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Effect of various physical parameters on surface and build-up dose for 15-MV X-rays.

Yadav G, Yadav RS, Kumar A - J Med Phys (2010)

Bottom Line: The blocking tray increased PDD(0) of 10 × 10 cm(2) field to 26.29%, 14.01%, and 11.53%, while the motorized 60° wedge decreased PDD(0) to 11.32%, 9.7%, and 8.9 % at these FSDs.The maximum PDD difference seen at surface for 5 × 5 cm(2), 15 × 15 cm(2), and 30 × 30 cm(2) fields are 5.6%, 22.8%, and 29.6%, respectively, for a 1.0-cm perspex-blocking tray as the FSD is changed.The maximum PDD difference was seen at the surface (i.e., skin) and this decreased with increasing depth.

View Article: PubMed Central - PubMed

Affiliation: Department of Physics, D.A.V. (P.G.) College, Kanpur, U.P, India.

ABSTRACT
The purpose of this study was to find out the effect of various physical parameters on the skin and build-up doses of 15-MV photon beams. The effects of field dimensions, acrylic shadow tray, focus to-skin distance (FSD) on surface and buildup dose were determined for open, motorized 60° wedge (MW) and blocked fields. A 'Markus' plane parallel plate chamber was used for these measurements in an Elekta (6-15MV) linear accelerator. The surface dose for MW fields was lower than the dose for an open field, but the trend reversed for large fields and higher degree wedges. With the use of an acrylic shadow tray, the surface dose increased for all field sizes, but the increase was dominant for large fields. The surface dose for blocked fields was lower than the dose for open fields. The percentage depth dose of 10 × 10 cm(2) field at surface (PDD(0)) for open beam were 13.89%, 11.71%, and 10.74% at 80 cm, 100 cm, and 120 cm FSD, respectively. The blocking tray increased PDD(0) of 10 × 10 cm(2) field to 26.29%, 14.01%, and 11.53%, while the motorized 60° wedge decreased PDD(0) to 11.32%, 9.7%, and 8.9 % at these FSDs. The maximum PDD difference seen at surface (i.e., skin) for 5 × 5 cm(2), 15 × 15 cm(2), and 30 × 30 cm(2) are 0.5%, 4.6%, and 5.6% for open field and 0.9%, 4.7%, and 7.2% for motorized 60° wedge field, when FSDs varied from 80 cm to 120 cm. The maximum PDD difference seen at surface for 5 × 5 cm(2), 15 × 15 cm(2), and 30 × 30 cm(2) fields are 5.6%, 22.8%, and 29.6%, respectively, for a 1.0-cm perspex-blocking tray as the FSD is changed. The maximum PDD difference was seen at the surface (i.e., skin) and this decreased with increasing depth.

No MeSH data available.


Related in: MedlinePlus

Comparision of build-up doses for open fields at 100 cm FSD vs. 80 cm and 120 cm FSD for the various field sizes
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Figure 0002: Comparision of build-up doses for open fields at 100 cm FSD vs. 80 cm and 120 cm FSD for the various field sizes

Mentions: Figures 2a and 2b show the build-up curves for a 5 × 5 cm2, 15 × 15 cm2, and 30 × 30cm2 field (as at 100 cm FSD), at 80 cm, 100 cm, and 120 cm FSD for open and motorized 60° wedge fields. It can be seen that percentage dose build-up does not vary significantly with FSD for open and motorized wedge fields. The maximum PDD difference seen at the surface (PDD0) for 5 × 5cm2, 15 × 15cm2, and 30 × 30 cm2 are 0.5%, 4.6%, and 5.6% for open field and 0.9%, 4.7%, and 7.2% for motorized 60° wedge field when FSD varies from 80 cm to 120 cm. The build-up curve for 5 × 5 cm2, 15 ×15 cm2, and 30 × 30 cm2 field sizes with a 1.0-cm Perspex blocking tray at 80 cm, 100 cm, and 120 cm FSD are shown in Figure 2c. The maximum PDD difference seen at the surface (PDD0) for 5 × 5 cm2, 15 × 15 cm2, and 30 × 30 cm2 fields are 5.6%, 22.8%, and 29.6%, respectively, as FSD varies from 80 cm to 120 cm. Figure 2d shows the comparison of build-up doses for open fields vs. motorized 60° wedge and block tray fields at 100 cm FSD.


