CHANGES IN PERFUSION OF MOUSE-TUMORS AFTER PHOTODYNAMIC THERAPY

The influence of photodynamic therapy (PDT) on vascular perfusion was investigated in 2 s.c. mouse tumours, a radiation-induced fibrosarcoma (RIFI) and a squamous-cell carcinoma (SCCVII). The Rb-86 extraction t echnique was used to measure changes in perfusion relative to cardiac output at various intervals after interstitial PDT. Control groups sho wed that vascular perfusion in the RIFI tumours decreased with increas ing tumour size. For both tumours, of constant size, vascular perfusio n decreased to less than 10% of control values within 5 min after high PDT doses. Significant decreases in vascular perfusion were also seen after lower, sub-curative doses. Thereafter there was slow recovery t owards control levels. Photofrin given at shorter intervals before ill umination generally resulted in even larger decreases in tumour perfus ion, and slower recovery. Comparison of tumour perfusion measurements after PDT with tumour response revealed an inverse correlation with tu mour growth delay both for the RIFI and for the SCCVII tumours. PDT wi th sub-curative light doses appears to decrease vascular perfusion in the RIFI and SCCVII for a period of at least 24 hr. The most severe re ductions in tumour blood flow were associated with the longest regrowt h delays, indicating a major role of vascular damage in tumour respons e to PDT. (C) 1994 Wiley-Liss, Inc.