title: In vivo measurement of parameters of dosimetric importance during interstitial photodynamic therapy of thick skin tumors.
abstract: A system for interstitial photodynamic therapy is used in the treatment of thick skin tumors. The system allows simultaneous measurements of light fluence rate, sensitizer fluorescence, and tissue oxygen saturation by using the same fibers as for therapeutic light delivery. Results from ten tumor treatments using delta-aminolevulinic acid (ALA)-induced protoporphyrin IX show a significant, treatment-induced increase in tissue absorption at the therapeutic wavelength, and rapid sensitizer photobleaching. The changes in oxy- and deoxyhemoglobin content are monitored by means of near-infrared spectroscopy, revealing a varying tissue oxygenation and significant changes in blood volume during treatment. These changes are consistent with the temporal profiles of the light fluence rate at the therapeutic wavelength actually measured. We therefore propose the observed absorption increase to be due to treatment-induced deoxygenation in combination with changes in blood concentration within the treated volume. A higher rate of initial photobleaching is found to correlate with a less pronounced increase in tissue absorption. Based on the measured signals, we propose how real-time treatment supervision and feedback can be implemented. Simultaneous study of the fluence rate, sensitizer fluorescence, and local tissue oxygen saturation level may contribute to the understanding of the threshold dose for photodynamic therapy.
authors.affiliation: Lund Institute of Technology, Department of Physics, Lund, Sweden. Ann.Johansson@fysik.lth.se
authors.forename: Ann
authors.initials: A
authors.lastname: Johansson
authors.forename: Thomas
authors.initials: T
authors.lastname: Johansson
authors.forename: Marcelo Soto
authors.initials: MS
authors.lastname: Thompson
authors.forename: Niels
authors.initials: N
authors.lastname: Bendsoe
authors.forename: Katarina
authors.initials: K
authors.lastname: Svanberg
authors.forename: Sune
authors.initials: S
authors.lastname: Svanberg
authors.forename: Stefan
authors.initials: S
authors.lastname: Andersson-Engels
mesh_terms: D003936:Diagnosis, Computer-Assisted / Q000295:instrumentation* / Q000379:methods; D004867:Equipment Design; D019544:Equipment Failure Analysis; D005260:Female; D005336:Fiber Optic Technology / Q000295:instrumentation* / Q000379:methods; D006801:Humans; D053685:Laser Therapy; D007834:Lasers; D008297:Male; D010778:Photochemotherapy / Q000295:instrumentation* / Q000379:methods; D011874:Radiometry / Q000295:instrumentation* / Q000379:methods; D011879:Radiotherapy Dosage; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D012878:Skin Neoplasms / Q000175:diagnosis* / Q000188:drug therapy*; D013813:Therapy, Computer-Assisted / Q000295:instrumentation* / Q000379:methods; D016896:Treatment Outcome