Biomedical subjects

B A Fraass

Publications and source records attributed to B A Fraass.

At least 55 records · Page 3Linked to original sources

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↗

PubMed1987

Is correction for lung density in radiotherapy treatment planning necessary?

From 1978-981 a series of 30 patients with cancer of the esophagus were treated at the National Cancer Institute. Each of these patients had a CT scan of the chest taken in the treatment position, but prior to any treatment being given. Using these scans a retrospective analysis of the effect of lung density on delivered dose was performed. This indicated that failure to correct for tissue inhomogeneity results in a much higher dose being delivered than is prescribed. This effect is dependent on the energy of the beam being used for treatment; it may exceed 30% for 60Co. It also showed that there is wide patient to patient variation in lung density and that this variation is non-randomly distributed. The average lung density in his group of patients was 0.21 compared to the standard estimate of 0.35 but some had densities substantially lower than this, these being the patients with the largest lung volumes. This variability acts to further increase the discrepancy between prescribed and delivered dose even in a very homogeneous group of patients being treated under identical conditions for the same malignancy. The implications of this for future clinical trials in thoracic malignancies are discussed.

Adult↗

PubMed1987

Integration of magnetic resonance imaging into radiation therapy treatment planning: I. Technical considerations.

This paper presents the results of a feasibility study specifically addressing the technical and operational difficulties in making quantitative use of Magnetic Resonance Imaging (MRI) in radiation therapy treatment planning (RTTP). Selected radiotherapy patients have been studied with both CT and MRI as part of the treatment planning process. Both sets of images, along with mechanically-obtained external contour and simulator film data, are entered into the treatment planning system. All of the capabilities of the fully three dimensional planning system U-MPlan are available to both the CT and MRI images, in which any image can be used as the backdrop for interactive beam positioning, beam portal simulation, and dose distribution displays for external beam and brachytherapy applications in both 2- and 3-dimensionally-oriented displays. The study has shown that to use MRI data for RTTP, one must (a) use careful patient positioning and marking, (b) transfer information from CT to MRI and vice versa, (c) determine the geometrical consistency between the CT and MR data sets, (d) investigate the unwarping of distorted MR images, and (e) have the ability to use non-axial images for determination of beam treatment technique, dose calculations, and plan evaluation.

Brain Neoplasms↗

PubMed1985

The imaging revolution and radiation oncology: use of CT, ultrasound, and NMR for localization, treatment planning and treatment delivery.

The explosion of new imaging technologies such as X ray computed tomography (CT), ultrasound (US), positron emission tomography (PET), and nuclear magnetic resonance imaging (NMR) has forced a major change in radiation therapy treatment planning philosophy and procedures. Modern computer technology has been wedded to these new imaging modalities, making possible sophisticated radiation therapy treatment planning using both the detailed anatomical and density information that is made available by CT and the other imaging modalities. This has forced a revolution in the way treatments are planned, with the result that actual beam configurations are typically both more complex and more carefully tailored to the desired target volume. This increase in precision and accuracy will presumably improve the results of radiation therapy.

Breast Neoplasms↗

PubMed1985

Dose to the contralateral breast due to primary breast irradiation.

The radiation dose received by the contralateral breast during primary breast irradiation is of concern because breast tissue is subject to cancer induction from low to moderate doses of radiation. In this paper the dose to the opposite breast has been studied in detail for common breast treatment techniques. Measurements have been made on 16 patients, a water phantom, a polystyrene phantom with cork inserts to simulate lung tissue, and a body-shaped phantom with wax breasts. Thermoluminescent dosimeters (TLD), ion chambers, diodes, and film have been used in the various configurations. The patient measurements have shown that there is a wide variation in the opposite breast dose received by patients, even when all are treated with, for example, tangential fields alone. Addition of more radiation fields, such as supraclavicular/axillary and internal mammary fields, may increase the dose to the opposite breast for a particular patient. Variations in the details of the technique such as what wedges are used, the use of blocks, and the orientation of the field edges are all important to the final dose received by the patient's contralateral breast. With the phantom measurements, it has been possible to determine the contributions to the opposite breast dose from each of the relevant factors. This makes it possible to explain the wide variation in patient dose measurements, and to make some relatively simple recommendations that will allow the reduction of the dose to the opposite breast from several hundred cGy to about 50 cGy for a typical treatment course dose of 5000 cGy.

Breast↗

PubMed1985

Peripheral dose to the testes: the design and clinical use of a practical and effective gonadal shield.

A simple and practical gonadal shield has been developed for use near megavoltage radiation fields. The lead shield encloses only the testes, allowing its use with nearly any radiation field that does not include the testes. The dose to the testes with and without the shield has been measured extensively both in phantoms and on patients. The gonadal shield allows a 3 to 10-fold reduction in dose to the testes depending primarily on the distance from the field edge to the gonads. When the shield is used, the gonadal dose is always less than 1% of the patient's prescription dose. Based on our patient studies of testicular injury following conventionally-fractionated irradiation, a dose of less than 50 cGy (1% of a typical 5000 cGy treatment regimen) should preserve normal testicular function.

Adolescent↗

PubMed1985

Intraoperative radiation therapy at the National Cancer Institute: technical innovations and dosimetry.

