Nuclear medicine

Cancer cells exhibit changes in their metabolism and function. As a result, they absorb, more than normal cells, radioactive substances, called "tracers", which are injected into patients and then detected on the images taken in nuclear medicine.

There are a large number of tracers. Some are conventional and commonly used in the nuclear medicine departments of most hospitals, while others, more specific, are generally only available in reference centers.

Nuclear medicine is also used for therapeutic purposes: some tracers are able to destroy the cancer cells to which they bind. This approach is used in new treatments.

Involved in both the diagnostic and therapeutic approaches to many cancers, nuclear medicine experts participate in multidisciplinary meetings whose objective is to define the most appropriate course of action according to the characteristics of the disease. They also strive to adopt a strategy that is in line with the most recent scientific data for each type of cancer.

Scintigraphy has long been the basic examination.

It consists in injecting into the body a tracer that concentrates in a particular tissue, such as iodine for the thyroid gland, phosphate for the bone, etc. This tracer emits radiations that are captured by a camera. Depending on the case, the abnormalities result in hyperfixation or hypofixation of the radioactive tracer.

The advent of PET-scan and, more recently, PET-CT has been a major advance in several respects. These technologies make it possible to refine the initial diagnosis, to better assess the tumor stage, to detect a possible recurrence more quickly, and to evaluate the response to treatment at an early stage.

High diagnostic accuracy

PET-scan provides very detailed three-dimensional images and information on the functioning of cells.

It is useful not only in detecting tumors but also in evaluating their extension. It therefore has an impact on the strategy adopted for treatment. For example, in lung cancer, PET-scan performs better than conventional scanner in detecting possible invasion of lymph nodes located near the organ. This parameter is very important because it makes it possible to determine whether a surgical procedure is indicated without necessarily resorting to a more invasive examination.

Assessment of response and localization of recurrences

PET-scan makes it possible to evaluate the response to radiotherapy or chemotherapy at an earlier stage. Indeed, the impact of these treatments on tumor volume, assessed by conventional radiology, is only apparent after several months, whereas the effect on tumor cell function is more immediate. In lymphoma, for example, the effectiveness of chemotherapy can be assessed after only two weeks and, if necessary, the treatment can be adapted quickly. This property of the PET-scan is also used to evaluate the effectiveness of new treatments.

Cancer recurrences are often detected by markers whose concentration is measured in the blood. However, an elevation of these markers does not give any indication of the location of the recurrence. PET-scan, for its part, makes it possible to detect the site of the recurrence, regardless of its location in the body, and to detect metastases that have escaped conventional examinations, which also has an influence on the therapeutic strategy.

Finally, PET-scan helps to better define the volume to be irradiated when the tumor is treated by radiotherapy. The irradiation is better focused on the tumor and spares the surrounding healthy tissue. It is thus possible to use higher doses.

The tracers used in nuclear medicine are more and more sophisticated and differ according to the cell function that is being investigated. The most commonly used tracer is fluoride, coupled to a sugar molecule (to form fluoro-deoxy-glucose or FDG). This tracer is traditionally used for tumor detection, extension assessment, and evaluation of the response to treatment of cancers.

Carbon-labeled acetate is used as a tracer to evaluate the synthesis of cell membranes in liver tumors, carbon-labeled methionine to evaluate protein synthesis in brain tumors, sodium fluoride to provide information on bone formation, etc.

Several new tracers are being investigated in our center. They should notably make it possible to detect poorly oxygenated areas within tumors (these areas often lead to resistance to treatment) and to refine the diagnostic approach to prostate cancer, a disease for which conventional tracers are not very effective.

Although PET-scan has been available for several years, new tracers are continually increasing its performance. These tracers are developed in reference centers because they require a state-of-the-art infrastructure and research units.

Since March 2000, more than 11,000 examinations have been performed in patients with various tumors, mainly pulmonary, digestive, and lymphomatous. In March 2007, we installed a new camera combining PET-scan and CT-scan in a single machine. Combined PET-CT offers both the high detection sensitivity of PET-scan and the ability to precisely localize the tracer-binding sites, in order to guide a biopsy or a treatment, for example.

The installation of a latest generation PET-CT camera and the availability of multiple tracers provide the King Albert II Institute of the Cliniques universitaires Saint-Luc with a cutting-edge diagnostic platform for cancer imaging.