Publications (12)26.82 Total impact
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Article: Ultrasound-based guidance of intensity-modulated radiation therapy.
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ABSTRACT: In ultrasound-guided intensity-modulated radiation therapy (IMRT) of prostate cancer, ultrasound imaging ascertains the anatomical position of patients during x-ray therapy delivery. The ultrasound transducers are made of piezoelectric ceramics. The same crystal is used for both ultrasound production and reception. Three-dimensional (3D) ultrasound devices capture and correlate series of 2-dimensional (2D) B-mode images. The transducers are often arranged in a convex array for focusing. Lower frequency reaches greater depth, but results in low resolution. For clear image, some gel is usually applied between the probe and the skin contact surface. For prostate positioning, axial and sagittal scans are performed, and the volume contours from computed tomography (CT) planning are superimposed on the ultrasound images obtained before radiation delivery at the linear accelerator. The planning volumes are then overlaid on the ultrasound images and adjusted until they match. The computer automatically deduces the offset necessary to move the patient so that the treatment area is in the correct location. The couch is translated as needed. The currently available commercial equipment can attain a positional accuracy of 1-2 mm. Commercial manufacturer designs differ in the detection of probe coordinates relative to the isocenter. Some use a position-sensing robotic arm, while others have infrared light-emitting diodes or pattern-recognition software with charge-couple-device cameras. Commissioning includes testing of image quality and positional accuracy. Ultrasound is mainly used in prostate positioning. Data for 7825 daily fractions of 234 prostate patients indicated average 3D inter-fractional displacement of about 7.8 mm. There was no perceivable trend of shift over time. Scatter plots showed slight prevalence toward superior-posterior directions. Uncertainties of ultrasound guidance included tissue inhomogeneities, speckle noise, probe pressure, and inter-observer variation. Some published studies detected improvement in treatment based on gastrointestinal toxicity and the reduction of prostate movement.Medical Dosimetry 02/2006; 31(1):20-9. · 1.00 Impact Factor -
Article: Prostate motion and isocenter adjustment from ultrasound-based localization during delivery of radiation therapy.
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ABSTRACT: To study prostate motion from 4,154 ultrasound alignment fractions on 130 prostate patients treated with conformal radiotherapy or intensity-modulated radiation therapy at the University of Nebraska Medical Center. Each prostate patient was immobilized in a vacuum cradle. Daily treatment was verified by ultrasound scan after laser setup with skin marks and before radiation delivery by the same physician responsible for anatomic delineation during planning. Directional statistics were employed to test the significance of shift directions. Polar histograms showed the prevalence of prostate motion in superior-posterior directions. The average direction was about 27 degrees from the superior axis. The average changes of prostate position in superior to inferior (SI), anterior-posterior (AP), and left to right (LR) directions and in radial distance were 0.25, -0.13, 0.03, and 0.92, cm respectively. Our data indicated that prostate motion was not patient specific, and its average magnitude remained virtually unchanged over time. Recommended planning target volume (PTV) margins for use without ultrasound localization were 0.90 cm in SI, 1.02 cm in AP, and 0.80 cm in LR directions. Ultrasound localization revealed a predominance of prostate shift from planning position in the superior-posterior direction, with an average closer to the superior axis. The motion data provides recommended margins for PTV.International Journal of Radiation OncologyBiologyPhysics 04/2005; 61(4):984-92. · 4.11 Impact Factor -
Article: Effects of field parameters on IMRT plan quality for gynecological cancer: a case study.
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ABSTRACT: Traditional external beam radiotherapy of gynecological cancer consists of a 3D, four-field-box technique. The radiation treatment area is a large region of normal tissue, with greater inhomogeneity over the treatment volume, which could benefit more with intensity-modulated radiation therapy (IMRT). This is a case report of IMRT planning for a patient with endometrial cancer. The planning target volume (PTV) spanned the intrapelvic and periaortic lymph nodes to a 33-cm length. Planning and treatment were accomplished using double isocenters. The IMRT plan was compared with a 3D plan, and the effects of field parameters were studied. Delineated anatomical contours included the intrapelvic nodes (PTV), bone marrow, small bowel, bladder, rectum, sigmoid colon, periaortic nodes (PTV), spinal cord, left kidney, right kidney, large bowel, liver, and tissue (excluding the PTVs). Comparisons were made between IMRT and 3D plans, 23-MV and 6-MV energies, zero and rotated collimator angles, different numbers of segments, and opposite gantry angle configurations. The plans were evaluated based on dosevolume histograms (DVHs). Compared with the 3D plan, the IMRT plan had superior dose conformity and spared the bladder and sigmoid colon embedded in the intrapelvic nodes. The higher energy (23 MV) reduced the dose to most critical organs and delivered less integral dose. Zero collimator angles resulted in a better plan than "optimized" collimator angles, with lower dose to most of the normal structures. The number of segments did not have much effect on isodose distribution, but a reasonable number of segments was necessary to keep treatment time from being prohibitively long. Gantry angles, when evenly spaced, had no noticeable effect on the plan. The patient tolerated the treatment well, and the initial complete blood count was favorable. Our results indicated that large-volume tumor sites may also benefit from precise conformal delivery of IMRT.Journal of Applied Clinical Medical Physics 02/2005; 6(3):46-62. · 1.29 Impact Factor -
Article: X-ray energy choice for lung tumour irradiation depends on the density distribution of clonogenic cells.
