@article {MenEtAl2007, title = {An Exact Approach to Direct Aperture Optimization in IMRT Treatment Planning}, journal = {Physics in Medicine and Biology}, volume = {52}, number = {24}, year = {2007}, pages = {7333-7352}, doi = {http://dx.doi.org/10.1088/0031-9155/52/24/009}, author = {Chunhua Men and H. Edwin Romeijn and Z C Ta{\c s}k{\i}n and James F. Dempsey} }