bluuebunny/crossref_metadata_2025 huggingface dataset:
SU‐FF‐J‐32: Breathing Characteristics of Patients Undergoing Long Treatment Sessions
Authors: Wang P , Lovelock D , Yamada Y , Amols H , Mageras G
Published: July 2006

Purpose: To quantify the constancy of patient respiratory motion over the long treatment times required for high dose stereotactic body radiation therapy (SBRT) and to assess feasibility of the use of respiratory gating for SBRT Method and Materials: The respiratory motion of 26 patients undergoing SBRT to spinal sites was tracked for periods between one and two hours. A stereoscopic infra‐red camera tracked reflectors attached to the patient's abdomen, chest and bony areas such as over clavicles, sternum or hips in three dimensions. Variations in the amplitude, period, the mean position of each reflector averaged over several breathing cycles, and phase differences between chest and abdominal reflectors, were examined to monitor for departures from regular diaphragmatic breathing. The fraction of time patients were breathing irregularly between the first and second half of treatment was compared to assess patient tolerance of long treatment times. Results: In general, patients showed similar variability in both amplitude and period. Averaged over patients, the percent standard deviations were 30.6% and 29.4% respectively. Changes in relative amplitudes between the abdominal and chest markers, an indicator of a change from diaphragmatic to chest breathing, were infrequent. No increase in the frequency of chest breathing was observed with time. The standard deviation of the amplitudes and periods in the first half of the data was not significantly different from those in the second half, indicating no overall changes in breathing patterns. Conclusion: In spite of the long treatment times, no significant changes in respiratory patterns, nor increases in irregular breathing, were observed. This indicates that the long treatment time is not a factor in deciding whether or not gating can be used for patients treated to sites affected by respiratory motion.
SU‐FF‐J‐33: Building a PET Time Series Using Information From 4DCT Data
Authors: Cavedon C , Berna E , Francescon P , Cora S , Scalchi P , Polloniato P , Satariano N , Zanco P
Published: July 2006

Purpose: To build PET time series to be used for radiation treatment planning of lung cancer. Recent advances in time‐related treatment strategies call for datasets that account for respiratory motion. Gated PET techniques allow timing information to be used, but suffer from poor signal‐to‐noise ratio. Non‐gated PET images describe the distribution of metabolic activity as a temporal integral over several respiratory cycles. Non‐rigid image registration could be used to map this integral representation back to short intervals within the respiratory cycle. Method and Materials: CT/PET data were acquired by means of a GE Discovery scanner. 4DCT volumes in different respiratory phases were summed to obtain a volume corresponding to integral PET data. Deformation fields mapping integral CT to single‐instant CT volumes were obtained by means of a non‐rigid registration algorithm based on a local rigidity regularization method. Results were examined as a function of different regularization parameters. Once a proper value was chosen deformation fields were applied to corresponding PET datasets, obtaining single‐instant PET volumes with higher signal‐to‐noise ratio compared to gated techniques. Results: Light regularization parameters caused improbable transformations. In particular, the diaphragm is subject to large global displacement with low spatial frequency. Light regularization may cause high frequency deformations to take place. Optimum weighting factors of the regularization term were found to be between 0.01 and 0.1. Conclusion: Multi‐modality non‐rigid registration is challenging; we avoided it by performing intra‐modality registration between CT datasets and by applying obtained deformations to PET data. This strategy may help using PET for treatment planning in 4D treatment modalities. Strategies consisting of penalizing deformations that locally differ from rigidity must be carefully used in thoracic applications. A more suitable approach may consist of a linear combination of low frequency basis functions. Further investigation is needed, including feasibility of on non‐uniform control point spacing.
SU‐FF‐J‐35: Clinical Applications of 3D and 4D Deformable Image Registration for Image Guided Radiotherapy
Authors: Zhang T , Meldolesi E , Chi Y , Yan D
Published: July 2006

Purpose: To develop a framework of 3D and 4D deformable image registration and investigate its applications in image guided radiotherapy (IGRT). Method and Materials: We have developed 3D and 4D deformable image registration methods to register fan beam CT (FBCT) and cone beam CT (CBCT) images. Applications of the 3D and 4D deformable registration include: (1) Inter‐subject atlas‐based image segmentation to automatically contour normal tissue regions of interest (ROI) in treatment planning CT images; (2) Intra‐subject atlas‐based image segmentation to delineate daily ROIs by registering daily FBCT or CBCT images to treatment planning CT images. This method is an ideal ROI delineation method for online plan adjustments; (3) 4D deformable image registration to extract average voxel trajectories for real‐time tumor tracking and for 4D tomotherapy treatment planning; (4) Deformable fusion of 4D‐PET images, which is based on deformable registration of 4D‐CT images, to minimize motion blurring in PET images without increase of committed doses or data acquisition time. Results: The deformable image registration system was tested using clinical images. Registrations of inter‐ and intra‐subject images show acceptable results. The corresponding results are reported in our supporting document. Quantitative validation of intra‐subject atlas‐based image segmentation showed agreements with physicians' manual contours. 4D registration yields voxel trajectories smooth in both spatial and temporal spaces. Problems were noticed in the cases where the registration image pairs are intrinsically different, such as gas bubbles in rectums, or deformations are extremely large, such as empty vs. full bladders. Conclusions: We have developed a general framework of applying 3D & 4D deformable image registration in image guided radiotherapy. Our clinical applications showed the positive and convincing results.
SU‐FF‐J‐39: Comparison of Patient Positioning Corrections For Prostate IMRT Patients Using Competing Image Guided Radiation Therapy Technologies
Authors: Sohn J , Luo C , Monroe J , Pillai K , Einstein D , Wessels B , Kinsella T
Published: July 2006

