Benefit of dosimetry distribution for patients with brain metastases from non-small cell lung cancer by Cyberknife Stereotactic radiosurgery (SRS) system

BackgroundTo pursue high precision in tumor and steeper dose fall-off in healthy tissues of brain metastases stereotactic radiosurgery (SRS), this study investigated an opitimized planning by comparison only one multiple-lesions-plan (MLP) and multiple single-lesion-plans (SLP) in the treatment of brain metastases using Cyberknife (CK) Robotic Radiosurgery System. MethodsFifty non-small cell lung cancer (NSCLC) patients (28 males and 22 females) with 2-4 multiple brain metastases were retrospectively replanned with 12 to 32 Gy prescription dose in 1 to 3 fractions. Two different clinical SRS plans (SLP and MLP) for the same patients were generated, under the same collimator and prescription isodose line (62-68%) by CK Multiplan System. Both the SLP and MLP were able to get ＞95% PTV volume covered prescription isodose and meet the Timmerman 2011 OAR (brainstem, optic nerve and pituitary) constraints.ResultsCompared with the SLP, the maximum dose (Dmax) and mean dose (Dmean) of brainstem in the MLP decreased 0.22-3.13% (2.62%) and 2.71-12.56% (5.57%), over all P＜0.05. While the volumes of whole brain minus the tumors received a single dose equivalence of 8-16Gy (V8Gy-V16Gy) could effectively reduce in the MLP. And the treatment time parameters (the total number of beams and monitor units (MU)) of the MLP declined 3.31% and 1.47% (P＜0.05) respectively. Although there were a few differences of conformity index (CI) and homogeneity index (HI) between two treatment plans, it was no statistical significance (P = 2.94 and 1.08＞ 0.05). ConclusionOne multiple-lesions-plan for brain metastases could achieve higher precision in target and lower dose in healthy tissue, while shorten the treatment time and improve the treatment efficiency.