bluuebunny/crossref_metadata_2025 huggingface dataset:
SU‐E‐J‐08: Dependence of Imaging Dose on Image Quality of Free‐Breathing 3DCBCT of Moving Tumors
Authors: Kauweloa K , Park J , Song W
Published: June 2012

Purpose: To evaluate the impact on free‐breathing CBCT (FBCBCT) image quality to properly visualize the motion range of moving tumors as a function of imaging dose. Methods: A multi‐purpose body phantom (QUASAR) with a cylindrical cedar wood (density = 0.330g/cc), and an embedded 3‐cm diameter Polystyrene sphere (density = 0.855g/cc) were used to simulate lung tumor motion. Varian Trilogy with OBI system was used to acquire CBCT images (high‐dose mode: 125kVp, 80mA, 25ms/frame & low‐dose mode: 110kVp, 20mA, 20ms/frame). As the FBCBCT projections were acquired, the sphere moved in accordance to 30 simulated sinusoidal patient breathing patterns using a programmable motion platform, which were given the parameters: inhalation‐to‐exhalation (I/E) ratio ranging from 1‐0.2131, amplitudes of 1 and 3 cm, and periods 2, 4, and 6 seconds. Following the acquisition of FBCBCT images, the ITV contrast, defined as = (target pixel values inside the sphere ‐ avg. pixel values in background)/(avg. pixel values in background), were calculated per image slice. Results: All parameters, I/E ratio, period, and amplitude did not seem to have much impact on the percentage change of the ITV contrast as a function of imaging dose. The percentage‐change for all coronal images with a reduced ITV contrast when going from high‐dose to low‐dose was ‐ 4.61 ± 3.04%, while the percentage‐change for all coronal images with an ncreased ITV contrast when going from high‐dose to low‐dose, was 8.19 ± 3.61%. The overall percentage‐change of all 30 coronal images was 5.21 ± 6.49%. Conclusions: We found that imaging dose did not have much impact on the visibility of the ITV volume, irrespective of the amplitude, I/E ratio, or period. Thus, it seems that low‐dose FBCBCT may be just as suitable for clinical use while sparing a significant imaging dose to the patients.
SU‐E‐J‐09: Performance Optimization of Thick, Segmented Scintillators for Radiotherapy Imaging
Authors: El‐Mohri Y , Choroszucha R , Antonuk L , Zhao Q , Jiang H
Published: June 2012

Purpose: Thick segmented scintillators, incorporating a 2‐dimensional matrix of optically‐isolated scintillator elements, have shown considerable potential for improving the performance of megavoltage active matrix, flat‐panel imagers (MV AMFPIs). While over a factor of 20 improvement in DQE at zero spatial‐frequency has been demonstrated for prototypes incorporating CsI(Tl) and BGO scintillators, less‐than‐optimal element‐to‐element alignment (misalignment) as well as mis‐registration to the underlying AMFPI array pixels can result in spatial resolution loss, reducing DQE improvement at higher spatial frequencies. In this presentation, a method to restore spatial resolution and DQE, based on the use of a high resolution AMFPI array along with special binning techniques, is investigated. Methods: The effect of misalignment and mis‐registration of segmented scintillators on imaging performance was investigated theoretically and empirically through determination of the modulation transfer function (MTF) and DQE, as well as through realization of reconstructed images of a phantom in a cone‐beam CT geometry. The empirical investigation, which was conducted using a 6 MV photon beam, employed a prototype BGO segmented scintillator consisting of 120×60 elements separated by 50 μm‐thick septal walls and an element‐to‐element pitch of 1016 μm. The scintillator was coupled to a higher resolution 127‐μm‐pitch AMFPI array. Results: Misalignment and mis‐registration result in significant degradation of spatial resolution, leading to DQE reduction at non‐zero spatial frequencies. While mis‐registration for a well‐aligned scintillator can be overcome through 8×8 binning of the array pixels to match the scintillator elements, any misalignment will affect such binning and lead to spatial resolution loss. However, the use of ‘selective’ binning, consisting of the selection of those pixels corresponding to the interior locations of each element, improves resolution while preserving DQE. Conclusions: The use of high‐resolution AMFPI arrays combined with selective binning allows prototype AMFPIs incorporating thick, segmented scintillators to achieve imager performance limited only by scintillator performance. Work Supported by NIH grant R01‐CA051397
SU‐E‐J‐10: Accuracy of Image Guidance Using Cone‐Beam CT with Multiple Breath Hold Using Active Breathing Coordination
Authors: Zhuang T , Magnelli A , Liu H , Qi P , Djemil T , Stephans K , Videtic G , Xia P
Published: June 2012

