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Skin dose estimation for various beam modifiers and source-to-surface distances for 6MV photons.

Yadav G, Yadav RS, Kumar A - J Med Phys (2009)

Bottom Line: The effect of SSDs on the surface dose for motorized 60 degrees wedge fields was not significant for a small field size (difference was less than 1% up to a 15 x 15 cm(2) field size), but for a larger field (field size more than 15 x 15 cm(2)), the difference in a percentage skin dose was significant.Skin doses were increased as the SSD decreased and were dominant for larger field sizes.The surface dose was weakly dependent on the MLC block.

View Article: PubMed Central - PubMed

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

ABSTRACT
The purpose of this study was to learn the skin dose estimation for various beam modifiers at various source-to-surface distances (SSDs) for a 6 MV photon. Surface and buildup region doses were measured with an acrylic slab phantom and Markus 0.055 cc parallel plate (PP) ionization chamber. Measurements were carried out for open fields, motorized wedge fields, acrylic block tray fields ranging from 3 x 3 cm(2) to 30 x 30 cm(2). Twenty-five percent of the field was blocked with a cerrobend block and a Multileaf collimator (MLC). The effect of the blocks on the skin dose was measured for a 20 x 20 cm(2) field size, at 80 cm, 100 cm and 120 cm SSD. During the use of isocentric treatments, whereby the tumor is positioned at 100 cm from the source, depending on the depth of the tumor and size of the patient, the SSD can vary from 80 cm to 100 cm. To achieve a larger field size, the SSD can also be extended up to 120 cm at times. The skin dose increased as field size increased. The skin dose for the open 10 x10 cm(2) field was 15.5%, 14.8% and 15.5% at 80 cm, 100 cm and 120 cm SSDs, respectively. The skin dose due to a motorized 60 degrees wedge for the 10 x 10 cm(2) field was 9.9%, 9.5%, and 9.5% at 80 cm, 100 cm and 120 cm SSDs. The skin dose due to acrylic block tray, of thickness 1.0 cm for a 10 x 10 cm(2) field was 27.0%, 17.2% and 16.1% at 80, 100 and 120 cm SSD respectively. Due to the use of an acrylic block tray, the surface dose was increased for all field sizes at the above three SSDs and the percentage skin dose was more dominant at the lower SSD and larger field size. The skin dose for a 30 x 30 cm(2) field size at 80 cm SSD was 38.3% and it was 70.4% for the open and acrylic block tray fields, respectively. The skin doses for motorized wedge fields were lower than for open fields. The effect of SSDs on the surface dose for motorized 60 degrees wedge fields was not significant for a small field size (difference was less than 1% up to a 15 x 15 cm(2) field size), but for a larger field (field size more than 15 x 15 cm(2)), the difference in a percentage skin dose was significant. The skin dose for the open field was more than that for the MLC blocked field and lower than that for the acrylic blocked tray field. The block was 25% of the 20 x 20 cm(2) open field. Skin doses were increased as the SSD decreased and were dominant for larger field sizes. The surface dose was weakly dependent on the MLC block.

No MeSH data available.


Related in: MedlinePlus

Comparison of percentage skin dose at 100 cm SSD vs. 80 cm and 120 cm SSD for acrylic block tray fields
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Figure 0008: Comparison of percentage skin dose at 100 cm SSD vs. 80 cm and 120 cm SSD for acrylic block tray fields

Mentions: Figure 6 shows the impact of SSD on the skin doses, for open fields. Skin doses at 120 cm SSD were slightly greater than at 100 cm SSD for all the measured fields, but deviations were not significant (deviation was less than 1% up to 25 × 25 cm2 field). Skin doses at 80 cm SSD were greater than at 100 cm SSD for all measured fields except 3 × 3 cm2 and 5 × 5 cm2 fields and maximum deviation was 4.2% for a 30 × 30 cm2 field. Figure 7 shows that percentage skin dose values at 100 cm SSD were nearly the same at 120 cm SSD up to a 20 × 20 cm2 field (deviations were less than 1%), and maximum deviation on the skin dose was 2.6% for a 30 × 30 cm2 field. Percentage skin dose values at 80 cm SSD were greater than at 100 cm SSD for all measured fields, except 3 × 3 cm2 and 5 × 5 cm2 fields and maximum deviation was 5.1% for a 30 × 30 cm2 field. Figure 8 shows that percentage skin dose values for block tray fields at 120 cm SSD were lower than at 100 cm SSD for all measured fields except 3 × 3 cm2 field and maximum deviation was 5.2% for a 30 × 30 cm2 field. Percentage skin dose values at 80 cm SSD were greater than at 100 cm SSD for all measured fields and maximum percentage skin dose deviation was 23.1% for a 30 × 30 cm2 field size. It may be concluded that the effects of the blocking tray on skin doses at low SSD were much more significant, and increased with increased field size.