We compared prostate position corrections using ultrasound and megavoltage CT image guided systems following initial patient positioning with lasers. Internal prostate movements between the two patient cohorts were assumed to be equivalent given a sufficient number of measurements, so we hypothesize the image guided shifts should average out to the same magnitude. Therapists adjusted patient positions with physician supervision based on daily imaging prior to each treatment. A total of 17 prostate patients were studied. Ten patients (Group I) were scanned in 3‐D mode using an ultrasound system. Contours (prostate/bladder/rectum) from the treatment planning system were transposed on the image set to register the ultrasound image. Therapists shift the contours to match the ultrasound image set and then adjust the patient by these same shifts. The number of shifts recorded from Group I was 432. Group II patients (seven subjects yielding 315 recorded shifts) were treated using Tomotherapy. Patients were scanned over the prostate region and the megavoltage CT image was registered with the treatment planning CT and contours. Shifts were produced for each axes and in roll. The patient table is adjusted to match the registration shifts. Roll corrections were minor and deemed insignificant for this study. The average prostate size from Group I was 104.9cc with a standard deviation of 42.1cc while Group II was 104.2cc and 54.8cc. A panel of four was formed to evaluate the quality of images to check possible operator bias due to image quality. Group I showed an average shift magnitude of 6.1mm with a standard deviation of 3.4mm. The average shift from Group II was 10.6mm with a standard deviation of 6.1mm. Tomotherapy imaging averaged 43% larger shifts compared to ultrasound. Possible explanations for this difference include operator laxity in initial tomotherapy positioning while depending on imaging and auto‐adjustment to compensate.
SU‐FF‐J‐40: Comparison of Prostate Implanted Fiducials with CT and Ultrasound for Prostate Target Localization: Initial Results
Authors: Johnson J , Lee A , Kudchadker R , Amos R , Frank S , Cheung R , Kuban D , Dong L
Published: July 2006

Purpose: To compare prostate localization methods of implanted fiducials, CT‐guided, and ultrasound‐guided (US) techniques. Method and Materials: Data were collected from an on‐going institutional review board approved protocol for comparing different target localization techniques for image‐guided prostate cancer radiotherapy. The protocol is designed to have CT scans with an in‐room CT‐on‐rails three times a week; US‐guided localization twice a week for the initial two weeks, then weekly; and orthogonal electronic portal imaging for fiducial measurements daily. Patients will have three gold seed implanted fiducials for prostate localization. The NOMOS BAT system and MedTec's Acculoc software are used for US and fiducial localization, respectively. All shifts reported by the three methods are relative to the same daily reference point set on patient's skin during the entire imaging session. The differences in the three methods were compared and the mean and standard deviation were computed in each of the orthogonal shifted positions: anterior‐posterior (AP), superior‐inferior (SI), and laterals (RL). Correlation coefficients were determined relative to the CT localization method. Results: We report the results for the first patient who had just completed treatment. The mean differences (one standard deviation) (in cm) between the implanted fiducials and CT were −0.03 (0.18), 0.0 (0.12), −0.03 (0.15), while US and CT were 0.14 (0.68), −0.21 (0.68), and 0.32 (0.28), in AP, SI, and RL directions, respectively. The Spearman's correlation coefficients relative to the CT registration were 0.83, 0.60, and 0.81 for the implanted fiducial method (p<0.003 for all directions) and −0.18, −0.09, and 0.90 for the US localization technique (p>0.05 for AP and SI directions). Note that simultaneous measurements were 22 for CT and fiducials while only 9 for CT and US. Conclusions: Implanted fiducial registration correlates better than the US relative to the CT‐guided approach. More patients are needed to make a firm conclusion.
SU‐FF‐J‐43: Correlation Between External Abdominal and Internal Liver Fiducial Motion in 4D‐CT
Authors: Kainz K , Beddar A , Briere T , Tsunashima Y , Pan T , Prado K , Crane C , Mohan R , Gillin M , Krishnan S
Published: July 2006

