R. Engenhart

Stereotactic single high dose radiation therapy of benign intracranial meningiomas

Seventeen patients with intracranial meningiomas were treated with single high dose irradiation at the German Cancer Research Center in Heidelberg. Indications for radiosurgery included unresected tumors, gross disease remaining despite surgery, and recurrences. Therapy was carried out by a technique using multiple non-coplanar arc irradiations from a 15 MeV linear accelerator. This technique coupled with secondary tungsten collimators allowed a high concentration of the dose in the target volume with an extremely steep dose gradient at the field borders. The patients were treated with a single irradiation dose ranging from 10 to 50 Gy (mean of 29 Gy). Four of 17 patients died: one death was tumor-related and not attributable to the treatment, one died of a treatment related complication, and two patients died of intercurrent diseases. The remaining 13 of the 17 patients with a median follow-up time of 40 months have no evidence of tumor relapse. Late severe side effects include five patients with a large area of brain edema, three of which were concurred with tumor necrosis. We conclude from these initial data that single high doses of irradiation concentrated to the tumor volume by stereotaxic methods can achieve local tumor control. It is also clear from these data that the effective therapeutic dose range must be better defined.

The role of high-dose, single-fraction irradiation in small and large intracranial arteriovenous malformations

PURPOSE Radiosurgery with external beam irradiation is an accepted treatment for small intracranial vascular malformations. It has been proven effective and safe for lesions with volumes of less than 4 cc. However, there is only some limited clinical data for malformations of grade 4 and grade 5, according to Spetzler and Martin. METHODS AND MATERIALS At the Heidelberg radiosurgery facility equipped with a linear accelerator, 212 patients with cerebral arteriovenous malformations have been treated since 1984. Thirty-eight percent of the arteriovenous malformations treated were classified inoperable, 14% grade 5, 19% grade 4, and 29% grades 1-3. Radiation doses between 10 and 29 Gy were applied to the 80% isodose contour. RESULTS Above a threshold dose of 18 Gy, the overall obliteration rate was 72%. After 3 years, the obliteration rates were 83% with volumes of less than 4.2 cc, 75% with volumes of up to 33.5 cc, and 50% with volumes of up to 113 cc. Of the patients presenting with seizures and paresis, 83% and 56%, respectively, showed improvement, which correlated with the degree of obliteration. After a follow-up period of up to 9 years, the rate of radiation-induced severe late complications was 4.3%. In grade 5 lesions, the risk of side effects was 10%. No serious complications occurred if a maximum dose of less than 25 Gy was applied to treatment volumes of less than 33.5 cc. CONCLUSION The success of stereotactic high-dose irradiation of arteriovenous malformations depends on the dose applied. The incidence of radiation-induced side effects increased with the applied dose and treatment volumes. From our experience, doses of less than 25 Gy and treatment volumes of up to 33.5 cc are safe and effective. In the future, new techniques of radiosurgery with linear accelerators and dynamically reshaped beams will allow us to apply homogenous dose distributions. Additional use of magnetic resonance angiography for 3D treatment planning will help to identify the nidus more easily.

Use of MR angiography for stereotactic planning.

With the introduction of MR angiography (MRA) into clinical routine MR protocols, it has become possible now to image flowing as well as stationary tissue with excellent contrast using a single modality. This has opened up new perspectives for planning stereotactic approaches, which are characterized by high risks for damaging intracerebral vessels or vital brain structures. In this article we present an MRA based planning method for the treatment of arteriovenous malformations by stereotactic radiosurgery. It includes flow compensated gradient echo pulse sequences for the acquisition of angiographic MR datasets, a stereotactic MR marker system, an algorithm for the correction of geometric distortion of MR image data, and a three-dimensional workstation system for the creation and evaluation of treatment plans. The latter is based on the concept of simultaneously displaying both MR slice and angiographic projection images. This allows the evaluation of intracerebral vasculature together with brain anatomy. The MRA guided planning approach was tested and compared to a conventional X-ray angiographic technique in a clinical study. Our satisfactory results suggest that MRA is a technique that can be used advantageously for stereotactic planning.

3d tof mr angiography of cerebral arteriovenous malformations after radiosurgery

To investigate the potential of three-dimensional time-of-flight MR angiography (MRA) to complement SE imaging, 18 patients with intracerebral arteriovenous malformations were prospectively followed after undergoing radiosurgery. Vessel occlusion after stereotaxic single high dose radiotherapy develops slowly. The MRA detected signs of nidus obliteration earlier and with a higher sensitivity than did SE imaging. Six months after radiosurgery, MRA showed a reduction of the nidus flow signals in nine patients and after 1 year it showed reduction in 15 of the 18 patients. As shown by MRA, the loss of flow signals was related to a reduction of the nidus size in 4 patients after 6 months and in 11 after 1 year. The SE imaging revealed a reduction of the nidus size in only two patients after 6 months and in eight after 1 year. The signal intensity of the feeding arteries was reduced in nine patients and that of the draining veins was reduced in six. The T2-weighted images exhibited white matter lesions in eight patients after 1 year. For complete follow-up, SE imaging should be performed together with MRA.

