Dosimetric study for spine stereotactic body radiation therapy: MRidian Lianc Vs volumetric modulated arc therapy
Background: Stereotactic body radiation therapy (SBRT) given in 1-5 fractions is an effective treatment for vertebral metastases. Real time magnetic resonance-guided radiotherapy (MRgRT) improves soft tissue contrast which translates into accurate delivery of spine SBRT. Here we report on the quality of MRgRT plans when compared to TrueBeam based volumetric modulated arc therapy (VMAT) plans in the treatment of spine metastases.
Patients and methods: Ten metastatic lesions from nine patients were included in this study for plan comparison. Lesions were spread across thoracic spine and lumbosacral spine. Three fraction spine SBRT plans: 27Gy to planning target volume (PTV) and 30Gy to gross tumor volume (GTV) were generated on the ViewRay MRIdian Linac system and compared to TrueBeamTM STx -based VMAT plans. Plans were compared using metrics such as minimum dose, maximum dose, mean dose, ratio of the dose to 50% of the volume (R50), conformity index, homogeneity index and as well as dose to the spinal cord.
Results: MRIdian plans achieved equivalent target coverage and spinal cord dose when compared to VMAT plans. The maximum and minimum PTV doses and homogeneity index were equivalent for both planning systems. R50 was lower for MRIdian plans when compared to VMAT plans, indicating a lower spread of intermediate doses with MRIdian system (5.16 vs. 6.11, p=0.03).
Conclusions: MRgRT can deliver high-quality spine SBRT plans compared to TrueBeam VMAT plans. Additionally, MRgRT enables better visualization of the spinal cord when compared to computed tomography, and this could prove to be a valuable tool in facilitating accurate delivery of planned dose.
Keywords: MR guided radiotherapy, spine radiotherapy, SBRT, treatment planning, VMAT