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Epithelial skin cancer is a common neoplasm. More than 200 new cases are treated at the authors’ hospital each year. The majority of these are basal cell carcinomas followed by squamous cell carcinomas. Both are the result of many years of ultraviolet light exposure from sunlight. With appropriate treatment, preferably at an early stage, excellent local control (equivalent to that of surgery) and cosmesis can be achieved. The treatment options are diverse, including plastic surgical excision, Moh’s microsurgery, electrocautery, topical 5-fluorouracil and imiquimod, photodynamic therapy and superficial radiotherapy. Advances in surgical techniques have meant that the population of patients treated with radiotherapy has changed. Indeed, radiotherapy for basal cell carcinoma is used as a primary treatment in only 8% of patients in the UK.
Radiotherapy, however, has many advantages in this setting, including the preservation of anatomy and avoidance of surgery, which is particularly useful in elderly patients who may be unsuitable for general anaesthetic or those on anticoagulants. The spectrum of cancers treated by radiotherapy is wide and includes lentigo maligna, lentigo maligna melanomas, Kaposi’s sarcoma, cutaneous T-cell lymphomas and Merkel cell tumours, and sweat gland tumours, in addition to basal cell and squamous cell carcinomas. Most patients are never given the chance of having radiotherapy; they are seen by either a dermatologist or a surgeon, and treated accordingly. At the authors’ institution, there is a joint skin clinic, with plastic surgeons, dermatologists and clinical oncologists.
Features of Kilovoltage X-rays
Kilovoltage X-ray equipment has been used therapeutically for the treatment of skin cancers for more than 100 years. More recently, in some centres, its use has diminished as megavoltage (the use of high energy X-rays delivered using linear accelerators) and electrons (often preferred because their depth of penetration can be accurately prescribed according to the energy used) have replaced it for many clinical applications. Kilovoltage X-rays units have the advantage of being low in cost compared with megavoltage units because of the relative simplicity of design and operation, and the use of simple collimation and beam shaping. The housing of such equipment requires less in the way of radiation protection compared to linear accelerators. (Linear accelerators are often housed in the basements, whereas superficial machines can be placed on the ground floor.) The use of a kilovoltage machine means that departments can optimise the use of their megavoltage machines for treating other non-cutaneous malignancies. X-ray therapy in the kilovoltage range is conventionally divided into four areas: