bluuebunny/crossref_metadata_2025 huggingface dataset:
SU‐FF‐T‐400: Computational Study of the Rigid Body Image Registration Accuracy
Authors: Michalski D , Bednarz G
Published: June 2005

Purpose: To study, using a computational simulation, the accuracy of the rigid body based image registration of the brain with special considerations for the type of the distribution of the homologous fiducial points used in the registration. To determine how the registration affects the resultant accuracy for target points. Method and Materials: The condition numbers of all the combinations of at least four out of the 25 candidate fiducial points are examined. This yields the sets of points with the best and the worst condition number. The Gaussian noise is imposed on the simulation points. The algorithms' accuracy for the sought rotation matrix and the translation, fiducial registration error (FRE), and target registration error (TRE) are investigated as a function of the number of fiducial points used in the registration. Three different algorithms are used: SVD based, the subspace method for the translation computation and the simultaneous optimization of the Euler angles and translation. Results and Conclusion: The robustness of all the algorithms is similar. For the lower number of fiducial points there is a risk of big TREs. Thus the condition number reveals a bad prospective input for the algorithm. The number of points needed to reach 1.0 mm accuracy for 0.5×0.5×1.0 mm3 pixel size should be six points or more. This method of the condition number examination can be used to predetermine the accuracy of the registration for a given input.
SU‐FF‐T‐410: Target Localization of Intensity Modulated Radio‐Surgery Patients Using ExacTrac System
Authors: Li S , Ayyangar K , Pillai S , Nehru R , Fung A , Djajaputra D , Thompson R , Raman N , Zhen W , Enke C
Published: June 2005

Purpose: The Novalis body system, ExacTrac®, was used to verify target localization and to improve patient positioning for daily treatment with patient pre‐positioning by mask and head frame in intensity modulated radio‐surgery(IMRS). This study is to present preliminary results of quantitative measurements from the ExacTrac system. Method and Materials: Accuracy of image fusion and correct calibration of ExacTrac system were investigated using the head section of anthropomorphic phantom. The phantom was randomly moved away from the target position manually and re‐positioned using the ExacTrac system. Couch final position was then compared with target position to determine positioning errors. ExacTrac recorded data from 12 patients was used for this study. A verification plan for exporting DRRs to ExacTrac was created for each patient using reference point as localizer. The patient was placed on the couch with mask and isocenter was aligned with target positioner. Two x‐ray images were taken and registered to DRRs using automatic 3D fusion. After visual examination of the match of bony structures surrounding the isocenter, the necessary couch movements were performed based on shifts computed from 3D fusion. Results: For 7 cranial patients with total 106 treatments, the lateral, longitudinal and vertical average shifts were 0.80, 1.91, and 0.99 mm respectively; for 4 orbital patients with total 103 treatments, the shifts were 0.6, 1.4, and 0.6mm respectively; for one C‐spine patient with total 28 treatments, shifts were 1.5, 1.6, and 2.3 mm respectively. According to 11 phantom measurements, our ExacTrac system had accuracy of 0.27, 0.64, and 0.55 mm respectively. Conclusion: Target shifts in patient positioning by mask and head frame could be more than 1.0 mm and was larger in longitudinal direction for treatment of cranial and orbital tumors. With x‐ray image guidance, ExacTrac system localizes target with accuracy of less than 1.0 mm.
MO‐D‐I‐609‐01: Improved Target Localization in Low Field MR Using Local Weighted Mean(LWM) for Spatial Distortion Correction
Authors: Samant S , Xia J
Published: June 2005

Purpose: A methodology using local approximation method is presented for improving spatial distortion correction of Philips Panorama 0.23T MR‐Simulator. The effect on accurate MR based segmentation is evaluated. Method and Materials: Standard T2 MR data was collected using the 0.23T MR‐Simulator. For spatial distortion evaluation/ correction, a standard phantom with dimension of 14″*17″*1″ containing a grid of MR markers at 2.5cm spacing was imaged. The spatial fidelity of the MR data was compared with the physical measurements of marker position using both the vendor supplied spatial distortion correction algorithm and our LWM algorithm, which employs local polynomial fitting and marker centroids serving as control points. The markers are automatically detected using a Gaussian kernel. CT‐MR image registrations using normalized mutual information were applied to estimate the effect of spatial distortion on image registration. Results: Using LWM, the diameter of the imaging region with minimal spatial distortion (marker localization error < 1mm) increased to 300mm, in contrast to the Philips' correction method characterized by diameter=70mm. Visual inspection of clinical imaging data, including a case of craniopharyngioma, indicated such distortion is not readily discernible to the human eye. CT‐MR registration results indicated that the normalized mutual information (NMI) increased about 5% after applying LWM to the MR data compared to using the vendor supplied algorithm. Shifts of up to 3mm were observed in segmentation involving off‐axis target regions between LWM and vendor corrected MR data. Conclusion: LWM provides a significantly superior correction for spatial distortion associated with low field MR imaging compared to the vendor supplied correction. This improves target localization accuracy based on segmentation of off‐axis structures, and increases NMI value of CT‐MR registration. MR imaging with minimal spatial distortion allows the MR‐simulator to be used to monitor tumor regression during radiotherapy.
MO‐D‐I‐609‐03: Fast Dynamic MR Imaging for Tracking Lung Tumor Motion During the Respiratory Cycle
Authors: Cai J , Sheng K , Christopher J , Read P , Molloy J , Brookeman J
Published: June 2005

