Dose modeling in ultraviolet phototherapy

Abstract

This method could potentially serve as a basis for a full computational dose model for quantifying patient dose.

Ultraviolet radiation therapy and UVR dose models

“…20 It is also important to note that the penetration depth of UVR tends to be very shallow; at 311 nm, penetration is only 20-40 µm. 17,18 Radiometric terminology can vary greatly between various branches of optics, and in this work we shall use the convention laid down by Sliney, 14 where irradiance is defined as the power per unit area, and denoted E. The irradiance at a skin or detector surface is angle dependent 19 so surface orientation of a target site is an important factor to consider when estimating or measuring irradiance in practice. The most commonly encountered radiometric calculation in phototherapy relates prescribed dose D p to irradiance through…”

“…As all UVR is incident and absorbed superficially by the skin, the orientation of the skin surface is of paramount importance if accurate dosimetry is to be achieved. A first principles model of UVR dose that factors in skin orientation was published in 2010, 19 which treats the UVR tube as a line source continuum of point sources. Figure 13(a) shows the vector convention used in such a formulation for a skin surface and Fig.…”

“…This was found to range from 0.96-0.99. 18,19,68 The model was tested using hand-held dedicated photodiode UVR irradiance meters by International Light (International Light Technologies, MA) and the automated rotating detector to provide variation of the detector orientation relative to a test lamp, 74 yielding agreement of within 1% between model and measured values. A comparison of model and measured data is shown in Fig.…”

“…This is typically around 37 mm (Ref. 19) and some of the radiation from the mirror is "shielded" by the tube itself in or close to this region. This is difficult to quantify analytically, and an ad hoc approximation for tube clipping has been introduced in the analysis to factor in clipping effects due to the physical extent of the tube obstructing reflected UVR.…”

Investigations of cabin design in UV phototherapy

“…To this end, the authors have worked on characterizing tube emissions from the lamps 7 and reflector behavior. 8 These models describe the situation well for isolated cases, but it is important to test them in a clinical and nonidealized environment with existing cabins to ascertain their predictive power. This work focuses on narrow-band UVB sources centered around 311 nm which in recent years have shown great effectiveness in alleviating several skin complaints though the points discussed herein are of course still applicable to PUVA.…”