Purpose: To complete a CBCT for a treatment using ABC, multiple breath hold (BH) (>3) were used due to the slow gantry rotation and the short BH period. Inter‐BH tumor position variability may introduce distortion in the reconstructed images. This study aims to determine a threshold of the inter‐BH scan displacement so that the inconsistency can be identified from the CBCT images. Methods: A numerical phantom was constructed to represent the thorax region of a human body. To simulate the inter‐BH displacements, known magnitudes of motion (s = 0, 1, 3, 5 mm) along the longitudinal direction were introduced for the ‘tumor’ and ‘diaphragm’ in the phantom. Two different irregular motion patterns (s1=s3=/=s2 and s1=/=s2=/=s3) during CBCT scans were tested. Furthermore, a physical phantom with a movable insert was scanned using a commercial CBCT system. The insert of the phantom was programmed to move in the longitudinal direction according to the same motion patterns as designed in the numerical simulations. Subsequently, nine CBCT's in ‘half‐fan’ mode for the physical phantom were acquired with the insert in various positions. These CBCT images were then fused to the reference CT by aligning to either the body of the phantom or the ‘tumor’ inside the insert. Results: Based on numerical simulation, position variation >1mm can be observed from the reconstructed CBCT images. Based on acquired CBCTs of the physical phantom, position variations of >3mm or 5mm were observed, depending on the motion pattern during the data acquisition. Because of the use of half‐fan mode, we observed the order of position displacements of the tumor during CBCT acquisition drastically affected the outcome of imaging registration. Conclusions: Using ABC device, the inter‐BH variability during a CBCT acquisition affects accuracy of tumor localization. A patient individualized planning margin might be necessary to account for this effect.
SU‐E‐J‐11: Characterization of Interfractioanal Anatomical Variations in Post‐Operative Radiation Therapy for Prostate Bed
Authors: Liu F , Ahunbay E , Christian R , Lawton C , Wang D , Li X
Published: June 2012

Purpose: To quantitatively characterize the interfractional anatomic variations in post‐operative radiation therapy (RT) for prostate bed, so that appropriate strategy that can fully address these variations can be developed. Methods: A total of 102 daily pre‐treatment CT acquired using an in‐room CT (CTVision, Siemens) for 10 patients treated with post‐operative IG‐IMRT of prostate bed. Prior to each fraction, patients were repositioned to correct for interfractional translational shifts based on the alignment of both anterior rectal wall and surgical clips between the daily CT and the planning CT. The PTV was assumed to be the volume enclosed by the 95% prescription isodose surface generated for the conventional four field box. Contours of the PTV, rectum and bladder on each daily CT were generated by populating the planning contours using an auto‐segmentation tool based on deformable registration (ABAS, Elekta) with manual editing. Interfrcational variations in the volumes, shapes and positions of these contours were obtained. The displacement of the center of mass (DCOM) with respect to the isocenter was used to measure interfractional organ motion, and the maximum overlap rate (MOR) was used to measure organ deformation. Results: Interfractional variations in the volumes of rectum and bladder were in the range of 50–270% (average 116±41%) and 30–180% (average 67±26%), respectively. The averages of DCOM for rectum are: ‐ 0.35±0.46cm (lateral, varying from −1.58 to 1.23cm), −0.33±0.99cm (longitudinal, varying from −2.4 to 1.8cm), and −3.41±1.14cm (vertical, varying from −5.56 to −0.99cm). These values for bladder are: −0.20±0.50cm (lateral, varying from −1.48 to 0.61cm), 3.63±1.10cm (longitudinal, varying from −5.7 to 3.1cm), and −0.31±0.97cm (vertical, varying from −1.68 to 2.77cm). Conclusions: Large interfractional changes in organ volumes, shapes and positions are seen in post‐operative RT for prostate bed. These changes cannot be accounted for by the current standard practice of IGRT repositioning. This work is supported partially by MCW Cancer Center Fotsch Foundation.
SU‐E‐J‐17: Evaluation of Metal Artifact Reduction in MVCTs Using a Model Based Image Reconstruction Method
Authors: Paudel M , MacKenzie M , Fallone B , Rathee S
Published: June 2012

Purpose: To evaluate the performance of a model based image reconstruction in reducing metal artifacts in MVCT systems, and to compare with filtered‐back projection (FBP) technique. Methods: Iterative maximum likelihood polychromatic algorithm for CT (IMPACT) is used with pair/triplet production process and the energy dependent response of detectors. The beam spectra for in‐house bench‐top and TomotherapyTM MVCT are modelled for use in IMPACT. The energy dependent gain of detectors is calculated using a constrained optimization technique and measured attenuation produced by 0 – 24 cm thick solid water slabs. A cylindrical (19 cm diameter) plexiglass phantom containing various central cylindrical inserts (relative electron density of 0.28–1.69) between two steel rods (2 cm diameter) is scanned in the bench‐top [the bremsstrahlung radiation from 6 MeV electron beam passed through 4 cm solid water on the Varian Clinac 2300C] and TomotherapyTM MVCTs. The FBP reconstructs images from raw signal normalised to air scan and corrected for beam hardening using a uniform plexi‐glass cylinder (20 cm diameter). IMPACT starts with FBP reconstructed seed image and reconstructs final image at 1.25 MeV in 150 iterations. Results: FBP produces a visible dark shading in the image between two steel rods that becomes darker with higher density central insert causing 5–8 % underestimation of electron density compared to the case without the steel rods. In the IMPACT image the dark shading connecting the steel rods is nearly removed and the uniform background restored. The average attenuation coefficients of the inserts and the background are very close to the corresponding theoretical values at 1.25 MeV. Conclusions: The dark shading metal artifact due to beam hardening can be removed in MVCT using the iterative reconstruction algorithm such as IMPACT. However, the accurate modelling of detectors' energy dependent response and physical processes are crucial for successful implementation. Funding support for the research is obtained from “Vanier Canada Graduate Scholarship” and “Canadian Institute of Health Research”.
SU‐E‐J‐18: Evaluation of the Effectiveness of Compression Methods in SBRT for Lung
Authors: Liao Y , Tolekids G , Yao R , Templeton A , Sensakovic W , Chu J
Published: June 2012

