Dosimetric properties of magnetically collimated electron beams for radiation therapy

A method of generating magnetically collimated electron beams is developed and the dosimetric properties of magnetically collimated electrons are investigated. An in-air magnetic collimator device was designed and constructed for the study. The magnetic collimator was placed above the exit port of a 14 x 14 cm2 electron cone. Axial magnetic field of approximately 0.6 Tesla is generated inside the collimator via an array of permanent magnets. Fixed and rotational magnetically collimated electron beams were delivered and measured in phantoms. We found that magnetically collimated electron beams significantly lower the surface dose as compared with conventional electron beams. A magnetically collimated arc beam further reduces the surface dose to less than 20% of the maximum dose inside the target. The dose per monitor unit at d(max) for the magnetically collimated electron beams was significantly (approximately 40%) higher than that of the conventional electron beams. The use of magnetic collimation may lead to improved delivery techniques for breast and head and neck cancer treatments.