Biomedical subjects

B A Fraass

Publications and source records attributed to B A Fraass.

16 recordsLinked to original sources

PubMed1992

A quantitative assessment of the addition of MRI to CT-based, 3-D treatment planning of brain tumors.

Quantitative 3-D volumetric comparisons were made of composite CT-MRI macroscopic and microscopic tumor and target volumes to their independently defined constituents. Volumetric comparisons were also made between volumes derived from coronal and axial MRI data sets, and between CT and MRI volumes redefined at a repeat session in comparison to their original definitions. The degree of 3-D dose coverage obtained from use of CT data only or MRI data only in terms of coverage of composite CT-MRI volumes was also analyzed. On average, MRI defined larger volumes as well as a greater share of composite CT-MRI volumes. On average, increases in block margin on the order of 0.5 cm would have ensured coverage of volumes derived from use of both imaging modalities had only MRI data been used. However, the degree of inter-observer variation in volume definition is on the order of the magnitude of differences in volume definition seen between the modalities, and the question of which imaging modality best describes tumor volumes remains unanswered until detailed histologic studies are performed. Given that tumor volumes independently apparent on CT and MRI have equal validity, composite CT-MRI input should be considered for planning to ensure precise dose coverage for conformal treatments.

Astrocytoma↗

PubMed1992

The clinical utility of magnetic resonance imaging in 3-dimensional treatment planning of brain neoplasms.

Results of the clinical experience gained since 1986 in the treatment planning of patients with brain neoplasms through integration of magnetic resonance imaging (MRI) into computerized tomography (CT)-based, three-dimensional treatment planning are presented. Data from MRI can now be fully registered with CT data using appropriate three-dimensional coordinate transformations allowing: (a) display of MRI defined structures on CT images; (b) treatment planning of composite CT-MRI volumes; (c) dose display on either CT or MRI images. Treatment planning with non-coplanar beam arrangements is also facilitated by MRI because of direct acquisition of information in multiple, orthogonal planes. The advantages of this integration of information are especially evident in certain situations, for example, low grade astrocytomas with indistinct CT margins, tumors with margins obscured by bone artifact on CT scan. Target definitions have repeatedly been altered based on MRI detected abnormalities not visualized on CT scans. Regions of gadolinium enhancement on MRI T1-weighted scans can be compared to the contrast-enhancing CT tumor volumes, while abnormalities detected on MRI T2-weighted scans are the counterpart of CT-defined edema. Generally, MRI markedly increased the apparent macroscopic tumor volume from that seen on contrast-CT alone. However, CT tumor information was also necessary as it defined abnormalities not always perceptible with MRI (on average, 19% of composite CT-MRI volume seen on CT only). In all, the integration of MRI data with CT information has been found to be practical, and often necessary, for the three-dimensional treatment of brain neoplasms.

Astrocytoma↗

PubMed1991

Technical considerations in the use of 3-D beam arrangements in the abdomen.

The practical utilization of 3-D treatment planning to reduce doses to normal tissues in the abdomen is illustrated for irradiation of hepatic masses using fields with central axes rotated out of the transverse plane. The beams were arranged to go through the minimum amount of normal liver tissue, while exiting above or below a kidney. Although these beam arrangements were not coplanar with standard transverse body sections, they were designed for dose delivery through use of standard Megavoltage equipment. The planning process for these techniques illustrates the need for and use of several tools usually associated with 3-D treatment planning systems. Beam's eye-view planning with perspective display of the relevant anatomy in the projective beam geometry is required for designing the placement of focused blocks for these oblique fields. Three-dimensional volumetric dose calculations are required to evaluate dose distributions. Additionally, port-film-type radiographs, digitally reconstructed from the CT dataset, are found to be useful in understanding the correctness of simulation and verification films. The reduction in dose to normal tissues over that achievable using standard plans with beams entering the patient at right angles to the central axis of the body is illustrated using dose-volume histograms. These techniques have allowed the initiation of a radiation dose escalation protocol for tumors involving the liver and porta hepatis.

Abdomen↗

PubMed1991

Three-dimensional treatment planning of astrocytomas: a dosimetric study of cerebral irradiation.

