Compact multileaf collimator for conformal and intensity modulated fast neutron therapy: Electromechanical design and validation

The electromechanical properties of a 120‐leaf, high‐resolution, computer‐controlled, fast neutron multileaf collimator (MLC) are presented. The MLC replaces an aging, manually operated multirod collimator. The MLC leaves project 5 mm in the isocentric plane perpendicular to the beam axis. A taper is included on the leaves matching beam divergence along one axis. The 5 ‐ mm leaf projection width is chosen to give high‐resolution conformality across the entire field. The maximum field size provided is 30 × 30cm 2 . To reduce the interleaf transmission a 0.254 ‐ mm blocking step is included. End‐leaf steps totaling 0.762 mm are also provided allowing opposing leaves to close off within the primary radiation beam. The neutron MLC also includes individual 45° and 60° automated universal tungsten wedges. The automated high‐resolution neutron collimation provides an increase in patient throughput capacity, enables a new modality, intensity modulated neutron therapy, and limits occupational radiation exposure by providing remote operation from a shielded console area.