Comparison with Conventional Arc and Split-Partial Arc Techniques of Volumetric Modulated Arc Therapy (VMAT) in Terms of Planning Efficiency for Stereotactic Radiotherapy (SRT) Treatment of Multiple Brain Metastases

Abstract

Purpose: In stereotactic radiotherapy of multiple brain metastases (BM), Conventional Arc (CA) of the volumetric modulated arc therapy (VMAT) technique with on a single isocentric is a frequently used technique with Linac (Linear Accelerator) treatment devices. Reducing the dose of healthy brain tissue as well as improved delivery efficiency in SRT treatment of BM is important to reduce possible treatment toxicity. Therefore, multileaf collimator (MLC) movements in wide arcs of CA technique may result in non-optimal dose distribution and increasing low-dose volume in the brain. To evaluate improve the protection in brain of SPA technique having reduced field sizes which minimizes physical limitations of MLC moves. Methods: 28 patients with 3≤, ≥6 of multiple BM included in this retrospective planning study. All plans were generated 27 Gy in 3 fractions using conventional arcs with automated wide of fields and split partial arcs with the manual arrangement of fields according to tumors localization in brain. Dosimetric parameters included tumor coverage, conformity index (CI), gradient index (GI), V4Gy, V10Gy and V12Gy volumes of brain from both techniques were compared by Wilcoxon signed-ranked tests. Results: Both techniques satisfied clinical requirements in coverages of PTV and CI. CA technique had a significantly higher GI than SPA of VMAT (GI; 4.19 vs. 3.58; p < 0.001). SPA technique was found significantly lower V4Gy (18.50 vs. 21.30 cm3, p < 0.001), V10Gy (30.71 vs. 40.76 cm3, p < 0.05) and V12Gy (213.32 vs. 305.71 cm3, p<0.05) volumes. Conclusions: Due to rapid MLC modulation and less tongue-and-groove effect in arcs with smaller field widths, SPA technique can reduce OAR and brain dose radiation exposure in brain stereotactic radiotherapy for different tumor localizations in the brain. This technique may be the first choice compared to the CA technique for SRT of BM having distant and scattered targets.