bluuebunny/crossref_metadata_2025 huggingface dataset:
SU‐GG‐J‐96: Fiducial Placement Guidelines for Thoracic Radiation Therapy Determined by 4DCT
Authors: Silver E , Parikh P , Yang D , Smith R , Low D
Published: July 2008

Purpose: To determine the volume of lung where a fiducial would accurately represent lung tumor motion. Method and Materials: A 4DCT scan with spirometry was performed on 4 patients, and the results were evaluated by a deformable image registration and a lung motion model was applied to determine motion vectors for each point in the lung. The position vector of the lung tumor centroid at peak inhalation, peak exhalation, mid inhalation and mid exhalation of was compared to the position vector of points throughout the rest of lung to find the difference in relative positions. Results: Cubes were constructed containing a volume in which we could accurately predict the position of the tumor within 2mm, 3mm and 4mm. These cubes showed at least 95% of the contained points having motion differences below the selected thresholds. The average side length of the cube for patients with upper lobe tumors when the motion was followed within 2 mm was 2.5 cm. These side lengths increased to an average of 4.3 cm and 6.0 cm for thresholds of 3 mm and 4 mm respectively. For patients with lower lobe lung tumors, the average side lengths of the cubes were 1.0 cm, 1.8 cm, and 2.6 cm for thresholds of 2 mm, 3 mm, and 4 mm respectively. Conclusion: 4DCT scans as evaluated with a lung motion model show that points near lung tumors have similar trajectories as the lung tumor itself. It is also apparent that fiducials need to be placed closer to lower‐lobe tumors compared to upper lobe tumors. As expected, allowing for an increased difference between the motion of the tumor and other points in the lung yields a larger volume. Further work will focus on extending these results past average breathing cycles.
SU‐GG‐J‐98: Functional Lung Preservation Using Four‐Dimensional Computed Tomography and Intensity‐Modulated Radiation Therapy for Lung Cancer
Authors: Chao M , Xing L
Published: July 2008

Purpose: The goal of this work is to reduce irradiation to functional lung using the four‐dimensional computed tomography (4D CT) derived images. The proposed technique is incorporated into intensity‐modulated radiation therapy (IMRT) to minimize radiation damage to healthy lung and pulmonary toxicity. Method and Materials: Fifteen patients with non‐small‐ cell lung cancer (NSCLC) were selected for this study. A BSpline deformable registration was employed to map each tissue element across the 4D CT data set to establish the correspondence of each voxel. Based on the changes in voxel intensities of each patient, functional image set was generated using pairs between expiration phase and other phases using the equalized histogram technique which equalizes the lung volume under each pixel intensity bin. All functional images were imported into the treatment planning system. The highly functional lung volumes formed by the percentile functional volumes were chosen to be the regions of interest (ROIs) for avoidance in IMRT treatment planning. Two IMRT plans with (fIMRT) and without (aIMRT) the functional image constraint were created and dose distributions including dose volume histograms (DVHs) and dose function histograms (DFHs) and other dosimetric parameters for the planning target volume (PTV) and critical structures in both plans were computed and compared. Results: Compared to aIMRT, the mean dose in fIMRT at 90 and 50 percentile levels were reduced by 2.5 Gy and 4.3 Gy, respectively. The mean reductions in the percentage of irradiated volume of 5 Gy (V5) and 20 Gy (V20) were significantly reduced from that of fIMRT. Conclusion: The dynamic functional images derived from 4D CT was used to guide IMRT planning and it was shown to be effective in preserving normal lung function for NSCLC cancer patients.
SU‐GG‐J‐100: Guidelines for Optimizing Image Quality and Minimizing Technique‐Specific Uncertainties in 3D Ultrasound Imaging for Online Image Guided Radiotherapy of the Prostate
Authors: Neicu T , Martin F , Nurushev T , Hammoud R , Movsas B , Chetty I
Published: July 2008

Purpose: To provide guidelines for improving image quality of ultrasound scans and to suggest specific techniques for optimal visualization and contouring of the prostate gland. Method and Materials: The Clarity™ 3D U/S‐IGRT system (Resonant Medical Inc., Montreal, Canada) is currently in clinical use as the standard practice at our institution for daily imaging of the prostate gland. The CT and U/S images are fused in the Clarity Workstation where the positioning reference volume is developed as the reference volume relative to which daily shifts are made. Primary factors in ensuring high quality U/S scans are the patient bladder filling and the therapist scanning technique. Therapists were asked to try four different scan techniques on the same patient at the same treatment session: angled scans and more vertical scans, each scan being acquired initially with no U/S probe pressure and then repeated with a firm and steady probe pressure. Inter‐user variability was assessed by evaluating scan techniques of different therapists and associating these techniques with the couch shifts. Results: A moderately full bladder allows for proper propagation of the ultrasonic signal thereby facilitating visualization of the prostate gland at the prostate‐bladder/rectum interfaces. To minimize variability in bladder filling each patient is given a set of written instructions at the time of consult, which stresses the importance of a proper bladder filling. Inter‐user variability was found to be significant (up to 8 mm) in some instances and was related primarily to the scanning technique. A recommended scanning technique is to use steady pressure on the U/S probe while scanning through bladder at an angle to avoid the shadow zone caused by the pubic bone. Conclusion: Patient bladder filling and the therapist scanning technique were found to be important factors in optimizing image quality for IGRT‐based U/S imaging of the prostate.
SU‐GG‐J‐102: Image Guided Radiotherapy of the Cervix with Biomechanical Model‐Based Deformable Registration
Authors: Brock K , Moseley J , Stewart J , Lim K , Xie J , Lundin A , Rehbinder H , Fyles A , Milosevic M , Jaffray D
Published: July 2008

