Monitoring photodynamic therapy of head and neck malignancies with optical spectroscopies

Abstract

In recent years there has been significant developments in photosensitizers (PSs), light sources and light delivery systems that have allowed decreasing the treatment time and skin phototoxicity resulting in more frequent use of photodynamic therapy (PDT) in the clinical settings. Compared to standard treatment approaches such as chemo-radiation and surgery, PDT has much reduced morbidity for head and neck malignancies and is becoming an alternative treatment option. It can be used as an adjunct therapy to other treatment modalities without any additive cumulative side effects. Surface illumination can be an option for pre-malignant and early-stage malignancies while interstitial treatment is for debulking of thick tumors in the head and neck region. PDT can achieve equivalent or greater efficacy in treating head and neck malignancies, suggesting that it may be considered as a first line therapy in the future. Despite progressive development, clinical PDT needs improvement in several topics for wider acceptance including standardization of protocols that involve the same administrated light and PS doses and establishing quantitative tools for PDT dosimetry planning and response monitoring. Quantitative measures such as optical parameters, PS concentration, tissue oxygenation and blood flow are essential for accurate PDT dosimetry as well as PDT response monitoring and assessing therapy outcome. Unlike conventional imaging modalities like magnetic resonance imaging, novel optical imaging techniques can quantify PDT-related parameters without any contrast agent administration and enable real-time assessment during PDT for providing fast feedback to clinicians. Ongoing developments in optical imaging offer the promise of optimization of PDT protocols with improved outcomes.

Keywords: Head and neck cancer; Photodynamic therapy; Monitoring and predicting response; Blood flow; Oxygenation; Oxygen metabolism; Diffuse optical imaging

Core tip: Most treatment approaches including chemo-radiation and surgery can induce prolonged morbidity and functional loss resulting in severe impairment of patients’ quality of life. Photodynamic therapy (PDT) is an emerging alternative treatment option without any significant accumulative side effects due to targeted light illumination and preferential accumulation of photosensitizers (PSs). However, PDT has not found widespread applications at the clinic mainly due to variable responses that originated from unstandardized treatment protocols such as different light and PS doses. Novel optical imaging techniques can quantify PDT-dosimetry related parameters such as local light and PS dose in tissue and PDT response related parameters such as tissue oxygenation and blood flow noninvasively without any contrast agent administration, thereby providing real-time feedback about the treatment efficacy for optimizing and standardizing PDT.