Purpose: To compare two MR sequences, HASTE and trueFISP, to track lung tumor motion and to assess tumor conspicuity and image artifacts. Method and Materials: A lung tumor motion phantom, three healthy volunteers and two lung tumor patients were examined using a clinical 1.5‐T scanner (Sonata, Siemens, Germany) with the following parameters: trueFISP (TE/TR 1.5/204.2ms; FA/55o; FOV/300×300; matrix/128×128; slice‐thickness/5mm), and HASTE (TE/TR 25/800ms; FA/160o; FOV/325×400; matrix/123×256; slice‐thickness/5mm). No contrast agent or gating was used. Parenchyma signal intensity, lung regions and diaphragm displacement were measured in three healthy subjects. Tumor displacement, tumor SNR and tumor‐to‐parenchyma CNR were calculated in the two lung tumor patients. Tumor conspicuity and imaging artifacts were evaluated in all subjects by two radiation oncologists. Results: HASTE visualized better in peripheral vessels, but blurred tumor and central vessels. TrueFISP visualized better in non‐peripheral vessels, but demonstrated ghost artifacts in the phase‐encoding direction. Relative to CT, both sequences showed high SNR and CNR in patient ♯1 with the metastatic adenocarcinoma (HASTE 42.26/24.48; trueFISP 37.72/17.41; CT 42.04/29.98), but reduced SNR and CNR in patient ♯2 with the primary squamous cell carcinoma adenocarcinoma (HASTE 24.51/4.81; trueFISP 8.54/1.73; CT 36.67/26.84). Conclusion: HASTE and trueFISP can both monitor lung tumor motion during free breathing. Tumor conspicuity and imaging artifacts depend upon the tumor type, size and location.
MO‐E‐T‐618‐03: Dynamic Intraoperative Prostate Brachytherapy Using 3D TRUS Guidance with Robotic Assistance
Authors: Wei Z , Downey D , Fenster A
Published: June 2005

Purpose: Develop a dynamic intraoperative prostate brachytherapy system, in which all phases of the procedure are performed in one session, including planning, monitoring of prostate changes, dynamic re‐planning, optimal needle insertion including oblique trajectories and automatic seed localization in US images, to deal with variabilities in the current procedure. Method and Materials: The system consists of 3D TRUS imaging, a robot and software tools for prostate segmentation, intraoperative planning, oblique needle segmentation and tracking, seed segmentation, and 3D dose planning. The robot and 3D TRUS coordinate systems are unified with robot and image calibrations. In 3D TRUS images, the prostate is segmented using discrete dynamic contour method, and optimal implantation plan is performed by applying geometric optimization followed by simulated annealing. The robot can be controlled to guide the needle to target points in 3D TRUS images along oblique trajectories accurately and consistently. The inserted needles are segmented and tracked using grey‐level change, and seed segmentation is performed using 3D line segment patterns. Results: Needle placement accuracy of the robot at “patient” skin was 0.15mm±0.06mm, and needle angulation error was 0.07°. Needle targeting accuracy was 0.79mm±0.32mm. The average difference between manual and the prostate segmentation algorithm of prostate boundaries was −0.20±0.28mm. In our needle tracking tests, errors in determining needle orientation were less than 2° in robot yaw and 0.7° in robot pitch orientations, for up to 20° needle insertion angles when the needle insertion distance was greater than 15mm. The true‐positive rates for the seed segmentation algorithm in 3D TRUS images were 100% for agar and 93% for chicken phantoms. With optimal planning tools provided, 98% of prostate volume receives 80% of dose coverage. Conclusion: The result of this work provides a tool to achieve dynamic intraoperative prostate brachytherapy using 3D TRUS imaging and robotic assistance together with efficient segmentation software.
TU‐B‐I‐609‐01: Therapeutic Ultrasound
Authors: Crum L
Published: June 2005

The use of ultrasound in medicine is now quite commonplace, especially with the recent introduction of small, portable and relatively inexpensive, hand‐held diagnostic imaging devices. Moreover, ultrasound has expanded beyond the imaging realm, with methods and applications extending to novel therapeutic and surgical uses. These applications broadly include: Tissue ablation, acoustocautery, lipoplasty, site‐specific and ultrasound mediated drug activity, extracorporeal lithotripsy, and the enhancement of natural physiological functions such as wound healing and tissue regeneration. A particularly attractive aspect of this technology is that diagnostic and therapeutic systems can be combined to produce totally non‐invasive, image‐guided therapy. This general lecture will review a number of these exciting new applications of ultrasound and address some of the basic scientific questions and future challenges in developing these methods and technologies for general use in our society. We shall particularly emphasize the use of High Intensity Focused Ultrasound (HIFU) in the treatment of benign and malignant tumors as well as the introduction of acoustic hemostasis, especially in organs which are difficult to treat using conventional medical and surgical techniques. [Supported in part by the NIH and the US Army]
TU‐C‐I‐609‐08: A Total‐Imaging‐System Generalized Performance Comparison of An X‐Ray Image Intensifier and a Microangiographic System in Neurovascular Angiography: Effect of Focal Spot and Scatter
Authors: Yadava G , Rudin S , Bednarek D , Hoffmann K , Kyprianou I
Published: June 2005