The technical complexity of intraoperative radiotherapy (IORT) requires modification of the standard physical and dosimetric methods used in external electron beam therapy. At the National Cancer Institute, a number of technical innovations have been integrated into ongoing clinical studies of IORT. These include: (1) an electron beam applicator system that is significantly different from other IORT systems and includes customized "squircle" applicators; (2) peripheral dose shields; (3) a modified surgical table replacing the standard radiation treatment couch; and (4) routine use of multiple IORT fields that necessitates field matching. The IORT applicator system and related devices and techniques are dosimetrically characterized in detail both for use in the IORT program and in order to illustrate many useful facets of electron dosimetry.

Electrons↗

PubMed1985

Effects of fractionated irradiation of endocrine aspects of testicular function.

We have examined the hormonal alterations of testicular function in 27 males (14 to 67 years of age) with soft-tissue sarcoma who were treated with surgery and high-dose radiation to the tumor bed. The testicular dose from scatter radiation ranged from 1 to 2,500 rad. There was a dose-dependent increase in the median per patient difference from baseline in serum follicle-stimulating hormone (FSH) values following irradiation, with the maximal difference seen at 6 months. Recovery of serum FSH level was biphasic with a decline in the median difference in values between 6 and 12 months, followed by a gradual descent toward baseline. Only patients receiving less than 50 rad show early complete recovery 12 months after radiation therapy. Radiation injury also induced dose-dependent increases in serum luteinizing hormone (LH) concentration, with the maximal median difference from baseline level occurring at 6 months. Only those patients receiving greater than 200 rad showed statistically significant LH changes from baseline levels at each time interval up to 30 months. No significant changes were observed in total testosterone values. These data provide quantitative guidelines for predicting seminiferous tubule injury and germ cell depletion in men exposed to fractionated radiation. The effects on seminiferous tubule and Leydig cell function, as judged by serum FSH and LH concentrations, suggest that subtle Leydig cell dysfunction, in addition to germ cell depletion, may also occur at exposures greater than 200 rad.

Adolescent↗

PubMed1983

Clinical use of a match-line wedge for adjacent megavoltage radiation field matching.

The divergence and sharp penumbra of linear accelerator beams pose notorious problems when joining such beams side by side. One way of reducing the dose distribution nonuniformity in the matching region is to create a wide pseudo-penumbra with the use of a "match-line wedge." A single match-line wedge shape has been developed for 6 MV and 10 MV photon beams. The wide pseudo-penumbra created by the wedge drastically reduces the effect of random set-up errors. Special attention has been paid to ensure simple and reliable clinical use of the wedge. Details of the design, construction, dosimetry, and rules of practical application are presented. Comparisons of several matching methods are made.

Film Dosimetry↗

PubMed1983

A technique for field matching in primary breast irradiation.

The intrinsic divergence of photon beams presents serious matching problems in three-field treatment of the breast and the adjoining supraclavicular area. A method is presented in which appropriate beam blocking combined with suitable isocentric rotation of the treatment couch neutralize the affects of divergence so that proper matching is achieved at all depths. The geometric principles and the set-up procedures are discussed and illustrated.

Breast Neoplasms↗

PubMed1983

Extremity preservation by combined modality therapy in sarcomas of the hand and foot: an analysis of local control, disease free survival and functional result.

A primary tumor arising in the hand or foot represents an uncommon presentation for patients with Ewing's sarcoma (ES) or soft tissue sarcoma (STS). While there exists considerable literature on the treatment of extremity sarcomas, very little deals specifically with lesions of the hand or foot. It remains controversial whether these lesions can be successfully treated with combined modality therapy which preserves the extremity and maintains function. From 1972 to 1979, 10 patients with sarcomas arising in the hand or foot were treated with combined modality therapy at the National Cancer Institute. Seven patients with ES of bone received local irradiation to 5000 rad and combination chemotherapy following an incisional biopsy. Three patients with STS received a gross tumor excision and local irradiation to 6000 rad. One STS patient also received combination chemotherapy. Local control was achieved in nine patients (90%) with a follow-up of 30-119 months (median 56 months). These patients have complete or almost complete function of the treated extremity. Nine patients are alive with five patients remaining disease-free following the initial combined modality treatment. Two patients with Ewing's sarcoma relapsed (1 patient with both local and distant failure) at 26 and 58 months and were again rendered disease-free with surgery, total body irradiation and further chemotherapy. One patient relapsed for a second time, being disease-free from the first relapse for 30 months. We conclude that for selected patients with sarcomas arising in the hand or foot, combined modality therapy which leaves the extremity intact results in excellent local tumor control and preserves function. Careful treatment planning is an essential aspect of successful radiation therapy of a hand or foot primary. Our treatment recommendations are outlined. This approach is a viable alternative to amputation in these patients.

Adolescent↗

PubMed1983

Television system for verification and documentation of treatment fields during intraoperative radiation therapy.

Intraoperative radiation therapy (IORT) involves direct treatment of tumors or tumor beds with large single doses of radiation. The verification of the area to be treated before irradiation and the documentation of the treated area are critical for IORT, just as for other types of radiation therapy. A television system which allows the target area to be directly imaged immediately before irradiation has been developed. Verification and documentation of treatment fields has made the IORT television system indispensable.

Intraoperative Care↗