Radiotherapy treatment simulation of bronchogenic carcinoma using an open low-field magnetic resonance system

Aim: The initial target volume for primary radiation therapy of lung cancer is usually determined with the aid of computed tomography. Due to the axia l CT-scans the simulaton of the RT-field is often difficult. MRI in its sup erior ability to demonstrate and characterize soft tissue and its possibili ties 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-s aving 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 c ancer. Patients and Methods: 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 we re superimposed onto the simulator radiograph using a subtrascope (MR-simul ation). Results: 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 1a to 1c). This allowed an exact and reproduc ible transfer of tumor contours onto the simulator radiograph. The MR-simul ation led to optimization in the field configuration in 5/15 patients (Figu re 2). Conclusions: Open low-field MRI-systems can be very useful in treatment pla nning. They are less expensive and need less extensive rebuilding compared to high-field MRI-systems. In the radiotherapy planning of bronchogenic car cinoma the MR-simulation is reasonable and clinically practicable. One of t he 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 o f treatment positions.