A comparison of multileaf collimator with conformal blocks for the boost phase of dose-escalated conformal prostate radiotherapy

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% (V-90) is lower (1.4 +/- 1.3%, 1 SD) for a three-field plan with gantry angles 0 degrees, 90 degrees, 270 degrees than for a six-held 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, V-90 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 V-90 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. (C) 2001 Elsevier Science Ireland Ltd. All rights reserved.