Feasibility Study of Navigated Endoscopy for the Placement of High Dose Rate Brachytherapy Applicators in the Esophagus and Lung

High dose rate brachytherapy is used in a limited number of esophagus and lung patients, often in combination with external beam radiation therapy. The procedure uses an applicator inserted into the lumen with the applicator connected to an automated "afterloader", a device with a radioactive brachytherapy source attached to a thick guide wire that positions the source within the applicator at set positions and times based on a treatment plan. Identification of the ideal applicator position is determined by white light endoscopy. With the endoscope in the lumen, fluoroscopic imaging can visualize the endoscope position. Temporary radio-opaque skin markers are placed on the patient's anterior surface under fluoroscopy imaging so that they align with the endoscope tip. The proximal and the distal ends of the target volume are marked in this manner by the surgeon stopping the endoscope at these positions. The endoscope is removed and the applicator inserted, with the positions of the applicator and "dummy" seeds (i.e. non-radioactive seeds used only for positioning purposes) aligned under fluoroscopy to match the skin markers. The procedure has 2 disadvantages: i. There is extra radiation dose to the clinical staff due to the fluoroscopy used to identify the source position.

ii. Visualization is only in 2D, which is inaccurate since it does not account for separations in the vertical direction and the angle of projection between the applicator and the so patient surface. Furthermore, any movement of the fluoroscopy device during the insertion leads to errors in visualization.

Medical applications of navigated endoscopy continue to grow, especially when used in combination with volumetricimaging for image-guided procedures. This feasibility study is aimed to use navigation endoscopy technology to overcome the disadvantages of the current practice and improve the overall process.

In the proposed protocol, applicator insertion, tracking and recording of the endoscope and applicator positions would enable placement of the applicator using 3D information, with greater accuracy and without extra radiation dose to the clinical staff. The tracking technology would be used to replace the use of radio-opaque skin markers; rather than placing these markers on the patient's skin, the location of the target volume boundaries would be noted by the tracker position within the endoscope. Applicator insertion would also be tracked, with the applicator positioning based on the location of the applicator relative to the previously recorded endoscope positions, including the locations of the distal and proximal ends of the target volume.