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Field size effect of radiation quality in carbon therapy using passive method
1Advanced Applied Science Department, Research Laboratory, IHI Corporation, 1 Shin-Nakahara-Cho, Isogo-Ku, Yokohama 235-8501, Japan. hiroyuki_nose@ihi.co.jp
Medical Physics
|April 22, 2009
Summary
Increasing carbon beam field size reduces radiation quality but increases absorbed dose. This effect is influenced by off-center particles and fragment particles, especially in deeper phantom regions.
Area of Science:
- Medical Physics
- Radiation Oncology
- Particle Therapy
Background:
- Understanding radiation field size effects is crucial for precise dose delivery in carbon beam therapy.
- Passive beam delivery techniques can influence radiation quality and absorbed dose distributions.
Purpose of the Study:
- To investigate how radiation quality and absorbed dose change with varying radiation field sizes in therapeutic carbon beams.
- To elucidate the underlying mechanisms, including the role of scattered particles and fragments.
Main Methods:
- Utilized a multileaf collimator to control field sizes from 20 to 100 mm.
- Employed microdosimetric techniques and Monte Carlo simulations to evaluate absorbed dose and radiation quality at various depths in a water phantom.
Main Results:
- Increasing field size led to a decrease in radiation quality at the beam center.
- Conversely, the absorbed dose at the beam center increased with larger field sizes.
- The influence of off-center particles, particularly fragment particles, was identified as a key factor.
Conclusions:
- The field size effect in carbon beams is significantly influenced by large-angle scattering of low-quality fragment particles from off-center regions.
- Fragment particles generated within the phantom play a substantial role in modifying the observed field size dependency, particularly at greater depths.
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