bluuebunny/crossref_metadata_2025 huggingface dataset:
SU‐FF‐I‐158: A New Method for Calculating the Half‐Value Layer of X‐Ray Beams
Authors: Boitnott K , Kappadath S , White A , Atkinson N , Cody D
Published: April 2010

Purpose: Traditionally, half‐value layer (HVL) of an x‐ray beam has been calculated through either linear (Eq. 2) or semi‐logarithmic (Eq. 3) interpolation under the assumption that attenuation varies linearly or monochromatically over a small range of attenuator thicknesses. Our aim is to evaluate the accuracy of HVL calculation using Lambert W interpolation (Eq. 4–6) and compare it to the traditional methods. Method and Materials: X‐ray exposure was measured over a wide range of attenuator thicknesses on a CT scanner (range: 0.49 mm Al – 33.03 mm Al), a mammography system (range: 0.1 mm Al – 1.08 mm Al), and a general radiography system (range: 0.5 mm Al – 10 mm Al; range: 0.1 mm Cu – 0.45 mm Cu). Exposure was measured using a RadCal exposure meter connected to a 10‐cm pencil ionization chamber for the CT scanner, a mammography chamber for the mammography system, and a 6 cc chamber for the general radiography system. Exposure values were measured at two different techniques for each system. Results: The percent transmission of the measured data was calculated and plotted versus measured attenuator thickness. The three interpolation methods used two measured data points that bracketed the HVL to construct percent transmission versus material thickness curves. Using data measured on a CT scanner for120 kVp, Lambert W interpolation yielded less than 5% error in the calculated HVL for approximately 89% of all possible interpolation and extrapolation point combinations. Using the same data, semi‐logarithmic and linear interpolation yielded less than 5% error in the calculated HVL for approximately 38% and 5.6% of all possible interpolation and extrapolation point combinations, respectively. Conclusion: Lambert W interpolation is more accurate and less sensitive to the choice of interpolation points compared to traditional methods.
SU‐FF‐J‐13: Decreasing CBCT Dose Without Compromising Its Clinical Fidelity
Authors: Lu H , Lu B , Palta J
Published: April 2010

Purpose: The objective of this study is to evaluate the effect of KV cone‐beam CT registration accuracy and image quality with reduced number of planar projections used in 3D reconstruction. The ultimate goal is to reduce patient dose while maintaining registration accuracy for different clinical disease sites. Methods and Materials: An Elekta Synergy Linear accelerator with onboard CBCT system (XVI) is used in this study. The image quality of XVI CBCT images reconstructed with decreasing number of projections was evaluated using a CAT phantom that provides quantitative data on spatial resolution, low contrast visibility, uniformity, and geometrical accuracy. Subsequently, we acquired volumetric imaging data on an anthropomorphic phantom with different rectilinear shifts and rotations. We used standard scanning protocol for CBCT imaging. However, we reconstructed images with reduced number of projections (as low as 1/6th). We evaluated image registration accuracy between planning CT and CBCT data generated with decreased number of projections used in reconstruction. We also reconstructed imaging data for 3 real patients with limited number of projections. Results: The CBCT images of CAT phantom reconstructed with half as many projections satisfied all image quality criteria defined by Elekta in its acceptance test document. The images reconstructed with 1/6th of the original number of projections failed only in low contrast resolution while satisfying all other quantitative image quality specifications. The CBCT images get noisier with reduced number of projections but their spatial resolution is hardly affected. The maximum registration error for both the phantom and real patients was found to be within 1mm and 1° Conclusions: This study demonstrates that the image registration accuracy is not compromised even when the numbers of planar projections are reduced significantly. This means that the patient dose from CBCT study can potentially be reduced by a factor of approximately six.
SU‐FF‐J‐18: Application of Deformable Mannequin in 3D Virtual Reality Simulation (VRS) for Noncoplanar Radiation Therapy
Authors: Shang C , Williams TR , Sloman B , Ward J , Phillips R , Percy J
Published: April 2010

Purpose: To evaluate the practicality of deformable mannequin in VRS for noncoplanar radiation therapy. Materials and Method: A deformable mannequin was introduced in 3D VRS system. The system was based on radiation therapy simulation software, FocalSim™ from CMS, Inc. Using 3D stereoscopic technology, the VRS system displays the virtual treatment environment on a DTI™ 3D LCD screen without aid of gaggles. During the process, the selected patient's CT was position to the treatment couch in VRS with either modeled Elekta Synergy or Varian CL21EX machines. The mannequin was then fused on to the CT segment and repositioned to simulate actual patient's setup. The dimensions of the mannequin can be altered to fit real sizes, and its extremities can be bent and rotated to simulate actual positions on different immobilization fixtures. Then the treatment isocenter was selected and confirmed via beam‐eye‐view for the contoured PTV. In the program, the gantry, couch and the collimator can be realistically manipulated by dragging apparatus on Wacom™ touch screen. If a possible collision may occur between gantry and the mannequin or the couch, collision warning will be immediately indicated. The freedom ranges for different noncoplanar settings were finally recorded for planning guidance. Results: Five treatment sites — central pelvis, left breast, pancreas, lungs, and mediastinum are evaluated. Depending on the size of the patient and relationship between PTV and OAR, exercises of noncoplanar settings can be greatly limited in conventional patient's position. The deformable mannequin enhanced VRS may maximize the usage of noncoplanner technique for both static and dynamic arc beam arrangements as suggested in this investigation. Conclusions: The application of deformable mannequin in VRS effectively guided simulation with noncoplanar static or dynamic arc beam settings for different treatment sites.
SU‐FF‐J‐20: A Multimodality Imaging Approach for Predicting Radiation Induced Lung Injury
Authors: El Naqa I , Vaidya M , Apte A , Fergus S , Deasy J , Bradley J
Published: April 2010

