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NB-UVB Cumulative Limits — SCE Dermatology MCQ

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ModeratePhotobiologyNB-UVB Cumulative LimitsSCE Dermatology

A 50-year-old woman has had multiple courses of phototherapy. Her cumulative NB-UVB treatment count has reached 500 sessions. What guidance exists about cumulative NB-UVB exposure limits?

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Correct answer: C — There is no established absolute limit for NB-UVB, but BAD guidelines recommend caution above 500 treatments; cumulative UV dose should be documented and the risk-benefit ratio reassessed

Unlike PUVA (which has a defined upper limit of approximately 200 treatments or 1000-1500 J/cm² due to proven dose-dependent SCC and melanoma risk), NB-UVB does not have an established absolute upper treatment limit. However, BAD phototherapy guidelines recommend: documenting cumulative NB-UVB sessions and dose, exercising caution above 500 treatments, and reassessing the risk-benefit ratio at high cumulative exposures. The theoretical skin cancer risk from very high cumulative NB-UVB exposure is plausible (DNA damage from any UV wavelength) but has not been conclusively demonstrated at standard treatment doses. Alternative treatments should be considered when cumulative NB-UVB exposure becomes very high.

Reference: BAD 2019 Phototherapy Guidelines