Wedge-shaped applicator for additional light delivery and dosimetry in thediaphragmal sinus during photodynamic therapy for malignant pleural mesothelioma

In situ light dosimetry during photodynamic therapy (PDT) of malignant pleu ral mesothelioma (MPM) after tumour resection facilitates the delivery of a controlled light distribution to the inner thoracic surface. Illumination of the diaphragm-induced sinus, however, remains difficult. Our aim was to develop a wedge-shaped light applicator with incorporated light dosimetry t o deliver an additional fluence limited to the sinus. The wedge-shaped appl icator contains a cylindrical diffuser for light delivery and two isotropic detectors for simultaneous light dosimetry. These detectors were placed at strategic positions where the fluence rate is maximal or minimal (middle a nd edge). Prior to its clinical use, the performance of the sinus light app licator was tested in several optical tissue phantoms with different optica l properties. The fluence rate distribution over the surface of the applica tor showed little change when the wedge was submerged in four different opt ical phantoms. During clinical PDT of MPM the applicator had to be re-locat ed manually four times in order to give an additional fluence of approximat ely 2 J cm(-2) to the entire sinus. The light applicator enables dosimetry- control led light delivery for additional illumination of the sinus region that is often under-illuminated during thoracic integral illumination of MP M.