Purpose: Evaluate the potential geometric and dosimetric improvements in image‐guided radiotherapy of the cervix using deformable registration. Method and Materials: Weekly MR images obtained prior to and during radiotherapy for 29 women with cervix cancer were selected. The bladder, rectum, and GTV were contoured on each image following rigid, bony anatomy based registration. Deformable registration was performed using MORFEUS, a multi‐organ finite element model‐based deformable registration algorithm. The bladder and rectum were explicitly registered between planning and each week. The GTV displacement was estimated by the biomechanical model and the bladder and rectum displacement. The improvements using couch shifts based on deformable registration were assessed using 3 metrics: 1) improvement in localization of tumor COM, 2) improvements in GTV coverage by the PTV, and 3) improvements in the dosimetric coverage of the GTV and CTV accumulated over the treatment using deformable dose accumulation in ORBIT Workstation. Results: The average error in COM alignment of the tumor improved by 0.3, 2.1, and 1.1 mm in the LR, AP, and SI directions, respectively with deformable registration. Following bony registration, 69% of GTVs were at least 95% covered by the PTV, improving to 86% following deformable registration. Dosimetric coverage of the GTV improved from 93% of patients achieving 98% volume coverage by 4900 cGy to 100% following deformable registration‐based couch shift for tumor COM correction. CTV coverage improved from 83% of patients achieving 98% volume coverage by 4750 cGy to 93% following deformable registration‐based couch shift for tumor COM correction. Conclusion: A method has been developed to perform deformable registration of surrounding anatomy to calculate the COM of the tumor for application in volumetric image guidance where the tumor is not visible. Both geometric and dosimetric improvements were demonstrated.

Supported by RaySearch Laboratories and National Cancer Institute of Canada — Terry Fox Foundation.
SU‐GG‐J‐106: Improved Planar and Megavoltage Cone‐Beam Imaging Using Low‐Z Linear Accelerator Targets
Authors: Orton E , Kelly R , Robar J
Published: July 2008

Purpose: to examine the effect of using low atomic number (Z) target materials on megavoltage portal and cone‐beam CT (CBCT) image quality. Method and materials: for experimental measurements, four low‐Z targets were installed in a linear accelerator carousel (Varian 2100EX) for the generation of experimental spectra for imaging. The targets were composed of beryllium or aluminum with thicknesses set to approximately 60% of the CSDA range of either 4 MeV or 6 MeV electrons. For CBCT acquisition, the beam and detector were fixed, and a rotation stage was controlled by software to acquire multiple angular projections of phantoms. To examine photon energy spectra and to provide a means for optimizing the imaging system, the beam generation and detector panel were modeled using BEAMnrc/DOSXYZ Monte Carlo package. For 6MV, the beam/detector model was validated by comparing experimental and MC‐generated images of open fields. Results: The modeled, experimental spectra demonstrate the recovery of photons below 150 keV. For the 4 MeV/Be beam, for example, approximately 1/3rd of photons have energies below 60 keV. MC models of planar imaging show significant improvement of image contrast compared to the standard 6MV beam, and suggest that i) of the four energy/target combinations studied, the 4 MeV/Be combination provides the greatest contrast improvement and ii) a modest additional increase in contrast is achieved by removing the copper buildup layer from the detector. Initial low‐Z target CBCT images show improved image contrast; full quantitative results will be presented. Conclusion: The use of megavoltage electron beams combined with low‐Z targets offers the potential for improved image quality, particularly in terms of image contrast. This approach may be promising for improved and highly‐integrated on‐board megavoltage imaging.

Conflict of interest: This research has been sponsored by Varian Medical Systems, Incorporated.
SU‐GG‐J‐110: Initial Assessment of Peripheral Dose for Image Guided Radiation Therapy (IGRT) Using Cone Beam CT
Authors: Perks J , Lehmann J , Yang C , Stern R , Purdy J
Published: July 2008

Purpose: With the growing use of intensity modulated radiation therapy (IMRT) combined with daily kilovoltage cone beam CT (CBCT) for image guided radiation therapy (IGRT) patient alignment, concerns are growing over the additional (typically unaccounted) dose outside the irradiated volume associated with the overall procedure. Published data exists for both the in‐field and organ specific doses that arise from IGRT. Additionally the peripheral dose associated with IMRT has been documented. This present study is intended to add to the data available on peripheral dose; particularly comparing IMRT and imaging dose for patient positioning with CBCT using an Elekta Synergy platform. Method and Materials: Measurements of both the in field and peripheral imaging doses were made in an anthropomorphic, solid water phantom where “thin” and “fat” patients were simulated with TLD detectors. These were then compared with peripheral dose measurements for typical prostate and head & neck IMRT treatments with MOSFET detectors. Results: The IGRT dose in the imaged volume correlates well with published data, with 3 – 7 cGy being measured depending on the phantom configuration. The peripheral imaging dose measured was found to be approximately half the amount associated with a typical prostate IMRT treatment at a given point outside the field; with 0.2cGy and 0.4cGy being measured 25cm from the central axis. Thus, a typical patient receiving daily IMRT and IGRT for a fractionated course of radiation therapy for prostate cancer the total peripheral dose would be of the order of 0.2 – 0.5Gy. Conclusion: This study showed that an appreciable dose is delivered outside the field when daily CBCT IGRT is utilized. These doses should be taken into account when a patient image is requested, as all doses, above the prescription, require justification.
SU‐GG‐J‐113: Interfraction Dose Variations for Head and Neck Cancer Assessed Using Daily KVCT
Authors: Peng C , Ahunbay E , Wood C , Wang D , Li X
Published: July 2008

