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About iodine-125

Iodine 125: a versatile medical isotope. It is increasingly used in both diagnostic and therapeutic applications, such as the treatment of prostate cancer. The radioactive isotope of iodine, has a half-life of 16.9 hours an can be made by irradiating xenon-125, which decays into I-125. Access to I-125 was in serious jeopardy in 2017 when one of the I-125 producing reactors was shut down unexpectedly.

Titanium Zaadjes I 125 2


More information about iodine-125?

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Martijn Jimmink
Business Manager Isotopes


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Prostate cancer

With approximately 1.3 million newly diagnosed cases a year, prostate cancer is a very common cancer worldwide. Various different treatment methods can be applied, depending on the type and stage of cancer.

Breast cancer

Breast cancer is a very common cancer, with over 2 million newly diagnosed patients per year worldwide. As with every cancer, there are various ways of treating this disease, depending on the type and stage of the tumour.

Various other types of cancer

Sometimes, I-125 brachytherapy is also used in some forms of head- and neck cancer, brain tumours and lung cancer among others.

From irradiation to use in brachytherapy

Iodine-125 is made by irradiating a highly pure xenon gas, xenon-124. Once xenon-124 (Xe-124) has been irradiated, a neutron is added to its atom by which it becomes xenon-125. However, this isotope is very unstable and quickly decays to the desired product of iodine-125.

The irradiation and separation of the xenon will occur at both the reactor in Petten (NRG) and at the reactor in Hamilton (McMaster University). The raw iodine-125 from NRG is shipped from the Netherlands to Canada, where the team at McMaster harvests the iodine-125, processes and qualifies it, and then dispenses it into a capsule meeting the stringent quality requirements.

So called “seed manufacturers” incorporate the liquid I-125 onto little beads or onto wires which are loaded into minuscule seeds (brachyseed), the size of a grain of rice. These seeds are implanted around a tumour. The type of energy emitted by I-125 effectively kills the tumour cells, leaving the healthy tissue unharmed.

I125 Periodiek Pictogram Advancing Nuclear Medicine
Mc Master Canada Lr

Application of I-125 in brachytherapy

Brachytherapy is radiation therapy with isotopes that have a short radiation distance. In other words: brachytherapy brings the radiation source close to where it is needed, mostly used inside the body.

Although not exactly new, brachytherapy is still widely used. The main ingredients for successful use of brachytherapy are radionuclides and sufficient information for patients.

In 2017, there was suddenly a worldwide shortage of iodine-125, because one of the large producers was temporarily shut down. McMaster & NRG joined forces for global supply.

McMaster sends I-125 to customers all over the world, throughout Europe, Asia, North and South America and even as far as New Zealand. 


How we improved the manufacturing process of iodine-125

Development Prod Process

Joint development with business partner, obtaining

  • Safe production, like radiation protection of operators
  • Continuity by extending production resources
  • Reproduction of high quality end product
  • Sustainability in iodine procurement
Filling Unit

Safe and efficient filling of irradiation capsules

  • Filling of double containment capsules
  • High-tech welding applied
  • Leakage check
  • Iodine filter
Special Irr Unit

Newly designed, in-house development

  • Key competences to design & develop
  • High-tech in-house tooling workshop
Extraction Unit

Fully automated process to extract the radioactive semi-finished product

  • Ensures reproduction of high quality level
  • Increased radiation protection operators
  • Joint design & development

Sustainable production process

  • Minimal waste through sustainable harvesting and re-use of Xe-124
  • Integrated waste treatment process