To demonstrate that 3-dimensional planning is both practical and applicable to the treatment of high-grade astrocytomas, 50 patients over a 2-year period have received cerebral irradiation delivered in focussed, non-axial techniques employing from 2 to 5 beams. Astrocytomas have been planned using rapid, practical incorporation of CT data to define appropriate tumor volumes. Tumor + 3.0 cm and tumor + 1.5 cm volumes have been treated to conventional doses of 4500 cGy and 5940 cGy, respectively, using beam orientations that maximally spared normal remaining parenchyma. Analyses of 3-dimensionally calculated plans have been performed using integral dose-volume histograms (DVH) to help select treatment techniques. Using identical CT-based volumetric data as input for generation of Beam's Eye View (BEV) designed blocks, DVH curves demonstrate dosimetric advantages of non-axial techniques over conventional parallel-opposed orientations. Assessment of the non-axial techniques in selected cases indicates that uniform target volume coverage could be maintained with a typical reduction of 30% in the total amount of brain tissue treated to high dose (95% isodose line).

Astrocytoma↗

PubMed1991

Design of MRI scan protocols for use in 3-D, CT-based treatment planning.

MRI has the potential of providing the radiation therapy treatment planner with new insights into the definition of target and normal tissue volumes to augment CT in 3-D treatment planning. The current speed of MR scan sequences is not sufficient to enable the acquisition of both T1 and T2 weighted images in all three orthogonal planes in a reasonable period of time. Therefore, compromises must be made in the design of protocols specifically for use in radiotherapy planning which: (1) provide enough information to readily enable image registration; (2) preserve the three-dimensionality provided by image acquisition directly in coronal and sagittal planes; (3) yield tissue contrast as well as tumor specificity (where available); but (4) can be completed in a short enough span of time (or with enough checks) that the patient position is not compromised. Protocols designed for use in planning treatment of the brain, head and neck, lung, prostate, cervix, and sarcomas are presented.

Humans↗

PubMed1990

Full integration of the beam's eye view concept into computerized treatment planning.

A complete set of beam's eye view (BEV) and beam portal design features have been integrated into a computerized 3-dimensional radiotherapy treatment planning system. Among the features implemented is the ability to mix BEV graphics with gray-scale images such as simulator and verification radiographs, and digital reconstructed radiographs. Image processing techniques have been developed to both enhance verification images and to detect radiation field boundaries. These portal simulation and presentation techniques are being used clinically to design and verify radiation fields with manual or automatically-designed field shaping blocks. The ability to perform computer dose calculations for planes which are parallel or perpendicular to a specified beam's central axis is available and this feature has also proven useful for treatment plan evaluation and optimization. Finally, direct comparison of computer-generated portal images with actual simulation and verification radiographs is also possible. These techniques allow the direct integration of "CT-directed treatment planning" with block design, simulator films and port films, and other Beam's Eye View-type displays.

Computer Simulation↗

PubMed1989

Boost treatment of the prostate using shaped, fixed fields.

Using a CT-based, 3-D treatment planning system and Beam's Eye-View (BEV) displays, shaped fixed-field techniques have been developed for external beam boost treatment of Stage C carcinoma of the prostate. The basic technique comprises three sets of opposing beams (laterals and +/- 45 degrees with respect to the lateral) into a 6-field arrangement. Target volumes together with bladder and rectal wall volumes are outlined on axial CT slices and combined to form 3-D volumes. For each field, an interactive BEV display is produced showing the target volume in its correct 3-D geometrical perspective and an auto-block routine is used to design focused blocks which conform to that volume. Full 3-D volume calculations computed for those plans on 17 patients were analyzed along with similar calculations for more traditional unblocked 4-field box and bilateral arc techniques. Compared to the 95% isodose volume for the 6-field conformational technique, traditional open beam full target coverage techniques typically produce high dose volumes which cover up to five times as much uninvolved tissue. Dose volume histograms illustrate that typically half as much bladder and rectal tissue is treated to high dose using the conformational boost techniques. From the dosimetric perspective of sparing normal tissues, shaped fixed-field boost techniques are shown to be clearly superior to traditional full coverage bilateral arc techniques. Smaller 8 cm X 8 cm arc techniques are shown to be quantitatively unacceptable for treatment of this advanced stage disease, as they typically misses 20-35% of the target volume.

