Document Type : Original Paper
Rajiv Gandhi Cancer Institute and Research Centre
Department of Physics, School of Advanced Sciences, Vellore Institute of Technology
Purpose: To compare the three-dimensional conformal radiotherapy (3DCRT), conformal arc therapy (DCA), and volumetric modulated arc therapy (VMAT) in stereotactic body radiation therapy (SBRT) of liver cases using 6MV and 10 MV flattened beam (FB) and flattening filter-free beam (FFFB).
Materials and Methods: Twenty liver SBRT patients were selected. The dose prescription was 40 Gy delivered in 5 fractions. 3DCRT, DCA and VMAT planning was performed using 6 MV FB, 6 MV FFFB, 10 MV FB and 10 MV FFFB. Planning target volume (PTV) coverage, organs at risk (OARs) doses, monitor units (MU), and beam ON time (BOT) were noted. Different dosimetric indexes were calculated and used for comparison.
Results: VMAT plan produces better PTV coverage in the D98% and D95% region. 6 MV and 10 MV VMAT FB and FFFB reduced the D700cc, V10Gy, and Dmean of the liver-GTV region compared to 3DCRT and DCA plans. FFFB in combination with VMAT producing highly conformal plan (CI=1.19), better conformity number (CN=0.85), and lowering Paddick gradient index (GIpad=3.29) in comparison to 3DCRT and DCA. The FFFB needs higher monitor units to achieve the plan in all the techniques. However, FFFB reduces the BOT, body-PTV mean dose and low dose volume coverage in the non-tumour volume.
Conclusions: VMAT combined with FFFB will produce a highly conformal plan, spare the OAR’s, deliver fast and dose fall off in the body-PTV region is more as compared to 3DCRT and DCA plan. The VMAT will more advantage to treat the multiple lesions simultaneously and helps in reducing the intra-fraction motion error in liver SBRT cases.