Indications

Definitive RT (no surgery)

BCC or cSCC where surgery is unsuitable (elderly, comorbidity, refusal, anticoagulation, anatomical complexity).
Lentigo maligna where surgery declined / unsuitable (Grenz rays, superficial X-rays).
Locally advanced cSCC unsuitable for surgery and ineligible for cemiplimab.

Adjuvant RT (after surgery)

cSCC: perineural invasion of named nerve, close / positive margin without further surgery, multiple involved nodes, extracapsular spread.
BCC: close / positive margin not amenable to re-excision; recurrent BCC after Mohs in selected cases.
Merkel cell carcinoma: adjuvant RT to primary site significantly reduces local recurrence; nodal RT for SLN-positive disease where completion dissection not undertaken.
Melanoma: adjuvant nodal RT considered for ECE or multiple nodes (less common in immunotherapy era).
DFSP: adjuvant RT for positive margin where re-excision not feasible.

Palliative RT

Cutaneous metastases — symptomatic bleeding, pain, ulceration.
Bone metastases (melanoma, MCC).
Brain metastases — stereotactic radiosurgery (SRS) for melanoma metastases.

Modalities

Modality	Depth	Typical use
Superficial X-rays (50–100 kV)	~5 mm	BCC / cSCC ≤5 mm depth on flat surfaces
Electrons (4–18 MeV)	1–5 cm	BCC / cSCC of the head and neck, deeper tumours, post-op boost
Photons (megavoltage)	Deep	Nodal basin RT, deep cSCC, metastatic disease
Brachytherapy	Surface contact	Selected periorbital and ear lesions; lip vermilion
Grenz rays / soft X-rays	~0.5 mm	Lentigo maligna where surgery declined

Fractionation regimens

BCC / cSCC examples from RCR 2024: 32.5–35 Gy in 4–5 fractions for small lesions; 45 Gy in 10 fractions; 50 Gy in 15–20 fractions; 55 Gy in 20 fractions; or 60 Gy in 30 fractions for large fields or areas of poorer radiation tolerance.
Adjuvant / complex head and neck cSCC: usually individualised at clinical oncology MDT, commonly using more protracted schedules when field size, nerve pathways, nodal basins or organ-at-risk constraints require it.
Palliative treatment: hypofractionated or single-fraction approaches may be used for bleeding, pain, ulceration or fungation; dose depends on intent, prognosis, field size and local radiotherapy protocol.
Stereotactic radiosurgery (SRS): single high-dose fraction for melanoma brain metastases.

Side effects

Acute (during and 0–6 weeks after)

Erythema, dry / moist desquamation.
Mucositis (head and neck fields).
Alopecia in field.
Fatigue.

Late (months to years)

Atrophy, telangiectasia, pigmentary change.
Permanent alopecia in field.
Dry eye / cataract (periocular fields).
Osteoradionecrosis (rare).
Second primary tumours in field — including new BCC and cSCC.

ImportantAvoid radiotherapy in Gorlin syndrome

RT can trigger numerous new BCCs within irradiated fields in Gorlin syndrome. Avoid where a surgical or non-radiotherapy alternative exists, and discuss extensively with the patient, clinical oncology and clinical genetics if RT is being considered.

Practical

Refer via skin cancer MDT to the appropriate radiotherapy centre (clinical oncology service).
Skin care during RT: gentle moisturiser, avoid friction, sun protection of treated field for life.
Counsel about late effects, especially in younger patients.
Combined modality therapy (e.g. concurrent cetuximab + RT for advanced cSCC) is occasionally used in specialist centres.

Radiotherapy in skin cancer