Volume 36, Issue 6, June 2009
Index of content:
- Joint Imaging/Therapy Symposium: Room 303A
The John S. Laughlin Science Council Research Symposium
WE‐C‐303A‐01: Stationary‐Gantry Tomosynthesis System for On‐Line Image Guidance in Radiation Therapy Based On a 52‐Source Cold Cathode X‐Ray Tube36(2009); http://dx.doi.org/10.1118/1.3182479View Description Hide Description
We present the design and simulation of an imaging system that employs a compact multiple source x‐ray tube to produce a tomosynthesisimage from a set of projections obtained at a single tube position. The electron sources within the tube are realized using cold cathodecarbon nanotube technology. The primary intended application is tomosynthesis‐based 3D image guidance during external beam radiation therapy. The tube, which is attached to the gantry of a medical linear accelerator(linac) immediately below the multileaf collimator, operates within the voltage range of 80 to 160 kVp and contains a total of 52 sources that are arranged in a rectilinear array. This configuration allows for the acquisition of tomographic projections from multiple angles without any need to rotate the linac gantry. The x‐ray images are captured by the same amorphous silicon flat panel detector employed for portal imaging on contemporary linacs. The field‐of‐view (FOV) of the system corresponds to that part of the volume that is sampled by rays from all sources. The present tube and detector configuration provides an 8 cm × 8 cm FOV in the plane of the linac isocenter when the 40.96 cm × 40.96 cm imaging detector is placed 40 cm from the isocenter. Since this tomosynthesis application utilizes the extremities of the detector to record image detail relating to structures near the isocenter, simultaneous treatment and imaging is possible for most clinical cases, where the treated target is a small region close to the linac isocenter. The tomosynthesisimages are reconstructed using the simultaneous iterative reconstruction technique (SART), which is accelerated using a graphics processing unit (GPU). We present details of the system design as well as simulated performance of the imaging system based on reprojections of patient CT images.
Conflict of interest: Sponsored by Siemens
WE‐C‐303A‐02: A Real‐Time Target Positioning Method Using Combined KV/MV Imaging and External Respiratory Monitoring for DMLC Target Tracking36(2009); http://dx.doi.org/10.1118/1.3182480View Description Hide Description
Purpose: To (1) develop a target position estimation method combining occasional kV/MV imaging of fiducial marker and continuous monitoring of external respiratory signal, (2) integrate the estimation method with a real‐time DMLC tracking system, and (3) quantify the tracking accuracy of the integrated system.Method and Materials: The experimental tracking system employed a Varian Trilogy system with kV/MV imagingsystems and RPM. A 3D motion stage with a gold marker reproduced three different patient‐measured lungtumor traces, while a separate 1D motion stage with an external marker reproduced the associated external surrogate signal acquired by a Cyberknife system. Occasional kV/MV imaging measured the gold marker position, while the RPM system continuously detected the external marker position. A state augmentation‐based correlation model between the gold marker position and the RPM signal was established in real‐time and used to estimate the marker position from the RPM signal. The estimated marker position was used to drive the MLC leaves to follow the marker. The tracking accuracy was evaluated at different imaging intervals (0.15, 10, and 180s), corresponding to the update interval of the internal/external correlation model. Results: For 3‐min tracking of the lung traces, the tracking RMS error in each axis was ∼1mm for 10s imaging intervals, and was not affected by the imaging interval significantly. Tracking reduced motion error more effectively for large motion excursion and large systematic error. Conclusion: For the first time, a real‐time target position estimation system combining kV, MV and respiratory signal has been developed and integrated with a DMLC tracking system. The system accuracy is typically within 1mm for patient tumor motion. This sub‐mm accuracy system has potential for broad application in managing respiratory motion for thoracic and abdominal tumors.
Conflict of Interest: Research supported by NIH/NCI R01‐93626.
WE‐C‐303A‐03: Pharmacokinetic Analysis of Hypoxia 18‐Fluoromisonidazole Dynamic PET Imaging in Head and Neck Cancer36(2009); http://dx.doi.org/10.1118/1.3182481View Description Hide Description
Purpose: This paper uses pharmacokinetic analysis of 18‐Fluoromisonidazole (FMISO) dynamic PETimaging to investigate if there is any correlation between tumor hypoxia (Ki ), tumor‐to‐blood ratio (T/B) in late‐time image, local blood perfusion (k1 ), and local vasculature fraction (β) for head‐and‐neck cancer patients. Methods and Materials: Newly diagnosed patients with head‐and‐neck cancer prior to chemotherapy or radiotherapy underwent dynamic FMISO‐PET scan. The data was acquired in 3 consecutive PET/CT dynamic scan segments, with start acquisition time [0, 1, 2, 3, 4, 5, 10, 15, 20, 25, 90, 95, 180, 185] minutes, consisting of 5 frames in 1‐minute frames, following by 5‐minutes frames. The dynamic PETimages were first registered with each other and then analyzed using Philips Resarch's Voxulus pharmacokinetic software. The (Ki, k1 , β) kinetic parameter images were derived for each patient. Results: Nine head‐and‐neck cancer patients' data were analyzed. Representative images of FDG‐PET (showing the tumor),CT (showing the anatomy), late‐time FMISO‐PET (showing T/B), and (Ki, k1 , β) kinetic parameter images were shown consisting of a patient example with good concordance of tumor hypoxia and high T/B, one with concordance of no tumor hypoxia and low T/B, and one with ambiguity between tumor hypoxia and T/B. Scatter diagrams were plotted between each pair of T/B, Ki, k1 , β and corresponding correlation coefficient computed. Conclusions: There is strong positive correlation between ROI's T/B and hypoxia index Ki . However, due to the statistical photon counting noise in PETimaging, and the amplification of noise in kinetic analysis, the direct correlation between individual pixel's T/B and hypoxia is not obvious. For a tumor ROI, there is slight negative correlation between k1 and Ki , moderate positive correlation between β and Ki , but no correlation between β and Ki .
