Physical factors affecting absorbed dose to the skin from cobalt‐60 gamma rays and 25‐MV x rays

Gagnon, William F.; Horton, John L.

doi:10.1118/1.594583

Cited by 26 publications

(9 citation statements)

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“…The shapes of the measured curves agree with those found by previous authors 20,21 . Electrons scattered back into the chamber by interactions in the first few millimetres of the backscattering material account for the sharp dose fall-off region before the interface.…”

Section: Dose Distributions In Air Cavity Phantomssupporting

confidence: 82%

Investigation of photon beam models in heterogeneous media of modern radiotherapy

Ding

Johnston

Wong

et al. 2004

Australas. Phys. Eng. Sci. Med.

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This study investigates the performance of photon beam models in dose calculations involving heterogeneous media in modern radiotherapy. Three dose calculation algorithms implemented in the CMS FOCUS treatment planning system have been assessed and validated using ionization chambers, thermoluminescent dosimeters (TLDs) and film. The algorithms include the multigrid superposition (MGS) algorithm, fast Fourier Transform Convolution (FFTC) algorithm and Clarkson algorithm. Heterogeneous phantoms used in the study consist of air cavities, lung analogue and an anthropomorphic phantom. Depth dose distributions along the central beam axis for 6 MV and 10 MV photon beams with field sizes of 5 cm x 5 cm and 10 cm x 10 cm were measured in the air cavity phantoms and lung analogue phantom. Point dose measurements were performed in the anthropomorphic phantom. Calculated results with three dose calculation algorithms were compared with measured results. In the air cavity phantoms, the maximum dose differences between the algorithms and the measurements were found at the distal surface of the air cavity with a 10 MV photon beam and a 5 cm x 5 cm field size. The differences were 3.8%. 24.9% and 27.7% for the MGS. FFTC and Clarkson algorithms. respectively. Experimental measurements of secondary electron build-up range beyond the air cavity showed an increase with decreasing field size, increasing energy and increasing air cavity thickness. The maximum dose differences in the lung analogue with 5 cm x 5 cm field size were found to be 0.3%. 4.9% and 6.9% for the MGS. FFTC and Clarkson algorithms with a 6 MV photon beam and 0.4%. 6.3% and 9.1% with a 10 MV photon beam, respectively. In the anthropomorphic phantom, the dose differences between calculations using the MGS algorithm and measurements with TLD rods were less than +/-4.5% for 6 MV and 10 MV photon beams with 10 cm x 10 cm field size and 6 MV photon beam with 5 cm x 5 cm field size, and within +/-7.5% for 10 MV with 5 cm x 5 cm field size, respectively. The FFTC and Clarkson algorithms overestimate doses at all dose points in the lung of the anthropomorphic phantom. In conclusion, the MGS is the most accurate dose calculation algorithm of investigated photon beam models. It is strongly recommended for implementation in modern radiotherapy with multiple small fields when heterogeneous media are in the treatment fields.

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Section: Dose Distributions In Air Cavity Phantomssupporting

confidence: 82%

Investigation of photon beam models in heterogeneous media of modern radiotherapy

Ding

Johnston

Wong

et al. 2004

Australas. Phys. Eng. Sci. Med.

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“…While there is little dosimetric impact from small angles

(< 40 °)

, the surface dose increases sharply at larger angles, the relative dose being 50% larger at an obliquity of

~ 55 °

. ( 23 , 25 ) There is only small dependence on beam energy, ( 26 , 36 ) and no impact from field modulation on this increase. ( 15 ) For a surface at 90° relative to the incident beam, the dose is

58 % - 65 %

of the

{normalD}_{max}

dose for a

10 \times 10 {cm}^{2}

field at both 6 MV and cobalt energies.…”

Section: Skin Dose Overviewmentioning

confidence: 99%

Skin dose during radiotherapy: a summary and general estimation technique

Kry

Smith

Weathers

et al. 2012

J Applied Clin Med Phys

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The skin dose associated with radiotherapy may be of interest for clinical evaluation or investigating the risk of late effects. However, skin dose is not intuitive and is difficult to measure. Our objectives were to develop and evaluate a general estimation technique for skin dose based on treatment parameters. The literature on skin dose was supplemented with measurements and Monte Carlo simulations. Using all available data, a general dosimetry system was developed (in the form of a series of equations) to estimate skin dose based on treatment parameters including field size, the presence of a block tray, and obliquity of the treatment field. For out‐of‐field locations, the distance from the field edge was also considered. This dosimetry system was then compared to TLD measurements made on the surface of a phantom. As compared to measurements, the general dosimetry system was able to predict skin dose within, on average, 21% of the local dose (4% of the normalDmax dose). Skin dose for patients receiving radiotherapy can be estimated with reasonable accuracy using a set of general rules and equations.PACS numbers: 87.53.‐j, 87.53.Bn, 87.55.ne

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“…Backscatter of electrons was estimated from experiments. Backscatters of 10 and 5% were estimated for 6oCo and 21 MV x-rays respectively Schnell 1976, Gagnon andHorton 1979).…”

Section: Comparison With Experiments and Other Calculation Methodsmentioning

confidence: 99%

Direct nucleophilic functionalization of C(sp²)–H-bonds in arenes and hetarenes by electrochemical methods

Shchepochkin¹,

Чупахин²,

Charushin³

et al. 2013

Russ. Chem. Rev.

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Relative lateral electron surface dose distributions from filters and air in high energy photon beams were determined using the Fermi-Eyges theory of multiple scattering. The model includes transmission and angular scattering in materials and in air. Backscatter from the phantom was also estimated. The variation of surface dose with different parameters such as atomic number, thickness and position of material, field size and photon energy was investigated. The calculated data show good agreement with experiment. For CO y rays, electron filters of medium atomic number give the lowest surface dose, whereas for higher energies a low to medium atomic number material should be used, especially for short material-phantom distances and large field sizes. The contribution to surface dose can be reduced by over 30% by placing a thin foil of high atomic number after a low to medium atomic number filter, thus scattering some electrons from the beam. For 6oCo y rays the air is often the dominant source of contaminating electrons because of high multiple scatter loss at this energy, while for higher photon energies the beam flattening filter is the main electron source because of the small emission angle of the electrons and the small scattering power at high energies. 60

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Physical factors affecting absorbed dose to the skin from cobalt‐60 gamma rays and 25‐MV x rays

Cited by 26 publications

References 0 publications

Investigation of photon beam models in heterogeneous media of modern radiotherapy

Investigation of photon beam models in heterogeneous media of modern radiotherapy

Skin dose during radiotherapy: a summary and general estimation technique

Direct nucleophilic functionalization of C(sp²)–H-bonds in arenes and hetarenes by electrochemical methods

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Physical factors affecting absorbed dose to the skin from cobalt‐60 gamma rays and 25‐MV x rays

Cited by 26 publications

References 0 publications

Investigation of photon beam models in heterogeneous media of modern radiotherapy

Investigation of photon beam models in heterogeneous media of modern radiotherapy

Skin dose during radiotherapy: a summary and general estimation technique

Direct nucleophilic functionalization of C(sp2)–H-bonds in arenes and hetarenes by electrochemical methods

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Product

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Direct nucleophilic functionalization of C(sp²)–H-bonds in arenes and hetarenes by electrochemical methods