Disclosed herein is a method of determining whether repair or replacement of a multi-leaf collimator for a radiotherapy device should be scheduled. The multi-leaf collimator comprises a leaf bank comprising a plurality of leaves, a leaf bank support configured to support the leaf bank, a leaf bank guide, and a guide actuation means configured to extend the leaf bank along the leaf bank guide into the path of a radiation beam. The device further comprises current sensing means configured to produce a signal indicative of the current supplied to the guide actuation means. The method comprises receiving signals from the current sensing means; processing the signals; and based on the processing, determining whether repair or replacement of the multi-leaf collimator should be scheduled.