AUTHOR=Cui Taoran , Weiner Joseph , Danish Shabbar , Chundury Anupama , Ohri Nisha , Yue Ning , Wang Xiao , Nie Ke 

TITLE=Evaluation of Biological Effective Dose in Gamma Knife Staged Stereotactic Radiosurgery for Large Brain Metastases

JOURNAL=Frontiers in Oncology

VOLUME=12

YEAR=2022

URL=https://www.frontiersin.org/journals/oncology/articles/10.3389/fonc.2022.892139

DOI=10.3389/fonc.2022.892139

ISSN=2234-943X

ABSTRACT=<sec><title>Objective</title><p>Gamma knife (GK) staged stereotactic radiosurgery (Staged-SRS) has become an effective treatment option for large brain metastases (BMs); however, it has been challenging to evaluate the total dose because of tumor shrinkage between two staged sessions. This study aims to evaluate total biological effective dose (BED) in Staged-SRS, and to compare the BED with those in single-fraction SRS (SF-SRS) and hypo-fractionated SRS (HF-SRS).</p></sec><sec><title>Methods</title><p>Patients treated with GK Staged-SRS at a single institution were retrospectively included. The dose delivered in two sessions of Staged-SRS was summed using the deformable image registration. Each patient was replanned for SF-SRS and HF-SRS. The total BEDs were computed using the linear-quadratic model. Tumor BED<sub>98%</sub> and brain V<sub>84Gy2</sub>, equivalent to V<sub>12Gy</sub> in SF-SRS, were compared between SF-SRS, HF-SRS, and Staged-SRS plans with the Wilcoxon test.</p></sec><sec><title>Results</title><p>Twelve patients with 24 BMs treated with GK Staged-SRS were identified. We observed significant differences (<italic>p</italic> &lt; 0.05) in tumor BED<sub>98%</sub> but comparable brain V<sub>84Gy2</sub> (<italic>p</italic> = 0.677) between the Staged-SRS and SF-SRS plans. No dosimetric advantages of Staged-SRS over HF-SRS were observed. Tumor BED<sub>98%</sub> in the HF-SRS plans were significantly higher than those in the Staged-SRS plans (<italic>p</italic> &lt; 0.05). Despite the larger PTVs, brain V<sub>84Gy2</sub> in the HF-SRS plans remained lower (<italic>p</italic> &lt; 0.05).</p></sec><sec><title>Conclusion</title><p>We presented an approach to calculate the composite BEDs delivered to both tumor and normal brain tissue in Staged-SRS. Compared to SF-SRS, Staged-SRS delivers a higher dose to tumor but maintains a comparable dose to normal brain tissue. Our results did not show any dosimetric advantages of Staged-SRS over HF-SRS.</p></sec>