Purpose: Radiation pneumonitis (RP), is a major dose limiting toxicity in thoracic irradiation for patients with lung or breast cancer. Multimodality imaging and particularly integrated PET/CT imaging is increasing used in radiotherapy treatment staging, planning, and monitoring. In this work, we are investigating the potential of a new hybrid feature‐based approach utilizing post‐radiotherapy PET/CT images to predict the risk of later RP. Method and Materials: As a demonstrative example for analyzing normal tissue toxicities using the proposed multimodality approach, we analyzed post‐treatment PET/CT scans (typically, 3 mos. post‐RT) of 20 lung cancer radiotherapy patients for the endpoint of pneumonitis. The rate of RP in this group was 20%. The lung region minus the Gross Tumor Volume (GTV) was designated as the region of interest (ROI). We extracted features based on descriptive statistics of intensity (in units of SUV in PET and Hounsfield in CT), image intensity volume histogram (IVH) metrics, and texture‐based features. Statistical association was performed using Spearman's rank correlation (Rs). Results: Thirty candidate features were extracted from each image modality. Preliminary results indicate that texture features in both PET and CT seems to predict RP. For instance, the PET ROI standard deviation had Rs=0.14 in PET and Rs=−0.035 in CT while the texture (related to roughness) local heterogeneity had Rs=0.33 (p=0.08) in PET and Rs=0.63 (p=0.002) in CT. Conclusion: We have proposed a new approach for predicting RP risk pneumonitis from hybrid PET/CT image features. Texture related features on the post‐RT CT scan provide the best prediction. Estimating of these features could provide the physician with an early warning enabling a more proactive management of RP symptoms. Further analysis of these multimodality features, their complementary effect, and the optimal time of imaging, is needed to fully understand this finding.

Partially supported by K25 CA128809 and R01 CA85181.
SU‐FF‐J‐21: Measurements of Fiducial Marker Positions for Real‐Time MLC Beam Tracking Delivery Using MV Fluence Video
Authors: Papanikolaou N , Liu Yaxi , Roland Teboh , Mavroidis P , Shi C
Published: April 2010

Purpose: The objective of this work was to perform fiducial marker position measurement for real‐time MLC beam tracking delivery using MV fluence video. Method and Material: Fiducial markers implanted in the tumor have been proposed for obtaining accurate target localization. Correlation of the on‐line acquired marker trajectory with the actual motion is crucial in real time tracking. This study was based on real‐time video, in which an EPID was used to acquire MV fluence of a dynamic phantom with an implanted fiducial marker. A QUASAR dynamic phantom was used to mimic patient respiratory motion. The motion of the dynamic phantom insert was achieved using an actuator generating sinusoidal motion to the moving rod. The measured fiducial marker position was compared with the actual marker position on the sinusoid curve for beams perpendicular to the direction of marker motion. Results: The integrated marker trajectory accumulated within a 1 mm vibration range in a straight line along the motion direction for a 15 respiratory cycle measurement. The acquired trajectory extent of motion (peak‐to‐peak amplitude) was exactly 20 grids which matched well with the actual marker peak‐to‐peak amplitude of 20 mm. A plot of the acquired and programmed curves showed latency (∼100 ms) between the acquired and actual marker trajectories for the first 2 ∼ 3 cycles. Thereafter, the measured fiducial maker positions matched its motion curve well within 50 ms latency with the amplitude vibrations within 2 mm error along the motion direction. Conclusion: Fiducial marker position measurement from MV fluence is a crucial step in real‐time tracking radiotherapy. This study demonstrated a close correlation between the acquired and actual marker positions for a simple sinusoidal motion. More complex trajectories involving actual patient breathing patterns will be analyzed in the future.
SU‐FF‐J‐22: A Comparison of Calypso Based Localization for Post Prostatectomy Patient in the Presence of High Geometric Residual (GR) Beacon Error: Comparison/correlation with Ultrasound Alignment
Authors: Huang Y , Wang B , Tward J , Shrieve D , Salter B
Published: April 2010

Purpose: For Calypso‐guided treatment of post‐prostatectomy patients, the geometric residual (GR) error of beacon positions can increase due to local tissue deformations second to healing. We evaluated the Calypso localization inaccuracy resulting from beacon positional errors in such circumstances, using ultrasound (US) image guidance. We report the difference of these two image guidance methods and measure degree of correlation of US shifts with the GR value. Method and Materials: The Calypso system calculates a GR value prior to each treatment, and warns against using the system if the value is greater than 0.2 cm. For a post prostatectomy patient under treatment in our clinic we used US guidance to determine shifts on days when Calypso GR was out of tolerance. We compared US‐derived shifts with Calypso derived shifts both on days when GR was acceptable, and on days when it was not. We calculated degree of correlation between high GR and large US‐derived shifts. Results: On days with large GR value (e.g. 0.33 cm), the Calypso and BAT did not agree well, with A/P differences as large as 0.55 cm, thus suggesting potential shifting of the Calypso transponders. We found a correlation (R2=0.798) between Calypso localization inaccuracy, characterized by large US shifts, and high GR values. When GR values were less than 0.15 cm, Calypso agreed well with US alignment. Conclusion: When using Calypso for post‐prostatectomy patient alignment, special attention should be paid when geometrical residual limit is exceeded, as GR value is a strong indication of the Calypso localization inaccuracy.
SU‐FF‐J‐28: A Guidance System for Optical Patient Alignment During Breast Radiotherapy
Authors: Schmitt J , Bakhtiari M , Malhotra H , Hoffmann K , Nazareth D
Published: April 2010