Purpose: To quantify the total‐system performance of an x‐ray image intensifier and compare it with a microangiographic system in terms of the generalized metrics of GMTF, GNNPS, GNEQ, and GDQE which include the effect of geometric‐unsharpness, scatter from the patient, as well as the detector characteristics. This presentation expands on our previous work with generalized imaging‐system metrics to include a detailed study of the effect of varying the focal‐spot. Method and Materials: A commercial x‐ray image intensifier (XII) C‐arm unit and a high‐resolution ROI microangiographic detector were evaluated with reference to their performance in neurovascular angiographic studies. The study was performed using clinically relevant spectra and conditions specific for each system. A uniform head‐equivalent phantom was used, and images were acquired for 60 to 100 kVp at a source‐to‐image distance of 100 cm for the XII and 75 cm for the microangiographic system. The detector, focal‐spot, and scatter unsharpness were quantified in terms of their respective MTF's, and the scatter fraction was determined. These were combined to express a Generalized MTF (GMTF) with spatial frequencies referenced to the object plane. The effect of varying field‐size, air‐gap and focal‐spot size (0.3 mm and 0.6 mm nominal) was studied. A detailed total‐system evaluation of the two systems was carried out in terms of the generalized performance metrics of GMTF, GNNPS, GNEQ, and GDQE. Results: The results of the GMTF and GDQE comparison of the two systems indicate that the microangiographic system performs substantially better than the II at higher spatial frequencies, as needed in image‐guided, neuro‐interventional procedures. Use of a smaller focal spot further improves its high frequency behavior. Conclusion: This generalized approach can provide a more realistic evaluation of total‐system performance leading to improved system designs tailored to the specific imaging task. (Partial support from NIH grants R01EB002873 and R01NS43924)
TU‐C‐I‐609‐09: Towards Low‐Dose Soft‐Tissue Visualization in Megavoltage Imaging: Initial Evaluation of a Prototype High Quantum Efficiency Segmented Crystal‐Based Portal Imager
Authors: Sawant Amit , Antonuk Larry E , El‐Mohri Youcef , Li Yixin , Wang Yi , Yamamoto Jin , Zhao Qihua , Du Hong
Published: June 2005

Purpose: To demonstrate the potential for low‐dose soft‐tissue visualization at megavoltage x‐ray energies using a novel, high‐QE segmented CsI(Tl) detector incorporated in an active matrix flat panel imager (AMFPI). Method and Materials: A prototype AMFPI EPID was developed, incorporating a 40 mm thick, non‐optimized, segmented detector comprised of 160×160 optically‐isolated, crystalline CsI(Tl) elements spaced at 1016 μm pitch. The detector was coupled to an indirect detection‐based active matrix array (508 μm pitch) ‐ each detector element registered to 2×2 array pixels. Detailed quantitative characterization of the prototype imager was performed under radiotherapy conditions (6MV) to determine x‐ray sensitivity, MTF, NPS and DQE. Images of a contrast‐detail phantom and step wedges of low‐contrast tissue equivalent materials were acquired at a dose corresponding to a single beam pulse. Monte Carlo simulations were performed to estimate the upper limits of the frequency‐dependent DQE for this prototype EPID as well as for a variety of hypothetical segmented detector configurations. Results: The prototype imager exhibited over an order of magnitude higher DQE at zero spatial frequency compared to conventional AMFPI systems, with gradual fall‐off at higher frequencies. Contrast differences between 1, 2 and 3 cm thick lung tissue phantom (density ∼0.3 g/cm3) overlying an ∼1 cm thick acrylic slab were observed in projection images acquired at a single 6MV beam pulse. Finally, theoretical calculations suggest that DQE up to 50%, along with further improvements in MTF, may be achievable through further optimization of the segmented detector design. Conclusion: The high DQE values and good contrast resolution exhibited by the prototype imager, as well as prospects for further significant improvements in DQE, open up the enticing possibility of obtaining soft‐tissue contrast at clinically practical doses in megavoltage tomographic and perhaps, even projection imaging. This work was supported by NIH grant R01‐CA51397.
TU‐C‐I‐609‐10: Preliminary Study of Pixel Pitch and Effect of Divergence On Thick Cadmium Tungstate Detector
Authors: Monajemi T , Fallone B , Rathee S
Published: June 2005

Purpose: To theoretically study the effects of pixel pitch and beam divergence on 1 cm thick crystals for use in megavoltage cone beam computed tomography (MVCBCT). Method and Material: linear array (80‐elements, each 0.275 × 0.8 × 1 cm3 in fan beam) has been proven to be a good candidate for MVCT in our lab. For this study, DOSXYZnrc Monte Carlo code was used to find the point spread function (PSF) as the distribution of energy deposited in a theoretical flat detector (30 × 30 × 10 mm3, 0.01 × 0.01 × 10 mm3 voxels). A pencil‐beam of 6 MV photons was incident at a range of angles (0°, 5°, 10°, 15°, 20°) with respect to the normal. In each case, the detector PSF (ignoring optical spread) was convolved with a realistic source function to give the system PSF in the plane of the object. A realistic object to detector magnification of 1.4 was used in the system PSF calculations. The PSF at 0.01 mm pitch was re‐binned into several pitches (0.5, 0.7, 1.0 mm) and Fourier transformed to obtain the system modulation transfer function (MTF). Results: This analysis suggests an optimum pitch of 0.5 mm which cannot be fabricated using because of the cleavage plane. However, the pre‐sampled detector PSF is further degraded due to small optical leakage through reflective coating and scintillator‐photodiode interface, and the scattered radiation from the object. So, in practice a pitch of 1 mm may be sufficient. The degradation of the system MTF with the increasing divergence is significant between 0° and 5°, and becomes large at 10°. Conclusion: Practical pitch of 1 mm is not ideal yet maybe sufficient. The use of flat panel photodiode arrays for MVCBCT is precluded due to divergence; instead a focused detector should be used.
TU‐C‐J‐6B‐04: Deblurring of Breathing Motion Artifacts in Thoracic PET Images
Authors: El Naqa I , Low D , Bradley J , Vicic M , Deasy J
Published: June 2005

