ABSTRACT
A multileaf collimator (MLC) is compared with conformal blocks for delivering the boost phase of dose-escalated conformal prostate radiotherapy. When using conformal blocks, the volume of rectum irradiated to 90% (V90) is lower (1.4+/-1.3%, 1 SD) for a three-field plan with gantry angles 0 degree, 90 degrees, 270 degrees than for a six-field plan with gantry angles 50 degrees, 90 degrees, 130 degrees, 230 degrees, 270 degrees, 310 degrees (2.1 +/- 1.3%, P = 0.002). However, when using an MLC in which the leaves and wedge are oriented at right angles, V90 is higher (4.7 +/- 3.0%) for a three-field plan than for a six-field plan (2.7 +/- 1.6%, P=0.05). The larger increase in V90 for the three-field plan when changing from conformal blocks to MLC is mainly due to the limitation imposed upon the MLC orientation by the use of wedges.
