Template-based high dose rate endobronchial brachytherapy for palliation of previously irradiated obstructive lung lesions.

174 Background: Local progression after external beam radiation therapy (RT) for lung cancer may result in clinical compromise from bleeding and/or airway obstruction, and additional RT may be precluded by radiation tolerance. High-dose-rate (HDR) endobronchial brachytherapy (EBT) is an effective salvage treatment for airway obstruction and/or bleeding, but requires significant time and resources; planning and treatment are performed bronchoscopically under anesthesia. We sought to reduce procedure and anesthesia time for EBT through template-based planning.

METHODS: EBT templates were created using the Brachyvision version 11.0.47 treatment planning system for the Varisource iX Ir-192 afterloader. Plans were optimized for dose uniformity at distance from the source following planning criteria of published works. Nine endobronchial centering tube templates were created for treatment lengths from 2-10 cm (1cm intervals) prescribed to 0.5cm distance from the applicator surface.

RESULTS: Standard EBT treatment requires a median of 47 minutes (range 44-49 minutes); 5 minutes for applicator placement and fluoroscopic confirmation, 15-17 minutes for plan design and optimization, 20 minutes for quality assurance and plan check, 2-5 minutes for radiation delivery, and 2 minutes for room clearance and applicator removal. Pre-planned templates were evaluated for plan quality, and achieved >90% of the prescription dose for the entire treatment length at the respective treatment depth. Changes to the prescription dose could be achieved through dwell time scaling. Changes to the prescription depth require re-optimization of the plan with the current templates as a base. Use of template-based planning was expected to reduce overall treatment time by 8-9 minutes (16-20% reduction in overall procedure time, 50-56% reduction in treatment planning time); median observed treatment time was 35 minutes (range 32-38 minutes).

CONCLUSIONS: Template-based HDR EBT treatment plans were developed for the palliative lung cancer program at our institution. Implementation of template-based plans resulted in reduced procedure and operative time, and are now our standard technique.