This work is supported in part by NIH PO1 CA115675.
WE‐C‐303A‐04: Quantifying the Reproducibility of Heart Position with Respect to Bony Anatomy in Daily Set Up and the Corresponding Delivered Heart Dose in Voluntary Deep Inhalation Breath Hold for Left Breast Cancer Patients Via External Beam Radiotherapy36(2009); http://dx.doi.org/10.1118/1.3182482View Description Hide Description
Purpose: Voluntary deep inhalation breath hold (DIBH) technique help reduce the heart toxicity during radiation treatment of the left breast. We present the results of the first study performed to quantify the reproducibility of heart position and the heartdose in daily setup for voluntary DIBH patients. Method and Materials: Ten left breast patients undergoing treatment with voluntary DIBH were studied. Each patient had two CT scans, one with free breathing and one with voluntary DIBH, to evaluate the dose under these two conditions to the Heart, anterior most point of left anterior descending (LAD) coronary artery, and left Lung. At the treatment machine, daily and weekly KV orthogonal images were acquired using onboard imaging for each patient. Mosaiq™ software was used to register the full bony anatomy of thorax (including the spine, ribs, anterior chest wall and heart) with KV images to the planning DRRs. Once the patient is aligned on the treatment machine using bony anatomy registration, the difference between the bony anatomy registration and the heart registration is the daily heart position. These differences were transferred into treatment planning system to obtain the delivered dose.Results: The dosimetric evaluation shows clinically significant reduced dose to heart,lung, and LAD in the DIBH case compared to the free breathing case, as previous studies have shown. The weekly heart position shifts are in the order of few mm. Dosimetric evaluations for these shifts indicate that dose to the heart in the daily treatment with DIBH remains low. Conclusion: The setup and breath hold accuracy and the daily delivered dose to the heart was evaluated for voluntary DIBH breast patients. Results indicate a clear reduction of dose delivered to the heart throughout the treatment when voluntary DIBH technique is employed.
WE‐C‐303A‐05: Variation in Radiation Doses in Pediatric and Adult Interventional Radiology Procedures: The Need for Dose Optimization36(2009); http://dx.doi.org/10.1118/1.3182484View Description Hide Description
Purpose: To determine the variation in pediatiric and adult doses in cardiac catheterization and angiography procedures and investigate factors that correlate with radiation. Methods and Materials: Effective doses were estimated from the dose area product values of 761 pediatric patients belonging to age groups 0, 1, 5 and 10 years old who underwent coarctation (COA) dilatation, patent ductus arteriosus (PDA) occlusion, pulmonary and diagnostic. The causes for high patient doses were investigated and the correlation of effective dose and DAP with patient weight, equivalent cylindrical diameter, fluoroscopy time and number of cine frames were analyzed. The maximum entance skindoses and effective doses were determined for 114 adult patients for cardiac catheterization and 320 adults for angiography procedures. Techniques to reduce patient entrance doses were investigated. Resuts: Pulmonary and PDA are high dose procedures with an average effective dose of 10 and 8.2 mSv respectively. DAP values showed a good correlation with effective doses for diagnostic and COA dilatation with r2 (p <0.0001) equal to 0.81 and 0.70 respectively. PTCA procedure delivered a maximum skindose (4.5 mGy) that exceeded the threshold dose for skin erythemia. Percutaneous Transhepatic Choleangiography (PTC) and Transjugular Intrahepatic Portosystemic Shunts (TIPSS) delivered the maximum skindose of 983 and 735 mGy. Conclusions: Review of the protocols and setting of image quality criteria for pediatric especially for age groups 0 and 1 and for adult patients in order that flurocospy time, peak kilovoltage and number of cine series be reduced is needed. Pooling all ages, an effective dose conversion coefficient of 120 cGy‐cm2 per mSv can be used for pediatric procedures.
This research was supported by IAEA.
