray energies are higher than 15 MeV or nominal potential is higher than 25 MV X ray, not only improve the image quality but also have good contrast or resolving capability which among tissues and anatomical structures. It integrated advantages together both kV and MV image mode and eliminate their disadvantages.
SU‐E‐J‐49: Pelvic Treatment Setup Differences Between Skin Markers‐Based and Bony References Using Brainlab Exactrac
Authors: Castro A , Bardella L , Panichella J , Erlich F , Batista D
Published: July 2013

Purpose: To quantify the translational and rotational setup differences between laseres on skin markers and bony references through X‐ray Brainlab Exactrac system for patients under pelvic treatment. Methods: 12 patients were initially localized via Exactrac and then received the isocenter laser projection marks on their skin. Over the course of treatment patients were daily localized by localization lasers and skin marks and then a pair of Brainlab Exactrac X‐rays were taken and registered to planning Digital Reconstructed Radiographies (DRRs) in order to calculate the translational and rotational patient shifts. 6D Robotic couch were used to apply shifts. Individual and population statistical analysis of those shifts were performed. Results: The average mean shifts for all directions (lateral, longitudinal and vertical) were close to zero, −0.6mm, −0.3mm and 1.6mm respectively. The average translational standard deviations were: lateral 2.7mm (ranging from 1.9 to 4.6mm), longitudinal: 2.3mm (1.0 to 4.4mm), and vertical: 3.5mm (1.3 to 5.0mm). For all patients studied the mean lateral angular shift (pitch) was always positive (mean 1.1°, ranging from 0° to 3.8°), while the overall longitudinal angular shift (roll) and vertical rotation were −0,1° (SD=0,6°, varying from −0,7° to 1.3°) and 0.0° (SD=0,4°, −0,5° to 0,9°) respectively. Conclusion: The low value of overall mean translational shift indicates there is no significant systematic error for the studied patients. Anterior Posterior direction is the most sensitive to daily differences between lasers and Exactrac. Recurrent positive mean lateral angular shift for all patients might be related to table top sagging and its relation to patient weight needs to be further investigated. Patient localization by skin markers may lead to significant differences compared to bony localization and such discrepancies must be considered for PTV margins. Patient positioning via bony references with Exactrac may potentially reduce PTV margins and consequently side‐effects.
SU‐E‐J‐51: Effect of Exactrac 6D Correction On Dose for SRT Patients with IR Body Markers
Authors: Prasad B Durga , Yarramma A , Reddy P , Murthy K Krishna , Reddy R , Babu A Ananda Giri , Karunakaran K , Lingampally S
Published: July 2013

Purpose: To study the 6D correction efficacy on dose to the target due to infrared(IR) body marker localization for stereotactic radiotherapy(SRT) patients Methods: Commercially available laboratory skull phantom, made of plastic is used in this study.It is filled with physiotherapy wax and a provision is made to insert CC13 ion‐chamber(0.13cc). The dose at a point in skull phantom is measured by CC13 ion‐chamber.An ordinary thermoplastic mould is prepared for skull phantom and 5 infrared body markers are placed at different places for localization as shown in figA. CT scan of the phantom is obtained using Siemens PET‐CT scanner with and without ion‐chamber. Treatment Planning is done on images which are without ion chamber .In the absence of ion chamber to fill the cavity a wax insert is inserted during the CT scan. 3mm slice thickness are obtained and imported to Eclipse treatment planning system(TPS) for contouring and planning.Treatment plans of 3D CRT/IMRT are planned in Eclipse on skull phantom images with isocenter placed at the chamber sensitive volume.The plan is exported to Exactrac imaging system for localization and verification. After setup of skull phantom imaging is done with exactrac stereoscopic imaging system and the 6D shifts (Vertical,logitudenal,lateral,yaw,pitch,roll) are applied. The focus to skin distance(FSD) is noted‐Table1.The radiation dose is delivered in Varian Novalis Tx.The charge collected /dose in CC13 ion chamber is noted from the DOSE1 electrometer‐Table2.The planned FSD and dose are noted from TPS. Results: The mean difference between planned and measured FSD and Dose are 0.55cm and 2.7% respectively. The mean SD of FSD and Dose are 0.383 and 1.58% respectively. Conclusion: Even though Exactrac‐6D couch shifts introduce change in FSD by 1–1.5cm the dose difference is within the range of 3% and is reasonable to treat frame less SRT treatments with IR body markers with ordinary mask.
SU‐E‐J‐52: Evaluation of Patient Setup Using Catalyst Surface Mapping Technique
Authors: Cao D , Xie X , Mehta V , Shepard D
Published: July 2013