Purpose: In FDG‐PET imaging, blurring due to breathing motion can significantly degrade the quality of the observed image, which can obscure the delineation of the tumor boundary. We demonstrate a new deblurring approach that combines patient‐specific motion estimates of tissue trajectories with image deconvolution techniques to partially remove breathing‐motion induced artifacts. Method and Materials: The human test data set consists of PET/CT co‐registered images of patients diagnosed with lung cancer. The motion measurements are obtained using a breathing model developed recently at our institution. The model linearly maps tidal volumes and airflow measu6red by spirometry into spatial trajectories. The parameters of the model are fitted using a template matching algorithm applied to CT data. The motion model is used to locally estimate the point spread function (PSF) due to breathing. The deconvolution process is carried by an expectation‐maximization (EM) iterative algorithm using the motion‐based PSF. Results: We evaluated the proposed motion‐based deblurring algorithm on idealized test data sets as well as two human PET images, one with a large and one with a small lung tumor. In this case, the estimated PSF would satisfy the shift‐invariance property. Rescaling was used to correct for limited image support in the case of small tumors, which could lead to undesirable ringing effects (Gibbs phenomena). The initial results showed improvement in the spatial resolution, especially in the cranio‐caudal direction. The EM algorithm converged within 20 iterations in both tumor cases. Generally, a compromise between entropy minimization and increase in MSE was used as a stopping criteria. Conclusion: We have implemented a method and algorithm for removing breathing motion from PET images. The initial results show that the method is promising for improving PET thoracic images.
TU‐C‐T‐6C‐01: Introduction: “How much complexity is necessary for IMRT?
Authors: Verhey L
Published: June 2005

IMRT treatment planning and delivery systems have developed rapidly over the past 5 years. Every manufacturer of linear accelerators now offers IMRT delivery systems using multileaf collimators and some sort of automated delivery scheme. Most treatment planning systems now offer “inverse” planning algorithms that optimize fluence and dose distributions given a set of dose constraints for tumors and normal tissues. For some accelerator manufacturers, the output of the planning system is a set of multileaf shapes, or “segments” with associated intensities, which combine to give a variable intensity distribution for each beam angle. This delivery system is referred to as static multileaf IMRT (or SMLC). For others, the intensity distribution is continuous and the leaves move with variable speed across the field with the beam remaining on. This is called dynamic multileaf IMRT, or DMLC. SMLC tends to be somewhat time consuming relative to conventional delivery, as there is overhead due to communication between the MLC controller and the accelerator. For DMLC, very little time is lost relative to conventional beam delivery times. Most IMRT planning systems have a mechanism for controlling the complexity of the resulting plan, which is determined by the number of beam angles and the number of intensity levels specified in the plan. Highly complex plans are those that end up with large numbers of beam segments and small monitor units per segment, translating into rapid dose gradients within the patient. These are presumably desirable when a tumor is immediately adjacent to a very sensitive normal tissue and the dose falloff must be rapid outside the tumor border. On the other hand, dose delivery errors are expected to be greater with highly complex plans, since the dosimetry of small fields and the linearity of the dose at small numbers of monitor units, are rather uncertain. This fact drives us to limit the complexity as much as reasonably possible. Since DMLC does not have a significant time penalty for high complexity, there is a tendency to plan highly complex IMRT for these delivery systems. For SMLC, the constraints of treatment time tend to drive the planner to choose less complex solutions. The question to be addressed in this Symposium is how much complexity is necessary for IMRT. Clearly, the answer is site‐dependent, but even at a given site, the answer is not clear. Today's speakers will describe the incentives for simplicity (time and dose accuracy), methods of controlling the complexity and the tradeoffs between complexity and conformality.
TU‐C‐T‐6E‐04: Clinical Reference Dosimetry of a “Hi‐Art II” Helical Tomotherapy Machine
Authors: Followill D , Molineu A , McGary J , Ibbott G
Published: June 2005

