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Biomedical subjects

J M Balter

Publications and source records attributed to J M Balter.

29 records · Page 2Linked to original sources
PubMed1997

Effects of implantable biomaterials on radiation dosimetry.

BACKGROUND: It is generally known that radiation dose is enhanced in front of and reduced behind metallic plates. This study evaluates metallic, ceramic, and bioabsorbable facial-reconstruction materials for their differential effects on radiation dosimetry. METHODS: Commercially pure titanium (cpt), stainless steel (steel), titanium alloy (tia), hydroxyapatite (HA), and poly-L-lactide (PLA, a bioabsorbable polymer) were obtained for this study. The radiation doses distal (behind) and proximal (in front of) to the test material were measured with an ionization chamber placed at several distances from the test material. Therefore, transmission (proximal to plate) and backscattering (distal to plate) factors were generated at several distances for each material. RESULTS: Poly-L-lactide transmitted nearly 100% of the incident radiation beam. The metals had the greatest effect on transmission with steel, followed by cpt, tia, and HA showing the greatest reduction of incident beam. Poly-L-lactide revealed minimal backscattering. Greater backscatter of the incident radiation beam was seen from steel, followed by cpt and HA. Poly-L-lactide also behaved similar to water in transmission and backscatters properties during electron irradiation. CONCLUSIONS: Poly-L-lactide has a minimal effect on the radiation-dose distribution and may be beneficial as a reconstructive device for patients undergoing head and neck cancer radiotherapy. Hydroxyapatite showed a relatively minor effect, whereas the metals (steel, followed by cpt and tia) revealed the greatest detrimental effect on the radiation-dose distribution.

Alloys↗
PubMed1996

Uncertainties in CT-based radiation therapy treatment planning associated with patient breathing.

PURPOSE: To evaluate uncertainties associated with treatment-planning computed tomography (CT) data obtained with the patient breathing freely. METHODS AND MATERIALS: Patients with thoracic or abdominal tumors underwent a standard treatment-planning CT study while breathing quietly and freely, followed by CT scans while holding their breath at normal inhalation and normal exhalation. Identical treatment plans on all three CT data sets for each patient pointed out differences in: (a) radiation path lengths; (b) positions of the organs; (c) physical volumes of the lung, liver, and kidneys; (d) the interpretation of plan evaluation tools such as dose-volume histograms and normal tissue complication probability (NTCP) models; and (e) how well the planning CT data set represented the average of the inhalation and exhalation studies. RESULTS: Inhalation and exhalation data differ in terms of radiation path length (nearly one quarter of the cases had path-length differences > 1 cm), although the free breathing and average path lengths do not exhibit large differences (0-9 mm). Liver and kidney movements averaged 2 cm, whereas differences between the free breathing and average positions averaged 0.6 cm. The physical volume of the liver between the free breathing and static studies varied by as much as 12%. The NTCP calculations on exhale and inhale studies varied from 3 to 43% for doses that resulted in a 15% NTCP on the free-breathing studies. CONCLUSION: Free-breathing CT studies may improperly estimate the position and volume of critical structures, and thus may mislead evaluation of plans based on such volume dependent criteria such as dose-volume histograms and NTCP calculations.

Abdominal Neoplasms↗
PubMed1996

Measurement of patient setup errors using port films and a computer-aided graphical alignment tool.

Patient orientations were measured for 49 patients treated in the abdomen, chest, and pelvic regions over the course of 20 months. Setup errors were determined using a curve-matching graphical interface to compare digitized port films to digitized simulation films. Data representing both "initial patient setup" and "patient setup at treatment" are presented and compared. Data were sorted by anatomic area and analyzed both at the population level and on a patient-by-patient basis. For each population, setup errors were observed to be primarily random, with population standard deviations of 5-6 mm for each of three translations and 2-3 degrees for each of two rotations. Rotations about the patients' inferior-superior axes were not measured. For each site, correlations between translations and/or rotations were small. The results are consistent with those from previous studies. The data set is among the largest collected to date.

Abdominal Neoplasms↗
PubMed1995

Automated localization of the prostate at the time of treatment using implanted radiopaque markers: technical feasibility.

