Density scaling of phantom materials for a 3D dose verification system

Area of Science:

• Medical Physics
• Radiation Oncology
• Dosimetry

Background:

• Accurate dose verification is critical in radiation therapy.
• Commercial 3D dose verification systems like Delta4 rely on phantom materials.
• The accuracy of dose calculations in phantom materials can be affected by density scaling factors.

Purpose of the Study:

• To investigate and determine the optimum density scaling factors (DSF) for phantom materials used with the Delta4 system.
• To improve the accuracy of calculated dose distributions in phantom materials.
• To enhance the reliability of intensity modulated radiation therapy (IMRT) dose verification.

Main Methods:

• Measured tissue-phantom ratios (TPRs) in water, PMMA, and PWDT for specific field sizes.
• Calculated TPRs using Monte Carlo simulation and various dose calculation algorithms (AdC, CCC, AXB).
• Determined optimal DSF by matching calculated and measured effective linear attenuation coefficients, then verified with Delta4 measurements.

Main Results:

• Optimum density scaling factors (DSF) were determined: 1.13 for PMMA and 0.98 for PWDT.
• DSF for PMMA showed good agreement with AdC and CCC algorithms for 6 MV X-ray, and AdC for 10 MV X-ray.
• DSF for PWDT demonstrated good agreement across different dose calculation algorithms and X-ray energies.

Conclusions:

• The determined density scaling factors (DSF) provide a reference for Delta4 phantom materials.
• Implementing these DSF can significantly improve the accuracy of IMRT dose verification using the Delta4 system.
• This study contributes to more precise and reliable radiation therapy quality assurance.