Abstract: A radiation beam modulator for modulating a radiation beam in a radiation system, includes an array of multiple columns of a radiation modulating fluid or liquid and a height adjuster which adjusts the heights of the multiple fluid columns so that the adjusted columns collectively will form a target radiation modulating profile. In a first embodiment, the modulator includes a bundle of capillaries in which the modulating fluid is conveyed to form the columns. An antagonizing fluid is conveyed into an opposite end of the capillaries to lock the modulating fluid in position between adjustments. In a second embodiment, the modulator includes a bath of the modulating fluid, in which bars can be immersed and retracted to generate the target radiation modulating profile.