bluuebunny/crossref_metadata_2025 huggingface dataset:
SU‐E‐J‐148: Dosimetric Changes During the Course of Image‐Guided Radiation Therapy of Prostate Cancer
Authors: Chen L , Shan G , Xu Q , Fan J , Chen X , Ma C
Published: July 2013

Purpose: This work investigates the dosimetric changes due to inter‐factional organ motion during the treatment course for IMRT of prostate cancer with in room CT guidance. Methods: Fifteen prostate cancer patients were recruited for this retrospective study. For each patient, MR and CT images were fused. IMRT treatment planning was performed on the simulation CT images. Inter‐fractional organ motion during the course of treatment was corrected using a Siemens CT‐on‐rails system. The prostate, rectum, bladder and femoral heads were outlined on both the original treatment plan and the subsequent daily CT images for 98 treatment factions by the same investigator. Dose distributions on these daily CT images were recalculated with the isocenter shifts relative to the simulation CT images. The doses from the subsequent daily CTs were co‐registered and compared with the original doses planned on the simulation CT. Results: Our results based on 15 patients (98 daily CT sets) with anatomical matching (i.e., matching the prostate contours from simulation CT scans with the prostate on daily CT‐on‐rails scans) showed that 7.1% of the treatment fractions exhibited poor target coverage (Dmin < 65Gy). For critical structures, 27.6% and 26.5% of the treatment fractions violated our rectal criteria of V65 < 17% and V40 < 35% for the rectum and 10% and 6% of the treatment fractions violated our bladder criteria of V65 < 25% and V40 < 50% for the bladder, respectively. Conclusion: The IGRT procedure for target localization using 3D imaging for prostate cancer is still not ideal if only anatomy matching is used. Future studies are warranted for improvements in target dose coverage using adaptive therapy through re‐planning or other target localization techniques such as that to match prescription isodose surfaces with target volumes to correct for both translational and rotational organ motion.
SU‐E‐J‐149: Heart Protection in Proton Therapy Using 4D Motion Analysis Based On Registration Between SENSE MRI and 4DCT
Authors: Chen T , Zou W , Zhang M , Yue N , Haffty B , Khan A , Goyal S
Published: July 2013

Purpose: Proton treatment on breast cancer requires optimal block on surrounding OARs including the heart to avoid radiation co mplications. The radiation dose to the heart is difficult to quantify since the heart moves under the influence of the respiratory motion and the cardiac motion; and as part of the cardiac motion the myocardium around the left ventricle rotates during the cardiac cycle. This study is to investigate the actual heart dose distribution by generating a 4D heart motion model through registration between SENSE MRI and planning CT. Methods: SENSE MRI has been utilized to acquire ECG gated 4D heart images for 4 patients. The slice thickness is 8mm, and the in plane spatial resolution is 1.4mm. 20 phases of MRI have been reconstructed to cover the whole cardiac cycle. The short axis (SA) images have been used to generate a 4D motion model through non‐rigid registration between phases. Anatomic land markers such as the papillary muscles and LV‐RV junctions have been used to constrain the registration to quantify the myocardial rotation. The reference MRI frame (end of systole) was registered to the treatment planning CT through model based meshless registration to translate the 3D dose distribution into the MRI image space and then the heart dose at different cardiac phases were derived based on registration results. Plan‐optimization was conducted to achieve optimal heart block. Results: The phase to phase registration demonstrated accuracy in the reconstructed motion. The average distance error at land markers is less than 1.5mm for two patients. The MRI‐to CT registration also has a satisfactory performance but still has the potential to be improved. A 4D dose reconstruction is possible given all the registration results. Conclusion: Based on the registration, 4D heart dose distribution can be generated to enable plan optimization for proton radiotherapy on breast cancer.
SU‐E‐J‐152: Fluoroscopic Treatment Verification for Gated Stereotactic Body Radiation Therapy of a Tumor Located Near the Dome of the Liver: A
Authors: Study Case , Gayou O , Christensen J , Kirichenko A
Published: July 2013

Purpose: To describe a method using pretreatment and intrafraction fluoroscopic verification of the gated treatment of a liver lesion located near the diaphragm. Methods: A 74‐year‐old female patient, who had previously received radiation to the lung, presented with a 13.8 cc tumor located 0.5 cm inferior to the superior border of the liver, moving 2 cm in the cranio‐caudal direction with breathing. A planning CT with contrast in full exhale breath hold (FEBH) was acquired to reduce motion artifact, followed by a 4‐dimensional (4D) CT. The gross target volume (GTV) was contoured on the FEBH CT and propagated only to the 25% inspiration (25In) and 25% expiration (25Ex) phases of the 4D‐CT, in order to reduce lung dose. An internal target volume (ITV) was created encompassing all 3 phases. A plan was created to deliver 50 Gy to the PTV (ITV+0.3cm laterally and inferiorly) in 5 fractions using 3D conformal planning gated on the FE, 25In and 25Ex phases. Digitally reconstructed radiographs (DRR) were created for each beam angle and for each of the 3 respiratory phases included in the gating window. Prior to treatment, a mega‐voltage (MV)‐CBCT was acquired and its projections were analyzed in cine‐mode. Intrafraction motion verification was monitored using MV‐fluoroscopy. On both cine and fluoroscopy movies, the respiratory phase was identified using the position of the diaphragm, and the frames were compared to the corresponding DRRs. Results: Qualitative analysis on both the pretreatment cine and intrafraction fluoroscopy movies showed a clinically acceptable agreement between plan and treatment position. Conclusion: We described a treatment verification method for gated SBRT of lesions near the dome of the liver, using pre‐treatment and intrafraction fluoroscopic movies. This method is a good gated treatment quality assurance tool allowing to confidently spare lung tissue.
SU‐E‐J‐155: Cardiac Dose Reduction in Left Sided Breast Using Breath Hold Tecnique
Authors: Lozares S , Fuentemilla N , Pellejero S , Manterola A , Miquelez S , Otal A , Olasolo J , Maneru F , Martin‐Albina M , Soto P , Rubio A
Published: July 2013

