Monte Carlo investigation of energy response of various detector materials in I125 and Yb169 brachytherapy dosimetry

Relative absorbed-dose energy response correction R for different detector materials in water, PMMA and polystyrene phantoms are calculated using Monte Carlo-based EGSnrc code system for ¹²⁵I and ¹⁶⁹Yb brachytherapy sources. The values of R obtained for ¹²⁵I source are 1.41, 0.92, 3.97, 0.47, 8.32 and 1.10, respectively, for detector materials LiF, Li₂B₄O₇ , A1₂O₃, diamond, silicon diode and air. These values are insensitive to source-to-detector distance and phantom material. For ¹⁶⁹Yb source, R is sensitive to source-to-detector distance for detector materials other than air and Li₂B₄O₇. For silicon, R increases from 3 to 4.23 when depth in water is increased from 0.5 cm to 15 cm. For ¹⁶⁹Yb source, the values of R obtained for air and Li₂B₄O₇ in PMMA and polystyrene phantoms are comparable to that obtained in water. However, LiF, Si and A1₂O₃ show enhanced response and diamond shows decreased response in PMMA and polystyrene phantoms than in water.