Dose Quantification in UV Phototherapy.

Ultraviolet light has long been used to alleviate a number of skin conditions, and its efficacy is well known. However, over-exposure to ultraviolet radiation has a number of detrimental effects and thus it is vital to maintain a dose to skin within the therapeutic window. To maximise treatment gain whilst circumventing potential side-effects of over-exposure requires accurate determination of irradiance and skin-dose. This is complicated by the fact that ultraviolet radiation is essentially absorbed at the skin surface, which means that changing orientation of the patient and source can modulate dose received. In addition, irregular patient shapes mean dose must be carefully calibrated. This chapter focuses on methods of determination of dose, clinical protocols for quantifying radiation dose received and mathematical models for estimating these quantities.

Ultraviolet radiation therapy and UVR dose models.

Ultraviolet radiation (UVR) has been an effective treatment for a number of chronic skin disorders, and its ability to alleviate these conditions has been well documented. Although nonionizing, exposure to ultraviolet (UV) radiation is still damaging to deoxyribonucleic acid integrity, and has a number of unpleasant side effects ranging from erythema (sunburn) to carcinogenesis. As the conditions treated with this therapy tend to be chronic, exposures are repeated and can be high, increasing the lifetime probability of an adverse event or mutagenic effect. Despite the potential detrimental effects, quantitative ultraviolet dosimetry for phototherapy is an underdeveloped area and better dosimetry would allow clinicians to maximize biological effect whilst minimizing the repercussions of overexposure. This review gives a history and insight into the current state of UVR phototherapy, including an overview of biological effects of UVR, a discussion of UVR production, illness treated by this modality, cabin design and the clinical implementation of phototherapy, as well as clinical dose estimation techniques. Several dose models for ultraviolet phototherapy are also examined, and the need for an accurate computational dose estimation method in ultraviolet phototherapy is discussed.

A computational simulation of reflector and tube effects in ultraviolet phototherapy.

While ultraviolet phototherapy is effective at treating a wide range of skin conditions, over exposure to ultraviolet radiation has a number of detrimental effects including but not limited to erythema, ocular damage and even oncogenesis. It is therefore important to quantify and control the dose received in order to maximize the effectiveness of treatment while minimizing the potentially damaging side effects. Recent dose models have been developed for this purpose, incorporating both the irradiance from the phototherapy lamps and the contributions from metallic reflectors. These models have good predictive power, but the situation is complicated by the huge variety of cabin and mirror geometries available. This work simulates a variety of possible treatment configurations to examine the implications these factors have on dose homogeneity and global irradiance, and shows that the relationship between global irradiance and number of tubes is complex and nonlinear. This has implications for both cabin design and treatment planning.

Investigations of cabin design in UV phototherapy.

PURPOSE: UVR phototherapy cabins exist in a huge variety of configurations and geometries. An accurate dose model has been developed which can be used to examine the question of cabin design to investigate factors influencing dose on a patient. METHODS: This work extends the existing dose model to entire cabins and investigates how cabin and reflector geometry influence resultant dose. RESULTS: The model predictions are in line with what is measured. It is found that the length and angle of the reflectors have a large influence on received dose. CONCLUSIONS: The influence of cabin geometry is important in estimating patient dose, and the findings of this work are applicable to future cabin designs.

Reflection modeling in ultraviolet phototherapy.

PURPOSE: Ultraviolet phototherapy is a widely used treatment which has exceptional success with a variety of skin conditions. Over-exposure to ultraviolet radiation (UVR) can however be detrimental and cause side effects such as erythema, photokeratisis, and even skin cancer. Quantifying patient dose is therefore imperative to ensure biologically effective treatment while minimizing negative repercussions. A dose model for treatment would be valuable in achieving these ends. METHODS: Prior work by the authors concentrated on modeling the output of the lamps used in treatment and it was found a line source model described the output from the sources to a high degree. In practice, these lamps are surrounded by reflective anodized aluminum in patient treatment cabins and this work extends the model to quantify specular reflections from these planes on patient dose. RESULTS: The extension of the model to allow for reflected images in addition to tube output shows a remarkably good fit to the actual data measured. CONCLUSIONS: The reflection model yields impressive accuracy and is a good basis for full UVR cabin modeling.

Dose modeling in ultraviolet phototherapy.

PURPOSE: Ultraviolet phototherapy is widely used in the treatment of numerous skin conditions. This treatment is well established and largely beneficial to patients on both physical and psychological levels; however, overexposure to ultraviolet radiation (UVR) can have detrimental effects, such as erythemal responses and ocular damage in addition to the potentially carcinogenic nature of UVR. For these reasons, it is essential to control and quantify the radiation dose incident upon the patient to ensure that it is both biologically effective and has the minimal possible impact on the surrounding unaffected tissue. METHODS: To date, there has been little work on dose modeling, and the output of artificial UVR sources is an area where research has been recommended. This work characterizes these sources by formalizing an approach from first principles and experimentally examining this model. RESULTS: An implementation of a line source model is found to give impressive accuracy and quantifies the output radiation well. CONCLUSIONS: This method could potentially serve as a basis for a full computational dose model for quantifying patient dose.