Physics in Medicine and Biology 05/2003; 48(8):L27-8; author reply L29-30. · 2.83 Impact Factor -
Article: Computed tomography localization of radiation treatment delivery versus conventional localization with bony landmarks.
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ABSTRACT: A computed tomography (CT) scanner was installed in the linear accelerator room (Primatom) at Morristown. Since June 2000, we have been providing prostate, lung, and liver cancer patients with fusion of CT and linac radiation treatment. This paper describes our registration methods between planning and treatment CT images, and compares treatment localization by CT versus conventional localization by bony landmarks such as portal imaging. For image registration, we printed out beforehand the beam's eye view of the treatment fields. Prostate tumor volume from each Primatom CT slice was mapped on the printouts, and the necessary isocenter shift relative to the skin marks was deduced. No port film was necessary for our Primatom patients. For ten patients we generated digitally-reconstructed radiographs (DRRs) with bone contrast from the CT scans, and deduced the required shift as the difference between the DRRs of the Primatom CT versus the planning CT. This represented the best observable shift should portal imaging be employed. Shift from bony landmark significantly correlated with the Primatom CT shift. Positioning adjustment based on bony anatomy was generally in the same direction as the CT shift for individual patient, but frequently did not go far enough. Our study confirmed that prostate organ motion relative to the bones has an average length of 4.7 mm (with standard deviation of 2.7 mm), and indicated the superiority of CT versus conventional bony structure (such as portal imaging) localization.Journal of Applied Clinical Medical Physics 02/2003; 4(2):112-9. · 1.29 Impact Factor -
Article: Towards integrating functional imaging in the treatment of prostate cancer with radiation: the registration of the MR spectroscopy imaging to ultrasound/CT images and its implementation in treatment planning.
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ABSTRACT: Dose-escalation to intraprostatic tumor deposits detected by magnetic resonance spectroscopy (MRS) is an example of tumor-targeted radiation therapy. Because treatment planning for prostate brachytherapy is performed based on ultrasound (US)/computed tomography (CT) images, a sine qua non of this technique is the ability to map MRS-positive volumes (obtained in a gland deformed by the endorectal balloon coil) to the US/CT images. An empirical algorithm designed to perform this function, and its validation, are described. Mathematically, the problem of mapping points between the MR and US/CT domains comes to: (a) ascertaining that the position of any point in the interior of the prostate is uniquely determined by the shape of the gland, and (b) finding an algorithm that describes this relationship. The image registration algorithm described here is based on the assumption that points within the gland maintain the same relative position with respect to both the axial contours of the prostate and the center of the prostate along the superior-inferior direction. Relative positions of MRS-positive voxels are calculated with this method in both MR and US/CT space. For a particular voxel in the MR space, one obtains first the z coordinate in the US/CT space, that is, along the superior-inferior direction. This determines the axial slice in the US/CT frame of reference where the other two coordinates (x, y) will be calculated. The validity of this algorithm was examined with the aid of a pelvic phantom built to simulate realistically the prostate and its surrounding bony and tissue structures and with CT scans of implanted patients obtained, at several weeks' intervals, as part of an edema-resolution study. Seventy-five "dummy" seeds were placed in the phantom, within the simulated prostate gland, in a quasi-regular pattern. The coordinates of these seeds were determined and thus served as markers of prostate deformation when an inflated rectal probe was introduced in the phantom. CT images of this phantom were taken for different volumes of the MR rectal probe and in each case the prostate outlines were contoured and seed coordinates calculated. Using these data, the predictions of the mapping algorithm could be directly verified. Absolute values of the 3D-positional errors in this algorithm were 2.2 mm +/- 1.2 mm (average +/- SD). Only 6 of 75 seeds had positional displacement of 4 mm or more. Similar results were obtained in the patient analysis. In comparison to the MRS voxel size (6.25 x 6.25 x 3.0 mm3), the present algorithm achieves the desired clinical accuracy. As well, with this 3D algorithm seed positions are reconstructed with an uncertainty that, along the z direction, is less than half the thickness of the typical US slice (0.5 cm).International Journal of Radiation OncologyBiologyPhysics 01/2003; 54(5):1558-64. · 4.11 Impact Factor -
Article: The syed temporary interstitial iridium gynaecological implant: an inverse planning system.