Purpose: to determine how well the anterior‐posterior location of a marker, placed on a supine patient's abdominal surface, correlates with the location of a radio‐opaque fiducial implanted within the liver. We investigate which respiratory phases exhibit the best correlation between the marker and the fiducial. Methods and Materials: data was obtained from five patients, each having a fiducial (either an implanted gold pellet or the tip of a stent) in the liver. Each patient received a cine‐mode 4D‐CT scan of the liver, with the position of an external marker used to associate each cine CT image with a specific respiratory phase. The trace of the anterior‐posterior motion of the marker was normalized under the assumption that, among ten phases of a full respiratory cycle (0%, 10%, 20% … 90%), the marker displacements correlated linearly with the fiducial's superior‐inferior displacements. Each cycle of the normalized marker trace was then superimposed upon a plot of the fiducial's displacement; the latter was measured within the 4D‐CT data set for each of the ten phases. Results: comparisons of the marker trace and the fiducial coordinate from 4D‐CT indicated that, in general, the marker motion correlated reasonably well with internal liver motion during the process of exhalation (from end‐inspiration to end‐expiration), with optimum correlation during end‐expiration (40% to 60% phase). The correlation tends to be poorer during inhalation, extending from 70% to 90% phase. Conclusions: a tight correlation near end‐expiration suggests that using an external‐motion‐based respiratory trace, as a guide for gated treatments for liver cancer, should enable reliable and reproducible coverage of the target volume. Poorer correlation during inhalation suggests that the marker's anterior‐posterior motion may not adequately characterize the internal motion during those phases, and that gating should be avoided during this stage of the respiratory cycle.
SU‐FF‐J‐44: Daily 3D On‐Line Setup Verification and Correction for 45 Prostate Patients Using Implanted Gold Markers
Authors: Pasma KL , Leijser V , Schimmel E
Published: July 2006

Purpose: To minimize the CTV‐PTV margin by correcting for prostate motion and positioning during external beam therapy using implanted gold markers and a 3D on‐line correction protocol. Method and Materials: 45 patients had four gold markers (1×7 mm) implanted in their prostate. They are inserted under ultra sound guidance by an urologist using a standard prostate biopsy tool. The beams eye view projection of the markers is outlined in the DRR's. Patients are treated with a three field technique. For each treatment session four images are acquired with a Theraview NT or Iview GT EPID and stored in a central database. First 5MU of the AP and 10MU of the LL beam are delivered. While the patient is on the couch, templates of the reference images are matched with the MV images. For shifts ⩾2 mm the technician enters the treatment room and moves the couch. Then the rest of the treatment is delivered and images are acquired of the LL and AP beam. These images were analyzed and the effect of using the NAL protocol or no correction was simulated. Results: The systematic (random) (Σ(sgr;)) variation was reduced in lateral, cranial‐caudal and AP direction to respectively 0.6 (1.1), 0.6 (1.1), 0.5(1.6) mm, compared to 1.3(1.7), 1.4(1.9), 1.8(2.5) mm when using the NAL protocol and 2.2, 2.4, 3.5 mm without correction. Based on these results we reduced, after treating 10 patients, the CTV‐PTV margin to 6 mm in all directions and increased the dose to the prostate from 74 to 78 Gy. The whole procedure could be done in a standard 10 minute treatment slot. To reduce the workload remote couch steering is currently being tested in cooperation with the linac manufacturer. Conclusion: Using a simple and effective method the CTV‐PTV margin was reduced to 6 mm in all directions.
SU‐FF‐J‐45: Daily Changes in Seminal Vesicle Location During Treatment of Prostate Carcinoma
Authors: McNeeley S , Paskalev K , Buyyounouski M , Ma C
Published: July 2006

Purpose: In this study we examined daily bladder filling variation and the effect it has on seminal vesicle (SV) location on patients treated for high‐grade prostate carcinoma. Currently there are several methods of image‐guided radiotherapy (IGRT) used to locate the prostate on a daily basis. These methods, however, do not account for the change in position of the SVs, relative to the prostate, determined during simulation (day 0). Using this displacement information, we would like to determine if our clinical SV PTV margin is adequate. Method and Materials: To determine SV displacement, 496 daily sagittal ultrasound images (BAT, North American Scientific, Chatsworth, CA) from 18 patients were examined. The images provided sagittal outlines of the day‐0 structures overlaid on the daily patient ultrasound. With the day‐0 prostate aligned to the day‐n prostate ultrasound image, differences between day‐0 and day‐n bladder and SVs positions can be determined. SV displacement was taken at the mid point of the SV. The change in bladder position was determined by the difference in posterior extent anterior to the SVs. Results: The SV displacement population mean and standard deviation (SD) was 2.1 mm 2.8 mm respectively. The bladder displacement population mean and SD was 2.7 mm and 3.3 mm respectively. The maximum SV displacement for all patients was 2.5 cm. The maximum SV and bladder displacement SD for any one patient was 7.4 mm and 7.7 mm respectively. Conclusions: The results show that in general typical SV motion is quite small averaged over a standard treatment course. Since the population SD is small, our 8 mm SV PTV is adequate using daily prostate alignment. There are however some patients who's SV location changes are substantial on a day to day basis given a SD of 7.4 mm. Consistent bladder filling may be critical when treating SVs.
SU‐FF‐J‐46: Determination and Validation of a 4D Trajectory for Respiration‐Induced Real‐Time Tumor Motion Tracking
Authors: Van Liew S , Nazareth D , D'Souza W
Published: July 2006

