bluuebunny/crossref_metadata_2025 huggingface dataset:
SU‐FF‐J‐41: Comparison of Various Respiration Measurement Methods for 4D Radiotherapy
Authors: Lim S , Park S , Ahn S , Yi B , Shin S , Lee S , Kim J , Choi E , Kwon S , Jeung T
Published: July 2006

Purpose: To find the best method corresponding with respiratory target motion, ten patients' respiratory patterns were measured by various methods simultaneously. Respective respiration monitoring methods were compared with fluoroscopic target motion during simulation. Method and Materials: A respiration monitoring system using thermocouple was developed to measure patient's respiration. Conventional spirometer and home made thermocouple were connected to a mouse piece to measure the patient's respiration simultaneously. A respiration acquisition program was built by using Labview 7.0 (National Instruments, Austin, TX), which acquire respiration signals and display its patterns. A fluoroscopic target tracking program was built by using IDL 6.1 (Research Systems, Inc, Boulder, CO). Ten patients with lung or liver cancer participated in this study. Fluoroscopic movies were captured during acquisition of their respiration patterns. At the same time their skin motion was measured by using Real‐time Position Management® (RPM®, Varian, Palo Alto, CA) system. Respiratory patterns from spirometer, thermocouple, and RPM® system were compared with fluoroscopic target motion respectively. Its relationships were evaluated as correlation coefficient. Results: Comparing each correlation coefficient for spirometer, thermocouple, and RPM®, skin motion detection is the most correspondent with fluoroscopic target motion. However, respiration monitoring methods with spirometer or thermocouple also correlate well (more than 0.9). Conclusion: Respiratory pattern depends on a patient and his/her conditions. The relationship between thermocouple and fluoroscopic target motion could be enhanced by correlating respiratory signal with target motion. Respiration monitoring methods with spirometer or thermocouple, and skin motion detection are feasible to monitor the target motion for applying 4D radiotherapy.
SU‐FF‐J‐42: Cone Beam CT Based Treatment Planning
Authors: Paliwal B , Tewatia D , Orton N , Tome W , Basavatia A
Published: July 2006

Purpose: To evaluate treatment planning based on cone beam CT (CBCT) using latest software on a LINAC 21IX CBCT imaging system. Method and Materials: An anthropomorphic chest phantom having bone, soft tissue, and lung components was used to create and evaluate treatment plans based on conventional CT and CBCT images. Conventional CT images of 2.5 mm slice thickness were taken with a GE discovery LS CT/PET system. CBCT images slices were also reconstructed from flat panel system on a Varian LINAC 21IX. Eclipse treatment planning system was used to compare treatment plans from the conventional CT and CBCT images. The AAA algorithm was used in the treatment planning system for inhomogeneity correction. Regions of interest around the bone, soft tissue, and lung in both CT and CBCT images using identical HU threshold values were drawn. Identical targets located in the lung were used in each treatment plan. Analysis of the treatment plans was performed by comparison of geometrical dimensions, total volumes and dose volume histograms of the target and regions of interest. Results: Geometric comparison of actual external spatial dimensions and others in lung and bone were found to be within 1 mm. Volumetric comparison of the regions of interest resulted in a 2.8% difference of the vertebrae, 3.3% of the right lung, and 3.7% of the total external volume. Dosimetric results show similar dose distributions. Dose volume histograms are also comparable. Conclusion: Results demonstrate that treatment planning based on CBCT is feasible. Plans created from CBCT images are comparable to plans created with conventional CT systems. Conflict of Interest: Partly funded by Prostate Cancer Foundation grant UW 133‐HR30.
SU‐FF‐J‐48: Developing In‐Line KV Fluoroscopic Verification for 4D Adaptive Radiotherapy
Authors: Li X , Khamene A , Tai A , Khater K , Celi J , Hristov D , Ofstad B
Published: July 2006

Purpose: To develop a system for on‐line real‐time treatment verification for 4D‐ART using in‐line kV fluoroscopy that will be included in a new generation of accelerator. Method and Materials: We have developed a software tool, as a component of the 4D‐ART verification system, to register fluoroscopic with dynamic (time‐sequenced) DRR (DDRR) images. The fluoroscopic images are obtained using kV x‐rays in‐line with the treatment‐beam direction. The DDRR images (DRRs at different phases during respiratory cycle) are generated from 4DCT. The image registration of DDRR and fluoroscopy is based on pre‐defined structures or points of interest and needs to be performed on‐line in real time, allowing the treatment parameters to be modified in real time if a discrepancy is observed. To approve the principle, we have employed a simulator (Siemens/Mevasim) to acquire the fluoroscopic images. Both hardware and software tools were developed to synchronize the acquisition of fluoroscopy with respiratory signal using a pressure sensor (Anzai). This synchronization, in turn, harmonizes fluoroscopic images with DDRR. The verification system was tested on a motion phantom and on lung cancer cases. Results: The system developed can effectively register respiration‐synchronized fluoroscopic and DDRR images for both phantom and patient data. The registration is able to detect discrepancies between planning images (DDRR) and verification images (in‐line fluoroscopy) for a 4D‐ART delivery. The system is found to be effective for validating respiratory gating. Conclusion: We have developed a treatment verification system for 4D‐ART. The system, employing in‐line kV fluoroscopy, may be used for validating respiratory gating and for 4D‐ART with the new generation of image‐guided delivery machine capable of in‐line dynamic imaging. The system can be also potentially useful for 4D real‐time tumor tracking based on fluoroscopy. Conflict of Interest: This work is supported in part by Siemens OCS.
SU‐FF‐J‐50: Dose Guidance in Radio Therapy by Means of Entrance Dosimetry
Authors: Hesse B M , Nill S , Tücking T , Oelfke U
Published: July 2006

