(Wednesday, 8/1/2018) 9:30 AM - 10:00 AM
Room: Exhibit Hall | Forum 8
Purpose: To evaluate entrance skin dose (ESD) using a dose area product (DAP) meter calibrated based on the ��Co absorbed dose to water for diagnostic x-ray beams.
Methods: Recently, we have developed new dosimetry to evaluate ESD for kilovoltage x-rays, using a Farmer ionization chamber calibrated with the ��Co absorbed dose to water. The ESD evaluated with new dosimetry agreed within their uncertainty to that based on the existing air-kerma calibration. The DAP meter used for ESD measurements has been conventionally calibrated based on the air-kerma. In this study, a PTW 23344 parallel-plate ionization chamber was cross-measured by a PTW 30013 Farmer chamber with a ��Co calibration factor, at a depth of 1 cm for a 20 × 20 cm² field in a water-equivalent phantom. Next, the DAP meter was directly cross-measured by the PTW 23344 chamber at the phantom surface for a 20 × 20 cm² field. In addition, the ESD was measured with the DAP meter for field sizes of 10 × 10 to 30 × 30 cm². Finally, the ESD was compared ESDs estimated directly by parallel-plate chamber for nine kilovoltage x-ray beams with aluminum half value-layers (Al-HVLs) of 1.80 to 6.72 mm.
Results: The calibration coefficient for the parallel-plate chamber was almost independent of the beam quality. This is because the PTW 23344 chamber has small window area density. The averaged value was 0.0829 mGy/pC ± 0.23%. The calibration coefficient of the DAP meter increased with increasing Al-HVL. The ESD measured by the DAP meter agreed within ± 5% to that measured by the PTW 23344 chamber for field sizes of 10 × 10 to 30 × 30 cm².
Conclusion: It made it possible to directly measure the ESD using the DAP meter cross-calibrated by a parallel-plate chamber at the phantom surface for diagnostic x-ray beams.
Keywords
Dosimetry, Monte Carlo, Calibration
Taxonomy
IM- Radiation dose and risk: Models
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