Purpose: In studies related to breast cancer and mortality, convincing evidence of an increased risk of cardiac morbidity following irradiation for leftsided breast cancer exists. The use of a breath hold technique enables a significant decrease of the dose to the heart as well as to the left anterior descending coronary artery (LAD). The purpose of deep inspiration Breath Hold (BH) is to expand the chest cavity during radiotherapy, which increases the distance between the breast to be treated and the heart. This allows for a lower heart dose as well as better PTV coverage. Methods: A study of 30 patients is showed. All patients underwent a free breathing (FB) and BH CT scan in supine treatment. Previously, the patient receives personal training to perform an adequate breathing and follows her own breathing cycle with glasses connected to the BH device. For simulation and treatment the same procedure as in the CT acquisition is performed. In the treatment, the patient placing includes daily image included in dosimetry. Results: The analysis compares the doses received in heart and LAD with FB and BH treatment. It presents data of medium dose with FB CT and BH CT and average and maximum dose (dose to 0.2 cm3) in LAD. The PTV coverage dose are between 95‐107 percentage of the prescribed dose is not present neither in the lung dose (V20) does not vary significantly.The DVH medium of LAD and heart (FB vs BH) is showed as well. Conclusion: The effects of radiation on the heart are late effects, which usually appear between 10 and 15 years after treatment. In young patients a dose reduction as drastic as that observed implies a reduced risk of heart disease a Result of radiation, which significantly increases the probability of survival over 10 years.
SU‐E‐J‐156: A 3D Camera Test‐Bed for Real‐Time Monitoring and Quantitative Tracking of Radiotherapy Treatment
Authors: Min Y , Santhanam A , Low D , Kupelian P
Published: July 2013

Purpose: To investigate methods for 3D camera‐based monitoring and quantitative tracking in the radiation therapy treatment room.Methods and Materials: A laboratory test‐bed for installing 3D cameras and testing 3D tracking algorithms was built to develop techniques for 3D treatment room monitoring. Kinect cameras were used as the 3D camera platforms. The cameras were anchored to a rigid framework attached to the laboratory walls to avoid vibrations and camera motion drift. Spatio‐temporal clustering algorithm was employed to remove camera fluttering noise. Features whose depth estimation varied by more than 3 mm in 1/3rd of a second were removed. A client server framework enabled the 3D treatment space to be visualized by remotely located experts in real‐time. A scalable multi GPU system that enabled 3D treatment space rendering in stereo and in real‐time was employed on the server side. For tracking both the patient body surface as well as the treatment room equipment, we investigated two different algorithms, using a Point Feature Histogram and multi‐resolution 3D Hough transform. For real‐time tracking we, also employed 2D multi‐resolution optical flow for effective temporal tracking on radiation equipment as well as the patient anatomy. Results: For remotely located experts, the treatment space visualization was conducted at 40 fps with a resolution of 640 × 480 pixels. Sub‐millimeter accuracy for tracking the patient body surface as well as the treatment room equipment was obtained when the tracked features were <120 cm from any of the 3D cameras, degrading with increasing distance. Conclusion: Remote real‐time stereoscopic patient setup visualization is feasible, enabling expansion of high quality radiation therapy into challenging environments. For both tested tracking approaches, the run‐time analysis showed the need for GPU hardware to track features in real‐time.
SU‐E‐J‐157: Evaluation of Surface‐Tracking and Respiratory Gating Capacities of a Novel Surface‐Mapping System Using Deformable Image Registration
Authors: Xie X , Cao D , Mehta V , Shepard D
Published: July 2013

Purpose: We have tested the capabilities of an innovative surface‐mapping system that utilizes deformable image registration tools (C‐RAD Catalyst). Its 3D positioning stability has been verified as well as its respiratory capabilities. Methods: The Catalyst daily QA phantom was used to test the stability of the system. A MatriXX ion‐chamber array in a solid water phantom was mounted on a motion platform which can provide longitudinal 1D motion.The vertical‐motion plate (respiratory plate) of the platform was used to mimic the chest movement in respiratory cycles. The respiratory plate was tracked by the Catalyst surface‐mapping system. A static 10×10 field was first delivered to establish the baseline. Gated deliveries using different gating windows (from 10% to 90% duty cycle) were also performed and the results were recorded. A comparison between the Catalyst surface tracking signal and ABC data was performed for a breast cancer patient on‐treatment. Results: Analysis of the experiment data indicates that the Catalyst is stable and reliable in detecting surface position and movement. With 50 numbers of phantom setups, the mean deviation of the shifts and rotations along all three directions was 0.6mm and 0.02 degrees, respectively. The gating capacity study suggested that respiratory gating using Catalyst system on an Elekta linac can be delivered safely and accurately. In fact, in gated beam delivery with the Catalyst system, dose distribution, dose profiles, gamma passing rates all show improvements as the gating window gets smaller. Gamma passing rates increase from 84.7% at non‐gating to 95.6% at 10% gating window. The Catalyst system also correctly recognizes the respiratory pattern of a patient under our ABC gated treatment delivery. Conclusion: Based on a phantom study and clinical observations, we have found that Catalyst system is robust in surface tracking and positioning. It also can serve as a respiratory gating solution. Funded by Elekta
SU‐E‐J‐163: The Imaging Dose to Patients Resulting From the ExacTrac X‐Ray System
Authors: Ding G , Luo G
Published: July 2013

