Dosimetric properties of equivalent‐quality flattening filter‐free (FFF) and flattened photon beams of Versa HD linear accelerator

Abstract

This study presents the basic dosimetric properties of photon beams of a Versa HD linear accelerator (linac), which is capable of delivering flattening filter‐free (FFF) beams with a beam quality equivalent to the corresponding flattened beams based on comprehensive beam data measurement. The analyzed data included the PDDs, profiles, penumbra, out‐of‐field doses, surface doses, output factors, head and phantom scatter factors, and MLC transmissions for both FFF and flattened beams of 6 MV and 10 MV energy from an Elekta Versa HD linac. The 6MVFFF and 10MVFFF beams had an equivalent mean energy to the flattened beams and showed less PDD variations with the field sizes. Compared with their corresponding flattened beams, Dmax was deeper for FFF beams for all field sizes; the ionization ratio variations with the field size were lower for FFF beams; the out‐of‐field doses were lower and the penumbras were sharper for the FFF beams; the off‐axis profile variations with the depths were lesser for the FFF beams. Further, the 6MVFFF and 10MVFFF beams had 35.7% and 40.9% less variations in output factor with the field size, respectively. The collimator exchange effect was reduced in the FFF mode. The head scatter factor showed 59.1% and 73.6% less variations, on average, for the 6MVFFF and 10MVFFF beams, respectively; the variations in the phantom scatter factor were also smaller. The surface doses for all beams increased linearly with the field size. The 6MVFFF and 10MVFFF beams had higher surface doses than the corresponding flattened beams for field sizes of up to 10×10cm2 but had lower surface doses for larger fields. Both FFF beams had lower average MLC transmissions than the flattened beams. The finding that the FFF beams were of equivalent quality to the corresponding flattened beams indicates a significant difference from the data on unmatched FFF beams.PACS number(s): 87.56.bd, 87.55.Qr

The comparison of spatial resolution of ion chamber, diode, and EBT3 film based on the dose profile

“…The tools usually used to measure the dose profile are an ion chamber (1)(2)(3)(4)(5) or a diode dosimeter with higher spatial resolution (6)(7)(8). The above two tools require a water…”

Enhancement of the Dose on 12 MV Linac with Free Flattening Filter Mode

“…Many studies have been carried out on Elekta precise and Varian clinac 2100C linacs. There were some differences between previous works for mean energy and photon energy spectra with FFF mode [1,2,8,14,16-18,20]. The most previous studies were based on simulation with FF removed from conventional flattened beam accelerators as our work but not on a real commercially clinical accelerators with FFF capability.…”

Surface doses of flattening filter free beams with volumetric modulated arc therapy dose delivery for breast cancer

“…The superficial doses of breast cancer RT treatments were studied with Elekta Infinity (Elekta AB, Stockholm, Sweden) linear accelerator equipped with Agility MLC with flattened and unflattened photon energies of 6 and 10 MV. It should be noted that unlike with Varian Medical System's FFF beams, the corresponding Elekta beams have higher maximum energy to achieve equivalent mean energy to the flattened beams thus resulting in deeper D max depths [10].…”

“…Furthermore, there is evidence that the use of flattening filter free (FFF) beams can decrease treatment duration which can have clinical significance, especially in the DIBH treatments [8,9]. In addition, the absence of the flattening filter can decrease the out-of-field doses to the patient decreasing the possibility of inducing secondary cancer [10]. However, one of the disadvantages of using FFF beams in breast RT is the higher degree of modulation needed when uniform dose distribution is required, thus requiring more monitor units (MUs) to achieve the uniform dose distribution [8,9].…”