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Pitfalls of tungsten multileaf collimator in proton beam therapy
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10.1118/1.3658655
/content/aapm/journal/medphys/38/12/10.1118/1.3658655
http://aip.metastore.ingenta.com/content/aapm/journal/medphys/38/12/10.1118/1.3658655

Figures

Image of FIG. 1.
FIG. 1.

A schematic diagram illustrating the geometry used in the Monte Carlo simulation.

Image of FIG. 2.
FIG. 2.

Neutron fluence from tungsten MLC (a) and brass aperture (b) modeled by absorber block of 6.5 cm thickness irradiated by 200 MeV proton beam.

Image of FIG. 3.
FIG. 3.

Energy distribution of neutrons escaping from tungsten MLC (a) and brass aperture (b) of 6.5 cm thickness irradiated by 200 MeV proton beam. Statistical uncertainty is less than 2%.

Image of FIG. 4.
FIG. 4.

Variation of the ambient dose equivalent H*(10) from secondary neutrons generated by 200 MeV proton beam in tungsten MLC and brass aperture: (a) H*(10) profile along the beam axis and (b) lateral profiles at various distances from the downstream surface along the beam axis (see Fig. 1). Tungsten MLC was modeled by absorber of thicknesses 6.5 cm (LinaTech), 8.2 cm (Varian), and brass aperture was modeled by a 6.5-cm thick brass absorber. Statistical uncertainty is less than 1%.

Image of FIG. 5.
FIG. 5.

Time dependence of activity per a unit volume of an irradiated part of the brass aperture. The aperture was used for 30 fractions with 5 treatments per week, 180 cGy per fraction delivered by 200 MeV proton beam. The activity was scored at time mark 24 h after previous fraction during the treatment course. The statistical uncertainty does not exceed 0.5%.

Image of FIG. 6.
FIG. 6.

The ambient dose equivalent H*(10) from residual activity of brass aperture after its usage for 30 fractions with 5 treatments per week, 180 cGy/fraction delivered by 200 MeV proton beam and 1 h of cooling time.

Image of FIG. 7.
FIG. 7.

Buildup and decay of the induced activity per unit volume of the irradiated part of the tungsten MLC over 1 h for the two scenarios: scenario I-h (solid line) and scenario II-h (dashed line). The statistical uncertainty does not exceed 0.3%.

Image of FIG. 8.
FIG. 8.

Activity per unit volume of the irradiated part of the tungsten MLC over 24 h. High activity trend represents the buildup of activity at the end of each irradiation. The low activity trend shows the residual activity between the treatments. The effective activity represents the average activity over 1 day. The statistical uncertainty of calculations is less than 1%.

Image of FIG. 9.
FIG. 9.

Monthly buildup of induced radioactivity. Activity is given per unit volume of tungsten in the irradiated part of the MLC for two scenarios: scenario I-m and scenario II-m. The statistical uncertainty of calculation does not exceed 2%.

Image of FIG. 10.
FIG. 10.

The ambient dose equivalent H*(10) from induced radioactivity of tungsten MLC after 1 yr irradiation and 1 h of cooling time.

Tables

Generic image for table
TABLE I.

Isotopes contributing to the residual activity of a unit irradiated volume of the brass block after a single irradiation delivering 180 cGy and 24 h cooling time. Activity is given in % of total activity 1 day after the irradiation. Here, notations are h—hours, d—days, EC—electron capture, β±—positron/negatron decays.

Generic image for table
TABLE II.

Isotopes contributing to the residual activity of a unit irradiated volume of brass block after 30 fractions, 180 cGy per fraction and 40 days cooling time. Activity is the % of total activity 1 day after the last fraction. Here, notations are d—days, y—years, EC—electron capture, β±— positron/negatron decays.

Generic image for table
TABLE III.

Isotopes contributing to the residual activity of a unit irradiated volume of the tungsten MLC. Activity is given in % of total activity at the end of a 4-week circle (week of operation – week cooling – operation – week cooling). Here notations are h—hours, d—days, y—years, EC—electron capture, and β±—positron/negatron decays.

Generic image for table
TABLE IV.

Isotopes are determining the residual activity of the unit volume of irradiated part of tungsten MLC. Activity is given in % from total activity after 1 yr of irradiation and 40 days cooling time. Here, notations are d—days, EC—electron capture, β±—positron/negatron decays.

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/content/aapm/journal/medphys/38/12/10.1118/1.3658655
2011-11-10
2014-04-20
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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: Pitfalls of tungsten multileaf collimator in proton beam therapy
http://aip.metastore.ingenta.com/content/aapm/journal/medphys/38/12/10.1118/1.3658655
10.1118/1.3658655
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