  We study the energy deposition by light and heavy nuclei in tissue-like media
as used for cancer therapy. The depth-dose distributions for protons, $^{3}$He,
$^{12}$C, $^{20}$Ne, and $^{58}$Ni nuclei are calculated within a Monte Carlo
model based on the GEANT4 toolkit. These distributions are compared with each
other and with available experimental data. It is demonstrated that nuclear
fragmentation reactions essentially reduce the peak-to-plateau ratio of the
dose profiles for deeply penetrating energetic ions heavier than $^{3}$He. On
the other hand, all projectiles up to $^{20}$Ne were found equally suitable for
therapeutic use at low penetration depths.
