bluuebunny/crossref_metadata_2025 huggingface dataset:
SU‐FF‐J‐74: Tumor Motion and Tumor Shape Changes During Radiotherapy of Bladder Cancer
Authors: Lotz H , Pos F , Hulshof M , van Herk M , Lebesque J , Remeijer P
Published: June 2005

Purpose: First, to quantify bladder tumor motion in three dimensions. Secondly, to relate the motion to changes in bladder filling. Thirdly, to evaluate shape and volume changes of the GTV during the course of the radiotherapy. Method and Materials: CT images were obtained for 21 bladder cancer patients. Next to the planning CT scan, each patient underwent 8 to 11 follow‐up CT scans. These scans were matched on the bony anatomy. Patients were instructed to empty their bladder and drink 250 cc water one hour prior to acquisition. Tumor, bladder and rectum were delineated manually. For each patient, the variation in tumor position (day‐to‐day tumor motion) was determined by calculating the shift of the center of gravity (CG) of each GTV relative to the mean CG. These shifts were compared with model results from a previous study, concerning patients with a healthy bladder. The correlation between bladder volume and GTV position was determined. To study GTV shape changes, we matched all GTVs and determined the residual shape errors in terms of SDs. Results: Tumor motion was largest in Cranial‐Caudal and A‐P direction and ranged from 0.1 to 0.9 cm. The movement was strongly correlated with the bladder filling and the tumor location on the bladder wall. The average SD of the GTV shape changes, excluding the 10% highest values, ranged from 0.1 to 0.35 cm. The SD of the GTV volume ranged from 0.5 to 13 cc and was not dependent on the GTV volume. We found no significant volume time trend. Conclusion: We demonstrated that, despite large differences in bladder filling, variations in GTV shape were small. We could not prove any GTV volume trend with time. Geometrical uncertainties of the GTV position were mainly caused by variation in bladder volume and depended strongly on the GTV location.
SU‐FF‐J‐75: Geometric Calibration of An Extended View C‐Arm Platform for Cone‐Beam CT
Authors: Cho Y , Kim S , Siewerdsen J , Moseley D. , Jaffray D
Published: June 2005

Purpose: A mobile C‐arm with a versatile detector mount (providing extended field‐of‐view) has been developed for multi‐mode fluoroscopy and cone‐beam CT image‐guidance of surgical procedures. Geometric calibration estimating a set of parameters that fully describe the geometry of the systems is essential for the accurate image reconstruction and precise surgical guidance. We have developed a general analytic method to calibrate this system. Method and Materials: The platform for the extended view C‐arm for Cone‐beam CT is a Siemens PowerMobil. Field of view can be extended originally from 18×24 to 18×40 cm2 with the computer controlled linear guide system attached to the arm to displace the position of the imaging detector. It allows imaging objects such as pelvis of patients on C‐arm. The calibration phantom, modified to fit in the field of view, consists of 16 ball bearings precisely located in two circular trajectories in a cylindrical plastic phantom. All the geometric parameters including source position, and detector position and rotation with respect to gantry angle are found at various detector shifts. The calibration algorithm previously developed and verified at the cone‐beam CT systems on optical bench and clinical linear accelerator was applied. Results: The uncertainty of the calibration algorithm is less than 0.6° (out of plan) and 0.01° (in plan) in detector angles, 0.01mm (normal to the beam direction) and 1.4mm (beam direction) in x‐ray source/detector position. Repeatability of the center of the detector in various gantry angle and detector shift was less than 1 pixel size. Optimal weight of the counter valance for precise motion of the extended view C‐arm was also found using the calibration parameters. Conclusion: Overall, a robust method has been developed for an accurate geometric calibration of systems demonstrating non‐ideal trajectory. This will allow an accurate cone‐beam CT reconstruction and manual/robot‐assisted image guided surgical procedures.
SU‐FF‐J‐76: Minimally‐Invasive Intraoperative Radiotherapy (MIR): Technique Development for Treatment of Canine Bladder Cancer
Authors: Gutierrez A , Murphy S , Jaradat H , Forrest L , Mackie T
Published: June 2005

Purpose: To develop, model, and quantify the dose reduction on critical structures using Minimally‐Invasive Intraoperative Radiotherapy (MIR) for the treatment of canine bladder cancer, and develop the technique for laparoscopic placement of the custom tissue expander. Method and Materials: A custom tissue expander was constructed and implanted between the bladder and descending colon of three Beagle cadavers. Two of the implants were placed via laparotomy, and one was laparoscopically placed. The cadavers were positioned in a body fix mold, and CT scanned with the custom tissue expander inflated with saline solution and deflated. A radiation therapy treatment plan was constructed on the tomotherapy treatment planning system for the inflated and deflated CT scans of each cadaver. TLD chips were placed on the bladder and colon side of the laparoscopically placed tissue expander. Pre‐treatment target localization was accomplished by using the onboard MVCT of tomotherapy. Both inflated and deflated treatment plans for one fraction of the laparoscopically placed cadaver were delivered. Results: Keeping the dose to the bladder fixed, the average dose reduction when the tissue expander is inflated for the colon is 42.7%, spine is 38.7%, left kidney is 50.52%, and right kidney is 31.9%. A significant maximum dose reduction to these structures is also achieved. TLD chip measurements on either side of the inflated tissue expander showed a dose reduction of 55.1%. Conclusion: The cadaver studies evaluated indicate the potential for a clinically significant dose reduction to the colon, spine, left and right kidneys using MIR. An effective laparoscopic technique was developed to allow for the quick placement of the custom tissue expander in the abdominal cavity with minimal incisions. Conflict of Interest: This work was partially supported by a grant from the NIH (P01 CA088960) and a contract from TomoTherapy Inc.
SU‐FF‐J‐82: Use of CT Based IGRT for Daily Set‐Up of Frameless Fractionated Stereotactic Patients
Authors: White K , Sibata C , Jenkins T , Wolfe M , Patel R , Allison R
Published: June 2005

