gms | German Medical Science

The most important base for RS/SRT is the exact definition of the isocenter as a precondition for the following high precise dose application, even in cases of very small target volumes. This aim can be achieved by an “overall process accuracy” including image fusion.

In the last 3.5 years, 447 patients were treated with RS/SRT. For each treatment planning procedure a fully automatic image fusion of all interesting image modalities was performed, visually controlled and, if necessary corrected. The planning CT (1.25mm slices) and for arteriovenous malformation also a stereotactic DSA was acquired using head fixation with stereotactic arc, in case of SRT a relocatable stereotactic mask. Different sequences of MRI (1-2mm slices) and, if necessary FET-PET (3.4mm) were acquired without head fixation. The transfer of all image data sets was accomplished by LAN except of external conducted studies where a CD/MOD was used.

The fully automatic integration of all interesting image data sets (several MRI- and CT- series, PET) into treatment planning procedure and follow-up studies could be realized in each patient. Precision of the automatic fusion result depended on slice thickness. Fusing thin slices of an enlarged region of interest into another data set was also possible with a good standard being achieved. Target volume could be outlined reliably and more satisfactorily using all the available information from the fused image data sets. Fused follow-up studies were exactly comparable and quantitatively evaluable.

The automatic image fusion is a high quality tool, especially for precision in RS/SRT planning and exact comparable follow-up studies respectively. It allows for a fast (about 1-2 min.) and precise fusion of different image data sets depending on the high quality in data acquisition.