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Radiation therapy for skin cancer


Medical editor Åse Bratland MD
Oncologist
Oslo University Hospital

General

Radiation treatment of non-melanoma skin cancer usually includes treatment of visible and palpable changes with margins and can be used for primary treatment or as preoperative or postoperative treatment. In some cases, it is also combined with chemotherapy. For difficult localizations and spreading, additional mapping with CT dosage-planning and more complicated treatment arrangements are required.

Radiation of basal cell carcinoma provides a cure rate of over 90%. Squamous cell carcinoma and other histological groups respond well to radiation treatment with a high success rate.

For brachytherapy, the radiation source is placed in or close to the tumor. In this way, the cancer cells obtain a high dose of radiation while the dose to the surrounding normal tissue can be limited. Brachytherapy can also be used in and around the nose (columella), in eyelids, and lips.

Whole-body radiation is used for mycosis fungoides.

Lymph node radiation is appropriate for squamous cell carcinoma which has metastasized or has a high risk for metastasis. For extremity-localized Kaposi's sarcoma, the treatment takes place in a water bath. For Merkel cell carcinoma, radiation treatment is often part of a combination of treatments.

Indications

  • Squamous and basal cell carcinoma. Appropriate for localizations in and around the ears, in the central facial triangle, and for larger, difficult operation localizations.
  • Kaposi's sarcoma
  • Mycosis fungoides 
  • Merkel cell carcinoma 

Goal

  • Curative treatment
  • Palliation against pain, bleeding, and other symptom relief. 

Definitions

Target Volume

 

 

Target volume definitions from ICRU
(International Commission on Radiation Units and Measurements)

GTV (= Gross Tumor Volume)

Tumor volume

Palpable or visible/identifiable area of malignant growth.

CTV (= Clinical Target Volume)

Clinical target volume

Tissue volume which contains GTV and/or subclinical microscopic malignant disease.

ITV (= Internal Target Volume)

Target volume

Volume containing CTV and one inner margin taking into account inner movements and revisions of CTV. 

PTV (= Planning Target Volume)

Planning volume

Geometric volume containing ITV and one Setup margin taking into account variations for patient movements, variations in patient positioning, and field modeling.


Preparation

For basal cell and squamous cell carcinomas < 4 cm in diameter which are not deeply infiltrating (max 1.5-2 cm), manually simulation is used with area margins of 0.5 cm outside the visible and palpable tumor.

For larger diameters, the margins should be increased to 1 cm especially when using X-rays.

Deeper and larger lesions require dose plan contouring with GTV and an ITV at a minimum of 1 cm according to normal guidelines. Many of these lesions can be treated with electrons, while others require multiple-field photon radiation.

For brachytherapy, the patient is placed under general anesthesia and the catheter is inserted into the tumor. Dosage planning is done after the radiation sources are in place.


Implementation

The radiation treatment is carried out mostly on an outpatient basis with daily treatments and weekly doctor follow-up. Individual assessments may require postponement of treatment. Causes may be:

  • general health status
  • risk of bleeding 
  • location of lesion

Standard Treatment

  • For lesions < 4 cm, 4 Gy x 12–15 is administered over the course of 2–4 weeks.
  • For lesions > 4 cm, 3 Gy x 17–18 is administered over the course of 3–4 weeks.
  • For lesions > 8 cm, 2.5 Gy x 25, possibly 2 x 35

Brachytherapy

  • Thin plastic tubes are inserted in or around the tumor. 
  • These are connected to a computer-controlled remote afterloading machine which pushes a radioactive isotope into the plastic tube for a period of time.
  • The dose is individual for each patient.

Follow-up

The first check after treatment for all patients is 6-8 weeks after finishing treatment to assess the result and side effects. Further follow-up is usually transferred to the referring physician or primary care physician.

Patients who are especially prone to skin cancer (for example immune-suppressed or hereditary factors) or have a more extensive illness are followed-up at a cancer clinic.

Side effects

  • Skin soreness
  • Formation of scars
  • Symptoms from surrounding normal tissue, for example salivary glands, mucosa, and throat 

The radiated area must be protected from sun exposure for the first two years after treatment as the skin in this area can be easily sunburned.


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