Purpose: Recently, we introduced a novel hardware design for an image and dose guidance in radiation therapy. An in‐line cone‐beam CT was integrated on a Siemens linear accelerator providing a radiographic localisation of bone and soft‐tissue targets and an on‐line in vivo 3D reconstruction of delivered dose. In this presentation we focus on the aspect of dose guidance. We will present a new developed method of 3D in vivo dosimetry and the first clinical results. Method and Materials: A flat‐panel detector RIDXXX (Perkin Elmer) is mounted at the Linac head, in front of the patient. The flat‐panel was calibrated against a film measurement to consider off‐axis variations of the photon spectrum. Images of each therapy beam were recorded by the flat‐panel during beam delivery and beside dark correction each measured image was deconvoluted using an empirically derived scatter kernel resulting in a 2D distribution of the primary photon fluence which is comparable with the TPS fluence. As a final step the measured fluence distribution for each IMRT beam was fed into the TPS in order to reconstruct the delivered dose distribution in 3D. This method of entrance dosimetry was applied to 12 patients. Results: A generally good agreement of planned and reconstructed dose distribution was also seen for all patients. The error was calculated to be less than +/− 3% for all cases and a very good reproduction of all isodose contours was achieved, with agreement to within +/− 1mm in most places. Conclusion: A new method of 3D in vivo dosimetry called “Entrance Dosimetry” was developed. This kind of 3D in‐vivo dosimetry can be used for an off‐line treatment plan verification and for dose guidance by means of an on‐line delivered beam verification as well. Conflict of Interest: This work was partly supported by Siemens OCS.
SU‐FF‐J‐51: Dosimetric Evaluations of Organs at Risk for Head and Neck Cancer Patients During Entire IMRT Treatment Course
Authors: Wu Q , Meldolesi E , Chen P , Yan D
Published: July 2006

Purpose: Significant anatomic changes occur during radiotherapy treatment course for head and neck cancer patients. The purpose of this study is to evaluate the dosimetric changes by estimating the cumulative doses to critical organs. The finding will help better understand the uncertainties in initial plans and decisions making for replanning. Method and Materials: Patients treated with IMRT at our institution are immobilized on MedTec IPPS for simulation, CT and treatment. Guidelines from RTOG protocol are followed in defining target and organs at risk (OAR) volumes. Weekly helical CTs are acquired and fused to planning CT based on bony anatomy. Therefore, effect of setup error is excluded. OARs are delineated by a single physician manually on each CT. Dose distributions are recomputed for each CT using same beams from initial plan. Dose is evaluated for each CT and cumulative dose is estimated and compared with the original plan. Results: Up to 10% reduction on skin volume is observed for a single patient. However the average reduction is only 2%, because bony structures are fairly stable and shrinkage only occurs in soft tissues. The cumulative maximum doses to cord, brainstem and mandible, expressed as the ratio to initial plan, are 1.00±0.03, 1.01±0.08, and 1.01±0.08 respectively. The changes are minimal. For parotid glands, mean dose and V30 (volume to 30 Gy) can be increased by 10%, with up to 20% for a single patient. This is because parotid gland tends to move into the center of the field. Conclusion: Repeated CT scans during treatment course allow more accurate evaluations of the dose distributions, which can be significantly different from original plan due to radiation response of tumor and soft tissue. The cumulative doses are more reliable in describing the actual doses delivered and can be used for correlative studies with clinical results.
SU‐FF‐J‐56: Estimation of Lung Tumor Setup Uncertainties Using Bony Landmarks and Implanted Fiducials
Authors: Nelson C , Starkschall G , Morice R , Stevens C , Britton K , Chang J
Published: July 2006

Introduction: Setup uncertainties require margins to be placed around the internal target volume (ITV) so that the tumor stays within the treatment portal during the course of treatment. The purpose of this work is to estimate setup uncertainties for lung tumors using both bony anatomy and implanted fiducials as surrogates for tumor position. Methods and Materials: Fiducials were implanted in the periphery of lung tumors of 4 patients who were treated using respiratory gating. Setup uncertainties were quantified using the fiducials in the gated images (acquired from the electronic portal imaging device (EPID) operated in cine mode) each day, using the fiducials in the repeat 4D image acquisitions, using the bony anatomy in the repeat 4D image acquisitions. Standard deviation (SD) of population systematic uncertainty (Σ), and SD of random uncertainty (σ) were determined (in cm) from each patient's mean systematic and random setup uncertainties. Results; For the Left/Right (LR), Superior/Inferior (SI), Anterior/Posterior (AP) directions, respectively, using implanted fiducials during treatment, Σ was 0.41, 0.70, 0.47, and σ was 0.34, 0.45, 0.43. For the LR, SI, and AP directions measured using implanted fiducials on the repeat 4DCTs, Σ was 0.26, 0.26, 0.42, and σ was 0.29, 0.27, 0.45. For the LR, SI, and AP directions measured using bony anatomy on the repeat 4DCTs, Σ was 0.08, 0.36, 0.27, and σ was 0.24, 0.33, 0.43. Conclusions. We were able to quantify setup uncertainties using two surrogates for lung tumors using repeat 4DCT image acquisitions and gated EPID images. The SD of the systematic and random components of setup uncertainties varied up to 4.5 mm as measured on 4DCT and up to 7 mm as measured on EPID images suggesting that setup uncertainties can be significant.
SU‐FF‐J‐57: Evaluating Lung Motion Variations in Repeated 4D CT Studies Using Inverse Consistent Image Registration
Authors: Lu W , Song J , Christensen G , Parikh P , Zhao T , Hubenschmidt J , Bradley J , Low D
Published: July 2006

