Method of identifying dynamic multileaf collimator irradiation that is highly sensitive to a systematic MLC calibration error

In intensity modulated radiotherapy (IMRT), radiation is delivered in a multiple of multileaf collimator (MLC) subfields. A subfield with a small leaf-to-leaf opening is highly sensitive to a leaf- positional error. We introduce a method of identifying and rejecting IMRT plans that are highly sensitive to a systematic MLC gap error (sensitivity to possible random leaf-positional errors is not addressed here). There are two sources of a systematic MLC gap error: centerline mechanical offset (CMO) and, in the case of a rounded end MLC, radiation field offset (RFO). In IMRT planning system, using an incorrect value of RFO introduces a systematic error delta RFO that results in all leafto-leaf gaps that are either too large or too small by (2·delta RFO), whereas assuming that CMO is zero introduces systematic error deltaCMO that results in all gaps that are too large by deltaCMO=CMO.