An occupational incorporation event occurred at the Radioactive Waste Treatment and Disposal Facility in December 2013 at Püspökszilágy, Hungary. Internal contamination due to 241Am was discovered by a regular routine whole body counting measurement at the Centre for Energy Research, Hungarian Academy of Sciences. After that, a whole body counter was calibrated for an organ counting geometry. For preliminary calibration, a home-made MIX-D chest phantom was applied simulating uniform lung activity distribution by 241Am point sources located in different positions within the lung volume of the phantom. In order to carry out a more precise calibration, a Lawrence Livermore National Laboratory (LLNL) chest phantom was provided by the International Atomic Energy Agency. For counting efficiency over the lungs, values of 0.46±0.19 and 0.55±0.07 cps kBq−1 were obtained for the MIX-D and the LLNL phantom, respectively; thus, the results are in good agreement.