Purpose: This study aims to evaluate the effectiveness of compression in immobilizing tumor during stereotactic body radiotherapy (SBRT) for lung cancer. Methods: Published data have demonstrated bigger respiratory motion in lower lobe than in upper lobe during normal breathing. We hypothesize that 4DCT‐based patient selection and abdominal compression would immobilize lung tumor volumes effectively, regardless of their location. We retrospectively reviewed 12 SBRT lung cases treated with Trilogy® (Varian Medical System, Palo Alto, CA). Either compression plate or Vac‐LokTM was used as abdomen compression of the SBRT immobilization system (Body Pro‐LokTM, CIVCO) to restrict patients' breathing during CT simulation and treatment delivery. These cases are grouped into 2 categories: lower and upper lobe tumor, each with 6 cases. Records for 33 treatments were studied. On each treatment day, the patient was set up to the bony anatomy using kV‐kV‐match. A CBCT was performed to further set up the patient to the tumor based on the soft tissue information. The shifts from CBCT‐setup were analyzed as displacement vectors demonstrating the magnitude of the tumor motion relative to the bony anatomy. Results: The mean magnitude of displacement vectors for upper lobe and lower lobe were 3.7±2.7 and 4.2±6.3, [1S.D.] mm, respectively. The Wilcoxon rank sum test indicates that the difference in the displacement vector between the two groups is not statistically significant (p‐value = 0.33). Conclusions: The magnitude of shifts from CBCT were small with mean value <5mm in SBRT lung treatments. No statistically significant difference were observed in the displacement of tumor between lower and upper lobes. With limited sample size, this suggests that our current 4DCT screening/abdominal compression approach is effective in restricting the respiration‐induced tumor motion despite its location within the lung. We plan to confirm this Result in additional patients.
SU‐E‐J‐30: Using Shifting Planned Dose Matrix to Evaluate Daily Dose Changes for IMRT Prostate Treatment
Authors: Ferjani S , Huang G , Shang Q , Xia P
Published: June 2012

Purpose: Summation of daily DVH from KV‐cone beam CT (KV‐CBCT) to obtain a composite dose volume histogram (DVH) is challenging. Directly translating the planned dose matrix according to measured daily prostate displacements provided a common reference frame for a composite DVH from daily DVHs. The purpose of this study is to evaluate the shifting planned dose matrix method compared to the dose recalculation method using daily KV‐CBCT. Methods: Six patients, who received concurrent IMRT treatment for prostate and pelvic lymph nodes with 124 daily CBCTs, were selected for this study. Contours for CBCT's were transferred from the planning CT after soft tissue registration for prostate and bony registration for pelvic lymph nodes. Using the same planning beam configurations, we re‐calculated doses for these CBCTs after shifting to corrected treatment isocenters. The planned dose matrix translation was performed by an in‐house program written in MATLAB and incorporated with Computational Environment for Radiotherapy Research (CERR) software. The corresponding daily DVH was obtained by shifting the planned dose matrix according to shifts of treatment iso‐centers. To compare these two methods, selected endpoint doses for tumor targets and sensitive structures were extracted from DVHs. Results: For prostate displacement less then 1.5 cm, the dose matrix shifting method resulted in 93% and 98% fractions within 5% differences from the recalculation method for D95 of prostate and pelvic lymph nodes, respectively. These numbers decreased to 58% and 71% when 2% dose difference criterion was used. Conclusions: Allowing 5% daily dose difference, shifting planned dose matrix provides effective means to evaluating daily dose changes for concurrent IMRT treatment for prostate and pelvic lymph nodes. The utility of this tool is to provide a common coordinate frame to obtain composite dose distributions.
SU‐E‐J‐34: Influence of Prone versus Supine Patient Position on Localization with Image Guided Radiotherapy of Prostate Cancer
Authors: Sheth N , Kandala S , Chen Y , Yang C
Published: June 2012

Purpose: To retrospectively assess the influence of prone versus supine patient position on setup shifts and target margins for image guided radiotherapy (IGRT) of prostate cancer. Methods: Ninety prostate cancer patients were treated at our institution between September 2006 and June2011 with IGRT utilizing daily megavoltage cone beam; 52 patients were prone receiving 1577 fractions and 38 supine receiving 1035 fractions. Patients were setup to skin tattoos, imaged with megavoltage cone beam, then moved to treatment position by the alignment of three intraprostatic fiducials with lateral, longitudinal, and vertical shifts. The magnitude of the daily shift is root sum of squares of the translations. Results: Patients positioned prone had a mean daily shift magnitude 1.4 mm greater than supine: 7.5 ± 4.0 mm vs. 6.1 ± 2.9 mm (p ≪ 0.001). The mean magnitude of the daily shift for prone vs. supine respectively were 3.7 ± 3.1 mm vs. 2.6 ± 2.3 mm laterally, 3.5 ± 3.0 mm vs. 3.3 ± 2.6 mm longitudinally, and 3.9 ± 3.5 mm vs. 3.1 ± 2.4 mm vertically. The percentage of daily shifts within our intuition's planning target volume (PTV) margin (7 mm posterior and 10 mm for all other directions) for prone vs. supine respectively were 97.3% vs. 99.5% laterally, 97.1% vs. 98.2% longitudinally, and 93.1% vs. 96.8% vertically. Conclusion: When prostate cancer patients were setup for IGRT utilizing daily megavoltage cone beam, the daily shifts from the skin tattoos to intraprostatic fiducials were greater on average if positioned prone vs.supine. Without IGRT, part of the prostate would be outside of the PTV for more treatments when positioned prone rather than supine.
SU‐E‐J‐37: Radiation Dose during Chemoembolization: A Predictive Model
Authors: Black B , Jones A , Bassett R , Wallace M , Tam A , Gupta S , Steele J
Published: June 2012

