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Geometrical splitting technique to improve the computational efficiency in Monte Carlo calculations for proton therapy
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10.1118/1.4795343
/content/aapm/journal/medphys/40/4/10.1118/1.4795343
http://aip.metastore.ingenta.com/content/aapm/journal/medphys/40/4/10.1118/1.4795343

Figures

Image of FIG. 1.
FIG. 1.

Treatment head at one gantry at the FHBPTC. The beam enters from the right. Dotted lines show the position of the split planes: upstream of the second scatterer (Sc2), at the second ionization chamber (IC2), and immediately upstream of the field specific aperture.

Image of FIG. 2.
FIG. 2.

Normalized efficiency values for a single split plane at the second scatterer (Sc2), the second ionization chamber (IC2), and the aperture (AP) for options A1 and A8_1 (see Table I ). The contribution of secondary particles other than protons was discarded for the reference calculation of efficiency. Solid lines represent the fits using Eq. (4) .

Image of FIG. 3.
FIG. 3.

Normalized efficiency versus the number of splits for the two proposed settings. (Left) Setting 2: Upstream of the second scatterer (Sc2) and upstream of the aperture (Ap). (Right) Setting 1: Downstream of the second ionization chamber (IC2) and upstream of the aperture. Normalization was done with respect to the simulation without variance reduction. Five different geometrical setups (options; labeled as A1 to A8_2) were considered as described in Table I .

Image of FIG. 4.
FIG. 4.

(Left) Effect on dose profiles by varying the split number for option A1. The difference from the reference curve (no splitting) is also shown, with the difference scale on the right side of the plot. (Right) Decrease in the efficiency due to the first split plane located upstream of the second scatterer (Sc2) rather than downstream of the second ionization chamber (IC2), with the second split plane located upstream of the aperture (Ap) (see Fig. 3 ).

Image of FIG. 5.
FIG. 5.

Planar fluence (left and top) and mean energy (right and top) per radial position for option A3 for the reference simulation (solid) and with variance reduction (dotted). The PHSP was divided into rings of equal area with a maximum radius of 5 cm to consider the penumbra of the beam. The dip at 4 cm in the mean energy is caused by the squared aperture (8 cm side). Relative differences in percent are shown at the bottom for both figures.

Image of FIG. 6.
FIG. 6.

Energy spectrum (left and top) and angular distribution (right and top) for option A3. Reference simulation (solid) and simulation with variance reduction (dotted) are shown. Their relative differences in percent are shown at the bottom of the plots.

Image of FIG. 7.
FIG. 7.

Depth–dose profile (left) and lateral dose profile at 5.5 cm and at 1 cm from the entrance of the water phantom for option A3. Percentage differences also are shown on the right axis.

Image of FIG. 8.
FIG. 8.

Depth–dose profile at depth (left) and lateral dose profile (right) at 23 cm and at 10 cm from the entrance of the water phantom for option A8_1. Percentage differences below of 2% also are shown on the right axis.

Image of FIG. 9.
FIG. 9.

Transverse view for a head treatment. Reference simulation (solid) and with variance reduction (dotted) are shown in the same image. The right side shows the gamma test values. The percentage of total voxels with a gamma value lower than unity is 98.9% by using a 2 mm and 2% criteria.

Image of FIG. 10.
FIG. 10.

Coronal view for a prostate case. (Left) Reference simulation (solid) and with variance reduction (dotted) are shown. The right side shows the gamma test values. The percentage of total voxels with a gamma value lower than unity is 99.7% by using a 2 mm and 2% criteria.

Tables

Generic image for table
TABLE I.

Proton beam configuration options used in the study for calculating dose distributions in water. These options cover the minimum and maximum proton ranges deliverable at the MGH gantry treatment heads.

Generic image for table
TABLE II.

Average simulation times per CPU, efficiency and normalized efficiency per CPU for the reference simulations and the simulations using variance reduction for the production of PHSP. The normalization was made with respect to the reference simulations. The planar energy fluence from a bin of 1 cm radius was considered to calculate the variance. The statistical uncertainty of the full PHSPs is on average lower than 0.2% for all options.

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/content/aapm/journal/medphys/40/4/10.1118/1.4795343
2013-03-20
2014-04-19
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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: Geometrical splitting technique to improve the computational efficiency in Monte Carlo calculations for proton therapy
http://aip.metastore.ingenta.com/content/aapm/journal/medphys/40/4/10.1118/1.4795343
10.1118/1.4795343
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