Purpose: The interfraction variations during head and neck cancer radiotherapy can be significant due to the setup errors, neck rotation and organ shrinkage. We investigated the dosimetric consequence of these interfraction variations, so that the proper correction strategies can be considered. Method and Materials: Daily kVCT images for 20 head and neck cancer patients treated with CT‐guided repositioning using a linac and CT‐on‐Rails combo (CTVision, Siemens) were analyzed. Complete structure sets including multiple targets and critical structures were generated by deformable registration (MIMvista, OH) on each daily CT of the entire treatment course. Original plans were applied on each daily CT with and without the repositioning shifts recorded during the daily IGRT process. The daily doses were analyzed and compared to the planned doses. Results: The rotation of neck is difficult to reproduce everyday for head and neck cancer treatments. Generally, the daily repositioning based on the rigid body registration can correct for most of the interfraction dosimetric deviations from the planned doses. For example, on average, D95 (dose covers 95% of the target volume) was 3% lower than that planned after repositioning. It was observed that, for certain treatment fractions, the targets were significantly underdosed (>%), and/or the cord doses were increased by more than 5%. A margin of 0.5 cm for cord could ensure the cord dose does not exceed the dose limit. Conclusion: Although large interfraction variations in neck rotation, organ shrinkage, and setup errors during head and neck RT, the overall dosimetric impact can be corrected in majority of treatment fractions with the current standard of rigid‐body repositioning during IGRT. More complex correction strategies are needed for a small portion of fractions.
SU‐GG‐J‐118: Jitter Reduction in Manually Delineated Clinical Target Volume (CTV) Contours for Prostate Cancer
Authors: Xu Q , Fan J , Chen Y , Chen L , Li J , Chi Z , Ma C
Published: July 2008

Purpose: Conventionally, prostate clinical target volume (CTV) is delineated by an oncologist slice by slice in the axial plane. When being reviewed in the sagittal or coronal planes, the CTV contours are often compromised by jitters due to the uncertainties and errors induced during contouring in the axial plane. Manual contour revisions in these planes are desired, but labor intensive and tedious. We propose an automatic 3D non‐shrinkage surface smooth algorithm to reduce the jitters caused by commonly adopted contouring methods. Method and Materials: The first step of our contour smoothing is triangulation of the polyhedral surface or the stack of 2D axial contours. Since the resolution of the CT image is non‐isotropic, we revise the triangulation method so that the neighbors for each contour point are found within a sphere of a pre‐defined radius. Taubin's two‐step algorithm, also known as a low‐pass filter design technique, is then applied to smooth the 3D CTV surface. First, each contour point is smoothed by neighbors using a Gaussian filter with a positive weight. Then, a negative weight is used to compensate for the low‐frequency component loss in the first step. This procedure iterates for N times to filter out high frequency jitters while maintaining the original CTV volume. The proposed algorithm is evaluated using simulation images and real patient cases. Results: For the simulation study, random noises added to the artificial object surface can be filtered well and the original shape is recovered. For the patient study, the CTV contours before and after smoothing are reviewed and approved by oncologists. The jitters in the sagittal and coronal planes are significantly reduced while the overall CTV definition meets our clinical requirements. Conclusion: A 3D CTV surface smooth algorithm is proposed and has the potential to improve treatment optimization and target coverage for IMRT.
SU‐GG‐J‐119: Localization Accuracy of Target Verification System Using Digitial Tomosynthesis (DTS)
Authors: Yan H , Ren L , Godfrey D , Yoo S , Yin F
Published: July 2008

Purposes: A research platform was developed for target verification using digital tomosynthesis (DTS). To verify its accuracy, a phantom study was conducted and several clinical cases were investigated. Method and Materials: customer‐developed reconstruction and image registration algorithms were implemented in this platform. The existing image reviewing software was employed for the purpose of manual registration. Phantom study was conducted to investigate the target localization accuracy using DTS with respect to different simulated shifts along three directions. In real clinical cases, the registration results of both CBCT‐based and DTS‐based methods were achieved and compared for identify their equivalency. Results: with respect to different simulated shifts of phantom ranging from 1 cm to 5 cm, the high target localization accuracy was obtained which is within 1 mm. The comparison between CBCT‐based and DTS‐based registration results on clinical cases shows that they are nearly identical. The maximal different is less than 0.5 mm and averagely 0.1 mm over three dimensions was observed. Conclusion: DTS is an effective way for fast target localization. With properly setting, the high registration accuracy comparable to CBCT can be achieved. Currently, more effects related to acquisition mode, scan angles, and reconstruction slice thickness, were under investigation. It is expected to present interested user a clear guidance on how to use this new image modality more effectively for image‐guided radiotherapy.