Purpose: There is a lack of reported data on imaging dose from Novalis ExacTrac use for image guided radiotherapy. This investigation is to assess the imaging doses to patients resulting from a variety of clinical default imaging acquisition protocols in the ExacTrac x‐ray imaging system. Methods: Novalis TX ExacTrac x‐ray system (BrainLab, Feldkirchen, Germany) is investigated. This system consists of two floor‐mounted kilovoltage X‐ray tubes projecting obliquely onto two flat‐panel detectors mounted on the ceiling. The dose measurements were performed using an ion chamber inserted in a phantom. The air kerma calibration factor of the ion chamber for x‐ray beams specified by the half‐value layer was obtained from an Accredited Dosimetry Calibration Laboratory. The imaging dose from clinical default protocols including Cranium, Thorax and Abdomen were studied. The phantom, in the size of 30×12×30 cm3, was made from slabs of water‐equivalent materials for low energy x‐rays, PW‐LR (CIRS, Norfolk, VA). Results: The field size of x‐rays from each tube is 20×20 cm2 at the isocenter. Small differences of 5–10 % in measured radiation dose at the isocenter between two x‐ray tubes were observed. The doses measured in the phantom at a depth of 1 cm from the treatment table were 0.05 cGy, 0.16 cGy, and 0.19 cGy resulting from a pair of obliquely beams of Cranium‐heavy, Thorax‐Heavy and Abdomen‐Heavy clinical protocols respectively. It was found that there was up to 77% dose reduction by selecting Abdomen‐Light instead of Abdomen‐Heavy acquisition protocols. Conclusion: Although the imaging doses to patients resulting from a single pair of beams are low, the sum of multiple acquisitions (10‐20 pairs) is still significant, which can be common for one treatment fraction if non‐coplanar beams are used. The imaging doses strongly depend on the image acquisition protocols. During treatment, the low dose protocols should be chosen, given that image quality is not compromised.
SU‐E‐J‐168: Investigating the Feasibility of Vertical CBCT Imaging Using the Varian TrueBeam LINAC
Authors: Fave X , Balter P , Martin R , Ahmad M , Pan T , Court L
Published: July 2013

Purpose: To assess the TrueBeam LINACs imaging capabilities for taking vertical CBCT in order to provide an alternative treatment position for radiation therapy patients. Methods: The TrueBeam LINAC was programmed to take upright (vertical) CBCT images as follows: The LINAC gantry was positioned at 0 degrees with the x‐ray tube and detector in lateral positions. The x‐ray tube remained stationary and took fluoroscopic (projection) images as the couch rotated 180 degrees from 90 to 270 degrees. The x‐ray tube current was normalized to give the same dose (measured using a calibrated Farmer chamber), as that received during a clinical scan, to the center of a cylindrical, polyethylene phantom. Images were taken of CATPhan and anthropomorphic phantoms and reconstructed using in‐house CBCT reconstruction software. For thoracic scans, the detector was moved 10cm in the superior direction before rotating the couch 180 degrees. Then the detector was moved 10cm in the inferior direction and the couch rotated 180 degrees again. This was done to increase our field of view. For each reconstruction, spatial linearity and image quality were compared. Results: CBCT images were reconstructed and compared for horizontal and vertical scans. Spatial linearity was measured to be correct within 1mm for vertical CBCT images. Image quality decreased in reconstructed vertical CBCT images from that achieved in clinical mode for supine patients. Reasons for this included reduced scan angle and lack of a bow‐tie filter in upright CBCT imaging. Conclusion: We studied the feasibility of using the TrueBeam LINACs imaging capabilities to take CBCT images of patients in an upright position. Research is ongoing to improve image quality in order to establish a clinical protocol for treatment planning and patient setup. Future plans include adding a bow‐tie filter and adjusting for drift in the couch rotation through the use of a pin phantom. This project was partially funded by Varian Medical Systems.
SU‐E‐J‐170: The Effect of Modified Metal Artifact Suppression Method for Proton Planning
Authors: Lin C , Lee T
Published: July 2013

