To PDT or Not to PDT, That Is the Question—A Retrospective Analysis of Carbon Emissions Associated With Travel for Photodynamic Therapy

The impacts of climate change are bidirectional within the specialty of dermatology; climate change has an effect on a multitude of dermatological conditions, but the provision of dermatological care also has an impact on our environment. While the impact of dermatological care on our environment may pale in comparison to the effect of global events, 'no one is too small to make a difference', to quote Greta Thunberg [1]. Climate change brings a universally increased risk of skin cancer due to the depletion of the Ozone layer. Inflammatory dermatoses are also particularly sensitive to changing environmental conditions. Furthermore, warming of our oceans poses an exposure risk for aquatically transmitted dermatoses [2]. The World Health Organisation (WHO) has called for urgent action to avert the catastrophic health implications of climate change. The promotion of actions that reduce carbon emissions has been listed by the WHO as an objective to target this human health crisis [3]. While strides have been made to make the specialty of dermatology more sustainable [4], further strategies exist to combat climate change. The delivery of photodynamic therapy (PDT) is one such area that generates a carbon footprint. We performed a retrospective review of patients attending a tertiary dermatology unit in the West of Ireland for PDT from the 1st of July 2023 to the 1st of January 2024 to determine the impact of travel for PDT on carbon emissions. To the best of our knowledge, this is the first study focusing on carbon emissions associated with travel for PDT appointments. We retrospectively reviewed all patients attending our dermatology department in the West of Ireland for PDT over a 6-month period from the 1st of July 2023 to the 1st of January 2024. Our department caters for a large catchment area in the region of 13,158 km2, and services approximately 1 million patients. Google MapsTM was used to calculate the distance travelled by patients. A total of 50 patients received 86 sessions of PDT during this timeframe; 50% of whom were female. The average age of PDT recipients was 74 years. Diagnoses included actinic keratosis (AK) (29%), squamous cell carcinoma in-situ (SCCis) (36%) and superficial basal cell carcinoma (sBCC) (36%). Certain patients had more than one lesion treated during a given PDT session. 80% of patients received two sessions of PDT. Those who received one session of PDT were typically those with AK, or those in whom the first session was poorly tolerated. The average distance travelled by patients to our department for PDT during the specified time period was 107 km (range 3–288 km). The total cumulative distance travelled was 9216 km which equates to 3.02 metric tonnes of carbon dioxide emissions per 6 months, assuming unknown fuel-type for an average car. Carbon emissions were calculated using an online tool recommended by the Environmental Protection Agency of Ireland [5]. Our study has limitations including the assumption that all patients travelled to our department for PDT via an average car. However, our department in the West of Ireland is poorly served by public transport so it is likely that the majority of patients did indeed travel by car. Ireland's total carbon emissions from the transport sector for 2023 was 11.791 million tonnes of CO2 equivalent [6]. Assuming a similar amount of carbon emissions from travel for PDT in our department for the first half of 2023 as the second (3.02 metric tonnes), our departmental PDT travel emissions accounted for 5.1 × 10−5% of Ireland's entire carbon emissions from travel in 2023, emissions which are not negligible. PDT is a well-established minimally invasive therapeutic modality used in dermatology for the treatment of pre-cancerous lesions and keratinocyte malignancies including AK, SCCis and sBCC. PDT uses photosensitisers that, after being excited by light at a specific wavelength, react with the molecular oxygen to create reactive oxygen species in the target tissue, resulting in cell death [7]. PDT can be delivered in one of two ways: conventional red-light PDT, which involves a red-light lamp, and daylight PDT [8]. It often requires two visits to a dermatology clinic to treat a given lesion, thereby generating an ecological footprint. Home daylight PDT (DL-PDT) for the treatment of AK has been the subject of recent research in the literature. The results of a recent randomised single-centre non-inferiority clinical trial demonstrated a non-inferior efficacy of DL-PDT for the treatment of AK using BF-200 ALA gel, a 7.8% aminolevulinic acid gel, self-applied by the patient at home, when compared to DL-PDT performed in the dermatology department by qualified medical personnel [8]. A further prospective, observational open study of AK treated with home DL-PDT demonstrated a response rate of 65.9% after 12 months [9]. A third study on the treatment of AK with DL-PDT by Karrer S. et al. demonstrated a 62% response rate at 3 months, as well as significant patient satisfaction [10]. These results are promising where the treatment of AK is concerned, and may shift us further towards carbon neutrality. This study demonstrates that a single dermatology unit delivering PDT leaves a substantial carbon footprint. Home DL-PDT is a promising and perhaps under-utilised treatment option for AK, but the literature is lacking on the treatment of keratinocyte malignancies such as SCCis and sBCC with home DL-PDT. Furthermore, patients with more hyperkeratotic AK disease appear to have poorer outcomes when treated with home DL-PDT [11]. While strides are being made to shift dermatology as a specialty into carbon neutrality, further work is required to optimise this therapeutic approach of home DL-PDT. It is imperative that, as a specialty, we continue to identify sustainable practices with a focus on actions that could be implemented in dermatology centres. As Albert Einstein once said, 'those who have the privilege to know, have the duty to act'. Nicola Kearney: conceptualisation, methods, writing – original draft. Ibrahim Afridi: methods, writing – original draft. Mary Laing: writing – review and editing subsequent drafts, supervision. The authors declare no conflicts of interest. The data that support the findings of this study are available from the corresponding author upon reasonable request.