Purpose: To develop a procedure for calibrating “Hi‐Art II” helical tomotherapy machines using TG‐51 and analyze the uncertainties associated with minor departures from the TG‐51 protocol. Method and Materials: Physical limitations of the tomotherapy unit (85cm SAD) restrict the user from performing a rigorous TG‐51 calibration. The Radiological Physics Center determined the ionization ratio (IR) using a water phantom and Exradin A12 ion chamber for a 40cm × 5cm field (8.92 eq.sq.). The IR was converted to %dd(10)x using a published relationship between %dd(10)x and IR. The beam quality conversion factor, kQ, was determined, Pion was measured and Ppol was assumed to be unity. The ion chamber center electrode was placed at dmax, instead of the recommended 10cm depth. The output/min was calculated using TG‐51 and verified using a newly designed TLD jig. Results: The measured IR indicates a beam energy slightly greater than that for a 4 MV x‐ray beam. The reference calibration resulted in a dose rate of 882.7 cGy/min at dmax for a 40cm × 5cm field at 85cm SAD that was within 1% of the dose rate (890.6 cGy/min) set by the factory where 0.4% of the difference was due to ADCL calibration differences and an un‐flattened beam. The TLD/ion‐chamber dose ratio was 0.993 (std.dev.= 0.007). An analysis of uncertainties associated with measuring IR and conversion to %dd(10)x, use of a 40 × 5 cm2 field instead of 10 × 10 cm2 and calibration at dmax instead of 10 cm results in a possible increased uncertainty of 0.5% in the final reference calibration. We believe this to be negligible. Conclusion: A procedure was developed to calibrate “Hi‐Art II” tomotherapy machines using TG‐51 with a minimal increase in the uncertainty of the final calculated dose rate. Work supported by PHS grant CA10953 awarded by NCI, DHHS.
TU‐C‐T‐6E‐08: Statistical Analysis of IMRT Treatment Verification Films
Authors: Zaini M , Forest G , Loshek D , Lokemoen J , Olds W
Published: June 2005

Purpose: To compare the delivery of an intensity modulated radiation therapy (IMRT) treatment with the computer generated plan and to quantify this comparison using statistical techniques. Method and Materials: Comprehensive quality assurance is performed for every patient who undergoes an IMRT treatment. Part of this treatment planning and delivery check involves irradiating a set of Gafchromic® EBT and/or Kodak EDR2 radiographic films. These images are converted to absolute dose and compared with the computer predicted dose maps. Two different implementations of principal component analysis (PCA) are employed for these comparisons. One system consists of creating a scatter plot of lexicographical representations of the irradiated film and the planar dose map (PDM) predicted by the treatment planning system, and the other utilizes the eigenvectors of the covariance matrix of the PDM and film for computing the PCA. Results: The results and merits of the mathematical PCA and geometrical variance techniques are compared with the pure image subtraction and distance‐to‐agreement (DTA) methods. The two statistical methods provide a more complete representation of potential radiation intensity delivery errors than the two latter ones. For some cases, small streaks of high‐level radiation that appeared in the films but not on the plans were more pronounced in the statistically produced images. On other cases, the fact that the subtraction and the PCA methods both indicated the same unplanned hot spots provided more assurance on the verification quality. Conclusion: All these approaches to IMRT image evaluations ‐namely the two statistical, image subtraction, and DTA methods‐ are sufficiently robust to decipher most treatment delivery errors. However, since each method performs the image analysis differently, combining all these techniques is more powerful in detecting discrepancies in treatment delivery versus the IMRT plans and guarantees discovering any anomalies in radiation delivery in almost all the cases.
TU‐D‐I‐609‐01: Overview
Authors: Nishikawa R
Published: June 2005

Laboratory experiments including observer studies suggest that CADe should be effective in improving the accuracy of mammography. However, the few clinical studies reported have not been as positive as the non‐clinical studies have indicated. There are several possible explanations for this that will be discussed in this forum. These include (a) methodological problems making it difficult to measure any true improvement; (b) laboratory experiments are too different from actual clinical conditions (c) CADe is an effective clinical tool only under certain conditions. This symposium will discuss these issues.
TU‐D‐J‐6C‐02: Radiation Dose Reduction in 4D Computed Tomography
Authors: Li T , Schreibmann E , Thorndyke B , Xing L
Published: June 2005

Purpose: 4D CT is useful clinically for detailed abdominal and thoracic imaging over the course of the respiratory cycle. However, it usually delivers 10∼15 times more radiation dose to the patient as compared to the standard 3D CT, since multiple scans at each couch position are required to obtain the temporal information. In this work we propose a method to obtain high quality 4D CT with low tube current, hence reducing the radiation exposure of patients. Method and Materials: The improvement of the signal‐to‐noise ratio (SNR) of the CT image at a given phase was achieved by superposing the imaging information from other phases with the use of a deformable image registration model. To further reduce the statistical noise caused by low tube current, we developed a novel 4D penalized weighted least square (4D‐PWLS) method to smooth the data spatially and temporally. The method was validated by motion‐phantom and patient studies using a GE Discovery‐ST PET/CT scanner. A Varian RPM respiratory gating system was used to track the motion and to facilitate the phase binning of the 4D CT data. Results: We calculated the SNRs for both studies. The average SNR of 10 mA phantom images increased by more than three‐fold from 0.051 to 0.165 after the proposed 4D‐PWLS processing, without noticeable resolution loss. The patient images acquired at 90mA showed an increase from 2.204 to 4.558 for the end‐inspiration phase, and from 1.741 to 3.862 for the end‐expiration phase, respectively. By examining the subtraction images before and after processing, good edge preservation was also observed in the patient study. Conclusion: By appropriately utilizing the temporal information in 4D‐CT, the proposed method effectively suppresses the noise while preserving the resolution. The technique provides a useful way to reduce the patient dose during 4D CT and is thus valuable for 4D‐radiotherapy.
TU‐D‐J‐6C‐04: Assessing Margins Using Known Tumor Motion Trajectory and a Stochastic Convolution/superposition Algorithm
Authors: Naqvi S , D'Souza W , Yu C
Published: June 2005

