Skin damage probabilities using fixation materials in high-energy photon beams

Area of Science:

• Medical Physics
• Radiation Oncology
• Radiotherapy Physics

Background:

• Patient immobilization in radiotherapy utilizes materials like thermoplastic masks and carbon-fibre plates.
• These low-density materials can alter radiation dose distribution in high-energy photon beams.
• Assessing the impact on skin dose and radiobiological consequences is crucial for patient safety.

Purpose of the Study:

• To measure the increase in skin dose caused by low-density immobilization materials.
• To calculate the radiobiological consequences of these dose increases, specifically early and late skin damage probabilities.

Main Methods:

• Utilized a thin-windowed plane-parallel ion chamber for experimental measurements.
• Measured skin doses with various low-density fixation materials under standardized conditions (10x10 cm field, SSD=100 cm, 4-10 MV photons).
• Evaluated radiobiological effects using the Linear-Quadratic (LQ) model based on measured surface doses.

Main Results:

• Established a correlation between skin dose and material thickness (mg/cm²).
• Quantified dose increases due to thermoplastic fixation, particularly at 4 MV.
• Determined that thermoplastic materials <100 mg/cm² result in comparable skin doses to other setup variations.

Conclusions:

• Thermoplastic fixation and 4 MV photons significantly increase skin dose in radiotherapy.
• Skin doses with thermoplastic materials <100 mg/cm² are clinically acceptable.
• Polystyrene cradles and carbon-fibre <100 mg/cm² should be avoided at 4 MV for doses >54-60 Gy.