bluuebunny/crossref_metadata_2025 huggingface dataset:
SU‐FF‐J‐59: Dose Calculation and Quantitative PTV Expansion Using Dynamic MRI Images
Authors: Sheng K , Cai J , Read P , Molloy J
Published: June 2005

Purpose: To extend the geometrically defined PTV expansion for lung cancer patients to dosimetrically relevant PTV expansion by incorporating dynamic MRI into dose calculation and to quantitatively compare the dosimetry of uniform PTV dose with the dosimetry of non‐uniform PTV dose for a moving tumor. Method and Materials: A 1.5‐T whole‐body Siemens MRI scanner was used in the experiment. The patient diagnosed with metastatic adenocarcinoma at lower right lobe was scanned by trueFISP (true Fast Imaging with Steady Precision) sequence. The tumor was contoured from the first frame and automatically tracked by normalized correlation and snake for the rest frames. Dynamic MRI images were rigidly registered to the CT images and the dose images from tomotherapy. Under the assumption of invariant dose distribution for slightly changed anatomy, accumulative dose and DVH for the target was calculated by convolving moving target volume with the dose image. In order to compare non‐uniform does distribution and uniform dose distribution, a 10% does boost was added to the superior/inferior end of the PTV dose when calculating the cumulative dose. Results: No significant dose fall off was observed when the craniocaudal (CC) PTV expansion reduced from 11 mm to 8 mm. The cold spot of tumor dose became noticeable when the CC expansion reduced to 7 mm and was substantial at 5mm. Compared with uniform PTV and 7 mm CC expansion, a 10% dose increase at the CC ends of the 5 mm CC expansion achieved same quality of dose distribution and reduced average lung dose for 7.1%. Conclusion: By incorporating dynamic MRI into dose calculation, the estimate of appropriate PTV expansion is more dosimetrically relevant and accuracy. With accumulative dose calculation and a specific patient, non‐uniform PTV dose shows superior quality than the conventional uniform dose. Generalization of this conclusion is under further investigation.
SU‐FF‐J‐62: Image‐Guided Radiotherapy Feasibility Study Using Kilo‐Voltage Cone‐Beam CT Images for Patient Alignment Verification
Authors: Shiu A , Wang C , Lii M , Chang E
Published: June 2005

Purpose: The objective of this work was to evaluate the feasibility to acquire the kilo‐voltage (KV) cone‐beam computer tomography (CBCT) images and to register the CBCT images with the conventional planning CT images for patient alignment verification. Method and Materials: A Varian high precision accelerator with on‐board KV imaging (OBI) system and CBCT was used in conjunction with a QA head phantom for patient setup position verification. In addition, the in‐house image registration and verification software was used for the analyses of patient alignment accuracy. First, we acquired the same reference image data sets of the QA head phantom from the CBCT and the LINAC/CT‐on‐rails unit. The conventional CT image set was used as the planning CT images. Applied the translation and/or the rotation to the QA head phantom to imitate the daily patient setup variation and then, acquired the daily CBCT images. Results: No differences were observed on the registration between the reference image sets obtained from the conventional planning CT and CBCT. Similar findings were also observed on the registration of the daily CBCT with the planning CT images when the translations were applied to the setup of the daily QA head phantom deviated from the planning QA head phantom setup. When the rotations were applied to the daily setup of the QA head phantom, the treatment target was registered well between the daily CBCT images and the planning CT images, but the difference of 1.3 mm was observed on the registration in the structure relatively far away from the target. Conclusion: Phantom studies indicated that the daily pretreatment CBCT images should be suitable to use for patient alignment verification with the planning CT images. Conflict of Interest: supported by Varian Medical Systems.
SU‐FF‐J‐65: Intrinsic Accuracy of I‐Beam's Coordinate Positioning System Technology
Authors: Goddu S , Li H , Klein E , Mutic S , Wood R , Michalski J
Published: June 2005

Purpose: I‐Beam, a 3D‐ultrasound guided prostate localization system, uses Coordinate Positioning System (CPS) Technology in registering live ultrasound images of the patient to the treatment machine coordinate system. The goal of this study is to verify the accuracy of I‐Beam's camera system and its precision in localizing the US images to the isocenter. Method and Materials: The first part of the study was to examine the I‐Beam camera system for integrity in tracking the probe position while translating the US probe in 3D‐space. We then examined alignment correctness when registering the captured US images and contours. A robotic arm of the Nomos BAT system was used for accurate translations. Both the arm and camera system were fixed to the treatment couch. Longitudinal translations of the camera system were confirmed by the Nomos Auto‐crane. An ultrasound phantom mimicking pelvic anatomy was employed in quantifying the precision of the image localization and contour alignment. The phantom was translated to known distances, recapturing the 3D‐ultrasound volume, and aligned the contours to determine the shifts computed by the I‐Beam system. Results: X‐, Y‐ and Z‐ translations recorded by the robotic system were subtracted from the coordinates of the camera system in computing the errors. When the camera system was repositioned within ±10 cm of the 3D‐space, the CPS technology predicted the ultrasound probe position within ±0.5 mm. The absolute deviations were (mean ± SD): 0.3±0.2, 0.2±0.2 and 0.2±0.2 in lateral, longitudinal and vertical directions, respectively. I‐Beam's image registration and contour alignment were accurate within ±1mm. Conclusion: The I‐Beam camera system is accurate to within ± 0.5mm in tracking the US probe position. Phantom measurement showed the US image acquisition and the contour alignment is also accurate within ±1mm. These new tests assured that the I‐Beam system is accurate in tracking, image‐registration and alignment.
SU‐FF‐J‐69: Pitch, Roll and Yaw Device for Helical Tomotherapy Head & Neck and Brain Treatment
Authors: Wu H , Rosen L , Katz S , Mirzasadeghi M , Akpati H
Published: June 2005