Purpose: To incorporate the effect of tumor motion in routine dose calculations for conventional and IMRT treatment planning so that tumor margins can be optimized for individual patients based on their respective motion waveforms. Method and Materials: We employed the Monte Carlo Superposition method, which uses random sampling of beams, field segments, photon energy and direction, interaction points and kernel rays from appropriate probability distributions. In this work, the isocenter is also randomly sampled from the motion‐time waveform of the patient's tumor. To verify the method, we performed film measurements on IMRT phantoms placed on a platform that moves sinusoidally in the left‐right or superior‐inferior direction with amplitude of 2‐cm. For a test clinical case, a hepatic tumor case was created on a humanoid phantom using the Pinnacle3 IMRT system. The optimized plan was re‐calculated using MC‐superposition dose engine using a motion waveform representative of typical respiratory induced motion. Results: Film measurements averaged over 10 fractions agreed with MC superposition with motion calculations (infinite fraction) within 1mm in isodose lines for both static and 2‐cm sinusoidal motion cases. In the test IMRT liver case with realistic breathing waveform, the isodose lines are seen to shift in the superior direction. Slight underdosing of the GTV and significant underdosing of the PTV can be seen on the inferior side of the tumor, indicating that the 1cm margin on the GTV was not adequate to cover the tumor on the inferior border. Conversely, the margin was found to be too large on the superior tumor border, suggesting the need to reassign the margins and create a new plan. Conclusion: Our method provides a way for the clinicians to make informed decisions about margins required to cover the tumor based on actual motion waveforms of the patient's tumor.
TU‐D‐J‐6C‐07: A Method for Acquiring PET Images Without Breathing Motion Artifacts
Authors: Low D , Parikh P , Laforest R , Dempsey J , Lu W , Mutic S , Hubenschmidt J , Nystrom M , Miller T , Grigsby P , Bradley J
Published: June 2005

Purpose: PET images typically require many minutes to acquire, so breathing motion can cause the tumor shape to be inaccurately reconstructed. Using a multislice PET/CT scanner to quantitatively acquire 4‐dimensional computed tomography (4DCT) and gated PET, a breathing motion‐artifact free PET image study can be generated achieving statistical precision as if the patient underwent breath‐hold throughout the PET‐scan procedure. Method and Materials: The motion of lung structures, including tumors, is mapped by 4DCT as a function of tidal volume using our novel 5‐dimensional breathing motion model. The PET scan is performed using spirometry‐measured tidal volume and the PET data is stored using list mode. The user selects the phase of breathing for which the PET image is to be reconstructed and the corresponding list‐mode data is extracted to reconstruct an image. The gated‐CT scans provide quantitative attenuation correction that is accurate with respect to breathing phase. This process is repeated for all breathing phases and using the trajectory maps the reconstructed images are deformably mapped to a reference‐breathing phase. This process was tested using a computer‐controlled phantom moving in a motion pattern mimicking breathing motion. Three target spheres (1cm, 2cm, 3cm diameters) filled with solution were embedded into a cylindrical phantom filled with solution to provide a series of relative target‐to‐background activities. Results: Without gating, the target spheres were deformed and the low target‐to‐background small‐target image was lost in the background noise. These problems were alleviated when the images were mapped to a common motion “phase”. Conclusion: The phantom data showed that motion artifacts can be quantitatively removed yielding a high statistics image dataset without compromising PET acquisition time or patient dose. This process will provide the radiation‐oncology clinician with PET images having unrivaled spatial resolution and sensitivity for target definition in the thoracic and abdominal regions.
TU‐D‐J‐6B‐01: Small Animal PET and SPECT: Instrumentation, Performance, and Applications
Authors: Levin CS
Published: June 2005

In recent years both industrial and academic institutions have been intrigued with the possibility of using in vivo imaging assays in small animal models to study cellular and molecular processes associated with diseases such as cancer, heart disease, and neurological disorders. The ultimate goals of these in vivo imaging efforts are to facilitate the discovery of new drugs and treatments for disease and accelerate their translation into the clinic. Positron Emission Tomography (PET) and Single Photon Emission Computed Tomography (SPECT) are highly sensitive in vivo imaging modalities that can detect extremely low concentrations of radionuclide‐labeled probes that target the disease process of interest at the molecular level. This presentation will review PET and SPECT small animal imaging instrumentation requirements, challenges, performance characteristics, and applications in imaging subtle molecular signals associated with disease.
TU‐D‐J‐6B‐04: Technology for Small Animal X‐Ray and CT Imaging
Authors: Boone JM
Published: June 2005

The laboratory mouse and other small rodents have become a principal tool of biomedical researchers. The ability to manipulate the genetic component of the mouse by adding or deleting specific genes has proved quite valuable in virtually all areas of medical research, from neurodegenerative diseases to cancer. In many applications of mouse research, a better understanding of the phenotype of a specific mouse model is important. X‐ray imaging including computed tomography (CT) of the mouse therefore is an important aspect of genetic research. In this presentation, novel high resolution technologies for x‐ray imaging of the mouse will be discussed. Applications of new classes of contrast agents designed for animal use in concert with x‐ray and CT imaging will also be presented. Radiation dosimetry methods pertinent to small animal imaging with x‐rays will be described in detail. The role that x‐ray and CT images have in conjunction with physiological imaging techniques (nuclear and PET imaging) will also be described.
TU‐D‐T‐617‐02: Dose Conformity Improvement Using Lead‐Shielded Intracavitary Mould Applicator for Patients with Rectal Carcinoma
Authors: Devic S , Vuong T , DeBlois F , Evans M , Verhaegen F
Published: June 2005

