Algorithmic determination of source orientations for the CivaSheet directional brachytherapy device.

Area of Science:

• Medical Physics
• Radiotherapy
• Medical Imaging

Background:

• The CivaSheet device utilizes multiple shielded Palladium-103 (Pd-103) CivaDot sources for directional planar dose distributions.
• Manual digitization of 3D source orientation from 2D images during postplanning is a complex and challenging task.

Purpose of the Study:

• To develop an automated algorithm for determining the direction of each CivaDot source.
• The algorithm aims to use the spatial relationships between adjacent sources to infer individual source orientation.

Main Methods:

• The algorithm calculates source direction by averaging normal vectors of local planes formed by adjacent sources.
• Validation involved CT scanning of a CivaSheet-like device in known flat and curved geometries.
• The algorithm's performance was also assessed on a postplan for a gynecological implant and compared to manual digitization.

Main Results:

• For controlled geometries, the algorithm achieved an average angular difference of 1.2° (flat), 1.7° (vertical curve), and 2.3° (horizontal curve) compared to known orientations.
• In a patient case, the algorithm's predicted orientation showed an average difference of 23.1° compared to manual digitization.

Conclusions:

• The algorithm accurately calculates source orientation, with precision better than 2.3° in controlled experiments.
• This automated approach offers consistent results and simplifies the challenging task of orienting partially shielded sources in brachytherapy planning.