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Dosimetric characterization of a new surface-conforming electron MLC prototype.
Holly M Parenica Paschal1, Christopher N Kabat1, Thomas Martin1
1Department of Radiation Oncology, School of Medicine, The University of Texas Health Science Center at San Antonio, San Antonio, Texas, USA.
Journal of Applied Clinical Medical Physics
|October 20, 2023
Summary
A novel surface-conforming electron multileaf collimator (SCEM) was developed to reduce radiation toxicity. The SCEM improves penumbra and out-of-field dose but increases surface dose, requiring further optimization.
Area of Science:
- Medical Physics
- Radiation Oncology
- Radiotherapy Equipment Development
Background:
- Electron therapy in radiation oncology aims to minimize normal tissue toxicity.
- Conventional collimation methods like Cerrobend cutouts have limitations in dose conformity and out-of-field dose reduction.
- The development of advanced collimation techniques is crucial for improving treatment efficacy and patient safety.
Purpose of the Study:
- To introduce and evaluate a surface-conforming electron multileaf collimator (SCEM) for electron therapy.
- To assess the SCEM's ability to reduce normal tissue radiation toxicity.
- To compare the SCEM's dosimetric properties against traditional Cerrobend cutouts.
Main Methods:
- Construction of an early prototype of the SCEM with acrylic leaves designed to conform to patient surfaces.
- Dosimetric measurements using water tank scans for various electron energies (6-15 MeV) and field sizes at a 100 cm source-to-surface distance (SSD).
- Comparison of SCEM measurements with Cerrobend cutouts at matched field sizes and 100/110 cm SSD, including output factor and percent depth dose (PDD) analysis.
Main Results:
- The SCEM demonstrated a significant decrease in penumbra, especially at lower energies (6-9 MeV), compared to Cerrobend cutouts at 110 cm SSD.
- Reduced out-of-field dose and lower bremsstrahlung production were observed with the SCEM.
- Percent depth dose (PDD) curves shifted shallower with the SCEM, and a higher surface dose was noted (up to 9.8% increase).
Conclusions:
- The SCEM offers significant improvements in penumbra and out-of-field dose reduction compared to Cerrobend cutouts by enabling close-to-surface collimation.
- Increased shallow PDD values due to added scatter from the SCEM require further investigation and mitigation.
- Future research will focus on optimizing the SCEM design to minimize scatter while preserving its dosimetric advantages.