Purpose: To model the tumor trajectory non‐invasively by modeling the instantaneous tumor position using the “average” tumor position derived from a 4D CT scan. A real‐time motion‐synchronized idealized moving treatment couch was used to validate the trajectory dosimetrically. Methods and Materials: In this study, we consider data from 7 patients who underwent a 4D CT scan ‐ 5 lung tumors and 2 pancreas tumors. The CT images were retrospectively sorted according to phase, and the tumor contoured by a physician. The tumor's trajectory was modeled parametrically, using a 5‐term Fourier series to fit individual coordinate trajectories. These were then combined to yield a continuous 3D tumor trajectory. Compensation of this trajectory was modeled using a moving treatment couch with idealized dynamics. To validate the compensation, both a 7‐beam conformal plan, and a 7‐beam IMRT plan were ran for both the original and compensated tumor volumes for each patient. Results: The RMS residual error for the fitted trajectories averaged 0.41 ± 0.22 mm, with a corresponding average tumor motion amplitude of 9.7 ± 5.3 mm. For patients with motion amplitudes greater than 5 mm, the average improvement in the 100% dose coverage between end‐inhale and end‐exhale was 24.3% for the 3D conformal plan, and 31.1% for the IMRT plan. Tumors with motion amplitudes less than 4 mm saw improvements in the 100% dose coverage of less than 1% for 3D conformal plans, and 8.2% for IMRT plans. Conclusion: High‐resolution tumor trajectories can be established with a 4D CT scan, and the tumor position can be sampled at a rate comparable to fluoroscopy tracking of implanted markers. Tracking and compensation using this technique has been shown to greatly improve the dose coverage and conformality for both 3D conformal and IMRT plans in comparison.
SU‐FF‐J‐47: Determination of Internal Target Volume Reconstruction Algorithm Beyond the Time Dimension Using Second Model of a 256‐Slice CT
Authors: Mori S , Endo M , Kanematsu N , Asakura H , Tomoyasu Y , Shuhei K , Susumu K , Masayuki B
Published: July 2006

To observing trajectory of moving tumor under free breathing, we compared two image‐processing methods and two reconstruction algorithms based on the FDK and adapted to the 256‐slice CT. These algorithms were namely 4D image average (4DIA) and 4D image maximum intensity projection (4DIM), 4D projection data average (4DPA) and 4D projection data maximum intensity projection (4DPM). The concept of 4DIA and 4DIM was generated on CT image after backprojection process. 4DIA was averaged each pixel value on the volumetric CT data along the time axis, and 4DIM was selected maximum each pixel value along the time axis. With regard to the 4DPA and 4DPM, these essential concepts are to process projection data along the time axis, rather than reconstructed CT images as 4DIA and 4DIM.

Evaluations of these algorithms were done in the image noise, CT‐number accuracy, and target moving distance with various reconstruction time conditions using lung cancer patients and compared these results with those with volumetric cine images. As the results, it is difficult to observe the edge of the tumor in 4DIA and 4DPA images due to decreasing CT number from the original tumor CT number. While 4DIM images emphasized pulmonary vessels as increasing the processing time ranges and it makes difficult to observe the accurate tumor edge. From these results, 4DPM provides the accurate tumor movement and accurate CT‐number independent of the reconstruction conditions.
SU‐FF‐J‐49: Dose Comparsion of MVCB and Orthogonal Pair Portal Images
Authors: Peng L , Yang C , Tsai P , Chen Y , Sim S , Weiss M , Murphy S , Wu G
Published: July 2006

Purpose: To evaluate the delivered patient doses resulting from MVCB(Mega‐Voltage Cone Beam)and ORTH(orthogonal pairs)portal imaging techniques, and report dose per MU(cGy/MU)and absolute dose(cGy)at isocenter, max dose, and mean doses to the target and critical organs. Method and Material: Both image techniques are based on a Siemens 6 MV LINAC equipped with an A‐Si flat panel and dose calculation done on a Pinnacle 3DRTP system. The ORTH technique was simulated by two orthogonal beams, total 6 MUs and 20cm×20cm field size. The MVCB technique was delivered with a 200° arc beam, total 9 MUs and the same field size. 30 patients representing 6 treatment sites were analyzed. Calculated doses were reported for max dose in patient, dose at the isocenter, and mean doses to target and critical organs. Results: For the cGy/MU analysis, the value at isocenter was similar. The difference of max dose was greater in pelvis and abdomen. The mean dose in normal lung or contralateral breast differed greater than other critical organs. In contrast, the dose difference in the target or critical organs close to isocenter was very small. The absolute dose difference and 2D absolute dose distributions are shown. The high dose area for ORTH technique is located at the proximal corner of rectangular areas intersected by the two beams but anteriorly for MVCB due to the anterior arc, and contributes more dose to anterior organs like normal lung and contralateral breast. Conclusions: From our analysis, high dose region generated by MVCB is shown inside the critical organs, and tends to be larger compared to the ORTH technique. Due to the potential biological effects, the extra dose burden to the critical structures should be monitored carefully. This study provides a quantitative analysis and suggests the number of projections and total MUs are the most important factors for the MVCB technique.
SU‐FF‐J‐52: Dosimetric Impact by Temporal Changes of the GTV in Head and Neck Cancers
Authors: Maxim P , Le Q , Loo B , Pawlicki T
Published: July 2006

