Field flatness and symmetry of photon beams: Review of the current recommendations

Abstract

Flatness and symmetry are main parameters determining the quality of a photon beam produced by linear accelerators. The quality assurance in routine clinical practice of radiotherapy and consequently the treatment-outcome depend definitely on the physical parameters of treatment-delivery. Several recommendations from national and international associations are reported. By reviewing the current literature and mainly according to the World Health Organization (WHO) report of quality assurance in radiotherapy, we may suggest that for flatness and symmetry, the optimal level of deviation should be within +/- 3%. Flatness and symmetry should be checked monthly or once a year in accordance to the guidelines of national societies.