Purpose: To compare orthogonal port films against CT based Image Guided Radiation Therapy (IGRT) for patient isocenter verification and assess the use of CT based IGRT for daily patient set‐up. Method and Materials: Eleven patients with brain metastases were CT'd for each of their fractionated radiosurgery treatments. The patients were immobilized in the supine position with a stereotactic head cast. Two of the patients had a bite block in their cast to minimize rotational movement. The daily CT was taken on a SOMATON Emotion Duo CT on rails and the treatment was delivered by a SIEMENS PRIMUS linear accelerator (linac). The daily CT images were then fused to the planning CT using fiducial markers and anatomy as guides. The shifts in the X, Y, and Z directions were computed by the Coherence Dosimetry Workstation and the patient was shifted accordingly to within 1 millimeter accuracy. Results: We assessed the accuracy of the orthogonal port film technique against the CT based IGRT for 8 frameless stereotactic treatments. The implementation of IGRT increased the importance of patient immobilization while decreasing the need for accurate initial patient set‐up since the patient would be imaged immediately prior to treatment and corrections could then be made to the set‐up. Furthermore it was observed that using a bite block inside the head cast significantly improved patient immobilization and decreased the magnitude of IGRT shifts. Conclusion: Orthogonal port film validation of the isocenter is adequate for an accuracy of 5mm for frameless stereotactic treatments. CT based IGRT provides an adequate verification of the isocenter for frameless stereotactic treatments to within 2–3mm accuracy. Furthermore, CT proves to be of clinical benefit to the patient since the mean dose used for each CT was only .7cGy where port films use 3cGy each for the two orthogonal images.
SU‐FF‐J‐84: Accuracy and Feasibility of Cone Beam Computed Tomography (CBCT) for Stereotactic Radiosurgery (SRS) Setup
Authors: Chang J , Yenice K , Lovelock D , Narayana A , Yamada Y , Gutin P , Amols H
Published: June 2005

Purpose: To investigate the accuracy and feasibility of cone beam computed tomography (CBCT) for stereotactic radiosurgery (SRS) setup. Method and Materials: A stereotactic BRW frame was attached to a Rando head phantom with imbedded radio‐opaque markers (1mm in diameter) simulating the target locations. The head phantom with a CT localizer was first simulated for radiosurgery planning on a conventional CT scanner and then scanned on a treatment machine using CBCT. The differences between the conventional and CBCT localizations of the target positions were computed using a radiosurgery planning software. The translational corrections for target positions were calculated as the differences between the CBCT coordinates of the machine isocenter and the planned isocenters, which were the planned BRW coordinates from the conventional CT scan multiplied by the transformation matrix between the BRW and CBCT coordinate systems on the CBCT scan. The setup accuracy of CBCT was assessed from the analysis of orthogonal projection images for each radio‐opaque target at the machine isocenter. Results: All nine fiducial markers of BRW localizer were successfully identified on all but one slice of the CBCT scan. The average localization difference between the conventional CT and CBCT BRW target coordinates was 0.28mm (SD 0.10mm). The mean distance error for all the radio‐opaque targets localized using the CBCT and orthogonal projection images was 1.28mm (SD 0.61 mm). The major contributing factor to this cumulative setup error was the uncertainty in the superior‐inferior direction due to the 2mm slice thickness in conventional CT. Conclusion: The CBCT image guidance can be used to setup SRS patients within accuracy comparable to the current SRS standard using an external fiducial system. The technique described here can serve as a gold standard for evaluating the accuracy of alternative immobilization and setup devices for SRS.
SU‐FF‐J‐85: Automatic Seed Detection in MVCT Images for Prostate Radiotherapy
Authors: Chen Q , Lu W , Kupelian P , Langen K , Meeks S , Ruchala K , Olivera G
Published: June 2005