Purpose: To evaluate lung motion variations in repeated, amplitude‐based 4D CT studies using inverse consistent image registration. Method and Materials: Three patients with lung cancers were scanned twice with our 4D CT protocol. A 4D CT dataset was reconstructed using the amplitude and direction of an external respiratory signal. A thresholding‐based method was used to segment the lung. An inverse consistent image registration was used to estimate the intrafraction motion within each 4D study and the interfraction motion between two studies. This diffeomorphic registration jointly estimates the forward and reverse transformations providing more accurate correspondence between two images. We evaluated the lung motion variations in repeated 4D studies. Results: On average, the mean respiratory period changed by 11.5%, and the mean peak to peak amplitude changed by 6.8% for the three patients. The consistent image registration generated dense displacement vector fields which represented physiologically reasonable lung motion. In one patient, we observed that the motion patterns are similar in the inferior and posterior parts of the lung, but are different at the superior and anterior parts of the lung. In the other two patients, we observed less variation in lung motion patterns between the two studies. The interfraction motion at end of exhalation is generally small (< 3 mm). Conclusions: The results suggest that lung motion variation may be large for some parts of the lung in some patients. An updated 4D CT study may be needed on a treatment day for some patients. For other patients, one may use the 4D model built on a planning day to estimate lung motion with an external respiratory signal. Quantitative evaluations are under investigation.
SU‐FF‐J‐59: Evaluation of Segmenting Anatomical Sub‐Regions for Deformable Registration of Patient Lung 4DCT
Authors: Wu Z , Sharp G , Rietzel E
Published: July 2006

Purpose: To evaluate the advantages of segmenting the moving and less‐moving tissues for deformable registration of lung 4DCT data. Method and Materials: Deformable registration based on B‐spline optimization is used to register lung 4DCT data from end‐inhalation to end‐exhalation phase. The moving tissues (lungs, mediastinum, and abdomen) and less‐moving tissues (the rest) are segmented at each respiratory phase. Deformable registration between phases was conducted in two different ways and compared. The first method registers the entire CT volume at once. The other method registers the moving and less‐moving tissues separately, and merges the resultant vector fields together. Results: The performance of the registration methods with and without segmentation was evaluated on two lung 4DCT data sets. The deformation vector field near the chest wall as generated by the registration with segmentation demonstrates a discontinuity of deformation along the plural interface. Quantitative analysis shows that the vector fields produced by the two methods are comparable in most of the areas, but have significant differences along the plural interface. Conclusion: Our experiments suggest that registering the anatomical sub‐regions separately allows the registration to properly account for motion discontinuity along the plural interface. While the two methods produce similar overall warping, the segmentation will generate a more realistic registration in the vicinity of the plural interface. Conflict of Interest: research was supported in part by Varian Medical Systems.
SU‐FF‐J‐60: Evaluation of the Three Dimensional Localization Accuracy Using Cone‐Beam Computed Tomography of Varian On‐Board Imager (OBI)
Authors: Zhang L , Yan H , Yoo S , Yin F
Published: July 2006

Purpose: To evaluate 3 dimensional (3D) localization accuracy using cone‐beam computed tomography of a Varian On‐Board Imager (OBI) in a phantom study. Methods and Material: An anthromorphic pelvic phantom was used to simulate an actual patient positioning scenario. The possible patient shifts were simulated by moving the treatment couch on which the phantom was placed and immobilized. While the phantom was shifted from its planning position, a CBCT scan was taken, and 3D/3D matching was performed. The CBCT 3D volumetric image was registered with the planning CT images to reveal the displacement of the real phantom position from its planning position (i.e., the positioning error of the phantom). Then, the phantom position was automatically re‐positioned to compensate for the detected shift. Afterward, a second CBCT scan was taken, and 3D/3D matching was performed again to verify the re‐positioning accuracy (should be zero). A range of 3D translations are simulated and the corresponding positioning accuracy using CBCT of the OBI system was examined. Results: The results for translational shifts indicate that CBCT‐based 3D/3D matching is capable of detecting displacements ranging from 1mm to 10mm, and the accuracy is within 1mm. After re‐positioning of phantom, the phantom is positioned within 1mm from its planning position. Conclusion: The current results indicate that CBCT is capable of detecting positioning errors within 1 mm in three translation directions. More characteristics is to be investigated in the future, such as rotational shifts, image quality (slice thickness), treatment site (other than pelvic), and others. The study is partially supported by a Varian research grant.
SU‐FF‐J‐61: Evaluation of Two CT/MRI Fusion Algorithms Used for Treatment Planning
Authors: Workie D , Sehgal V , Roa D , Al‐Ghazi M , Kuo J , Ramsinghani N
Published: July 2006