Purpose: Breast radiotherapy, particularly IMRT, involves large dose gradients and difficult patient positioning problems. A critical requirement for successful treatment is accurate reproduction of the patient's position assumed during CT simulation and planning. We have developed an optical image‐guided technique, which assists in accurately and reproducibly positioning the patient, by displaying her real‐time optical image superimposed on a perspective projection image of her 3D CT data. Methods and Materials: The Single Projection Technique (SPT) accurately determines the 3‐D position and orientation of a camera from a single image acquired of a known model. A calibration jig, composed of ten identifiable reflecting spheres, was constructed and CT imaged to provide this model. To implement our method, a digital photograph of the jig was acquired and the 2D coordinates of the spheres were found. Using this information, 3D CT patient data is projected onto the camera's imaging plane, and is displayed on a monitor, superimposed on the real‐time patient image. This enables the therapist to view both the patient's current and desired positions, and guides proper patient positioning. Results: The SPT can determine the position and orientation of the camera to an accuracy of 0.2 cm and 0.3°, respectively. Investigations are ongoing to determine the accuracy and reproducibility of our method in terms of the dose distribution of IMRT plans. Film measurements performed on a breast phantom will allow us to determine the spatial accuracy of isodose curves measured in several planes. Conclusions: We have developed a method to calibrate an optical camera system and superimpose a perspective projection of a CT image on a patient's real‐time optical image. Displaying this visual information will assist in accurate setup during breast radiotherapy. Future work will enable us to quantify the setup and dose delivery accuracy of this technique.
SU‐FF‐J‐29: Accuracy Evaluation of Using MV EPID and / Or Integrated KV Imaging System to Locate 3D Positions of Internal Fiducial Markers by a Calypso System
Authors: Mao W , Foster R , Solberg T
Published: April 2010

Purpose: In order to use MV EPID and/or integrated kV imaging system to obtained 3D positions of implanted fiducial markers for the purpose of patient setup and / or image‐guided radiation therapy in real‐time, it is essential to investigate the accuracy of this method. Method and Materials: A Calypso QA phantom with three Beacons was imaged by both MV and kV beams at a series of gantry angles on a Trilogy (Varian Medical Systems, Palo Alto, California, USA) while Beacon positions were simultaneously tracked using a Calypso 4D localization system (Calypso Medical Technologies, Inc., Seattle, WA, USA). Beacons were automatically detected on kV and MV projection images using in‐house software, their 3D positions were calculated from MV‐MV, kV‐kV, or MV‐kV pairs with a 60° or larger gantry angle separation between each pair, and compared with Calypso results. A special QA procedure was developed to assess geometric accuracy of MV and kV imaging systems on the Trilogy, and geometric parameter deviations, particularly detector center offsets, were applied to correct the 3D position calculations. Results: A phantom was placed at known positions based on the detected Calypso Beacon centroids. Both MV and kV images were acquired at 12 gantry angles with an increment of 30°. 2D and 3D positions were calculated. The different calculation modalities resulted in noticeable discrepancies from the Calypso 3D positions. The application of a geometric correction is capable of reducing these deviations, with the measured net shifts matching calypso results within 0.1 mm. Conclusion: Geometric correction after QA of imaging geometry helps improve detection accuracy. Implanted fiducial markers can be detected by multiple projections of either MV or kV x‐ray beams with an accuracy of approximately 1 mm.
SU‐FF‐J‐31: Quantitative Analysis of Prostate Motion Using Implanted Fiducial Markers Based On Port Film Image Guidance
Authors: Avadhani. J , Sasidharan S , Carton C , Lowen M , Klapproth T , Licitra C
Published: April 2010

Purpose: To assess daily localization of prostate using implanted fiducial markers with port film based image guidance. Methods and Materials: 2640 Prostate shift data for 60 patients were used to analyze the interfraction movement of the prostate. Three non‐migratable gold seeds were implanted approximately at base, apex and mid prostate. Prior to treatment, orthogonal radiographs were taken at 45° and 315° for clear visibility of the markers. The images were imported to dedicated software and the required positional shifts calculated in superior‐inferior, left‐right and anterior‐posterior directions by digitizing seeds. If shift exceeded 3 mm in any direction, the treatment table was moved to required distances and radiographs were repeated to confirm the target was within 3 mm. The dose at isocenter was also measured with port films in a phantom. Results: From the analyzed data, 57% of patients had shifts had >3mm, 28% between 3–5 mm, 25% between 5–10mm and 5% >10mm. The median values of deviation from all data were: 1.7 mm laterally, 2.0 mm longitudinally, and 3.6 mm vertically. From this data there is a risk of underdosing the PTV and delivering higher doses to the rectum and bladder without image guidance. With our treatment protocol of 7740 cGy/43 fractions the repeat portal imaging required for field verification after shift delivers an estimated average additional 287 cGy. Conclusion: From the analysis, image guidance with the appropriate modality is of prime importance for treatment of prostate cancers. The present technique of daily portal imaging gives good beam localization but with higher potential total dose than with kV based cone beam CT published in the literature.
SU‐FF‐J‐32: Comparison of Manual Plus MI Registration to SWMI Registration Using MVCT for Head‐And‐Neck Cancer Patients
Authors: Park SB , Yao M , Sohn JW
Published: April 2010

