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Radiotherapy Physics
Published in Debbie Peet, Emma Chung, Practical Medical Physics, 2021
Andrea Wynn-Jones, Caroline Reddy, John Gittins, Philip Baker, Anna Mason, Greg Jolliffe
Superficial X-rays have limited penetration so can only be used to treat lesions near, or on, the skin surface, typically at depths in tissue of 2–10 mm [Figure 6.8(b)]. Typically, 80–220 keV X-rays can be used. In the UK, most superficial treatments are for basal cell carcinomas.
Non-Melanoma Skin Cancer
Published in Pat Price, Karol Sikora, Treatment of Cancer, 2020
Irene De Francesco, Sean Whittaker, Stephen L. Morris
Most superficial lesions are treated with superficial x-rays (40–100 kV) or orthovoltage (100–300 kV). The tumor must be carefully assessed macroscopically for its lateral extent, and particular attention must be paid to the depth of the tumor in sites such as the inner canthus, nasolabial fold, ala nasi, tragus, and post-auricular area, where deep infiltration may occur. The visible tumor is drawn on the skin; typical radial margins to create the field to treat a BCC are 6 mm around the visible tumor, but this must be interpreted in the light of the clinicopathological type of BCC, the clinical site, organs at risk, and size of the lesion being treated. For example, a morphoeic BCC may require a margin of 1–1.5 cm. Percentage depth doses for different field sizes at different energies are consulted to select a beam energy that will encompass the target volume by the 90% isodose. The treatment volume needs to be larger than the target volume due to dose fall-off at the field edges. Sheets of lead cut out to surround the treatment field protect the surrounding skin and any organs at risk. The thickness of the lead depends on the energy used. A lead shield may be required to protect the eye and to protect the nasal mucosa and cartilage when the ala nasi is treated. In this case, it is inserted using local anesthetic drops.
Skin cancer
Published in Peter Hoskin, Peter Ostler, Clinical Oncology, 2020
Superficial x-rays or electrons are used to limit irradiation of subcutaneous tissues. Treatment can be given as a large single fraction or a course of daily treatment over 2–6 weeks. Large single doses are preferred for patients with small tumours who would find travelling difficult due to age or infirmity, but this approach gives an inferior cosmetic outcome. Post-operative radiotherapy is indicated where surgical excision is incomplete and to nodal areas if there is extracapsular extension on microscopy of lymph nodes removed at surgery.
Radiation therapy techniques in the treatment of skin cancer: an overview of the current status and outlook
Published in Journal of Dermatological Treatment, 2019
Ali Pashazadeh, Axel Boese, Michael Friebe
Superficial X-ray therapy concern with the application of photons generated by an X-ray source, working at the potential energy of 50-150 kV, to treat superficial tumors. The first machines used for superficial X-ray therapy were introduced between 1930 and 1940 (26). Due to the low energy of the generated photons, they deposit a significant portion of their energies in the first layers of the tissue, making them a suitable option for irradiation of lesions up to 5 mm depth in dermatology. For 1–2 mm lesions it is used in 75 kV, and for 3–5 mm lesion 100 kV is applied (27). The source to skin distance (SSD) in superficial X-ray therapy is generally between 10 and 30 cm (28).