Photosensitizers play a key role in photodynamic therapy as a drug that is activated by light. In this thesis, the effect of ionizing radiation on the generation of singlet oxygen when using photosensitizers (Chlorin e6) and photocatalysts (titanium dioxide) was studied. By using radionuclides and photosensitizers (PS), cells can be killed with reactive oxygen species (ROS) which are produced by PS under influence of radiation that is emitted by radioactive decay. ROS are produced naturally in cells, but an excess of ROS can lead to damage to proteins, nucleic acids, lipids, membranes and organelles, which can lead to activation of cell death processes such as apoptosis. The focus of this thesis is the production of singlet oxygen which is a type of ROS. Indium-111, lutetium-177 and yttrium-90 which decay by different types of radiation have been used as radiation sources. In this research, the influence of these different radiation sources have been tested on Ce6 and TiO2 and their ability to produce singlet oxygen. Results show that Ce6 and TiO2 have increased production of singlet oxygen when exposed to ionizing radiation. Ce6 generates singlet oxygen when irradiated by both low energy gamma sources and high energy beta-minus radiation, while TiO2 generates singlet oxygen when irradiated by high energy beta-minus radiation.