Purpose: To measure the value of manual adjustment after MI (Mutual Information) image registration technique for head‐and‐neck cancer cases, we compared the result to those performed with Spatially Weighted Mutual Information (SWMI) measure. Methods and Materials: We chose 6 head‐and‐neck cancer patients treated with Helical Tomotherapy machine and retrieved 199 daily MVCT image sets. Each patient had three CTVs and total superior‐inferior extent of CTVs was greater than 15cm. The daily images were manually aligned after automated registration with the MI software provided by Tomotherapy. Then, it was compared to the registration result of in‐house image registration software using SWMI with a Gaussian‐shaped weight. Gaussian‐shaped weight function was set to be centered in the primary CTV. And the variance of the Gaussian for each direction was set to cover CTVs and the critical organs. Each patient had the same variance of the Gaussian setup through a whole treatment course. Our in‐house image registration software was implemented to receive DICOM and DICOM‐RT from various planning systems. Since the Tomotherapy machine without a robotic couch cannot deliver yaw and pitch corrections, only roll was considered among the rotational transformation. Results and Discussion: Manual registration is not accurate enough if there is organ deformation. Fifty nine treatments among 199 treatments for 6 head‐and‐neck cancer patients showed the difference from our automated SWMI registration by more than 3mm. Our PTVs were created from CTVs by adding a 3mm margin. The minimal dose of CTV was reduced by 52% in maximum. SWMI incorporated with the Gaussian‐shaped weight shows better target coverage for all 199 cases. The main advantage of the automated SWMI is not relying on the user's expertise of visual image matching.

(This work is partly supported by Susan G. Komen Breast Foundation Grant: BTCR126506)
SU‐FF‐J‐33: Error Propagation in Tracking Geometry and Dose Through the Course of Treatment for Dose Accumulation in Adaptive Therapy of Head‐And‐Neck Cancers
Authors: Kashani R , Jee K , Feng M , Balter J , Dong L , McShan D , Haken R Ten , Fraass B
Published: April 2010

Purpose: In making re‐planning decisions in response to observed geometric changes in head‐and‐neck patients, the daily dose distribution is often compared to the initially planned dose distribution. A more accurate approach would evaluate the total delivered dose up the point when new patient model becomes available, making decisions based on deviations of the accumulated dose from the planned dose. The aim of this study is to compare the accuracy of two different dose accumulation methodologies that utilize deformable image registration for tracking dose. Methods: In the first method, the dose is tracked directly from each fraction to the new patient model, which requires N‐1 deformable registrations for dose accumulation at fraction N. In the second method, the total delivered dose is accumulated starting with fraction 2, such that at fraction N, the dose is already mapped to fraction N‐1 and a single deformation map would be sufficient to track dose to the new geometry. This study evaluates the accuracy of each technique by comparing deformed contours generated using each method for a single head‐and‐neck patient. Contours at fractions 5, 15, and 25 are compared visually and quantitatively using distance to agreement at specific points of interest. Results: Visual assessment indicates that method 1 is more accurate than method 2. The largest difference between the two simulated surfaces of CTV was observed near the edge of pharynx and was measured to be 0.49, 0.39 and 0.53 cm, for fractions 5, 15, and 25 respectively. Discussion: Propagation of deformable alignment errors has the potential to negatively impact cumulative dose evaluation. Caution is recommended in evaluating adaptive therapy implementations that relay on the accumulation of deformations for summation of dose evaluation in later treatment fractions.

Supported by NIHP01CA59827
SU‐FF‐J‐34: Can 4D Dose Be Constructed Without Using Deformable Organ Registration?
Authors: Liang J , Chi Y , Qin X , Yan D
Published: April 2010

Purpose: Image based deformable organ registration has been the primary means for 4D dose construction of moving organ. However, patient free breathing cone beam CT (FB‐CBCT) is more routinely obtained, instead of 4D CBCT. In this study, we examine if FB‐CBCT imaging can be directly applied for 4D dose construction. Method and Materials: Organs with the mean shape obtained from 4D reference CTs were mapped on a FB‐CBCT image by applying rigid‐body matching. The 4D dose in the organ was then constructed on the mean CT image using the 3‐dimenional‐motion pdf detected by the CB projection images. Three lung cancer patients with a planning and multiple daily 4D CTs were used to evaluate this method. The daily FB‐CBCT was constructed using the daily 4D CT. For each patient, dose distributions obtained from a 3D inverse planning and a 4D inverse planning were used in the evaluation. Dose distribution constructed using the mean organ and motion pdf was compared to the 4D dose calculated using the deformable organ registration on the daily 4D CTs. The minimal dose (D99) and EUD for the target, and the maximum dose (D1) for critical structures were used in the comparison. Results: Dose discrepancy (the mean ± SD) for D99 and EUD of the targets was −0.6%±2.6% and 0.0%±1.0%. Dose discrepancy of D1 was 1.5%±1.5% for heart, −1.6%±3.3% for Aorta and −0.6%±3.7% for Esophagus. Dose discrepancy in the lung was not evaluated in the current study due to the need of using variable pdfs at different location of the lung. Conclusion: 4D dose in organs of interest could be directly constructed using daily FB‐CBCT and measured pdf. The construction accuracy seems acceptable for the organs of interest inside of the lung.