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ABSTRACT: Patients with advanced gynaecological cancer are often treated with a temporary interstitial implant using the Syed template and Ir- 192 ribbons at the Memorial Sloan-Kettering Cancer Center. Urgency in planning is great. We created a computerized inverse planning system for the Syed temporary gynaecological implant, which optimized the ribbon strengths a few seconds after catheter digitization. Inverse planning was achieved with simulated annealing. We discovered that hand-drawn target volumes had drawbacks; hence instead of producing a grid of points based on target volume, the optimization points were generated directly from the catheter positions without requiring an explicit target volume. Since all seeds in the same ribbon had the same strength, the minimum doses were located at both ends of the implant. Optimization points generated at both ends ensured coverage of the whole implant. Inverse planning took only a few seconds, and generated plans that provide a good starting point for manual improvement.Physics in Medicine and Biology 09/2002; 47(16):N203-8. · 2.83 Impact Factor -
Article: Automated planning volume definition in soft-tissue sarcoma adjuvant brachytherapy.
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ABSTRACT: In current practice, the planning volume for adjuvant brachytherapy treatment for soft-tissue sarcoma is either not determined a priori (in this case, seed locations are selected based on isodose curves conforming to a visual estimate of the planning volume), or it is derived via a tedious manual process. In either case, the process is subjective and time consuming, and is highly dependent on the human planner. The focus of the work described herein involves the development of an automated contouring algorithm to outline the planning volume. Such an automatic procedure will save time and provide a consistent and objective method for determining planning volumes. In addition, a definitive representation of the planning volume will allow for sophisticated brachytherapy treatment planning approaches to be applied when designing treatment plans, so as to maximize local tumour control and minimize normal tissue complications. An automated tumour volume contouring algorithm is developed utilizing computational geometry and numerical interpolation techniques in conjunction with an artificial intelligence method. The target volume is defined to be the slab of tissue r cm perpendicularly away from the curvilinear plane defined by the mesh of catheters. We assume that if adjacent catheters are over 2r cm apart, the tissue between the two catheters is part of the tumour bed. Input data consist of the digitized coordinates of the catheter positions in each of several cross-sectional slices of the tumour bed, and the estimated distance r from the catheters to the tumour surface. Mathematically, one can view the planning volume as the volume enclosed within a minimal smoothly-connected surface which contains a set of circles, each circle centred at a given catheter position in a given cross-sectional slice. The algorithm performs local interpolation on consecutive triplets of circles. The effectiveness of the algorithm is evaluated based on its performance on a collection of soft-tissue sarcoma tumour beds within various anatomical structures. For each of 15 patient cases considered, the algorithm takes approximately 2 min to generate the planning volume. Although the tumour shapes are rather different, the algorithm consistently generates planning volumes that visually demonstrate smooth curves compactly encapsulating the circles. This general-purpose contouring algorithm works well whether the catheters are all close together, spread far apart in the plane or arranged in a convoluted way. The automatic contouring algorithm significantly reduces labour time and provides a consistent and objective method for determining planning volumes for soft-tissue sarcoma. Further studies are needed to validate the significance of the resulting planning volumes in designing treatment plans and the role that sophisticated brachytherapy treatment planning optimization may have in producing good plans.Physics in Medicine and Biology 07/2002; 47(11):1891-910. · 2.83 Impact Factor -
Article: C-Arm imaging for brachytherapy source reconstruction: geometrical accuracy.
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ABSTRACT: We study the accuracy of brachytherapy source reconstruction using C-Arm images. We use a phantom embedded with dummy ribbons in a regular pattern, placed at the rotation center of the C-Arm. With a commercial reconstruction jig, radiographic films are taken without the image intensifier. The average error in reconstructed seed coordinates is 0.1 cm. However, the jig is inconvenient for patient procedures. For C-Arm reconstruction without the jig, the magnifications of the image intensifier along orthogonal directions are different. We "stretch" the image to equalize the magnifications. Afterward, seed reconstruction has an average error of 0.1 cm in all directions.Medical Physics 06/2002; 29(5):724-6. · 2.83 Impact Factor -
Article: Optimized planning for intraoperative planar permanent-seed implant.