Purpose: To demonstrate the effectiveness of a new pitch, roll and yaw device for helical Tomotherapy head and neck and brain treatment. Methods & Materials: The pitch, roll and yaw device is a headrest frame with a mechanism for adjusting angular orientation. It is fabricated using two overlaying Lucite panels mounted on an adjustable wheel base. With the use of the pitch, roll and yaw headrest device three MVCT image sets are obtained, and two displacement adjustments (first angular, second translational) are made. Since the axis of rotation may not be located in the center of the image volume, adjustments for the rotational and translational displacements have to be made independently. The rotational adjustments are made after the first scan, and the translational adjustment is made after the second scan. A third MVCT scan is obtained for final verification prior to treatment. Results: Using the headrest device, on average the pitch, roll and yaw angular displacements can be reduced to less than 0.2°, 0.3°, and 0.25°, respectively, after three MVCT scans. The final translational x, y, z, displacements are still be minimized to less than 1mm after rotational adjustments. Conclusion: As a mechanism for adjusting angular displacements, the pitch, roll and yaw device provides additional degrees of freedom for target localization. However, one additional MVCT image set is needed in order to independently adjust the rotational and translational displacements.
SU‐FF‐J‐71: Shifting MLC Shapes to Adjust for Daily Motion of the Prostate in the Concurrent Treatment of Pelvic Lymph Nodes and Prostate
Authors: Ludlum E , Xia P , Chen H , Roach M , Akazawa P
Published: June 2005

Purpose: To determine if adjusting the multileaf collimator (MLC) leaf positions to follow daily motion of the prostate is a feasible alternative to moving the patient, and to apply this adaptive strategy to concurrent treatment of the prostate and pelvic lymph nodes Method and Materials: A leaf‐shifting algorithm was proposed to adjust MLC leaf positions to follow prostate movement while keeping the MLC portal shape unchanged. The MLC shift for each segment was calculated based on the beam direction, and the direction and magnitude of prostate movement. A computer program was written to implement this algorithm. The shifted MLC shapes were subsequently imported back into a commercial treatment planning system for the final dose calculation. For prostate‐only plans, isodose distributions were compared between the shifted MLC plans and shifted isocenter plans, which mimic the adjustment of patient position. For plans including the prostate and pelvic lymph nodes, isodose distributions were compared between the partially shifted MLC plans and shifted isocenter plans. Results: For prostate‐only plans, the isodose distributions were the same for shifted MLC positions and for shifted isocenters. For pelvic lymph node plans, shifting patient treatment position to follow prostate movement significantly reduced the dose coverage to the pelvic lymph nodes. Shifting MLC leaves associated with the prostate while keeping the MLC leaves associated with the lymph nodes unchanged resulted in improved dose coverage to both the prostate and the pelvic lymph nodes. Conclusion: Shifting MLC portal shapes is equivalent to shifting patient treatment position. In order to concurrently treat the prostate and pelvic lymph nodes, with the prostate moving independently, shifting the MLC shape is a better adaptive strategy than shifting the patient. Conflict of Interest : Research supported in part by Siemens.
SU‐FF‐J‐72: The Effect of MV Cone‐Beam CT Cupping Artifacts On Dose Calculation Accuracy
Authors: Chen J , Morin O , Chen H , Aubin M , Pouliot J
Published: June 2005

Purpose: MV cone‐beam (CB) CT imaging can be used to position the patient prior to external‐beam radiotherapy. If calibrated, these images may also be used in dose calculations, opening the possibility to reconstruct the delivered dose or re‐optimize the treatment plan before delivery. This study investigates the effect of imaging artifacts on dosimetric accuracy. Method and Materials: Two water cylinders of 13 cm and 22.5 cm diameters were imaged using A) a MV CBCT system integrated with a Siemens accelerator and B) a conventional kV CT imager. Cupping trends observed in the MV CBCT were imposed on the kV CT images to create artificial data with simulated artifacts. Using the Phillips Pinnacle planning system, a 6 MV 10 × 16 cm2 field was applied to 1) the original kV CT of the smaller cylinder and 2) the kV CT with simulated artifacts. Similarly, a 18 × 18 cm2 field was applied to the original and artificial kV CT of the larger cylinder. Results: For the smaller cylinder, the MV CBCT water signal relative to air at the cylinder center differs from the radial and axial extremities by approximately 14% and 17% respectively. For the larger cylinder, the differences are 38% and 20% in radial and axial directions. The dose distributions for the artificial images show a systematic deviation which increases with depth. In the high‐dose, low‐gradient regions, the largest deviation for the smaller cylinder is 1% of the maximum delivered dose. For the larger cylinder, the largest deviation is 4%. Conclusion: Cupping artifacts in water phantoms produce dosimetric errors much smaller in magnitude than the cupping trend itself but as large as 4% for large phantoms. These results suggest that rough correction of MV CBCT artifacts may be sufficient for dosimetric accuracy. Conflict of Interest: Research supported by Siemens OCS.
SU‐FF‐J‐77: Implementation of Averaged 4D CT Imaging for Extracranial Stereotactic Radiation Therapy
Authors: Liu J , Drzymala R , Bradley J , Lu W , Goddu S , Parikh P , Low D
Published: June 2005