Purpose: In this study, we evaluated the accuracy and clinical effectiveness of a novel surface mapping system utilizing deformable image registration. Comparisons were made between the shifts determined using conebeam CT (CBCT) and those calculated using the surface mapping tool, the C‐RAD Catalyst. Materials and Methods: For the CBCT and surface mapping comparisons, a turkey was used as a patient surrogate. A reference CT scan was first taken when the turkey was frozen (non‐deformable). Initial setups were made using the Catalyst system for each of two locations (spine and left breast). A CBCT scan was performed immediately after each Catalyst setup. The three dimensional shifts and rotations along three axes were recorded for comparison purposes. Setups were made using both the frozen (non‐deformable) and unfrozen (deformable) turkey. Results: When the turkey was frozen, surface mapping and CBCT setups agreed within 2mm. A 2‐degree rotation along longitudinal axis detected by the Catalyst system was confirmed with CBCT based alignment. For tests performed after the turkey was defrosted, differences of up to 10mm were observed in the vertical positioning when comparing setups performed using surface mapping and CBCT. The left breast site setup using Catalyst agreed closely with the CBCT data even when significant body deformation was introduced. The rotations obtained from Catalyst and CBCT data agreed within 2 degrees for both treatment sites with body deformation. Conclusions: As a surface mapping technology, the C‐RAD Catalyst system can provide accurate and efficient patient setup when there is no significant body deformation. Caution must be exercised, however, in using this tool in cases where significant deformation may occur particularly when the isocenter is significantly displaced from the detected patient surface. Research was partially funded by Elekta
SU‐E‐J‐53: A Self‐Calibrating Optical System to Improve Patient Positioning During Breast Radiotherapy
Authors: Nazareth D , Merrow C , Malhotra H , Hoffmann K
Published: July 2013

Purpose: Breast radiotherapy, particularly electronic compensation, may involve large dose gradients and difficult patient positioning problems. We have developed a simple self‐calibrating optical image‐guided system, which assists in accurately and reproducibly positioning the patient, by displaying her real‐time optical image from a single camera superimposed on a perspective projection of her 3D CT data. Our method requires only a standard high‐zoom digital camera capable of live‐view mode, set up in the treatment suite at a fixed orientation and position (rotation, R and translation, T). Methods: A 10‐sphere calibration jig was constructed and CT imaged to provide a 3D model. The camera R and T were determined by taking a photograph of the jig and optimizing an objective function, which compares the true image points to points calculated with a given candidate R and T geometry. Using this geometric information, 3D CT patient data, viewed from the camera perspective, is plotted using a Matlab routine. This image data is superimposed onto the real‐time patient image, acquired by the camera, and displayed using standard live‐view software. This enables the therapists to view both the current and desired positions of the patient, and guide her into assuming the correct position. The method was evaluated using an in‐house developed breast phantom, mounted on a supporting platform, which could be tilted at various angles to simulate treatment‐like geometries. Results: Our system allowed us to align the breast phantom, with an accuracy of about 0.5 cm and 5°. Better resolution could be possible with a camera with higher‐zoom capabilities. Conclusion: We have developed a system to superimpose a perspective projection of a CT image on a patient real‐time optical image. Such a system has the potential to improve patient setup accuracy during breast radiotherapy, and could possibly be used for other disease sites as well.
SU‐E‐J‐54: The Characterization of a 3D Real‐Time Surface System with a Single High‐Definition (HD) Camera
Authors: Peng J , Jacqmin D , McDonald D , Koch N , Ashenafi M , Vanek K
Published: July 2013

