Variations in skin dose using 6MV or 18MV x-ray beams

Area of Science:

• Medical Physics
• Radiation Oncology

Background:

• Accurate dose delivery is crucial in radiation therapy.
• Understanding dose distribution in superficial tissues is important for minimizing side effects.
• High-energy x-ray beams (6MV and 18MV) are commonly used in clinical practice.

Purpose of the Study:

• To quantitatively compare dose differences between 6MV and 18MV x-ray beams within the first centimeter of tissue.
• To provide data on dose variations in basal, dermal, and subcutaneous layers.
• To inform oncologists about energy selection based on skin and subcutaneous tissue dose considerations.

Main Methods:

• Measurement of percentage depth dose (PDD) build-up curves for clinical field sizes.
• Utilizing 6MV and 18MV x-ray beams.
• Calculations to determine dose differences at various depths within the skin and subcutaneous regions.

Main Results:

• No significant dose difference was observed at the basal cell layer between 6MV and 18MV beams.
• Measurable and significant dose differences were found at depths beyond the basal cell layer.
• Dose variations reached up to 20% at 1 mm and 22% at 1 cm depth, with larger variations for smaller field sizes.

Conclusions:

• While superficial skin doses are similar, deeper tissues receive significantly different doses from 6MV and 18MV beams.
• Dose variations are more pronounced at greater depths and with smaller field sizes.
• Quantitative data on dose differences can aid oncologists in selecting optimal beam energies when skin or subcutaneous doses are critical.