Purpose: To implement Averaged 4D CT imaging to measure the motion of lung tumor during breathing Method and Materials: Averaged 4D CT images are obtained by averaging 4D CT images. A Philips Brilliance 16P CT scanner is used to obtain 4D CT images. The scanner acquired 16 parallel slices per couch position and 25 cinematographic images per slice to produce a ciné image set. The corresponding images are then averaged at each slice. All averaged images are assembled longitudinally to produce a series of Averaged 4D CT images, whose pixel value therefore contains the information about the movement of the target anatomy. An egg‐shaped object and a block‐shaped object were used for testing. A few patients were also studied and evaluated. Results: Phantom results showed that Averaged 4D CT images could accurately record the movement of a target having a natural breathing frequency. Results with lung tumor showed that Averaged 4D CT images gave a significantly larger GTVs resulting in larger PTVs, compared with helical CT images. Both the phantom and patient results clearly showed fuzzy areas as a consequence of moving anatomy. The time needed for creating an Averaged 4D CT image set from original 4D CT image set with 5 cinés and 400 slices per ciné is about 370 seconds. Conclusion: This technology can be accurate and practical for approximating the location of moving anatomy if used properly. Therefore, Averaged 4D CT images can replace helical CT images for radiation planning and treatment purposes with the advantage that they have greater precision than standard helical scans. Conflict of Interest:: Part of this work was funded by Elekta, Inc., Norcross GA.
SU‐FF‐J‐79: Local Tomography Using Adapted Feldkamp and Expectation Maximization Algorithms
Authors: Zhang J , Shi D , Anastasio M
Published: June 2005

Purpose: There has been much interest utilizing megavoltage CT to verify patient positioning in conformal radiation therapy. Local tomography methods have been proposed for reconstructing tumor volumes. In this work, we use simulated and experimental phantom projection data to investigate and compare 3D local tomography approaches based on the Feldkamp‐Davis‐Kress (FDK) and Expectation Maximization (EM) reconstruction algorithms. Method and Materials: We have implemented numerically local tomography versions of the EM and FDK reconstruction algorithms. An ensemble of numerical phantoms was created that contained structures of varying size and contrast. Multiple noisy simulated data sets were computed. Untruncated experimental projection data corresponding to a head and torso phantom were also acquired. From these data sets, truncated data were created by keeping only subsets of the complete data. 3D images of the tumor volumes were reconstructed by use of the local FDK and EM algorithms. The reconstructed images were assessed visually to determine if the boundaries and interfaces within the tumor volume were reconstructed accurately. The contrast of the reconstructed boundary information was quantified. Results: For the low‐noise data sets that contained a large number of uniformly spaced projections, the local FDK algorithm produces images that had better boundary contrast than those produced by the EM algorithm. However, the EM algorithm reconstructed images with reduced artifact levels when the projections contained high noise levels and were few in number. Conclusion: In many applications of MV CT, the number of truncated projections is limited. In these cases, the EM is more appropriate than the FDK algorithm for reconstructing geometric information regarding the tumor volume. However, the local FDK algorithm is better suited for reconstructing low contrast boundaries when the number of acquired projections is sufficient.
SU‐FF‐J‐83: Use of CT‐Simulation Tools Located On the CT Scanner for Localization Guidance in Extracranial Stereotactic Radiotherapy: A Feasibility Study
Authors: Mutic S , Drzymala R , Hampton C , Pierburg B , Esthappan J , Low D , Bradley J
Published: June 2005

Purpose: To quantify the accuracy of CT‐simulation localization tools located on the CT‐scanner control console for guidance in extracranial stereotactic radiotherapy (ESRT). Method and Materials: ESRT applies stereotactic treatment principles to irradiate extracranial tumors in few fractions (typically 2–6) with high dose/fraction. To accomplish this, an anatomic reference coordinate system is replaced by an external stereotactic coordinate system and improved patient immobilization methods are also used. Because the patient is scanned prior to each treatment while in the immobilization device, it may be possible to use a low‐sag (<1mm at 250lbs) CT couch and CT‐simulation tools in place of the stereotactic coordinate system. With adequate immobilization, use of the CT‐simulation tools may allow implementation of this technique at institutions where a stereotactic frame and specialized ESRT software are not available. Four ESRT patients, for a total of twelve treatment fractions, were scanned in a body frame on a CT‐simulator equipped with CT‐simulation localization tools prior to each treatment. Treatment isocenter coordinates were determined based on target volumes contoured by the physician using the stereotactic frame and specialized ESRT software. A second set of treatment coordinates was determined based on the same contours using the CT‐simulation software. The two sets of coordinates were compared to quantify the accuracy of CT‐simulation method. Results: The maximum, mean, and standard deviations between the CT‐simulation and stereotactic coordinates for the twelve treatment fractions in X (left/right), Y (anterior/posterior), and Z (cranio/caudal) directions in millimeters were (Xmax=1.1, Xmean=0.5, XSD=0.4), (Ymax=1.2, Ymean=0.3, YSD=0.3), (Zmax=2.5, Zmean=1.1, ZSD=0.8). CT study voxel dimensions in X, Y, and Z directions were 0.94mm, 0.94mm, and 3.0mm. Conclusion: The excellent agreement between the CT‐simulation and stereotactic coordinates indicates that CT‐simulation tools with appropriate immobilization can be used for target localization or independent verification in ESRT.
SU‐FF‐J‐86: Megavoltage CT Image Characterization, Quality, and Enhancement
Authors: Mahan S , Ramsey C
Published: June 2005