Functional magnetic resonance imaging in a stereotactic setup

The localization of critical structures within the brain is important for the planning of therapeutic strategies. Functional MRI is capable to assess functional response of cortical structures to certain stimuli. The authors present two techniques for functional MRI (fMRI) in a stereotactic set-up. The skull of the patients has been immobilized for stereotactic treatment planning either with a self developed stereotactic ceramic frame and bony fixation or with an individual precision mask system made of light cast. It has been shown that this frame does not produce any image distortion. fMRI was performed using a modified FLASH sequence on a conventional 1.5 T MRI scanner with a specially developed linear polarized head coil. The imaging technique used was an optimized conventional 2D and 3D, first order flow rephased, gradient echo sequence (FLASH) with fat-suppression and reduce bandwidth (16-28 Hz/pixel) and TR = 80-120 ms, TE = 60 ms, flip angle = 40 degrees, matrix = 128 x 128, FOV = 150-250 mm, slice-thickness = 2-5 mm, NEX = 1, and a total single scan time for one image of about 7 sec. The motor cortex stimulation was achieved by touching each finger to thumb in a sequential, self-paced, and repetitive manner. Statistical parametric maps based on students test were calculated. Pixels with a highly significant signal increase (p < 0.001) are overlaid on T1w SE images. The primary motor and sensory cortex could be visualized with this method in all 10 patients that were imaged in this study. Due to tight fixation of the patients skull there have been no motion artifacts. These results show that functional MRI is feasible in an stereotactic set-up with an standard 1.5 T scanner. This is a prerequisite for the exact pre therapeutic assessment of the function of cortical centers.

Radiologische Diagnostik und Therapie

Die Radiologie ist eines der wichtigsten Fachgebiete fur die Erkennung, Behandlung und Verlaufskontrolle von Krebserkrankungen. Die Fachbezeichnung Radiologie schliest heute neben den bekannten rontgenologischen Diagnose- und Therapieverfahren auch jene neuen Methoden ein, bei denen nichtionisierende Strahlen zum Einsatz kommen.

Radiological Diagnostics and Therapy

Radiology is one of the most important specializations in medicine for the detection, treatment, and follow-up of cancer diseases. Today, radiology not only encompasses conventional radiological methods of diagnosis and therapy, but also advanced techniques that make use of non-ionizing forms of radiation.

Positron Emission Tomography Studies of Tumor Metabolism: A Prognostic Factor in High-Dose Radiotherapy of Recurrent Rectal Cancer?

Rectal recurrence following a complete resection of a rectal carcinoma accounts for about 50% of all tumor-related deaths in this tumor [12, 13]. These occur with an incidence of 20%–50%, depending on tumor stage, grade, and therapy procedure [9, 19]. About 70%–80% occur within the first 2 years following primary surgery. Radiotherapy is known to be the most effective treatment modality for rectal recurrence, with symptomatic response rates of 50%–90%, but the palliative effect lasts only about 6 months. Because rectal recurrence seems to be relatively radioresistant compared with the primary disease, high linear energy transfer (LET) radiation should bring better results. Based on clinical and radiobiological observations, it has been suggested that patients with macroscopic recurrence may benefit from neutron therapy. An improvement in symptomatic response compared with photon therapy has been reported [2, 3, 4, 5].

External Stereotactic Focal Irradiation

“Radiosurgery” is a somewhat provocative term for a special concept of radiotherapy (Leksell 1951). It describes a percutaneous, stereotactically guided irradiation delivering a single high dose with collimated narrow beams. The precise stereotactic localization of the target point and a steep dose gradient outside the target volume allow the administration of high doses to a lesion without damage of adjacent normal tissue.

Side Effects of High-Dose Radiation Therapy of Soft-Tissue Sarcoma with 14 MeV DT Neutrons: A Correlation to Irradiated Volume

Soft-tissue sarcomas (STS) are a highly heterogeneous group of malignant tumors of mesodermal origin with some contribution from neuroectoderm. STS are classified on a histogenetic basis according to the adult tissue which they resemble, and the tumors are capable of invasive or destructive growth as well as recurrence and distant metastasis. These tumors may occur anywhere in the body, but the majority arise from the large muscles of the extremities [3]. The most important consideration in determining the patient’s prognosis and the treatment strategy is the histological grading [1, 2]. To gain local control a radical surgery is necessary [1, 6, 11, 13], but achievement of safe margins is often limited. Radiotherapy is a potent and well-accepted treatment modality. Even in those patients in whom surgical treatment was not possible, a response of the tumor and significant local control rate following high-dose irradiation has been reported [5]. Radiobiology gave reasons for the use of fast neutrons in STS. Several authors have reported superior results of neutron therapy, compared to photon therapy, especially in those patients with low-grade STS [4, 6, 7, 9–12].