A comparison between 2-Step IMRT and conventional IMRT planning

Background and purpose2-Step intensity modulated radiation therapy (2-Step IMRT) is an IMRT segmentation procedure based on analytical approximations [Bratengeier K. 2-Step IMAT and 2-Step IMRT: a geometrical approach. Med Phys 2005;32:777–785; Bratengeier K. 2-Step IMAT and 2-Step IMRT in three dimensions. Med Phys 2005;32:3849–3861]. The aim was to benchmark it with other IMRT algorithms and to establish it as planning tool for fast IMRT application with a reduced number of segments.Materials and methods2-Step IMRT plans were compared with IMRT-solutions obtained with methods from a commercial planning system (Pinnacle™ TPS). The four clinical cases chosen were: paraspinal tumour, carcinoma of the prostate, head and neck carcinoma and breast carcinoma. In addition the “Quasimodo” phantom study was used to compare the quality of the 2-Step IMRT method with respect to other planning procedures in the ESTRO study.ResultsThe number of segments (and – to a minor degree – the monitor units per dose) of the majority of 2-Step IMRT plans was lower than for the commercial algorithms. The quality of the 2-Step IMRT-plan was comparable. In the Quasimodo comparison 2-Step IMRT plans with nine beams would place in the mid-range of all participants, whereas the 15-beam arrangements could compete with the best results.Conclusions2-Step IMRT is a valuable IMRT segmentation method, especially if the number of segments is to be limited (e.g. for reasons of precision, speed and leakage radiation).