Purpose: To evaluate the quality of two CT/MRI image fusion algorithms used for 3D‐CRT and IMRT treatment planning Method and Materials: Computed tomography‐magnetic resonance imaging (CT‐MRI) fusion was performed for nine patients with brain/head & neck lesions. Some patients have undergone both three dimensional conformal therapy (3D‐CRT) and intensity modulated radiation therapy (IMRT) using two commercially available treatment planning systems which we will refer to as system (1) and system (2), respectively. In order to quantify the fusion results bony landmarks, such as the ramus of the mandible or part of the skull bone, were outlined on the reformatted MRI and the position of the outline in reference to the same bony landmark on the CT image were measured. Results: Based on what was acceptable fusion for our clinicians, this preliminary study showed registration accuracy between CT and MRI within 3 mm and 2 mm for system (1) and (2), respectively. On system 2 the quality of the fusion, the bar display, was in the range 62.5% – 100%. We also found that getting full bar (100% — ‘perfect match’) is possible with reasonable effort if one uses three fiducial marks. Though the bar showed 100% fusion quality the fusion results were not satisfactory. We found better fusion using five or more fiducial points with 62.5 % to 75 % fusion quality. Conclusion: Fusion software in both systems provides sufficient CT‐MRI fusion accuracy. However, one has to be careful in interpreting the semi‐quantitative bar display in system (2) fusion results. We found that instead of going for a perfect matching bar using few fiducial marks one has to use more points, at least five, even if one gets lower percentage match as this is averaged over more landmarks.
SU‐FF‐J‐65: Feasibility Study of Management of Respiration Induced Target Motion for the Radiotherapy Treatment of Lung Cancer Patients in the Absence of a 4DCT Simulator
Authors: Sontag M , Chen H , Michalski D , Andrade R , Usiene I , Li F , Yue N , Heron D , Huq M
Published: July 2006

Purpose: Varian's RPM™ system for respiration induced tumor motion management allows acquisition of CT images and gated treatments under free breathing. 4DCT may not be possible because of lack availability of appropriate CT hardware or software. This study evaluated whether a breath hold CT scanning technique can be used as a substitute for a 4DCT scan. Materials and Methods: A 4DCT scan is obtained on a 4 slice GE Lightspeed™ scanner with the patient breathing freely and the respiratory period regulated using audiovisual cues from RPM™. Additional helical scans are obtained using an end inhalation or exhalation breath hold modified gating method (MGM). The PTV is drawn on the MGM scan(s) and for each of phase of the 4DCT scan. Comparison of target volume, centroid and extent of target volume is made between the MGM scan and the corresponding phase of the 4DCT scan. A treatment plan is developed using the MGM scan. Dose is recalculated using the 4DCT scan with the beam's isocenter and apertures obtained from the MGM scan. DVH comparison is made. Results: 20 patients had both a 4DCT scan and at least one MGM scan. 8 patients exhibited respiration induced target motion of >5 mm during free breathing. Maximum target motion observed was 25 mm. For 14 end inhalation scans, 9 passed, 3 passed marginally, and 2 failed the equivalency tests to the corresponding 4DCT scan. For 18 end exhalation scans, 14 passed, 4 passed marginally, and 0 failed the equivalency tests to the corresponding 4DCT scan. Conclusion: All end exhalation breath hold scans are suitable substitutes for the corresponding phase 50 4DCT scan. However only 6/18 patients exhibited sufficient (>5 mm) respiration induced target motion on which to base any conclusions about the suitability of MGM. Conflict of Interest: Research supported by Varian Medical Systems.
SU‐FF‐J‐73: Helical Tomotherapy Sinogram Deformation for Daily Adaptive Therapy
Authors: Outten S , Ramsey C
Published: July 2006

Purpose: To develop an algorithm for modifying a helical tomotherapy treatment delivery sequence based on a measured deformation and to test the algorithm by displacing artificially created test cases, and clinical test cases. Method and Materials: A geometric test case was created consisting of an equilateral triangle with a 5.2‐cm base located inside a circle with a 3.14‐cm radius. The circle/triangle extended uniformly superior/inferior for 3‐cm, and was centered at the machine isocenter. An inverse plan was created with the triangle irradiated to 2 cGy, and the circle irradiated to 1.5 cGy, yielding a 64 × 701 delivery sinogram. A clinical prostate treatment delivery was also used, where the Planning Target Volume (PTV) consisted of the prostate and seminal vesicles. The PTV was treated to 2 cGy per fraction, resulting in a 64 × 660 delivery sinogram. A program was developed to shift the MLC positions in each sinogram by a measured displacement of the target. A dose profile (measured with an ionization chamber) was incorporated into the algorithm to correct for off‐axis factors. The dose distributions for displacement test cases were offset by known amounts, and then measured using Kodak EDR2 radiographic film and Computed Radiography (CR) plates placed axially on a tomotherapy treatment couch. The distance of the dose shifts from isocenter, and the absolute doses were measured and compared between the original film, and the film with the vertical shift with and without off‐axis correction. Results: The delivery sinograms for the test cases were offset by 2.5 cm in only the vertical direction, 2.5 cm in only the horizontal direction, and 2.5 cm diagonally using the deformation algorithm. The measured distances were within 5 mm of the desired position. Conclusions: Presently, the deformation algorithm can correct for displacements up to 5 cm on a treatment slice.
SU‐FF‐J‐75: High Performance Dual KV & MV Imaging with One Detector
Authors: Ghelmansarai F , Gangadharan B , Bani‐Hashemi A , Hill D
Published: July 2006

