Monitor unit calculation for large wedged high-energy photon beams

Chen, Zhe; Reinstein, L. E.; Ramsay, E. B.

doi:10.1088/0031-9155/40/3/009

Cited by 3 publications

(2 citation statements)

References 11 publications

(1 reference statement)

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“…There are a large amount of experimental and theoretical data regarding the dependence of the wedge factors with depth and field size. [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19] The reported wedge factor variations with field size are drastic, from no clear increasing pattern with field size 1, 16 to more than 10%. 6,10,15 Similarly, wide variations of wedge factor dependence with depth are also reported in the literature with values from 2% to more than 10% at 20 cm depth.…”

Section: Introductionmentioning

confidence: 99%

Wedge factor dependence with depth, field size, and nominal distance- A general computational rule

et al. 1999

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We have investigated the dependence of the wedge factors with field size, depth, nominal, and extended distances for 4, 6, 18, and 24 MV photon beams. Analysis of the experimental data suggests a general linear dependence of the wedge factors with field size and depth. The study shows that changes in wedge factors are insignificant (< or = +/-1.0%) with respect to measurements at nominal SSD, SAD, or extended SSD. This independence of the wedge factors on source-to-surface distance was studied for different photon energies (4-24 MV) and for different attenuating wedges (external and internal wedges). For clinical applications, an algorithm is presented to calculate the wedge factor dependence with field size and depth. The new algorithm has been successfully implemented to replace wedge look-up tables for dose and MU calculations in PRISM 1.2 treatment planning system used in our department.

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Section: Introductionmentioning

confidence: 99%

Wedge factor dependence with depth, field size, and nominal distance- A general computational rule

et al. 1999

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“…[1][2][3][4][5][6] It is becoming more common to incorporate the wedge factor as a function of field size and depth in treatment planning or monitor unit calculation. 7,8 However, such an approach is still inadequate to account for various treatment situations, such as irregular fields, asymmetric fields, or different SSDs for a SAD treatment. Thus measurements of wedge factors for individual fields may be required, which could be labor intensive and time consuming in clinical practice.…”

Section: Introductionmentioning

confidence: 99%

Calculating dose and output factors for wedged photon radiotherapy fields using a convolution/superposition method

1997

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We have developed a convolution/superposition method to calculate dose distributions in photon treatment fields with beam modifiers such as physical wedges. The dose component due to wedge generated radiation was accounted for by using an extended phantom model, which integrated a wedge, an air gap, and a patient phantom as the calculation phantom. The inhomogeneities in the extended phantom and the effect of beam hardening by the wedge were both corrected for in the convolution dose calculation. The calculated dose was verified by Monte Carlo simulation of the same extended phantom. A new dual photon source model was also used in the convolution method to account for both primary photons from the target and extra-focal photons from the primary collimator and flattening filter. Thus, realistic photon energy fluence distributions in the extended phantom were used for the dose calculation. The calculated dose distributions and the wedge factors agreed with the measured data within 2% for a variety of treatment fields including asymmetric fields. Our results showed that the wedge-generated radiation could contribute a significant fraction of the total dose in patients. This dose component depends on a specific field configuration, thus wedge factor changes with photon energy, wedge angle, field size, depth, and patient phantom SSD. The variation of the wedge factor can be predicted accurately by our convolution approach with the extended phantom model, which allows for more accurate dose or monitor unit computation for photon fields with beam modifiers.

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Radiation Therapy of Large Intact Breasts Using a Beam Spoiler or Photons with Mixed Energies

Lief¹,

Hunt²,

Hong³

et al. 2007

Medical Dosimetry

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Monitor unit calculation for large wedged high-energy photon beams

Cited by 3 publications

References 11 publications

Wedge factor dependence with depth, field size, and nominal distance- A general computational rule

Wedge factor dependence with depth, field size, and nominal distance- A general computational rule

Calculating dose and output factors for wedged photon radiotherapy fields using a convolution/superposition method

Radiation Therapy of Large Intact Breasts Using a Beam Spoiler or Photons with Mixed Energies

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