MRI and MRA in treatment planning of subdiaphragmatic radiation therapy

Radiotherapy treatment planning needs optimum definition of target volume in its relative position to normal tissue. The aim of our study was to achieve individual field definition in subdiaphragmatic radiotherapy by visualization of the target volume using fast, breath-held MRI and MR angiography. A modified rapid acquisition SE technique (SE 150/10) was used to obtain a coronal image within a 14 s breath-holding period, displaying kidneys, spleen, and lumbar spine on one slice. Coronal MR angiography acquisition in breath-hold technique was performed using a sequential FLASH-2D sequence (FLASH-2D 30/10/30 degrees). For reconstruction of the MR angiogram in coronal view, we used a maximum intensity projection algorithm. A computer program superimposed the MR angiogram onto the MR image. Correct magnification of the superposition image allowed direct projection onto the simulation film. Problems of distortion and different projection techniques were taken into account and quantified by phantom measurements. The localization error measured in a reference plane was less than 5 mm within a radius of 140 mm. Fourteen cases of Hodgkin disease and non-Hodgkin lymphomas were treated employing the novel technique. By superposition of the MR image and the MR angiogram, demarcation of vascular architecture from parenchymatous organs was achieved. Projection of the MR superposition onto the simulation film yielded accurate and convenient field definition using noninvasive imaging techniques.