ESTRO 2023 - Abstract Book

S2096

Digital Posters

ESTRO 2023

PO-2327 3D GRE vs bSSFP-SPAIR for image registration in case of prostate cancer patients

B. Kraan 1

1 LUMC, radiotherapy, Leiden, The Netherlands

Purpose or Objective Gold markers are implanted in the prostate to improve the image-guided irradiation of prostate cancer patients. These markers are also used for image registration of the planning. Besides a T2 weighted MRI sequence (for target definition ), a 3D gradient echo (GRE) MRI sequence is used for detection of the markers in the prostate. These markers depict as black, signal voids on the MRI images. Distinguishing between the markers and any calcifications/bleeding can be difficult. The aim of this study is to investigate whether the balanced steady-state free (bSFFP)-SPAIR sequence offers added value compared to the current 3D GRE sequence in terms of accuracy of marker detection. Materials and Methods This is a retrospective quantitative analysis of MRI images of 18 prostate cancer patients with implanted gold markers. For this analysis the standard protocol was followed. Markers were defined on both the planning CT (p-CT) and the MRI by placing a Point Of Interest (POI) in the center of the marker/void. Then a point-based image registration (IR) was done of the p-CT and the MRI (Raystation v10B). An in-house developed script was used to calculate the residual deviation between the two POIs. The same procedure was also performed on the SPAIR sequence. Results A first observation of the MRI images shows that the markers present as smaller signal voids on the bSSFP-SPAIR (smaller black holes) relative to the GRE, see Figure 1A. In addition, when there are bleedings or calcifications, fewer holes can be seen, making it easier to define the POI on the right marker (black hole), see figure 1B.

The results of the quantitative analysis can be found in Table 1.