Dosimetric evaluation of four whole brain radiation therapy approaches with hippocampus and inner ear avoidance and simultaneous integrated boost for limited brain metastases

Aijun Jiang,Suzhen Wang,Dongping Shang,Zhenxuan Wu,Qingxi Yu,Jian Zhu,Fengchang Yang,Fen Zhao,Weipeng Sun,Shuanghu Yuan

doi:10.1186/s13014-019-1255-7

Abstract

AimsTo perform a dosimetric evaluation of four different simultaneous integrated boost whole brain radiotherapy modalities with hippocampus and inner ear avoidance in the treatment of limited brain metastases.MethodsComputed tomography/magnetic resonance imaging data of 10 patients with limited (1–5) brain metastases were used to replan step-and-shoot intensity-modulated radiotherapy (sIMRT), dynamic intensity-modulated radiation therapy (dIMRT), volumetric-modulated arc therapy (VMAT), and helical tomotherapy (Tomo). The prescribed doses of 40–50 Gy in 10 fractions and 30 Gy in 10 fractions were simultaneously delivered to the metastatic lesions and the whole-brain volume, respectively. The hippocampal dose met the RTOG 0933 criteria for hippocampal avoidance (Dmax ≤17 Gy, D100% ≤10 Gy). The inner ear dose was restrained to Dmean ≤15 Gy. Target coverage (TC), homogeneity index (HI), conformity index (CI), maximum dose (Dmax), minimum dose (Dmin) and dose to organs at risk (OARs) were compared.ResultsAll plans met the indicated dose restrictions. The mean percentage of planning target volume of metastases (PTVmets) coverage ranged from 97.1 to 99.4%. For planning target volume of brain (PTVbrain), Tomo provided the lowest average D2% (37.5 ± 2.8 Gy), the highest average D98% (25.2 ± 2.0 Gy), and the best TC (92.6% ± 2.1%) and CI (0.79 ± 0.06). The two fixed gantry IMRT modalities (step and shot, dynamic) provided similar PTVbrain dose homogeneity (both 0.76). Significant differences across the four approaches were observed for the maximum and minimum doses to the hippocampus and the maximum doses to the eyes, lens and optic nerves.ConclusionAll four radiotherapy modalities produced acceptable treatment plans with good avoidance of the hippocampus and inner ear. Tomo obtained satisfactory PTVbrain coverage and the best homogeneity index.Trial registrationClinicaltrials.gov, NCT03414944. Registered 29 January 2018

Highlights

Brain metastases occur in 20–40% of cancer patients [1], and with improvements in local control and new effective systemic treatments, this incidence continues to increase [2]
Simulation and contouring Ten consecutive patients with 1–5 brain metastases confirmed by magnetic resonance imaging (MRI), who were treated between September 2017 and October 2017, were included
According to the biological equivalent dose (BED) formula, the equivalent dose in 2 Gy/fraction (EQD2) for planning target volume of metastases (PTVmets) prescription dose ranged from 54.4 Gy to 62.5 Gy

Summary

Introduction

Brain metastases occur in 20–40% of cancer patients [1], and with improvements in local control and new effective systemic treatments, this incidence continues to increase [2]. Whole brain radiotherapy (WBRT) is a fundamental radiation modality used for patients with extensive brain metastases [3,4,5,6,7]. WBRT is associated with a short local control time and side effects including neurocognition dysfunction [8] and hearing deficits [9]. It is known that radiation-induced damage to the hippocampus plays an important role in the cognitive dysfunction [4, 8, 10,11,12], and hearing impairment can be linked to damage to the inner ear [13]. The results of the RTOG 0933 trial have shown that hippocampus avoidance can effectively reduce the cognitive impairment caused by WBRT [8]

Methods

Results

Conclusion