Pre-clinical dosimetry of a new six-channel applicator for high-dose-rate treatment of esophageal cancer

Introduction
To evaluate the dosimetry of a six-channel high-dose-rate (HDR) applicator for treatment of esophageal cancer with respect to lateral directionality and heterogeneous media.

Material and methods
A computed tomography (CT)- and magnetic resonance imaging (MRI)-compatible esophageal applicator consisting of 2 inflatable portions (anchor and therapeutic balloons) with 6 longitudinal treatment catheters equally spaced circumferentially was constructed. Treatment plans were prepared using Oncentra 4.5 for various catheter loadings and target locations and sizes. Calculated dose distributions were compared to measured distributions obtained using film and a water phantom. Balloon inflations with water and with air were tested.

Results
TG-43 dose calculations matched measurements well when inflation balloons were filled with water. When air was used to inflate, model-based dose calculations (TG-186) improved the comparison with measurement. Several cases with simulated ring targets demonstrated better dose conformity to non-uniform targets compared to a single central catheter. Additionally, the use of this applicator compared to a single catheter, gave rise to considerable improvement in sparing non-target tissue.

Conclusions
Lateral dose modulation is achievable with the applicator described in this work. The use of TG-186 dose calculation made a small improvement in heterogeneous media.