SU‐GG‐T‐382: Modeling of a Commercial CdTe Photodiode Detector Using the MCNP Code

Purpose: To model a commercial CdTe photodiode detector using the MCNP code for the optimization of various x‐ray measurement tasks related with an animal study to demonstrate the tumor dose enhancement by gold nanoparticles and kilovoltage x‐rays. Method and Materials: The MCNP code was used to model a commercial CdTe photodiode detector (XR‐100T, Amptek Inc.). MCNP calculations were performed with a phantom made of the mixture of gold nanoparticles and water at various gold concentrations to investigate photon attenuation, scattering, and gold fluorescence x‐ray generation. A circular 100 kVp x‐ray beam with a diameter of 1 cm was assumed to be incident on a phantom at a source‐to‐surface distance at 12.5 cm. The detector model was tested for the detection of gold fluorescence x‐rays from the phantom by scoring photons coming out of the phantom at two different off‐axis angles (i.e., 135° and 90°) with respect to the x‐ray beam direction to minimize unwanted scatters to the detector. Three different concentrations (i.e., 3%, 1% and 0.1%) of gold nanoparticles were used for these simulations. Results: MCNP results indicated that the current CdTe detector model was capable of producing expected results, for example, showing the fluorescence x‐ray peaks from gold. As expected, the height of these peaks was proportional to the concentration of gold nanoparticles within the phantom. The detector located at 135° off‐axis angle resulted in more prominent gold fluorescence peaks than that located at 90° off‐axis angle. Conclusion: The current study indicates that an MCNP model of a CdTe detector would be helpful to optimize x‐ray measurement tasks required for in vivo demonstration of tumor dose enhancement by gold nanoparticles and kilovoltage x‐rays.