Skin dose estimation using virtual structures for Contura Multi-Lumen Balloon breast brachytherapy.

Area of Science:

• Medical Physics
• Radiation Oncology
• Medical Imaging

Background:

• Accurate assessment of skin dose is crucial in radiation therapy, particularly for treatments involving brachytherapy applicators like the Contura Multi-Lumen Balloon.
• Conventional methods for monitoring applicator position and skin distance often rely on computed tomography (CT), which can be resource-intensive and increase patient radiation exposure.

Purpose of the Study:

• To propose and validate a novel workflow for evaluating the maximum skin dose in patients treated with Contura Multi-Lumen Balloon applicators.
• To integrate ultrasound (US)-measured skin-balloon distances and virtual structure creation within treatment planning systems (TPS).

Main Methods:

• A workflow was developed utilizing ultrasound (US) to measure skin-balloon distances and creating virtual structures on planning CT scans.
• Twenty-three patients were analyzed, comparing CT- and US-measured distances and assessing the accuracy of predicted skin doses using virtual structures.
• Fitted curves and equations were derived from skin-balloon distance versus maximum skin dose plots.

Main Results:

• The average difference between CT- and US-measured skin-balloon distances was minimal (-0.5 ± 1.1 mm).
• The proposed virtual structure method predicted maximum skin doses with an average difference of -1.7% when based on CT data.
• When using US-measured distances within the derived trendline equation, the predicted maximum skin dose showed an average difference of 0.7 ± 6.4% compared to actual doses.

Conclusions:

• Ultrasound (US) can effectively monitor interfraction skin-balloon distance variations, serving as a potential replacement for CT acquisition.
• The proposed workflow, combining virtual structures defined on planning CT with US-measured distances, allows for reasonable estimation of maximum skin doses.