PURPOSE: Prostate movement is a major consideration in the formation of target volumes for conformal radiation therapy of prostate cancer. The goal of this study was to determine the technical feasibility of using implanted radiopaque markers and digital imaging to localize the prostate at the time of treatment, thus allowing for reduction of the margin required for uncertainty in target position. METHODS AND MATERIALS: Radiopaque markers implanted around the prostate prior to treatment are visible on electronic radiographs generated with a portal imager or diagnostic imaging device. The locations of the images of these markers on the digital radiographs were automatically determined by a template-matching algorithm. The coordinates of the markers were found by projecting rays through the marker locations on orthogonal radiographs using a three-dimensional (3D) point-matching algorithm. Prostate and/or patient movement was inferred from the marker displacements. Images generated from known movements of a phantom with implanted markers were tested with this algorithm. Locations of markers from daily images of patients with implanted markers were determined by both manual and automatic techniques to determine the efficacy of automated localization on typical clinical images. RESULTS: Prostate movements can be automatically detected in a phantom using low-energy photons within 30 s after image acquisition and with a precision of better than 1 mm in translation and 1 degree in rotation (indistinguishable from the uncertainty in measuring precision). CONCLUSION: The studies show that on-line repositioning of the patient based on localization of the markers at the time of treatment is feasible, and may reduce the uncertainty in prostate location when combined with practical on-line repositioning techniques.

Feasibility Studies↗
PubMed1995

Measurement of prostate movement over the course of routine radiotherapy using implanted markers.

PURPOSE: To measure the range and frequency of occurrence of intertreatment movement of the prostate gland over the course of radiotherapy, and to demonstrate that the prostate may move independently of the surrounding bones of the pelvis. METHODS AND MATERIALS: Ten patients underwent implantation of radiopaque markers around the prostate. Orthogonal portal films were taken at multiple stages during the course of treatment and digitized. An image registration tool was used to solve for film detector placement and, subsequently, to determine positional changes between structures on a reference portal image pair and all subsequent pairs for each patient. Transformations describing prostate movement were measured independently of those describing setup variations of the pelvic girdle. RESULTS: Translation and/or rotation of the prostate was detected in 70% of the treatments for which films were taken. The maximum measured displacement was 7.5 mm along a major axis. Typical translations of the prostate were between 0-4 mm. The translation and rotation had a predominant direction, suggesting a natural axis for prostate movement. CONCLUSION: Although significant prostate displacement can occur between treatments, the typical range of movement seen along a major axis was less than 5 mm. Proper treatment planning should consider the movement of the target independent of surrounding bony anatomy. Advances in online portal imaging, image registration, and dynamic field shaping may permit shaped fields that encompass the prostate gland in its position at the time of treatment, allowing for the use of smaller fields while ensuring proper target coverage.

Humans↗
PubMed1995

Mechanical and dosimetric quality control for computer controlled radiotherapy treatment equipment.

Modern computer controlled radiotherapy treatment equipment offers the possibility of delivering complex, multiple field treatments with minimal operator intervention, thus making multiple field conformal therapy practical. Conventional quality control programs are inadequate for this new technology, so new quality control procedures are needed. A reasonably fast, sensitive, and complete daily quality control program has been developed in our clinic that includes nearly automated mechanical as well as dosimetric tests. Automated delivery of these quality control fields is performed by the control system of the MM50 racetrack microtron, directed by the CCRS sequence processor [D. L. McShan and B. A. Fraass, Proceedings of the XIth International Conference on the use of computers in Radiation Therapy, 20-24 March 1994, Manchester, U.K. (North Western Medical Physics Department, Manchester, U.K., 1994), pp. 210-211], which controls the treatment process. The mechanical tests involve multiple irradiations of a single film to check the accuracy and reproducibility of the computer controlled setup of gantry and collimator angles, table orientation, collimator jaws, and multileaf collimator shape. The dosimetric tests, which involve multiple irradiations of an array of ionization chambers in a commercial dose detector (Keithly model 90100 Tracker System) rigidly attached to the head of the treatment gantry, check the output and symmetry of the treatment unit as a function of gantry and collimator angle and other parameters. For each of the dosimetric tests, readings from the five ionization chambers are automatically read out, stored, and analyzed by the computer, along with the geometric parameters of the treatment unit for that beam.(ABSTRACT TRUNCATED AT 250 WORDS)

Humans↗
PubMed1993

Online repositioning during treatment of the prostate: a study of potential limits and gains.