Acknowledgements: this study was supported by NIH grant (R21‐CA128368).
SU‐GG‐J‐120: Longitudinal Resolution of the TomoTherapy® MVCT Image and Potential Improvements
Authors: Chao E , Bichay T , Lucas D , Ruchala K , Olivera G
Published: July 2008

Purpose: To quantify the longitudinal resolution of the TomoTherapy® MVCT image and evaluate potential improvements to the resolution. Method and Materials: The image slice sensitivity profile is measured using a thin‐disc method to approximate a delta impulse function in the longitudinal direction. The sensitivity profile is measured for several different helical pitches and beam widths. In addition, the clinical image longitudinal resolution is limited not only by the image slice sensitivity profile, but also by the image spacing. For a constant image slice profile (constant helical pitch and beam width), the image spacing is varied to investigate the impact of image spacing. Results: With the current TomoTherapy® factory settings for the jaw and the default image pitches (Fine, Normal, and Coarse corresponding to 4, 8, and 12 mm of couch translation per gantry rotation), the slice sensitivity profiles are measured to have a full‐width at half‐maximum of 6, 7, and 8 mm for the Fine, Normal, and Coarse pitches, respectively. Reducing the jaw‐width by an amount corresponding to a 3 mm decrease in the field‐width at isocenter, and keeping the same couch speeds of 4, 8, and 12 mm/rot, results in slice sensitivity profiles with a full‐width at half‐maximum of 4, 5, and 7 mm. Finally, using the thin jaw setting and “Normal” pitch (8 mm/rot), images are reconstructed at the default 4 mm interval as well as at a smaller interval of 2 mm. The sagittal and coronal images are observed to have a significantly improved resolution using the smaller image interval. Conclusion: The TomoTherapy® system currently offers users a balance between imaging speed and image quality. However, a thinner jaw setting and reduced image spacing result in significantly improved longitudinal resolution for TomoTherapy® MVCT images, yielding improved image quality at the same scanning speed.
SU‐GG‐J‐121: Lung Tumor Setup Using 2D‐3D Registration of Respiratory‐Gated Oblique X‐Rays and the Planning 4D‐CT
Authors: Choi B , Dong L , Balter P , Sun X , Pan T , Mohan R
Published: July 2008

Purpose: To investigate the feasibility of using intensity based 2D‐3D registration to directly setup on respiratory gated lung tumors using x‐ray source angles tailored for each patient. Method and Materials: A 2D‐3D registration software was developed in‐house which renders digitally reconstructed radiographs (DRR) in real time with a consumer graphics card. The user was then able to conveniently view DRRs at various source angles to choose the angles where the tumor is less obstructed by surrounding structures during the planning phase. The 2D‐3D software, using mutual information, simultaneously aligned DRRs from the end‐expiration planning 4D‐CT with four end‐expiration projection x‐rays (lateral, Anterior‐Posterior (AP), and 2 oblique) on a sub‐image based on the projection of the tumor. For the analysis, the x‐ray projection data was taken from three lung patients in a separate research protocol for 4D cone‐beam CT. The 2D‐3D results were compared with 3D‐3D alignment of the end‐expiration 4D cone‐beam CT with the end‐expiration planning 4D‐CT on a region around the tumor. Respiration phase information was deduced from a commercial external fiducial system (Real‐time Position Management, Varian Medical Systems). The volumes of the three tumors were 14.0 cc, 45.8 cc, and 17.9 cc. The extents of motion in the Superior‐Inferior (SI) direction were 2 mm, 4 mm, and 11 mm. Results: The mean differences between the 3D‐3D and 2D‐3D registrations were −0.1 mm, 0.1 mm, and 1.6 mm in the lateral, AP, and SI directions respectively. The standard deviations were 2.2 mm, 1.8 mm, and 1.0 mm. Conclusion: We have demonstrated the feasibility of direct lung tumor setup with per‐patient x‐ray source angles. The preferred oblique x‐ray angles were anterior and posterior angles on the same lateral side as the tumor. Future work will investigate the optimal number of x‐rays and the lower limit of the tumor's size.
SU‐GG‐J‐123: Making High Volume OBI CBCT Work in “the Real World”
Authors: Lehmann Joerg , Glass J Stacy , Skubic Stan , Asche Dave
Published: July 2008

Purpose: This report outlines the hurdles and successes encountered in integrating a Varian On‐Board Imaging (OBI) system with an existing linear accelerator (linac) in a mixed vendor environment with the goal to perform high volume routine Cone Beam CT (CBCT). Method and Materials: Varian OBI was added to an existing linac concurrently with the requisite installations of an MV Portal Vision (PV) and a Varian 4D integrated treatment console (4DITC). The system was connected to an existing IMPAC MOSAIQ environment with a Philips Pinnacle planning system. Results: The integrated system is functioning and is used daily for more than 20 CBCT patients. Pending the OBI software update, patients are predominantly scanned with the “low dose protocol”. Isocenter accuracy and system safety checks have been implemented as routine quality assurance (QA) measures. Several glitches with the OBI system software have surfaced, which necessitated intervention from the vendor's highest tiered technical support personnel. These glitches include unexplained loss of calibration data, non‐functioning components, and the display of seemingly non‐essential error messages, which appear to be unrelated to the functioning of the system. Furthermore, the robotic arms moving the kV source and imaging panel have at multiple instances crashed into themselves. For patient safety they are now only moved when in the lateral position. Workflow problems also have arisen with the recording of offsets and the preparation of the planning CT data set used for reference in CBCT. Conclusion: An add‐on OBI system for CBCT is a viable clinical solution, which however requires much patience and persistence, especially in a mixed vendor environment.
SU‐GG‐J‐134: MRI‐Guided Adaptive Brachytherapy of Cervical Cancer: Initial Experience with High Resolution Diffusion Imaging
Authors: Zhu JM , Li H , Lu W , Mutic S , Low DA , Grigsby PW
Published: July 2008

