Surface dose measurement using TLD powder extrapolation

Area of Science:

• Medical Physics
• Radiation Oncology
• Dosimetry

Background:

• Accurate surface dose measurement is critical for radiation therapy to protect skin layers.
• Determining precise surface dose, especially in steep dose gradients, presents a significant challenge.

Purpose of the Study:

• To develop and validate a novel method for measuring surface/near-surface doses using thermoluminescent dosimeter (TLD) powder extrapolation.
• To assess the precision and clinical applicability of the TLD powder technique for therapeutic x-ray beams.

Main Methods:

• A specialized device was created to vary TLD powder thickness down to 0.125 mm.
• The TLD powder extrapolation technique was evaluated for precision and procedural ease.
• Surface dose was measured for a Cobalt-60 beam, comparing results to D(max).

Main Results:

• The TLD powder extrapolation method achieved a precision of +/- 1.2% (2 SDs) in steep dose gradient regions.
• A clinically practical procedure yielded a measured surface dose of 20.4 +/- 2% of the D(max) dose.
• Results favorably compared with existing surface dose measurement methods.

Conclusions:

• The TLD powder extrapolation technique offers a simple, economical, and precise tool for surface dose measurement in radiation therapy.
• This method is particularly valuable for facilities equipped for TLD powder measurements.
• The technique has been successfully applied clinically for assessing surface dose effects.