Embodiments of the present disclosure are directed to radiotherapy systems. An exemplary radiotherapy system may comprise a radiotherapy output configured to deliver a charged particle beam to a patient. The system may also comprise a detector array. The detector array may have an axis that extends parallel to an axis along which the charged particle beam is delivered by the radiotherapy output. The detector array may comprise a plurality of detectors configured to detect a magnetic field generated by the charged particle beam during delivery of the charged particle beam from the radiotherapy output.