Purpose: To identify variables correlated with radiation dose during hepatic chemoembolization, quantify their individual impact, and apply these findings to build a dose prediction model. Methods: A retrospective review of 77 patients undergoing hepatic chemoembolization between 1/2010–10/2010 was performed. Variables included: Radiation dose metrics[DAP, CD, number of cone beam CT and fluoroscopy time] and clinical parameters(BMI, session number, extrahepatic embolization, lesion number, chemoembolization regimen and lobe(s) treated). CD was the primary outcome measurement used for the dose model. Univariate and multivariate linear regression models were used to assess the association between dose metrics and predictive variables and assess the relative impact of each variable on dose. Variables were considered statistically significant at the p<0.05 level. Coefficient of determination(R2)and root mean square error(RMSE) were calculated for CD. R2 was used to evaluate goodness of fit and RMSE was used to establish a measurement of the typical size of the error in predicting the cumulative dose. Results: Based on the multivariate analysis: higher BMI, regimen, single lesions, 1° tumor and initial session were statistically significant and incorporated into the following dose prediction model: Predicted Dose(mGy)= −672+BMI(56.3)+558(session #1)+1789(extrahepatic a. embolized)+232(1°tumor)+[−667(2–4 lesions)or ‐ 12(>5 lesions)]+[370(dox‐bead regimen)or 1618(ethiodol based regimen)]. Plots of the predicted vs actual CD were performed and the adjusted R2 for CD is 52.9%(RMSE = 697). The model is accurate at predicting 52% of the variation. When the model predicts a dosage of 1000 or 2000 mGy the actual dose interval ranges from 519–2519 mGy or 384–3616 mGy, respectively. Conclusions: Creating a radiation dose prediction model is feasible. This is the first known attempt at creating a dose model for image guided intervention and refinements to the model will be required to improve its accuracy. Prospective dose modeling will become more relevant as the cost benefit analysis of radiation exposure enters the decision making process in patient care. Alda Tam: Angiodynamics Inc., research funding Joseph Steele: MedicaSafe, Inc ownership Intelliject medical ownership INTIO medical consultant/ownership Caymus Medical ownership Cayenne Medical ownership
SU‐E‐J‐48: Real Time Image Guided Localization in SBRT Lung/Liver Patients Radiation Treatment
Authors: Liu Y , Campbell J
Published: June 2012

Purpose: Stereotactic body radiation therapy (SBRT) lung/liver patientradiation treatment requires high precision of patient position and target localization. For SBRT lung/liver patients positioning, cone beam CT imaging has been widely used, generally with zero couch rotation. The purpose of this study is to implement Stereotactic radiation surgery (SRS) patient positioning technology to SBRT by expanding patient positioning with couch rotation. Methods: A Varian® Novlis Tx for SRS treatment wasused to treat SBRT lung/liver patients implementing CBCT. BrainLAB® X‐ray imaging system in conjunction with optical guidance is primarily used for SRS patients. CBCT and X‐ray imaging system were independently calibrated with 1.0 mm accuracy. The X‐ray imaging system was implemented through BrainLAB® ExacTrac system with CBCT localized position at the initial zero position for the X‐ray imaging system. For the other couch positions, X‐ray images were fused with patient DRRs for positioning. Results: Based on daily imaging QA records for a period oftwo years, the longitudinal, vertical and lateral coordination between CBCT and X‐ray imaging average 0.3+/−0.5, 0.2+/−0.5 and 0.5+/−0.5 mm. The shiftfrom the CBCT imaging isocenter to the X‐ray imaging isocenter is 0.5+/−0.5 mm accuracy for a 24‐month period of tracking. Patient position accuracy: After initially localizing the patient with CBCT at the zero couch position, the patient was positioned with the X‐ray imaging system. The computed translational and rotational shift accuracy are 0.5+/−0.5 mm and0.4+/−0.3 degree respectively, based on 66 SBRT lung/liver patients couchrotations. Conclusions: Accurate coordination of CBCT and X‐ray imaging in conjunction with optical imaging guidance can be expanded to patient positioning with couch rotation. The X‐ray imaging capability at rotated‐couch positions improved the physician confidence level during SBRT lung/liver patients treatment.
SU‐E‐J‐51: Interfractional Trend Analysis of Dose Discrepancies Based on 2D Portal Dosimetry
Authors: Persoon LCGG , Nijsten SMJJG , Podesta M , Snaith JAD , van Elmpt WJC , Verhaegen F
Published: June 2012

Purpose: During a radiotherapy treatment course the dose delivery can be influenced by a number of factors, e.g. anatomical changes over time. Thiscan Result in discrepancies between planned and delivered dose. The electronic portal imaging device has been demonstrated to be valuable fortransit dosimetry verification. The aim of this study is to investigate theinformation that can be derived from 2D transit portal dosimetry by examining interfractional dose changes over a treatment course. Methods and Materials: To create a trend overview of the interfractional changes intransit dose, the predicted portal dose for the different beams is compared to a measured portal dose using a ? evaluation. For each beam of the delivered fraction information is extracted from the ? images to differentiatesystematic from random dose delivery errors. From the systematic dose errors of a fraction for different projected contours, derived from the treatment planning contours several metrics are extracted like percentage pixels with ? exceeding unity. Finally the extracted metrics from each contour and beam are weighted with beam weight and the average andstandard deviation are calculated, resulting in a fraction Result. For this study, we analyzed 6 lung cancer patients and 20 prostate cancer patients. Results: In some prostate cases the rectal filling was causing the dose delivery problems. For the lung cancer patients, anatomy changes from the diminishing atelectasis caused a transit dose difference and adaptations to the plan were applied. Conclusion: We have shown that from interfractional trend overview valuable information can be derived. However, to use this for adaptive radiotherapy, 2D transit dose differences with this methodshould be correlated with the 3D delivered dose, to define decision criteria.By optimizing these decision criteria it should be possible to prevent eitherover or under dosage of the tumor or OARs.
SU‐E‐J‐53: A Phantom Validation Study of a 3D Background Phase Model for MR Thermometry
Authors: Yung J , Fuentes D , Hazle J , Stafford R
Published: June 2012