Skin dose estimation for various beam modifiers and source-to-surface distances for 6MV photons.

Yadav G, Yadav RS, Kumar A - J Med Phys (2009)

Comparison of percentage skin dose at 100 cm SSD vs. 80 cm and 120 cm SSD for acrylic block tray fields
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC2805895&req=5

Figure 0008: Comparison of percentage skin dose at 100 cm SSD vs. 80 cm and 120 cm SSD for acrylic block tray fields
Mentions: Figure 6 shows the impact of SSD on the skin doses, for open fields. Skin doses at 120 cm SSD were slightly greater than at 100 cm SSD for all the measured fields, but deviations were not significant (deviation was less than 1% up to 25 × 25 cm2 field). Skin doses at 80 cm SSD were greater than at 100 cm SSD for all measured fields except 3 × 3 cm2 and 5 × 5 cm2 fields and maximum deviation was 4.2% for a 30 × 30 cm2 field. Figure 7 shows that percentage skin dose values at 100 cm SSD were nearly the same at 120 cm SSD up to a 20 × 20 cm2 field (deviations were less than 1%), and maximum deviation on the skin dose was 2.6% for a 30 × 30 cm2 field. Percentage skin dose values at 80 cm SSD were greater than at 100 cm SSD for all measured fields, except 3 × 3 cm2 and 5 × 5 cm2 fields and maximum deviation was 5.1% for a 30 × 30 cm2 field. Figure 8 shows that percentage skin dose values for block tray fields at 120 cm SSD were lower than at 100 cm SSD for all measured fields except 3 × 3 cm2 field and maximum deviation was 5.2% for a 30 × 30 cm2 field. Percentage skin dose values at 80 cm SSD were greater than at 100 cm SSD for all measured fields and maximum percentage skin dose deviation was 23.1% for a 30 × 30 cm2 field size. It may be concluded that the effects of the blocking tray on skin doses at low SSD were much more significant, and increased with increased field size.

Bottom Line: The effect of SSDs on the surface dose for motorized 60 degrees wedge fields was not significant for a small field size (difference was less than 1% up to a 15 x 15 cm(2) field size), but for a larger field (field size more than 15 x 15 cm(2)), the difference in a percentage skin dose was significant.Skin doses were increased as the SSD decreased and were dominant for larger field sizes.The surface dose was weakly dependent on the MLC block.

View Article: PubMed Central - PubMed

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

ABSTRACT
The purpose of this study was to learn the skin dose estimation for various beam modifiers at various source-to-surface distances (SSDs) for a 6 MV photon. Surface and buildup region doses were measured with an acrylic slab phantom and Markus 0.055 cc parallel plate (PP) ionization chamber. Measurements were carried out for open fields, motorized wedge fields, acrylic block tray fields ranging from 3 x 3 cm(2) to 30 x 30 cm(2). Twenty-five percent of the field was blocked with a cerrobend block and a Multileaf collimator (MLC). The effect of the blocks on the skin dose was measured for a 20 x 20 cm(2) field size, at 80 cm, 100 cm and 120 cm SSD. During the use of isocentric treatments, whereby the tumor is positioned at 100 cm from the source, depending on the depth of the tumor and size of the patient, the SSD can vary from 80 cm to 100 cm. To achieve a larger field size, the SSD can also be extended up to 120 cm at times. The skin dose increased as field size increased. The skin dose for the open 10 x10 cm(2) field was 15.5%, 14.8% and 15.5% at 80 cm, 100 cm and 120 cm SSDs, respectively. The skin dose due to a motorized 60 degrees wedge for the 10 x 10 cm(2) field was 9.9%, 9.5%, and 9.5% at 80 cm, 100 cm and 120 cm SSDs. The skin dose due to acrylic block tray, of thickness 1.0 cm for a 10 x 10 cm(2) field was 27.0%, 17.2% and 16.1% at 80, 100 and 120 cm SSD respectively. Due to the use of an acrylic block tray, the surface dose was increased for all field sizes at the above three SSDs and the percentage skin dose was more dominant at the lower SSD and larger field size. The skin dose for a 30 x 30 cm(2) field size at 80 cm SSD was 38.3% and it was 70.4% for the open and acrylic block tray fields, respectively. The skin doses for motorized wedge fields were lower than for open fields. The effect of SSDs on the surface dose for motorized 60 degrees wedge fields was not significant for a small field size (difference was less than 1% up to a 15 x 15 cm(2) field size), but for a larger field (field size more than 15 x 15 cm(2)), the difference in a percentage skin dose was significant. The skin dose for the open field was more than that for the MLC blocked field and lower than that for the acrylic blocked tray field. The block was 25% of the 20 x 20 cm(2) open field. Skin doses were increased as the SSD decreased and were dominant for larger field sizes. The surface dose was weakly dependent on the MLC block.

No MeSH data available.


Related in: MedlinePlus