36(2009); http://dx.doi.org/10.1118/1.3182485View Description Hide Description
Introduction — During proton therapy,positron emitting radio‐isotopes are produced along the trace where incident protonbeam interacts with human tissue. The isotope activity profile is related to the proton dose distribution. Such isotope activities can be measured and imaged using a PET scanner. Therefore an accurate and sensitive PETimage of the isotope activities can be used for verification of proton dose. Our work is to design an efficient PET system for in situproton dose measurement in order to measure the activities of short‐lived isotopes.Method — A non‐rotating partial PET ring configuration is advantageous for such measurements as the decay of short‐lived isotopes can be measured almost immediately after the stop of proton irradiation. The PET design is optimized by varying 1)crystal cross‐section that is related to spatial resolution; 2) crystal types that affect intrinsic sensitivity and Time of Flight information; 3) angular coverage of the PET ring that is related to system sensitivity and reconstructed image quality. This study uses EGS4 based Monte Carlo simulation software that has been developed at Penn for PET scanner design studies. Geant4 software is used to produce the protonisotope activity. This isotope distribution is parameterized and used as the source distribution in EGS4. It is placed in a cylindrical water phantom initiating from phantom surface inward to mimic the patient treatment configuration. Iterative image reconstruction, together with data corrections for scatter, and attenuation, are incorporated to achieve high‐quality images and quantitative data. Results — The reconstructedisotope source from PETimages agrees well with the source activity for several design configurations. The distal falloff region of the isotope trace can be clearly identified. Summary — The design of PET system can be optimized so that the configuration yields an accurate and efficient reconstruction of the isotope activities.
36(2009); http://dx.doi.org/10.1118/1.3182486View Description Hide Description
Purpose: To present a deformable image registration (DIR) model based on maximum likelihood estimation (MLE) with improved robustness to image noise and selection of registration parameters. Method and Materials: Optical flow based DIR, such as free‐form deformable registration (FDR), usually assumes invariance of pixel intensities, which may not be true for noisy images. Moreover, the smoothing parameter must be judiciously chosen and typically remains fixed over all iterations of the registration. A robust registration model (FDR‐MLE) based on minimization of smoothing term, standard for FDR, and MLE of the residual image is proposed. The advantages of the proposed model are 1) matching image pixels between the source image and the target image within an optimized variation to account for image noise; and 2) adaptive adjustment of the smoothing parameter during the registration process. Validations of FDR‐MLE were carried out using a simulated digital phantom and clinical lungimages. Validation criteria included correlation coefficient (CC) and average phantom error (PE). Results: FDR‐MLE outperformed FDR and was more robust to selection of registration parameters. For the same parameters (step size = 0.3, smoothing weighting factor = 2.0), in the simulated phantom, FDR‐MLE increased the CC by 11% compared to FDR. FDR‐MLE had PE=0.49 pixels, compared to 1.08 pixels for FDR. Robustness was measured by computing standard deviations (STD) of CC and PE for various step sizes. Using CC, STD of FDR‐MLE was 0.0066, which was only 12% of STD of CC for FDR (0.053). PE for FDR‐MLE was 0.044 pixels, compared to 0.21 pixels for FDR. Conclusion: The proposed FDR‐MLE model can significantly improve the registration accuracy, convergence, and robustness. It is well suited for DIR in a clinical environment where time constraints and limited expertise of the user limit optimization of the registration parameters.
Image Guided Interventions: Imaging Guidance and New Technologies for Interventional Procedures
36(2009); http://dx.doi.org/10.1118/1.3182570View Description Hide Description
Recent advances in imaging technology, image modeling and registration, and advanced therapeutics offer the potential for precise, image‐guided therapies that will transform existing approaches to planning, intervention, adaptation, and monitoring of therapeutic response. Such therapies are marked by a dramatic increase in the application of image information from multiple modalities and demand accurate coregistration of morphological and functional information across a broad range of spatial and temporal scales. The scope of advanced therapeutic modalities enabled by such advances is broad, ranging from high‐precision image‐guidedradiation therapy and surgery to minimally invasive target ablation, cell‐based therapies, and other forms of novel therapeutics. Moreover, the information acquired during the course of intervention will drive patterns of therapy delivery that are increasingly adaptive and patient‐specific. This symposium focuses on the scientific principles and recent advances in imaging, guidance, image modeling, registration, adaptation, and advanced therapy delivery techniques. Three speakers will present on topics central to such advancement: Dr. Siewerdsen will discuss principles of imaging performance, guidance, and the development and integration of new technologies for therapy guidance; Dr. Hawkes will address principles of rigid and deformable image registration, fusion, visualization, and augmented reality; finally, Dr. Keall will discuss the latest advances in imaging, adaptation, and novel treatmentdelivery techniques in image‐guidedradiation therapy.
1. Gain exposure to new developments in imaging technologies for image‐guided interventions.
2. Understand challenges in rigid and deformable image registration, fusion, and visualization.
3. Learn the latest advances in imaging, adaptation, and therapy delivery techniques in IGRT.