Purpose: Over a 6 week head and neck cancer treatment course, radiation and chemotherapy induce considerable changes in the volume and geometry of the tumor and normal tissues. When using highly conformal radiotherapy, even relatively small changes in the tumor volume could alter target coverage and possibly the therapeutic efficacy. The purpose of this study is to investigate the dosimetric impact of anatomic changes during the treatment course. Method and Materials: A representative patient with nasopharynx cancer treated with IMRT was studied. Cone beam CT scans covering the skull base and upper neck were acquired at the beginning and after every 10 treatment fractions. The GTV was contoured on the initial treatment planning CT scan and recontoured on subsequent CBCT scans to reflect treatment‐related changes over time. Radiation dose was recalculated on each CBCT using the same treatment isocenter and the original IMRT fields, MLC sequences, and monitor units. The GTV DVH's were compared to assess changes in tumor coverage. Results: Somewhat counterintuitively, GTV coverage decreased over time as the tumor volume decreased. GTV volume decreased by 15% after 10 fractions and 40% after 20 fractions. Conversely, 100% of the prescribed dose covered 95% of the GTV initially, 80% after 10 fractions, and 74% after 20 fractions. Conclusion: These results show that temporal changes in tumor volume and geometry can have a potentially clinically significant effect on the dosimetry. The decreasing GTV coverage over time implies the need to re‐evaluate the treatment plan during the course of treatment and incorporate changes necessary to achieve adequate tumor coverage.
SU‐FF‐J‐53: Effect of Tumor Motion On the Use of PET Images for Target Volume Delineation in Radiation Treatment Planning
Authors: Saoudi A , Pourmoghadas A , Cygler J
Published: July 2006

Purpose: To assess the effect of both motion and medium heterogeneity on automatic PET target delineation fused with CT images for radiation treatment planning of lung tumors. Method and Materials: The data were acquired on Philips Gemini PET‐CT scanner. A movable lung phantom was built using the NEMA IEC body phantom containing 6 hollow spheres with diameters ranging from 10 to 37 mm. The phantom volume was packed with Styrofoam beads and filled with water to reach the density close to the density of lung 0.3g/cc. The tumor motion was simulated by a movable acrylic table that provided variable amplitudes and frequencies of movement to the phantom. The spheres were filled with 1.14 mCi/ml of FDG. There was no background activity in the body phantom outside of the spheres. Scans were performed for variable amplitudes ranging from 0.5 to 2 cm. CT and PET images were auto‐contoured on Pinnacle workstation using variable thresholds relative to the maximum SUV. The threshold that best measured the volume of each sphere in static mode and the effective volume in dynamic mode was assessed. Results: The SUV threshold that best defines the target volume in static mode and the effective volume in dynamic mode when no respiratory gating is applied depends on the motion amplitude. The small spheres are more sensitive to the inhomogeneity of the medium, most probably because the positron range is greater in lung equivalent medium then in water. Conclusions: The study shows that it is not accurate to apply a constant threshold for target volume delineation in radiation therapy for all tumor sizes and variable tumor movement. The change of target delineation threshold is more due to the increase of the partial volume effect when the tumor activity is spread over a large volume proportional to the magnitude of movement.
SU‐FF‐J‐54: Effectiveness of 4D CT On Stereotactic Radiosurgery of Lung Cancer
Authors: Ko Y , Park S , Ahn S , Lee S , Shin S , Noh Y , Kim J , Choi E
Published: July 2006

Purpose: In order to spare the normal tissues as much as possible during stereotactic radiosurgey (SRS) of lung cancer by limiting the tumor motion within 5 mm, 4D CT was implemented and its usefulness was evaluated. By comparing CT during the simulation with CT during the treatment, the interfractioanl positioning errors were assessed and image guided radiotherapy was performed using the images from ExacTrac x‐ray system (BrainLab, Germany) in the treatment room. Method and Materials: For 11 lung cancer patients positioned in the SRS frame, 4D CT was acquired and treatment was planned based on 4D CT. For the patients whose tumor motion was larger, the motion was controlled to be less than 5 mm using the real‐time positioning management (RPM, Varian, USA) system. To verify the interfractional patient positioning errors, CT was acquired twice during the course of treatment and ExacTrac x‐ray system was used to reproduce the patients' setup. Results: From the 4D CT, mean GTV and PTV were 15.9±9.6 cc and 40.7±16.6 cc, respectively. Tumor motions were 2.9±1.4 mm, 3.4±3.2 mm, and 12.1±5.0 mm in lateral, vertical, and longitudinal direction, respectively, for the full respiratory phases, which were reduced to 3.7±1.1 mm during 30 ∼ 70 % phases selected for the gated radiotherapy. Discrepancy between planning CT and two CT during treatment was 1.2±1.0 mm, 1.4±1.2 mm, and 2.3±1.5 mm, and setup errors from ExacTrac system were 1.0±1.8 mm, −0.3±2.2 mm, and −0.6±3.2 mm in lateral, vertical, and longitudinal direction, respectively. Conclusion: The use of 4D CT, the repeated CT scans during treatment, and image‐guided technique using x‐ray imaging system in treatment room for setup correction was effectively implemented for SRS of lung cancer, which assured the tumor motion and positioning errors within 5 mm during treatment.
SU‐FF‐J‐55: Effects of Motion On Cone Beam CT Image Quality
Authors: Santanam L , Mutic S , Esthappan J , Goddu S , Malinowski K , Parikh P , Low D
Published: July 2006