Purpose: Recent developments in Adaptive Radiation Therapy (ART) leverage MV and kV X‐ray imaging to acquire patient images in treatment position. We have developed a kV X‐ray imaging system, in line with the MV treatment beam, which enables us to acquire: (i) 2D kV X‐ray images (single acquisitions and fluoroscopy) simultaneously with the MV treatment, (ii) 3D tomographic kV X‐ray images, and (iii) MV beam pattern and profile (for entrance dosimetry). Our imaging system utilizes a detector with wide dynamic range allowing us to achieve these technically challenging objectives. Methods and Materials: In the in‐line imaging system, the kV source is opposite to the linear accelerator target with its focal point 100cm from the isocenter. During kV imaging, the kV detector is deployed close to the exit window of the MV beam, which adds to the intensity of the MV beam seen by the detector. Providing all the possible modes of imaging requires a large dynamic range for the flat panel imager. Two multiple gain detectors from Perkin Elmer Optoelectronics were evaluated (XRD1640AN & XRD1621AN), their acquisition and interface parameters were defined. Results: kV CBCT imaging allows for 1% contrast in 4mm object to be visible with a dose of 3.4cGy (120kV) using 1mm slice thickness. Cross sectional images of a bar resolution phantom with a 5123 reconstruction allow for 0.9 lp/mm bars to be resolvable. Both detectors were evaluated for saturation at multiple MV energies. Conclusion: We have developed an imaging system that provides a challenging combination of high quality 2D KV imaging simultaneous with the MV treatment beam, 3D kV CBCT volumetric images, and the acquisition of the MV beam shape and profile (for entrance dosimetry). Conflict of Interest: Sponsored by Siemens.
SU‐FF‐J‐76: How to Account for Patient‐Specific Tumor Motion in Target Definition for Lung Cancer Treatment Planning: Dosimetric Comparison of a Multi‐Phase CT Simulation Approach and MRI Cine Study
Authors: Wang L , Feigenberg S , Chen L , Paskalev K , Jin L , Ma C
Published: July 2006

Purpose: In order to account for tumor motion, a multi‐phase CT scanning and MRI cine imaging were used to assist planning target volume (PTV) definition in treatment planning. In this work, we compared tumor coverage in the subsequent treatment delivery using these two approaches. Materials & Methods: Consented patients underwent CT simulation consisting 2 short scans taken at maximum inspiration and expiration breath holding conditions, in addition to a normal free‐breathing scan. These same patients went through MRI cine scanning. For treatment planning and delivery, we constructed a PTV from a combination of the targets delineated on all 3 CT scans after image registration by applying 3 mm margin (termed PTV_3CT). For this study, another PTV expansion was generated from the gross tumor volume (GTV) on the free breathing scan by margins that were determined by MRI cine (termed as PTV_MRI). Treatment planning using the same beam configurations and weights was performed on the PTV_MRI. Since a localization CT scan was obtained for each patient using a CT‐on‐rails system prior to each treatment, we are able to obtain the actual GTV in treatment position (GTV_tx) and compare their coverage for the plans designed for either the PTV_3CT or PTV_MRI. Results: For 5 patients and 20 GTV_tx studied, they were all within the PTV_MRI geometrically and have full dose coverage in terms of D95. However, for plans designed for PTV_3CT, 9 out of 20 of the GTV_tx were found, at a varying degree, to be partially out of the PTV_3CT and the coverage varies from 95.9% to 100% of the planned values. Although the difference in coverage is small, it is statistically significant, as the p‐value for the t‐test is 0.006. Conclusions: The MRI‐cine appears to be a better study of motion than the multiphase CT approach in this study.
SU‐FF‐J‐79: Implementation of Four Different Image‐Guided Radiotherapy (IGRT) Systems in a Radiotherapy Department
Authors: Li S , Hammoud R , Jin J , Liu D , Kim J , Guan H , Chen Q , Nurushev T , Andrews S , Walker E , Pradhan D , Ryu S , Ajlouni M , Movsas B
Published: July 2006

Purposes: to implement and compare four newly developed image‐guided radiotherapy systems (Varian's Cone‐Beam CT, BrainLAB ExacTrac, Restitu Ultrasound (U/S)‐Sim and Guide, and in‐house stereovision) in one department. Methods and Materials: The cone‐beam CT (CBCT) and the ultrasound (US) systems provide volumetric images of the target at daily setup. The ExacTrac system acquires the biplanar radiographs at patient setup. Both the US and ExacTrac systems are integrated with infrared‐tracking systems for patient‐couch positioning. The in‐house stereovision system captures 3D surface images of the patient at the instants of daily patient setup and during individual beam irradiation. All of four IGRT systems have used treatment planning volumetric imaging information for target position verification and adjustment. Electronic portal images are routinely used for patient position verification. External markers and possible internal markers such as seeds or small cysts or calcifications can be localized and used for additional verification. Results: Emerging data from several institutional IRB‐approved clinical trials demonstrate that the target reposition error and dose delivery uncertainties can be significantly reduced by using such image‐guided systems, each of which may be most useful in specific clinical situations. Conclusions: Our customized stereovision system, which, like US, involves no radiation exposure, is extremely efficient (<2 minutes) and accurate (<2 millimeters) for superficial sites, such as breast cancer. The ExacTrac system appears ideal for lesions associated with bony structures, such as spine and skull. The US and CBCT may be most useful for deformable internal structures, such as prostate cancer. Special methods for dealing with imaging artifacts, such as ring patterns in CBCT, shadow casts and multiple reflections in stereovision and US, and patient motion in ExacTrac and stereovision will be presented.
SU‐FF‐J‐81: Importance of Daily Portal Imaging for Head and Neck IMRT Treatments
Authors: Wolfsberger L , Tishler R , Allen A , James S , Killoran J , Court L
Published: July 2006