Purpose: The presence of high atomic number (high‐Z) materials in CT images may create significant artifacts, called metal artifacts, which are accompanied by bright and dark shadows and streaks on CT images. The impact of incorrect CT numbers caused by metal artifacts may lead to inaccurate dose distribution in treatment planning system, especially for proton therapy. The goal of this study is to reduce the metal artifacts using modified metal artifact suppression method (MMAS) for gold fiducial markers and discover the differences of dose distribution with and without it. Methods: CT images of water phantom with gold fiducial markers were used. First, the metal artifact suppression method was used to reduce the streak artifacts. The metal parts were properly extracted by thresholding and preserved. Using smoothing and polynomial interpolation methods to reduce artifacts around metal object. Then, the treatment plans with and without MMAS CT images for proton therapy were compared using dose distributions, conformity index and homogeneity index. Results: Comparisons of the plans with CT images with and without MMAS show significant changes in dose around gold fiducial markers. These errors of CT numbers caused by metal artifacts appear underdosage or overdosage to the tumor and surrounding normal tissues shown on proton treatment plans. Conclusion: This work indicates the importance of reduction of metal artifacts for proton therapy planning. Underestimation or overestimation to tumor dose and / or critical organs would impact the treatment outcome.
SU‐E‐J‐173: Brachytherapy for Prostate Cancer Under Computed Tomography Control: Reduction of CT Dose
Authors: Sanin D
Published: July 2013

Purpose: The aim of this work is the selection of the optimal algorithm of brachytherapy for prostate cancer under control of computer tomography (CT), to reduce CT effective dose received by the patient during the procedure, while maintaining the quality of the treatment. Methods: Estimation of effective dose was carried out by using the DLP. Results: Derating of the X‐ray tube for 10% of the effective dose is reduced by almost 50%, a further reduction of parameters increases the noise in the image, which is unacceptable for the visualization of critical organs during brachytherapy. Conclusion: It is shown that with the right approach to the planning and implementation of brachytherapy for prostate cancer under control of computer tomography is possible to reduce the effective dose of X‐rays up to 50%. This capability reduces the risk of long‐term effects, and improves the quality medical services. Based on data from the study formed a specialized protocol of brachytherapy for prostate cancer.
SU‐E‐J‐174: Performance and Operation of a New Magnetic Resonance Simulator for Radiation Therapy
Authors: Hua C , Uh J , Brady S , Krasin M , Merchant T
Published: July 2013

Purpose: To characterize system performance and describe clinical operation of a new magnetic resonance simulator for radiation therapy. Methods: Radiofrequency receiver coils consist of standard diagnostic and special coils for radiation therapy, including a flat indexed body coil and an immobilization device‐compatible head coil under development. The system performance of a 1.5 Tesla magnetic resonance (MR) simulator, SciMedix SM160, was characterized based on the acceptance testing and quality assurance procedures for MR imaging (MRI) described in the AAPM report No. 100, the MRI accreditation quality control manual of the American College of Radiology (ACR), and tests adapted from quality assurance programs for computed‐tomography simulators. Results: All test results of image quality met ACR acceptance criteria. B0 inhomogeneity measured over 45 cm diameter sphere was 8.8 ppm peak to peak. The B0 drift rate measured over 10 consecutive days after acceptance testing was 0.22 ppm/day. The maximum signal intensity was demonstrated with 90 degree spin nutation, indicating the transmitter gain was properly calibrated. Luminance non‐uniformity of the display monitor was 6%. TG18‐QC test patterns were resolved on the monitor. We have established routine quality assurance tests and facility safety checklists. Imaging protocols tailored to our unique patient population and tumor locations were built. Conclusion: The evaluated MR simulator demonstrated satisfactory system performance and suitable clinical image quality of anatomical imaging sequences. The patient couch is being redesigned to meet radiotherapy requirements of high positional accuracy. We have begun to utilize this system clinically for tumor and normal tissue delineation in treatment planning and for monitoring tumor volume change during the radiation therapy course.
SU‐E‐J‐185: Comparison of Iodine‐Labeled Sc‐Fv‐Fc Protein Biodistributions to Indium‐Labeled Biodistributions in Nude Mice
Authors: Kenanova V , Olafsen T , Wu A , Yazaki P , Williams L
Published: July 2013

Purpose: Animal biodistributions (BDs) are necessary to demonstrate radiopharmaceutical targeting. Radioiodine labeling requires considerably less novel agent material as compared to radiometal labeling. Yet iodine BDs show uptakes that are reduced in magnitude due to tissue metabolism and dehalogenation. It is important to measure the magnitude of this effect and thereby determine whether an iodine‐BD could be converted mathematically into the comparable metal‐BD. Methods: LS174T human colon tumors were implanted in nude mice. Simultaneous (I‐125 and In‐111) BDs were obtained using the H310A single‐chain Fv‐Fc antibody (105 kDa) fragment against CEA. Animals were sacrificed at 0, 2, 4, 6, 12, 24, 48 and 72 h post injection. Excised organs, tumor and blood were assayed for percent injected dose per gram of tissue (%ID/g). Curves were generated of %ID/g vs. time for liver, kidney, spleen, lungs, tumor and whole blood. In analogy with radiodecay, ratios of the iodine/indium BDs were fitted with single‐exponential functions to determine initial halftimes of organ loss of iodine. Results: For solid tissues at time > 0, iodine‐125 BD values were lower than the simultaneous In‐111 BD. Hepatic results were the most dramatic with losses of nearly 90% of the iodine by 12 h into the study. For the colon tumor, there was a moderate decrease (approx. 50%) in the iodine BD as compared to the In‐111 BD over 24 h. Blood showed no significant clearance difference between labels. Conclusions: Iodine losses for liver, kidneys, spleen and lungs could be described by initial T1/2 values of 1.3, 3.6, 3.5 and 10 h respectively. Tumor clearance (7 h) was comparable to lung. Liver was the most effective organ in removing iodine with similar but reduced effects seen in other solid tissues. No dehalogenation appeared in the blood out to 72 h. Dept of the Army grants DAMD 17‐00‐1‐203 and 17‐00‐1‐0150 for Anna Wu
SU‐E‐J‐191: Detectability of Dose Delivery Changes in Cancer Patients Based On Portal Dosimetry
Authors: Persoon LCGG , Troost EGC , Podesta M , Nijsten SMJJG , Verhaegen F
Published: July 2013

