131 Performance analysis of new Delta4 Phantom+ using Flattening-Filter and Flattening Filter-Free beams

Abstract Purpose There is a recent increase in the use of Flattening Filter-Free (FFF) beams with the aim of reducing treatment time and consequently intrafractional motions. The goal of this study was to evaluate the performances of the new pre-treatment system Delta4 Phantom+ (Scandidos) in terms of a stable and sensitive tool for achieving a reliable verification. Methods Delta4+ was evaluated for verification with 6 MV and 6 MV FFF beams using static beam arrangement. The accelerator output was monitored with the ionisation chamber inserted into the Phantom. The device was tested for dose-rate dependence, linearity and stability using its daily output correction. The response of Delta4+ was evaluated for energy, measuring the gamma index of four Volumetric modulated arc therapy (VMAT) plan with different energies (6 MV, 6 FFF MV, 10 MV, 10 FFF MV). Results The response of Delta4+ as a function of accelerator dose rate is in agreement with the ionisation chamber with a difference smaller than 0,1%. The Delta4+ output is constant for different MU, being the difference within 0,4%. The stability was measured during a 6 months period and the standard deviation obtained is 0,7% for 6 MV and 1% for 6 FFF MV. VMAT plan analysis show values higher of 99% for all energies with a threshold of 3%-3 mm, while with a threshold of 2%-2 mm the values are within 93,5%-97,5%. The plans calculated with FFF beams have the lowest value in the range. Conclusions This study shows that the Delta4+ is an accurate device, in fact, for all the measurements made, uncertainties below 1% were obtained.