Photodynamic therapy utilizes light for the medical treatment of cancer and psoriasis. In the photodynamic therapy (PDT) process, light excites photo-sensitizer molecules from the ground state of the molecules to excited states. The excited states subsequently undergo intersystem crossing to photo-sensitizer triplet states. The photo-sensitizer triplet states then transfer energy to oxygen (O2) molecules, causing the oxygen molecules to be excited from triplet ground states to excited singlet states. Singlet oxygen is highly reactive, and can attack target molecules in nearby cancer cells and subsequently kill the cancer cells. Singlet oxygen can also attack and neutralize the photo-sensitizer molecules in an undesirable side reaction (photo-bleaching), but this can be designed to occur at a slower rate than the desired therapeutic rate.

See also: Energy transfer and energy transfer with upconversion.

SimphoSOFT logo SimphoSOFT® supports simulation of photodynamic therapy App Notes

Screenshot of SimphoSOFT® M-CAD with energy level diagram for
Photofrin (left stack of levels), Oxygen (center), Cancer molecules (on the right),
containing chemical reactions (encircled) and energy transfer (yellow)


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