Purpose: The use of Image‐Guided Radiation Therapy (IGRT) has increased dramatically over the past five years. The purpose of this work was to evaluate quality of Megavoltage CT (MVCT) image and to develop methods for image enhancement. Method and Materials: The accuracy of MVCT imaging was measured using repeat imaging of an anthropomorphic head phantom in a known geometry. A technique for improving Image quality was developed using stable iterative deconvolution technique that utilizes that obtains an estimated inverse linear filter for a given instrumental response function or point spread function. The investigators also developed a technique for reconstructing 4D MVCT images. Image data was collected axially with the couch stationary during the imaging of each slice. The detector data was over‐sampled to capture different phases of respiration. The data corresponding to each projection was then re‐binned data and reconstructed for each phase of the respiration cycle Results: The Tomotherapy image‐guidance software yielded total imaging system errors of ±0.6 mm, ±0.5 mm, and ±0.6 mm with the automatic image fusion algorithm set to “Bone”, “Bone and Soft Tissue”, and “Full‐Image” respectively. Deconvolution image enhancement was performed on MVCT images of a prostate patient sharpened high contrast landmark. This increased the contrast resolution of bone, bowel gas, and soft tissue. 4D image reconstruction was also used to eliminate motion artifices from motion phantom. Conclusion: The MVCT images acquired on a helical tomotherapy delivery system have the positional accuracy to position the dose distributions to within 1‐mm of the desired position using the current clinical system. Deconvolution image enhancement has been used to improved superior‐inferior contrast resolution, and respiration artifacts have been corrected with retrospective 4D image reconstruction. Conflict of Interest: Research supported by TomoTherapy, Inc.
SU‐FF‐J‐87: Linac Based KV Cone‐Beam CT for Extended Field of Views: Evaluation of An Approximate Reconstruction Strategy
Authors: Seeber A , Nill S , Tücking T , Oelfke U
Published: June 2005

Purpose: To evaluate an approximate image reconstruction method for a kV‐cone‐beam CT system with an increased field‐of‐view (FOV) obtained by an asymmetric detector placement. Method and Materials: An approximate reconstruction method for width‐truncated projections based on projection weighting was implemented and tested on both synthetic and real CT‐projection data. Real data were taken with a 40.96cm × 40.96cm (1024×1024 pixels) flat panel detector, which was shifted by 8.4cm from its central position to achieve an asymmetric detector design corresponding to a detector width of 57.76cm, increasing the theoretical FOV at the isocentre‐plane from 28.8cm to 40.7cm. For the tests on real data an anatomical phantom of the abdomen and a spherical contrast phantom with inserts of different densities and differently sized holes were used. With synthetic data created for a cylindrical contrast phantom, the quality of the reconstructed images was examined for larger distances from the central slice and for different detector offsets (8.4cm, 12cm and 16cm), corresponding to FOV sizes of 40.7cm, 45.7cm and 51.4cm. Results: For the spherical contrast phantom, the measured absorption coefficients differed on average by 3% from those obtained in the normal cone‐beam reconstruction, with a slightly higher standard deviation. The spatial resolution was equally good. The anatomical phantom showed good results for the internal structures, with the outer contours missing because of detector saturation effects. For synthetic data, deviations in measured density increased with larger detector offset (from 1.4% to 2.7% in the central slice) and with larger distance from the central slice (up to 3.1% at z = 12.2cm for a 16cm detector offset). Conclusion: The investigated method to increase the FOV in cone‐beam CT showed promising results both on synthetic and real data. The achievable FOV allows for full‐size images even of the extra‐cranial region. Conflict of Interest: Research supported by Siemens‐OCS.
SU‐FF‐J‐88: Portal Imaging Capability of Motion Detection
Authors: Klein E , Esthappan J , Hubenschmidt J , Low D
Published: June 2005

