Three-dimensional movement of a liver tumor detected by high-speed magnetic resonance imaging
Introduction
Small field, high dose radiotherapy was reported to be useful for solitary liver tumors using convergent X-ray beams and sophisticated localization techniques [1], [2].
Three-dimensional conferral radiotherapy (3D CRT) is expected to be a new strategy to give higher dose to the target volume and reduced dose to normal tissues compared to conventional radiotherapy [3], [4]. Computed topographic (CT) images are used for the treatment planning and dose calculation of these treatments. Liver tumors are expected to be a good candidate for 3D CRT because they can be visualized well by computed tomography (CT). However, since the tumor may change location due to respiratory movement, uncertainty of CT planning is recognized as a major obstacle for 3D CRT of liver tumor [5].
It is desirable to determine the target volume taking into account the 3D respiratory movements of the clinical target volume. However, there has been little information about 3D movement of liver tumors. In this study, movement of a solitary liver tumour during respiration was investigated with MRI using a high-speed sequence.
Section snippets
Methods
The MRI study was performed in a patient with a solitary spherical metastatic liver tumor of nasopharyngeal carcinoma using a Magnetom Vision 1.5T MRI scanner (Siemens AG, Erlangen, Germany) and its whole-body coil. The patient was scanned in the supine position. A marker, which has five parallel bars in every 2 cm, was placed on the surface of the patient as a ruler for measuring purpose. Each bar can be seen as a dot on a MR image, when they are scanned vertically to their axis. A phased
Results
The tumor was well visualized with high speed MR imaging. Movements of tumor and liver contour in sagittal and coronal planes were visualized at a real-time rate (one image in 1.5 s) on the image viewer. It was apparent that the liver and the tumor contour moved not only in the cranio–caudal direction but also in the ventro–dorsal direction.
The 20 tumor contours extracted during the 30 seconds free-breathing period were superimposed on sagittal and coronal MR images and are shown in Fig. 1a,b,
Discussion
Three-dimensional conformal radiotherapy requires CT simulation and 3D treatment planning. Tumor location in the liver is usually calculated from CT images taken in a single session. There have been reports about movement of liver surface due to respiratory movement [6], [7], [8] but little has been known about the movement of tumor itself in the liver. Rapid CT scanning may be useful to detect the movement of liver tumors in a trans–axial plane as we have seen for lung tumor in a previous
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