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Electron beam characteristics at extended source-to-surface distances for irregular cut-outs.

Arunkumar T, Supe SS, Ravikumar M, Sathiyan S, Ganesh M - J Med Phys (2010)

Bottom Line: There is a +7 mm shift in the R(100) depth when compared with regular and irregular field sizes.The symmetry was found to be within limits for all the field sizes as the treatment distance extended as per International Electro technical Commision (IEC) protocol.This suggests that target coverage at extended SSD with irregular cut-outs may be inadequate unless relatively large fields are used.

View Article: PubMed Central - PubMed

Affiliation: Department of Radiation Physics, Kidwai Memorial Institute of Oncology, Hosur Road, Bangalore, India.

ABSTRACT
Electron beam therapy is widely used in the management of cancers. The rapid dose fall-off and the short range of an electron beam enable the treatment of lesions close to the surface, while sparing the underlying tissues. In an extended source-to-surface (SSD) treatment with irregular field sizes defined by cerrobend cutouts, underdosage of the lateral tissue may occur due to reduced beam flatness and uniformity. To study the changes in the beam characteristics, the depth dose, beam profile, and isodose distributions were measured at different SSDs for regular 10 × 10 cm(2) and 15 × 15 cm(2) cone, and for irregular cutouts of field size 6.5 × 9 cm(2) and 11.5 × 15 cm(2) for beam energies ranging from 6 to 20 MeV. The PDD, beam flatness, symmetry and uniformity index were compared. For lower energy (6 MeV), there was no change in the depth of maximum dose (R100) as SSD increased, but for higher energy (20 MeV), the R(100) depth increased from 2 cm to 3 cm as SSD increased. This shows that as SSD increases there is an increase in the depth of the maximum dose for higher energy beams. There is a +7 mm shift in the R(100) depth when compared with regular and irregular field sizes. The symmetry was found to be within limits for all the field sizes as the treatment distance extended as per International Electro technical Commision (IEC) protocol. There was a loss of beam flatness for irregular fields and it was more pronounced for lower energies as compared with higher energies, so that the clinically useful isodose level (80% and 90%) width decreases with increase in SSD. This suggests that target coverage at extended SSD with irregular cut-outs may be inadequate unless relatively large fields are used.

No MeSH data available.


Related in: MedlinePlus

Isodose perpendicular to the beam central plane for 6-MeV electron beam at 100 cm SSD for 6.5 × 9 cm2 field size
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Figure 0013: Isodose perpendicular to the beam central plane for 6-MeV electron beam at 100 cm SSD for 6.5 × 9 cm2 field size

Mentions: Figures 3a–d show the isodose distribution along the central axis for a 6-MeV beam for irregular field sizes at 100 cm SSD and 120 cm SSD. Isodose bulging was observed with increase in treatment distance. It can be seen that there is a reduction in the field flatness. Figure 4–d show the isodose distribution perpendicular to the beam central plane for a 6-MeV beam for 6.5 × 9.0 cm2 and 11.5 × 15 cm2 field sizes at 100 cm and 120 cm SSD. The figure shows the irregular shape of thecut-out used and the divergence of the isodose lines as the SSD increased.


Electron beam characteristics at extended source-to-surface distances for irregular cut-outs.

Arunkumar T, Supe SS, Ravikumar M, Sathiyan S, Ganesh M - J Med Phys (2010)

Isodose perpendicular to the beam central plane for 6-MeV electron beam at 100 cm SSD for 6.5 × 9 cm2 field size
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC2990115&req=5

Figure 0013: Isodose perpendicular to the beam central plane for 6-MeV electron beam at 100 cm SSD for 6.5 × 9 cm2 field size
Mentions: Figures 3a–d show the isodose distribution along the central axis for a 6-MeV beam for irregular field sizes at 100 cm SSD and 120 cm SSD. Isodose bulging was observed with increase in treatment distance. It can be seen that there is a reduction in the field flatness. Figure 4–d show the isodose distribution perpendicular to the beam central plane for a 6-MeV beam for 6.5 × 9.0 cm2 and 11.5 × 15 cm2 field sizes at 100 cm and 120 cm SSD. The figure shows the irregular shape of thecut-out used and the divergence of the isodose lines as the SSD increased.

Bottom Line: There is a +7 mm shift in the R(100) depth when compared with regular and irregular field sizes.The symmetry was found to be within limits for all the field sizes as the treatment distance extended as per International Electro technical Commision (IEC) protocol.This suggests that target coverage at extended SSD with irregular cut-outs may be inadequate unless relatively large fields are used.

View Article: PubMed Central - PubMed

Affiliation: Department of Radiation Physics, Kidwai Memorial Institute of Oncology, Hosur Road, Bangalore, India.

ABSTRACT
Electron beam therapy is widely used in the management of cancers. The rapid dose fall-off and the short range of an electron beam enable the treatment of lesions close to the surface, while sparing the underlying tissues. In an extended source-to-surface (SSD) treatment with irregular field sizes defined by cerrobend cutouts, underdosage of the lateral tissue may occur due to reduced beam flatness and uniformity. To study the changes in the beam characteristics, the depth dose, beam profile, and isodose distributions were measured at different SSDs for regular 10 × 10 cm(2) and 15 × 15 cm(2) cone, and for irregular cutouts of field size 6.5 × 9 cm(2) and 11.5 × 15 cm(2) for beam energies ranging from 6 to 20 MeV. The PDD, beam flatness, symmetry and uniformity index were compared. For lower energy (6 MeV), there was no change in the depth of maximum dose (R100) as SSD increased, but for higher energy (20 MeV), the R(100) depth increased from 2 cm to 3 cm as SSD increased. This shows that as SSD increases there is an increase in the depth of the maximum dose for higher energy beams. There is a +7 mm shift in the R(100) depth when compared with regular and irregular field sizes. The symmetry was found to be within limits for all the field sizes as the treatment distance extended as per International Electro technical Commision (IEC) protocol. There was a loss of beam flatness for irregular fields and it was more pronounced for lower energies as compared with higher energies, so that the clinically useful isodose level (80% and 90%) width decreases with increase in SSD. This suggests that target coverage at extended SSD with irregular cut-outs may be inadequate unless relatively large fields are used.

No MeSH data available.


Related in: MedlinePlus