Purpose: MRI has the potential to provide wealthy information related to tumor biology and function, and therefore is the idea imaging modality to provide accurate guidance for radiotherapy. The purpose of this study is to develop and integrate a high resolution diffusion imaging protocol into clinical treatment planning for image‐guided adaptive brachytherapy of cervical cancer. Method and Materials: MR imaging was performed on a clinical 1.5T system using a four‐element phased array RF coil. Patients who underwent routine MRI simulation in conjunction with their weekly brachytherapy treatments were included in the study. Brachytherapy was performed with MRI‐compatible tandem and ovoid applicators, and MRI was performed right after placement of the applicators, but before the treatment. In additional to T2‐weighted TSE sequences for routine treatment planning purposes, high resolution diffusion‐weighted images were also acquired. Diffusion images in the form of apparent diffusion coefficient (ADC) maps were computed, and evaluated along with treatment planning using Brachyvision. The add‐on values of ADC maps for treatment planning were assessed. Results: Diffusion imaging was successfully performed on all the selected patients using DW‐EPI sequence without obvious distortion artifacts from the applicators. Overall image qualities were analyzed, and the diffusion gradient b‐value for optimal tumor delineation was found to be 800 to 1000. When b‐value increased, the signal contrast between the tumor and adjacent normal tissue became stronger, however, image became noisier. With the optimized protocol, ADC maps provided better tumor delineation than T2‐weighted images for treatment plan optimization. Conclusion: High resolution diffusion imaging provided physiological information for tumor and normal tissue, which is less achievable by other imaging modalities. The ADC maps offered excellent image sets for not only depicting the tumor extend for adaptive treatment optimization, but also assessing the overall tissue physiological changes during the treatment course.
SU‐GG‐J‐146: Piecewise Rigid‐Body Image Registration for Adaptive Radiation Therapy
Authors: Park SB , Sohn JW
Published: July 2008

Purpose: To accelerate image deformation and registration for Adaptive Radiation Therapy (ART), we propose a piecewise rigid‐body image registration (PRIR). This algorithm is faster than full deformable registration by up to a factor of ten without sacrificing accuracy. Method and Materials: Deformable Image Registration (DIR) may not reflect the biomechanical characteristics of the anatomy. In short, DIR may try to deform the body in ways that are not physically possible. Fluid dynamic models were adopted to address this problem. However, DIR consumes too much time to be utilized for routine clinical ART. PRIR considers the biomechanical characteristics of the anatomy while retaining the speed of rigid‐body transformations. First, we import contours from a Radiation Therapy Plan (RTP) through DICOM‐RT. We assume that the contour delineates an organ (or tumor), which is modeled as an independent rigid‐body. Two image sets (planning CT and Conebeam CT) were aligned with our rigid‐body registration using Spatial Weighted Mutual Information (SWMI). Then, rigid‐body registration was performed with each organ independently from the rest of image using Mutual Information or SWMI. Users can select a specific type of registration: full translation and rotation, 3‐D scaling, or 2‐D scaling by considering biomechanical characteristics. One prostate case (9 image sets) and one head‐and‐neck case (7 image sets) were tested. Results and Discussion: Our image registration for 6 contoured organs took 95seconds on average. We succeeded in transforming deformable contours from RTP images to daily cone beam CT images. Our method can be utilized to re‐optimize plans for Adaptive Radiation Therapy. The speed can be further improved with parallel processing. Accelerating deformable registrations is critical for implementing real‐time ART. (This work is partly supported by Susan G. Komen Breast Foundation Grant: BTCR126506)
SU‐GG‐J‐150: Positron Emission Based Technique for Linear Fiducial Marker Tracking During Radiation Therapy
Authors: Xu T , Churchill N , Chamberland M
Published: July 2008

Purpose: To develop a tracking algorithm for linear positron emission marker for external beam radiation therapy. Method and Materials: The delivery accuracy of external beam radiation therapy is currently limited by the motion of tumour during treatment. By implanting positron emission fiducial markers into the tumor, and using pairs of position‐sensitive detectors to track the resulting annihilation gamma rays, the position of the tumor can be tracked in real‐time with high accuracy. Positron emission based technique will deliver a lower radiation dose to normal tissue than x‐ray fluoroscopy, and the smaller size of the positron emission markers reduces risk to the patient during implantation. Some previous studies have shown that multiple point markers can be tracked using this technique. In this study, we further extended the technique to track a linear marker. Using a single linear marker has many advantages as compared with multiple point markers: single implantation instead of three can further reduce the patient risk and totally eliminates the possibility of marker migration. An algorithm that iteratively estimates the location and orientation of the linear marker is proposed. The algorithm was then evaluated using data obtained from Monte Carlo simulation. Results: The accuracy of the tracking algorithm improves with increased number of events used. The center of the linear marker was localized to sub‐millimeter accuracy with a total of 1000 events. The end‐points of linear marker were localized with average accuracy of about 2.5 mm, which converts to about 6 degree of uncertainty on the orientation. Conclusion: Linear fiducial marker labeled with positron emission isotope can be localized with sub‐millimeter accuracy and can be potentially used for real‐time tumour tracking during radiation therapy.
SU‐GG‐J‐154: Quality and Accuracy of Cone Beam Computed Tomography Gated by Active Breathing Control.
Authors: Thompson BP , Hugo G
Published: July 2008

