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
Highlights
The Versa HD linear accelerator is capable of delivering flattened and flattening filter-free (FFF) beams
The average MLC transmission for FFF beams was found to be lower than that of the corresponding flattened beams. This is the first study to report on the dosimetric properties of flattened and FFF beams with equivalent-beam qualities from a Versa HD linac that is commercially available for clinical use
The linear variation in surface dose with the field size is consistent with the findings reported by Wang et al[14] for the Varian linac, in which FFF beams were not matched with flattened beams
Summary
The Versa HD linear accelerator (linac; Elekta AB, Stockholm, Sweden) is capable of delivering flattened and flattening filter-free (FFF) beams. The enhanced leaf and diaphragm speed helps to improve the treatment plan modulation with a high dose rate feature. 359 Meshram et al.: Properties of equivalent-quality FFF beams. Modalities such as the IMRT and VMAT use varying fluence patterns and do not require flat homogeneous beams for plan optimization. Many studies have reported the advantages of FFF beams over conventional flattened beams, such as a higher dose rate, reduced head scatter, smaller leakage, and lower out-of-field dose. The high dose rate is especially beneficial in SRS and SBRT, as well as in treatments that require organ motion management. Various studies have reported the characteristics of FFF beams based on measurements[1,2,3]
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