Purpose: To investigate a single high‐definition (HD) camera of 3D realtime surface system (AlignRT_1HD, VisionRT, Inc.) as the potential alternative to the standard configuration of the system with three charge‐coupled device (CCD) cameras (AlignRT_3C) and to evaluate the localization accuracy of AlignRT_1HD compared to AlignRT_3C. Methods: Both AlignRT_3C and AlignRT_1HD were installed in the same treatment room with Varian LINAC. A commercial daily QA phantom (DailyQA3TM, Sun Nuclear) and 5 IMRT patients with intracranial and head and neck tumors receiving non‐coplanar treatment were used to evaluate system characteristics and position‐tracking accuracies of AlignRT_1HD through comparison with the AlignRT_3C and kV‐CBCTs. Surface‐image data sets were acquired simultaneously by both systems for the evaluation of inter‐and intra‐fractional motion at daily treatment of each patient. Results: The system origin displacements agreed to within 0.5 mm/0.5°. Compared to the CBCTs without couch rotations, the mean registration errors obtained using AlignRT_1HD were approximately 0.4 mm/0.8° (for phantom displacements up to ± 3cm in 3 axes), 1.1 mm/0.8° (for inter_frational motion in patients), and 0.3 mm/0.4° (for intra_frational motionin patients) less than those obtained using the AlignRT_3C. For non‐coplanar treatments, without the surface images acquired by two side camera pods using AlignRT_1HD in this study, the accuracy of patient setup was only guaranteed up to ±10° couch angles. The average setup time using AlignRT_1HD was reduced by approximately 1 min per session. Conclusion: As judged by CBCTs, AlignRT_1HD is capable of increasing in positioning accuracy and setup efficiency for high precision treatment, with the enhancements in image resolution, frame rate and field of view using HD cameras. The standard configuration with 3‐camera‐pods of AlignRT_3HD was essential for non‐coplanar treatment and the localization accuracy with couch angle up to 90° needs to be further quantified.
SU‐E‐J‐55: Influence of Patient Weight and Couch Rotation On the Accuracy of a Surface Tracking System for Stereotactic Radiosurgery
Authors: Pearson C , Song W , Kim G
Published: July 2013

Purpose: To evaluate the influence of patient weight and couch angle on the treatment accuracy of brain SRS guided by the AlignRT system integrated with TrueBeam couch system. Method and Materials: A Winston Lutz phantom with a facemask on top was used to simulate a brain SRS treatment with surface monitoring. The phantom contained small fiducial markers that guided the initial setup using kV and CBCT imaging. A CT scan of the phantom was taken and used to form a plan that included 15 sets of different combinations of couch and gantry angles. Once the phantom was set up, a reference image for surface was acquired and motion monitoring was initiated. The gantry and couch were then moved to their respective positions and an EPID image was acquired. A motion report was generated on the AlignRT system. EPID image registration was performed using the OBI system with DRRimage and the shifts were recorded. The method was repeated for evaluation of patient weight with five different weights in the range of 20 and 120 kg. Results: Examination of the AlignRT data suggests that the accuracy of TrueBeam couch system is slightly compromised for the longitudinal direction (< 0.9 mm) after applying couch rotation during the tracking. The accuracy did not seem to be affected by varying patient weight if couch sagging is compensated for initial setup. All of the deviations of the AlignRT record showed that the accuracy was within 1 mm to the deviations from image registration of isocenter. Conclusions: Our data suggests that TrueBeam couch system maintains geometric accuracy of up to 120 kg of weight, at various gantry and couch angle positions, suggesting that the system is reliable for use with Brain SRS treatments. Addition of AlignRT for intrafraction monitoring helps to ensure that the treatment remains accurate.
SU‐E‐J‐56: Surface Imaging for Breast Patients
Authors: Padilla L , Kang H , Washington M , Hasan Y , Chmura S , Al‐Hallaq H
Published: July 2013

