Secondary neutron ambient dose equivalent measurement of the wobbling system of a proton beam radiotherapy facility

•H*(10)/D of wobbling system proton therapy: 4.8–1.3 mSv/Gy at d from 50 to 225cm.•H*(10)/D proportional to proton beam energy, wobbling diameter, and SOBP width.•H*(10)/D of middle and large wobbling size are 2.1 and 3.3 times to small wobbling size.•H*(10)/D of wobbling system similar to other passive scattering method facilities.