Support in part by Elekta Research Grant
SU‐FF‐J‐37: Cumulative Rectal Dose Surface Histogram (DSH) Using Homologous Point Sets
Authors: Barbiere J , Beninati G , Mistry J , Hanley J
Published: April 2010

Purpose: Present a metric to compare the outer rectal wall surface cumulative daily treatment dose with the original plan. Materials and Methods: The rectum outer surface was contoured for 28 fractions of a patient undergoing prostate tomotherapy without bowel preparation. The rectal variations could be divided into three ranges corresponding to a rectal filling of “empty”, “half” and “full” with approximately 61%, 21% and 18% of the data in each respective region. We use points on the outer surface of the rectum to calculate a Dose Surface Histogram (DSH). The set of points on the planning surface is the reference for all daily treatments. Doses on the daily contour are mapped onto the reference contour. Every point on the planning contour has a homologous point on the daily contour. Rapid calculations are performed using an in‐house MATLAB algorithm. For each treatment fraction, the dose D(i) to point i on the planning contour is equal to the dose D(j) where j is the previously determined corresponding point on the daily contour. The cumulative dose to point i is the sum of all the daily D(j). Results: A DSH was calculated for the plan and a representative daily MVCT slice. The cumulative DSH was compared to the nominal “average” DSH computed by simply averaging the plan and daily DSHs. There are significant differences above 80% of the prescribed dose. DSHs for a representative contour in each of the empty, half, and full rectum regions indicated 5% difference between the cumulative and planned rectum for doses below 70% and variations of 10 to 20% at higher doses. Conclusions: Cumulative DSHs accurately indicate the dosimetric effect of daily variations in rectal filling. A general technique to compute cumulative DSHs has been developed as an efficient metric to determine if adaptive planning is required.
SU‐FF‐J‐40: A Simple Method for Dosimetric Assessment in H&N Radiotherapy with Rotational Setup Errors
Authors: Chen Y , Feigenberg S , Xu Q , Price R , Ma C
Published: April 2010

Purpose: Rotational setup error for H&N patients is detected using cone‐beam CT. Fusion with 3D image can determine a sequence of three Euler angles for the best matching with the planned patient position. Currently, correction for rotational errors is not available except with the use of a 6‐degree‐of‐freedom treatment couch. However, it is possible to compensate an arbitrary rigid‐body rotation by just a simple couch rotation in addition to gantry and collimator angle changes. We introduce a formulation for compensating a rotational error with respect to a given planned beam position for adaptive treatment or easy dosimetric evaluation for no correction. Method: For each planned beam position, the beam axis in patient coordinates upon rotational error is calculated, pointing out of the beam source plane. A couch rotation is first applied to move the planned beam axis back to the source plane. The adapted gantry and collimator angles are then calculated to align with the planned beam axis and radiation portal. The inverse transformation determines the effective beam position in planning CT for dosimetric evaluation with no correction. Results: Our method was validated by phantom experiments. Light fields were compared for various beam positions before and after phantom rotations. The delivered dose distribution for two patients with 2∼3 degrees of rotations were calculated and compared with the planned distribution, showing marginal deterioration with 1.5% target dose reduction and 2% parotid dose increase. Conclusions: A simple “theoretical” solution is available for handling rotational setup error when rigid‐body approximation applies. Its practical application is to evaluate the dosimetry for no correction, and our data showed that rotational error was less of a concern compared to as large as over 5% dose variation with patient anatomy change due to weight loss or tumor shrinkage.
SU‐FF‐J‐41: Clinical Management of Detected Target Deviations in IGRT: A Geometrical Approach
Authors: Liu D , Jin J , Wen N , Elshaikh M , Movsas B , Chetty I
Published: April 2010

Purpose: To investigate an efficient method for assessing the impact of target deviations detected by daily image‐guidance on planning volumes. We hypothesize that, using this method, on‐line daily correction may not be warranted. Method and Materials: Geometrical surface models of the CTV and PTV were generated from the respective planning volumes via a surface reconstruction algorithm. Given a set of target deviations, represented by 6‐degree positioning shifts (translation, pitch, roll, yaw) from IGRT systems (e.g. Varian's OBI/CBCT), collision detection was performed to find geometric distance between CTV and PTV surface models when the shifts are applied to the CTV. Since the method is based on shifts, which do not incorporate intra‐fraction motion, a criterion was defined such that on‐line shifts are not applied if the CTV and PTV surfaces are greater than a distance defined by a population‐based margin for intra‐fraction motion. Results: A software module was developed to: import IMRT plans, generate surface models, communicate with the IGRT system, and calculate CTV/PTV spatial geometric distances. Surface model generation is performed off‐line. Collision detection between CTV and PTV surface models from daily shifts is done on‐line within minutes on a desktop PC. In the examples shown, “collisions” are defined by minimum distances of 3 mm in any direction (intrafraction motion margin) between the CTV and PTV. If a collision is detected, an on‐line shift is applied; otherwise the treatment proceeds as planned. Conclusions: The proposed method represents a quick and quantitative way to manage target deviations determined during image‐guidance, without the need to apply on‐line corrections. The approach is not limited to target analysis, but may also include normal tissues, such as the bladder and rectum. Adaptive and on‐line treatment planning studies are under way to determine the validity of the hypothesis, and to improve the collision detection criteria.
SU‐FF‐J‐44: Application of a Routine Geometric QA Tool for Integrated MV and KV Imaging Systems On Trilogy, Synergy, and Vero
Authors: Mao W , Speiser M , Medin P , Papiez L , Solberg T , Xing L
Published: April 2010

