Patent ID: 7961843

Claim:
A radiotherapeutic apparatus comprising: a source able to emit a beam of therapeutic radiation along a beam axis, wherein the source is rotatable about a rotation axis that is substantially orthogonal to and intersects with the beam axis thereby to describe an arc around the rotation axis; a multi-leaf collimator arranged to collimate the beam to a desired shape; and a control means able to control dose/time rate of the source, rotation speed of the source, and a position of the multi-leaf collimator, the control means being arranged to receive a treatment plan in which the arc is divided into a plurality of arc-segments, the treatment plan specifying a total dose for an arc-segment and a start and end MLC position, and to control the source in accordance with the treatment plan over the arc-segment by calculating total time required for the arc-segment for a plurality of factors including: i. an MLC leaf movement from a prescribed position at the start of the arc-segment to a prescribed position at the end of the arc-segment, at a maximum leaf speed; ii. rotation of the source from the start to the end of the arc-segment at a maximum source rotation speed; iii. delivery of the dose at a maximum dose rate per time; the control means being arranged to select a factor dictating a longest time, and control the apparatus so that the selected factor operates at its respective maximum and remaining factors are operated at a reduced rate selected to match the longest time.