Purpose: On‐board cone‐beam imaging is being used to collect kilovoltage CT images for treatment position verification and analysis of tumor response. One challenge of cone‐beam imaging is that full sinogram acquisition takes more than 1 minute. While breathing motion in the lungs, influence both cone‐beam and fan‐beam modalities, its profound effects in cone‐beam CT are well known. However, there are many portions of the body where voluntary and involuntary processes can yield small motions. The purpose of this study is to investigate the influence of small motions on cone‐beam reconstruction quality. Materials and Methods: A commercial CT performance phantom (Catphan, Phantom Laboratory, Salem, NY) containing various image quality assessment tools was imaged using a kilovoltage on‐board cone‐beam CT system (Varian Medical Systems, Palo Alto). The imaging phantom was moved using an in‐house developed “4D phantom” (with a 0.4 mm position accuracy), in sinusoidal patterns with amplitudes of 1.25mm and 2.5 mm in the three orthogonal directions and elliptical patterns with axes from 1 mm to 2.5 mm in steps of 0.5 mm. To quantify the effect on the image quality, the CT number accuracy, spatial integrity, image uniformity, high and low contrast resolution were compared. Results: CT number accuracy and spatial linearity were unaffected by motion. While single‐dimensional motion did not affect the low‐contrast resolution, elliptical motion yielded degradation. The visibility of the 1% cylindrical low contrast resolution targets was 7 mm, 8 mm and 15 mm for static through 1 mm, 2.0 mm, and 2.5 mm ellipses. High contrast spatial resolution was improved slightly for in‐plane motion, but degraded sharply with out‐of‐plane motion. Conclusions: This information will allow investigators to evaluate the ultimate utility of cone‐beam imaging for imaging studies when patient immobilization is not perfect.
SU‐FF‐J‐58: Evaluation of Immobilization Devices Using EPID Measurements of Patient Set Up Variations
Authors: Fong L , Herman M , Beltran C , Brown P
Published: July 2006

Purpose: Methodology to evaluate the performance of immobilization devices for head and neck (H&N) treatments using EPID measurements and a multiple linear regression model. Method and Materials: The immobilization devices considered for the analysis were: UON™ mask, Type‐S™ and Bear Claw™ head/neck/shoulder systems. We acquired daily electronic portal images for 35 H&N patients. PortalVision™ software was used to perform anatomy matches using the Digital Reconstructed Radiograph from the CT‐simulation, as the matching anatomy reference. The two‐dimensional mismatch data decomposed into the appropriate components along each body axis and the orientation of the patient, gantry and couch angles were considered. In order to evaluate the impact of the immobilization device on the deviation of a particular reference structure between simulation and treatment, we used a multiple linear regression model. Results: Although the mean values of the estimators are adequately estimated under the simple statistical procedures, the standard deviations of those estimators will be biased due to the clustered nature of data. The biasness in standard deviations will invalidate the T‐ and F‐tests. In order to correct for biasness of the standard deviations, we used a linear regression approach to generate robust standard errors corrected for clustering. We compared the results of an uncorrected linear regression with the corrected ones. Even though the uncorrected model showed statistically significant impact of using a particular device on the mean of the variation, the significance is eliminated when using corrected standard errors. Conclusion: By correcting for clustered and heteroscedastic nature of the data in a multiple regression setting, we assessed the degree of inter‐fractional variation and concluded that it is independent of the immobilization method. The effect of other factors (i.e. patient characteristics, experience of staff) on mean deviation may need to be considered for further analysis. Conflict of Interest: Partially funded by Varian.
SU‐FF‐J‐62: Evolution of Tumor Volume and Motion in Non‐Small Cell Lung Cancer During Radiotherapy
Authors: Ford E , Song D , Tryggestad E , McNutt T , Wong J
Published: July 2006

Purpose: To assess changes in tumor volumes and motion trajectories of non‐small cell lung cancer patients over the course of radiotherapy. Materials and Methods: We acquired repeat CT scans at three time points through the treatment course. Scans were acquired on a Philips large‐bore 16‐slice scanner using either a respiration‐correlated 4D‐CT protocol or a breath‐hold protocol at moderate‐deep inspiration enforced with the Active Breathing Coordinator system. We utilized the Pinnacle treatment planning system to co‐register based on vertebral bodies. We contoured the lesions in each data set and measured lesion volumes using model‐based segmentation tools. Windowing parameters were kept constant for all scans. Using the contours at each respiratory phase we measured the excursion of the lesion and changes of the excursions from scan to scan. Results: Tumor sizes decreased through treatment by 5%, 46% and 48% in three patients analyzed here. The change in the average GTV excursions was (mean ± s.d. over patients): 3.2±4.3 mm (A/P), 0.4±0.6 mm (R/L) and −0.1±3.1 mm (S/I). The 3D vector excursion increased by 2.9±4.2 mm on average. The changes in motion extent are similar to the motion excursion themselves, and there appears to be a strong variability between patients. Conclusions: These preliminary data indicate noteworthy trends of tumor size and motion over the course of radiation therapy. The tumor volume decreases and there is indication that the tumor excursion increases. Further analysis is underway and will be presented. Such long term evolution has important implications for the design and delivery of radiotherapy to lung tumors.
SU‐FF‐J‐63: Experience On Cone Beam CT IGRT in Busy Community RT Clinic
Authors: Lam S , Woo C , Applegate B
Published: July 2006

