“…However, in some cases the optimisation of beam angles can eliminate significant differences between anatomical and functional plans obtained from fixed beam-only plans [98]. Interestingly, the largest functional V20 differences of 5-7% have been found when using fixed beams [96,98,109,113] in contrast to optimised beam angles which tend to produce 2-3% differences [17,60,99,107,97], although both methods have also produced a large number of cases with no significant difference due to additional functional data [5,98,100,104,105,111].…”