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Biomedical subjects

J M Balter

Publications and source records attributed to J M Balter.

At least 19 recordsLinked to original sources
PubMed2001

Determination of ventilatory liver movement via radiographic evaluation of diaphragm position.

PURPOSE: To determine the accuracy of estimation of liver movement inferred by observing diaphragm excursion on radiographic images. METHODS AND MATERIALS: Eight patients with focal liver cancer had platinum embolization microcoils implanted in their livers during catheterization of the hepatic artery for delivery of regional chemotherapy. These patients underwent fluoroscopy, during which normal breathing movement was recorded on videotape. Movies of breathing movement were digitized, and the relative projected positions of the diaphragm and coils were recorded. For 6 patients, daily radiographs were also acquired during treatment. Retrospective measurements of coil position were taken after the diaphragm was aligned with the superior portion of the liver on digitally reconstructed radiographs. RESULTS: Coil movement of 4.9 to 30.4 mm was observed during normal breathing. Diaphragm position tracked inferior-superior coil displacement accurately (population sigma 1.04 mm) throughout the breathing cycle. The range of coil movement was predicted by the range of diaphragm movement with an accuracy of 2.09 mm (sigma). The maximum error observed measuring coil movement using diaphragm position was 3.8 mm for a coil 9.8 cm inferior to the diaphragm. However, the distance of the coil from the top of the diaphragm did not correlate significantly with the error in predicting liver excursion. Analysis of daily radiographs showed that the error in predicting coil position using the diaphragm as an alignment landmark was 1.8 mm (sigma) in the inferior-superior direction and 2.2 mm in the left-right direction, similar in magnitude to the inherent uncertainty in alignment. CONCLUSIONS: This study demonstrated that the range of ventilatory movement of different locations within the liver is predicted by diaphragm position to an accuracy that matches or exceeds existing systems for ventilatory tracking. This suggests that the diaphragm is an acceptable anatomic landmark for radiographic estimation of liver movement in anterior-posterior projections for most patients.

Diaphragm↗
PubMed2001

Technical note: acquisition of CT models for radiotherapy applications with reduced tube heating.

The potential or changing computed tomography (CT) protocols to provide data sets that generate high quality digitally reconstructed radiographs (DRRs) from scans with very low tube currents is demonstrated. DRRs were generated from CT data acquired with slice thickness of 1, 3, and 5 mm, using high current to reduce noise in axial images. These DRRs were compared to one generated from a CT scan acquired using 1 mm aperture and very low (10 mA) current. The DRR generated via this technique is comparable to that generated with high current and 1 mm aperture, and higher resolution than from the 3 and 5 mm CT scans.

Humans↗
PubMed2001

Clinical use of electronic portal imaging: report of AAPM Radiation Therapy Committee Task Group 58.

AAPM Task Group 58 was created to provide materials to help the medical physicist and colleagues succeed in the clinical implementation of electronic portal imaging devices (EPIDs) in radiation oncology. This complex technology has matured over the past decade and is capable of being integrated into routine practice. However, the difficulties encountered during the specification, installation, and implementation process can be overwhelming. TG58 was charged with providing sufficient information to allow the users to overcome these difficulties and put EPIDs into routine clinical practice. In answering the charge, this report provides; comprehensive information about the physics and technology of currently available EPID systems; a detailed discussion of the steps required for successful clinical implementation, based on accumulated experience; a review of software tools available and clinical use protocols to enhance EPID utilization; and specific quality assurance requirements for initial and continuing clinical use of the systems. Specific recommendations are summarized to assist the reader with successful implementation and continuing use of an EPID.

Biophysical Phenomena↗
PubMed2000

A comparison of ventilatory prostate movement in four treatment positions.

