P185 Development and evaluation of a wearable optical sensor for personalized patient dosimetry in daylight photodynamic therapy

Abstract

Daylight photodynamic therapy (D-PDT) is an effective and less painful alternative to conventional PDT for treatment of actinic keratosis. However, the dose of light received is variable and dependent on the time of year and weather conditions. At present, there is no single, straightforward method for personalized dose measurement. A passive optical sensor technology has been developed for D-PDT dosimetry. The sensor consists of a photosensitive film-fabricated holographic grating. During D-PDT treatment the sensor produces a measurable signal proportional to the daylight dose received, which is read using an LED and photodiode. This low-cost, wearable sensor can be positioned adjacent to the treatment site and quantifies the dose of daylight received for the overall treatment or at intervals, thus facilitating optimization of dose delivery. The aim of this work is to optimize the optical sensor for translation into the clinical environment with dosimetry accuracy comparative to the gold-standard spectro­radiometer. The holographically patterned photosensitive films were optimized to mimic the absorption properties of protoporphyrin IX. The performance of the optical dosimetry sensor was evaluated under exposure to monochromatic 532-nm laser light, a white-light floodlight and daylight. The doses from the sensor were compared with effective doses calculated from illuminance measurements and spectroradiometer data. An optimum sensor configuration was identified to maximize both the sensitivity (i.e. change in grating diffraction efficiency) and response rate. Sensors fabricated on flexible substrates were tested in a clinical D-PDT setting for 2 h. The sensor has a cosine response and performed well for different daylight irradiances. The effective doses determined agreed favourably with those from established methods. The proposed optical sensor is a compact (∼0.5-mm thickness, ∼10-mm diameter), wearable dosimeter that enables remote D-PDT outside of traditional clinical settings. The sensor formulation and characteristics can be adapted, making it suitable for other visible-light therapies.