Humans↗

PubMed1989

A CT-compatible version of the Fletcher system intracavitary applicator: clinical application and 3-dimensional treatment planning.

A new acrylic version of the familiar Fletcher intracavitary applicator, the Ann Arbor (AA) applicator, has been developed. This new device eliminates the problem of "streak" artifacts on CT images, but unlike other plastic applicators the ability to shield portions of the bladder and rectum is retained through the use of tungsten alloy shields which are afterloaded with the radioactive sources. To minimize changes in placement geometry and to take advantage of the wide clinical experience with the Fletcher system, the new applicator nearly duplicates the physical dimensions of the Fletcher applicator. With the Ann Arbor applicator in place, dummy sources are easier to locate on standard radiographic simulations. CT scans are free of artifact and provide clear, detailed visualizations of cross-sectional anatomy. The new applicator thus allows CT images to be used to their potential in evaluating crucial anatomic relationships and in performing 3-D dosimetry with dose volume analysis. Using a treatment planning system with 3-D capabilities, solid surface graphic display of applicator, cervix, rectum, bladder, and treatment isodose volume has been performed. In addition, dose volume histograms can be generated to obtain precise measurements of the volume of cervix, rectum, or bladder receiving specified doses.

Brachytherapy↗

PubMed1989

Comparison of automated and manual shielding block fabrication.

This work reports the results of a study comparing computer controlled and manual shielding block cutting. The general problems inherent in automated block cutting have been identified and minimized. A system whose accuracy is sufficient for clinical applications has been developed. The relative accuracy of our automated system versus experienced technician controlled cutting was investigated. In general, it is found that automated cutting is somewhat faster and more accurate than manual cutting for very large fields, but that the reverse is true for most smaller fields. The relative cost effectiveness of automated cutting is dependent on the percentage of computer designed blocks which are generated in the clinical setting. At the present time, the traditional manual method is still favored.

Humans↗

PubMed1988

The influence of lung density corrections on treatment planning for primary breast cancer.

Primary breast cancer is generally treated with opposed radiation beams oriented tangentially with respect to the breast. This technique attempts to minimize the dose to the lung and other normal tissues, while at the same time producing a uniform dose distribution throughout the irradiated breast. Although a part of the lung is always included in the tangential breast fields, the effect of this low density tissue on the dose distribution is rarely taken into account. In the present work, the effect of lung density correction on the dose distribution resulting from tangential breast fields is analyzed. Treatment plans for a series of 34 patients treated for breast cancer have been performed using CT data. To study the effect of density corrections on the tangential field treatment plans for these patients, eight separate treatment plans for each patient have been optimized. For each of four photon energies (60Co, and 4, 6, and 10 MV X rays), treatment plans have been optimized for each patient when density correction is employed, and when unit density is assumed. Four additional dose calculations have been obtained for each patient corresponding to use of the unit density plan, but with density corrections employed in the calculation. The effects that density correction has on the wedge angles used, on the maximum dose ("hot spot") for each of several cross-sectional cuts, on the prescription isodose level which is chosen for each plan, and on homogeneity of the dose distribution over the target volume are all analyzed for the above described plans.

Breast Neoplasms↗

PubMed1988

From manual to 3-D computerized treatment planning for 125-I stereotactic brain implants.

Aspects of planning for the treatment of high grade primary or recurrent brain tumors with stereotactically placed catheters afterloaded with high activity 125-I seeds are discussed. At our institution, planning has evolved from a simple manual process, which assumed geometric symmetry, through a more advanced manual process, that took advantage of certain mechanical properties of the stereotactic frame used, into a sophisticated, computerized planning approach that includes optimization of the source distribution and 3-D displays. Use of the simple manual method is limited to the rare situations where target volumes are quite regular in shape. The advanced manual method provides some customization for irregularly shaped volumes, but is slow and tedious to implement. The interactive, computerized approach permits identification of target volumes directly on CT slices, reconstructions in arbitrary planes, and optimization of catheter placement, source separation along each catheter, and selection of source strengths from an available inventory. A multi-format display feature which includes a probe's eye view perspective is provided to aid in planning. Integral dose-volume histograms for the target volume point out the advantages in using sophisticated, 3-D, computerized planning systems for these implants.

