Electron beam characteristics at extended source-to-surface distances for irregular cut-outs
T Arunkumar1, Sanjay S Supe, M Ravikumar
1Department of Radiation Physics, Kidwai Memorial Institute of Oncology, Hosur Road, Bangalore, India.
Journal of Medical Physics
|December 21, 2010
Summary
Electron beam therapy can lead to underdosage with extended source-to-surface distance (SSD) and irregular fields. Beam flatness decreases, potentially causing inadequate target coverage, especially at lower energies.
Area of Science:
- Medical Physics
- Radiation Oncology
Background:
- Electron beam therapy is crucial for superficial cancer treatment.
- Extended source-to-surface distance (SSD) and irregular fields can alter beam characteristics.
Purpose of the Study:
- To investigate the impact of extended SSD and irregular field sizes on electron beam characteristics.
- To assess potential underdosage in lateral tissues during extended SSD treatments.
Main Methods:
- Measured depth dose, beam profiles, and isodose distributions for regular and irregular fields.
- Evaluated beam flatness, symmetry, and uniformity index across energies (6-20 MeV) and SSDs.
- Compared results for regular (10x10, 15x15 cm²) and irregular (6.5x9, 11.5x15 cm²) fields.
Main Results:
- Depth of maximum dose (R100) increased with SSD for higher energies (20 MeV) but not lower energies (6 MeV).
- A +7 mm shift in R100 depth was observed for irregular fields compared to regular fields.
- Beam flatness decreased significantly for irregular fields, more so at lower energies, reducing clinically useful isodose width.
Conclusions:
- Extended SSD with irregular fields can compromise target coverage due to reduced beam flatness and uniformity.
- Careful field size selection and treatment planning are necessary for extended SSD electron beam therapy with irregular fields.
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