Identification of key measurement points for accurate surface radiation dose assessment in cephalometric radiography

The objective of this study was to evaluate variations in entrance skin dose across different anatomical regions of a head phantom and to present entrance skin dose results obtained from a limited number of measurement points. By identifying key anatomical landmarks, the study aims to rationalize the number of entrance skin dose measurement points using thermoluminescence dosimeters (TLDs).

A tissue-equivalent head and neck phantom was examined with a 1-shot cephalometric X-ray machine under standardized settings. A detailed measurement protocol (140 TLDs for protocol 1) was compared to 3 alternative protocols using fewer measurement points (40 TLDs for protocol 2, 30 TLDs for protocol 3, and 6 TLDs for protocol 4).

Protocol 1 yielded an average entrance skin dose of 1.042 mSv, with higher doses at the parotid gland and above the left eye corner. Protocols 2 and 3 produced similar mean doses (1.003 mSv and 1.04 mSv, respectively), demonstrating that fewer dosimeters can still generate reliable results. Protocol 4, which targeted radiosensitive sites such as the thyroid and parotid glands, provided a comparable mean entrance skin dose for the beam-facing side (1.76 mSv) relative to the other protocols.

These findings suggest that the selected dosimetry approach is effective in assessing exposure to key tissues such as the skin. The results provide a foundation for a more representative, reproducible, and cost-effective dosimetric method in cephalometric radiography.