Purpose: To investigate the set up variation for head and neck IMRT patients based on daily portal imaging. Method and Materials: Reproducible patient setup is critical to accurate delivery of head and neck IMRT. At our institution, these patients are immobilized using a head‐neck‐shoulder thermoplastic immobilization system (S‐Type, Medtec) and a customized headrest. Orthogonal digital portal images are taken daily to check patient positioning and are compared with plan DRRs. Isocenter misalignments are corrected by the therapists using a couch shift, with a 3mm action level. Therapists also carefully examine patient positioning in the mask, especially shoulder position, and re‐position the patient in the mask if considered necessary. Isocenter shifts and frequency of patient repositioning were investigated by review of record‐and‐verify records for 15 patients. The magnitude of the shoulder respositioning was evaluated for 10 patients by comparing portal images and plan DRRs for a point 8cm inferior of isocenter, which is typically located at C2. Results: Isocenter discrepancies of 3mm or smaller were recorded for a median of 92.5% of fractions (range: 71.4 – 100%). Isocenter shifts larger than 5mm were only recorded twice (2 patients, 1 fraction each; 0.38% of all fractions). On the basis of pre‐treatment daily imaging, patients were repositioned in the immobilization mask before treatment for a median of 14% of fractions (range: 3–34%). Fifty nine percent of these repositioning were for a shoulder shift of less than 5mm. Thirty percent, however, were for shoulder shifts of 1cm or larger. Conclusion: With our current immobilization, daily isocenter positioning accuracy is excellent, while correct shoulder position is more variable. Frequent imaging of head and neck IMRT patients is essential to accurate delivery of therapy, with shoulder position an important factor.
SU‐FF‐J‐82: Improving Soft Tissue Contrast in 4D CT Images of Liver Cancer Patients Using Deformable Image Registration Method
Authors: Wang H , Krishnan S , Wang X , Beddar A , Briere T , Crane C , Mohan R , Dong L
Published: July 2006

Purpose: To investigate image quality improvement in 4DCT images of liver cancer patients by using deformable image registration. The low soft‐tissue contrast in liver CT images is always a challenge for accurate target delineation. Method and Materials: Ten patients with liver cancers were selected in this study. These patients received 4DCT scans for radiotherapy treatment planning using 120kVp and 150mA on a GE PET/CT system. The 4DCT images were retrospectively sorted and binned into 10 equispaced phases. The end‐expiration phase was chosen to be a reference phase, and the images from the other 9 phases were co‐registered to the reference phase using an intensity‐based, automatic deformable image registration algorithm. Then the 10 matched 4DCT images were averaged to give a single, high quality reference‐phase CT image for tumor target delineation. The image quality enhancement was quantified relative to the original CT by calculating the signal‐to‐noise ratio (SNR) inside the liver region. The incremental improvement in image quality was also studied by combining fewer 4DCT data sets. Results: The image contrast in the soft tissue region is noticeably improved. SNRs inside the liver increased for all patients by a factor of at least 2.3 (average at 3.0). The improvement in image quality is not linearly proportional to the number of images averaged. Averaging 6 CTs can achieve 85% of the SNR enhancement obtained by averaging all 10 CTs of different phases. Conclusion: We developed an effective method to improve soft tissue contrast in the liver by co‐registering and combining multiple CTs within the 4DCT data set using a deformable image registration method. The resultant, high‐quality, single‐phase CT could be used for better delineation of tumor target volume and critical avoidance structures. The deformable image registration method can also map these contoured structures back to each individual phases for motion‐compensated 4DCT planning.
SU‐FF‐J‐85: Inter‐Observer Variation In The Planning Of Head/Neck Radiotherapy
Authors: Lu L , Cuttino L , Barani I , Song S , Fatyga M , Murphy M , Keall P , Siebers J , Williamson J
Published: July 2006

Purpose: Understanding inter‐observer variation is not only important for evaluating deformable image registration (DIR) which can be used to automatically transform the manual contours of a treatment plan into daily contours facilitating offline or online adaptive radiotherapy, but also helps physicians set reasonable margins on the regions of interest (ROI) when they make treatment plans. The purpose of this study is to determine the observer variation for Head/Neck patients using the implemented radial‐difference approach and the common‐area method to study the observer‐drawn contour pairs. Method and Materials: Two sets of images for each of seven head and neck patients were taken several weeks apart, and the original image sets were used for treatment plans. For each image set, the ROIs: Primary GTV, Nodal GTV, Cord, left Parotid, and right Parotid were contoured by three experienced physicians. The difference of two contours drawn by different physicians was measured using: (1) the radial difference of the paired contours where the center‐mass of a contour is used as the origin of the polar coordinate system, and (2) the ratio of the common area of two contours over the total area of those contours, R=2[C1∩C2/(C1∪C2)]. Results for all the ROI are plotted in histograms to quantify the observer variation.