Purpose: In radiotherapy treatment of prostate, a common approach to prostate localization for each treatment fraction is to insert several seeds into the prostate as a marker. The seeds are visually identified and aligned by the radiation therapist prior to treatment. Manual seed identification and registration is a time‐consuming process, and the precision of the seed localization is on the order of voxels. We developed an algorithm that can detect the seeds automatically and achieve sub‐voxel precision. Method and Materials: The CT number of the MVCT images was calibrated by matching their histogram to the reference KVCT image histogram. An edge‐preserving image smoothing filter was applied to MVCT images of prostate. This filter can effectively remove the noise while preserving the edge of organs and seeds. After the noise was reduced, the images were scanned and a connected‐threshold method was used to label isolated high‐CT‐number regions. These regions include seeds and bone structures. A seed classifier was designed based on the size and the mean CT‐number of the region. The position of the seed was determined with sub‐voxel accuracy by calculating the mass center of the seed assuming the CT‐number corresponding to the mass density. The entire process is fully‐automatic. Results: The algorithm was tested on 39 MVCT images, each containing three seeds. It achieved over 90% success rate in the detection of all three seeds without false‐positive. When we restrict our search range within a box that encases the prostate, we achieve 100% success rate. Conclusion: We have demonstrated a fully‐automatic, high‐precision seeds detection algorithm that works very well in MVCT prostate images. The performance can be further improved if the MVCT image quality is better, or if we confine the seeds searching area to the prostate location.
SU‐FF‐J‐91: Assessment of Prostate Position During External Beam Treatments for Patients Post Brachytherapy Implantation
Authors: Miller B , Narayana V , McLaughlin P
Published: June 2005

Purpose: To localize the prostate for patients undergoing an external beam boost after receiving an I‐125 implant to within 3mm and confirm the position of the prostate post‐treatment using marker seeds implanted in the prostate as a surrogate for its position. Method and Materials: Twenty patients receiving an I‐125 prostate implant had three marker seeds implanted in the prostate during the procedure. After the implant the patients underwent a CT simulation for an external beam radiotherapy boost. The marker seeds were contoured and projected onto a DRR with a reference field. Prior to each treatment, radiation therapists imaged the patient with an EPID. The therapists then localized the seeds relative to reference field and determined the error in the alignment of the prostate. If the alignment error was greater than 3mm in any one direction the patient was shifted and re‐imaged to verify the shift. A portal image was acquired after the patient's treatment to confirm the position of the prostate post‐treatment. Results: Averages and standard deviations for pre‐treatment prostate alignment error ranged from −0.10 ± 0.18 to 0.15 ± 0.14 cm, −0.13 ± 0.16 to 0.16 ± 0.16 cm, and −0.17 ± 0.24 to 0.14 ± 0.19 cm in the right/left, superior/inferior, and anterior/posterior direction, respectively. Averages and standard deviations for the difference between the pre‐treatment and post‐treatment prostate alignment error ranged from −0.13 ± 0.08 to 0.09 ± 0.16 cm, −0.12 ± 0.18 to 0.21 ± 0.26 cm, and −0.15 ± 0.17 to 0.09 ± 0.15 cm in the right/left, superior/inferior, and anterior/posterior direction, respectively. Conclusion: Pre‐treatment the prostate was localized to within 3mm using markers seeds implanted in the prostate and an EPID. Post‐treatment portal images confirmed the prostate position to be within 3mm of its pre‐treatment position.
SU‐FF‐J‐94: Comparison of Analytic and Iterative Algorithms for Image Reconstruction in Gated Megavoltage CT
Authors: Zhang J , Sillanpaa J , Chang J , Amols H , Mageras G , Anastasio M
Published: June 2005

Purpose: To assess and compare the merits of analytic and iterative algorithms for reconstructions of 3D images from gated megavoltage (MV) projection data that are non‐uniformly sampled in projection angle. Method and Materials: 2D projection images are acquired in a full fan cone beam geometry using the 6MV beam from a Varian 2100 EX accelerator and a prototype Varian 4030HE electronic portal imager. Because a respiratory gating system is used to confine radiation delivery to a predetermined part of the respiratory cycle, the projection image sets containing angular gaps of varying length. This non‐uniform angular sampling of the projection data can be expected to result in image artifacts when an analytic reconstruction algorithm is employed. We compare two different methods, a filtered backprojection (FBP) algorithm and the expectation maximization (EM) method, for reconstructing 3D images of phantoms and patients from gated cone‐beam MV projection data. Several data sets are considered that contain different sized gaps in the angular sampling of the cone‐beam projections. The quality of the reconstructions is assessed by calculating contrast to noise ratios (CNRs) of inserts in an electron density phantom and by observer preference. Results: The CNRs are consistently higher in the images reconstructed by use of EM algorithm. This can be attributed to the lower noise and artifact levels in the images. The computational burden of the EM algorithm is large, but it may be reduced considerably by use of the ordered subsets expectation maximization (OS‐EM) version of the algorithm. Conclusion: The EM reconstruction algorithm produced 3D images with reduced artifact levels and higher CNRs than those in images produced by the FBP algorithm. Iterative reconstruction methods can significantly improve image quality in gated MV CT applications, but is not suitable for immediate clinical use without implementation on high‐performance computers or dedicated hardware.
SU‐FF‐J‐99: Automation of Image Registration and Verification for Image‐Guided Stereotactic Body Radiotherapy
Authors: Wang C , Shiu A , Lii M , Chang E
Published: June 2005

