The role of radiotherapy in skin cancer

René Botha explains when radiotherapy is appropriate to be used as treatment for skin cancer and the types of skin cancer it can be used for.

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The skin is the largest organ of the body and skin cancer is one of the most commonly diagnosed cancers. When skin cancers are diagnosed early, most can be cured.

Skin cancers are classified according to which cell type within the skin they originate from and are divided into melanoma and non-melanoma skin cancers. The most common non-melanoma skin cancers are basal cell carcinoma (BCC) and squamous cell carcinoma (SCC).

Regarding early skin cancers, the mainstay of treatment is surgical excision. For non-melanoma BCCs and SCCs, there are other treatment options which may be appropriate. The number one priority of treatment is eradication of the tumour, however, good functional and cosmetic results are also important considerations.

The treatment modalities for BCC and SCC include surgery, skin creams, photodynamic therapy and radiotherapy. In cases where modalities have similar cure rates but the functional or cosmetic results differ, the modality that provides the better functional or cosmetic result is preferable. Although surgery remains the preferred treatment modality of treatment, radiotherapy still plays a role.

Radiotherapy

Radiotherapy, the application of X-ray radiation to the cancerous area, is an effective treatment for SCC and BCC. When surgical removal of BCC and SCC may be difficult, in areas of recurrence, or when the tumours are located in places of functional or cosmetic significance, such as the face, eyelids, lips, nose and ears, radiotherapy may be chosen instead.

The main advantage of radiotherapy is that it’s non-invasive. The disadvantages include cost, multiple daily treatments over four to seven weeks, and chronic skin and soft tissues changes.

Radiotherapy may be delivered by different modalities and entails attending short, daily treatments at a specialised treatment unit for up to seven weeks. The duration of treatment is dependent on the treatment intent, the area being treated and the modality used. Where cosmesis is of more concern and when the treatment area is overlying critical structures, the treatment may need to be spaced out over a longer period.

Superficial skin lesions may be treated with kilovoltage X-rays or with electrons. Kilovoltage X-rays require a specialised treatment unit, whereas electrons can be delivered by a linear accelerator, which is also used to deliver megavoltage X-rays. Linear accelerators are more readily available than the kilovoltage units.

For larger, or deeply infiltrating tumours, megavoltage X-rays may be needed. Advanced techniques, such as intensity-modulated radiation therapy may be used when the tumour is near critical structures.

Brachytherapy, which includes temporary implants, superficial applicators, or permanent implants may be used in certain areas.

This modality is used sparingly and requires specialised equipment and expertise.

The selected modality would depend on the size, depth of invasion, location of the tumour and which modality is available.

Side effects

The side effects are divided into early effects, which occur during the treatment and in the weeks after, and late effects, which may occur in the months to years following treatment.

Early effects may include inflammatory redness of the skin, pigment changes in the skin, skin peeling (desquamation), hair loss, and decreased or absent sweat and oil production from the glands in the skin.

The skin will never go back to its pre-treatment state. The late side effects may include the skin having a firmer, rougher appearance due to fibrosis, areas of redness with dilated capillaries appearing on the treated skin (telangiectasia), increased sun sensitivity with areas of pigment changes in the treated area, and the skin may be thinner and more susceptible to injury.

Early diagnosis

The biggest key to successful skin cancer treatment is early diagnosis. It’s advisable to routinely consult a dermatologist for regular assessments. Self-inspection on a regular basis is also useful to detect any changes which may need investigation.

The ABCDE rule tells us what to watch for:

• Asymmetry: irregular shape.
• Border: blurry or irregularly shaped edges.
• Colour: mole with more than one colour.
• Diameter: larger than a pencil eraser (6 mm).
• Evolution: enlarging, changing in shape, colour, or size.

References

1. Washington CM, Leaver DT. Principles and practice of radiation therapy. 4th ed. St. Louis, MO: Mosby; 2015.
2. Skin cancer information [Internet]. The Skin Cancer Foundation. 2018 [cited 2023 Mar 5]. Available from: https://www.skincancer.org/skin-cancer-information/
3. UpToDate [Internet]. Uptodate.com. [cited 2023 Mar 5]. Available from: https://www.uptodate.com/contents/non-melanoma-skin-cancer-the-basics?search=types%20of%20skin%20cancer%20&source=search_result&selectedTitle=1~150&usage_type=default&display_rank=1
4. Skin cancer [Internet]. Cleveland Clinic. [cited 2023 Mar 5]. Available from: https://my.clevelandclinic.org/health/diseases/15818-skin-cancer

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