PURPOSE: To ensure target coverage during radiotherapy, all sources of geometric uncertainty in target position must be considered. Movement of the prostate due to breathing has not traditionally been considered in prostate radiotherapy. The purpose of this study is to report the influence of patient orientation and immobilization on prostate movement due to breathing. METHODS AND MATERIALS: Four patients had radiopaque markers implanted in the prostate. Fluoroscopy was performed in four different positions: prone in alpha cradle, prone with an aquaplast mold, supine on a flat table, and supine with a false table under the buttocks. Fluoroscopic movies were videotaped and digitized. Frames were analyzed using 2D-alignment software to determine the extent of movement of the prostate markers and the skeleton for each position during normal and deep breathing. RESULTS: During normal breathing, maximal movement of the prostate markers was seen in the prone position (cranial-caudal [CC] range: 0.9-5.1 mm; anterior-posterior [AP] range: up to 3.5 mm). In the supine position, prostate movement during normal breathing was less than 1 mm in all directions. Deep breathing resulted in CC movements of 3.8-10.5 mm in the prone position (with and without an aquaplast mold). This range was reduced to 2.0-7.3 mm in the supine position and 0.5-2.1 mm with the use of the false table top. Deep breathing resulted in AP skeletal movements of 2.7-13.1 mm in the prone position, whereas AP skeletal movements in the supine position were negligible. CONCLUSION: Ventilatory movement of the prostate is substantial in the prone position and is reduced in the supine position. The potential for breathing to influence prostate movement, and thus the dose delivered to the prostate and normal tissues, should be considered when positioning and planning patients for conformal irradiation.

Adenocarcinoma↗
PubMed2000

Stereotactic radiosurgery of cerebral arteriovenous malformations with a multileaf collimator and a single isocenter.

OBJECTIVE: To prospectively demonstrate the safety and efficacy of stereotactic radiosurgery for arteriovenous malformations (AVMs) of the brain with a linear accelerator fitted with a multileaf collimator. METHODS: A novel radiosurgery system was developed at the University of Michigan Medical Center with a standard multileaf collimator and a computer-controlled radiotherapy system. Data were accumulated prospectively on all patients undergoing treatment with this system since treatment began in 1995. RESULTS: Thirty-six patients with 37 AVMs have undergone treatment to date. At more than 3 years since treatment, 15 of 16 AVMs with a volume of less than 10 cc were proven to be obliterated by angiography or magnetic resonance imaging, and one was considered a treatment failure. At more than 24 months since therapy, all four AVMs with a volume of 10 to 25 cc were obliterated. Four patients with AVMs with a volume of more than 25 cc have undergone staged therapy, treating the entire volume to 10 Gy twice, but none has been followed long enough to demonstrate a final outcome. There were four transient and no permanent complications. CONCLUSION: Our early data indicate that stereotactic radiosurgery of cerebral AVMs with a linear accelerator and a multileaf collimator is safe and effective. Large AVMs may be especially suitable for this mode of therapy. Staged treatment of very large AVMs seems to be a promising addition to standard treatment, but longer follow-up is necessary to confirm that complete obliteration can be achieved.

Adolescent↗
PubMed1999

The treatment planning of segmental, conformal stereotactic radiosurgery utilizing a standard multileaf collimator.

Over a period of approximately 3 years, our institution has implemented and refined a system of Stereotactic Radiosurgery (SRS) which utilizes the standard multi leaf collimator (MLC) of the Scanditronix MM50 Racetrack Microtron and treats in an arrangement of segmental "pseudo-arcs." This system employs a commercial BRW based stereotactic frame which is mounted to the treatment table. With the exception of the table-mounted frame hardware there have been no modifications to the treatment machine to accommodate these treatments. By use of standard evaluation parameters (e.g., treatment time, planning time, dose conformance and dose heterogeneity ratios) this system compares quite favorably with reported data from institutions treating SRS with either a GammaKnife or a standard linear accelerator with tertiary collimators.

Brain↗
PubMed1999

A method for incorporating organ motion due to breathing into 3D dose calculations.