Purpose: To facilitate image‐guided stereotactic body radiotherapy (SBRT) with high precision and fully automated target localization and patient position verification. Method and Materials: A mutual information based image registration algorithm was developed to register the patient's daily 3D computed tomography (CT) images with those taken for treatment planning to assess and correct patient position shifts in all three translational and three rotational directions. A digitally reconstructed radiograph (DRR) algorithm generates and displays the corresponding DRRs in one frame in a split screen format along with their intensity differences to enhance verification. In the same way, the portal image verification algorithm processes the portal image and displays it with the corresponding planning DRR in the same frame as final verification of the patient's position. The algorithms were programmed using MatLab and were assembled seamlessly in one package and the operation was fully automated. Results: Target localization and patient position verification process in our image‐guided SBRT is significantly simplified and the time needed for this process is reduced from 30 minutes or more to 3–4 minutes. The image registration algorithm was found to be accurate to within 0.1 mm with a head and neck phantom. The DRR generation algorithm generates high quality DRRs with a spatial resolution of 0.289×0.289 mm2/pixel. It removes unrelated anatomical structures for a cleaner background in the DRR to help identify the target isocenter more easily and more accurately. The DRR comparison and portal image verification algorithms readily detect misalignments of less than 0.2 mm. Conclusion: Application of the algorithms in determining patient position shift in actual SBRT cases demonstrated that they were accurate, fast, and reliable. They serve as a useful tool for image‐guided radiotherapy.
SU‐FF‐J‐100: Mutual Information as a Metric of Multimodality Contrast Agent Efficacy
Authors: Hoisak J , Zheng J , Perkins G , Brock K , Allen C , Jaffray D
Published: June 2005

Purpose: Mutual information (MI) has been previously employed for image registration. Assuming a priori registration, MI becomes an estimator of image similarity. We apply the concept of MI to the analysis of a feature space formed from multimodality signal intensity distributions. We demonstrate the utility of this concept through the development of a reproducible inter‐image metric to evaluate the efficacy of a multimodal contrast agent for x‐ray computed tomography (CT) and magnetic resonance (MR) imaging. Method and Materials: MR and CT scans were acquired of an anesthetized rabbit in the presence of a multimodal contrast agent. MR and CT scans were acquired pre‐ and post‐injection at fixed time intervals. For each time interval, the MR and CT images were registered, the multimodality feature space was formed and the mutual information between MR and CT was computed using in‐house software. The resulting MI metric was compared with measurements of signal intensity enhancement in user‐defined regions‐of‐interest within the liver, kidneys and aorta. Results: The MI metric correlates with measurements of signal enhancement in MR and CT due to the presence of contrast agent as seen in the liver, kidneys and aorta. Voxels identified as contributing to the increase in MI correspond to areas of visual contrast enhancement observed on MR and CT. Conclusion: We have developed an inter‐image metric for the characterization and optimization of a multimodal contrast agent. The computation of the MI metric is automated and can be extended to 3D for the assessment of image volumes and allows for the inclusion of other modalities such as positron emission tomography. Future investigations will further the development of MI and multimodality feature space analysis as a tool in radiation therapy applications including image registration, target definition and treatment response monitoring.
SU‐FF‐J‐101: Evaluation of Two Image Registration Systems
Authors: Zhang Y , Hsi W , Chu J , Khan A , Mehta P , Bernard D , Abrams R
Published: June 2005

Purpose: We compare the performance of image registration algorithms adopted by BrainSCan and Philips Syntegra and give a general guide when using these systems. Method and Materials: BrainLab BrainScan System and Philips Syntegra System apply volume‐based automatic rigid image registration algorithms. Philips Syntegra provides Cross Correlation (CC), Local Correlation (LC) and Normalized Mutual Information (NMI) as optimization metrics and BrainScan applies Mutual Information as an optimization metric. These algorithms are compared for: 1) synthesis images, i.e., the images obtained by applying known transformations to a set of original images, 2) phantom images and 3) patient images. Results: For synthesis images, sub‐voxel accuracy is achieved. The maximum discrepancies between the registration results of translations and rotations and the known values are less than 0.5 mm and 0.5° for all algorithms. For phantom images, manual registration based on external markers is served as a gold standard to compare with the registration results. The discrepancies are at the order of 2 mm and 2°. For patient images, two radiation oncologists manually registered images independently and compared their results with the results by an automatic image registration system. The discrepancies become much larger due to the complexity of patient setups and density distributions. The capture regions and speeds of these algorithms are compared. Conclusion: The algorithms themselves can reach the accuracy of sub‐millimeter in translation and sub‐degree in rotation. But for clinical uses, the accuracy is reduced because of many errors introduced by positioning and patient motion. Preprocess is important to avoid being trapped in a narrow capture region. Final visual assessment is essential to guarantee reasonable and desired results.
SU‐FF‐J‐102: A New Method for Improving PET and CT Registration in the Thorax On PET/CT
Authors: Pan T , Mawlawi O , Nehmeh S , Erdi Y , Luo D , Liu H , Hunjan S , Balter P , Prado K , Mohan R , Macapinlac H
Published: June 2005

