Dosimetric comparison of mono-isocentric and multi-isocentric plans for oligobrain metastases: A single institutional experience

Abstract

PuposeTo compare dosimetric plans for the treatments of oligobrains metastases (2–6) using mono-isocentric arc therapy and multi-isocentric volumetric modulated arc therapy (VMAT). Material and methodsA total of sixteen patients with multiple brain metastases were selected. Prescription dose was between 24 and 15Gy depending on the tumor size. For every patient,arctherapy and VMAT plans were generated respectively, with Elements Multiple Brain Mets SRS version 2.0 (BrainLab) and Eclipse SRS Treatment Planning Systeme version 15.5. The conformity index (CI), homogeinity index (HI), gradient index (GI), dose volume histogram for each organs at risk, total Monitor Units were evaluated. ResultsFor coverage of the PTV, mono-isocentric plans showed a better CI and a better GI than multi-isocentric plans, respectively CI of 1.18±0.11 vs 1.41±0.20 (P<0.01), and GI of 3.55±0.59 vs 4.03±1.20 (P<0.01). Homogeneity index was not better with mono-isocentric plans, with respectively HI 24.32±3.87 vs 14.05±4.46 (P=1). For organs at risk, there were no statistical differences between mono and multi-isocentric plans for both eyes, both lenses, both optic nerves, chiasma, brainstem, and hippocampi.V12Gy and V10Gy of normal brain were statistically lower with mono-isocentric plans than with multi-isocentric plans, respectivellyV12Gy of 3.06Gy 95%CI [2.25;3.86]vs 5.18Gy 95%CI [3.43;6.93] (P<0,01) and V10Gy 4.66Gy 95%CI [3.33;5.98] vs7.30Gy 95%CI [4.73;9.87] (P<0.03). Total number of MU was significantly lower with mono-isocentric plans than with multi-isocentric plans, respectively 6668±1463 vs 12403±4941 (P<0.01), then treatment time was lower with mono-isocentric plans. ConclusionMono-isocentric plans had a better conformity index and gradient index than multi-isocentric plans for the treatment of multiple brain metastases. Moreover, mono-isocentric techniques gave fewer doses to normal brain and used less monitor units than multi-isocentric techniques.