Purpose: A geometric QA tool has been adapted as a routine QA tool for three different types of linear accelerators with integrated kV imaging systems. It quantitatively evaluates geometric accuracy of kV and MV cone beam imaging systems including their coincidence. Method and Materials: Three linacs are a Varian Trilogy (Varian Medical Systems, Palo Alto, California, USA), an Elekta Synergy (Elekta, Stockholm, Sweden), and a Brainlab Vero (Brainlab AG, Feldkirchen, Germany). Both the Trilogy and Synergy linacs are equipped with a retractable kV x‐ray tube and a flat panel detector. The Vero is based on the MHI‐TM2000 (Mitsubishi Heavy Industries, Ltd., Tokyo, Japan). It utilizes a rotating, rigid ring structure integrating a MV x‐ray head mounted on orthogonal gimbals, an electronic portal imaging device (EPID), two kV x‐ray tubes, and fixed two flat panel detectors. Two QA phantoms were built to suit different field sizes. Projection images of a QA phantom were acquired by MV and kV imaging systems at a series of gantry angles. In‐house software was used to analyze projection images and calculate eight geometric parameters for each projection. They are three parameters describing the actual x‐ray source position, three parameters describing the position of the detector center, and two parameters describing the detector angular orientation. Results: Over 4,300 individual projections have been acquired and analyzed. The Trilogy was calibrated 4 times over a six month period while the Synergy and the Vero were calibrated twice and once, respectively. Quantitative geometric parameters of both MV and kV imaging systems were successfully evaluated. Isocenter consistency of the imaging systems was evaluated. Additionally, the gimbal‐based x‐ray source positioning of the Vero was examined. Conclusions: Geometric accuracies of both MV and integrated kV imaging systems were quantitatively evaluated by this QA tool.
SU‐FF‐J‐50: Concurrent Wireless Electromagnetic Tracking and CT Imaging
Authors: Parikh P , Wen J , Smith R , Noel C , Santanam L , Petersen J , Newell J , Dimmer S
Published: April 2010

Purpose: Currently, electromagnetic tracking cannot be done inside a CT scanner. We wanted to determine if wireless electromagnetic tracking can be performed accurately in the CT environment. Method and Materials: A research version of the Calypso® 4D Localization System™ (Calypso Medical Technologies, Seattle, WA) was utilized in a Brilliance Big Bore CT scanner (Philips Healthcare, Cleveland OH) with the carbon fiber table removed. Three transponders were oriented vertically (Z orientation) or parallel (Y orientation) to the sensor array and fixed at 20cm below the array. Standard deviation of the positioning data was observed and comparison was made for array position high (toward the top of the gantry) versus low, array gain high versus low, transponder orientation Y versus Z. 60 seconds of tracking data was collected for each measurement. The standard deviation was used to determine precision, and the transponders were imaged with the CT scanner to determine accuracy. Standard deviation below 0.2 cm was considered appropriate for clinical use. Results: The standard deviation became higher when distance between array and transponders increased. The system performed best when array position was low, beacon orientation in the Y axis, and sensor gain set to low. In all cases with the array position low and array gain low, the system met the clinical goal of standard deviation less than 0.2 cm for a 12×12×12 cm3 volume. Conclusion: This work describes the first electromagnetic tracking system that works in a CT environment. Potential applications include using implanted transponders to guide correlated imaging measurements of respiratory motion (‘tumor correlated imaging’ versus ‘respiratory correlated imaging’) as well as wireless tools for intervention procedures in the CT bore. Further mechanical work will be necessary to optimize the ergonomics, and signal processing work to optimize the performance, of a combined tracking/imaging system. Conflict of Interest: Calypso Medical
SU‐FF‐J‐51: The Impact of Source‐To‐Background Ratio, Tumor Size, Scan Duration, and Smoothing Filter On a Two‐Stage PET Tumor Segmentation Method
Authors: Li H , Laforest R , Thorstad W , Zhu J , Low D , Lu W
Published: April 2010