Purpose: We propose a new method of acquiring the CT data to improve the registration of the PET and CT data in imaging the thorax on PET/CT. Method and Materials: In a conventional PET/CT acquisition, the CT and PET data are acquired at two different breathing states. There is an inherent mismatch of the PET and CT because the temporal resolutions of the PET and CT are not matched. We have proposed a new method of acquiring the average CT (ACT) data from the 4D‐CT imaging to provide the CT data consistent with the PET data on temporal resolution. We have applied this approach to one esophagus and seven lung patients. The helical CT data were taken helically at 120 kV, 300 mA, pitch 1.35:1, 8×2.5 mm collimation, and 0.5 s rotation and the patients were instructed to hold a breath at mid‐expiration during the HCT of the thorax. The PET acquisition was 3 mins per bed. The 4D‐CT data of the thorax were taken right after the PET/CT study at 120 kV, 50 to 150 mA, cine duration of one breathing cycle plus 1 s, 8×2.5 mm collimation, and 0.5 s CT rotation cycle. We compared the registration between the ACT and PET data, and the registration between the HCT and PET data. Results: The PET and ACT data were all consistent at all tumor locations. The mismatch between the HCT and PET data were significantly improved on 4 out of the 8 patients with the ACT data over the HCT data. Conclusion: We have proposed the use of the ACT to improve the registration of the PET and CT data, and demonstrated a significant improvement in lesion localization between the PET and ACT data.
SU‐FF‐J‐110: Comparison Between Free Breathing, Slow and Respiratory Correlated CT in Radiation Treatment Planning for Lung Cancer Patients
Authors: Dekker A , Bosmans G , Buijsen J , Velders M , Boersma L , De Ruysscher D , Wanders R , Minken A , Lambin P
Published: June 2005

Purpose: Radiotherapy for lung cancer requires a margin for internal movement of the tumor. Reduction of this margin and thus dose escalation may be possible by using a slow or a respiratory correlated CT (RC‐CT) during radiation treatment planning. In this study these two novel methods are compared to the use of a conventional free breathing CT (FB‐CT). Method and Materials: On a modified Siemens Sensation 10 an FB‐CT and an RC‐CT scan were acquired in nine patients. The RC‐CT scan was used to measure tumor motion and to reconstruct a CT at 10 respiratory phases (10p‐CT). One of these was termed the mid‐ventilation CT (MV‐CT) and by averaging all CTs, a slow‐CT could be reconstructed. Four treatments were planned based on the FB‐CT (with conventional internal margin); the slow CT; the 10p‐CT, and the MV‐CT (with an internal margin of (motion amplitude)/4). Mean tumor dose was calculated for these four plans for a fixed mean lung dose of 15Gy. The possibility of coldspots (<95%) was investigated by determining minimum tumor dose that occurred during respiration. Results: The mean tumor dose in the FB‐CT based plan was 74Gy, for the MV‐CT 100Gy, for the 10p‐CT 95Gy, and for the slow‐CT 101Gy (p=0.0001 for FB‐CT vs. other; p=0.12 for MV‐CT vs. 10p‐CT). Coldspots occurred occurred in the patient with the largest tumor motion (15mm amplitude) in the case of a plan based on a slow‐CT scan. Conclusion: Since radiation treatment planning based on a slow‐CT can lead to underdosage in tumors moving with a large amplitude and the delineation of the 10p‐CT is rather cumbersome, we conclude that using an RC‐CT scan to reconstruct a mid‐ventilation CT and applying a margin of one quarter the tumor motion amplitude, is the most suitable method for radiation treatment planning in lung cancer patients.
SU‐FF‐J‐111: Correlation of Target Movement, Diaphragm Motion and External Sensor Signals for Respiratory‐Gated Hepatoma Radiotherapy Using TACE as a Target Indicator
Authors: Lee C , Hong J , Ho C , Chao T
Published: June 2005

Purpose: To assess the correlation among target movement, diaphragm motion and external sensor signals to predict the internal safe margin required for respiratory‐gated radiotherapy for hepatoma patients. Impact of gating window size on internal safe margin selection was also evaluated. Method and Materials: 5 hepatoma patients who previously received trans‐arterial chemoemobolization (TACE) treatments were enrolled in this study. The patients were imaged fluoroscopically for 60 seconds to record the internal motion patterns of the diaphragm and of the TACE through an image‐capture device. The skin motion pattern was obtained by an in‐house developed sensor. Locations of the diaphragm and the TACE on the fluoroscopic images were identified manually frame‐by‐frame. Means and standard deviations of the differences between the displacements of the sensor signal and the diaphragm (SD), of the sensor signal and the TACE (TS) and of the diaphragm and the TACE (TD) were calculated for various gating window settings. Internal safe margins as defined by mean±1.5*standard deviation were calculated. Results: Displacement differences of patient ♯1–5 for 50% gating window size were determined to be 1.3±1.3, 1.2±1.1, 2.9±2.1, 3.0±1.9 and 2.4±1.7 mm for SD; 2.2±1.5, 1.1±0.7, 1.3±1.1, 4.8±1.5 and 2.1±1.5 mm for TS; and 0.8±0.4, 1.4±0.2, 1.2±0.1, 2.9±1.0 and 1.1±0.2 mm for TD. The results also showed that selection of different gating window sizes had limited effect on the size of the internal safe margin. Conclusion: Inconsistent motion patterns among target, diaphragm and external skin sensor must be taken into consideration when determining internal safe margin for hepatoma patients.
SU‐FF‐J‐117: Inter and Intra‐Fractional Patient Motion for a Set of Immobilization Devices
Authors: Engelsman M , Rosenthal S , Michaud S , Adams J , Schneider R , Bradley S , Flanz J , Kooy H
Published: June 2005