Purpose: X‐ray volume imaging (XVI) in image‐guided radiation therapy (IGRT), has been under clinical investigation since July 2003 in a few major hospitals. Only since late 2005 the XVI system is available for the general application. We began using the system immediately. The purpose of this presentation is to demonstrate the usefulness of this cone beam XVI system, in a busy single‐machine, stand‐alone radiation therapy clinic in routine practices; and the results on some typical clinical applications. Method and Materials: This clinic has a single accelerator, Elekta Synergy, (Crawley, UK,) with XVI and IView, began clinical application in mid Dec. 2005. In three months, the clinic is currently treating 40 patients daily, with about 30% of the patients receiving IMRT. Within days of training the staff has already adapt the procedure into clinical use. Within a week, the processing time was reduced to three to four minutes per patient. We have done 25 patients; 20 patients are still under treatment. The procedure is applied to soft tissue cases in the abdomen; prostate, anal and rectal, head and neck cases. Results: Statistics of the three‐dimensional shift are documented for each daily procedure. Over all experience showed that body procedures, abdomen and pelvis procedures; the range of shift required is from zero to 5 millimeters. For head and neck cases, the shifts are in the range of zero to three millimeters. Conclusion: Our experience showed that Elekta Synergy, XVI system is relatively easily to apply to the community clinic setting, without too much complication. We hope to gather more experience on the how IGRT improves upon the non‐IGRT IMRT procedures.
SU‐FF‐J‐64: Feasibility of a Feedback‐Guided Breath‐Hold Technique for Thoracic Radiation Therapy
Authors: Kainz K , Liu H , Balter P , Tutt T , Hunjan S , Prado K , Liao Z
Published: July 2006

Purpose: To determine whether respiratory traces can be used to visually guide breath holds at specified respiratory phases for thoracic radiation therapy; and whether such breath‐holds are reducible and effective to reduce treatment margins. Methods and Materials: Feedback‐guided breath‐hold (FGBH) technique was used to provide real‐time respiratory traces to patients undergoing radiation therapy of the thorax. The visual signals, depicting the thoracic‐motion amplitude and targeted breath‐hold levels, e.g. end‐expiration (EE) or end‐inspiration (EI) were fed back to patients via eye goggles. Patients with distal esophageal cancers near the diaphragm were evaluated for the effectiveness and reproducibility of the FGBH. Simulation CT scans at EE and EI were acquired with repeated FGBHs at multiple sessions. In addition, twice‐weekly portal images were acquired with FGBH at EE during treatment courses. On the CT‐DRR and portal images, positions of the isocenter and the diaphragm representing the breathing level were measured relative to vertebral axis. The systematic and random errors of the isocenter and diaphragm positions among various image sets were also analyzed. Results: The diaphragm movement during free breathing was about 2–3 cm as measured from two patients who completed the clinical protocol so far. For the first patient, the systematic and random errors of the EE diaphragm positions were on the order of 0.6–0.8 cm. The second patient was able to perform the EE breath‐hold better with systematic and random errors of the diaphragm positions less than 0.2 cm. The margin needed for the FGBH treatment was 59.1% and 30.7%, respectively, relative to that of the free‐breathing treatment for the two patients. Conclusions: FGBH technique can be used to effectively reduce the respiratory motion and treatment margin. However, the accuracy of the respiratory monitor, patient training, and compliance are critical steps to ensure the consistency and reproducibility of the breath‐hold.
SU‐FF‐J‐66: Feasibility Study of Mobile Target Tracking by Breathing Synchronized Delivery (BSD)
Authors: Tewatia D , Zhang T , Paliwal B
Published: July 2006

Purpose: To investigate the feasibility of mobile target tracking by Breathing Synchronized Delivery (BSD).

Method and Materials: Target breathing motion compensation by real‐time tracking of dynamic multi‐leaf collimator (dMLC) is under development. We have used an alternative approach to circumvent this problem. Breathing‐delivery phase correlation is set in Breathing Synchronized Delivery (BSD) planning. During treatment the feedback is provided to the patients to maintain the correlation. A retrospectively binned 4D‐CT was acquired. The full exhalation (50%) phase images were exported to treatment planning system for planning. Smooth tumor trajectory was obtained using deformable registration algorithm and Fourier filtering. With constant dose rate (300MU/min) and breathing period, a motion incorporated BSD plan was obtained by superimposing instantaneous target motion to the leaf position at corresponding phase. BSD plan was delivered using the dynamic dose mode with a Varian's dMLC. For dosimetric verification, a computer controlled mobile phantom was used to simulate the actual superior‐inferior target motion obtained from 4D image registration. Dose was measured at the isocenter of the phantom in the coronal plane using EDR‐2 film. Three films were exposed, first for static phantom and conventional plan, second for the moving phantom and conventional plan and third moving phantom with motion compensated BSD plan. Results: The dose distributions in superior‐inferior direction were very similar if BSD planning is used on mobile phantom. Underdose and overdose of the order of 20% were observed at the superior‐inferior direction if motion is not compensated. Conclusion: Phantom dosimetry results show that BSD planning and delivery method can effectively compensate target motion. For the patients who may maintain reproducible breathing pattern with video or audio instructions, BSD method is a simple alternative to real‐time tracking.
SU‐FF‐J‐67: Fiducial‐Based Translation Alignment Accuracy of An AC Electromagnetic Tracking System and On‐Board Kilovoltage Imaging Localization System
Authors: Santanam L , Parikh P , Malinowski K , Esthappan J , Hubenschmidt J , Goddu S , Dimmer S , Mutic S , Low D
Published: July 2006

