An optical edge detector for the accurate delineation of the light field in radiotherapy machines

A hand-held detector was developed which allows for the unambiguous and con sistent determination of the edge of the light (optical) field on treatment machines conveniently and practically. The design incorporates an electron ic circuit using three miniature photodiodes. The complete module is housed conveniently in a hand-held box measuring 6 cm x 10 cm x 1.5 cm. The devic e eliminates any observer subjectivity on the position of the edge of the l ight field and hence facilitates greatly any commissioning and quality assu rance procedures requiring light-radiation field coincidence. Other applica tions are possible, including alignment of the light field on patients. (C) 2001 American Association of Physicists in Medicine.