Purpose: Quantitative determination and validation of tumor motion is required for Image‐Guided Radiotherapy (IGRT) of mobile tumors. One method for validating motion is portal imaging using electronic portal imaging devices (EPIDs). Ability to detect and delineate moving tumors depends on EPID specifications and image acquisition protocol. Requirements include accurate object definition and the capability to localize objects throughout the breathing cycle, at different locations within the body. We devised a straightforward test to assess EPID performance. Method and Materials: Water‐filled spheres of different diameters were attached to a computer‐controlled linear stage programmed to move spheres at constant velocities over a range of distances (up to 60mm) and speeds (from 5–40mm/s), within a stationary phantom. Images were captured during motion cycles using Varian PortalVision and Elekta iView amorphous silicon EPIDs. Accuracy of the projected target position was evaluated for images consisting of 1–3 averaged frames. We tested the image quality across the EPID while maintaining fixed source‐to‐object (isocenter) distances. Results: Both imaging systems accurately reproduced projected target shapes. The accuracy of range and speed measurements were 0.5mm and 0.1mm/s, respectively. The iView system detected the 60mm range of motion to within 2.5mm, for all tested speeds. The PortalVision system detected 60mm range of motion to within 3.5mm, up to 20mm/s, but performance degraded at greater speeds, with images missing in parts of motion cycles. At 30mm/s, only 45mm was detected. For both systems, range measurement errors were proportionally smaller for shorter ranges. Both imagers performed consistently throughout their imaging surface and both were comparable for image quality. Conclusion: We've devised a process that can simultaneously assess motion detection capability and test EPID systems. Both imagers performed well in static conditions, implying accelerator feedback system led to missing images. We'll investigate methods to improve the dynamic imaging characteristics of these EPID systems.
SU‐FF‐J‐89: MV Portal Imaging with Sub‐MU Exposure
Authors: Sillanpaa J , Chang J , Seppi E , Yorke E , Mageras G , Amols H
Published: June 2005

Purpose: To acquire megavoltage portal images for radiation therapy verification with less than 1 MU. Method and Materials: Portal images were acquired using the 6 MV beam from a Varian 2100 EX accelerator and a prototype Varian 4030HE electronic portal imager (EPID). The EPID has an 8mm thick, pixelated CsI scintillating layer, allowing good quality images with less than 1 MU. A synchronization circuit reduced the dose to one beam pulse/image (up to 30 images/s can be acquired). Image noise was improved by averaging several images. We acquired images of an aluminum contrast‐detail (Las Vegas) phantom and calculated the contrast‐to‐noise ratios of the indentations in it. The noise inside an open field was plotted as a function of the number of averaged frames. We also acquired weekly gated orthogonal localization images of the thorax for five lung cancer patients for physician review. Results: Good quality images were acquired with an average of 10 one‐beam‐pulse images, corresponding to 0.3 MU. The CNS of the portal images of the Las Vegas phantom using the 4030HE and 0.3 MU was as good as that using the aS500 and 4 MU; the noise levels in the open field were also the same. Image quality and discernibility of of anatomic features in the patient images were deemed by the physician to be comparable to those from a standard 4MU portal image. Conclusion: The new EPID can produce portal images with the same quality as the aS500, with a fraction (0.3 MU) of the dose conventionally used (usually 4 MU/image in our department). The imager also works with the Varian RPM respiratory gating system, allowing us to acquire gated portal images for verification of respiratory gated radiotherapy. This work was supported in part by U.S. National Institutes of Health grant P01‐CA59017 and by Varian Medical Systems.
SU‐FF‐J‐92: Dosimetric Comparison of Skin, Bone, Ultrasound, and CT Alignments for Prostate Cancer
Authors: O'Daniel J , Dong L , Zhang L , Wang H , de Crevoisier R , Bonnen M , Mohan R , Kuban D
Published: June 2005

Purpose: To quantify the dosimetric impact of four alignment methods (skin marks, bone, ultrasound, and CT) on the daily treatment of prostate patients. Method and Materials: Six prostate patients received 3 CT scans per week immediately before treatment using an integrated CT‐linear accelerator (135 CT scans total). We simulated the delivery of the clinical treatment plan by re‐aligning the plan on each CT scan using four techniques. The alignments used skin marks, bony registration of the CT scans, ultrasound, and prostate center‐of‐volume (COV). To compare the dosimetric effects of these alignments, we collected dose‐volume histograms of the prostate, seminal vesicles, bladder, and rectum. Results: These six patients could be divided into a stable group (3/6 cases) with average anterior‐posterior prostate motion ⩽ 2mm, and an unstable group (3/6 cases) with motion ⩾ 2mm. The stable group showed minimal dosimetric changes with the four alignment techniques. For the unstable group, the average minimum prostate dose (to 1cm3) was 75.6Gy with prostate COV, 72.3Gy with ultrasound, 67.2Gy with bone, and 65.4Gy with skin. The variation in daily minimum prostate doses was smallest with prostate COV alignment. Ultrasound alignment also reduced the daily variation except for two patients with large gas. For one case where the prostate tended to move anteriorly, re‐alignment decreased the rectal dose while increasing the bladder dose. For two cases where the prostate moved posteriorly, the reverse occurred. Conclusion: Patients can be separated into two groups based on the average prostate motion. Patients with average anterior‐posterior prostate shifts above 2mm can improve their prostate coverage by using ultrasound (better than skin and/or bone) or prostate COV (best) alignment techniques. Rectal doses will increase with posterior prostate motion. More than one CT scan is required to determine if a particular patient will significantly benefit from ultrasound and prostate COV alignment.
SU‐FF‐J‐97: A Novel Metric for Automatic Assessment of Deformable Image Registration Accuracy
Authors: Brock K , Moseley J , Jaffray D
Published: June 2005