Purpose: On‐board kilovoltage imaging is being used for accurate fiducial‐based alignment of tumors. However, these systems deliver additional dose to the patient and do not allow interactive repositioning with the therapist in the room. The purpose of this study is to measure and compare static localization accuracy of a commercial on‐board kilovoltage imaging system and a novel AC electromagnetic tracking system. Materials and Methods: A kilovoltage imaging system (Trilogy™ System, Varian, Palo Alto, CA) and an electromagnetic tracking system (Calypso® 4D Localization System, Calypso Medical, Seattle, WA) which provides a continuous measurement of the implanted transponder positions, were compared for localization accuracy. A phantom containing three radiofrequency transponders was moved, using an in‐house developed 4D phantom (with a 0.4 mm position accuracy), in steps from 0.4 cm to 5 cm in the lateral, longitudinal, and vertical directions. The transponder positions were measured using the commercial matching software using antero‐posterior and lateral images and comparing against DRRs. These results were compared against the Calypso System measurements. Results: The localization accuracy, defined as the average difference of the measured positions (by the localization systems) to the actual positions (as determined by 4D‐ phantom positioning system) was found to be 0.0 ± 0.00 cm, 0.1 ± 0.1 cm and 0.1 ± 0.0 cm in three directions for KV system and 0.0 ± 0.0 cm for the Calypso system. Results showed that both systems provided excellent positioning accuracy.
SU‐FF‐J‐68: First Clinical Results of An Adaptive Off‐Line Radiation Scheme Using Cone‐Beam CT Scans for Treatment of Prostate Cancer
Authors: Nuver T , Nijkamp J , Lakeman A , Smitsmans M , van Herk M , Pos F , Lebesque J
Published: July 2006

Purpose: We developed an adaptive scheme for prostate cancer radiotherapy based on kV cone‐beam‐CT (CBCT) images that are obtained on the machine during the first six treatment days. The aim of this scheme is to improve knowledge of the average prostate position and average rectum shape and safely reduce the PTV margin. Method and Materials: CBCT‐scans, acquired our on Elekta Synergy systems, were first matched on the planning CT scan using the pelvic bones. Automatic grey‐value matching was then used to match the prostates of the CBCT‐scans to the prostate of the planning CT scan. The mean of the obtained translations and rotations was used to move the prostate of the planning CT scan to its average position. Subsequently, the rectal wall was delineated in the CBCT‐scans, and coordinates of corresponding points of the 7 rectums were averaged to obtain the average rectal wall. Based on average prostate and rectum a new IMRT treatment plan was made with a reduced PTV margin of 7 mm. Weekly CBCT‐scans were made to verify that the new PTV encompasses the prostate. Results: So far, 16 patients were successfully treated with our adaptive treatment scheme. For 85% of the CBCT‐scans a successful grey‐value match was obtained, the other scans were discarded. For 88 out of 89 verification scans the prostate was inside the PTV. The mean dose received by the rectum reduced on average by 7.6%, and the equivalent uniform dose (a=12) by 1.5%. Conclusion: This is the first routine clinical application of soft tissue image guidance for the prostate using kV CBCT. Contrary to adaptive schemes that use implanted markers, our method is non‐invasive and improves localization of both prostate and rectum. Conflict of Interest: Elekta, Inc financially supported part of this study.
SU‐FF‐J‐70: Geometric Accuracy of a Real Time Target Tracking System with Dynamic MLC
Authors: Keall P , Cattell H , Pokhrel D , Dieterich S , Wong K , Murphy M , Vedam S , Wijesooriya K , Mohan R
Published: July 2006

Purpose: Dynamically compensating for target motion during radiotherapy will increase treatment accuracy. A laboratory system for real time target tracking with a dynamic MLC has been developed. In this study, the geometric accuracy limits of this DMLC target tracking system were evaluated. Method and Materials: A motion simulator was programmed to follow patient‐derived tumor motion paths, parallel to the leaf motion direction. A target attached to the simulator was optically tracked, and the leaf positions adjusted to continually align the DMLC beam aperture to the target. Analysis of the tracking accuracy was based on video images of the target and beam alignment. The system response‐time was determined and the tracking error measured. Response‐time‐corrected tracking accuracy was also calculated to investigate the accuracy limits of an improved system. Results: The response‐time of the system is 160±2ms. Because of this response‐time, the tracking error is largest when the target velocity is highest. The geometric precision for tracking patient motion is 0.6–1.1mm (1σ) for the three patient datasets tested. The systematic tracking error is very small in all cases (<0.1mm). Conclusion: A DMLC target tracking system has been developed that can account for detected motion parallel to the leaf direction. The overall geometric accuracy of this system is very promising, with negligible systematic tracking errors and ∼1mm random tracking errors. Reducing the response‐time will further increase the overall system accuracy. Conflict of Interest: Two authors are principal investigators on sponsored research agreements between Varian Medical Systems and their respective institutions. One author is an employee of Varian Medical Systems.