On the Development of a Light Dosimetry Planning Tool for Photodynamic Therapy in Arbitrary Shaped Cavities: Initial Results.

Previous dosimetric studies during photodynamic therapy (PDT) of superficial lesions within a cavity such as the nasopharynx, demonstrated significant intra- and interpatient variations in fluence rate build-up as a result of tissue surface re-emitted and reflected photons, which depends on the optical properties. This scattering effect affects the response to PDT. Recently, a meta-tetra(hydroxyphenyl)chlorin-mediated PDT study of malignancies in the paranasal sinuses after salvage surgery was initiated. These geometries are complex in shape, with spatially varying optical properties. Therefore, preplanning and in vivo dosimetry is required to ensure an effective fluence delivered to the tumor. For this purpose, two 3D light distribution models were developed: first, a simple empirical model that directly calculates the fluence rate at the cavity surface using a simple linear function that includes the scatter contribution as function of the light source to surface distance. And second, an analytical model based on Lambert's cosine law assuming a global diffuse reflectance constant. The models were evaluated by means of three 3D printed optical phantoms and one porcine tissue phantom. Predictive fluence rate distributions of both models are within ± 20% accurate and have the potential to determine the optimal source location and light source output power settings.

Adjuvant photodynamic therapy in head and neck cancer after tumor-positive resection margins.

OBJECTIVE: In case of close or positive resection margins after oncological resection in head and neck surgery, additional treatment is necessary. When conventional options are exhausted, photodynamic therapy (PDT) can play a role in achieving clear margins. The purpose of the current study was to evaluate the clinical benefit of PDT as adjuvant therapy next to surgery with positive resection margins. The role of the time interval between surgery and PDT on survival outcomes also was investigated. STUDY DESIGN: Retrospective cohort analysis. METHODS: Adjuvant PDT was performed in patients with a malignancy in the head and neck region with close or positive resection margins who were not eligible for conventional treatment options. The primary endpoint was progression-free survival. Secondary endpoints were disease-free survival, overall survival, and optimal time interval between surgery and PDT. RESULTS: Fifty-four patients were treated with surgery followed by meta-tetrahydroxyphenylchlorin-mediated PDT. There was a large diversity in tumor location and histopathology, as well as in time interval between surgery and PDT. The 2-year progression-free survival rate was 30%; 2-year disease-free survival rate was 28%; and 2-year overall survival was 51%. Disease-free survival was significantly better when the time interval between surgery and PDT was ≥ 6 weeks (P = 0.02). CONCLUSION: PDT can be applied as adjuvant therapy after surgery in cases of a malignancy with close or positive tumor resection margins. However, the clinical benefits are yet to be determined. There is a significantly better disease-free survival with a time interval between surgery and PDT of minimal 6 weeks. LEVEL OF EVIDENCE: 4. Laryngoscope, 128:657-663, 2018.