Purpose: Compares surface imaging (SI) to MV films for positioning of 13 patients receiving whole‐breast irradiation. Methods: AlignRT v5.0 was used to capture non‐gated, 3D surface images during filmed fractions (n=55) after positioning with skin marks and correction for rotations. Registrations of SI to a reference surface, generated from 3mm‐thick CT data, were analyzed off‐line for both the “entire” and the “breast” regions. MV films were compared to digitally‐reconstructed radiographs generated from the same CT dataset. The group mean, systematic error (σ), and random error (g) were calculated for positioning with MV and SI both before and after positioning correction. The 95% limits of agreement (LOA) were used for statistical comparisons. Results: Inter‐fraction systematic/random errors calculated from MV filming were 1.6/2.1mm (Anterior‐Posterior), 2.9/3.0mm (Cranio‐Caudal), and 2.4/4.1mm (Left‐Right), resulting in a setup margin of 5.5/9.4/9.0mm in AP/CC/LR dimensions using the van Herk formulation. Registering the “entire” and “breast” surfaces acquired before MV positioning correction resulted in setup margins that were larger by 1.6– 3.3mm in AP/LR but smaller by 0.4–0.6mm in CC direction, thereby indicating comparable inter‐fraction errors. After positioning with films, group means for the “entire” surface decreased by 0.5–2mm and the systematic/random errors decreased by 0.3–0.9mm. In contrast, group mean for “breast” increased in the CC direction. The LOA showed large discrepancies between the two modalities (smallest:‐3.5 to 10.3mm along AP for “entire”, largest:‐11.3 to 9.9mm along CC for “breast”). Conclusion: This study shows that the two modalities provide comparable systematic/random errors for breast positioning. However, MV positioning of bony anatomy led to a consistent cranio‐caudal offset (i.e., larger group mean) from the position indicated by AlignRT probably due to deformation of the breast tissue. These results suggest that the use of MV and SI should be integrated to ensure simultaneous coverage of chestwall and soft tissue targets.
SU‐E‐J‐61: Design, Construction, and Characterization of the Ultra‐Wideband (UWB) Directional Antennae for Biological Tissue Penetration
Authors: Oh E , Han‐Oh S
Published: July 2013

Purpose: The need for non‐invasive, non‐ionizing, non‐contact, and real‐time technique to detect lung‐tumor position during radiotherapy is an elusive feat. CT and MRI scans during radiotherapy are technically difficult and ultrasound cannot penetrate through the lung tissues. Recently, the development of the UWB radar promises a glimpse of hope in such an endeavor. Historically, the UWB was used to penetrate through walls and concrete for behind‐the‐wall imaging. Applying this technology to medical applications, as a first step, we investigate whether UWB can penetrate through biological tissues. For this purpose, we build and characterize unidirectional antennae to focus beam power and detect objects in free‐space. Methods: Our UWB system generating short pulses has omni‐directional antenna elements. We changed to uni‐directional beam by placing the element inside in‐house built horn‐antennae. A horn‐antenna is an antenna that consists of a flaring‐metal waveguide shaped like a horn to direct radio waves in a beam. We use waveguide theory to design the horn‐antenna. After successful construction, we measure angular energy distribution in both the H‐plane and the E‐plane. The spatial resolution is measured from the time‐of‐arrival of the returned pulse reflected from an aluminum plate which is moved in 1‐cm increment. Also, a small gold fiducial (0.1 cm by 1cm) is targeted for position detection. Results: The in‐house built unidirectional horn‐antennae have beam widths containing >50% energy within for H‐plane, and for E‐plane at 3.5 GHz. The spatial resolution of the current system is 0.915 cm. However, with future electronics modification, the spatial resolution can improve to 0.03 cm. The gold fiducial is detected with SNR=8. Conclusion: We built uni‐directional horn‐antenna and characterized angular beam width and spatial resolution. The system can detect a small size object such as gold fiducials with a high SNR. We will need further investigation to test penetration through biological tissues.
SU‐E‐J‐65: Evaluation of a Correction Algorithm for Improving the Accuracy of a Deformable Image Registration Algorithm
Authors: Mallya Y , Bzdusek K
Published: July 2013