Purpose: During the course of radiotherapy the dose delivery can be influenced by a number of factors, e.g., anatomical changes over time. This can Result in discrepancies between planned and delivered dose. The electronic portal imaging device has been demonstrated to be valuable for 2D transit and 3D in‐vivo dose verification. The aim of this study was to investigate what type of patient‐related errors can be detected by quantifying the discrepancies based on 2D transit portal dosimetry. Methods: For 25 cancer patients treated with volumetric modulated arc therapy, changes were artificially introduced in the planning CT. The artificially introduced changes were: 1) Development and reduction of atelectasis in the lung; 2) weight loss and gain; 3) shift of the patient, and 4) base‐line shifts in anatomical structures. After introduction of the changes, 3D dose distributions were recalculated with the Eclipse treatment planning system and compared to the planned dose distribution using a 3D γ evaluation. The 2D portal dose images were predicted with in‐house developed algorithms and compared with 2D γ evaluation and dose difference maps. Results: Several of the introduced changes were found to lead to significant discrepancies in dose metrics derived from dose‐volume histograms or 3D γ distributions, which could also be detected by 2D transit portal dosimetry. Clear dose discrepancy trends over time were observed with increasing geometrical aberration. Conclusion: We have shown the relationship between 3D dose discrepancies and 2D portal dosimetry. Lower detection limits will be determined for the different anatomical changes introduced. This analysis may form the basis for decision making in adaptive radiotherapy.
SU‐E‐J‐196: Evaluation of the Relationship Between Tumor Thickness and Relative Pixel Value in Dual Energy (DE) Imaging
Authors: Jung F , Luce J , Roeske J
Published: July 2013

Purpose: To determine the relationship between simulated tumor thickness and signal intensity in a dual energy (DE) subtraction image. Methods: A phantom was constructed using cork (simulating lung), tissue equivalent material, and pork ribs. While keeping the total phantom thickness constant (16 cm), the thickness of cork was varied from 8–12 cm. Simulated tumors with thicknesses ranging from 1–5 cm were placed within inserts inside the cork. Ribs were placed on top of the phantom such that they overlapped the simulated tumor on a planar radiograph. Planar x‐ray images were subsequently acquired using 60 kVp (4 mAs) and 120 kVp (1 mAs) for the various combinations of cork and simulated tumor thicknesses. DE subtraction was performed for each image set to provide rib suppression. Pixel intensity values of the simulated tumor on DE images were obtained and plotted vs. tumor thickness. Results: This study yielded a linear relationship between the simulated tumor thickness and DE pixel value. The relative pixel value increased with increasing tumor thickness. Moreover, the slope was nearly independent of the thickness of cork. The effect of the cork was to shift the intercept, with larger thicknesses of cork resulting in a more negative intercept value. Conclusion: The results of this study illustrate a linear relationship between DE signal intensity and simulated tumor thickness. By demonstrating this relationship, DE imaging may be used as a quantitative means to quickly and efficiently assess 3D tumor response in lung cancer patients. Using this technique, DE imaging may provide a means of screening for patients who are candidates for adaptive radiotherapy. Project supported by a grant from Varian Medical Systems.
SU‐E‐J‐199: An Image‐Based Model of Glioblastoma Growth for Treatment Response Assessment
Authors: Schreibmann E , Crocker I , Shu H , Fox T
Published: July 2013

Purpose: To develop a mathematical model of tumor growth based on MRI imaging to predict tumor growth, with potential applications in treatment response assessment to differentiate responding and non‐responding tumor types. Method: The model is composed of 3 terms describing tumor proliferation, diffusion in various tissue types, and radiation treatment effect. The proliferation terms describes the rate at which the cell replicates while the diffusion term describes tumor invasion into adjacent tissue. The radiotherapy effect term models cell response to radiation through a linear quadratic radiobiological model. Tissue‐specific evolution taking into account the differential diffusion in white and gray matter is accomplished by segmenting T1Pre, T1POST and FLAIR images using a support vector machine (SVM) algorithm. Patient specific model parameters of perfusion and diffusion are deduced from 3 serial apparent diffusion coefficients (ADC) imaging maps that are evolved under the guidance of a partial differential equation to deduce tumor evolution at later times. Results: The model tumor was applied on 19 glioblastoma patients and initialized from their ADC maps acquired before, after and 1 month after treatment completion. Voxel wise maps of the perfusion, diffusion and tumor spreading speed were created to assess treatment efficiency. The proliferation was measured in region enhancing in the pre‐treatment imaging and ranged between −0.0189 and 0.00820 mm/day while the diffusion coefficients ranged between 0.0317 and 0.4721 per day. Conclusion: We have developed a tumor growth model and applied it on clinical patients to estimate response to treatment. The model may find also applications follow‐up method for radiation treatments as well as in designing treatment margins that take into account tumor diffusion speed and direction.
SU‐E‐J‐201: Correlations Between Mechanical and Structural Anisotropy: A Foundation for Non‐Invasively Assessing Radiation Injury
Authors: Feng Y , Okamoto R , Du D , Mutic S , Genin G , Bayly P , Hu Y
Published: July 2013

