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Radiosurgery of meningiomas.

In early experience, radiosurgery proved to be a relatively safe and effective therapy for selected patients with symptomatic meningiomas, including those for whom surgical resection failed. Radiosurgery also has been an effective primary treatment alternative for patients whose advanced age, medical condition, or high-risk tumor location preclude microsurgery. The long-term response to treatment, as defined by imaging and clinical findings, is not yet available. In addition, further clinical and laboratory work is necessary to determine the appropriate tumoricidal radiosurgical dose, dose-volume relationships for individual tumors, and the variable radiation tolerance of the different brain structures that closely surround meningiomas.

Follow-Up Studies↗

The role of radiosurgery in the treatment of malignant brain tumors.

Most studies describing the results of radiosurgery have concentrated on the definitive treatment of small, histologically benign lesions such as vascular malformations, acoustic neurinomas, and pituitary adenomas. More recently, the role of radiosurgery using the gamma knife or LINAC-based systems to treat malignant neoplasms has become better defined. Most solitary metastases, ependymomas, well-circumscribed (on imaging studies) AAs, and a few glioblastomas (and other tumors) have responded dramatically to radiosurgery. Provided that the tumor volume was small (less than or equal to 14 cm3; 30-mm diameter), radiosurgery safely has caused tumor disappearance, shrinkage, or stabilization, regardless of prior surgery, conventional fractionated irradiation, or tumor radioresistance. For patients with recurrent or persistent, small, malignant intracranial tumors, radiosurgical treatment has obviated the need for prolonged hospitalization and has eliminated the risks associated with general anesthesia and open craniotomy.

Adolescent↗

Stereotactic radiosurgery for pineal region tumors.

Our present treatment strategy for treating pineal region tumors is shown in Figure 5. We believe that stereotactic biopsy should be the first procedure in pineal region tumors so that a histologic diagnosis can be obtained. Based on the biopsy findings, the appropriate subsequent therapy, whether microsurgery, fractionated irradiation, or stereotactic radiosurgery, can be administered. Although our experience currently is limited to nine patients, we have found that stereotactic radiosurgery is a valuable alternative to microsurgery in the treatment of selected pineal region tumors.

Adolescent↗

Physics and dosimetry of the gamma knife.

Since 1968, the gamma knife has been one of the major radiosurgical devices. Although approximately 4300 patients worldwide had been treated with the gamma knife units through June 1990, gamma knife installments in the United States are still rather scarce compared to linear accelerators adapted for radiosurgery. This article describes the basic physical characteristics of the gamma knife, patient set-up procedures, the existing treatment-planning system, the measurements of dosimetry and physical parameters, dose delivery accuracy, and quality assurance procedures. It also includes a vision of future developments and improvements in these areas.

Brain Neoplasms↗

Dose prescription and dose-volume effects in radiosurgery.

The optimal use of radiosurgery as a treatment technique requires thorough planning, including careful fitting of the high-dose treatment volume to the target volume, and an understanding of the effects of high-dose single-fraction irradiation on both the target volume and the surrounding normal brain. The integrated logistic formula appears to be useful as an aid for predicting the risks of complications from radiosurgery, but greater understanding of the radiation tolerance for all the different areas of the brain (particularly the cranial nerves) is needed. The risk of developing MR imaging-defined changes after radiosurgery for AVMs was significantly related to predictions from the integrated logistic formula. The obliteration rate of AVMs after radiosurgery was volume dependent. Our assessment of the integrated logistic formula to date also indicates that it provides a reasonable guide for predicting complications in the radiosurgical treatment of meningiomas and in the treatment of solitary brain metastases using a combination of fractionated whole-brain irradiation and radiosurgery. The formula did not adequately predict complications in the treatment of AOVMs, however. In the treatment of acoustic tumors, the risks of injury to cranial nerves V, VII, and VIII clearly varied with treatment volume. Further data are needed to fully understand the therapeutic dose-response functions and volume effects for the obliteration of AVMs, the prevention of rebleeding from AOVMs, and growth arrest of meningiomas and acoustic neuromas.

