G. Gademann

Computer systems and mechanical tools for stereotactically guided conformation therapy with linear accelerators

An integrated system for fractionated, stereotactically guided conformation radiotherapy has been developed. The system components are a stereotactic fixation system that can be used each treatment day, a localization, and positioning unit that can be used during x-ray computer tomography, magnetic resonance imaging, positron emission tomography, and radiographical examinations as well as for treatment. Conformal precision radiotherapy is planned with a new three-dimensional treatment planning system (Voxel-Plan-Heidelberg) which comprises, among others options, a three-dimensional image correlation procedure as well as routines for the calculation of coplanar and non-coplanar irradiations with irregularly shaped fields. Two different multi-leaf collimators have been designed for precision radiotherapy in the head and neck region. A manual multi-leaf collimator is used for irradiations with stationary beams or for moving beam treatments with invariable irregularly shaped fields. This collimator system is now being used for patient treatments. The design of a computer controlled multi-leaf collimator unit for multiple fixed field irradiation techniques is discussed. All system components are aimed at conforming dose distributions for fractionated radiotherapy treatments to the target to improve sparing of adjacent normal tissues, and at achieving a sufficient geometrical accuracy in the dose application.

Stereotactically guided fractionated radiotherapy: technical aspects.

A system for high precision radiotherapy in the head and neck region has been developed. The components of the system are a head mask connected to a stereotactic frame, a localization unit that can be used during CT- and MR-imaging and a stereotactic target positioner. Conformal precision radiotherapy is planned with a new treatment planning system (Voxelplan-Heidelberg). Three different multi-leaf collimator systems are used. An evaluation of the precision and accuracy of the head fixation system, which was performed with a photogrammetry system, is presented.

Fractionated stereotactically guided radiotherapy of head and neck tumors: a report on clinical use of a new system in 195 cases

Between November 1988 and December 1992, 195 patients with tumors of the head and neck (low grade gliomas, meningiomas, neurinomas, chordomas and miscellaneous) were treated with a newly developed stereotactical system for fractionated, conformal, high-precision radiotherapy. The overall preparation time, including head mask production for fixation, CT, MRI, 3-D treatment planning and stereotactical localisation could be reduced to 4-5 h per patient. The use of MR in the target definition was increased to a mean of about 60%. The medial follow-up time is 22 months. Three different patient groups were selected according to pretreatment. Patients with full high-precision radiotherapy survived in 95% of cases, patients with boost treatment in 86% and patients with preirradiated recurrent disease in 64%. Meningiomas as the largest histology group (n = 62) showed partial response in 27% and complete response in 10% of cases. Progression occurred in two patients. All patients are alive. Acute side-effects were minimal and of the order of 10%, no late complications occurred despite tumor doses ranging up to 72 Gy. High-precision radiotherapy as it is performed in Heidelberg can be regarded as an effective, reliable and tolerable system for selected tumors of the head and neck.

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.

Impact of hyperthermic regional perfusion therapy on cell metabolism of malignant melanoma monitored by 31P MR spectroscopy

For the first time, the influence of hyperthermic regional perfusion therapy on tumor cell metabolism has been monitored by means of 31P MR spectroscopy. Shortly after treatment, a complete depletion of high energy phosphates, a significant increase of inorganic phosphate, phosphomono- and phosphodiester resonances and a decrease of pH have been observed. Healthy muscle tissue showed only minor effects caused by this aggressive therapy. The time course of the transient variation of phosphate metabolite concentrations is explained in the framework of a simple pathophysiological model. The results demonstrate that the imediate effect of chemotherapy on tumor tissue can be detected by 31P MRS before any clinical signs of tumor response are visible.

CHARGED PARTICLE THERAPY TO PEDIATRIC TUMORS OF THE RETROPERITONEAL REGION: A POSSIBLE INDICATION

Despite a very successful interdisciplinary therapy regimen for pediatric solid tumors dominated by surgery and chemotherapy, the role of radiotherapy might become again more important if new techniques will allow a better dose localization to the target volume combined with a better protection of the normal tissue. This characteristic is known for charged particle beams. In a field study based on German cooperative trials, the possibility of a charged particle radiotherapy to retroperitoneal tumors of childhood will be discussed regarding indications in risk groups and recurrences. Absolute patient numbers are estimated from the clinical experiences and the incidences of the diseases. A stepwise introduction of this new therapy modality is proposed.

A 3D T1-weighted gradient-echo sequence for routine use in 3D radiosurgical treatment planning of brain metastases: first clinical results

The authors report on a 3D sequence for MRI of the brain and its application in radiosurgical treatment planning of 35 brain metastases. The measuring sequence, called magnetization — prepared rapid gradient echo (MPRAGE), was compared with 2D T1-weighted spin-echo (SE) sequences following intravenous contrast-medium application in 19 patients with brain metastases. The average diameter of all lesions was similar in both sequences, with 16.8 and 17.0 mm for SE and MPRAGE, respectively. Target point definition was equal in 29 metastases, and in 6 cases superior on MPRAGE, due to better gray-white matter contrast and increased contrast enhancement. In cases of bleeding metastases there was improved depiction of internal structures in 3D MRI. Postprocessing of 3D MPRAGE data created multi-planar reconstruction along any chosen plane with isotropic spatial resolution, which helped to improve radiosurgical isodose distribution in 4 cases when compared to 2D SE. However, sensitivity of 3D MPRAGE to detect small lesions (< 3 mm) was decreased in one patient with more than 50 metastases. We conclude that 3D gradient-echo (GE) imaging might be of great value for radiosurgical treatment planning, but does not replace 2D SE with its current parameters.

Therapieverlaufskontrolle nach Chemotherapie an Tumoren des Menschen mit Hilfe der In-vivo-31P-Spektroskopie

Die Therapieverlaufskontrolle ist eine Routineaufgabe in der onkologischen Praxis und wird vorwiegend mit bildgebenden Verfahren durchgefuhrt. Der Kontrollparameter ist im allgemeinen die Tumorgrose. Die Grosenreduktion des Tumors setzt im allgemeinen erst in einem Zeitraum von mehreren Tagen – meist Wochen – nach Beginn der Therapie ein.

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].

Radiodiagnostics and Radiotherapy

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.