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Radiotherapy takes hair only where the beam passes through the scalp, and whether it returns depends on the dose the follicles received. Below a threshold it regrows in months; above it, the patch can stay thin for good.
Radiation alopecia is local, not systemic: hair falls from the area the beam enters and leaves, beginning two to three weeks into treatment. The National Cancer Institute's guidance says hair often grows back three to six months after radiotherapy ends, and that after a very high dose it may grow back thinner or not at all in the treated area.
The dose relationship has been measured twice. Lawenda and colleagues (2004) scored 61 scalp regions in 26 patients after cranial irradiation and found that permanent alopecia correlated with the calculated follicle dose and with nothing else they tested, not age, sex, family history of baldness, smoking, diabetes or beam energy. In a later cohort of 71 children and adults treated for central nervous system tumours or head and neck sarcoma (Phillips et al., JAMA Dermatology 2020), the median estimated scalp dose was 39.6 Gy and the dose at which half of patients were estimated to have moderate (grade 2) alopecia was 36.1 Gy (95 per cent confidence interval 33.7 to 39.6 Gy); higher dose and proton irradiation were each associated with greater severity. Of 34 patients treated with topical minoxidil 5 per cent, 28 (82 per cent) responded, and a small number were helped by hair transplantation or surgical reconstruction.
The practical consequence is a question for the radiotherapy planning team rather than a treatment: what dose does this plan deliver to the scalp, and can the beam arrangement reduce it without compromising the tumour. Scalp-sparing intensity-modulated planning is used where tumour position allows.
Showing the technology this term belongs to: IMRT / IGRT (modern external beam).
Shares Scalp care during and after cancer treatment, Anagen effluvium (chemotherapy hair loss), Persistent chemotherapy-induced alopecia, Minoxidil for persistent chemotherapy- and endocrine-therapy hair loss.
Shares Camouflage and restoration: fibres, micropigmentation, transplantation, Persistent chemotherapy-induced alopecia, Minoxidil for persistent chemotherapy- and endocrine-therapy hair loss.
Shares Anagen effluvium (chemotherapy hair loss), Persistent chemotherapy-induced alopecia, Minoxidil for persistent chemotherapy- and endocrine-therapy hair loss.
Shares Anagen effluvium (chemotherapy hair loss), Persistent chemotherapy-induced alopecia, Minoxidil for persistent chemotherapy- and endocrine-therapy hair loss.
Shares Anagen effluvium (chemotherapy hair loss), Minoxidil for persistent chemotherapy- and endocrine-therapy hair loss.
Shares Persistent chemotherapy-induced alopecia, Minoxidil for persistent chemotherapy- and endocrine-therapy hair loss.
Shares Persistent chemotherapy-induced alopecia, Minoxidil for persistent chemotherapy- and endocrine-therapy hair loss.
Shares Camouflage and restoration: fibres, micropigmentation, transplantation, Scalp care during and after cancer treatment, Minoxidil for persistent chemotherapy- and endocrine-therapy hair loss.