Purpose: To evaluate the quality and accuracy of cone beam computed tomography (CBCT) gated by active breathing control (ABC) for image guidance. Method and Materials: Comparisons were made between conventional ABC‐CBCT (stop and go), modified ABC‐CBCT (a method to speed up the acquisition by slowing the gantry instead of stopping during free breathing), and free breathing respiration correlated CBCT. All CBCT images were acquired with an Elekta LINAC equipped with an on board KV imager with two gantry speed settings. Speed changes for the modified ABC‐CBCT were triggered by the ABC. Breath hold and free breathing patterns used were: (breath hold seconds / free breathing seconds) 3 / 15, 5 / 10, and 10 / 15. Image quality was assessed with a CATPHAN with high contrast, low contrast, and uniformity inserts. CT number linearity was evaluated. Registration assessment (bony and soft tissue) was quantified with both an anthropomorphic and a quality assurance phantom. A calibration phantom was used to assess gantry angle accuracy with respect to gantry speed modulation. Results: Conventional ABC‐CBCT scan time for the breath hold patterns assessed ranged from 2.3 to 5.8 minutes. Modified ABC‐CBCT scan time ranged from 1.4 to 1.8 minutes, and respiratory correlated CBCT scans took 2.1 minutes to complete. CT number linearity for ABC gated scans was comparable to a normal clinical scan with all projections. Registration accuracy for small, large, and rotational corrections was within 1 mm and 1. Conclusion: Modified ABC‐CBCT (slow gantry during breath hold) scans can potentially improve the efficiency of conventional ABC‐CBCT (stop and go), or replace respiration correlated CBCT, without degradation of performance for image guidance purposes. Conflict of Interest: Research sponsored by Elekta, Inc.
SU‐GG‐J‐159: Radiation Dose Estimates for in Vivo MicroCT Studies
Authors: Seo Y , Hasegawa B
Published: July 2008

Purpose: Repeated scans of microCT can deliver radiation dose levels that can perturb the biological response of an animal model. The purpose of this study is to determine if a simple phantom having dimensions that approximate the size of a typical mouse can be substituted for the animal model for radiation dose measurements of microCT scans. Method and Materials: Phantom measurements of radiation dose were performed with a hollow water‐filled acrylic cylinder (OD: 25.4 mm, ID: 19.0 mm) and a lithium fluoride TLD in a PVC pouch immersed in the water compartment of the phantom. CT was performed using a microCT system (X‐O™, Gamma Medica‐Ideas, Northridge, CA) with an x‐ray source of two settings, 75 kVp/0.325 mA and 60 kVp/0.530 mA which are typical for in vivo studies. CT data were acquired using 512 projections over 120 seconds of continuous x‐ray exposure. For comparison, a TLD placed within the thorax of a euthanized mouse (∼30 g) was exposed using the same x‐ray techniques as the phantom. A total of 4 TLDs (one each with two x‐ray settings for the phantom and animal measurements) were read using a Harshaw 6600 TLD reader with correction factors applied for 60–75 kVp x‐ray. Results: The TLD measurements produced dose measurements of 3.645 and 4.255 cGy in the cylindrical phantom, and 4.137 and 4.690 cGy in the euthanized animal, for x‐ray techniques of 75 kVp/0.325 mA and 60 kVp/0.530 mA, respectively. The readings obtained from the phantom measurements were 9–12% lower than those obtained from the animal. Conclusion: The radiation dose measurements using TLDs in the mouse‐sized cylindrical phantom were in a good agreement with the dose measurements in the euthanized animal. This phantom, in combination with TLDs, potentially is a useful tool for estimating radiation dose for serial in vivo studies with microCT.
SU‐GG‐J‐165: Reconstruction of Missing Data On Kilovoltage and Megavoltage Cone‐Beam CT Images for Adaptive Radiation Therapy
Authors: Cheong K , Kang S , Hwang T , Bae H , Kim K , Kim S , Lee M , Oh D , Suh T
Published: July 2008