Purpose: We present dose distribution results of Monte Carlo (MC) based treatment planning, employing Intracavitary Mould Applicator, used in pre‐operative high dose rate brachytherapy treatment of patients with rectal carcinoma, with the central lumen filled with lead as a shielding material. To justify the application of this shielding technique, the MC dose kernel calculations have been compared with experimental measurements. Method and Materials: Eight catheter channels are equally distributed over the circumference of the applicator with a central lumen intended to be used for insertion of an additional extending central catheter. Two dose kernels have been calculated for 192Ir source using the DOSXYZnrc Monte Carlo code: one for water phantom that includes air in the central lumen and another one for water phantom that includes lead shielding in the central portion of the applicator. For the dose measurements, we have used an Exradin planar ionization chamber (Model A14P). For the sake of MC dose kernel experimental verification, we have simulated the experimental phantom with scoring regions corresponding to the measurement points to increase the number of simulated photons and decrease the resulting uncertainty of the scored dose. For the clinical result presented in this paper, we have calculated two dose distributions: one with the air‐kernel, and another one with the lead‐kernel. Both distributions have been optimized in such a way to cover the target volume with the 100 % isodose surface. Results: Experimental dose ratios for particular points with and without lead shielding in the central position of the applicator differ from MC calculated ratios by 1 % for points in close proximity and up to 10 % for distal points. Conclusions: In this work, we demonstrated the increase in dose conformity using lead‐shielded Intracavitary Rectal Mould Applicator for patients with locally advanced rectal carcinoma.
TU‐E‐I‐611‐04: Bone Marrow and Bone Endosteum Dosimetry Methods Comparison for External Photons
Authors: Lee C , Lee C , Bolch W
Published: June 2005

Purpose: To compare and verify different bone endosteum and bone marrow photon dosimetry methods through the use of a high‐resolution micro CT‐based radiation transport model. Method and Materials: Two different Monte Carlo dosimetry algorithms for bone endosteum and bone marrow were compared to a high‐resolution microCT image‐based radiation transport model developed in our laboratory. Bone marrow dosimetry methods are (1) the dose response function method by Eckerman (DRF), and (2) the mass energy absorption coefficient ratio method (MEAC). Bone endosteum dosimetry methods include (1) DRF method and (2) homogeneous bone dose approximation (HGB). Each method was compared to results obtained from the microCT‐based paired‐image radiation transport (PIRT) model. Two ex‐vivo bone samples of a 66‐year male (lumbar vertebrae and cranium) were chosen for the comparison because of their distinctively different microstructures. Simple mono‐energetic parallel photon beams were simulated from 0.01 to 4.0 MeV. Results: For the bone marrow dose, the DRF method shows good agreement with PIRT result in the lumbar vertebra, but showed over estimates of bone marrow dose in the cranium, while the MEAC method shows good agreement with PIRT in both bone sites. For the bone endosteum dose, the DRF method shows closer results to the PIRT model at lower energies, but shows significant over‐ estimates of endosteum dose in higher photon energies. This can be explained by the fact the Eckerman model assumes that secondary electrons are followed through an infinite expanse of trabecular spongiosa, with no loss of energy to the bone cortex at high energy. Conclusion: For the bone marrow dose assessment, the MEAC method seems to be the best choice among the methods considered, while for the bone endosteum dose, the HGB method shows better agreement with PIRT than is seen with the DRF method, especially at higher photon energies.
TU‐E‐I‐611‐05: Point‐To‐Organ Dose Scaling Factors for Use in Pediatric Radiology
Authors: Staton R , Jones A , Bolch W , Hintenlang D
Published: June 2005

Purpose: The purpose of this study was to develop a comprehensive set of point‐to‐organ dose scaling factors (SFPOD) for pediatric radiology. Method and Materials: A physical tomographic newborn phantom was used in conjunction with an identical computational model to develop SFPOD. SFPOD were developed using Monte Carlo simulations of various radiographic and CT exams of a pediatric patient. Doses calculated included both organ doses and point doses, which were calculated at the same places at which doses were measured using MOSFET dosimeters in the physical phantom. Bone marrow dose was calculated using fluence‐to‐dose conversion coefficients. The resultant SFPOD values can then be used to calculate organ doses in the physical phantom from point dose measurements. The SFPOD were calculated at several energies and an average was used to generate general SFPOD. Results: Individual SFPOD ranged from 0.82 to 1.08. Also, the SFPOD for the sigmoid colon/rectum was 1.71. This was due to improvements or updates to the computational phantom that occur on a regular basis as more sophisticated tools become available. Therefore, SFPOD are useful not only for organ dose calculation in the physical phantom, but can also be used to incorporate improvements to the computational phantom into the physical phantom when physical alteration is impossible. Conclusion: This work demonstrates the benefits of having both physical and computational phantoms created from the same data set. A physical phantom alone is of limited use due to errors associated with only measuring point doses in organs. A 20% uncertainty in dose for an exam may seem trivial, but consider a pediatric patient subjected to 10 exams during childhood. The same 20% uncertainty propagated over 10 exams takes on new meaning. Also, it has been demonstrated that improvements to the computational phantom can be transferred to the physical phantom by using associated SFPOD.
TU‐E‐T‐6E‐02: ABR Perspective On the ABR Written Exam
Authors: Chaney E
Published: June 2005

