Photodynamic therapy lasers and light sources

Photodynamic therapy needs a photosensitiser, oxygen and light of the wavelength the drug absorbs. The light sources are therefore drug-specific. Porfimer sodium, approved in the 1990s for oesophageal and endobronchial cancer, is activated at 630 nm by a diode laser coupled to a cylindrical diffusing fibre passed down an endoscope; temoporfin for head and neck cancer at 652 nm; the topical aminolevulinic acid and methyl aminolevulinate for actinic keratosis and superficial basal cell carcinoma by red LED panels such as Aktilite or simply by daylight; padeliporfin, the vascular-targeted agent for low-risk prostate cancer, at 753 nm through interstitial fibres placed under ultrasound guidance; and cetuximab sarotalocan, the antibody-dye conjugate approved in Japan in 2020 for recurrent head and neck cancer, at about 690 nm from Rakuten Medical's BioBlade laser through frontal or cylindrical diffusers. Vendors of the lasers and fibres include biolitec, Modulight and Photocure's partners, and the same blue-light platforms that reveal bladder tumours with hexaminolevulinate come from endoscope makers.

Against surgery and radiotherapy, photodynamic therapy is repeatable, spares connective tissue so it heals with little scarring, and can be delivered through an endoscope; its limits are light penetration of only a few millimetres, skin photosensitivity for weeks with systemic drugs, dependence on tissue oxygen, dosimetry that is hard to measure, and a small evidence base for most indications.