The importance of postoperative CT image fusion verification of stereotactic interstitial irradiation for brain tumors.

Purpose: The aim of our study was verification of the position of implanted catheters with (125)I seeds after the catheter implantation for the brachytherapy of brain tumors.

Methods And Materials: The fusion of the CT image used at planning and after the implantation of the catheters enabled us to verify the position of the catheters containing the isotopes. After this, the tumor volume covered by the prescribed dose (TV(PD)) and the normal tissue volume covered by the prescribed dose (NTV(PD)) were compared between the plan and the actual result. The image fusion was performed by the BrainLab-Target 1.19 software on an Alfa 430 (Digital) workstation.

Results: The position of the catheters was adjusted in 14 (20%) of the 70 image fusion cases being studied. The position of 16 of the 116 catheters (13.8%) required adjustment after the fusion of control images in the 70 cases studied. The Student t probe revealed a significant difference between the TV(PD) values of the reality and the plans (75.8% vs. 92.4%, p < 0.0001). There was a significant difference between values of the real performances and planning for NTV(PD) (86.8% vs. 76%, p = 0.001) and for the conformity index (0.37 vs. 0.54, p = 0.0001), too.

Conclusion: The application of the interstitial irradiation with CT control allows us to identify and correct possible inaccuracies in catheter positioning during the operation. The procedure then becomes far more accurate and reliable, and as such, the irradiation becomes more conformal than without catheter adjustment.