A Planning Comparison of Dynamic IMRT for Different Collimator Leaf Thicknesses with Helical Tomotherapy and RapidArc for Prostate and Head and Neck Tumors

Purpose: A comparative analysis of the three most advanced intensity-modulated radiotherapy (IMRT) techniques currently commercially available was performed. Treatment plans made in rotational techniques (helical tomotherapy [HT] and RapidArc) were compared with sliding-window IMRT (dIMRT) on a conventional linear accelerator using different leaf thicknesses (2.5 mm, 5 mm, and 10 mm). The influence of the different planning techniques on the coverage of planning volume and sparing of organs at risk (OARs) was investigated. Patients and Methods: Nine patients with localized prostate and nine patients with head and neck cancer were chosen for this study. Treatment planning was performed in Eclipse (Varian) and in Tomotherapy planning software. Treatment plans were compared according to target volume coverage and sparing OARs, as well as by conformity and homogeneity index. Results: For both investigated tumor sites, the dosimetric effects of leaf widths between 2.5 mm, 5 mm and 10 mm were shown to be small in regard to target coverage. Tomotherapy plans had better target coverage (higher minimum dose). For prostate cancer, better sparing of bladder and rectum was achieved with RapidArc and dIMRT plans. For head and neck cancer, best sparing of parotid glands was achieved in HT plans. There was no significant difference (p > 0.05) in sparing of OARs between the dIMRT plans with different leaf widths neither for prostate cancer nor for head and neck cancer. Conclusion: For prostate and head and neck cases, all investigated IMRT techniques provide highly conformal treatment plans in terms of both target coverage and critical structure sparing.