Effect of various physical parameters on surface and build-up dose for 15-MV X-rays.

Yadav G, Yadav RS, Kumar A - J Med Phys (2010)

Comparision of build-up doses for open fields at 100 cm FSD vs. 80 cm and 120 cm FSD for the various field sizes
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC2990114&req=5

Figure 0002: Comparision of build-up doses for open fields at 100 cm FSD vs. 80 cm and 120 cm FSD for the various field sizes
Mentions: Figures 2a and 2b show the build-up curves for a 5 × 5 cm2, 15 × 15 cm2, and 30 × 30cm2 field (as at 100 cm FSD), at 80 cm, 100 cm, and 120 cm FSD for open and motorized 60° wedge fields. It can be seen that percentage dose build-up does not vary significantly with FSD for open and motorized wedge fields. The maximum PDD difference seen at the surface (PDD0) for 5 × 5cm2, 15 × 15cm2, and 30 × 30 cm2 are 0.5%, 4.6%, and 5.6% for open field and 0.9%, 4.7%, and 7.2% for motorized 60° wedge field when FSD varies from 80 cm to 120 cm. The build-up curve for 5 × 5 cm2, 15 ×15 cm2, and 30 × 30 cm2 field sizes with a 1.0-cm Perspex blocking tray at 80 cm, 100 cm, and 120 cm FSD are shown in Figure 2c. The maximum PDD difference seen at the surface (PDD0) for 5 × 5 cm2, 15 × 15 cm2, and 30 × 30 cm2 fields are 5.6%, 22.8%, and 29.6%, respectively, as FSD varies from 80 cm to 120 cm. Figure 2d shows the comparison of build-up doses for open fields vs. motorized 60° wedge and block tray fields at 100 cm FSD.

Bottom Line: The blocking tray increased PDD(0) of 10 × 10 cm(2) field to 26.29%, 14.01%, and 11.53%, while the motorized 60° wedge decreased PDD(0) to 11.32%, 9.7%, and 8.9 % at these FSDs.The maximum PDD difference seen at surface for 5 × 5 cm(2), 15 × 15 cm(2), and 30 × 30 cm(2) fields are 5.6%, 22.8%, and 29.6%, respectively, for a 1.0-cm perspex-blocking tray as the FSD is changed.The maximum PDD difference was seen at the surface (i.e., skin) and this decreased with increasing depth.

View Article: PubMed Central - PubMed

Affiliation: Department of Physics, D.A.V. (P.G.) College, Kanpur, U.P, India.

ABSTRACT
The purpose of this study was to find out the effect of various physical parameters on the skin and build-up doses of 15-MV photon beams. The effects of field dimensions, acrylic shadow tray, focus to-skin distance (FSD) on surface and buildup dose were determined for open, motorized 60° wedge (MW) and blocked fields. A 'Markus' plane parallel plate chamber was used for these measurements in an Elekta (6-15MV) linear accelerator. The surface dose for MW fields was lower than the dose for an open field, but the trend reversed for large fields and higher degree wedges. With the use of an acrylic shadow tray, the surface dose increased for all field sizes, but the increase was dominant for large fields. The surface dose for blocked fields was lower than the dose for open fields. The percentage depth dose of 10 × 10 cm(2) field at surface (PDD(0)) for open beam were 13.89%, 11.71%, and 10.74% at 80 cm, 100 cm, and 120 cm FSD, respectively. The blocking tray increased PDD(0) of 10 × 10 cm(2) field to 26.29%, 14.01%, and 11.53%, while the motorized 60° wedge decreased PDD(0) to 11.32%, 9.7%, and 8.9 % at these FSDs. The maximum PDD difference seen at surface (i.e., skin) for 5 × 5 cm(2), 15 × 15 cm(2), and 30 × 30 cm(2) are 0.5%, 4.6%, and 5.6% for open field and 0.9%, 4.7%, and 7.2% for motorized 60° wedge field, when FSDs varied from 80 cm to 120 cm. The maximum PDD difference seen at surface for 5 × 5 cm(2), 15 × 15 cm(2), and 30 × 30 cm(2) fields are 5.6%, 22.8%, and 29.6%, respectively, for a 1.0-cm perspex-blocking tray as the FSD is changed. The maximum PDD difference was seen at the surface (i.e., skin) and this decreased with increasing depth.

No MeSH data available.


Related in: MedlinePlus