Purpose: Kilovoltage (kV) or megavoltage (MV) cone‐beam CT (CBCT) technique become popular nowadays for patient setup verification and dose recalculation aiming image‐guided radiation therapy. In case of kV CBCT, field‐of‐view (FOV) is large enough to cover whole thoracic or pelvic region at detector off‐set mode while length of image set is limited and MV CBCT, vice versa. In this study, we dealt with missing data issue; compensation of missing part with kV CT images used for treatment planning. Method and Materials: First, obtained kV or MV CBCT images were registered with the planning kV CT images respectively. For kV CBCT, CT slices beyond the obtained volume were filled with planning CT data. For MV CBCT, overlapped regions in the kV CT images with the MV CBCT images after registration were substituted with the MV CBCT data. To reduce statistical discrepancies of pixel numbers between CBCT images and kV CT images and to minimize dose recalculation error, pixel number mapping and spatial filtering were employed. Varian Clinac iX and Siemens Primus linacs were used for CBCT image acquisition. Image registration and dose recalculation were implemented using Pinnacle3 ver 8.0d. Proposed algorithm were tested for chest and pelvic regions of a humanoid phantom and patients. Isodose comparison and gamma index were adopted as evaluation criteria. Results: Dose calculation result with the reconstructed CT image set agreed with calculation done with kV CT meaningfully within 2% on a phantom but error was up to 5% for clinical cases. Discrepancies were mainly due to anatomic changes and incomplete match of boundaries at the interface of two image set. Conclusion: The reconstruction algorithm showed a possibility of adaptive radiation therapy using CBCT images but image quality of CBCT data needs to be improved more.

Research sponsored by MOST (Korean government).
SU‐GG‐J‐167: Resonant X‐Ray Irradiation of High‐Z Nanoparticles for Cancer Theranostics
Authors: Pradhan A , Nahar S , Montenegro M , Sur C , Mrozik M , Pitzer R , Silver E , Yu Y
Published: July 2008

Purpose: Broadband X‐ray sources employed in current cancer therapy are indiscriminant of tissue composition. We demonstrate significant dose enhancement by high‐Z (HZ) sensitizing agents at resonant energies below the K‐edge. This is of particular interest in cancer theranostics using agents such as gold nanoparticles embedded in malignant tissue. Method and Materials: Relativistic R‐matrix calculations were performed for radiative transitions and photoionization for many HZ elements from Fe to U. Accurate cross section data and monochromatic attenuation coefficients were computed in energy ranges where the large k‐a resonance complexes occur. Scaling laws up to HZ species such as Pt, Au, and U are studied. Depth dose curves based on photon transport in a numerical model containing muscle, bone, and tumor with 1mg/cc concentration of gold nanoparticles were calculated using the new resonant atomic data and compared with those calculated using standard evaluated data. Results: Giant resonance complexes were identified in all HZ species at energies below the respective K edge. For example, the resonant attenuation coefficient for k‐α transitions in Fe and Au are more than 1000 times higher than at their K edge. The average absorption efficiency in cm2/g of Au at ∼68 keV is 7400, compared to 3.3 at the Au K‐edge, and only about 0.2 for C, N, O and 0.24 for Ca. The gold resonance complexes lie in the range 67–80 keV, below the K‐edge. The calculations reveal preferential dose deposition ratio of 3 to 4 between the gold nanoparticle‐bearing tumor and soft tissue (including surface) or bone. Conclusion: Opportunities exist to specifically target HZ‐bearing tumors while sparing normal tissue at monochromatic or narrowband X‐ray sources tuned to resonant energies. We identify and discuss potential sources for the generation of sufficiently intense K‐alpha resonant radiation, such as laser produced plasma devices and electron‐beam ion traps.
SU‐GG‐J‐170: Small Animal Conformal Radiation Therapy Device
Authors: Sharma S , Moros E , Corry P
Published: July 2008

Purpose: To develop a Small Animal Conformal Radiation Therapy Device (SACTRD) that will provide a degree of geometric/anatomic targeting comparable to what is achievable in current clinical radiotherapy practice to promote translational research in radiation oncology. Method and Materials: The SACRTD will integrate 3D‐conformal radiation therapy delivery with cone beam CT (CBCT) imaging for image‐based treatment planning and guided‐delivery. The main system components are: A Seifert Isovolt Titan 225kV X‐ray tube with focal spot sizes of 0.4 and 3 mm, which is mounted on a custom made “gantry” and has a special collimating assembly that allows field sizes down to 0.5 mm diameter at the 34 cm isocenter. A second main component is a computer‐controlled robotic arm (Adept Viper S650) for animal positioning. The six degrees of freedom (6DOF) robot can be programmed to move with an accuracy ±0.020 mm in XYZ directions. A third main component is a digital X‐ray flat panel detector for CBCT. The X‐ray source, the flat panel imager and the robot will be integrated for radiation delivery and imaging. A shielded enclosure housing the SACRTD is presented in a companion abstract. The final system will be capable of precise, accurate and quantifiable conformal delivery of radiation dose to selected targets within small animals in single or multiple fractions. Results: The development of SACRTD is in progress and current work is focused on stable gantry design, characterization of the X‐ray beam at various energies and programming of the robotic animal positioning system. Conclusion: The development of the SACRTD in an academic laboratory is a feasible but challenging undertaking, which has been motivated by the need for a R&D tool for biological, functional and molecular studies in radiation oncology using small animals which can effectively mimic current and future clinical systems.
SU‐GG‐J‐175: Target Registration Error Analysis Via KV Imaging and Conebeam CT in Accelerated Partial Breast Irradiation
Authors: Schuller B , Nawaz A , Wolfgang J , Gierga D , Willins J , Kachnic L , Chen G
Published: July 2008

