A multileaf collimator for neutron radiation therapy

A multi-leaf collimator (MLC) has been designed for installation on the super-conducting cyclotron at the Gershenson Radiation Oncology Center. This MLC will replace the existing multi-rod collimator and the increased efficiency thus achieved should allow for a 50% increase in the number of patients treated. A study of the penumbra region of the neutron beam with focused and unfocused collimator leaves has been completed, together with activation measurements in steel and tungsten. Results of these studies were used to finalize the collimator leaf design. A steel collimator leaf with a 5 mm projection at the isocenter and a wedge shaped section has been chosen, to provide beam divergence in the direction perpendicular to the leaf motion. The leaf profile is 'stepped' to prevent neutron leakage. The rationale for this leaf design is discussed. The overall design of the collimator system and the incorporation of a remote wedge-changing device will be presented. Each leaf is positioned using a stepping motor; the leaf position is independently confirmed using an optical system incorporating a coherent fiber optic and a CCD camera. The control system is being designed to allow for the implementation of intensity modulated neutron radiation therapy (IMNRT)