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Published on: February 20, 2021
Practical considerations for reporting surface dose in external beam radiotherapy: a 6 MV X-ray beam study
1Institute of Medical Physics, School of Physics, University of Sydney, NSW, 2006, Sydney, Australia. jung.kim@sydney.edu.au
Australasian Physical & Engineering Sciences in Medicine
|June 28, 2012
Summary
This study evaluated surface dose accuracy in radiotherapy. Treatment planning system calculations and direct measurements were compared to Monte Carlo simulations, finding EBT2 film useful for surface dose assessment.
Area of Science:
- Medical Physics
- Radiation Oncology
- Dosimetry
Background:
- Accurate surface dose determination is crucial in radiotherapy for effective treatment and minimizing skin toxicity.
- Treatment planning systems (TPS) and direct measurement methods are commonly used, but their accuracy near the surface requires validation against benchmark methods.
- Monte Carlo (MC) simulations provide highly accurate dose calculations, serving as a benchmark for evaluating other methods.
Purpose of the Study:
- To assess the accuracy of surface doses determined by direct measurement (Attix chamber, EBT2 Gafchromic film) and TPS calculations (Eclipse analytic anisotropic algorithm - AAA) relative to benchmark MC doses.
- To evaluate the performance of EBT2 film and AAA in both homogeneous and heterogeneous phantom conditions for surface dose measurements.
- To provide recommendations for reporting TPS doses near the surface and highlight the utility of EBT2 film for surface dose assessment.
Main Methods:
- Surface doses were benchmarked using Monte Carlo (MC) calculations at 70 μm for a 6 MV, 10 × 10 cm clinical radiotherapy beam.
- Direct dose measurements were performed using an Attix chamber and EBT2 Gafchromic film in homogeneous and heterogeneous phantoms.
- Treatment planning system (TPS) doses were calculated using the Eclipse analytic anisotropic algorithm (AAA) and compared with MC and measured doses.
Main Results:
- Attix chamber underestimated MC surface dose by 2.9%, while EBT2 film overestimated it by 0.9% in homogeneous phantoms.
- Eclipse AAA showed significant over-response (up to 20%) at < 2 mm depth in open fields, reducing to < 2% at 2 mm depth.
- EBT2 film overestimated relative dose by up to 3.1% in heterogeneous phantoms; AAA at 2 mm depth agreed within 1.5% with MC but overestimated surface dose by up to 2.5%.
Conclusions:
- TPS doses near the surface should be reported at a depth of at least 2 mm to ensure accuracy.
- EBT2 Gafchromic film is a useful tool for measuring surface dose, with its effective point of measurement equivalent to 70 μm in homogeneous conditions.
- These findings are important for treatment planning, especially when surface dose is a critical factor.
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