A method is proposed that incorporates the effects of intratreatment organ motion due to breathing on the dose calculations for the treatment of liver disease. Our method is based on the convolution of a static dose distribution with a probability distribution function (PDF) which describes the nature of the motion. The organ motion due to breathing is assumed here to be one-dimensional (in the superior-inferior direction), and is modeled using a periodic but asymmetric function (more time spent at exhale versus inhale). The dose distribution calculated using convolution-based methods is compared to the static dose distribution using dose difference displays and the effective volume (Veff) of the uninvolved liver, as per a liver dose escalation protocol in use at our institution. The convolution-based calculation is also compared to direct simulations that model individual fractions of a treatment. Analysis shows that incorporation of the organ motion could lead to changes in the dose prescribed for a treatment based on the Veff of the uninvolved liver. Comparison of convolution-based calculations and direct simulation of various worst-case scenarios indicates that a single convolution-based calculation is sufficient to predict the dose distribution for the example treatment plan given.

Algorithms↗
PubMed1999

Quantization of setup uncertainties in 3-D dose calculations.

Random setup errors can lead to erroneous prediction of the dose distribution calculated for a patient using a static computed tomography (CT) model. Multiple recomputations of the dose distribution covering the range of expected patient positions provides a way to estimate a course of treatment. However, due to the statistical nature of the setup uncertainties, many courses of treatment must be simulated to calculate a distribution of average dose values delivered to a patient. Thus, direct simulation methods can be time consuming and may be impractical for routine clinical treatment planning applications. Methods have been proposed to efficiently calculate the distribution of average dose values via a convolution of the dose distribution (calculated on a static CT model) with a probability distribution function (generally Gaussian) that describes the nature of the uncertainty. In this paper, we extend the convolution-based calculation to calculate the standard deviation of potential outcomes sigmaD(x,y,z) about the distribution of average dose values, and we characterize the statistical significance of this quantity using the central limit theorem. For an example treatment plan based on a treatment protocol in use at our institution, we found that there is a 68% probability that the actual dose delivered to any point (x,y,z) will be within 3% of the average dose value at that point. The standard deviation also yields confidence limits on the dose distribution, and these may be used to evaluate treatment plan stability.

Algorithms↗
PubMed1999

A mathematical model for correcting patient setup errors using a tilt and roll device.

An algorithm is presented for determining how to adjust the actuators of a tilt and roll table. The algorithm is based on a geometrical model of the table, which was designed with six degrees of freedom. This design and algorithm allows complete translational and rotational corrections to be applied to the target volume position on a daily basis.

Algorithms↗
PubMed1998

Improvement of CT-based treatment-planning models of abdominal targets using static exhale imaging.

PURPOSE: CT-based models of the patient that do not account for the motion of ventilation may not accurately predict the shape and position of critical abdominal structures. Respiratory gating technology for imaging and treatment is not yet widely available. The purpose of the current study is to explore an intermediate step to improve the veracity of the patient model and reduce the treated volume by acquiring the CT data with the patients holding their breath at normal exhale. METHODS AND MATERIALS: The ventilatory time courses of diaphragm movement for 15 patients (with no special breathing instructions) were measured using digitized movies from the fluoroscope during simulation. A subsequent clinical protocol was developed for treatment based on exhale CT models. CT scans (typically 3.5-mm slice thickness) were acquired at normal exhale using a spiral scanner. The scan volume was divided into two to three segments, to allow the patient to breathe in between. Margins were placed about intrahepatic target volumes based on the ventilatory excursion inferior to the target, and on only the reproducibility of exhale position superior to the target. RESULTS: The average patient's diaphragm remained within 25% of the range of ventilatory excursion from the average exhale position for 42% of the typical breathing cycle, and within 25% of the range from the average inhale position for 15% of the cycle. The reproducibility of exhale position over multiple breathing cycles was 0.9 mm (2sigma), as opposed to 2.6 mm for inhale. Combining the variation of exhale position and the uncertainty in diaphragm position from CT slices led to typical margins of 10 mm superior to the target, and 19 mm inferior to the target, compared to margins of 19 mm in both directions under our prior protocol of margins based on free-breathing CT studies. For a typical intrahepatic target, these smaller volumes resulted in a 3.6% reduction in Veff for the liver. Analysis of portal films shows proper target coverage for patients treated based on exhale modeled plans. CONCLUSIONS: Modeling abdominal treatments at exhale, while not realizing all the gains of gated treatments, provides an immediate reduction in the volume of normal tissue treated, and improved reliability of patient data for NTCP modeling, when compared to current "free breathing" CT models of patients.

