Surface contact therapy (synonyms: surface brachytherapy, surface radiation therapy) is a variant of brachytherapy (short-distance radiotherapy). It is a procedure from the field of radiation medicine, which is primarily used as a therapeutic measure in dermatology and ophthalmology. The main field of application of surface contact therapy is the treatment of tumors located on the skin, in the epipharynx (nasopharynx) or in the eyeball. In surface contact therapy, the target volume is very superficial. Thus, the released radiation must penetrate only a few millimeters below the irradiated surface.
Indications (areas of application)
Dermatology
- Skin tumors – Tumors of the skin, such as basal cell carcinoma (BZK; basal cell carcinoma; white skin cancer; epithelioma basocellulare; English : basal cell carcinoma, basalioma, basal cell epithelioma); it is a tumor (cancer) of the epithelium of the skin), can be treated palliatively (no curative approach) or curatively (cure as a therapeutic goal) by surface contact therapy, depending on the tumor stage. The indication for radiotherapy occurs, among other things, when surgical removal of the tumor is not possible due to unfavorable localization or excessive tumor extension. It is necessary to confirm the diagnosis histologically (by fine tissue) and then to perform surface contact therapy. In malignant melanoma (synonyms: Melanoma, melano(cyto)blastoma or black skin cancer (English : [malignant] melanoma); a highly malignant tumor of melanocytes/pigment cells) stage IV (stage of distant metastasis/settlement of tumor cells from the site of origin via the blood/lymphatic system to a distant site in the body and growth of new tumor tissue there), surface contact therapy can be used as a treatment option to reduce the tumor mass. In this case, however, the brachytherapy option has only a palliative character (treatment aimed not at curing an existing underlying disease, but at reducing its consequences). When selecting treatment options, it is necessary to weigh the burden on the patient and the expected outcome.
Ophthalmology
- Choroidal melanoma – choroidal melanoma is the most common and important malignant (malignant) primary tumor type of the interior of the eye in adult patients. The need for therapy is determined by a progression assessment of the size of the tumor. If there is evidence of tumor growth, surface contact therapy is a treatment option. For this purpose, the radiation carrier is sutured onto the sclera (sclera of the eye; synonym: “white eye skin”; it encloses the eyeball almost completely and protects the eye; together with the cornea (cornea), it belongs to the outer eye skin) and left in place for a defined period of time in order to achieve the necessary radiation dose. In the treatment planning must be included that the prognosis of the patient after surface contact therapy is usually not worse than after removal of the eyeball.
- Conjunctival tumors – for tumors of the conjunctiva, such as conjunctival carcinoma (conjunctival carcinoma), surface contact therapy is an alternative to lamellar ablation of the conjunctiva and sclera with adequate clearance in healthy individuals. If necessary, follow-up treatment with mitomycin C eye drops.
Gynecology
- Recurrent breast carcinoma – if a recurrence (recurrence of cancer) of the pre-irradiated thoracic wall (chest) occurs after breast carcinoma (breast cancer), surface contact therapy is a promising alternative to further brachytherapy procedures, depending on the overall situation of the patient. In contrast to, for example, repeat percutaneous radiotherapy (radiation source is outside the body), surface contact therapy represents a method of therapy with fewer side effects. The use of surface contact therapy is particularly recommended if there are no clearly limiting late effects of the preceding radiation therapy. In addition, this form of brachytherapy is indicated when the resection margins (edges of the excised tissue) are smaller than 1 cm or a residual tumor is present.
Contraindications
Contraindications vary depending on the tumor being treated.
Before therapy
Before surface contact therapy can be used as a treatment modality, grading (assessment of tumor differentiation) and staging (involvement of other organ systems) must first be performed. Furthermore, a detailed review of the indication must be performed.
The procedure
The radiation source for surface contact therapy is β-emitters, such as 90Sr (strontium) preparations or 106Ru (ruthenium)/106Rh (rhodium) emitters with a small gamma component (1-2%). These radiation sources have a therapeutic range of approximately 7 mm. Depending on the area of application, different applicators are used for radiation delivery. For example, in surface contact therapy of the eyeball, small trays are used for application to the eyeball. When irradiating the surface of the skin, primarily plastically deformable material is used, from which so-called moulages are formed on the basis of external contours. When the method is applied to internal cavities, such as the roof of the throat, plastically deformable material is also used into which radiation sources can be introduced.
After therapy
Depending on the type of tumors, examinations are necessary at a defined period of time to monitor tumor growth or tumor remission (tumor regression). Furthermore, the occurrence of complication must be monitored and treated if necessary.
Possible complications
- Secondary tumors (second tumors) – as a result of brachytherapy, secondary tumors may develop because surface irradiation damages not only tumor cells but also healthy body cells.
- Radiogenic dermatitis (radiation-induced skin inflammation) – especially when using surface contact therapy for the treatment of skin tumors, there is a high risk for the development of skin inflammation such as radiogenic dermatitis.
- Mucositides (mucosal damage) – depending on the location of the target tissue, the risk of mucosal damage is significantly increased. Inflammatory reactions can affect almost any organ exposed to radiation.
- General blood count changes – leukopenias (reduction in the number of white blood cells) and thrombocytopenias (reduced number of platelets in the blood compared to the norm) often occur during therapy. Other consequences of this include an increased risk of infection and bleeding.