A radiotherapy system includes: a waveguide, an adjustable waveguide, and
a non-reciprocal circuit element. The waveguide transmits a
high-frequency wave from a high-frequency power source to an acceleration
tube. The adjustable waveguide is included in said waveguide and
transforms a part of said waveguide. The non-reciprocal circuit element
is provided between said acceleration tube and said adjustable waveguide
in said waveguide. Said acceleration tube accelerates charged particles
for generating therapeutic radiation by using said high-frequency wave.