Implications of a high-definition multileaf collimator (HD-MLC) on treatment planning techniques for stereotactic body radiation therapy (SBRT): a planning study

James A Tanyi,Paige A Summers,Martin Fuss,Yiyi Chen,Charles L Mccracken,Li-Chung Ku

doi:10.1186/1748-717x-4-22

Abstract

PurposeTo assess the impact of two multileaf collimator (MLC) systems (2.5 and 5 mm leaf widths) on three-dimensional conformal radiotherapy, intensity-modulated radiotherapy, and dynamic conformal arc techniques for stereotactic body radiation therapy (SBRT) of liver and lung lesions.MethodsTwenty-nine SBRT plans of primary liver (n = 11) and lung (n = 18) tumors were the basis of this study. Five-millimeter leaf width 120-leaf Varian Millennium (M120) MLC-based plans served as reference, and were designed using static conformal beams (3DCRT), sliding-window intensity-modulated beams (IMRT), or dynamic conformal arcs (DCA). Reference plans were either re-optimized or recomputed, with identical planning parameters, for a 2.5-mm width 120-leaf BrainLAB/Varian high-definition (HD120) MLC system. Dose computation was based on the anisotropic analytical algorithm (AAA, Varian Medical Systems) with tissue heterogeneity taken into account. Each plan was normalized such that 100% of the prescription dose covered 95% of the planning target volume (PTV). Isodose distributions and dose-volume histograms (DVHs) were computed and plans were evaluated with respect to target coverage criteria, normal tissue sparing criteria, as well as treatment efficiency.ResultsDosimetric differences achieved using M120 and the HD120 MLC planning were generally small. Dose conformality improved in 51.7%, 62.1% and 55.2% of the IMRT, 3DCRT and DCA cases, respectively, with use of the HD120 MLC system. Dose heterogeneity increased in 75.9%, 51.7%, and 55.2% of the IMRT, 3DCRT and DCA cases, respectively, with use of the HD120 MLC system. DVH curves demonstrated a decreased volume of normal tissue irradiated to the lower (90%, 50% and 25%) isodose levels with the HD120 MLC.ConclusionData derived from the present comparative assessment suggest dosimetric merit of the high definition MLC system over the millennium MLC system. However, the clinical significance of these results warrants further investigation in order to determine whether the observed dosimetric advantages translate into outcome improvements.

Highlights

Stereotactic body radiation therapy (SBRT) is a modern precision radiation therapy delivery concept characterized by one to five fraction delivery of focal high-dose radiation [1,2]
The current work seeks to assess if a novel high-definition 2.5mm leaf multileaf collimator (MLC) system (HD-MLC) integrated into a dedicated stereotactic linear accelerator system (BrainLAB/Varian Novalis TX) provides dosimetric advantages compared with a clinically widely utilized 5 mm leaf system for SBRT of lung and liver lesions, and if potential gains realized may be clinically meaningful
Target dose conformity and normal/critical structure dose The mean values of the conformity and heterogeneity indices, along with p-values of paired t-tests comparing corresponding planning techniques of the MLC systems under consideration, are summarized in Additional file 2 according to internal target volume (ITV) groups

Summary

Introduction

Stereotactic body radiation therapy (SBRT) is a modern precision radiation therapy delivery concept characterized by one to five fraction delivery of focal high-dose radiation [1,2]. SBRT has become an established treatment technique for lung [3,4,5], liver [6,7,8], and spinal lesions [911]. Derived from cranial stereotactic radiosurgery, the planning and delivery of SBRT is characterized by highly target-conformal dose distributions with steep dose gradients towards normal tissues, which allow the administration of potent tumor-ablative radiation doses. Beam shaping for linear accelerator-based SBRT planning and delivery is mostly afforded by multileaf collimator (MLC) systems. The current work seeks to assess if a novel high-definition 2.5mm leaf MLC system (HD-MLC) integrated into a dedicated stereotactic linear accelerator system (BrainLAB/Varian Novalis TX) provides dosimetric advantages compared with a clinically widely utilized 5 mm leaf system for SBRT of lung and liver lesions, and if potential gains realized may be clinically meaningful

Methods

Results

Discussion

Conclusion