  Beam angle optimization (BAO) largely determines the performance of
fixed-field intensity modulated radiation therapy (IMRT), and it is usually
considered as non-convex optimization and an NP hard problem. In this work, BAO
is reformulated into a highly efficient framework of standard quadratic
optimization. The maximum of beamlet intensities for each incident field as the
surrogate variable indicating whether one radiation field has been selected. By
converting the function of maximum value in the objective into a set of linear
constraints, the problem is solved as standard quadratic optimization via
reweighting l1-norm scheme. The performance of the proposed BAO has been
verified on a digital phantom and two patients. And the conclusion is drawn:
the proposed convex optimization framework is able to find an optimal set of
beam angles, leading to improved dose sparing on OARs in fixed-field IMRT.