Brain Neoplasms↗

Stereotactic radiosurgery of brain vascular malformations.

Stereotactic radiosurgery using the gamma unit was performed in 251 patients with brain vascular malformations in a 3-year interval. Our efforts include the identification of factors related to both success and complications, including analysis of the malformation location, volume, and dose used. Radiosurgery is a valuable alternative treatment for many patients with brain vascular malformations, including those currently believed to be poor surgical candidates.

Adolescent↗

Physics for radiosurgery with linear accelerators.

Radiosurgery had a long development period and, for more than three decades, was used only in a few specialized centers around the world. The development of LINAC-based radiosurgical techniques combined with the concurrent advances in imaging modalities during the 1980s, however, caused so much interest in this treatment modality that most major radiotherapy centers now offer this service or at least plan to offer it in the near future. When considering a LINAC for radiosurgical use, one should remember that technical and clinical requirements for accurate radiosurgery are far more stringent than those applied to standard radiotherapy. This is because in radiosurgery, the targeted volumes are much smaller and the dose is usually delivered in a single irradiation session, whereas in radiotherapy, the dose is delivered to a relatively large target volume on a fractionated basis. Linear accelerator-based radiosurgery broadens the scope of radiotherapy departments. The impetus to introduce this service at a medical center usually comes from neurosurgeons, however. Even after the service becomes routine at an institution, it is the neurosurgeon who refers the patient and who plays the most important role in determining the target volume and its location within the brain. The decision on the choice of isodose surface and the prescribed dose, however, belongs to the radiotherapist. It is becoming clear that radiosurgery is a complex treatment modality for which a successful outcome requires a collaborative team effort by several hospital-based professionals, including neurosurgeons, radiation oncologists, neuroradiologists, and medical physicists. As in standard radiotherapy, physics plays an important role in radiosurgery, not only in the development of target localization, treatment-planning, and dose delivery techniques, but also in the actual patient contact, from the diagnostic target localization procedures, through treatment planning, to patient preparation on the device and dose delivery.

Brain Neoplasms↗

Charged-particle radiosurgery for intracranial vascular malformations.

Heavy charged-particle radiation has unique physical characteristics that offer several advantages over photons and protons for stereotactic radiosurgery of intracranial AVMs. These include improved dose distributions with depth in tissue, small angle of lateral scattering, and sharp distal fall-off of dose in the Bragg ionization peak. Under multi-institutionally approved clinical trials, we have used stereotactic helium-ion Bragg peak radiosurgery to treat approximately 400 patients with symptomatic, surgically inaccessible vascular malformations at the UCB-LBL 184-in synchrocyclotron and bevatron. Treatment planning for stereotactic heavy charged-particle radiosurgery for intracranial vascular disorders integrates anatomic and physical information from the stereotactic cerebral angiogram and stereotactic CT and MR imaging scans for each patient, using computerized treatment-planning calculations for optimal isodose contour distribution. The shape of an intracranial AVM is associated strongly with its treatability and potential clinical outcome. In this respect, heavy charged-particle radiosurgery has distinct advantages over other radiosurgical methods; the unique physical properties allow the shaping of individual beams to encompass the contours of large and complexly shaped AVMs, while sparing important adjacent neural structures. We have had a long-term dose-searching clinical protocol in collaboration with SUMC and UCSF and have followed up over 300 patients for more than 2 years. Initially, treatment doses ranged from 45 GyE to 35 GyE. Currently, total doses up to 25 GyE are delivered to treatment volumes ranging from 0.1 cm3 to 70 cm3. This represents a relatively homogeneous dose distribution, with the 90% isodose surface contoured to the periphery of the lesion; there is considerable protection of normal adjacent brain tissues, and most of the brain receives no radiation exposure. Dose selection depends on the volume, shape, and location of the AVM and several other factors, including the volume of normal brain that must be traversed by the plateau portion of the charged-particle beam. The first 230 patients have been evaluated clinically to the end of 1989. Using the clinical grading of Drake, about 90% of the patients had an excellent or good neurologic grade, about 5% had a poor grade, and about 5% had progression of disease and died, or died as a result of unrelated intercurrent illness. Neuroradiologic follow-up to the end of 1989 indicated the following rates of complete angiographic obliteration 3 years after treatment: 90% to 95% for AVM treatment volumes less than 4 cm3, 90% to 95% for volumes 4 to 14 cm3, and 60% to 70% for volumes greater than 14 cm3.(ABSTRACT TRUNCATED AT 400 WORDS)

Adult↗

A megavoltage CT scanner for radiotherapy verification.

