Existing cancer treatments, while perhaps proving effective in being destructive of tumours, can also cause significant damage to surrounding healthy tissue. This can cause severe side effects which one would wish to avoid. In order to improve the localisation of the inflicted damage in the tumours, as well as increase the actual damage itself when using X-rays as therapy, the potential effect of attaching a high Z atom into the DNA of the cancer cells as markers or antenna for the X-rays is investigated. The larger size and higher absorption cross section of the iodine makes it favourable for this purpose, as it becomes more sensitive to the X-rays. This has been studied for a single stranded DNA molecule which is three bases long, loaded with iodine, using quantum mechanical/molecular dynamical simulations in SIESTA. The purpose was to study in what way the presence of the iodine affected and possibly increased the fragmentation of the molecule due to ionisation of the 2p orbital and the following Auger cascade, as well as use the results to better interpret mass over charge spectra from experiments. If the molecule fragments more, it becomes more difficult for the cell to repair it and thus perform effective DNA replication. It has been found that by matching the X-rays to above the 2p orbital of the iodine, the parent molecule fragments into much more and smaller remains, than when matching the X-rays to below this edge, meaning an increased damage when using the high Z atom. In addition to this, the results in this thesis provide a complement to existing experimental data, contributing with detailed information about specific fragmentation pathways of the molecule, facilitating the interpretation of mass over charge spectra from experiments.