Brachytherapy↗

PubMed1988

Recent advances in radiotherapy treatment planning.

The need for accurate treatment planning in radiation therapy arose as more powerful radiation technology became available. Computers now make it possible to use increasingly sophisticated dose calculation methods. Over the last two decades, modern imaging modalities, faster computer hardware, advanced graphics techniques, and new calculational algorithms have made it easier to plan radiotherapy treatment. The prospect is bright for continued improvement during the next several years. Tumor localization will become more precise using three-dimensional displays of integrated radiographic imaging data, as described in this article.

Computer Graphics↗

PubMedDate not supplied

Improving precision and safety in the use of beam modifying devices in radiation therapy.

Reliable and safe implementation of beam modifying devices such as wedges and block trays requires careful design and construction. Inappropriate design may pose problems ranging from user-hostile operation to hard-to-track, but significant variations in actual position in a beam. This may cause variation in actual wedge output factors, or variation in the position of a block tray. In case of simple mechanical failure or personnel mistake, design related mechanical conditions may result in injury to either a patient or a staff member. This paper is based on experience with linear accelerators from one manufacturer, but similar conditions are likely to exist with other radiation machines. A simple technical modification is offered which improves both accuracy and reproducibility in the placement of wedge-type filters. For our machines the solution also provides improved safety in the use of both wedge trays and block trays.

Equipment Design↗

PubMedDate not supplied

Verification data for electron beam dose algorithms.

The Collaborative Working Group (CWG) of the National Cancer Institute (NCI) electron beam treatment planning contract has performed a set of 14 experiments that measured dose distributions for 28 unique beam-phantom configurations that simulated various patient anatomic structures and beam geometries. Multiple dose distributions were measured with film or diode detectors for each configuration, resulting in 78, 2-D planar dose distributions and one, 1-D depth-dose distribution. Measurements were made for 9- and 20-MeV electron beams, using primarily 6 x 6- and 15 x 15-cm applicators at several SSDs. Dose distributions were measured for shaped fields, irregular surfaces, and inhomogeneities (1-D, 2-D, and 3-D), which were designed to simulate many clinical electron treatments. The data were corrected for asymmetries, and normalized in an absolute manner. This set of measured data can be used for verification of electron beam dose algorithms and is available to others for that purpose.

Algorithms↗

PubMedDate not supplied

Generation and use of measurement-based 3-D dose distributions for 3-D dose calculation verification.

A 3-D radiation therapy treatment planning system calculates dose to an entire volume of points and therefore requires a 3-D distribution of measured dose values for quality assurance and dose calculation verification. To measure such a volumetric distribution with a scanning ion chamber is prohibitively time consuming. A method is presented for the generation of a 3-D grid of dose values based on beam's-eye-view (BEV) film dosimetry. For each field configuration of interest, a set of BEV films at different depths is obtained and digitized, and the optical densities are converted to dose. To reduce inaccuracies associated with film measurement of megavoltage photon depth doses, doses on the different planes are normalized using an ion-chamber measurement of the depth dose. A 3-D grid of dose values is created by interpolation between BEV planes along divergent beam rays. This matrix of measurement-based dose values can then be compared to calculations over the entire volume of interest. This method is demonstrated for three different field configurations. Accuracy of the film-measured dose values is determined by 1-D and 2-D comparisons with ion chamber measurements. Film and ion chamber measurements agree within 2% in the central field regions and within 2.0 mm in the penumbral regions.

Humans↗

PubMedDate not supplied

Investigating the potential of three-dimensional treatment planning.

3-D treatment planning has received a great deal of attention in the radiation therapy community over the last several years. This new technology makes use of the continuous improvements in computer hardware and graphics capabilities, along with major improvements in treatment planning software, to provide a fully three dimensional simulation of the patient, radiation beams, and dose distributions which are used for radiation therapy of various cancers. With these capabilities, the physician and treatment planner may now optimize the radiation beams used to treat the patient much more effectively than in the past, when only a limited description of the patient, beams, and doses was available. This paper describes several of the new capabilities of these 3-D planning systems, some research studies which are currently being performed to evaluate the usefulness of the new technology, and finally some of the costs associated with its implementation.

Computer Simulation↗