Radio-frequency (RF) electrode for a cyclotron. The RF electrode includes a hollowed dee having first and second surfaces that oppose each other and define a gap therebetween. The hollowed dee is configured to be electrically controlled to direct a beam of charged particles through the gap and along an orbit plane of the cyclotron. The orbit plane extends parallel to the first and second surfaces through the gap. The RF electrode also includes a bridge structure that is coupled to and extends away from the hollowed dee. The bridge structure includes a side wall that defines an interior cavity of the bridge structure. The side wall has a particle opening therethrough that coincides with or is proximate to the orbit plane such that the particle opening receives neutral particles from an orbit of the charged particles.