Tumours and soft tissues

Abstract

The concept of using radioactive tracers to locate sites and evaluate extent of primary or metastatic malignant tumours originated from one of the earliest clinical uses of radio-isotopes, namely to identify metastatic thyroid cancer. At the time of the original observations, over 50 years ago, there were few other methods of localizing tumours. Chemotherapy of cancer was in its infancy and surgical excision and radiotherapy were the only treatments generally available. Radio-iodine was a major innovation. Subsequent developments in surgery, chemotherapy and radiotherapy for many other tumours have substantially altered the nature of information required clinically. Ultrasound, computed tomography (CT) and magnetic resonance imaging (MRI) have revolutionized non-invasive demonstration of tumour boundaries. Staging is increasingly important in deciding the most effective plan of therapy and for differentiating between residual or recurrent tumour, fibrosis and other late changes. Radioisotope imaging does not provide the anatomical detail of other imaging modalities and with few exceptions is no longer used to determine the extent of primary or metastatic malignancies. Nuclear medicine retains a role where perceptibility is limited by contrast rather than resolution, when functional information is therapeutically relevant and for therapy of an increasing number of tumours. Radioactive tracers continue to be used when they can provide higher contrast, enabling deposits not visible by other modalities to be seen, or to provide specific data about metabolic or receptor activity.