Purpose: The purpose of this research is to develop a metric that automatically assesses the accuracy of deformable image registration by evaluating the difference in voxel values and the minimum distance to agreement between the predicted and actual images. Method and Materials: A metric, κ, has been developed, which is based on two parameters 1) difference in voxel value and 2) minimum distance to voxel agreement. Voxels within the predicted image, or a selected subregion within the region, are randomly selected for evaluation. Each voxel is assessed to determine if it is within 3 image units (i.e. Hounsfield Units or MR number) of the voxel value on the actual image or within 0.3 cm of its corresponding voxel on the actual image. The κ index indicates the percentage of points passing at least one of the parameter. The correlation between κ and the error in the image was established by introducing known random error into an image. Mathematically deformed CT and MR data was generated for analysis (mean = 0 − 0.5, SD = 0 − 1.0 cm). Results: Although the metric can overestimate the percentage of points meeting the criteria, due to similar voxel values in the search region, a unique correlation was established between the effective error in the image with known deformation and κ. A power law relationship between described 98% of the variance between the known error and κ. This relationship was then used to assess the error in deformable image registration using a finite element based method. The results show good agreement with prior manual accuracy evaluation. Conclusions: A novel metric, κ, describing the error in deformable image registration has been investigated providing a unique correlation between κ and the residual error in registration. Conflict of Interest: This research was supported in part Varian Medical Systems.
SU‐FF‐J‐107: Tumor‐Delineation Uncertainties in FDG‐PET and FMISO‐PET Images and the Effect On Radiation Therapy Plans
Authors: Ford E , Kinahan P , Phillips M , Alessio A , Hanlon L
Published: June 2005

Purpose: To quantify the uncertainties in tumor boundary delineation in head and neck and lung cancer patients using FDG‐PET and FMISO‐PET images and evaluate the dosimetric impact on radiotherapy plans. Method and Materials: We contoured FDG‐PET and FMISO‐PET based tumor volumes using images from the GE Advance PET scanner. We use the autocontour function of the ADAC/Pinnacle radiation planning system to delineate tumor boundaries at successively higher PET signal levels. CT‐based tumor volumes are also contoured by a physician on coregistered PET/CT images. We generated intensity‐modulated radiotherapy (IMRT) plans for head and neck patients treating 66 Gy to CT‐based gross disease and 54 Gy to nodal regions at risk, followed by a boost to the PET‐based tumor. Results: The volumes of PET‐based tumors are a sensitive function of threshold intensity level for all patients. For FDG‐based volumes, a 10% decrease in threshold translates into an approximately 200% increase in volume. Lesions smaller than approximately 8 cm3 display a more pronounced threshold‐volume dependence. The threshold‐volume dependence in FMISO scans is significantly more sensitive than in FDG scans. Lung cancer patients show a similar trend to head and neck patients with a possible overall shift in sensitivity. IMRT planning results on head and neck patients show that the boost dose limit of FDG‐based volumes depends on the threshold level chosen for contouring. In one patient the D95 of the planning target volume decreased from 7770 cGy to 7230 cGy when the contour level changed from 42% to 55%. Conclusion: PET‐based tumor volumes are strongly affected by the choice of threshold level which has a direct dosimetric impact. Further validation and refinement of delineation methods, including a determination of the proper threshold level, should reduce PET‐related delineation uncertainties for radiotherapy applications.
SU‐FF‐J‐108: A Non‐Invasive Respiratory Motion Compensation System for Predicting Organ Motion in Respiratory‐Gated Radiotherapy of the Chest
Authors: Kim Y , Lee D , Kim J , Ji Y , Hong S
Published: June 2005

Purpose: Non‐invasive respiratory gated radiotherapy systems, like those based on external anatomic motion, give better comfort to patients than invasive system during treatment. But to treat efficiently, such systems need a higher correlation between the motion of the external and internal anatomy. So we developed the system to track the motion and compensate for the correlation between internal and external anatomy to accurately predict the dynamic position of internal structures such as the diaphragm and tumor. Method and Materials: The respiratory motion compensation apparatus consists of two image boards, a camera and a fluoroscopy system. The camera and one of the image boards captures the abdominal motion of the patient, while the other image board captures the motion of internal anatomy through the fluoroscopy system. Software interfaced to the camera and fluoroscopy tracks the internal anatomy targets and abdominal surface motion induced by respiration simultaneously, using only image processing without any additional physical markers. The fluoroscopic movie was analyzed to obtain the correlation of internal and external anatomy motion in different parts of the diaphragm, abdominal surface and tumor where possible. Using this correlation coefficient, motion of the internal structures in later sessions was predicted based on the same point of abdominal surface motion. Results: The range of standard deviations between the predicted positions and the observed positions of some sample structures in each patient was measured about in phase and out of phase respectively. The difference between the predicted and observed positions of the abdominal surface, diaphragm or tumor was reduced a maximum 10 mms under the out of phase to 2mms under the in phase. Conclusion: This non‐invasive respiratory motion compensation system accurately predicts the respiratory motion of internal structures within 2 mms. Thus, this may improve the accuracy of gated or conventional 3D conformal radiotherapy.
SU‐FF‐J‐114: Dose Escalation Resulting From Reduced Margins Used to Generate the Planning Target Volume
Authors: Nelson C , Starkschall G , Chang J
Published: June 2005

