FIRST EXPERIENCES WITH COMPUTER-ASSISTED FRAMELESS STEREOTACTIC INTERSTITIAL BRACHYTHERAPY (CASIB)

Purpose: To reach an optimal treatment result and to avoid damage to c ritical structures a homogenous dose distribution in the tumor volume with a rapid decreasing dose to the surrounding structures is necessar y. Fractionated interstitial brachytherapy of tumors in the ENT region employing needles depends on exact localization of the target volume during all fractions. Therefore reproducibility of positioning of the needle(s) plays an important role. Material and Methods: We used the I SG Viewing Wand system in combination with the Vogele-Bale-Hohner (VBH ) head holder and a new targeting device. Point of entrance, pathway, and target point of the needle were planned and insertion of the needl e simulated in advance. To date we have treated 7 patients with inoper able tumors in the ENT region. The actual position of the needle in th e control CT was compared to the planned position. Results: The accura cy of positioning of the needle depended on the location of the tumor. In a patient with a recurrent retroorbital adenocarcinoma the mean ac curacy was 1 mm. Due to soft tissue displacement in the neck region an d the resulting necessity to readjust the targeting device the needle was placed with a mean deviation of 1 mm between the planned and the a ctual position. Conclusions: Computer-assisted frameless stereotactic interstitial brachytherapy allows for precise, reproducible and prepla nned insertion of hollow needles into target structures closely adhere nt to the surrounding tissue: thus avoiding damage of neighbouring str uctures. This technique is of great advantage in treating deeply seate d tumors which are fixed to bony structures. especially at the skull b ase. Inaccuracy in the neck region caused by soft tissue shift require s improvement of the immobilization in this region.