PURPOSE: With on-line portal imaging devices and image registration tools, the verification of radiation field position prior to each treatment becomes technically feasible. In this paper, we analyze the impact of pre-treatment verification and field position adjustment on target coverage and normal tissue sparing. METHODS AND MATERIALS: Port films were compared with corresponding simulation films to determine the magnitude of setup variations in patients treated for prostate cancer. From these data, an analytic function was determined between geometric coverage of the target and field margin size. A paradigm for on-line patient repositioning was employed to generate a new relationship between margin and target coverage. Margins were selected for the situations of normal treatment and on-line repositioning to ensure target coverage. Dose-volume histograms were generated for a typical prostate treatment using these margins. RESULTS: On-line repositioning, when setup errors exceed 1 cm, results in a 6 mm reduction in margin, suggesting that 10% of the volume of bladder and rectum may be spared of high dose. CONCLUSION: The use of on-line imaging and image registration to guide adjustment of patient setup may lead to a reduction in the volume of normal tissues irradiated, and possibly improve the probability of complication-free survival in future treatments.

Computer Simulation↗
PubMed1992

The use of beam's eye view volumetrics in the selection of non-coplanar radiation portals.

In 3-dimensional treatment planning, beam's eye view (BEV) is used as an interactive tool to define portal entry angles that exclude critical structures while fully encompassing the target volume. With beam's eye view volumetrics (BEV volumetrics), the volume of intersected normal tissues is also calculated and is used as a quantitative tool to choose portal orientations that minimize normal tissue volumes irradiated. The axial beam entry angle and a polar angle (relative to the patient longitudinal axis) are specified to define the central axis orientation. Using BEV volumetrics, we have studied the quantities of normal tissues irradiated when treating tumors in the abdomen, thorax, and pelvis. The reduction of normal tissue irradiated is a strong function of site and patient-specific tumor size and location. Volumetrics combined with BEV is found to be useful in treatment planning because it (a) provides quantitative information needed in rationally choosing portal entry angles, (b) provides a near interactive speed approach to understanding the relative merits of different multiple field plans, and (c) compliments the information provided by the more time-consuming generation of dose volume histograms.

Humans↗
PubMedDate not supplied

Functional mapping of human motor cortical activation with conventional MR imaging at 1.5 T.

A conventional 1.5-T magnetic resonance (MR) imager was used to detect signal intensity changes on T2*-weighted images of human motor and sensory cortices during performance of hand and tongue movements. Narrow receiver bandwidths were used to improve the signal-to-noise ratio. Protocols consisting of baseline, motor task, rest, and second motor task periods were performed by nine volunteers. Two-dimensional cross correlation was applied to correct in-plane translation and rotation of the head during the imaging session before the control images were subtracted from the task images. Measurements obtained during finger movement tasks indicated a 3%-8% increase in signal intensity near the contralateral central sulcus and smaller ipsilateral signal intensity increases. Bilateral signal intensity increases were also observed during tongue movement studies. A retrospective image registration technique was used to map the signal changes onto conventional anatomic images, which were used to create integrated three-dimensional models of brain structure and function. These integrated images showed that the highest signal intensity due to hand movement was near the putative central sulcus.

Adult↗
PubMedDate not supplied

Correlation of projection radiographs in radiation therapy using open curve segments and points.

A method for determining differences in patient position between projection radiographs such as those routinely used in radiation therapy has been developed. Determination of a transformation relating two radiographs permits registration of simulation and portal images and the transfer of information between them. The algorithm is based on spatially registering segments of open curves or points seen on both images, and does not require identification of corresponding curve endpoints. The method as implemented is both fast and accurate. After user definition of the curves or points to be registered, the optimal transformation is calculated in approximately 1 s. Calculational experiments indicate that corresponding points on open curves are registered to better than 2 mm, even when random errors (FWHM 1 mm) in digitization are included. Experiments on the registration of clinical portal and simulation images (pixel size = 0.5 by 0.5 mm) indicate an accuracy on the order of 2 mm or less in translation and 2 deg or less in rotation. Analysis of portal and simulation radiographs of the brain, thorax, and pelvis indicates this algorithm to be robust and clinically applicable. The rapid and accurate registration of portal and simulation images is potentially important in the application of real time portal imaging devices in radiation therapy.

Algorithms↗