Results: The radial differences for primary GTV, nodal GTV, cord, left parotid, and right parotid are 2.7 ± 2.0 mm, 2.4 ± 1.9 mm, 1.8 ± 0.8 mm, 2.6 ± 2.1 mm, and 2.5 ± 1.9 mm, respectively, and the values of R are 0.75 ± 0.14, 0.82 ± 0.11, 0.82 ± 0.07, 0.80 ± 0.10, and 0.80 ± 0.12, respectively. Conclusion: The inter‐observer variations in the planning of Head/Neck patients are about 3 mm for Cord and 5 mm for the others. These values place an upper limit on the accuracy of DIR algorithm.
SU‐FF‐J‐86: Intra‐ and Inter‐Breath‐Hold Position Variations for OBI Guided Amplitude Gating Treatment with Breath Hold
Authors: Wang Z , Yin F , Marks L , Wu Q , Yoo S , Willett C
Published: July 2006

Purpose: We have applied OBI guidance together with a respiratory gating system to effectively control patient positioning for amplitude gating treatment with breath hold. The deep inspiration breath‐hold treatment has been proven effective in reducing the heart dose for left‐breast treatment. Breath‐hold technique is also useful for other sites where respiratory motion exists. In this study, we quantified the degree of intra‐fraction motion detected via continuous monitoring of patient position throughout treatment delivered during a single breath hold or multiple breath holds. Method and Materials: A real‐time position management (RPM) system (Varian, CA) was used to monitor radiation treatment for patients with tumors located in the thoracic through upper‐abdominal regions and the left breast. Simulation CT scans were acquired during breath holds when the breathing level was between the upper and lower thresholds that were preset in the RPM system. OBI kV radiographs and CBCT images were used to verify the patient position and breath‐hold level during the treatment sessions. To assure accurate positioning, the OBI/CBCT images were acquired only when the breathing level was within the same thresholds as those used for the simulation CT. Cine mode portal vision images were acquired every second during treatment. The intra‐ and inter‐breath‐hold position variations were analyzed based on the cine mode portal vision and kV radiographic images. Results: The intra‐/inter‐ breath‐hold position variations were analyzed for a total of ninety two fractions in six patients undergoing OBI guided breath‐hold treatments. The breath hold length ranged from 10 to 50 seconds. The intra‐breath‐hold position variation was within 2 mm. The inter‐breath‐hold position variation, within the same fraction, was within 4 mm. Conclusion: With proper OBI guidance and respiratory gating, the breath‐hold technique can effectively control the target position for treatment of cancer sites where respiratory motion exists.
SU‐FF‐J‐88: Intra‐Fraction Prostate Motion and Margin Calculations for Prostate Radiotherapy Using Electronic Portal Imaging, Implanted Fiducials and Four Localization Methods
Authors: Beltran C , Herman M
Published: July 2006

Purpose: This study presents the margins required for prostate EBRT if daily localization is based on skin marks, daily gold seed localization with a fixed threshold for correction, daily gold seed localization with no threshold, and daily bony anatomy alignment. The extent of intra‐fraction motion of the prostate is also presented. Method & Materials: Fiducial markers were placed in the prostate and their position was determined based on CT. Skin marks established initial localization (84 patients). The second localization method (40 patients), used orthogonal pretreatment electronic portal images to visually match the markers. If the 3D offset exceeded 5mm, the patient was shifted. The no threshold result was taken as the subset of the patient fractions where shifts occurred in method 2 (40 patients, average of 21 fractions). The final localization technique was bony anatomy match (67 patients). Through‐treatment EPIs were taken to document the prostate position during treatment; they were used to determine the margin for the fiducial localization and intra‐fractional analysis. Intra‐fractional analysis on 40 patients was accomplished by comparing the position of a particular seed between opposing treatment fields. Results: Margins for tattoo localization: Left‐Right 5.1mm, Inf‐Sup 5.8mm and Ant‐Post 8.4mm. Margins for the EPID with fiducials: Left‐Right 3.4mm (2.9mm with no threshold), Inf‐Sup 3.3mm (2.7mm with no threshold) and Ant‐Post 3.3mm (2.8mm with no threshold). Bony anatomy margins: Left‐Right 2.6mm, Inf‐Sup 7.3mm and Ant‐Post 8.9mm. Margins intra‐fraction motion: Left‐Right 2.1mm, Inf‐Sup 2.8mm and Ant‐Post 3.0mm. Conclusion: EPID localization allows a drastic (∼60%) margin reduction when compared to tattoo localization. Except for the Left‐Right, localizing on the bony anatomy leads to worse margins then tattoo setup. A significant intra‐fractional prostate motion exists which is a limiting factor on margin reduction. Conflict of Interest: Partial funding provided by Varian Medical Systems.
SU‐FF‐J‐91: Linear Methods for Hepatic Perfusion Imaging
Authors: Alspaugh JD , Cao Y
Published: July 2006

