- Preferred for lesions that would require reconstructive surgery, where irradiation may be considered to produce better cosmesis, e.g. nose, upper and lower eyelid (preferably avoid the middle third of the upper eyelid), the lip and lesions involving the commissure of mouth, the nasolabial sulcus, lesions arising in the pre and post auricular areas and the ear.
- Large superficial lesions.
- Older patients.
- Patients who refuse or are unfit for surgery (RT avoids anaesthesia).
- Post surgery-for incomplete/marginal excision, perineural invasion.
Radiotherapy is not normally used in the following circumstances as some skin sites tolerate radiotherapy poorly:
- Sites of previous burns.
- Sites of prior radiotherapy.
- Fragile “tissue-paper” skin after steroids.
- Areas of vascular insufficiency e. Middle third of the upper eyelid.
- The skin of the back overlying the spine (this being an area of skin placed under pressure, leading to compromised healing and late skin necrosis).
- The skin overlying the shin and malleoli of the lower leg (the skin is under tension and there may be impaired healing).
Patients with ataxia telangiectasia, xeroderma pigmentosa .
- Histology/cytology (skin scrape, punch biopsy, excision biopsy).
- Fine needle aspirations of enlarged lymph nodes.
- Imaging in high risk sites to delineate deep extent and bone or cartilage involvement.
- Informed consent is obtained. Patients are treated in a position that best suits the location of the lesion. Immobilisation is achieved as appropriate.
- Generally lesions around the eye, ear, nose and those with an irregular border will require a customised lead cut-out, necessitating a prior mould room appointment. All other areas are treated as ‘mark on set’ using standard lead cutouts to shield the non-target areas using the appropriate thickness of lead.
- The eye requires special protection when eyelids are treated. A lead spatula (if one eyelid involved) or a lead internal eye shield (if both eyelids involved) is inserted under local anaesthetic (LA) to protect the cornea, the lens and uninvolved eyelid (with lead spatula). Patients’ will usually require an eye pad for 2 to 3 hours after the procedure until the LA effect is reversed & corneal reflex restored. Ensure that patient has an escort, as he/she may not be able to drive back.
- The nasal septum and gum are respectively shielded when lower nose and lip are treated. Wax or aluminium is used to cover the lead shield to absorb electron backscatter.
Tumours are defined according to the gross tumour volume (GTV) which is the visible and demonstratable extent of the tumour and the planned target volume (PTV) which is the GTV plus a margin to allow for inclusion of microscopic disease and set up accuracy .
- All patients are examined under a bright light with a magnifying glass, to define the tumour borders.
- Squamous cell carcinoma (SCC); PTV = GTV + 1cm margin all around laterally and a minimum 5 mm depth, according to clinician’s discretion.
- Basal cell carcinoma (BCC); PTV = GTV + 0.5 cm margin laterally (1 cm if morphoeic, large or poorly defined) and 0.5 cm deep margin. If on mobile skin a 0.25 cm deep margin is adequate.
- Clinical photographs are taken for record, clearly indicating the site, extent of lesion and orientation of the photograph.
Energy / Modality
- Aim to cover PTV with the 90% isodose, both laterally and at depth.
- Low energy photons are used depending on depth, site, size and availability. Avoid electrons near eyes (lateral scatter) and where field sizes are <4 cm. Try and avoid treatment with superficial X-rays over cartilage and bone due to risk of radionecrosis (absorption by photoelectric effect). In exceptional circumstances 300 kV photons maybe used after discussion with the consultant and senior radiographer.
- Low energy photons (<150 kV) deliver almost 100% to the skin and so do not require ‘build-up’.
- The depth dose characteristics of the beam depend on energy and field size.
Prescriptions are defined as applied doses (Dmax) for therapeutic X-Ray beams
Doses depend upon lesion size, histology and patient characteristics.
Basal Cell Carcinoma – prescribed doses:
- 18 Gy in 1 fraction(#) – Small tumours where cosmesis is relatively unimportant.
- 24 Gy in 2# – Both fractions given five weeks apart, where cosmesis is less important and target <5 cm.
- 32·5 Gy in 5# over 1 week – For small lesions under 2 cm diameter but not when over cartilage.
- 40·5 Gy in 9# over 2 to 3 weeks – Target size up to 5 to 6 cm diameter; this can be given as alternate day fractions over a 3 week period if patient access to hospital is limited, or in the elderly.
- 55 Gy in 20# over 4 weeks – Target < 6 cm, in areas of poor radiation tolerance.
- 50 Gy in 15# over 3 weeks – Target is between 4 and 6 cm diameter and not in an area of poor radiation tolerance.
- 60 Gy in 30# over 6 weeks – Target > 6 cm in areas of poor radiation tolerance.
Squamous Cell Carcinoma – prescribed doses:
- 45 Gy in 10# over 2 weeks – Target size up to 5 to 6 cm diameter this can be given as alternate day fractions over a three week period if patient access to hospital is limited.
- 55 Gy in 20# over 4 weeks – Target < 6 cm diameter, in areas of poor radiation tolerance.
- 60 Gy in 30# over 6 weeks – Target > 6 cm at sites of poor radiation tolerance.
- 24 Gy in 2# – Both fractions given five weeks apart for treatment of elderly and frail patients where cosmesis is less important and target <5 cm (Sambrook Split Course)