Historically, inverse planning algorithms [
1], derived from tomographic calculations, have played a more important role than "forward planning" techniques [
2‐
4] for IMRT. In contrast to traditional "trial and error" methods for three-dimensional conformal radiotherapy (3DCRT), progressive "forward planning" techniques for IMRT analyse the geometrical constellation to create beam segments. The weights of these segments can then be optimised in the same fashion as in conventional inverse IMRT planning. A few hospitals have specialised in such "forward planning" and can compete with "inverse planning" techniques [
5‐
8]. Their approach is presumed not to be as conformal and flexible as an inverse planning based one; often "forward planning" is used in terms of class solutions. However, algorithms such as 2-Step IMRT [
9,
10] are utilized for a variety of tumour localizations [
6,
11]. 2-Step IMRT is a segmentation technique, which creates segments, reflecting the shape of the tumour and OARs but also highly weighted narrow segments close to critical structures to obtain steep dose gradients [
12]. On the other hand, contemporary "inverse planning" uses iterative optimisation elements. The latest generation of planning systems integrates machine parameters in the iterative optimisation process, such as HYPERION [
13] and direct aperture optimisation (DAO) [
14‐
16]. The Pinnacle3
® planning system refers to it as "direct machine parameter optimization" ("DMPO", Raysearch™ laboratories). Such algorithms are clearly superior to those with sequencing after a complete fluence optimization process [
17]. Fine-tuning of the segment parameters, such as with DMPO, could possibly also enhance "forward planning" techniques. The aim of this work is to explore whether a technique like 2-Step IMRT could not only compete with a former generation planning systems (fluence optimisation followed by subsequent segmentation) as shown before [
6], but also compete with a planning system of the latest generation where segmentation is integrated in the optimisation procedure such as with DMPO. A further motivation for this planning study is to investigate the possibility of daily ad-hoc adaptation of IMRT-plans[
10,
18] based on 2-Step IMRT. This could only be useful if the primary plan can concur with the results of up to date IMRT planning systems. Without an initial IMRT plan of sufficient quality, all adaptive efforts would be non-optimal. With this in mind, it should be noted that the adaptation process itself is not subject of this paper.