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Dose behind various immobilization and beam-modifying devices
1University of Michigan, Ann Arbor 48109, USA.
Summary
Beam modifiers like immobilization devices and custom blocks can reduce skin sparing in high-energy photon therapy. Compensators generally do not impact skin sparing, while device density and thickness are key factors.
Area of Science:
- Medical Physics
- Radiation Oncology
- Radiotherapy Physics
Background:
- Skin sparing is crucial in radiotherapy to minimize side effects.
- High-energy photon beams require careful consideration of beam modifiers.
- Understanding dose build-up is essential for accurate treatment planning.
Purpose of the Study:
- To quantify the loss of skin sparing caused by beam modifiers in high-energy photon therapy.
- To evaluate the impact of compensators, immobilization devices, and custom blocks on skin dose.
- To provide data for predicting and explaining skin reactions in patients.
Main Methods:
- Dose build-up curves were measured using an extrapolation chamber for 6 and 15 MV photon beams.
- Various materials simulating clinical use were tested: gypsum/lead compensators, thermoplastic masks, cradle foam, and cerrobend blocks.
- Measurements were performed in geometries mimicking clinical scenarios.
Main Results:
- Compensators (gypsum, lead) in the wedge slot did not significantly alter the build-up region.
- Immobilization devices (foam, thermoplastic) degraded skin sparing proportionally to their thickness and density.
- Surface doses behind custom blocks were comparable to equivalent open fields.
Conclusions:
- Results help explain and predict skin reactions associated with specific beam modifiers.
- Provides a baseline for evaluating alternative materials for immobilization and blocking.
- Informs clinical decisions regarding the use of beam modifiers to optimize patient outcomes.