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Feasibility study of multileaf collimated electrons with a scattering foil based accelerator
1Mallinckrodt Institute of Radiology, Radiation Oncology Center, St. Louis, MO 63110, USA. i:klein-ee@castor.wustl.edu
Summary
Multileaf collimated electron beams (MLCEB) showed inferior dosimetric performance compared to applicator collimated electron beams (AEB). MLCEB is not recommended for clinical use, particularly for posterior neck node (PNN) fields.
Area of Science:
- Medical Physics
- Radiation Oncology
- Radiotherapy Technology
Background:
- Electron beam delivery techniques are continuously evolving.
- Multileaf collimators (MLCs) are standard for photon beam shaping.
- Recent advancements include exploring MLCs for electron beams.
Purpose of the Study:
- To evaluate the dosimetric characteristics of multileaf collimated electron beams (MLCEB).
- To compare MLCEB performance against traditional applicator collimated electron beams (AEB).
- To assess the feasibility of MLCEB for clinical applications like posterior neck node (PNN) treatments.
Main Methods:
- Dosimetric parameters including percent depth dose, isodose profiles, output factors, and surface dose were measured.
- Comparisons were made at various source-surface distances (SSDs), including 70 and 80 cm.
- Film and ion chamber measurements were utilized for data acquisition.
Main Results:
- MLCEB demonstrated inferior performance in isodose distribution, uniformity index (UI), and penumbra analysis compared to AEB.
- The worst-case scenario was observed at 80 cm SSD for low-energy, small fields.
- For a 6 MeV beam, MLCEB at 80 cm SSD showed a significantly wider penumbra (29 mm) than AEB (10 mm).
Conclusions:
- MLCEB is not suitable for clinical use, especially for PNN fields, due to dosimetric limitations.
- MLCEB cannot be effectively matched with adjacent photon fields treated with MLCs.
- The characteristic "stair-stepping" effect seen with MLC photons is absent in electron beams.