We have shown that it is sufficiently accurate to use the MCNP peak-to-total calibration results to correct for cascade summing effects in a gamma-spectrum. Also, it is sufficient to use only approximate detector characterization data with empirical peak-to-total to obtain good cascade summing correction results. The intrinsic P/T-curve for detectors with the same efficiency is very similar and it may be considered a common characteristic of the whole detector's family with given efficiency.