Comment on “Intercomparison of normalized head‐scatter factor measurement techniques” [Med. Phys. <b>22</b>, 249–253 (1995)]

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

doi:10.1118/1.597573

Cited by 6 publications

(3 citation statements)

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“…The use of a miniphantom with a measurement depth of 5 or 10 cm can lead to problems in some dose calculation systems, as was previously reported by Frye et al 8 Based on their experimental results, these authors argued that, if the data are meant to be employed in a TMR dosimetry system, a miniphantom is not an appropriate tool for use in head scatter measurements. van Gasteren et al 9 stated that a miniphantom is a useful tool, provided the results are used in a consistent formalism. The effect of contaminant electrons is ''then taken into account in the depth-dose data required for transferring results obtained at a reference depth to the depth of the peak absorbed dose for the reference field.''…”

Section: Introductionmentioning

confidence: 99%

“…The effect of contaminant electrons is ''then taken into account in the depth-dose data required for transferring results obtained at a reference depth to the depth of the peak absorbed dose for the reference field.'' 9 In reply Frye et al agreed to the principle and argued that it was their intention to ''alert the profession that for the high energy photon beams significant inaccuracies may result if the head scatter measurement technique is incompatible with the charged particle environment at the point of normalization of the dosimetry system.'' 10 The convenience of using one reference depth beyond the range of the electron contamination was further stressed by Ten Haken 11 and by Li et al 12 The purpose of this article is to explain in a quantitative way how a dose calculation system based on quantities defined at d max can be related to scatter correction factors measured in a miniphantom at a depth of 5 or 10 cm.…”

Section: Introductionmentioning

confidence: 99%

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Effect of electron contamination on scatter correction factors for photon beam dosimetry

Venselaar

Heukelom²,

Jager

et al. 1999

Med. Phys.

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Physical quantities for use in megavoltage photon beam dose calculations which are defined at the depth of maximum absorbed dose are sensitive to electron contamination and are difficult to measure and to calculate. Recently, formalisms have therefore been presented to assess the dose using collimator and phantom scatter correction factors, Sc and Sp, defined at a reference depth of 10 cm. The data can be obtained from measurements at that depth in a miniphantom and in a full scatter phantom. Equations are presented that show the relation between these quantities and corresponding quantities obtained from measurements at the depth of the dose maximum. It is shown that conversion of Sc and Sp determined at a 10 cm depth to quantities defined at the dose maximum such as (normalized) peak scatter factor, (normalized) tissue-air ratio, and vice versa is not possible without quantitative knowledge of the electron contamination. The difference in Sc at dmax resulting from this electron contamination compared with Sc values obtained at a depth of 10 cm in a miniphantom has been determined as a multiplication factor, Scel, for a number of photon beams of different accelerator types. It is shown that Scel may vary up to 5%. Because in the new formalisms output factors are defined at a reference depth of 10 cm, they do not require Scel data. The use of Sc and Sp values, defined at a 10 cm depth, combined with relative depth-dose data or tissue-phantom ratios is therefore recommended. For a transition period the use of the equations provided in this article and Scel data might be required, for instance, if treatment planning systems apply Sc data normalized at d(max).

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Effect of electron contamination on scatter correction factors for photon beam dosimetry

Venselaar

Heukelom²,

Jager

et al. 1999

Med. Phys.

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“…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.…”

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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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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Comparison of parameterization methods of the collimator scatter correction factor for open rectangular fields of 6–25 MV photon beams

Jager

Heukelom

Kleffens

et al. 2000

Radiotherapy and Oncology

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Comment on “Intercomparison of normalized head‐scatter factor measurement techniques” [Med. Phys. 22, 249–253 (1995)]

Cited by 6 publications

References 0 publications

Effect of electron contamination on scatter correction factors for photon beam dosimetry

Effect of electron contamination on scatter correction factors for photon beam dosimetry

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

Comparison of parameterization methods of the collimator scatter correction factor for open rectangular fields of 6–25 MV photon beams

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