Purpose: We assessed the magnitude of inter‐ and intra‐fractional patient motion for a broad set of immobilization devices. Method and Materials: In our practice for proton radiotherapy, we verify patient setup prior to each treatment field by means of digital imaging. Deviations from the “expected” patient position (with 6 degrees of freedom on our patient positioner) are stored in a database and were retrospectively analyzed for patient setup accuracy. Data was analyzed for each ordinal direction and for the combined spatial displacement. Immobilization devices were separated into “rigid” and “non‐rigid” devices depending on their connection to the patient positioner. Results: Systematic offsets in intra‐fractional motion are small for all immobilization devices, and less than 0.2mm for translations and less than 0.1 degrees for any rotational axis. Although the mean translation per ordinal direction is often smaller than 1mm, the mean spatial displacement for intra‐fractional motion for rigid devices is 1.3mm compared to 1.9mm for non‐rigid devices. The modified Gill‐Thomas‐Cosman frame controlled intra‐fractional patient motion best, with a 95% probability (v95) of observing less than 1.8mm of motion. For the widely used IC‐mask, the v95 value is below 3mm. All other immobilization devices have a v95 greater than 3.0mm for intra‐fractional patient motion, while the mean spatial inter‐fractional displacement (rigid devices only) was at least 3mm with a v95 of at least 6mm. Conclusion: Intra‐fractional patient motion is generally smaller than inter‐fractional patient motion, which indicates that immobilization devices are better at maintaining a certain patient position than at reproducing this position between fractions. Immobilization devices that rigidly connect to the patient positioner ensure better immobility than those that do not. However, none of the immobilization devices achieved sub‐millimeter immobility. Patient position verification remains necessary to achieve high setup accuracy. Research supported in part by NCI grant 5_PO1‐CA21239‐24
SU‐FF‐J‐122: Planning Target Volumes for Image‐Guided Radiation Therapy of Prostate Cancer
Authors: Craig T , Sharpe M , Keller H , Jaffray D
Published: June 2005

Purpose: Image‐guided radiation therapy has the potential to reduce the uncertainty in targeting the clinical target volume (CTV) for prostate cancer. This allows a reduction in the size of the planning target volume (PTV). Determination of an appropriate PTV is a non‐trivial task. Issues that need to be considered include the magnitude of the uncertainties, the shape of the dose distribution, and the desired treatment goal. This work examines the PTV requirements for image‐guided radiation therapy of prostate cancer. Method and Materials: The effect of geometric uncertainties is modeled to determine appropriate PTV margins. Random uncertainties are modeled as a convolution of the dose distribution, and systematic uncertainties as probability weighted shifts of the dose distribution. PTV margin requirements are examined as a function of the use of image‐guided positioning (no correction vs. on‐line correction), treatment technique (conformal vs. intensity modulated radiation therapy), and probability of achieving 95% minimum dose to the CTV (95% vs. 99%). Results: For a 95% probability of achieving the treatment goal, PTV margins of 6–7 mm are required if no correction is performed. The use of on‐line position correction reduces the required margin to 1–2 mm. Achieving the treatment goal with 99% probability requires >10 mm margins with no corrections, while 2 mm margins are sufficient with on‐line corrections. The use of conformal vs. IMRT techniques has minimal impact on the required PTV. Conclusion: The results suggest image‐guided on‐line positioning correction allows substantial reduction of PTV margins. Achieving specific treatment goals with a very high level of confidence may be impossible without on‐line corrections. Since patient positioning and internal organ motion may no longer be the dominant sources of uncertainty when on‐line corrections are performed, these results should be interpreted cautiously until factors such as intrafraction motion are incorporated into the analysis.
SU‐FF‐T‐11: Dosimetry Comparison of LDR 137Cs and LDR 252Cf Brachytherapy Sources
Authors: Melhus C , Zinkin H , Rivard M
Published: June 2005

Purpose: Hundreds of patients have received gynecological brachytherapy treatments in the US using applicator tube‐type (AT) low dose rate (LDR) 252Cf sources. However, its mixed‐field radiation dose distributions have not been characterized using the AAPM Task Group 43 dosimetry formalism, nor quantitatively compared to conventional photon‐emitting sources. Towards clinical implementation of LDR 252Cf brachytherapy for gynecological applications, the mixed‐field dosimetry for this source type has been modeled using Monte Carlo methods and compared to dose distributions produced by LDR 137Cs brachytherapy sources. Method and Materials: Mixed‐field dose distributions in the vicinity of an AT LDR 252Cf brachytherapy source were calculated using MCNP5 in a 50 cm diameter spherical phantom composed of water, soft tissue, and muscle. ENDF 252Cf neutron energy spectrum was used. Published 252Cf photon energy spectra were employed and compared. The MCNP F4 and F6 calculation tallies were utilized for determining various dosimetric components. These include the source photon, neutron capture photon, fast neutron, and thermal neutron dose components. The LDR 137Cs source used for comparison was the 3M Model 6500. Results: Brachytherapy dosimetry parameters for LDR 252Cf neutrons were in agreement with previously published values. TG‐43 dosimetry parameters for 252Cf photons exhibited a maximum g(r) value at 10 cm due to induction of capture photons in the phantom and a general decrease in anisotropy with increasing radial distance. 252Cf photon spectra including estimates of delayed photons exhibited −2% difference in g(r) and 5% relative variation in anisotropy at θ = 0°. Dose distributions generated from dosimetry parameters for LDR AT 252Cf were similar to those produced by conventional 137 Cs sources using the Pinnacle 3 Planning System. Conclusion: Using appropriate radiobiological weighting for 252Cf neutrons, treatment planning for AT LDR 252Cf sources may be performed and compared to conventional 137Cs dosimetry for gynecological applications.
SU‐FF‐T‐15: On the Prescription Dose in Permanent Cs‐131 Seed Prostate Implants
Authors: Yue N , Heron D , Komanduri K , Huq M
Published: June 2005