Purpose: The proton resonance frequency (PRF) shift method is the most widely accepted method for magnetic resonance thermal imaging to provide real‐time treatment monitoring of thermal therapies. However, the PRF shift technique involves the subtraction of a reference phase map, which causes the technique to be easily perturbed by tissue motion and other background contaminations. In this study, a three‐dimensional background phase is estimated in order to create a phase reference for each time point. Methods: A magnetic resonance spectroscopy (MRS) sphere was scanned within a 3T MRI scanner employing a 3D fast SPGR sequence. Real and imaginary images were acquired to obtain phase images as the control. The ability to predict the background phase was investigated by systematically removing phase information from the control data set. Data was initially removed from a spherical region of interest (ROI) to simulate a region where ablativeheating would take place. In a second case, the same spherical ROI was removed as well as every other slice to further reduce the amount of existing data. A 3D finite element model was implemented to solve the Dirichlet problem given a measured phase on the boundary of the simulated available data. Results: Line profiles taken through the phantom indicate phase estimates to compare well with actual phase measurements. The phase estimation still shows good agreement when reducing the amount of data to every other slice. Conclusions: The 3D multi‐slice temperature estimate potentially provides a robust technique that is not as susceptible to through‐plane or in‐plane motion‐induced temperature artifacts as compared to thecurrent PRF shift method. The research in this paper was supported in part through 1R21EB010196‐01
SU‐E‐J‐56: Localization Error in Gamma Radiosurgery with 3T MR Due to Fiducial Box Chemical Shift from Incorrect Liquid Filling Materials
Authors: Ding X , Bourland J , Dolesh W
Published: June 2012

Purpose: Use of a 3D MAGIC (Methacrylic and Ascorbic acid in Gelatin Initiated by Copper) polymer gel dosimeter to evaluate potential localization and positioning errors due to the use of incorrect liquid filling material (baby oil instead of copper sulfate) for a gamma radiosurgery (GSR) MRI fiducial box. Method and Materials: Two phantoms were used to evaluate geometric errors due to chemical shift for ‘baby oil' fiducial markers: 1) a cylindrical grid phantom with Teflon rod insert; 2) a human skull phantom with a MAGIC (Gelatin 9%; Methacrylic acid 4%; CuSO4 0.1mM; Ascorbic acid 2mM; Glucose 10%) gel capsule to simulate an intracranial target. Both phantoms were stereotactically MR and CT scanned for GSR treatment planning using a ‘baby oil' GSR MRI fiducial box and a standard CT fiducial box. The gel capsule was given 15Gy @ 50% isodose line using the 4mmcollimator based on ‘baby oil' fiducial box MR images. Then, the skull phantom with capsule was scanned in 3T GE Signa® EXCITETM clinical scanner (Spin Echo pulse sequence) for 3D dose distribution read‐out. Dose distribution errors were analyzed based on gel results for the combined MR and CT plans. For comparison, deviation of grid phantom teflon rods were directly measured from MR and CT stereotactic images. Results: Gel dose profile measurements indicate a 3.8mm shift in the phase encoding direction for the ‘baby oil' fiducial marker for 3T MRI based GSR treatment planning. A 3.7mm shift in Teflon rod position was also confirmed through direct comparison of CT and MR images. Conclusion: Both results showsignificant target localization and positioning errors can be caused if inappropriate filling materials are used for GSR MRI fiducial boxes. Thisstudy also indicates that MAGIC polymer gel can be used as a versatile toolfor GSR 3D quality assurance.
SU‐E‐J‐57: MRI‐Linac (MRL) Guided Treatment for Esophageal Cancer
Authors: Lips I , Lever F , Reerink O , Moerland M , Meijer G , van Lier A , van den Berg C , Philippens M , Crijns S , Raaymakers B , van Vulpen M , Lagendijk J
Published: June 2012

