A CT-assisted method of dosimetry in brachytherapy of lung cancer. Rotterdam Oncological Thoracic Study Group.

Abstract

The toxicity of endobronchial brachytherapy (EB), in particular fatal haemoptysis and bronchial wall necrosis, has been correlated with the total dose, fraction size, volume encompassed by the 100% isodose, and a proximal tumor location. We describe a CT-based planning method which, by improving target volume definition and volumetric dose information, can improve the therapeutic ratio of EB. Sixteen CT-assisted EB procedures were performed in patients who were treated with palliative high-dose rate EB. The CT data were used to analyze applicator position in relation to anatomy. An example of a three-dimensional optimized treatment plan was generated and analyzed using different types of dose-volume histograms. The procedure was well tolerated by patients and no post-procedure complications were observed. The bronchial applicator was eccentrically positioned at the level of the carina/mainstem bronchus in 12 (of 14) CT scans. A planning CT prior to EB was not found to be useful as the final target volume and/or the final applicator position were not reliably predicted before the therapeutic bronchoscopy. CT-scans performed with the applicator in situ allowed the bronchial segments in the target volume to be identified and enabled dose prescription to the bronchial mucosa. CT-assisted EB is feasible and underlines the need for using centered applicators for proximally located tumors. By enabling accurate mucosal dose prescription, CT-assisted EB may reduce the toxicity of fractionated EB in the curative setting. However, faster on-line EB treatment planning is needed for the routine clinical application of this technique.