We have further developed a system for generating megavoltage CT images immediately prior to the administration of external beam radiotherapy. The detector is based on the scanner of Simpson (Simpson et al 1982)--the major differences being a significant reduction in dose required for image formation, faster image formation and greater convenience of use in the clinical setting. Attention has been paid to the problem of ring artefacts in the images. Specifically, a Fourier-space filter has been applied to the sinogram data. After suitable detector calibration, it has been shown that the device operates close to its theoretical specification of 3 mm spatial resolution and a few percent contrast resolution. Ring artefacts continue to be a major source of image degradation. A number of clinical images have been presented. The next stage of this work is to use the system to make clinical measurements of patient set-up inaccuracies building on our work making such measurements from digital portal images (Evans et al 1992).

Evaluation Studies as Topic↗

Limited-angle 3D reconstruction of PET images for dose localization in light ion tumour therapy.

In vivo dose localization in light ion tumour therapy can be performed by measuring the range distributions of beta+ active ions in tissue employing positron emission tomographic techniques. For this purpose a multiplicative iteration scheme for reconstructing three-dimensional images from shift-variant, limited-angle data is presented. In the iterative correction steps the algorithm uses the geometric means of quotients calculated from the three-dimensional Radon transforms of the backprojected measured and approximated source distributions. When sources measured with poor statistics are reconstructed, an effective noise suppression is achieved.

Algorithms↗

Radiotherapy technique integrates MRI into CT.

The 1970s saw the introduction of computed tomography, which enabled soft tissue anatomy to be seen. Today simulation of therapeutic fields by x-ray is augmented by radiotherapy treatment planning using CT data. The 1980s brought magnetic resonance imaging with superior soft tissue contrast. This article describes a technique correlating three-dimensional MRI/CT data sets used routinely in treatment planning of tumors in the head.

Brain Neoplasms↗

High-performance computing in radiation cancer treatment.

In 1989 a consortium of the Radiation Oncology and Computer Science Departments at the University of North Carolina, BellSouth Corporation, GTE, and the MCNC was formed in response to the high-speed network initiative proposed by the National Science Foundation and the Defense Advanced Research Projects Agency. One of the purposes of this effort has been to demonstrate that applications exist that require gigabit per second networks. Our consortium, known as VISTAnet, proposed to use real-time radiation therapy treatment planning as the application that would require the use of a gigabit network. The plan was to develop a system that could rapidly calculate and display a three-dimensional radiation dose distribution for any configuration of radiation beams. The gigabit network would be used to tie the dose calculations done with the Cray Y-MP at the Research Triangle to the graphics engine at the Department of Computer Science (Pixel-Planes 5) and the medical workstation at Radiation Oncology. The system would then provide the radiation physician with the capability of considering hundreds of potential treatment plans, instead of the usual two or three, with the goal of arriving at a highly optimized plan within a few minutes.

Computer Communication Networks↗

Bayesian statistics: a guided tour.

An overview of Bayesian statistical decision theory is presented in the tutorial spirit. A section on fundamental principles is followed by selected applications of the Bayesian approach to parameter estimation, pattern recognition, image processing, computer-aided medical diagnosis, optimal diagnostic test selection, and radiotherapy treatment planning.

Decision Making↗

Computer-aided medical decision making in radiotherapy.

