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

Abstract

Background: In order to obtain a high dose conformal index of tumor and steep dose fall-off in healthy tissues for brain metastasis stereotactic radiosurgery (SRS), the aim of this study was to investigate SRS planning optimization by comparing one multiple-lesions plan (MLP) with multiple single-lesion plans (SLPs) for patients with multiple brain metastases using the Cyberknife (CK) system.

Methods: Fifty non-small cell lung cancer (NSCLC) patients (28 males and 22 females) with 2-4 brain metastases, inter-tumour distances less than 3 cm, were retrospectively replanned with the original prescription dose (12-32 Gy) in the original fractions (1-3). Two different clinical CK SRS plans (SLPs and MLP) were generated for the same patients with the same collimator and prescription isodose line (62-68%) by the CK Multiplan System. Both SLPs and MLP were able to achieve > 95% PTV volume covered prescription dose and met the Timmerman 2011 organs at risk (brainstem, optic nerve and pituitary) constraints.

Results: Compared with those in the SLPs, the maximum dose (D_max) and mean dose (D_mean) of brainstem in the MLP were reduced 0.22-3.13% (2.62%) and 2.71-12.56% (5.57%), respectively, all P < 0.05. Meanwhile, the volumes of the whole brain minus the tumors that received a single dose equivalent of 8-16 Gy (V8Gy-V16Gy) were effectively reduced in the MLP. The treatment time parameters, the total number of beams and monitor units, of the MLP were reduced by 3.31 and 1.47% (P < 0.05), respectively. Although there were a few differences in the conformity index (CI) and homogeneity index (HI) between the two treatment plans, the differences were not statistically significant (P = 2.94 and 1.08 > 0.05).

Conclusion: One multiple-lesions plan for brain metastases could achieve higher precision in the target and lower doses in healthy tissue while shortening the treatment time and improving the treatment efficiency over multiple single-lesion plans.

Keywords: Cyberknife; Multiple brain metastases; Multiple-lesions plan; Single-lesion plans.

Fig. 1

Different CK SRS plans for the same patient with multiple brain metastases. The representative patient had axial images taken, (a) shown the location of the tumors (red line area), healthy brain tissue around the PTVs (green line area), the whole brain (blue line area) and OAR (Light blue line area was brainstem), (b) and (c) were single-lesion-plan (SLP) and multi-lesions-plan (MLP). The red and purple lines indicate the GTV and the PTV, respectively. Black and blue lines represent brain tissue and brainstem. Green contour was covered with 6-mm thick zone adjacent to the PTV. Isodose: Orange-Prescription dose, Red-100 and 90%, White-70%, Yellow-60%, Pink-50%, Purple-40%, Blue represents 10 to 30 from light to deep, respectively

Fig. 2

The statistical results of V4Gy-V16Gy in the whole brain tissue excluding the PTVs