Selective Internal Radiation Therapy
Targeting for Better Care
François Hébert, m.i.t.
Selective Internal Radiation Therapy: Targeting for Better Care
Although cancer is likely to affect all parts of the body, it may be more difficult to treat depending on its location. This is particularly the case of unresectable cancers, i.e. cancers that cannot be completely removed by surgery. Liver cancer fits this profile. In addition, this organ has the disadvantage of being particularly sensitive to the radiation of external radiotherapy, so that the dose that can be administered is limited. But a technique, currently used as a last resort, may well change the situation: selective internal radiotherapy, also known as radioembolization. The principle is that of radiotherapy and its ionizing radiation (radioactive) to treat the patient. The peculiarity of this treatment is that the ionizing rays are delivered from the inside. The huge advantage is of course that they specifically attack the cancer cells, thus sparing the surrounding normal cells as much as possible and resulting, of course, in much less side effects.
Microspheres to the Rescue
The treatment involves administering microspheres filled with radioactive material into the arteries that supply the tumor. The intervention is done in interventional radiology by placing a catheter in the femoral artery and guiding it to the arterial vessels. These microspheres are made of glass or resin and are thinner than a hair. They play two important roles: they allow high-energy radiation to be deposited locally without irradiating healthy cells and, because of their size, they agglomerate in the blood vessels that supply the tumor, thus depleting its blood supply. For each patient the dose to be injected is determined according to tumoral and normal liver volumes. Once calibration is done, it should be ensured that the microspheres travel safely. There are indeed natural links between different parts of the human body, and there may be a leak. In that case it is necessary to evaluate the liver-lung shunt, i.e. the quantity of radioactivity which would pass in the lungs instead of going towards the liver. Up to 10% is tolerated.
The last step is to determine if the treatment has worked. "The quantification of the dose to be administered is extremely important, especially for this treatment, says Dr. François Lamoureux, Associate Professor of Clinical Medicine in Nuclear Medicine at the Faculty of Medicine of the University of Montreal and president elect of the Canadian association of nuclear medicine. It is also necessary to be able to evaluate the doses of radiation actually transmitted on the site of the tumor as well as in the surrounding tissues". Using imaging techniques, specialists can estimate whether the treatment is working or not, that is, they can determine whether the proposed amount of radioactivity has a positive effect in attacking the tumor or whether they should reevaluate the procedure.
If several companies offer analysis and/or follow-up at key moments of the treatment, Hermes Medical Solutions is the only company currently to offer imaging follow-ups along the entire chain of work: before, to plan the dose to administer, during, to follow the evolution of the microspheres, and after, to evaluate the effect of the radioactivity on the tumor. Selective internal radiotherapy is still considered a "rescue" technique, but it could be one of the most promising avenues to treat cancer and become a first-line treatment.