Radiotherapy departments are becoming sophisticated in working with computers for isodose computations, treatment machine verifications and administrative and medical records. The next step lies in computer-assisted medical decision making. The logic for a patient's diagnostic work-up and treatment protocol can be stored in a computer. It can then be used as an aid in making the diagnosis, in prescribing the treatment and for quality control. For patients who fit established protocols the computer can select and list treatment using the logic of that protocol. Such a system has been implemented for the postoperative radiotherapy of breast cancer on a trial basis. Its potential usefulness is illustrated by results in 25 consecutive patients. Physician acceptance and costs of the program are under investigation.

Breast Neoplasms↗

[Ultrasound in tumor diagnostics and treatment planning (author's transl)].

The fundamental requirements of irradiation planning are discussed delimitating the minimum and maximum demands of planning. Different possibilities to represent the topographic relations within the irradiation plane of the patient's cross-section are described. The computer-assisted system for irradiation planning, installed at our hospital by means of MAT construction, is discussed. A pathway is shown which leads to individual treatment planning and considers dosimetrically the actual conditions of the patient who will undergo radiation therapy. The possibilities and limits of ultrasonic cross-sectional imaging are demonstrated.

Diagnosis, Computer-Assisted↗

A finite-size pencil beam model for photon dose calculations in three dimensions.

A three-dimensional dose computation model employing a finite-size, diverging, pencil beam has been developed and is demonstrated for Cobalt-60 gamma rays. The square cross-section pencil beam is simulated in a semi-infinite water phantom by convolving the pencil beam photon fluence with the Monte Carlo point dose kernel for Cobalt-60. This finite-size pencil beam is calculated one time and becomes a new data base with which to build larger beams by two-dimensional superposition. The pencil beam fluence profile, angle correction for beam divergence, the Mayneord inverse square correction, radial and angular sampling rates, error propagation, and computation time have been investigated and are reported. Radial and angular sampling rates have a great effect on accuracy and their appropriate selection is important. Percent depth doses calculated by finite-size pencil beam superposition are within 1% of values calculated by full convolution and the agreement with values from the literature is within 6%. The latter disagreement is shown to be due to a low-energy photon component which is not modeled in other calculations. Computation time measurements show the pencil beam method to be faster than full convolution and one implementation of the differential-scatter-air-ratio (dSAR) method.

Cobalt Radioisotopes↗

Prognostic significance of DNA quantitation in stage D1 prostate carcinoma with the use of image analysis.

BACKGROUND: A characteristic feature of prostatic adenocarcinoma is its great variation in biologic behavior. This variation and the observation that most carcinomas are of intermediate grade make standard histologic grading of limited value in determining the prognosis of a patient. METHODS: DNA quantitation with the use of computer-assisted image analysis on Feulgen-stained nuclei was performed on the metastatic lymph nodes from patients with Stage D1 prostate carcinoma to determine whether ploidy was a useful predictor of survival or progression. The Gleason histologic score of the primary tumor, the number and extent of lymph node metastases, and the progression and survival intervals were documented. Treatment modalities included pelvic lymph node dissection, radical prostatectomy, external beam radiation therapy, and iodine 125 implantation. RESULTS: DNA ploidy quantitation showed that 65% (33 of 51) of cases were aneuploid, 2% (1 of 51) were tetraploid, and 33% (17 of 51) were in the diploid range. Progression to Stage D2 disease occurred in 76% of the patients with aneuploid cases and 53% of those with cases in the diploid range. CONCLUSION: There was a significant difference in progression between the two ploidy groups (Cox regression analysis, P less than 0.05).

Combined Modality Therapy↗

Computer-assisted 3D-reconstruction and statistics of the limbic system. 1. Computer-assisted 3D-reconstruction of the hippocampal formation, the fornix, and the mamillary bodies.

The hippocampal formation of eight perfusion-fixed human brains was examined using new methods according to stereotactic and morphometric principles (macrovibratome and computer-aided 3D reconstruction). The reconstructions form part of a neuroanatomical reference system (NeuRef). This reference system allows for 3D visualisation of the brain and its components on a computer graphic workstation, as well as for the presentation of the union set based on a neuroanatomical structure taken from this sample of brains. This retrievable knowledge of neurofunctional systems is important for the preoperative planning of neurosurgeons and the adjustment of radiotherapy.

Adult↗