Diaphragm↗
PubMed1998

Determination of rotations in three dimensions using two-dimensional portal image registration.

The relative relationships among anatomic features visualized on planar radiographic images change due to rotations of the patient out of the imaging plane. These changes can be predicted a priori from a three-dimensional radiographic model of the patient. In this study we assess the feasibility of using that information together with a planar image feature alignment tool to account for out-of-plane rotations in the evaluation of subsequent clinical patient images. A series of digitally reconstructed radiographs (DRRs) with known patient rotations was generated from a computed tomography scan of an anthropomorphic head phantom. Fixed anatomic features were extracted, as seen in the DRRs of rotated anatomy and entered into a database. Alignment of features from test radiographs with those from an entry in this database yielded an estimate of rotation out of plane (database entry that resulted in the best fit via planar transformation) along with the planar components of setup errors in the rotated plane. Tests using DRRs and films show that it is possible to select anatomic features in AP skull radiographs with position and orientation sensitive to out-of-plane rotation.

Databases as Topic↗
PubMed1998

A tilt and roll device for automated correction of rotational setup errors.

A tilt and roll device has been developed to add two additional degrees of freedom to an existing treatment table. This device allows computer-controlled rotational motion about the inferior-superior and left-right patient axes. The tilt and roll device comprises three supports between the tabletop and base. An automotive type universal joint welded to the end of a steel pipe supports the center of the table. Two computer-controlled linear electric actuators utilizing high accuracy stepping motors support the foot of table and control the tilt and roll of the tabletop. The current system meets or exceeds all pre-design specifications for precision, weight capacity, rigidity, and range of motion.

Biophysical Phenomena↗
PubMed1998

A room-based diagnostic imaging system for measurement of patient setup.

A room-based diagnostic x-ray imaging system for routine measurement of radiotherapy patient orientation has been developed. The system consists of a pair of room-mounted x-ray tubes and a portable imager consisting of an orthogonal pair of phosphor screens, a mirror/lens system, a CCD camera, and computer software for comparing images of the patient to reference images. Orthogonal pairs of images can be acquired quickly and with relatively little exposure, allowing correction of patient setup on a daily basis. This could limit patient setup error to the uncertainty in the measurement and repositioning processes, a potentially significant improvement over the present standard.

Humans↗
PubMed1997

Potential benefits of eliminating planning target volume expansions for patient breathing in the treatment of liver tumors.

PURPOSE: To investigate potential benefits derived from reduction or elimination of planning target volume (PTV) margins associated with patient breathing through examination of hepatic tumors treated with conformal therapy. METHODS AND MATERIALS: We reviewed the treatment plans of 50 patients who had previously received conformal partial organ liver irradiation for treatment of hepatic malignancies. PTVs for these plans included expansions (1-2 cm) for patient breathing. Data consisted of the three-dimensional dose distributions computed for the conformal plans generated for these volumes, and also for plans using identical beam arrangements but smaller block margins to treat planning target volumes that did not include the expansions for breathing. We calculated effective volumes (V(eff)) and normal tissue complication probabilities (NTCP) using dose-volume histograms for normal liver and analyzed changes in: V(eff), NTCP at the prescription dose, doses associated with selected NTCP levels, and tumor control probabilities (TCP) at these new dose levels. RESULTS: Elimination of the patient breathing components of the PTVs for these conformal treatments of liver tumors: (a) decreased the average V(eff) by 5%; (b) decreased the average predicted NTCP at the prescription (isocenter) dose used to treat the patients by 4.5%; (c) increased the average target volume (isocenter) dose associated with low (1-10%) predicted normal liver NTCP by 6-8 Gy, which corresponded to (d) a predicted average 6-7% increase in TCP for aggressive liver tumors. Plans with PTV expansions for breathing that occurred mostly within the liver showed greatest potential benefit. CONCLUSIONS: Elimination of the margin added to hepatic target volumes for patient ventilation could lead to clinically meaningful increases in dose without increasing the predicted frequency of complications.

Humans↗
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↗