Purpose: To investigate dose perturbations created by high-atomic number (Z) materials in high dose rate (HDR) Iridium-192 (192Ir) treatment region. Methods and materials: A specially designed parallel plate ion chamber with 5μm thick window was used to measure the dose rates from 192Ir source downstream of the high-Z materials. A Monte Carlo (MC) code was employed to calculate the dose rates in both upstream and downstream of the high-Z interfaces at distances ranging from 0.01 to 2mm. The dose perturbation factor (DPF) was defined as the ratio of dose rate with and without high-Z material in a water phantom. For verifying the Z dependence, both 0.1- and 1.0mm-thick sheets of Pb, Au, Ta, Sn, Cu, Fe, Ti and Al were used. Results/conclusions: The DPF depends on the Z and thickness of layer. At the downstream of a 0.1mm layer of Pb, Au, Ta, Sn, Cu, Fe, Ti and Al, the DPF by MC were 3.73, 3.42, 3.04, 1.71, 1.04, 0.98, 0.92, or 0.94 respectively. When Z is greater than or equal to 50, the MC and experimental results disagree significantly (>20%) due to large DPF gradient but are in agreement for Z less than or equal to 29. Thin layers of Z greater than or equal to 50 near a 192Ir source in water produce significant dose perturbations (i.e. increases) in the vicinity of the medium-high-Z interfaces and may thus cause local over-dose in 192Ir brachytherapy. Conversely, this effect may potentially be used to deliver locally higher doses to targeted tissue.
- Dose perturbation
- High-Z interface
ASJC Scopus subject areas
- Radiology Nuclear Medicine and imaging
- Physics and Astronomy(all)