Purpose: Tour long‐term goal is to develop techniques for evaluating radiation injury based upon mechanical changes to tissue. Here, we study the mechanical response of white matter ex vivo using dynamic shear testing (DST) and indentation testing in an animal model, with the goals of establishing in normal (non‐radiation‐injured) tissue (1) a baseline degree of mechanical anisotropy, and (2) correlations between mechanical and structural anisotropy. Methods: Fresh whole brains were acquired from local slaughter house. White matter samples were dissected and from the central corpus callosum region, while gray matter samples were acquired from temporal region. Dynamic shear testing and indentation testing were applied to both white and gray matter samples. White matter samples were tested in shear with axonal fibers aligned or perpendicular to the shear force direction, and in indentation with the fiber axis parallel or perpendicular to the long side of the indenter head. Gray matter samples were tested in an arbitrary direction and rotated 90 degrees for the second test, for each testing procedure. Shear modulus and indentation stiffness were calculated for each sample. Results: The storage and loss moduli of the white matter samples were significantly larger when the samples were tested with primary axonal fibers aligned with the shearing direction. The indentation stiffness was also significantly higher when indented perpendicular to the fiber direction. No significant differences were observed for gray matter samples for both testing procedures. Conclusion: The results confirm that white matter exhibits larger moduli when stretched or sheared along the fiber direction; mechanical anisotropy correlates with structural anisotropy. The mechanical isotropy observed in gray matter is consistent with the structural isotropy. These results will be useful for investigations of changes in mechanical properties after radiation therapy in cerebral tumor patients, and for numerical modeling of surgery and traumatic brain injury (TBI).
SU‐E‐J‐206: Delivered Dose to Organs From CBCT‐Based IGRT of the Prostate
Authors: Liu C , Kumarasiri A , Chetty I , Kim J
Published: July 2013

Purpose: To estimate the actual delivered dose to organs from CBCT‐based image‐guided radiation therapy for localized prostate cancer treatments. Methods: Seven localized prostate cancer treatments were retrospectively selected, each with ∼40 CBCT images. All patients were treated with 9 IMRT beams. The PTV margin was 6 mm in the posterior direction, and 10 mm otherwise around the prostate. For each patient, the original plan was used to calculate treatment dose on each CBCT image at treatment position. The calculated daily dose was then warped back to the original planning CT via an intensity‐based B‐spline deformable image registration (DIR) algorithm. The DIR algorithm employed mutual information with a multi‐resolution and multi‐stage scheme. From the transferred total cumulative dose, dosimetric parameters were recorded for comparison with the original plan. The quality of prostate registration was quantified using three implanted fiducial markers. Only those cases with < 2mm error were included in the dose analysis. Results: The overall marker displacement was 1.8±1.8 mm after registrations. 75 of 281 registrations (27%) exceeded the 2 mm error threshold. The primary causes were the excessive noise level on CBCT images especially for large patients, presence of rectum gas, and lower abdominal motion artifacts. Excluding these cases, a total of 206 CBCT images were included in dosimetric analysis. Changes in dose coverage to the prostate was minimal (<1%). Dose deviations for rectum (Dmax, V50, V65, V75) were (0.5±1.0%, 2.6±2.5%, 3.5±3.7%, 2.3±4.2%) and (−1.1−0.9%, −2.5±5.3%, −3.0±5.3%, −3.8±4.9%) for bladder, respectively. Conclusion: With the conventional PTV margins, deviations in dose coverage of the prostate in the face of daily anatomic changes were minor However, relatively larger deviations were observed for rectum and bladder (1SD=∼4.3%). Reduced margins may lower dose to critical organs while maintaining target coverage. However, margin reduction must be viewed cautiously and with consideration of clinical outcomes.
SU‐E‐J‐213: An Evaluation of the Reproducibility of Radiotherapy Contouring Utilizing Multiple Institutions and Treatment Planning Systems
Authors: Pogson E , McNamara J , Jameson M , McDowall R , Lim A , Dempsey C , Metcalfe P , Holloway L
Published: July 2013

