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New empirical formula for neutron dose level at the maze entrance of 15 MV medical accelerator facilities
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10.1118/1.3096417
/content/aapm/journal/medphys/36/5/10.1118/1.3096417
http://aip.metastore.ingenta.com/content/aapm/journal/medphys/36/5/10.1118/1.3096417

Figures

Image of FIG. 1.
FIG. 1.

Geometry definitions for the Kersey method.

Image of FIG. 2.
FIG. 2.

Geometry of the treatment room for the empirical model developed in this study. One maze parameter, , the height from the floor to the ceiling, is not shown in this figure. Two modes of gantry rotation plane were considered: rotation plane 1–3 (mode I) and rotation plane 2–4 (mode II).

Image of FIG. 3.
FIG. 3.

Calculated neutron energy spectra per photon dose (Gy) at the isocenter in the case of a typical room design (: 260 cm, : 803 cm, : 90 cm, : 225 cm, : 170 cm, : 290 cm) The fractional standard deviations in the estimates of the neutron energy spectrum were within 5%. The beam is pointing toward the opposite wall to the maze entrance, parallel to the maze wall.

Image of FIG. 4.
FIG. 4.

Effect of the distance on the neutron dose equivalent at the outer maze entrance when other maze parameters are fixed (: 90 cm, : 890 cm, : 200 cm, : 170 cm, : 290 cm). The fractional standard deviations in the estimates of the neutron dose rate by MCNPX were within 5%. The beam is pointing toward the opposite wall to the maze entrance, parallel to the maze wall. The distance from the isocenter to the wall opposite to the maze wall was assumed to be the same as that of . The comparison was made on the assumption that was related to in the Kersey and Wu-McGinley formulas.

Image of FIG. 5.
FIG. 5.

Effect of the distance on the neutron dose equivalent at the outer maze entrance when other maze parameters are fixed (: 310 cm, : 90 cm, : 200 cm, : 170 cm, : 290 cm). The fractional standard deviations in the estimates of the neutron dose rate by MCNPX were within 5%. The beam is pointing toward the opposite wall to the maze entrance, parallel to the maze wall. The distance from the isocenter to the wall opposite to the maze wall was assumed to be the same as that of . The comparison was made on the assumption that was related to in the Kersey and Wu-McGinley formulas.

Image of FIG. 6.
FIG. 6.

Effect of the height on the neutron dose equivalent at the outer maze entrance when other maze parameters are fixed (: 360 cm, : 872 cm, : 100 cm, : 204 cm, : 196 cm). The fractional standard deviations in the estimates of the neutron dose rate by MCNPX were within 5%. The beam is pointing toward the opposite wall to the maze entrance, parallel to the maze wall. The distance from the isocenter to the wall opposite to the maze wall was assumed to be the same as that of . The comparison was made on the assumption that was related to in the Kersey and Wu-McGinley formulas.

Image of FIG. 7.
FIG. 7.

Comparisons of the doses from the formula derived in this study [Eq. (6)] with the results of MCNPX simulations for the 697 maze configurations

Tables

Generic image for table
TABLE I.

Range of the maze parameters observed at the 11 operating treatment rooms.

Generic image for table
TABLE II.

Relative neutron dose equivalent at the maze entrance as a function of beam direction illustrated in Fig. 2. [All data have been normalized to 1 for the gantry in the position such that the beam was directed toward point 3 when the gantry rotates on the plane 1–3 of Fig. 2 (mode I).]

Generic image for table
TABLE III.

Maze parameters of accelerator facilities used in validation of the new empirical formula [Eq. (7)].

Generic image for table
TABLE IV.

Comparison of neutron dose equivalents at the maze entrance of seven operating treatment rooms evaluated by MCNPX simulations, this study method [Eq. (7)], and the Kersey method.

Generic image for table
TABLE V.

Comparison of measured neutron dose equivalent rates at the maze entrance with the calculations by this study method [Eq. (7)] and the MCNPX simulations with the conditions of the measurements.

Generic image for table
TABLE VI.

Comparison of measured neutron dose equivalent rates at the maze entrance with the calculations of this study method [Eq. (7)] and the Wu-McGinley formula based on the conditions of the measurements in Table V.

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/content/aapm/journal/medphys/36/5/10.1118/1.3096417
2009-04-08
2014-04-17
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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: New empirical formula for neutron dose level at the maze entrance of 15 MV medical accelerator facilities
http://aip.metastore.ingenta.com/content/aapm/journal/medphys/36/5/10.1118/1.3096417
10.1118/1.3096417
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