Treatment-Plan Comparison of Three Advanced Radiation Treatment Modalities for Fractionated Stereotactic Radiotherapy to the Head and Neck

He Wang ,Xiaodong Zhang,Dershan Luo,Jack Phan,David I Rosenthal,Amol J Ghia,Steven J Frank,Zhongxiang Zhao,Jing Li,Shaan M Raza,Congjun Wang,Mark S Chambers,Adam S Garden,Franco De Monte,Paul D Brown,C.d Fuller ,James N Yang ,G.b Gunn ,Jay P Reddy ,X.r Zhu ,Shirley Y Su ,S Tung

doi:10.4236/ijmpcero.2019.82010

Abstract

Purpose: Fractionated stereotactic radiosurgery (FSRS) can be given with at least three modalities: Gamma Knife, with the noninvasive frameless extend system (GKE); linear accelerator-based volumetric modulated arc therapy (VMAT); and intensity-modulated proton therapy (IMPT). We extracted treatment plans for patients who had received FSRS with GKE for recurrent skull base or intracranial tumors, created corresponding plans for VMAT and IMPT, and compared the quality of the three sets of plans. Methods and materials: Plans were extracted for 9 patients with recurrent malignant skull-base tumors (n = 6) or large intracranial tumors (n = 3) who had received FSRS with GKE (median dose 24 Gy in 3 fractions) in 2013 through 2015. Plans for VMAT were generated with a TrueBeam STx LINAC machine using 6-MV photons, and plans for IMPT were generated with multi-field optimization. The optimized VMAT and IMPT plans were normalized to achieve the best possible target coverage while meeting the same dose-volume constraints on organs at risk (OARs) as the GKE plans. Plans were evaluated on the basis of target coverage, conformity index, homogeneity index, gradient index, and treatment efficiency. Results: The median target volume was 10.2 cm3 (range 1.9 - 33.8 cm3). The VMAT and IMPT plans met all OAR constraints, and target coverage and conformity were comparable among all plans. VMAT and IMPT plans showed significantly better target uniformity and treatment delivery efficiency (P P

Highlights

Intracranial tumors of a certain size range are often treated with single-fraction stereotactic radiosurgery (SRS), in which a rapid dose fall-off to spare normal tissues is achieved by using multiple beam directions and a high degree of collimation
Plans for volumetric modulated arc therapy (VMAT) were generated with a TrueBeam STx linear accelerators (LINACs) machine using 6-MV photons, and plans for intensity-modulated proton therapy (IMPT) were generated with multi-field optimization
The three intracranial target volumes ranged from 2.5 cm3 to 18.2 cm3, and the six skull-base target volumes ranged from 1.9 cm3 to 33.8 cm3

Summary

Introduction

Intracranial tumors of a certain size range (i.e. up to about 3 cm) are often treated with single-fraction stereotactic radiosurgery (SRS), in which a rapid dose fall-off to spare normal tissues is achieved by using multiple beam directions and a high degree of collimation. The Leksell Gamma Knife Perfexion system (GK), for example, has 192 high-activity Cobalt-60 sources that can be collimated to a single focus, capable of delivering a highly focal and conformal ablative radiation dose with a rapid dose fall-off toward surrounding healthy tissue [1] [2] [3] [4]. In contrast to single-session SRS, fractionated stereotactic radiosurgery (FSRS), in which radiation is delivered in 3 - 5 large fractions, is an attractive option for larger intracranial tumors or skull base tumors [6] because the single-fraction dose required for tumor control often exceeds the tolerance of adjacent critical neuro-optic structures. Delivery of FSRS with the GK is facilitated by the use of an alternative to the head frame, in which the patient’s head position is fixed by means of a customized vacuum-assisted mouthpiece (e.g. the Extend system; Figure 1)

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