Purpose: Consistency of radiotherapy contours is required to ensure consistency of treatment and for this reason many studies have been undertaken and are expected in the future comparing contours of multiple observers or systems. This study was undertaken to determine the minimum uncertainty achievable when undertaking this type of investigation including multiple centres and treatment planning systems. Methods: A Computed Tomography (CT) scan was taken of a commercially available uniformity Phantom. This dataset was then imported into various contouring software programs including Pinnacle, Xio and Focal at the same institution and variations at different institutions. Contours of the perimeter of the phantom and a detailed cylinder inside the phantom were contoured using the same observer at provided window levels. The perimeter of the phantom was auto‐contoured using auto‐threshold. The inside circle was contoured manually. Contours were then exported from the treatment planning systems and into CERR for analysis. Results: A comparison of the phantom perimeter from Focal and Pinnacle at a single institution demonstrated a Concordance Index (CI) of 0.98, while the manually contoured cylinder has a CI of 0.77. When comparing between institutions the CI ranged from 0.75–0.85 for the cylinder. Variation in the phantom perimeter contours was mainly in the Z direction with 2 slices (0.4cm) not being contoured in Focal compared to Pinnacle. Maximum variation in the X and Y direction for the phantom perimeter was 0.098cm. The centre of mass of all phantom perimeter contours were within 0.10cm, with the largest variance between institutions occurring in the anterior‐posterior direction. Conclusion: The variation between auto‐contouring and manually contouring a high contrast object for different treatment planning systems has been established. As expected manually contouring produces greater variation than auto‐threshold contours between different treatment planning system. Funding from Cancer Australia and The National Breast Cancer Foundation, Project grant 1033237
SU‐E‐J‐218: Dosimetric Uncertainty Induced by CT‐MRI Fusion in Prostate Treatment Planning
Authors: Chen X , Xue J , Fan J , Chen L , Ma C
Published: July 2013

Purpose: Fused CT‐MRI data are increasingly used in prostate cancer radiotherapy to achieve more accurate definition of target and critical organs. However, fusion uncertainty may cause target miss or healthy tissue overdose. This study aimed to investigate the dosimetric uncertainty induced by the CT‐MRI fusion in prostate treatment planning. Methods: Patients (n=10) were treated with IMRT and image‐guidance techniques including CBCT/BAT‐ultrasound, gold seed markers, or Calypso for target localization. Each patient had both CT and MRI simulations, and the CT‐MRI scans were performed with a <30 minute interval to minimize organ changes, except for Calypso patients who had MRI scans before radio‐transponders implantation followed by CT scans one week after MRI. Paired CT‐MRI images were fused primarily based on bony structure matching. The prostate, rectum and bladder were delineated both on CT and MRI, separately. Following our clinical acceptance criteria, prostate treatment plans were created using Eclipse based on MRI‐defined target/organs. The dosimetric differences between CT‐and MRI‐defined target/organs were analyzed. Results: Most patients showed adequate coverage for both CT‐and MRI‐defined targets (100%). The difference between CT‐and MRI‐defined targets is 2.1±4.8% for minimal dose, 0.3±0.4% for maximal dose, and 0.1±0.1% for mean dose. The maximal difference is 11.9% for minimal dose, 0.9% for maximal dose, and 0.2% for mean dose. Conclusion: With bony structure matching, most patients showed acceptable dosimetric uncertainty induced by CT‐MRI fusion. Particularly, the target is well covered by the prescribed dose. However, significant underdose may exist, for example, 11.9% minimal dose difference between CT‐and MRI‐defined targets. With CT‐MRI fusion as a systemic error, the additional inter‐fractional or intra‐fractional motion may further increase the dosimetric uncertainty. Attention should be paid to the fusion uncertainty for the soft tissue target and proper PTV margins should be made to ensure target coverage, if necessary.
SU‐E‐J‐219: The Performance Test of EPID for In‐Vivo Dosimetry
Authors: Saotome N , Kida S , Imae T , Sasaki K , Sakumi A , Masutani Y , Haga A , Gawa K Naka
Published: July 2013

Purpose: An electronic portal imaging device (EPID) imaging is one of the promising tools to observe the dose in real time with a dynamic treatment. From our previous measurement, it was found likely that irradiation field was displaced more than 0.5 mm on the gantry‐rotating axis, and such an error has never detected by MLC log file. An EPID, on the other hand, may overcome this problem. In this study, we show the feasibility for MLC detection for in‐vivo dosimetry. Methods: An EPID (iViewGT; Elekta) and a gantry angle sensor (DosimetryChack; Math Resolutions) were employed. An in‐house program written in c++ code was developed to detect the MLC position and the detected position was compared with MLC log file. In this study, we employed two algorithms for the detection; threshold algorithm and Gradient algorithm. MLC position was determined as most nearest position from intensity of each threshold. To estimate the uncertainty of the MLC detection using EPID, a reproducibility of EPID panel position in initial setting and position difference depending of the gantry angle at the open were measured. Static irregular shape fields and rotating rectangular field were used for the performance evaluation test of algorithm. Convex and concave shapes was acquired and processed by two algorithms. Results: Reproducibility of EPID panel position results less than 0.5 mm. Position difference depending of the gantry angle at the open was less than 1.0 mm. For convex‐shape field, algorithm dependency was enhanced. Uncertainty of gradient method was found to be least in this study. Whereas threshold method was sensitive to scatted radiation, gradient method detecting the inflection point was less sensitive. Conclusion: It was determined that uncertainty of this system was totally 1.1 mm when gradient method was employed.
SU‐E‐J‐221: MVCT‐Detector Data Sinograms for In Vivo Quality Assurance of Helical TomoTherapy Treatments of Left Sided Breast Cancer Patients: Effect of Soft‐Tissue Deformations
Authors: Rodriguez V , Garsa A , Zoberi I , Klein E , Goddu S
Published: July 2013

