Medical physicsTarget delineation in post-operative radiotherapy of brain gliomas: Interobserver variability and impact of image registration of MR(pre-operative) images on treatment planning CT scans
Section snippets
Patient population and image acquisition
This is a retrospective study on patients who underwent diagnostic pre-operative MR, surgical resection and radiotherapy at our Institution. Between November 1999 and December 2001, seven patients affected by glioblastoma multiforme (n=5) or anaplastic oligodendroglioma treated with macroscopically total resection for whom preoperative MR scans were available, were selected for this study. Five were males, median age was 51.5 years (range: 42–69) and median Karnofsky performance status was 90
Results
In the qualitative evaluation of CT/MR registration, the physician found good spatial correspondence in each image pair. Quantitative registration accuracy values are summarised in Table 1: for all five patients the maximum error in 3D space is less than or close to the slice thickness.
The maximum dimensions of volumes measured on BEV plots along the three main axes are similar for CT+MR(conv) and CT+MR(matched) procedures: the mean values are 37.8±13.7 vs 38.6±12.9 mm along cranio–caudal
Discussion
In this work, registration was carried out by a surface-matching algorithm [30]; this registration approach has been widely investigated by many authors, reporting, in the case of brain application, an accuracy of within a few millimetres [42]. The analysis of registration accuracy, carried out in our study on five patients, confirms previous data, showing an average residual misalignment error of 2 mm or less, indicating the adequacy of the technique in correcting not only for spatial
Conclusions
There exists quite a great degree of inter-observer variability in target volume delineation of high-grade gliomas submitted to total resection.
The use of CT and MR registered images greatly reduces uncertainties in the spatial location of target volume within the skull. This is more evident for cases in which MR and CT images are acquired with the patient head in different positions.
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