For radiotherapy, oesophageal cancer is located in a difficult area. Spatial control of the dose distribution is difficult to achieve with current CT‐based radiation techniques, as on CT, soft‐tissue contrast is too low. Furthermore, the oesophagus moves and organs at risk (e.g. lung, heart, liver, spinal cord) are in close proximity. An 1.5 T MRI‐accelerator (MRL) has sufficient soft‐tissue tumour visualization possibilities to allow for precise real‐time, online, position verification and for dose escalation without organ at riskoverdose. Our research consists of the preparatory work for the first clinical study on the MRL for patients with oesophageal cancer. To improve image quality and reduce the motion artefacts, the benefit of cardiac triggering and breath holds is evaluated on fifteen oesophageal patients. Results show the superb image quality of these MRI sequences. The use of this high quality MRI gives the possibility for non‐invasive real‐time visualization andtracking of the tumour. We quantify oesophageal tumour motion on cineMRI. The tumour is tracked on sequential mixed T1/T2w images (acquisition time: 60s, temporal resolution: 0.5s, slice thickness: 7mm) of a single coronal and sagittal slice using a Minimum Output Sum of Squared Error (MOSSE) adaptive correlation filter. Tumour registration within the individual images can typically be done at a millisecond time scale. Motion of oesophageal tumours can well be tracked and is highly variable between patients. The greatest mobility is seen in cranio‐caudal direction, with amaximum peak‐to‐peak amplitude of tumour movement of 24.5mm followed by the dorso‐ventral and the medio‐lateral direction. Movement seems greatest in tumours located in the lower part of the oesophagus. This study shows both the superb image quality for GTV localisation and the possibility for on‐line and real time tumour tracking. The study opens thepossibility for tracked radiation delivery with a 1.5T MRI accelerator. Partial funding has been obtained by Elekta and Philips
SU‐E‐J‐68: An Optical Image Guidance System: To Detect Arbitrarily Attached Markers Behind a Full Facemask
Authors: Kim H , Park Y , Son T , Lee K , Kim I , Ye S
Published: June 2012

Purpose: We developed an optical image guidance system to manage patient's inter‐fractional set‐up errors by tracking external markers at the specific positions (e.g., nose tip) behind a full facemask. However, a problem associated with the reproducibility of the marker positions during the entire course of treatments still remains. In order to remove this disadvantage, we applied the arbitrary‐point‐to‐plane registration method to our existing system. Methods: Infra‐red (IR) reflecting markers were attached on arbitrary positions of the head phantom's face and then the phantom was immobilized by a full face thermoplastic mask. 3D coordinates of the IR markers behind the full facemask were reconstructed by the calibrated stereo camera system using the direct linear transform (DLT) algorithm. In order to match arbitrarily attached markers with a planning CT image, rough positions of three markers were manually defined (rough registration) and then the coordinates of all markers were determined through the point‐to‐plane registration using the contractive projection point (CPP) algorithm (fine registration). In addition, the marker registration error in 6 DOF was calculated. In order to validate accuracy of the system, the phantom was intentionally moved according to 10 sets of known translation parameters. Results: A mean target registration error (TRE) determined by the experiments for arbitrarily attached markers was 1.24 ± 0.32 mm. The fine registration following the rough registration allowed fast and robust registrations. Conclusions: The proposed solution for arbitrarily attached markers behind a full facemask enables us to avoid any daily errors in attaching the external markers at the specific positions. This work was supported in part by the SNU interdisciplinary project (2009–2010) and the SNU Brain Fusion project (2010–2011).
SU‐E‐J‐70: A Study of the Correlation of 3D Surface Matching and KV Imaging for Chestwall IMRT
Authors: Al‐Hallaq H , Gerry E
Published: June 2012

Purpose: We investigated the accuracy of surface matching compared to kV positioning of 10 post‐mastectomy chestwall patients receiving inverse‐planned, non‐gated IMRT. Methods: During 130 treatment sessions, non‐gated 3D surfaces were captured using AlignRT (v4.5) before and after table translations as indicated by kV imaging. Surfaces were compared to a reference generated from CT data. Pearson's correlations between ‘indicated’ AlignRT and kV shifts were studied for surface registration of user‐defined regions‐of‐interest (ROIs): the entire surface (‘all’) and the chestwall (‘cw’). In 21% of sessions, two consecutive surfaces of patients in identical positions were used to estimate variability. Finally, the ‘implemented’ shifts detected by AlignRT were calculated and compared to the absolute table translations. Results: Correlations between ‘indicated’ AlignRT and kV shifts were higher for ‘cw’ than for ‘all‘: r=0.65 (Anterior‐Posterior), r=0.65 (Superior‐Inferier), r=0.44 (Left‐Right). Correlations exhibited large inter‐patient variability; 60% had r<0.6 in at least 1 direction thereby resulting in ow correlation between 3D Euclidian shift distances (r=0.48). Correlations between ‘cw’ and kV increased (r>0.8) for ‘implemented’ table shifts; only 2 patients demonstrated r<0.6 in any single direction. Comparison of consecutively‐acquired ‘cw’ surfaces controlled for patient movement demonstrated standard deviations (STDs) of: 1.2mm (A‐P), 2.0mm (S‐I), 1.6mm (L‐R). While STDs between ‘implemented’ and kV shifts were on the same order, STDs between ‘indicated’ and kV shifts were twice as large: 2.9mm (A‐P), 3.5mm (S‐I), 4.1mm (L‐R). Rotational differences >1degree were calculated more often when registering ‘cw’ (22%) than ‘all’ (5%). At the treatment position, residual STDs remained high (3.0–3.6mm). Conclusions: On average, ‘cw’ shifts correlated with kV shifts but exhibited significant inter‐patient variability and larger rotations than ‘all’. Differences between AlignRT and kV were ∼3mm for initial patient positioning. The lack of a one‐to‐one correspondence between surface and kV shifts in any single session must be further investigated before clinical implementation.
SU‐E‐J‐71: Dosimetric Impact of Setup Tolerance for Breast Radiation Therapy with 3D Surface Imaging
Authors: Havnen‐Smith A
Published: June 2012

