A 4 MV flattening filter-free beam: commissioning and application to conformal therapy and volumetric modulated arc therapy

Abstract

Recent studies have indicated that radiotherapy treatments undertaken on a flattening filter-free (FFF) linear accelerator have a number of advantages over treatments undertaken on a conventional linear accelerator. In addition, 4 MV photon beams may give improved isodose coverage for some treatment volumes at air/tissue interfaces, compared to when utilizing the clinical standard of 6 MV photons. In order to investigate these benefits, FFF beams were established on an Elekta Beam Modulator linear accelerator for 4 MV photons. Commissioning beam data were obtained for open and wedged fields. The measured data were then imported into a treatment planning system and a beam model was commissioned. The beam model was optimized to improve dose calculations at shallow, clinically relevant depths. Following verification, the beam model was utilized in a treatment planning study, including volumetric modulated arc therapy, for a selection of lung, breast/chest wall and larynx patients. Increased dose rates of around 800 MU min(-1) were recorded for open fields (relative to 320 MU min(-1) for filtered open fields) and reduced head scatter was inferred from output factor measurements. Good agreement between planned and delivered dose was observed in verification of treatment plans. The planning study indicated that with a FFF beam, equivalent (and in some cases improved) isodose profiles could be achieved for small lung and larynx treatment volumes relative to 4 MV filtered treatments. Furthermore, FFF treatments with wedges could be replicated using open fields together with an 'effective wedge' technique and isocentre shift. Clinical feasibility of a FFF beam was therefore demonstrated, with beam modelling, treatment planning and verification being successfully accomplished.

A dosimetric evaluation of flattening filter-free volumetric modulated arc therapy in nasopharyngeal carcinoma

“…[11121524] All the results reported could well meet the clinical criteria. From all these investigations, it could be extrapolated that dose calculation accuracy in state-of-the-art TPS will certainly not be impaired when removing the FF.…”

“…This has been previously accomplished by replacing the conical reduction which simulating the FF with a negative reduction. [11] In the present work, the energy fluence was modeled by an easier way of providing the TPS with an arbitrary profile. The resulting model, as presented in the previous section, was satisfying.…”

“…[8] During the past years, feasibility of treating various cancers including prostate, lung, larynx, chest wall, and esophagus using unflattened beams have been reported. [910111213141516] Also exclusive use of a linear accelerator in FFF mode in 3D CRT planning has also been reported to be feasible. [17] From all these published results, a reduced beam on time (BOT) and comparable plan quality seem to have been confirmed for VMAT plan with unflattened beams.…”

Beam properties and stability of a flattening‐filter free 7 MV beam—An overview

“…[18][19][20][21][22][23] Only very few centers worldwide have so far, to our knowledge, worked with FFF Siemens accelerators, and information on the dosimetric properties is not yet available. Hence, we feel a detailed overview of the Siemens Artiste FFF 7XU beam is still missing in the medical physics literature, which we aim to remedy in the following work.…”

Beam characterization of 10-MV photon beam from medical linear accelerator without flattening filter

“…The dose distribution for FFF linacs determined using Monte Carlo (MC) simulations,[34567891011] as well as measured data from treatment apparatuses in clinical use,[89101112131415161718] has been published. Most of such experimental studies employed commercial linacs with a metal plate, such as copper or aluminum, inserted to absorb the primary and secondary electrons created in materials in the linac head.…”