☀️ Phototherapy Cumulative Skin Cancer Risk Simulator

UV-Induced DNA Damage Per Phototherapy Session

Each session creates measurable DNA photoproducts in the epidermis.

• ~10³–10⁴: Dimers per session (per cell, placeholder estimate)
• ~24–48h: Repair window (nucleotide excision repair)
• 0.5–3 J/cm²: Typical session dose (depends on modality)
• 296–313nm / 320–400nm: Wavelength band (NB-UVB / PUVA)

How a single session damages keratinocyte DNA

Placeholder: UV photons form cyclobutane pyrimidine dimers in exposed skin cells.

Placeholder: most damage is repaired before the next scheduled session.

Tracking Cumulative Lifetime UV Dose

Dose accumulates arithmetically across hundreds of sessions over years.

• 20–40 sessions: Typical course length (per treatment cycle)
• multiple: Lifetime course count (for chronic psoriasis/vitiligo)
• J/cm² total: Cumulative dose metric (summed across sessions)
• per-patient log: Dose record keeping (required for safety)

Why cumulative dose matters more than per-session dose

Placeholder: long-term risk correlates with total lifetime dose, not single exposures.

Placeholder: clinics track running dose totals per patient chart.

Non-Melanoma Skin Cancer Risk Rises With Dose

Squamous and basal cell carcinoma risk climbs nonlinearly with sessions.

• cumulative dose: Risk driver (not single sessions)
• SCC > BCC: Cancer type (non-melanoma skin cancer)
• years: Latency period (after high cumulative exposure)
• nonlinear rise: Threshold behavior (placeholder risk curve)

Why risk accelerates past a cumulative threshold

Placeholder: repair capacity saturates as unresolved mutations accumulate.

Placeholder: risk rises steeply once lifetime sessions pass a few hundred.

PUVA Carries Higher Long-Term Risk Than NB-UVB

Psoralen photosensitization increases mutagenicity relative to narrowband UVB.

• higher: PUVA SCC risk (vs NB-UVB, dose-matched)
• psoralen + UVA: Mechanism (crosslinks DNA strands)
• lower risk: NB-UVB profile (placeholder comparative estimate)
• NB-UVB first-line: Clinical preference (when comparably effective)

Comparative mutagenicity of PUVA and NB-UVB

Placeholder: psoralen crosslinking adds mutagenic burden beyond UVB alone.

Placeholder: PUVA courses need stricter lifetime session limits.

Long-Term Dermatologic Monitoring Recommendations

High cumulative dose patients require scheduled skin surveillance.

• annual exam: Low-dose interval (placeholder guideline)
• every 3 months: High-dose interval (placeholder guideline)
• lifelong follow-up: PUVA history (placeholder recommendation)
• full skin exam: Key action (placeholder recommendation)

Setting a monitoring schedule from cumulative history

Placeholder: monitoring frequency scales with total dose and modality history.

Placeholder: PUVA patients typically need indefinite dermatology follow-up.