Mucosal dose prescription in endobronchial brachytherapy: a study based on CT-dosimetry.

Abstract

To investigate the consequences of using different dose prescription methods for endobronchial brachytherapy (EB), both with and without the use of a centered applicator. A CT scan was performed during EB procedures in 13 patients after insertion of the lung applicator. A dosimetric analysis was subsequently performed in five of these patients using a 3D-brachytherapy treatment planning system (PLATO v13.3, Nucletron). Dose prescription to the mucosa yields uniform dose distributions to the bronchial mucosa when a centrally positioned applicator is used. When non-centrally positioned applicators are used, mucosal dosing results in a significant underdosage to parts of the target volume. Due to the rapid dose fall-off in EB, dose prescription to the mucosa resulted in inadequate coverage of the outer portion of the bronchial wall and adjacent peribronchial space. When compared to mucosal dose prescription, prescription to the outer aspect of the bronchial wall appears to improve target coverage while limiting the hyperdose (i.e., 200%) volume. The diameters of the different bronchial segments, as determined by CT measurements in 13 patients, correlated well with calculated values based upon the tracheal diameter. Mucosal dose prescription should only be used in combination with centered EB applicators. Given the rapid dose fall-off in EB mucosal dose prescription should be used with caution in curative treatments where EB, without additional external radiotherapy, is used as the sole treatment modality. In curative EB, both improved target coverage and a limited hyperdose volume can be achieved by dose prescription to the outer aspect of the bronchial wall.