Phototherapy Dose Calculator

Narrowband UVB (NB-UVB) phototherapy dosing follows a skin-response protocol: start low for the patient's Fitzpatrick skin type, then adjust each subsequent dose based on how the skin reacted last time. This calculator's Protocol Start Dose and Maximum Dose are fixed per Fitzpatrick type, both per the AAD-NPF joint phototherapy guideline's skin-type-based dosing table -- lighter skin types (I-II) start at 300 mJ/cm2 and cap at 2000, mid types (III-IV) start at 500 and cap at 3000, and darker types (V-VI) start at 800 and cap at 5000 mJ/cm2, reflecting the higher minimal erythema dose darker skin tolerates. Because these two figures are looked up purely from skin type, they never change based on how many sessions the patient has already had or how many days have passed since the last one. For a first session, or whenever Last Dose is left at 0, the dose is simply the protocol starting dose -- this calculator's defaults are set mid-course (Treatment Session # 5, a non-zero Last Dose) specifically so you can see the session-to-session titration logic run rather than always landing on the first-session case. For later sessions, the calculator applies an erythema-response rule: no redness increases the dose by a skin-type-specific increment, faint pink holds it steady, definite redness cuts it by 25%, and a painful reaction cuts it in half.

On top of that, a gap since the last treatment triggers its own reduction -- a week or more trims the dose, two weeks or more halves it, and four weeks or more resets to the starting dose -- because UVB tolerance fades between sessions. Exposure Time divides the recommended dose by an assumed lamp irradiance of 10 mW/cm2 (shown in the Assumed Lamp Irradiance output) -- a representative mid-range figure for a panel NB-UVB booth, not a measurement of any specific device, so always confirm actual exposure time against your unit's own dosimetry rather than this assumption. Cumulative Dose Est. replays that same escalate-then-cap logic session by session up to the entered Treatment Session #, so it plateaus once a session's dose hits Maximum Dose instead of compounding without limit -- a realistic multi-month NB-UVB course total lands in the tens to low hundreds of J/cm2 (thousands to low hundred-thousands of mJ/cm2), not the astronomical figures an uncapped exponential formula would produce. Exact starting doses, increment percentages, and missed-day thresholds vary meaningfully between phototherapy units and published protocols, so treat this as a general planning reference and always follow your treating clinic's specific dosing protocol and physician orders.