Purpose: Hepatic perfusion imaging could be valuable for assessment of therapeutic response and normal tissue toxicity in patients undergoing treatment for hepatic lesions. However, visual‐by‐visual estimation of liver perfusion using non‐linear least squares (NLLS) fits of dynamic contrast‐enhanced (DCE) CT or MRI data to a compartmental model with dual input functions is a computational expensive process. The purpose of this study is to develop and evaluate efficiency, stability, and bias of three linear methods for computation of hepatic perfusion parameters. Method and Materials: Through simple mathematical manipulation, the single compartmental model is converted into a linear equation (linear in three unknown parameters: arterial perfusion ka, portal vein perfusion kp, and the outflow rate k2). The ordinary least squares (OLS), total least squares (TLS), generalized linear least squares (GLLS), and NLLS methods were used for estimates of the perfusion parameters from simulated data that mimic normal liver perfusion. Gaussian‐distributed random noise was added into the theoretic time‐contrast concentration curves. The stability and bias of the three parameters were calculated from 5000 simulations as a function of contrast‐to‐noise ratio of the liver parenchyma, CNRL, and the temporal sampling interval, Δt, for each of the four methods. Results: Dependencies of the stability on CNRL (varied from 10 to 20) and Δt (1 to 8 seconds) were similar among all four methods, with NLLS and GLLS having slightly better stability. The increase in bias with Δt was greater for NLLS and GLLS than for TLS and OLS, particularly for estimates of ka. However, the computation time for NLLS was 10–100 times greater than for the linear methods. Conclusion: This study suggests that the linear methods can achieve the stability and bias similar to or better than NLLS, but substantially reduce the computation time, making liver perfusion imaging practical for use in clinical trials.
SU‐FF‐J‐92: Measurement of Linear Accelerator Photon Beam Spot Size and Assessment of Its Long‐Term Stability
Authors: Yeboah C
Published: July 2006

Purpose: To characterize the beam spot size of Siemens linear accelerators and assess its long‐term stability for megavoltage cone‐beam CT (MV‐CBCT) application. Method and Materials: A laminated beam spot camera of length 20 cm was constructed for the measurement of the beam spot size. With the linac gantry at 180°, the camera was positioned on the compensator tray and a Kodak XV film placed on it. An exposure was delivered using photon (6, 10, 18 MV) beams and the FWHM of the resulting source intensity profile used as a measure of the beam spot size. Measurement of the beam spot size was performed in both the gun‐target direction (in‐plane) and the cross‐plane direction for seven Siemens accelerators. To assess the long‐term stability of the beam spot size, measurements taken 1 year apart were compared to each other. Results: The measured beam spot diameters (FWHM) range from 1.6–2.8 mm. For all accelerators, the in‐plane spot size was equal to or larger than the corresponding cross‐plane spot size by up to 0.6 mm. Treatment units of the same design had spot sizes that were, in general, not identical but differed by up to 1 mm. Comparison of measurements on the Primus' and Mevatrons showed the introduction of the former (new generation accelerators) did not necessarily lead to a reduction in the spot size. Also, beam spot sizes measured 1 year apart were found to be similar. Conclusions: The new accelerator models did not in general provide an improvement in the spot size compared to the old models. Assessment of the long‐term stability of the beam spot showed the spot size remains fairly stable over time. However, the observed spot sizes are large in relation to focal spot size of diagnostic x‐ray imaging devices, and this might compromise MV‐CBCT image quality.
SU‐FF‐J‐93: Mechanical Accuracy of A Robotic Couch
Authors: Chung H , Jin H , Suh T , Palta J , Kim S
Published: July 2006

Purpose: To take full advantage of image guided radiation therapy (IGRT), the target shifts must be done accurately and efficiently. Recently, University of Florida, Radiation Oncology Department has implemented Medical Intelligent HexaPOD™ 6D Robotic Treatment CouchTOP. The purpose of this study is to determine the accuracy and efficiency of the HexaPOD™ CouchTOP system. Materials and Methods: The accuracy and efficiency of HexaPOD™ CouchTOP system were evaluated and compared with those of Varian and Elekta couch systems. All three couch systems were displaced in all three Cartesian coordinates and measured by BrainLab ExacTrac infrared (IR) camera system. To determine the efficiency of each couch system, average time spent for couch adjustment was recorded. Since HexaPOD™ system can be rotated with respect to three Cartesian axes, the rotation angular movement was evaluated for the HexaPOD™ system. Because the HexaPOD™ couch's default pivot point is not located at linear accelerator's isocenter, a user defined pivot point had been determined using a simple mathematical relationship. Results: For the average time of couch adjustment, 25 sec/1‐direction, 60 sec/1‐direction and < 20 sec/3‐direction were obtained for Varian, Elekta and HexaPOD™ couch systems, respectively. The average displacement differences in lateral direction for Varian, Elekta and HexaPOD™ were 0.33 ± 0.21, 0.33 ± 0.21 and 0.09 ± 0.11 mm, respectively. Similar results were observed for longitudinal and vertical directions. For roll angular movement, HexaPOD™ CouchTOP system was observed to be 0.01 ± 0.01°. Similar results were seen for both pitch and yaw angular directions. Conclusion: It is concluded that HexaPOD™ CouchTOP system has the capability to make target shifts to the accuracy of within sub‐millimeter and sub‐degree with efficiency.