Purpose: This work systematically evaluates the effect of source‐to‐background ratio, tumor size, scan duration, and smoothing filter on a novel two‐stage PET tumor segmentation method in phantoms. The two‐stage method uses an adaptive region‐growing algorithm and a dual‐front active contour model, resulting in advantages of reproducibility and no need of choosing a threshold. Method and Materials: Six spherical tumor phantoms (0.5 – 20 mL) in a warm cylindrical container were scanned for 120 minutes in a PET/CT scanner. The source‐to‐background (S/B) ratio ranges from 16 to 0.5. For every 2‐min scan, three PET images were reconstructed using the iterative Ordered Subset Expectation Maximization (OSEM) algorithm with 5mm‐FWHM, 2mm‐FWHM post‐reconstruction smoothing filters and without the filter, respectively. At S/B ratio 2, images for longer scan durations were also generated. The two‐stage method was applied to segment the tumor phantoms with optimized parameters. Results: The segmentation accuracy depends mainly on the S/B ratio and tumor size, with a higher accuracy for larger tumor or higher S/B ratio. The 5mm‐FWHM filter reduces more noise than the 2mm‐FWHM filter and the unsmoothed. This leads to better segmentation for images smoothed with the 5mm‐FWHM filter. Lengthening scan duration did not improve the segmentation for tumors ⩾ 6 mL, but made the imperceptible 1 mL tumor detectable. The overall differences were not statistically significant between scan durations or between OSEM‐2mm and unsmoothed, but were statistically significant between OSEM‐5mm and unsmoothed. Conclusions: We concluded that a computerized PET tumor segmentation method should incorporate these factors (S/B ratio, tumor size, scan duration, and smoothing filter) if known or estimable. Secondly, it is very important to use the same PET/CT protocol for consistent quantitative evaluation. Finally, longer scan duration improves small tumor detection in PET.
SU‐FF‐J‐70: An Investigation of Interference Between Electromagnetic Transponders and Wireless MOSFET Dosimeters
Authors: Su Z , Zhang L , Ramakrishnan V , Hagan M , Anscher M
Published: April 2010

Purpose: A phantom study to systematically investigate potential interferences between Calypso® Medical electromagnetic transponder and Sicel® DVS wireless MOSFET dosimeter when used in same patient. Method and Materials: A 30×30×5cm3 (Virtual Water®) phantom has a center hole for two separate 8cm diameter inserts with grooves for three pairs of transponders and dosimeters on each insert, respectively. The grooves of orthogonal and parallel orientations between transponders and dosimeters (long axes) were machined on the two inserts, respectively, with transponder‐dosimeter distance at 0, 1 and 2cm. In the transponder‐localization test (test1), transponder locations were obtained without and with dosimeters at different distances. Multivariate analysis tested the null hypothesis: the localized transponder coordinates are the same among datasets of control and various dosimeter locations. The 95% confidence‐intervals were also determined for the localization difference between control and test groups. In the dose‐measurement test (test2), 7 fractions of 1Gy were administrated to the dosimeters inside the phantom in an alternating fashion of without (fraction♯ 1, 3, 5, 7) and with transponders. Readings from fractions of no transponders were fit using a 2nd order polynomial. The dose differences between fit‐interpolated and corresponding measured values of fraction 2, 4, 6 were calculated. Results: For test1, multivariate analysis indicated that transponder localization accuracy was affected by the dosimeter. However, the 95% confidence‐intervals of the localized positional differences between control and test groups were less than 0.1mm, which is less than Calypso clinical display increment, 0.5mm. For test2, the maximum deviation of polynomial fitted dose values from measurements are within 1.5% and 0.8% for orthogonal and parallel configurations, respectively. Conclusion: This study showed no clinically significant interference between the transponder and dosimeter systems and demonstrated feasibility of combined use of transponders and dosimeters in the same patient.

Research sponsored by Calypso Medical Technologies, Inc. and Sicel Technologies, Inc.
SU‐FF‐J‐71: A Prototype Fiducial Marker Composed of Gold Nanoparticles and Bone Cement for Proton Therapy of Prostate Cancers
Authors: Lim YK , Kwak JW , Kim DW , Shin DH , Yoon MG , Ahn SH , Park SA , Lee DH , Lee SB , Park SY , Kim DY
Published: April 2010

Purpose: The feasibility of using mixtures of gold nanoparticles and bone cement as fiducial markers was examined to solve the problems of conventional gold markers for proton therapy of prostate cancers. Method and Materials: To investigate the feasibility of replacement of a conventional gold fiducial marker by a mixture of gold nanoparticles and bone cement, two kinds of interactions were examined: one is the interactions of them with kV and MV X‐rays, and the other is their interactions with a therapeutic proton beam. We qualitatively and quantitatively compared radiographic visibility, CT artifacts, and dose reduction of each material. Results: The gold nanoparticle‐bone cement mixtures could extremely reduce the distortions of depth‐dose distribution behind them as well as the artifacts around them, in comparison with the conventional gold fiducial. The gold nanoparticle‐bone cement mixtures could also be easily distinguished from high density organs, such as pelvic bone in kV and MV X‐rays, while it was nearly transparent to a proton beam. Conclusion: We fabricated prototype fiducial markers composed of gold nanoparticle and bone cement, and examined their excellent potential, such as good radiographic visibility, low distortion of depth‐dose distribution, and few CT artifacts, for serving as fiducial markers for proton therapy of prostate cancer.
SU‐FF‐J‐73: Targeting Accuracy Using Exac‐Trac® and Synergy® CBCT Image‐Guided Radiotherapy Systems for Lung Stereotactic Body Radiotherapy
Authors: Ding M , Stuhr K , Newman F , Hu A , Rice H , Miften M
Published: April 2010