Purpose: 3D surface image guidance (3D SIG) has been shown to improve patient positioning accuracy in the treatment of breast cancer, but limited information is available regarding the dosimetric consequences of setup tolerances associated with breast radiation therapy techniques. The purpose of this study was to determine the magnitude of dose‐delivery errors associated with setup tolerances of 3 mm/3deg and 5 mm/5deg for set‐up and monitoring of whole breast radiation treatment using (3D SIG). Methods: Five test patients were selected for direct simulation of the maximum acceptable deviation from reference position for tangential beams using field‐in‐field (FinF) techniques. Dosimetric impact was determined by simulating the maximum allowable patient translations and rotations, recalculating the dose distribution, and propagating the dosimetric error for a full treatment course. For the planned and off‐set positions, dosimetric consequences were evaluated by examining the plan maximum dose, the percent coverage of the prescription dose for the lumpectomy bed, the V20Gy and V13Gy percentages for the ipsilateral lung, and the maximum point dose to the heart. The results are shown in Table I below. Results: For both 3 mm/3deg and 5 mm/5deg off‐sets in relatively large‐breasted patients (> 500 cc) no significant change is observed. The ipsilateral lung V20Gy and V13Gy had a maximum increase of 5.4% and 5.7%, respectively. Maximum dose to the heart increased by a maximum of about 8% for those patients being treated to the left breast. The patient with the largest dosimetric impact was relatively small‐breasted with a lumpectomy cavity in close proximity to the field borders. Conclusions: As tumor bed coverage and ipsilateral lung dose were heavily impacted for the studied tolerances, it may be beneficial to utilize an appropriately tighter tolerance in patients with breast volume < 500 cc with tumor bed volumes near the periphery of the field apertures.
SU‐E‐J‐74: Evaluation of the Commercial Prototype Open Face Mask Used with Surface Rendering Imaging System for Proton Therapy Patients with Cancers of the Brain and Head: Successful Preclinical Study
Authors: Mamalui‐Hunter M , Li Z
Published: June 2012

Purpose: Evaluation of the commercial prototype open face mask (Fibreplast, Q‐FixTM) used with surface rendering imaging system (AlignRTTM, London, UK) for setup and monitoring of proton therapy patients with cancers of the brain and head. Methods: Fibreplastic open face masks were used with Base‐of‐Skull frame/moldcare pillow. Two sizes of the pre‐made cutouts in the masks were investigated: leaveing open skin surface in the oval‐shaped area between (I) upper lip and forehead boss, II) between mandible and forehead boss in superior‐inferior direction; and between zygomatic (cheek‐) bones/sphenoid bones laterally. Calibration of AlignRT system was verified with SRS cube phantom (VisionRT)and 2D X‐ray patient positioning system (DIPS, IBA). The accuracy of translational shifts and rotations was a) verified using a head&neck phantom and b) tested using volunteers. Within AlignRT software, only the open area was used as ROI for the registration; the option ‘Intracranial SRS’ used for surface capture. Results: For the isocenter determination accuracy within 0.3mm/0.2 degrees, the head&neck phantom registration was performed with the 0.5mm/0.5 degree accuracy; the volunteer tests showed the registration accuracy within 0.5mm ±0.2mm (1 s)/0.7±0.2 (1 s) degree. The simulation of the noise in the surface data such as eye blinking and attempts to swallow/chew was performed, with negligible effect on the registration. No significant differences between the study results between the masks of type (I) and (II) were noticed. Conclusions: The AlignRT surface rendering system has sufficient accuracy when used with the open face head&neck mask for localization/registration of the proton therapy patients with tumors of the head and brain.
SU‐E‐J‐75: Practical Annual Quality Assurance Program for a Real Time Optical Tracking System
Authors: Lasher D , Kassas B , Wojcicka J
Published: June 2012

Purpose: To verify the accuracy of a real time optical surface tracking system using a practical annual quality assurance program with an anthropomorphic breast phantom. Methods: An anthropomorphic breast phantom was used to determine the accuracy of registration, shift, source to surface distance (SSD), and live monitoring features of the AlignRT system. Both the two and three camera AlignRT systems were tested. Registration and shift accuracy were evaluated by comparing software output with known phantom displacements and rotations at 0, 90, and 270 couch angles. These tests were performed in static capture and live monitoring modes. SSD accuracy was determined by comparing AlignRT results with expected values from the treatment planning system and optical distance indicator at 0, 90, and 270 degree couch rotations. Results: For the two camera system, registration accuracy at 0, 90, and 270 degree couch angles was within 1.0mm in the lateral, longitudinal, and vertical directions and 0.04 degree. For shifts of +/−10mm and +/−5 degree, static mode shift accuracy was within 1.6mm and 0.23 degree. Registration accuracy of the shifted phantom in live monitoring mode was within 1.7mm and 0.2 degree. For the three camera system, registration accuracy at 0, 90, and 270 degree couch angles was within 1.1 mm in the lateral, longitudinal, and vertical directions and 0.2 degree. For shifts of +/−10mm and +/−5 degree, static mode shift accuracy was within 0.9mm and 0.2 degree. Registration accuracy of the shifted phantom in live monitoring mode was within 1.1mm and 0.2 degree. SSD determination was accurate to within 2mm for both systems and modes. Conclusions: The AlignRT system accuracy can be easily verified for annual quality assurance using a realistic clinical setup to within 2mm/0.5 degree. System accuracy was comparable for both two and three camera systems in static and live monitoring modes.
SU‐E‐J‐76: Clinical Use of a Real‐Time Surface Image‐Guided Positioning and Tracking System in Proton Therapy
Authors: Hsi W , Kang Y , Ding X , Mascia A , Ramirez E , Zheng Y , Zeidan O
Published: June 2012