Purpose: Decreasing margins that account for setup uncertainty and respiratory‐induced tumor motion can potentially result in improved treatment of lung cancer. The present work was designed to examine the dosimetric impact of reducing the margins used to generate the planning target volume (PTV). Method and Materials: Eighteen patients treated for non‐small cell lung cancer were selected. Treatment plans were generated based on two sets of CTVs. One obtained while free‐breathing explicitly accounted for respiratory‐induced tumor motion, while the other acquired at end‐expiration or inspiration simulated treatment under breath‐hold. Margins used to generate the PTV were uniformly reduced in 2‐mm increments from the clinically used 7‐mm margins while escalating dose to the CTV. In the first part of the study, the dose to the CTV was escalated as long as normal tissue toxicity levels did not exceed that of the treatment plan actually used. In the second part, dose to the CTV was escalated until structures received the maximum dose‐volume constraints allowed in our clinic. Results: Preliminary results showed that reducing the margin used to expand the breath‐hold CTV from 7 to 3‐mm allowed an increase of slightly higher than 10% of the prescription dose to be delivered to the tumor without exceeding normal tissue toxicity levels. When explicitly accounting for respiratory motion, a 1‐mm margin was needed to observe statistically significant increases in dose to the CTV. By increasing the dose until critical structures received the maximum permissible dose, dose escalation of over 25% was observed using a 5‐mm margin to generate the CTV. Statistically significant increases in dose were only slightly higher using a 3‐mm uniform CTV expansion to generate the PTV. Conclusion: As a result of this study, we have observed that increased doses can be delivered to the tumor by reducing margins used to generate the PTV.
SU‐FF‐J‐116: Image‐Guided Adaptive Radiation Therapy for Improving Level I Lymph Node Coverage for Head and Neck Cases
Authors: Chase D , Ramsey C , Mahan S , Seibert R
Published: June 2005

Purpose: Correcting anterior‐posterior, lateral, superior‐inferior, pitch, roll, and yaw with Image‐Guided Radiation Therapy (IGRT) will not completely correct for anatomical deformation. The purpose of this work was to identify anatomical deformation error and develop multiple strategies for addressing this error using adaptive IGRT. Method and Materials: Ten H&N patients have been treated with helical tomotherapy. Megavoltage CT (MVCT) images were acquired prior to treatment The daily setup were then used to calculate the random positional setup errors between the setup marks on the patient's mask and the internal anatomy. Level I lymph nodes (LV1) and the cord were contoured on each MVCT image. DVHs and LV1 EUDs were then calculated for each fraction. If the 2 Gy per fraction isodose line did not cover the LV1 nodes, then the treatment delivery was re‐planned and adapted to account for anatomical deformation. Results: The total shifts were measured for over 400 treatment fractions. The standard deviation was ±2.8 mm in the AP direction, ±2.9 mm in the lateral direction, and ±3.2 mm in SI direction. Dose reconstruction results indicated that the LV 1 nodes were frequently being under‐dosed (even with IGRT). Using IGRT to align the patient relative to the spinal cord resulted in a reduction in the LV1 nodal EUD by 2 to 6 Gy. This is of particular concern because the risk (5 to 50 percent) of LV1 involvement for node‐positive patients. By utilizing adaptive therapy, the LV1 were completely covered by the prescribed dose (50 Gy) in all cases. In addition, dose to the cord and mandibles were minimized. Conclusion: Adapting the treatment delivery by modifying the anterior border of the field can correct for the decrease in coverage due to anatomical deformation. This technique is an alternative to increasing PTV margins that allows increased sparing of normal tissues.
SU‐FF‐J‐120: Patient Motion During Extracranial Stereotactic Radiosurgery
Authors: Dieterich S , Xia Y
Published: June 2005

Purpose: Advances in image‐guided treatments have made frameless stereotactic radiosurgery (SRS) feasible. Extracranial SRS treatments are highly conformal, and technical delivery precision on phantoms has been shown to be less than 1 mm. The human component of error, i.e. voluntary and involuntary motions during the treatment, plays an increasing role in the determination of PTV margins. The residual motion between imaging intervals during image‐guided treatments constitutes the treatment uncertainty and needs to be compensated by the application of a PTV margin. Method and Materials: During Cyberknife extracranial SRS, the patient position is verified by orthogonal x‐ray images every 80 seconds on average. Data of 90 extracranial SRS patients have been analyzed. The extent of patient motion has been studied during the whole treatment, the first 5 minutes and first 15 minutes of each treatment. Motion patterns of anatomical sub‐sites were studied. Results: The maximum frequency of all translational patient motions was in the range of 0.02–0.2 mm, with 90% of all motions below 1 mm. No differences between the three translational directions have been observed. The maximum frequency of rotational patient motions was between 0.1–0.2 degrees, with a wider distribution in the degree of roll. The average patient motion for cervical spine was 0.47 mm, thoracic spine 0.34 mm, and lumbar spine 0.29 mm. In the 214 fractions analyzed, patients moved on average 1 mm away from their original setup position after 5 minutes of treatment. No statistically significant difference exists for the range of patient motion during the first 5 or 15 minutes as compared to the whole treatment. Conclusion: For image‐guided treatments, PTV margins of 1.0 mm include 90% of observed patients motions for static lesions. Larger margins may be necessary if the treatment field is not rotationally symmetric around the isocenter.
SU‐FF‐T‐03: Design and Quantitative Analysis of a Novel Brachytherapy Robot
Authors: Meltsner M , Ferrier N , Thomadsen B
Published: June 2005

