Epidermal Radioisotope Therapy

Epidermal radioisotope therapy (dermo-beta-brachytherapy, epidermal brachytherapy with open radioisotopes), is a nuclear medicine procedure using beta-emitters for the treatment of non-melanoma skin cancer (NMSC).
Method
In the epidermal radioisotope therapy, artificially produced radioactive isotopes - here rhenium-188 (188Re) - are applied within a matrix over a foil which has previously been placed over the lesion. The beta radiation of Rhenium-188 has a therapeutic range of 2-3 mm deep, and it is therefore used for the treatment of superficial skin cancers such as the NMSC.
Rhenium-188 (188Re)
Rhenium-188 is an artificial radioactive isotope that decays emitting beta radiation (96.7%) and a small amount of gamma radiation. The half-life 188Re - the time span in which half of the atoms of a radioactive substance decay - is 17.0 hours, which allows treating within a very short period of time. With a maximum of 2.1 MeV, the beta-radiation of Rhenim-188 has a penetration depth of 2-3mm in human tissue (92% of its dose is delivered within the first 2-3mm). The energy of the beta radiation is localized and deposited exactly in the tumor tissue, leaving the surrounding healthy tissue unharmed. The situation is different with gamma radiation, which can penetrate several centimeters into the tissue. However, the proportion and energy of gamma radiation from the Rhenium-188 is so low that it does not cause radiation-induced damage in a patient's body. In the epidermal radioisotope therapy, the gamma radiation can go up to the 8% (0.17 mSv, millisievert), normally being the 2.5-5% (0.05-0.1 mSv) of the total radiation, which corresponds to the annual radiation exposure in Germany.
Availability
Rhenium-188 is extracted from tungsten-188, another artificial radioactive isotope produced in a generator. Since the half-life of rhenium-188 is only 17.0 hours, transport of the active beta-emitter to the patient is time-critical.
Medical effect
The medical effect of epidermal radioisotope therapy is based on the local direct cytotoxic effect of the beta particles, which triggers a local apoptosis and immunity reaction. This is an effective therapy for the treatment of NMSC independent of the size, localization or severity of the tumor.
Indication
Epidermal radioisotope therapy is mainly used in the treatment of non-melanoma skin cancer such as basal cell carcinoma, spinocellular carcinoma (squamous cell carcinoma), Queyrat Erythroplasia (so far only on the penis) and Bowen's disease. Another area of application is the extramammary Paget's disease.
Epidermal radioisotope therapy is a painless therapy with no anesthesia needed. In 89% of the cases requires only a single session to eliminate the tumor and it is a non-invasive medical procedure, which leaves no stitches or the possibility of secondary infection. It results in little to no scarring and maintains functionality, which makes it a helpful treatment for lesions whose anatomical position may result in a suboptimal cosmetic result using conventional approaches.
Therapy procedure
Therapy sequence using the example of epidermal radioisotope therapy.
1. Using a special pen, the dermatologist marks the skin area to be treated with Rhenium-188 plus, which includes the area of the lesion and a safety margin of 5mm. Then, the nuclear medicine professional applies the special transparent protective foil.
2. After the foil is applied over the area needed to treat (lesion and 5mm security margin), the rhenium-188 matrix is applied using a special applicator. The foil with the radioactive material is removed after the end of the therapy.
3. Normally, special aftercare is not necessary. The dead tumor cells are eliminated by the body and replaced by healthy tissue.

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