Purpose: To analyze the targeting accuracy using Exac‐Trac® (BrainLAB) and Synergy® CBCT (Elekta) systems for lung SBRT, and discuss the difference between these two IGRT systems. Methods: The target localization for lung patients treated with SBRT on Novalis® with Exac‐Trac® system and on Synergy® with CBCT system was analyzed. Prior to each treatment, patient's setup correction using Exac‐Trac® is performed by fusing (bone structure matching) two oblique x‐ray images with related DRRs computed from the planning CT, the correction using the CBCT system is by fusing (grey volume registration) CBCT with the planning CT. The position error is adjusted by shifting the table in lateral, longitudinal and vertical directions. If the shifted distance is >5mm in one direction, we usually repeat the image capturing and fusing procedures to double check the position error—the “second” shifting distance. In this study, we used the “second” shifting distance to analyze the targeting accuracy for both systems. Results: Sixteen and twenty‐nine setup correction cases were studied for Exac‐Trac® and Synergy® CBCT systems, respectively. The first shifted distances were in the ranges of 8.6–22.7mm and 3.5–18.3mm, with the average of 15.2mm and 8.2mm. The “second” shifting distances were in the ranges of 0.5–4.9mm and 0.6–3.4mm, with the averages of 2.8mm and 1.9mm, respectively. For both systems there was no correlation between the first shifted and the “second” shifting distances. The average position error after table shifting in Exac‐Trac® was larger than that in Synergy® CBCT system. We think the 3D volume registration is more practical or accurate than the 2D imaging matching for soft tissue localization. Conclusion: Using volume registration, Synergy® CBCT system is more accurate compared to Exac‐Trac® system in IGRT for lung SBRT. Detailed comparison and discussion of targeting accuracy for different tumor locations between the two systems will be reported.
SU‐FF‐J‐78: Assessment of An Interpolated Ray Trace Algorithm for Deriving Motion From CBCT Scans
Authors: Siochi R
Published: April 2010

Purpose: To asses the accuracy of an interpolated ray‐trace algorithm for deriving respiratory motion from megavoltage cone beam computed tomography (MVCBCT) scans. Method and Materials: 21 Siemens Oncor MVCBCT scans were taken of a tungsten pin attached to a motion phantom positioned with various orientations and table shifts to create motion with variable amplitudes of up to 1 cm along posterior‐anterior and right‐left axes and 3 cm in the cranio‐caudal axis. Edge detection found the pin in all 200 CBCT raw data projections. The intersection of ray‐traces, from the pin's image to the source, for two full exhale projections defined the exhale bounding point, while using two full inhale projections yields the inhale bounding point. These bounding points were ray‐traced into all projections. The position of the pin's image, relative to the projected bounding points, was used to interpolate between bounding points to find the pin's room coordinates for all projections. A plot of pin position versus projection time stamp was compared to the expected motion. Results: A bounding box, whose opposite corners are the projected bounding points, will contain the tungsten pin only if angular separations between projections used for bounding point determination are between 15 and 163 degrees, and differences in full inhale amplitudes are accounted for. Under these conditions, deviations between expected and calculated cranio‐caudal motion are primarily due to flat panel geometry error. The errors are worst at the edges of the CBCT reconstruction volume, with maximum and mean errors of 1.06 and 0.34 mm, respectively. When flat panel errors are corrected, the worst case mean error is 0.16 mm.

Conclusion: For bounded motion of up to 3 cm, the interpolated ray‐trace algorithm will contribute little to the overall error for applications that determine diaphragm motion from patient CBCT scans.
SU‐FF‐J‐141: Volumetric Response Analysis During Chemoradiation as Predictive Tool for Optimizing Treatment Strategy in Locally Advanced Unresectable NSCLC
Authors: Bral S , Duchateau M , Tournel K , Linthout N , Verellen D , Gevaert T , Reynders T , Storme G
Published: April 2010

Background In the treatment of locally advanced non‐small cell lung cancer (LANSCLC) there is a trend towards concurrent chemoradiation because of the advantage on local control and survival (Auperin et al, IASLC 2007). Chemoradiation however is burdened by a marked increase in toxicity. This calls for a more patient‐tailored approach, trying to identify those patients that benefit from a more aggressive approach. We studied the feasibility of measuring volumetric changes in the primary tumor on tomotherapy MVCT, correlating with local response to assess its usefulness in reliable, early detection of patients with poor local therapy outcome. Methods Fifteen consecutive patients with stage III, inoperable LANSCLC were treated using helical tomotherapy. They were monitored for acute toxicity and evaluated with daily MVCT imaging. The tumor volume was delineated daily in a standardized way and the volumetric changes were fitted to a negative exponential resulting in a regression coefficient (RC). Local response evaluation was done using PET‐scan. Results The mean volume decrease (±standard deviation) was 77% (±18%). With a mean treatment time of 42 days this treatment schedule resulted in a mean decrease of 1.83%/day. Out of the 13 evaluable patients 7 developed a metabolic complete remission (MCR). The mean RC of the patients with MCR is 0.050 versus a mean RC of 0.023 in non‐responders (p=0.0074). Using a proposed cut‐off value for the RC of 0.03 80% of the non‐responders will be detected correctly while misclassifying 16.4% of patients who eventually achieve a MCR. Conclusions The RC derived from volumetric analysis of daily MVCT is prognostic and predictive for local response in patients treated with chemoradiation for a locally advanced NSCLC. Because of the possible toxicity of chemoradiation, MVCT can be a tool for the implementation of patient‐individualized treatment strategies.