Purpose: To design a novel brachytherapy robot and compare its static manipulability characteristics to two well‐known robotic manipulators: the Puma560 and the Stanford Arm. Method and Materials: The open‐source 3‐D Slicer program was used to model the prostate from clinical CT data. Workspace dimensions were determined and applied to the design of a new robot. The robot was modeled mathematically using the modified Denavit and Hartenberg representation of robotic manipulators. The static force and velocity manipulability ellipsoids were calculated for all three robots in several different poses using the Robot Toolbox for Matlab® (P.I. Corke, CSIRO, Australia, 2002). The force and velocity transformation ratios were computed and compared for similar poses. A small transformation ratio indicates the robot is sensitive to errors in control tasks, but not well‐suited for actuation tasks. The manipulability measure was also calculated. The manipulability measure is a quantitation of the range‐of‐motion of a robot in a given pose. Results: The calculations show the brachytherapy robot can implant a needle with a good balance of force and velocity with a high percentage of the maximum values. The Puma560 is relatively balanced, however most transformation ratios are less than 10% of the maximum. The Stanford Arm is not well balanced in both configurations studied. The Stanford Arm's transformation ratios are also relatively low percentages of the maximum. The manipulability measures for the brachytherapy robot were between 1.6 and 5 times higher than the other robots. Conclusion: Several robots have been developed for brachytherapy implantations. None have provided quantitative comparisons to other robots. Here, static manipulability calculations compare different robots with a specific pose (initial task‐oriented configuration). Our brachytherapy robot has balanced transformation ratios and also shows a high degree of manipulability. Initial calculations show that this robot is well configured for needle insertion tasks.
SU‐FF‐T‐04: Experimental Method Development for Direct Dosimetry of Permanent Prostate Brachytherapy Implants
Authors: Jarrett J , Sajo E
Published: June 2005

Purpose: To ascertain if PET DICOM data can be used for the quantitative description of dose distribution in support of direct prostate seed dosimetry. Method and Materials: Simulated brachytherapy seeds were constructed containing trace amounts of a positron emitter F‐18, such that all annihilation events took place in the encapsulation wall. An acrylic prostate phantom containing these seeds was imaged with a GE Discovery PET/CT scanner. The PET scan data was used as source in the input for Monte Carlo calculation of dose distribution due to the F‐18. This dose distribution was then compared to computations wherein the source was restricted to the encapsulation wall. This was done to determine if the measured data could be used to accurately compute the annihilation dose, which in turn could be used to compute the therapeutic dose due to known seed activity. Results: Examination of the dose distributions indicates a close agreement between the measured data and theoretical computational experiments for certain cases. We found that 2D acquisition with default reconstruction resulted in a maximum difference in transaxial dose distribution of 15% in a single voxel and a mean difference of 4% for the remaining voxels. The mean discrepancy between the ideal and PET based computations are within or close to calculation error of 2% to 4%. These results do not reflect any optimized acquisition protocol that can further reduce the observed differences. Conclusion: This work indicates there is potential for using PET data for the proposed link between the therapeutic brachytherapy dose and the dose due to a trace amount of encapsulated positron emitter developed by Sajo and Williams. Without needing seed location information, clinical implementation of this method could significantly reduce the time needed for post‐implant evaluation, and several of the uncertainties and limitations inherent in current prostate brachytherapy dosimetry.
SU‐FF‐T‐05: Interactive CT Based Seed Visualization, Localization and Verification in 3D
Authors: Feng W , Van den Heuvel F , Chu A , Narayana V , Yudelev M
Published: June 2005

Purpose: This work is to introduce an intuitive tool utilizing a home‐made user‐interactive 3D visualization interface for prostate seeds verification after automatic and manual seed searching. Method and Materials: This home‐made program is written In C++ and QT (Trolltech, Inc) and VTK library (Kitware, Inc) for both Windows and Linux. CT raw data was reconstructed with a slice thickness of 0.7mm to reduce under sampling problem. First threshold with user chosen value, then iso‐surfaces were rendered with a user‐chosen color for easy visualization. An automatic method will localize the well‐separated seeds whose volume is within 0.5–1.5 times of actual seed size. Then manual pick up could select the overlapped seeds by just one mouse click. All distances between the newly selected seed to already selected seed coordinates are calculated. If less than 1mm, the seed will be discarded. The seed orientation is defined as the orientation of the longest axis of the volume bounding box. The seed coordinates and orientations can be exported as an ASCII file. Results: A phantom with dummy seeds in different orientation and regular spacing and a clinical prostate CT data set were used for testing. The standard deviation for positioning is 0.29mm, 0.34mm in plane and 0.19mm in axial direction. Clinical patient CT data is used to test the seed localization program, the fake seed like bone or calcification can be deleted, by selecting structure then assigning background CT number. Conclusion: Manually seeds identification and verification are necessary even though there are many automatic seeds searching algorithms proposed. Unlike viewing conventional 2D slice‐by‐slice CT images, user can visualize the 3D object in any direction and from any position, interactively by zooming, rotating, translating. The seeds being selected will change color for easy recognition.