Clinical outcomes of multileaf collimator-based CyberKnife for spine stereotactic body radiation therapy.

OBJECTIVE Stereotactic body radiotherapy (SBRT) for spinal metastases is becoming a prevalent therapeutic option. We aimed to evaluate the clinical feasibility and outcomes of the recently developed multileaf collimator (MLC)-based CyberKnife (CK-M) for spine SBRT. METHODS We reviewed 119 patients of 144 cases with 229 lesions treated with CK between November 2014 and March 2016. The lesion features, dosimetric parameters and clinical outcomes were compared between fixed cone collimator based CK (CK-F) and CK-M. RESULTS Of 144 cases, 78 and 66 were treated with CK-F and CK-M, respectively. CK-M achieved an adequate target volume coverage that was comparable with CK-F (median 92 vs 90%; p = 0.03) even in larger targets (median 64.2 vs 46.7 cm3; p = 0.01), respectively. CK-M showed an improvement in the gradient index (p < 0.001) and no difference in conformity (p = 0.16). With CK-M, the median beam delivery time was significantly reduced by 30% (to 34 vs 48 min; p < 0.001). CK-M showed 1 year local control rates that were comparable to CK-F (77 vs 78%, respectively; p = 0.83). CONCLUSION CK-M exhibits dosimetric data and local control that are comparable with CK-F, but with significant treatment time reduction. CK-M could be widely used in spine SBRT. Advances in knowledge: Given the recently developed MLC in CK, we aimed to evaluate the clinical feasibility and outcomes of MLC compared with fixed cone-based CK. MLC showed equivalent plan quality and significant treatment time reduction with comparable radiological control. We report here MLC as an effective and tolerable treatment option in CK.