Purpose: Recently, 131Cs seeds have been introduced for prostate permanent seed implants. This type of seed has a relatively short half‐life and has its most prominent emitted photon energy peaks in the 29 keV to 34 keV region. Traditionally, 145 Gy and 125 Gy have been prescribed for 125I and 103Pd seed prostate implants, respectively. Since both the half‐life and dosimetry characteristics of 131Cs seed are quite different from those of 125I and 103Pd, the appropriate prescription dose for 131Cs seed prostate implant may well be different. This study was to determine an appropriate dose prescription scheme for permanent 131Cs seed prostate implants. Method and Materials: A linear quadratic radiobiological model was used in this study. Prostate edema of different durations and sizes was taken into consideration in the dose and tumor cell survival fraction calculations. The tumor cell survival fractions in 103Pd and 125I permanent seed implants were taken as reference values to derive the appropriate dose prescription value for 131Cs seed implants. Calculations were also performed for tumors of different tumor doubling times. Results: As expected, the derived prescription dose values were dependent on type of tumors and types of edema. For fast growing tumors, the derived prescription doses were different depending on the type of reference implant was used: 125I or 103Pd seed implant. However, for slow growing tumors such as prostate cancer, the derived prescription dose values were very similar and it was determined that 124 Gy was an appropriate prescription dose for permanent 131Cs seed prostate implants. Conclusion: An appropriate prescription dose has been derived for 131Cs permanent seed prostate implants. The dose value was determined to be 124 Gy.
SU‐FF‐T‐16: Treatment Planning Isodose Calculations with the Gliasite Radiation Therapy System
Authors: Sabbas A , Kulidzhanov F , Trichter S
Published: June 2005

Purpose: From published data of dose rates and fractional depth doses (FDD) for various sizes of 125I liquid‐filled brachytherapy balloon applicators (the Gliasite RTS) we have developed templates of TG‐43 compatible dosimetric parameters to be used in computerized treatment planning calculations and isodose generation. Method and Materials: The Gliasite radiation therapy system is an intracavitary brachytherapy source that is implanted in brain cavities following excision of the tumor. The balloon can be inflated anywhere between 4 to 35 cc in order to achieve good conformance with the surrounding brain tissue. The initial dose rate in cGy/hr is a function of the balloon size, depth of prescription from the balloon surface and net afterloaded activity in mCi. FDD's, normalized to the balloon surface, are available for determining doses at various depths from the balloon. Based on tables of initial dose rates we have derived the dose rate constant Λ in (cGy/hr.U) at 1 cm from the balloon center for various balloon sizes. We have also calculated a two‐dimensional table of the radial dose function g(r) for various balloon sizes and depths in tissue. These dosimetric parameters have then been entered into our brachytherapy planning system (ADAC Pinnacle), where the Gliasite balloon is modeled as a point source. Results: Our CT‐based three‐dimensional dose calculations yield doses to the surrounding normal brain tissue and critical structures. In addition to isodose generation, we also calculate DVH's for critical structures, target volume and normal brain tissue and are able to add doses from external beam or other brachytherapy procedures that a patient may have received. We have spot‐checked these isodose calculations using the Gliasite calculation tables. Conclusion: CT‐based isodose display is useful in assessing doses to neighboring critical structures and is also indicated when the balloon conformance to the surrounding tissue is not optimal.
SU‐FF‐T‐22: Application of Neural Network Algorithm for Treatment Planning Verification of Permanent Prostate Implants
Authors: Wojcicka J , Silvern D , Kudynskis R , Bagan E
Published: June 2005

Purpose: The objective of this project is the evaluation of a software brachytherapy nomogram equivalent. This program was designed to predict the required air kerma strength and source count for implants based on site dimensions and volumes. Method and Materials: The nomogram equivalent is based on a three‐layer feed‐forward neural network (NN). The software consists of two separate programs. One program is used for training the NN and the second program is executed for realizing the nomogram equivalent. The NN was trained using site dimensions, volumes and implanted air kerma strengths for 117 prostate cases. The network was then tested on 30 cases not included in the training set. The results of the NN calculations were also compared with the Anderson nomogram predictions. Results: The accuracy of the NN nomogram equivalent is a function of the quality and quantity of training data, the number of iterations set to obtain the desired results, and a consistent source loading methodology. The NN predictions of the total activity and source count are in good agreement (within 11%) with the computer optimized preplanning results for all but two cases. Upon review, significant treatment volume underdosing was observed for these two cases. The Anderson nomogram prediction of the planned total activity was within 13% for all but the two outlier cases. Conclusion: The NN based program implemented in the clinic can be an easy, fast, and accurate tool for performing independent verification of interstitial prostate implants. The NN is field‐customizable, a capability not possible with a standard nomogram.
SU‐FF‐T‐29: Dose to the Physician's Extremity During I‐125 Prostate Seed Implant Using a Commercial Loading Device
Authors: Avadhani J , Malhotra H , Cunningham B , Rajagopalan B , Wagner T , Podgorsak M , Kuettel M
Published: June 2005

