Magnetic resonance imaging (MRI): considerations and applications in radiotherapy treatment planning

Aging changes in lumbar discs and vertebrae and their interaction: a 15-year follow-up study.

Das initiate Zielvolumen zur primaren Strahlentherapie von Bronchialkarzinomen wird meist anhand der Tumorausdehnung im CT bestimmt. Die transversale Schnittfuhrung erschwert hierbei die Umsetzung in die Simulation der Bestrahlungsfelder. Die MRT bietet durch den besseren Weichteilkontrast und die freie Wahl der Schnittebenen Vorteile. Mit der Entwicklung der Niederfeld-MRT-Systeme steht jetzt eine kostengunstige Alternative zur Verfugung. Ziel dieser Studie war die klinische Evaluierung eines offenen Niederfeld-MRT-Gerates in der Therapiesimulation von nichtkleinzelligen Bronchialkarzinomen. 15 Patienten mit primarer Strahlentherapie bei Bronchialkarzinom wurden mittels eines offenen Niederfeld-MRT (Picker Outlook, 0,23 T) untersucht. Die Fremd-CT-gestutzte Simulatortechnik wurde mit einem MRT-gestutzten Vorgehen verglichen. In Bestrahlungsposition angefertigte koronare native T1-gewichtete MRT-Schnitte wurden dazu subtraskopisch mit den Simulatoraufnahmen uberlagert. Die Niederfeld-MRT unter Verwendung von nativen T1-Sequenzen zeigte eine gute Abgrenzbarkeit des Tumorgewebes vom mediastinalen Fettgewebe und vom Gefas- und Bronchialbaum sowie eine gute Darstellung der feinen Tumorauslaufer ins Lungenparenchym. Die Wahl der Schnittfuhrung in der Simulationsebene erlaubte eine topographisch exakte und gut reproduzierbare Ubertragung des Tumors auf die Simulatoraufnahme. Insgesamt muste bei 5/15 Patienten aufgrund der MRT-Simulation eine Optimierung der Bestrahlungsfelder durchgefuhrt werden. Offene Niederfeld-MRT-Systeme konnen eine wertvolle Erganzung fur die Therapieplanung sein. Sie sind vergleichsweise kostengunstig. Bei der Bestrahlungsplanung von Bronchialkarzinomen erscheint die MRT-Simulation in speziellen Fallen sinnvoll, und sie ist klinisch anwendbar. Ein entscheidender Vorteil der offenen MRT gegenuber der CT und auch der geschlossenen MRT liegt in den freier wahlbaren Lagerungsmoglichkeiten des Patienten. The initial target volume for primary radiation therapy of lung cancer is usually determined with the aid of computed tomography. Due to the axial CT-scans the simulaton of the RT-field is often difficult. MRI in its superior ability to demonstrate and characterize soft tissue and its possibilities of multiplanar imaging can be beneficial. As MRI is less available and more expensive the use of MRI in radiotherapy planning is still restricted. With the introduction of open low-field MRI-systems there is now a cost-saving alternative. The aim of this study was the clinical evaluation of the use of a new open low-field MRI in radiotherapy planning of bronchogenic cancer. Fifteen patients undergoing primary radiotherapy for lung cancer were studied using an open low-field MRI-system (Picker Outlook 0.23 Tesla). Conventional CT-assisted treatment planning was compared to a MRI-assisted procedure. Contours from coronary T1-weighted MRI-sections were superimposed onto the simulator radiograph using a subtrascope (MR-simulation). Open low-field MR-imaging using T1-weighted sequences resulted in excellent delineation of tumor masses from mediastinal fat, the airways and the vascular structures as well as the radial tumor infiltration into the vicinity of the lung (Figures la to 1c). This allowed an exact and reproducible transfer of tumor contours onto the simulator radiograph. The MR-simulation led to optimization in the field configuration in 5/15 patients (Figure 2). Open low-field MRI-systems can be very useful in treatment planning. They are less expensive and need less extensive rebuilding compared to high-field MRI-systems. In the radiotherapy planning of bronchogenic carcinoma the MR-simulation is reasonable and clinically practicable. One of the main advantages of open MRI-systems in comparison to CT and standard MRI-systems in radiotherapy planning is that there is a much greater variety of treatment positions.

MRT-Simulation von Bronchialkarzinomen mittels eines offenen Niederfeld-MRT

In radiotherapy of malignant lymphoma radiotherapy has been delivered using opposed AP/PA large fields on linear accelerators for more than 20 years (Hoppe 1987; Wannenmacher et al. 1978). A basic precondition for treatment planning has always been the adequate localization of lymphoma, lymph node bearing areas, and organs at risk, which may have to be shielded by individual blocking. The procedure of localization is performed based on clinical, pathological, and imaging information. As imaging technology has evolved dramatically during the past two decades with the introduction of computed tomography (CT), ultrasound, digital subtraction angiography, and magnetic resonance imaging (MRI), the role of imaging has changed — becoming the most important tool in the localization procedure for malignant lymphoma nowadays. Nevertheless, the most widespread basic procedure for treatment planning in malignant lymphoma remains fluoroscopic imaging on the therapy simulator (Hoppe 1987; Timothy et al. 1989; Wannenmacher et al. 1978). Tumor, target volume, and organs at risk are defined on the X-ray simulation film based on information about the localization of tumor and target which must be “translated” from transverse cross-sectional, parallel projected imaging (mostly CT) onto the centrally projected coronal X-ray images, the simulation films. This rather complicated translation procedure entails many uncertainties, in particular a considerable risk of mislocalization.

Technique of Magnetic Resonance Imaging Assisted Simulation Based on Direct Coronal Imaging for Treatment Planning of Supradiaphragmatic Malignant Lymphoma

D. Westrick

Papers

Technique of Magnetic Resonance Imaging Assisted Simulation Based on Direct Coronal Imaging for Treatment Planning of Supradiaphragmatic Malignant Lymphoma