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ABSTRACT: We describe a fast, PC-based optimization planning system for a planar permanent-seed implant. Sites where this system is applicable include brain, lung, and head and neck. The system described here allows placing ribbons of different strengths and of different lengths along and across the implant plane. The program takes full advantage of the availability of different source strengths in inventory, and attempts to find configurations of ribbons that result in optimal dose uniformity over the prescription plane. Dosimetry is based on the AAPM TG 43 Report [R. Nath et al., Med. Phys. 22, 209-234 (1995)]. Compared with TG 43 parameters, the classical tables underestimate the I-125 source strengths needed by 40%. The use of several source strengths improves the plan. Typical optimization yields dose uniformity of 10%, and computing times are within 2-3 min. No further enhancement is obtained if ribbons are placed in a grid pattern as opposed to the (simpler) arrangement along parallel lines. Nor is it valuable to have variable ribbon lengths. For an I-125 implant the optimization system described here is a practical alternative to the (strictly speaking inapplicable) classical systems. It calculates correctly the total source strengths, and--most notably--generates plans with optimal dose uniformity. The fast computing time is well suited for planning during surgery in the operating room.Journal of Applied Clinical Medical Physics 02/2002; 3(3):221-6. · 1.29 Impact Factor -
Article: From track structure to stochastic chemistry and DNA damage: Microdosimetric perspective
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ABSTRACT: The effect of all types of ionizing radiations on higher organisms is nonspecific in the sense that all interactions occur through the agency of ionization and excitation processes. This, and the relative constancy of the amount of energy required to induce such processes, has led to the concept of absorbed dose as a quantifier for the amount of radiation delivered. However, equal doses of different radiations have different effects depending on the stopping power of the charged particles and on the temporal pattern of irradiation. Because individual energy transfers depend on neither one of these factors, it follows that the biological effectiveness of ionizing radiation depends on their spatial and temporal configuration. Microdosimetry is the study of the distribution in space and time of elementary energy deposits and their relation to subsequent damage. We discuss physico-chemical events that occur within the first microsecond following the interaction of charged particles with deoxyribonucleic acid (DNA) and argue that this particular time interval is uniquely important for understanding the biological effectiveness of radiation. Radiation biologists distinguish between direct hits and damage induced indirectly by radicals produced in the condensed medium surrounding the DNA target. The interaction and diffusion of these radicals (primarily OH) are described with the techniques of stochastic chemistry because—unlike “regular” chemistry—their initial spatial distribution is highly nonuniform. The information thus obtained is usually summarized in terms of proximity functions or microdosimetric distributions. The ultimate object of such studies is to obtain information on specific DNA alterations (e.g., strand breaks) or chromosomal damage and correlate them to such events as mutagenesis and carcinogenesis. © 2000 John Wiley & Sons, Inc. Int J Quant Chem 80: 327–340, 2000International Journal of Quantum Chemistry 09/2000; 80(3):327 - 340. · 1.36 Impact Factor -
Article: A comparison of two image fusion techniques in ct-on-rails localization of radiation delivery.
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ABSTRACT: A computed tomography (ct) scanner on Rails has been installed in a linear accelerator room at Morristown Memorial Hospital since 2000. The ct-on-Rails has been used for the localization of patient position during radiation delivery for prostate, lung and liver cancer patients. The image management system, the Siemens Syngo system, is the primary software employed in the registration of the planning ct and the treatment ct images. This study compares the two image fusion methods available in the system: Landmark Registration and Visual Alignment. Shifts in 6 ct scans with Rando phantom were deduced from Landmark Registration (automatic algorithm) and from Visual Alignment (manual registration), and compared with the shifts directly measured on the phantom. For Visual Alignment, the isocenter shifts deduced from the fused images generally agreed well with the directly measured shifts on the Rando phantom, with average absolute error of 0.9 mm in anterior-posterior (ap) direction, 1.0 mm in right-left (rl) direction, and 2.0 mm in superior-inferior (si) direction. The image fusion algorithm was confirmed to be accurate. Some scans with Landmark Registration gave erroneous ap shifts when the anterior radio-opaque marker (bb) registration was of in the ap direction. Visual Alignment was more robust than Landmark Registration in these clinical situations.Physica Medica 21(3):113-9. · 1.07 Impact Factor
Top co-authors
Top Journals
Institutions
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2005–2006
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University of Nebraska at Omaha
- Department of Radiation Oncology
Omaha, NE, USA
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2000–2003
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Memorial Sloan-Kettering Cancer Center
- Department of Medical Physics
New York City, NY, USA
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2002
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Emory University
- Department of Radiation Oncology
Atlanta, GA, USA
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