Purpose: Objectives are to compute delivered doses in megavoltage CT (MVCT) datasets using the MVCT‐detector‐data sinograms (MVCT‐DDS), collected during breast‐cancer treatments, and to study the impact of soft‐tissue‐deformations (SD) on dose‐volume‐histograms (DVHs) of the PTVs and organs at risk (OARs). Methods: Tomotherapy Delivery Verification (DV) software was used to reconstruct delivered fluence using pretreatment MVCTs and MVCT‐DDS for 4 patients (20 fractions) treated in our clinic. Delivered fluence was back projected onto the MVCT datasets to compute dose distributions to the patients anatomy at the time of delivery. A commercial deformation algorithm was used to deform planning CT‐datasets to match the pre‐treatment anatomy. The same deformation matrix was applied to plan structures (PS) for true volumes. Both image fusions and deformed structures (DS) were reviewed by a radiation oncologist and a medical physicist. DS were manually edited when necessary. Only fractions with the entire treatment volume contained in the MVCT scans were used. CT‐datasets, planned and reconstructed‐doses (RD), PS and DS were exported to CERR for computing dose‐volume‐indices (DVI). DVI of the planned and reconstructed doses, of both non‐deformed (RD‐ND) and deformed (RD‐D) structures, were averaged and compared. Dose deformations were ignored in this study. Results: PTV D9 5 was 49.1±0.6Gy, 48.0±0.8Gy, 45.8±1.0Gy for the plan, RD‐ND and RD‐D volumes. PTV dose heterogeneity (D5–D9 5) increased by 3.0Gy for deformed targets. Mean dose (MD) of both lungs reduced slightly for both non‐deformed and deformed volumes, however, they were not significant. Heart MD, V2 5 and V3 5 were also non‐significantly reduced. The Sign tests revealed that absolute relative differences between planned and delivered dose distributions were significantly greater than 5% (p<0.05) for D9 5 and D5–D9 5 and heart V2 5 . Conclusion: This study showed that its feasible to reconstruct delivered fraction‐doses in pretreatment MVCT datasets utilizing MVCT‐DDS. Soft‐tissue deformations are important for accurate dose volume evaluations. Research is partly funded by Tomotherapy Inc now called Accuray Inc
SU‐E‐T‐07: Estimation of Effective Field Size with Leaf‐Based Algorithm
Authors: King RP , Cheung AA
Published: July 2013

Purpose: Demonstrate a geometric algorithm for calculating equivalent squares of multileaf collimator defined fields. Methods: Equivalent square (Q) can be modeled as the product of a field's size (square root of area) and a function of its shape, f(E), where f(E)=1 for squares and f(E)<1 for elongated or eccentric shapes. It follows from Sterling's approximation that f(E) = (2*S^0.5)/(S+1) for rectangles with aspect ratio S. By Day's approximation, f(E)=1.8/pi^ 0.5 for circles. For MLC‐defined fields, effective width can be modeled as the average separation between opposing leaf‐tips, where leaf position is weighted both by leaf thickness and by inverse‐square distance of the leaf tip from central axis. Inverse‐square weighting is heuristic, based on the observation that scatter‐air‐ratio is concave with radius. A ratio by area yields effective length and Sterling's approximation yields equivalent square. This algorithm was benchmarked against both Sterling and Day using square, circular, and rectangular fields. Ratios of phantom dose in blocked versus open fields were also used to determine Q through iterative comparison to clinical Sp and TMR tables. Results: The leaf‐based algorithm produced f(E) values of approximately one, greater than one, and less than one where these were expected. It also produced good agreement with benchmarks, with a maximum difference of 3%. In heavily blocked fields, the agreement between the leaf‐based algorithm and the benchmark was superior to the agreement between the benchmark and the measurement. Conclusion: The separation of size from shape is a useful construct in evaluating the equivalent squares of MLC defined fields. The leaf‐based algorithm is a promising technique for calculating equivalent square that produces results consistent with classic benchmarks and accuracies consistent with the limitations of the underlying equivalent square model.
SU‐E‐T‐09: Evaluation of Depth Dose Distribution with Limit Scatter Condition and Comparing with Treatment Planning System
Authors: Zhou P , Das I
Published: July 2013

Purpose: Beam co mmissioning data are acquired in full scatter co ndition but some body parts such as fingers, hands and legs are treated with limited scatter. An evaluation of depth dose distribution in carried out to study limited scatter situation and co mpared with treatment planning system.Material and Methods: Radiation scatter is co nsidered as an important co ntribution of dose in patients. This experiment evaluated the depth dose distribution under different size of water phantoms and co mpared the dose calculated by Eclipse treatment planning software (AAA Algorithm). Measurements were made specially designed limited scatter phantom that were stackable with 6 and 16MV photon beams. The phantom was 3.5cmX12cmX5cm (deep) paper co ntainer filled with water was used as a water phantom unit cell that were added to achieve variability in scatter. For different scatter co ndition purpose, measurement was made by adding different number of phantom unit. An ion chamber reading is used to co mpare the dose. Results: The measurements show that the depth dose distribution at central axis has weakly dependent on lateral scatter co ndition. The dose from 6 and 16 MV beams at 1.0 cm depth has 1.02% and 2.70% difference from single unit (co nsidered as 3.5cmX5cmX12cm water phantom) to 9 units (co nsidered as 10.5cmX15cmX12cm water phantom). The difference at dmax for both 6x and 16x are less than 0.5%. Co nclusion: The lateral scatter co ntributes relatively small on central axis doses when the phantom size is comparable to the field size. Advance algorithm used in TPS provides reasonable (<1%) good dose information evaluation in limited scatter condition.