Dosimetric characteristics of a new linear accelerator under gated operation

Kriminski, S; Li, Alex N.; Solberg, Timothy D.

doi:10.1120/jacmp.2027.25372

Cited by 8 publications

(6 citation statements)

References 32 publications

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“…Gating is initiated with different respiratory monitoring systems at the moment and various studies have been performed in order to assess the differences between them [ 8 - 11 ]. Several others additionally investigated the question whether or not a linac is able to being gated, [ 3 ] or the linac’s performance under gated treatment [ 12 - 14 ].…”

Section: Introductionmentioning

confidence: 99%

Characteristics of gated treatment using an optical surface imaging and gating system on an Elekta linac

et al. 2015

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BackgroundKnowing the technical characteristics of gated radiotherapy equipment is crucial for ensuring precise and accurate treatment when using techniques such as Deep-Inspiration Breath-Hold and gating under free breathing. With one of the first installations of the novel surface imaging system Catalyst™ (C-RAD AB, Sweden) in connection with an Elekta Synergy linear accelerator (Elekta AB, Sweden) via the Elekta Response Interface, characteristics like dose delivery accuracy and time delay were investigated prior to clinical implementation of gated treatments in our institution.MethodsIn this study a moving phantom was used to simulate respiratory motion which was registered by the Catalyst™ system. The gating level was set manually. Within this gating window a trigger signal is automatically sent to the linac initiating treatment delivery. Dose measurements of gated linac treatment beams with different gating levels were recorded with a static 2D-Diode Array (MapCheck2, Sun Nuclear Co., USA) and compared to ungated reference measurements for different field sizes. In addition, the time delay of gated treatment beams was measured using radiographic film.ResultsThe difference in dose delivery between gated and ungated treatment decreases with the size of the chosen gating level. For clinically relevant gating levels of about 30%, the differences in dose delivery accuracy remain below 1%. In comparison with other system configurations in literature, the beam-on time delay shows a large deviation of 851 ms ± 100 ms.ConclusionsWhen performing gated treatment, especially for free-breathing gating, factors as time delay and dose delivery have to be evaluated regularly in terms of a quality assurance process. Once these parameters are known they can be accounted and compensated for, e.g. by adjusting the pre-selected gating level or the internal target volume margins and by using prediction algorithms for breathing curves. The usage of prediction algorithms becomes inevitable with the high beam-on time delay which is reported here.

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Section: Introductionmentioning

confidence: 99%

Characteristics of gated treatment using an optical surface imaging and gating system on an Elekta linac

et al. 2015

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“…Previous authors have reported gating results for three manufacturers: Varian Wang 2000 andJin andYin 2005); Siemens (Kriminski et al 2006 andWeibert et al 2009) and Brainlab (Hugo et al 2003 andVerellen et al 2003). The Varian system uses a gridded gun for gating.…”

Section: Introductionmentioning

confidence: 99%

Gating characteristics of an Elekta radiotherapy treatment unit measured with three types of detector

Evans¹,

Symonds-Tayler²,

Colgan³

et al. 2010

Phys. Med. Biol.

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Abstract. The characteristics of an Elekta Precise treatment machine with a gating interface were investigated. Three detectors were used: a Farmer ionisation chamber; a MatriXX ionisation chamber array and an in-house, single pulse-measurement ionisation chamber (IVC). Measurements were made of dosimetric accuracy, flatness and symmetry characteristics and duty cycle for a range of beam-on times and gating periods. Results were compared with a standard un-gated delivery as a reference. For all beam-on times, down to 0.5 s, dosimetric differences were below ±1 % and flatness and symmetry parameter variations were below ±1.5 %. For the shorter beam-on times the in-house detector deviated from the other two detectors, suggesting that this device should be used in conjunction with other detectors for absolute dosimetry purposes. However it was found to be useful for studying gated beam characteristics pulse by pulse.

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“…There are different sorts of algorithms to predict dosimetric portal images ͑DPIs͒. 4,[12][13][14][15][16][17][18][19][20][21] Among them, Monte Carlo ͑MC͒ simulation is highly attractive given its ability to accurately reproduce measurements. It has been demonstrated that MC is able to achieve agreement between the predicted and measured DPIs.…”

Section: Introductionmentioning

confidence: 99%

Monte Carlo-based adaptive EPID dose kernel accounting for different field size responses of imagers

et al. 2009

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The aim of this study is to present an efficient method to generate imager-specific Monte Carlo ͑MC͒-based dose kernels for amorphous silicon-based electronic portal image device dose prediction and determine the effective backscattering thicknesses for such imagers. EPID field sizedependent responses were measured for five matched Varian accelerators from three institutions with 6 MV beams at the source to detector distance ͑SDD͒ of 105 cm. For two imagers, measurements were made with and without the imager mounted on the robotic supporting arm. Monoenergetic energy deposition kernels with 0-2.5 cm of water backscattering thicknesses were simultaneously computed by MC to a high precision. For each imager, the backscattering thickness required to match measured field size responses was determined. The monoenergetic kernel method was validated by comparing measured and predicted field size responses at 150 cm SDD, 10ϫ 10 cm 2 multileaf collimator ͑MLC͒ sliding window fields created with 5, 10, 20, and 50 mm gaps, and a head-and-neck ͑H&N͒ intensity modulated radiation therapy ͑IMRT͒ patient field. Field size responses for the five different imagers deviated by up to 1.3%. When imagers were removed from the robotic arms, response deviations were reduced to 0.2%. All imager field size responses were captured by using between 1.0 and 1.6 cm backscatter. The predicted field size responses by the imager-specific kernels matched measurements for all involved imagers with the maximal deviation of 0.34%. The maximal deviation between the predicted and measured field size responses at 150 cm SDD is 0.39%. The maximal deviation between the predicted and measured MLC sliding window fields is 0.39%. For the patient field, gamma analysis yielded that 99.0% of the pixels have ␥ Ͻ 1 by the 2%, 2 mm criteria with a 3% dose threshold. Tunable imager-specific kernels can be generated rapidly and accurately in a single MC simulation. The resultant kernels are imager position independent and are able to predict fields with varied incident energy spectra and a H&N IMRT patient field. The proposed adaptive EPID dose kernel method provides the necessary infrastructure to build reliable and accurate portal dosimetry systems.

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Dosimetric characteristics of a new linear accelerator under gated operation

Cited by 8 publications

References 32 publications

Characteristics of gated treatment using an optical surface imaging and gating system on an Elekta linac

Characteristics of gated treatment using an optical surface imaging and gating system on an Elekta linac

Gating characteristics of an Elekta radiotherapy treatment unit measured with three types of detector

Monte Carlo-based adaptive EPID dose kernel accounting for different field size responses of imagers

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