Topic of interest: Clinical applications of AlignRT 3‐cameras real‐time surface image‐guided positioning system (IGPS) for positioning patients to reduce the number of X‐ray images and tracking intra‐fractional movements in proton therapy.Purposes: To position patients and track the intra‐fractional movements, the AlignRT system was implemented in proton incline‐beam‐line (IBL) at Procure Oklahoma‐City center. Methods: The AlignRT3c system was configured near perpendicular to the gantry rotation for accommodating the X‐ray IGPS. To evaluate positioning accuracy, more than 10 surfaces of each patient for ten patients with intracranial tumors were acquired after patients positioned by X‐ray IGPS. Displacements between acquired surfaces and the reference surface taken at 1st day of treatment were examined. Intra‐fractional movements with respiratory was studied with gated surface that allows setting the reference surface for patient at exhale during breathing. Intra‐fractional movements due to respiratory were monitored on 10 sections of each patient for three patients with thoracic tumors. Results: Accuracy of positioning patient is 2.0 mm at both anterior‐posterior and lateral directions, and is 3.5 mm in superior‐inferior (SI) direction by aligning the surfaces of masks. Observed larger displacements along SI direction can be due to patient's movements within the mask. Periodical displacements within 5 mm compared to its reference were seen for the three patients with thorax tumors. However, 10 mm sharp displacements with a few seconds were observed when patient moved the body. Conclusions: We have implemented the first AlignRT3c IGPS for proton therapy for positioning patients within 2.0 mm, and successfully tracked intra‐fractional respiratory motion during treatment after positioning patient.
SU‐E‐J‐79: Using the Distance of Closest Approach to Improve Compton Camera Image Quality
Authors: Mackin D , Peterson S , Polf J , Beddar S
Published: June 2012

Purpose: The prompt gamma radiation emitted from tissue during proton therapy offers a means of beam range verification. Compton camera (CC) imaging systems offer high efficiency and 3D imaging capability. However, Doppler broadening and the inaccuracies in the measurement of the scattering positions and energies reduce the image resolution. The purpose of our study is to determine if removing events with a distance‐of‐closest‐approach greater than a threshold value will improve the resolution of images reconstructed using the stochastic origins ensemble (SOE) algorithm. Methods: We first simulated a 3‐stage CC detecting gammas from a 0.511 MeV point source. We then used SOE to reconstruct images from the point source and from a) all gammas, b) gammas with DCA < 3 mm, and c) gammas with DCA < 1 mm. We measured the point‐spread‐function for the point source for a), b), and c). Next, we simulated a 3‐stage CC detecting prompt gammas emitted from tissue during proton therapy. We reconstructed the gammas using SOE and compared 2D images of all gammas, gammas with DCA < 3 mm, and gammas with DCA < 1 mm. Results: The FWHM of the PSF of the 0.511 MeV point source was reduced by 50% when DCA was required to be < 5 mm, and it was reduced by 65% when DCA was required to be < 3 mm. 2D images of a proton beam are of visibly higher quality as the DCA requirement is lowered. Conclusions: The DCA for MC events can be used to identify the events with significant resolution loss due to the detector effects. Removing these events before running the reconstruction algorithm results in higher quality images. We discuss methods to predict the DCA based on the measured scatter data, so that a similar technique can be applied to data from real detectors. This work was supported by the National Institutes of Health through award number R21CA137362 from the National Cancer Institute
SU‐E‐J‐95: Towards Optimum Boundary Conditions for Biomechanical Model Based Deformable Registration Using Intensity Based Image Matching for Prostate Correlative Pathology
Authors: Samavati N , McGrath D.M. , Lee J , van der Kwast T , Jewett M , MÃ©nard C , Pluim J.P.W. , Brock K.K.
Published: June 2012

Purpose: Deformable registration of histology to MRI is an essential tool to validate in vivo prostate cancer imaging. However, direct registration of histology to in vivo MR is prone to error due to geometric differences between the tissue sections and the in vivo imaging planes. To increase the accuracy of registration, an ex vivo high resolution MRI is acquired to compensate for the direct registration difficulties. A novel intensity‐based deformable registration algorithm based on local variation in image intensities is proposed to register the histology to ex vivo MRI of prostatectomy specimens. Methods: Four sets of ex vivo MR and whole mount pathology images from four patients were used to investigate and validate the technique. In addition, 9 synthetically deformed ex vivo MR images were used. The standard deviation in local windows within the images was calculated to generate intermediate images based on both MR and histology. The intermediate images were registered using the Drop package (Munich, Germany). To further increase the accuracy, a final refinement of the registration was performed using Drop with a finer B‐spline rid. The registration parameters were tuned to achieve a visually acceptable registration. Magnitude of Differences (MOD) and Angular Error (AE) were used to validate the synthetic data, and the Target Registration Error (TRE) of manually indicated landmarks was used for the clinical data. Results: MOD of 0.6mm and AE of 8.3 degrees showed the efficacy of using intermediate images, compared to 0.8mm and 10.0 degrees achieved with Drop without the intermediate images. The average mean±std TRE among the four patients was 1.0±0.6 mm using the proposed method compared to 1.6±1.1 mm using Elastix (Utrecht, The Netherlands). Conclusions: An intensity‐based deformable registration algorithm which uses intermediate images was evaluated on prostatectomy specimens and synthetically deformed clinical data, indicating improvement in overall accuracy and robustness. OICR, Terry Fox Ultrasound for Cancer Therapy. Dr. Brock is a Cancer Care Ontario Research Chair in Cancer Imaging and has financial interest in deformable registration technology through the licensing of Morfeus to RaySearch Laboratories.