Photon beam quality variations of a flattening filter free linear accelerator

Georg, Dietmar; Kragl, G.; Wetterstedt, Sacha af; McCavana, Patrick; McClean, Brendan; Knöös, Tommy

doi:10.1118/1.3264617

Cited by 59 publications

(46 citation statements)

References 21 publications

(27 reference statements)

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“…FF removal also affects the variation in the energy spectrum across the beam (making it much more uniform) but energy matching across the beam is not possible. In contrast, and in following with other work 10 , 23 the 10 MV beam has not been adjusted. The

{TPR}_{20 / 10}

for the 10 MV and 10 MV FFF beams are 0.737 and 0.716, respectively.…”

Section: Methodsmentioning

confidence: 99%

Surface dose variations in 6 and 10 MV flattened and flattening filter‐free (FFF) photon beams

Cashmore

2016

J Applied Clin Med Phys

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As the use of linear accelerators operating in flattening filter‐free (FFF) modes becomes more widespread, it is important to have an understanding of the surface doses delivered to patients with these beams. Flattening filter removal alters the beam quality and relative contributions of low‐energy X‐rays and contamination electrons in the beam. Having dosimetric data to describe the surface dose and buildup regions under a range of conditions for FFF beams is important if clinical decisions are to be made. An Elekta Synergy linac with standard MLCi head has been commissioned to run at 6 MV and 10 MV running with the flattening filter in or out. In this linac the 6 MV FFF beam has been energy‐matched to the clinical beam on the central axis (normalD10). The 10 MV beam energy has not been adjusted. The flattening filter in both cases is replaced by a thin (2 mm) stainless steel plate. A thin window parallel plate chamber has been used to measure a comprehensive set of surface dose data in these beams for variations in field size and SSD, and for the presence of attenuators (wedge, shadow tray, and treatment couch). Surface doses are generally higher in FFF beams for small field sizes and lower for large field sizes with a crossover at 10×10 cm2 at 6 MV and 25×25 cm2 at 10 MV. This trend is also seen in the presence of the wedge, shadow tray, and treatment couch. Only small differences (<0.5%) are seen between the beams on varying SSD. At both 6 and 10 MV the filter‐free beams show far less variation with field size than conventional beams. By removing the flattening filter, a source of contamination electrons is exchanged for a source of low‐energy photons (as these are no longer attenuated). In practice these two components almost balance out. No significant effects on surface dose are expected by the introduction of FFF delivery.PACS number(s): 87.53.Bn, 87.55.ne, 87.56.bd

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{TPR}_{20 / 10}

for the 10 MV and 10 MV FFF beams are 0.737 and 0.716, respectively.…”

Section: Methodsmentioning

confidence: 99%

Surface dose variations in 6 and 10 MV flattened and flattening filter‐free (FFF) photon beams

Cashmore

2016

J Applied Clin Med Phys

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“…It should be noted that newer multi-modality/ multi-energy medical linacs are being introduced that are capable of operating in a flattening filter free (FFF) mode (Georg et al 2010;Kouloulias et al 2003;Kragl et al 2009). Such linacs are able to generate photon beams having significantly higher dose rates; beam profile requirements for the patient's target volume are met by using the beam modulation feature.…”

Section: Dosimetry Parametersmentioning

confidence: 97%

Physics of Radiotherapy Planning and Delivery

et al. 2011

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“…The removal of the flattening filter alone, without any further modifications in the beam control parameters, results in a higher dose rate and reduced beam quality 1 , 2 , 3 , 6 , 7 , 11 , 12 . The beam quality can be increased to that of the corresponding flattened beam by matching the percentage depth dose (PDD) at 10 cm depth.…”

Section: Introductionmentioning

confidence: 99%

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

Meshram

Pramanik

Ranjith

et al. 2016

J Applied Clin Med Phys

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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

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Photon beam quality variations of a flattening filter free linear accelerator

Abstract: Off-axis energy variation is rather small in unflattened beams and less than half the one for flattened beams. Thus, ignoring the effect of off-axis energy variation for dose calculations in unflattened beams can be clinically justified.

Cited by 59 publications

References 21 publications

Surface dose variations in 6 and 10 MV flattened and flattening filter‐free (FFF) photon beams

Surface dose variations in 6 and 10 MV flattened and flattening filter‐free (FFF) photon beams

Physics of Radiotherapy Planning and Delivery

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

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