Goals of the American Board of Radiology: One of the main purposes of the American Board of Radiology is to certify medical doctors to practice Radiation Oncology in North America. Certification is issued to candidates who meet training requirements and who demonstrate their knowledge and proficiency by successfully completing comprehensive computer‐based and oral examinations. The purpose of the computer‐based cognitive examination covering physics is to test the candidate's knowledge of the principles of physics underlying the practice of radiation oncology. Accomplishments: Since 1989 the ABR has awarded 2442 certificates in Radiation Oncology. Between 1934 and 1989, 10,843 certificates were awarded in Radiology, a grouping that included both Diagnostic Radiologists and Radiation Oncologists. Resources to help physicists know what to teach: The ABR provides information on the certification process at its website (http://www.theabr.org/). Included at this website is a study guide for the cognitive examination. The guide is in the form of a detailed outline of topics covered by the exam. Upcoming changes: The current study guide is undergoing review and revision. Changes in the content are influenced by a number of sources including changes in Radiation Oncology such as technological advances and obsolescence, training requirements established by the Accreditation Council for Graduate Medical Education, reports and recommendations issued by professional societies and commissions, and federal and state regulations.
TU‐EE‐A3‐01: CT Number Accuracy of Simulated Lung Nodules Imaged with a Multi‐Detector CT Scanner
Authors: Goodsitt M , Chan H , Larson S , Christodoulou E , Kim J , Way T
Published: June 2005

Purpose: To investigate the accuracies of the CT♯'s of simulated lung nodules for a QCT technique. Method and Materials: Spherical balls of 4 diameters (3.2,4.8,9.5 and 16‐mm) and 2 compositions (50mg/cc and 100mg/cc ) were employed as simulated lung nodules. All were scanned in a liquid water‐filled container at the center of a 20‐cm diameter water‐equivalent‐plastic phantom using GE multi‐detector CT scanners. A subset of the nodules and some 6.2‐mm diameter acrylic balls were also scanned in a simulated lung region within a thorax section phantom that was bolused on both sides with water‐equivalent slabs. Based on initial results that showed a significant decrease in the CT♯ of a nodule when scanned in the thorax section, additional studies were performed with 2 size air cavities at the center of the water phantom. Results: The CT♯'s of the nodules in water were fairly independent of nodule size (average CT♯'s of 50mg/cc=59–66HU and 100mg/cc=108–115HU). The CT♯ of a 50mg/cc nodule scanned at the center of the water phantom was 66HU in water, 51HU in a 2‐cm air cavity and 36HU in a 4.9‐cm air cavity. The CT♯'s of the acrylic balls ranged from about 79 to 96HU within the lung section and had poor‐to‐good reproducibility on repeat scans (CT♯ changes of +19HU, −17HU and 1HU for 3 different balls). Conclusion: The CT♯ of a nodule is highly dependent upon the amount of air or low‐density lung tissue near the nodule. We believe this error is due to the assumed all‐water composition of the patient/phantom in the scanner's beam hardening correction algorithm. The unusual reproducibility of the CT♯'s of nodules in the thorax phantom is likely a combined effect of sub‐millimeter air gaps between the phantom sections and variability in helical scanning interpolation. Further studies and possible solutions will be discussed.
TU‐EE‐A4‐05: Validation of CT‐Assisted Targeting (CAT) Software for Soft Tissue and Bony Target Localization
Authors: Zhang L , Dong L , Court L , Wang H , Gillin M , Mohan R
Published: June 2005

Purpose: To evaluate the performance of an automatic CT‐to‐CT image registration algorithm for both soft tissue and bony targets. Method and Materials: CT‐Assisted Targeting (CAT) software was developed for on‐line CT‐guided radiotherapy using a CT‐on‐rails system. The algorithm was tested in two phantom studies and cross‐compared with other radiotherapy imaging techniques available in the same room. A BAT phantom (North American Scientific, Chatsworth) was intentionally shifted and imaged each time by (1) an electronic portal imaging device, (2) ultrasound, and (3) the CT‐on‐rails. A Rando pelvic phantom with imbedded gold markers for target localization using the ACCULOC™ software (Northwest Medical Physics Equipment) was also used. To test the software in patient images, 15 prostate cancer patients receiving 3 CT scans per week over 8 week's treatment were selected. The prostate was chosen as the soft tissue target and a bony structure in the pelvic region (excluding the femoral heads) was used as the bony alignment target. A total of 366 treatment‐day CT images were registered using the CAT software and verified by a single observer. Results: The phantom studies demonstrated that the CAT software can achieve sub‐millimeter accuracy in detecting the intended shifts and were generally agreed well with other established imaging modalities in this controlled phantom study. The CAT software also performed well in patient's CT images. The failure rate, as defined by greater than 3 mm differences between the automatic detected positions and the final positions adjusted by the human observer, was only 2.1 % for soft tissue target registration and 1.6% for bony target registration in 366 CT images. The automatic registration takes less than 12 seconds. Conclusion: We have designed a highly robust, accurate, and fast computer algorithm for CT‐to‐CT image registration. The software provides a quick and reliable application for CT‐guided radiotherapy.