Purpose: In accelerated partial breast irradiation (APBI), accurate localization of the lumpectomy cavity is important. We are investigating daily localization of the lumpectomy cavity in patients with implanted surgical clips by kV imaging followed by conebeam CT (CBCT). Initial data based on 2 patients are presented here. Target registration error (TRE) analysis was performed to assess the accuracy of available image‐guidance techniques for target localization during APBI. Method and Materials: APBI patients were positioned to the treatment isocenter initially by laser alignment to skin tattoos, followed by orthogonal kV radiographs to visualize bony anatomy and surgical clips and then by CBCT (once daily) to visualize both surgical clips and soft tissue architecture. Couch shifts were performed based on matching surgical clip position and lumpectomy cavity architecture (when visible) to the planned setup. The lumpectomy cavity position was assumed to be represented by the surgical clips. The TRE is defined as the residual setup error following isocenter alignment. Surface topology analysis on the serial CBCT datasets was performed post‐treatment by co‐registering the breast surfaces, as defined by CBCT, and then measuring the clip misalignment. Results: The average laser setup TREs (determined by kV imaging) for patients 1 (breast volume = 1335.5cc) and 2 (breast volume = 404.7cc) were 3.7mm and 6.1mm, respectively. The average kV imaging TREs (determined by CBCT, post‐kV imaging shifts) for patients 1 and 2 were 4.9mm and 1.4mm, respectively. The average surface topology TREs for patients 1 and 2 were 4.9mm and 1.6mm, respectively. Conclusion: Even after kV imaging, TREs around 0.5cm were detected using CBCT in the larger breast volume. Therefore, CBCT may improve targeting in APBI for patients with large breast volumes. Surface alignment may be more suitable for patients with small breast volumes and is currently under further investigation.
SU‐GG‐J‐176: The Accuracy and Stability of the Calypso System for Prostate Localization and Motion Tracking
Authors: Li JS , Price R , Jin L , Ma C‐M
Published: July 2008

Purpose: To investigate the long‐term accuracy and stability of a real‐time electromagnetic tracking system (“Calypso System” Calypso Medical Tech. Inc, Seattle, WA) that has been used for localization and motion monitoring for prostate IMRT. Method and Materials: Two Calypso Systems have been installed in our center and were calibrated bimonthly. A quality‐assurance (QA) phantom provided by the manufacture has been used to check the localization accuracy every day. The phantom was set up under the guidance of the room laser and checked with the beam crosshair. The measured isocenter offsets in three directions were recorded for different calibration periods (the time period between two calibrations). The mean value and the standard deviation of the offset for every calibration period were analyzed statistically. The systematic error and the random error for prostate localization were calculated and compared with the acceptance tests when the systems were first installed. Results: Phantom localization data for 9 calibration periods in one year were used for the calculation of the localization accuracy and stability. The mean offsets in lateral, longitudinal and vertical directions are 0.08mm towards right, 0.24mm toward inferior and 0.71mm toward posterior. The standard deviations in these three directions are 0.34mm, 0.49mm and 0.47mm for the systematic error and 0.67mm, 0.9mm and 1.29mm for the random error, respectively. The results agreed with the acceptance tests in which the average setup and tracking accuracy was 0.95mm and the maximum error was 1.5mm when only two transponders were used. Conclusion: The localization uncertainty using the Calypso System is less than 1mm based on the phantom measurements and it was confirmed through the acceptance tests. The system is accurate and stable for prostate patient localization and motion tracking based on long term phantom calibration measurements.
SU‐GG‐J‐177: The Application of An ASi‐Based EPID to Guide Intensity Modulated Radiation Therapy (IMRT) of Head‐And‐Neck Cancer
Authors: Chang Z , Yoo S , Wang Z , Yin F
Published: July 2008

Purpose: In head‐and‐neck IMRT treatment, doses to targets and critical organs are affected by many factors including patient positioning, weight loss and tumor shrinkage. To ensure therapeutic effectiveness, re‐planning with a new CT is often conducted. However, it remains unclear how to re‐plan in time before intolerable dose deviation occurs. We propose to use EPID to quantitatively monitor treatment delivery and guide re‐planning decision. Method and Materials: In the method, baseline exit intensity maps are obtained with EPID during the first treatment. Exit intensity maps during the following treatments are compared against the baseline. When deviation from the baseline is beyond a threshold, re‐planning may be considered. To test the method, a phantom study and a patient study are conducted. In the phantom study, a cylindrical phantom with a 2.5cm bolus is scanned with CT, and an IMRT plan is generated in an Eclipse workstation. The baseline intensity maps are first obtained with EPID. Then, two new sets of intensity maps are respectively acquired after a shift of the phantom by 2cm to simulate mis‐positionig and bolus removal to simulate tumor shrinkage. Deviations are quantified with gamma analysis. In the patient study, exit intensity maps are acquired for nine consecutive head‐and‐neck IMRT treatments. The first set is used as baseline and compared against the rest eight sets. Results: In the phantom study, the shift and bolus removal introduce considerable deviations, indicated by low pass rates of 50%. In the patient study, pass rates of certain fields after seven fractions are dropped to 70%, which is well below 95% pass rate of portal dosimetry at DUMC. This suggests a verification of patient positioning and targets with consideration of re‐planning. Conclusion: This work presents a real‐time, efficient and quantitative tool to monitor head‐and‐neck IMRT delivery. Future work involves automation of this method.