Impact of catheter positioning on planned target volume (PTV) coverage and organs at risk (OARs) in high-dose-rate...

High-dose-rate endobronchial brachytherapy (HDR-BTE) is an effective technique for the treatment of malignant tracheobronchial tumors. Although two-dimensional (2D) planning provides limited dosimetric information and does not accurately assess the relationship between the catheter and the tumor or the dose delivered to organs at risk (OARs), it continues to be used because it ensures adequate PTV coverage, is associated with low toxicity, and minimizes the risk of catheter displacement by avoiding patient transfer to the CT simulation room.

An 83-year-old patient with 2D HDR-BTE for tracheal recurrence of previously resected lung adenocarcinoma was analyzed and compared with four simulated 3D plans based on catheter position relative to the tumor volume, while keeping the active length and prescribed dose constant.

The favorable oblique scenario achieved the best PTV coverage (D90: 9.05 Gy; V100: 100%), although with highest V150 (96.47%) and homogeneity index (IH: 5.14). The unfavorable oblique and posterior positions significantly reduced coverage (V100: 51.4% and 61.29%, respectively). The esophagus was the most sensitive organ, showing the highest doses in the posterior orientation of the catheter. The contralateral lung and heart received low doses; while the aorta showed higher doses in the favorable oblique scenario due to the location of the PTV.

Catheter orientation in HDR-BTE has a significant impact on PTV coverage and the dose delivered to critical organs. Despite the trend toward 3D planning, there is no direct clinical evidence comparing the two techniques.