Nuclear medicine is a very useful imaging technique in diagnosis of cancer and assessing its extent. It also has a therapeutic aspect.
FROM DIAGNOSIS TO TREATMENT
Cancer cells show changes in their metabolism and function. This means that they are better than normal cells at capturing radioactive substances known as “tracers”, injected into patients and then detected on pictures taken as part of nuclear medicine treatment.
There are a large number of tracers. Some are conventional and regularly used in nuclear medicine departments in most hospitals, while others are more specific and not generally available away from reference centres.
Nuclear medicine is also used for therapeutic purposes: some tracers, in fact, can destroy the cancer cells to which they attach themselves. This approach is being used successfully in new treatments.
Involved in both diagnostic and therapeutic approaches to numerous cancers, nuclear medicine specialists take part in multidisciplinary meetings with the aim of defining the most suitable course of action depending on the characteristics of the disease. For each type of cancer, they also adopt a strategy consistent with the latest scientific data.
ADDED VALUE OF THE PET SCAN
The basic examination has, for some time now, been the scintigraph.
This involves injecting an organ with a tracer, which concentrates in a specific kind of tissue, for example iodine in the thyroid gland and phosphate in bones. The tracer gives off radiation, detected by a camera. Problems are shown, depending on the case, through unusually high or low levels of radioactive tracer fixation.
Diagnosis with finesse
A PET scan allows highly detailed three-dimensional images and information on cell function to be obtained.
It is useful not only in detection of tumours, but in evaluation of their extent. It therefore has an impact on the strategy adopted for the treatment. In lung cancer, therefore, PET scans are more effective than conventional scans in detecting possible involvement of ganglia located close to the organ. This very important parameter determines the need for a surgical procedure without the need for a more invasive exploratory procedure.
Evaluation of response and location of recurrences
A PET scan makes earlier evaluation of the patient’s response to radiotherapy or chemotherapy easier. In fact, the effect of this treatment on tumour volume, when assessed by conventional radiology, is only apparent after several months, while the effect on tumour cell function is more immediate. In a lymphoma, for example, efficacy of chemotherapy is assessed after just two weeks and, where necessary, allows rapid alteration of the treatment. This property of the PET scan is also helpful in assessing the efficacy of new treatments.
Markers, concentration of which is measured in blood, are often used to detect recurrences of cancers. Although increases in levels of these markers do not in themselves indicate the location of the recurrence, a PET scan reveals the site of the recurrence whatever its location in the body, and allows metastatic tumours that escape conventional examinations to be detected. This will affect the treatment strategy.
Finally, PET scans help better define the volume to be irradiated when tumours are treated with radiotherapy. Irradiation is better focussed on the tumour and respects the surrounding healthy tissue, meaning that higher doses can be used.
Consultez la fiche pratique du Pet-Scan.
VARIETY OF TRACERS
Tracers used in nuclear medicine are becoming more and more refined and varied according to the cellular function being investigated The most commonly used tracer is fluorine, combined with a molecule of sugar to form fluorodeoxyglucose or FDG. This tracer is used very frequently in detection, assessment of extent and evaluation of response to cancer treatments.
We also use carbon-marked acetate to assess synthesis of cellular membranes in liver tumours, carbon-marked methionin to assess protein synthesis in brain tumours, sodium fluoride to provide information on bone formation, and others.
Several new tracers have been researched at our centre. Most significantly, they should allow poorly oxygenated zones to be detected in tumours (these zones are often resistant to treatment) and diagnostic approaches to be refined in prostate cancer, a condition for which conventional tracers are not greatly effective.
Although PET scans have existed for several years, new tracers are continually improving their performance. They have been developed in research centres, as they require highly developed infrastructures and research units.
Since March 2000, over 11,000 examinations have been carried out on patients with various tumours, principally in the lungs and digestive and lymph systems. In March 2007, we introduced a new camera combining PET scan and CT scan into a single machine. Thanks to this PET-CT, we now benefit both from the PET scab’s high detection sensitivity and its capacity to determine the precise location of tracer-capturing seats. This will help determine a biopsy or a course of treatment.
Installation of the ultramodern PET-CT camera, and the availability of numerous tracers, have made the Cliniques Saint-Luc Cancer Centre a diagnostic platform in the imaging of cancers.