Proton nuclear magnetic resonance imaging as a predictor of the outcome of photodynamic therapy of tumours.

Abstract

The ability to monitor non-invasively and at early times, the cytotoxic efficacy of a cancer treatment in an individual subject, plainly of great potential clinical value. In a recent publication, Naruse et al (1986) showed proton nuclear magnetic resonance (NMR) images of a rat glioma that had been treated 48 h previously by radiofrequency (RF) hyperthermia. Regions of high signal intensity were readily distinguishable and were equated qualitatively with histological necrosis caused by the heat treatment. These increases in signal intensity almost certainly reflected an increase in water content associated with oedematous changes in the tumour. This might expected after in vivo hyperthermia, where an important contribution to the toxic effect is vascular collapse with subsequent secondary ischaemic necrosis of sheets of tumour cells (reviewed by Reinhold & Endrich, 1986). A similar form of damage occurs after photodynamic therapy (PDT), the combination of non-toxic photosensitizing drugs and non-thermal power densities of visible light (Star al, 1986), and it appeared to us that NMR imaging might be useful in assessing damage in this new form of cancer treatment. We have shown elsewhere that NMR images taken soon after a PDT treatment correspond quantitatively with histologically defined cell killing at the same interval (Dodd etal, 1989) and we present preliminary experimental results in which we relate quantitatively proton NMR images and the overall therapeutic outcome measured by tumour regrowth delay.