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1 October 2002 Effects of Combined Photodynamic Therapy and Ionizing Radiationon Human Glioma Spheroids
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Abstract

The effects of combined photodynamic therapy (PDT) and ionizing radiation are studied in a human glioma spheroid model. The degree of interaction between the two modalities depends in a complex manner on factors such as PDT irradiation fluence, fluence rate and dose of ionizing radiation. It is shown that gamma radiation and PDT interact in a synergistic manner only if both light fluence and gamma radiation dose exceed approximately 25 J cm−2 and 8 Gy, respectively. Synergistic interactions are observed only for the lower fluence rate (25 mW cm−2) investigated. The degree of interaction appears to be independent of both sequence and the PDT or ionizing radiation time intervals investigated (1 and 24 h). Terminal deoxynucleotidyl transferase–mediated deoxyuridine triphosphate nick-end labeling assays show that low-fluence rate PDT is very efficient at inducing apoptotic cell death, whereas neither high-fluence rate PDT nor ionizing radiation produces significant apoptosis. Although the mechanisms remain to be elucidated, the data imply that the observed synergism is likely not due to gamma-induced cell cycle arrest or to PDT-induced inhibition of DNA repair.

Steen J. Madsen, Chung-Ho Sun, Bruce J. Tromberg, Alvin T. Yeh, Rogelio Sanchez, and Henry Hirschberg "Effects of Combined Photodynamic Therapy and Ionizing Radiationon Human Glioma Spheroids," Photochemistry and Photobiology 76(4), 411-416, (1 October 2002). https://doi.org/10.1562/0031-8655(2002)076<0411:EOCPTA>2.0.CO;2
Received: 17 June 2002; Accepted: 1 July 2002; Published: 1 October 2002
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