Purpose: To evaluate a correction algorithm for enhancing the accuracy of deformation vector field generated by deformable image registration (DIR) techniques. Methods: Delineated contours of targets and organ at risk structures (OARs) in a pre‐treatment prostate CT image volume were automatically propagated to the treatment CT image volume using an intensity based deformable image registration. All of the datasets used in this study were associated with expert‐drawn contours for the structures in the treatment CT. The contours of the automatically propagated structures were corrected to match the corresponding expert‐drawn contours of the structures in the treatment CT image. A modified Demons DIR algorithm was used to compute the incremental displacement vector field(DVF) that represented the corrections made to the automatically propagated contours. The initial DVF that was used for contour propagation was synchronized to the corrected contours by creating a composite vector field from the initial and the incremental DVF. The composite DVF was then used to propagate contours of targets and organ at risk structures from the planning CT to the treatment CT. Resulting deformed contours for each structure were compared to its corresponding expert‐drawn contours using the Dice similarity coefficient(DSC) and Hausdorff distance(HD). Results: Visually the deformed contours using the corrected DVF were similar to the corrected and the expert‐drawn contours. The Hausdorff distance improved up to 0.24mm from 1.33mm(82% improvement) and the DSC improved from up to 0.96 from 0.78(24% improvement). Conclusion: The accuracy of the automatically propagated contours of targets and OARs using a corrected DVF were significantly higher than that obtained using the pre‐corrected DVF. Therefore the technique can be used as an independent post processing step to correct the DVF generated by a DIR technique. The method could potentially be used to improve accuracy of subsequent dose deformation and accumulation steps of adaptive therapy.
SU‐E‐J‐67: Regularized Deformable Registration of Computed Tomography Images Using Multiple Voxel Resolutions for Four Dimensional Radiation Therapy
Authors: Chao M , Lo Y
Published: July 2013

Purpose: Accurate, speedy, and robust image registration is deemed crucial in radiation therapy of cancer management. A multi‐resolution deformable image registration (DIR) using regularization strategy was developed for four dimensional radiation therapy. Methods: A multi‐resolution based deformable registration model was implemented with the regularization of energy term to smooth the deformation field. A B‐Spline model, although other models such as demons are applicable as well, was employed as the transformation with the Mattes mutual information as the objective function that was to be optimized the limited memory Broyden‐Fletcher‐Goldfarb‐Shanno algorithm (L‐BFGS) optimizer. A three level voxel resolution model was utilized for the coarse‐to‐fine strategy to improve the registration success rate and remove local optima at coarser scales. A regularization term was applied to the objective function and its parameters were investigated to have the optimal effect on the deformation vector field. Four dimensional computed tomography (4DCT) images from four thoracic and four abdominal cancer patients were used to evaluate the algorithm. Results: A quarter, half and full of the original voxel resolutions were adopted in the three levels respectively from the coarsest to the finest. An accuracy of 2 mm was achievable for thoracic cancer patients while slightly larger residual error at the average of 3 mm was observed in abdominal cancer patients. Under the same condition, larger errors were found from the calculation with a single resolution model. The smoothness of vector field was significantly improved with the regularization term. The parameters, however, have to be determined empirically. This feature is particularly useful when conducting dose warping. Conclusion: Significant improvement in DIR accuracy and robustness with the proposed algorithm is achieved. The novel deformable registration model, with more systematic study, will find its widespread application in radiation therapy.