The determination of phantom and collimator scatter components of the output of megavoltage photon beams: measurement of the collimator scatter part with a beam-coaxial narrow cylindrical phantom

Gasteren, J.J.M. van; Heukelom, S.; Kleffens, H.J. van; Laarse, R. van der; Venselaar, J.L.M.; Westermann, C.F.

doi:10.1016/0167-8140(91)90124-y

Cited by 108 publications

(81 citation statements)

References 22 publications

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“…For example, S c measurements can be made using a solid mini-phantom that is thick enough (in the beam direction) to eliminate electron contamination and small enough (perpendicular to the beam) to keep the amount of phantomscattered photons constant for all measured field sizes. Van Gasteren et al, 56 described the use of a mini-phantom that was constructed to best meet these requirements. Ideally, the solid phantom material should be water equivalent, i.e., it should have the same electron density and effective atomic number as water.…”

Section: A2 Phantomsmentioning

confidence: 99%

“…10,[61][62][63][64] The thickness of material perpendicular to the beam direction should provide enough lateral scatter 65 Mini-phantom so that the accuracy of the measured S c is maintained. This task group recommends a 4-cm diameter cylindrical miniphantom 56 coaxial with the central axis of the beam with the detector at 10-cm depth for the measurement of S c independent of the normalization depth. It is pointed out in the report of the AAPM Therapy Physics Committee TG 74 (Ref.…”

Section: B1c Tissue Phantom Ratiosmentioning

confidence: 99%

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Monitor unit calculations for external photon and electron beams: Report of the AAPM Therapy Physics Committee Task Group No. 71

et al. 2014

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A protocol is presented for the calculation of monitor units (MU) for photon and electron beams, delivered with and without beam modifiers, for constant source-surface distance (SSD) and source-axis distance (SAD) setups. This protocol was written by Task Group 71 of the Therapy Physics Committee of the American Association of Physicists in Medicine (AAPM) and has been formally approved by the AAPM for clinical use. The protocol defines the nomenclature for the dosimetric quantities used in these calculations, along with instructions for their determination and measurement. Calculations are made using the dose per MU under normalization conditions, D 0 , that is determined for each user's photon and electron beams. For electron beams, the depth of normalization is taken to be the depth of maximum dose along the central axis for the same field incident on a water phantom at the same SSD, where D 0 = 1 cGy/MU. For photon beams, this task group recommends that a normalization depth of 10 cm be selected, where an energy-dependent D 0 ≤ 1 cGy/MU is required. This recommendation differs from the more common approach of a normalization depth of d m , with D 0 = 1 cGy/MU, although both systems are acceptable within the current protocol. For photon beams, the formalism includes the use of blocked fields, physical or dynamic wedges, and (static) multileaf collimation. No formalism is provided for intensity modulated radiation therapy calculations, although some general considerations and a review of current calculation techniques are included. For electron beams, the formalism provides for calculations at the standard and extended SSDs using either an effective SSD or an air-gap correction factor. Example tables and problems are included to illustrate the basic concepts within the presented formalism.

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Section: A2 Phantomsmentioning

confidence: 99%

Section: B1c Tissue Phantom Ratiosmentioning

confidence: 99%

Monitor unit calculations for external photon and electron beams: Report of the AAPM Therapy Physics Committee Task Group No. 71

et al. 2014

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“…We used an ionisation chamber in a mini-phantom at the EPID position as a reference detector, because in this way only the primary dose component is measured. 32,124 Within the EPID, mainly lateral x-ray scatter takes place, but also optical photon scatter occurs. 131 For these reasons, the uncorrected EPID has a steeper field size dependent response than the ionisation chamber in a mini-phantom 36 (see Figure 5.1).…”