Purpose: To evaluate a physician's extremity (mainly finger) dose during clinical I‐125 prostate seed implants (PSI) using a Mick® loading device. Method and Materials: To establish the location of radiation leakage “hot‐spots” a piece of XV radiographic film was wrapped around an applicator loaded with a cartridge containing 15 I‐125 seeds each with air‐kerma strength of 0.44 U. A phantom assembly was developed to simulate the geometry of the interface between the user's hand and this “hot‐spot”. A piece of radiographic film was placed in the assembly to simulate the location of the user's finger relative to the “hot‐spot” and exposed directly or through 1 or 2 layers of radiographic glove material. Results: The exposure rate was found to be highest directly below the cartridge, probably due to the presence of small openings in the loader through which body fluids are meant to drain. This location is typically in contact with the physician's finger. For a fully loaded cartridge (15 seeds, air‐kerma strength of 0.44 U per seed) it was found that the dose‐rate on the surface of the finger is 2.4, 1.1 and 0.4 cGy/hr with 0, 1, and 2 layers of lead glove material, respectively, between the finger and cartridge. A theoretical calculation of the dose‐rate in this geometry gives similar results. Conclusion: For a volume of 150 PSI cases per year with 120 seconds of finger contact at the “hot‐spot” per case, the annual dose to the surface of the finger is expected to be on the order of 12, 5.6, and 2 cGy when the physician wears no gloves, 1 pair, or 2 pairs of gloves, respectively, well within maximum permissible limits for an extremity. This dose can be effectively reduced to zero if the implant needles are manipulated with no finger contact at the “hot‐spot”.
SU‐FF‐T‐34: Inversely Planned Catheter Positions for High Dose Rate Brachytherapy of the Prostate
Authors: Lessard E , Beaulieu L , Hsu I , Pouliot J
Published: June 2005

Purpose: To determine the dosimetric impact of the number of catheters used in prostate HDR brachytherapy and to evaluate the possibility of reducing the number currently used clinically. Method and Materials: Our in‐house inverse planning optimizes the catheter positions based on clinical objectives such as prostate dose coverage, dose homogeneity and urethra protection. This optimization displaces straight catheters on a 5 mm grid searching for the best pattern. The number of catheters is fixed, only their positions and the dwell times are optimized. For one prostate, 8 implants were generated with different number of catheters (5, 6, 8, 10, 12, 14, 16 and 18). Results: Implants with more than 10 catheters shows equivalent dosimetric indices with good dose coverage (V100>95%) and low dose delivered to the urethra (V120<5%). With less than 10 catheters the implant dosimetry deteriorates rapidly. The protection of the urethra from high dose (V150=0) is independent of the number of catheters. This demonstrates that decent dose coverage can be achieved with a reduced number of catheters without affecting the urethra protection. The optimization tends to produce implants with peripherally loaded catheters and manages to produce adequate dose coverage with just a few catheters in the middle part of the prostate close to the urethra. Conclusion: This study encourages the diminution of the number of catheters implanted around the urethra, improving the urethra protection and facilitating the implant procedure. This is only true when using an inverse planning to optimize the dwell times. Centers that are performing the treatment planning without an inverse planning need these central catheters to produce adequate dose coverage. This demonstrates that inverse planning brings the possibility to safely reduce the number of catheters currently used in prostate HDR brachytherapy. This research was supported by NCI Canada with funds from the CCS.
SU‐FF‐T‐45: Partial Volume Analysis in Permanent Seed Implantations
Authors: Baumann R , Warszawski A , Machtens S , Karstens J
Published: June 2005

Purpose: Permanent seed implantation is a well accepted therapy for the treatment of low risk prostate cancer. In Europe the number of treated patients increases considerably. New techniques and planning systems allow a very safe intervention. A retrospective analysis is performed to show if there are additional parameters to optimize dose distribution and therefore to reduce side effects. Method and Materials: In our institution 304 patients were implanted with I‐125 radioactive seeds following the recommendations of the ABS and the ESTRO/EORTC for a permanent prostate brachytherapy. Basis for the dosimetry was an ultrasound guided intraoperative interactive real‐time planning (VariSeed 6.7/7.0/7.1). Looking for coherences between dose distribution and side effects a partial volume analysis was performed particularly in the apical and basal part of the prostate. Dosimetric data analyzed were V100, V150, D90 and the mean dose. Results: Postoperative follow‐up is 1–54 months (mean 24 months). Different types of side effects such as urinary retention, proctitis, and erectile dysfunction occurred in 4%, 8% and 24% of our patients. Looking to the group with and without side effects we found relevant differences in the apical part of the prostate. The median for the V150 (apex) is 40,5% and 28,8%, the mean dose in the apex is 283,1Gy and 257,5Gy. The D90 and V100 is comparable in both groups (184,1Gy/182,3Gy, 98,9%/99,2%). No significant differences were found in the basal part of the prostate. Conclusion: A partial volume analysis of the prostate during the implantation offers the possibility to lower side effects. It is not sufficient to look to the standard values such as V100, D90 for the prostate and D30 and V100 for the urethra and rectum. Looking more into detail for the dose distribution a better dose homogeneity with a better quality of life for the patient can be achieved.