Absorbed dose to water reference dosimetry using solid phantoms in the context of absorbed-dose protocols

Area of Science:

• Medical Physics
• Radiation Dosimetry
• Radiotherapy Physics

Background:

• Liquid water is mandatory for reference dosimetry per AAPM TG-51 and IAEA TRS-398 protocols.
• Solid phantoms offer advantages for verification and quality assurance in dosimetry.
• Reproducibility and consistency of solid phantom materials are critical for accurate dose measurements.

Purpose of the Study:

• To establish a formal framework for measuring absorbed dose to water using solid phantoms.
• To introduce and validate a phantom dose conversion factor for absolute dose measurements in solid phantoms.
• To provide methods for verifying the consistency of solid phantom materials for clinical reference dosimetry.

Main Methods:

• Developed a phantom dose conversion factor to translate solid phantom measurements to absorbed dose to water.
• Measured and calculated the dose transfer from solid to water phantoms.
• Utilized an Exradin A12 ionization chamber for measurements across various solid phantoms (Solid Water, Lucite) and photon energies (60Co to 18 MV).

Main Results:

• The measured and calculated phantom dose conversion factors for certified Solid Water showed good agreement (0.0%–0.7% difference).
• For Lucite, the agreement between measured and calculated factors was within 0.2%.
• The average dose conversion factor for Solid Water was slightly lower (0.4%) than calculated values.

Conclusions:

• The developed framework and phantom dose conversion factor enable absolute dose measurements in solid phantoms.
• The study provides a method to verify the consistency and suitability of plastic phantom materials for clinical reference dosimetry.
• Accurate dosimetry with solid phantoms is achievable and essential for quality assurance in radiotherapy.