Section: 4a Scatter In the Epidmentioning

confidence: 99%

On Radiotherapy Dose Verification With a Flat-Panel Imager

McDermott¹

2009

Radiotherapy and Oncology

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“…First, we formulate [6] H jaw in equation 23 as , (24) , (25) , (26) where is the side of the equivalent square field for A jaw ; and a 1 , a 2 , λ S and λ F are constants, where it is assumed that a 1 (the monitor-backscatter coefficient) is influenced only by the jaw collimator, which forms the A jaw field, and not by the MLC or by the wedge. For the present 10-MV X-ray accelerator, we have obtained a 1 = 0.00146 cm -1 , a 2 = 0.0830, λ S = 0.299 cm and λ F = 3.097 cm.…”

Section: In-air Output Factor Calculation For Open Mlc Fieldsmentioning

confidence: 99%

“…in Appendix C), letting both A mlc and A jaw fields be symmetric with respect to the X beam and Y beam axes, and letting the other pairs of A and B MLC leaves be closed at Y beam = 0 cm. The measurement was performed using a cylindrical mini-phantom [24] with a 0.6 cm 3 chamber (PTW 30006 Waterproof Farmer Chamber, Radiation Products Design, Inc. Albertville MN, USA) in free air. It can be seen that the measurement, having small waveforms for each of the A jaw fields, seems to be influenced to a certain degree by scattered radiation from the MLC leaves.…”

Section: Mlc-s C Calculationmentioning

confidence: 99%

10-MV X-ray dose calculation in water for MLC and wedge fields using a convolution method with X-ray spectra reconstructed as a function of off-axis distance

Iwasaki¹,

Kimura²,

Sutoh³

et al. 2017

J Radiol Imaging.

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Purposes: This paper highlights a 10-MV X-ray convolution dose calculation method in water using primary and scatter dose kernels formed for energy bins of X-ray spectra reconstructed as a function of the off-axis distance for a linear accelerator equipped with pairs of upper and lower jaws, a multileaf collimator (MLC) and a wedge filter. Methods: The reconstructed X-ray spectra set was composed of 11 energy bins. To estimate the in-air beam intensities at points on the isocenter plane for an MLC field, we employed an MLC leaf-field output subtraction method, using an extended radiation source on each of the X-ray target and the flattening filter as well as simplified twodimensional plates to simulate the three-dimensional jaws and MLC structures. A special correction factor was introduced for nonuniform incident beam intensities, particularly produced at MLC fields. The in-phantom dose calculation was performed by treating the phantom, the wedge filter, the wedge holder and the MLC as parts of a unified irradiated body, where we proposed to use a special factor for the density scaling theorem within the unified irradiated body. Conclusions: The phantom dose was generally separated into nine dosecomponents: the primary and scatter dose-components produced in the phantom; the primary and scatter dose-components emanating from the wedge, the wedge holder and the MLC; and the electron contamination dose-component. From the calculated and measured percentage depth dose (PDD) and off-center ratio (OCR) datasets, we may conclude that the convolution method can achieve accurate dose calculations even under MLC and/or wedge filtration.Keywords: convolution method; X-ray spectra; dose kernels; wedge; multileaf collimation; MLC leaf-field output subtraction Citation: Iwasaki A, Kimura S, Sutoh K, Kamimura K, Sasamori M, Seino M, Komai F, Takagi M, Terashima S, Hosokawa Y, Saitoh H, Miyazawa M. 10-MV X-ray dose calculation in water for MLC and wedge fields using a convolution method with X-ray spectra reconstructed as a function of off-axis distance. J

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The determination of phantom and collimator scatter components of the output of megavoltage photon beams: measurement of the collimator scatter part with a beam-coaxial narrow cylindrical phantom

Cited by 108 publications

References 22 publications

Monitor unit calculations for external photon and electron beams: Report of the AAPM Therapy Physics Committee Task Group No. 71

Monitor unit calculations for external photon and electron beams: Report of the AAPM Therapy Physics Committee Task Group No. 71

On Radiotherapy Dose Verification With a Flat-Panel Imager

10-MV X-ray dose calculation in water for MLC and wedge fields using a convolution method with X-ray spectra reconstructed as a function of off-axis distance

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