Clinical trial holmium therapy was successful

Researchers at the Reactor Institute Delft played an important role in developing the optimal radiation method for the poly-lactate covered holmium microspheres. Delivering sufficient dosages without overheating or damaging the spheres proved to be challenging, however. During the clinical trial, the RID routinely radiated holmium spheres in response to requests from medical biologist, Dr Frank Nijsen, and head of radio pharmacy, Dr Fred van het Schip (UMC Utrecht). 

Fifteen terminal patients with tumors in the liverhave been treated between 2009 and 2011 in this first phase clinical trial. The trial is meant to establish that the treatment is safe and to screen for adverse effects – not to determine the effectiveness. Nonetheless, a remarkable reduction of liver tumors has been established at large enough doses. The treatment consists of two consecutive arterial injections of holmium spheres, a few hours apart. The first injection involves a low dose to check if the holmium particles reach the tumor. The holmium whereabouts can be traced with a gamma camera, since the particles emit gamma radiation (which is detectable outside the body) as well as beta radiation (high-energy electrons which kill cells in the direct vicinity of the blood vessels). The diameter of the particles (30 micrometre) is chosen so that the microspheres will get stuck in the capillaries to release their radiation charge at the spot. When the first shot indicates the blood vessel is leading to the tumor, a second shot will be delivered which delivers over 100 Gray of radiation locally. Despite the locally lethal dose, the patients seem to suffer only mild nausea in the first day after treatment. After that, they generally feel fine.

Next, a larger phase II clinical trial will be held to test the treatment’s effect and to establish the protocol. If – and it’s still a big if – the researchers succeed in effectively targeting only the tumour and avoid spilling radiation to other organs, holmium therapy may develop into an effective and patient-friendly form of radiotherapy for tumours that have suitable vascular structures.