Departments

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Medical Departments

Radionuclide Therapy (Nuclear Department)

Thyroïd Gland Cancer (Iodine-131 treatment)

Generalities

Thyroid gland cancers are rare and generally have a good prognosis.

 

In most cases, the diagnosis of these cancers is based on an analysis of the whole gland or of part of it (a ‘ball’ in the neck) which was surgically removed.

 

The first therapeutic approach to these cases is a total or subtotal thyroidectomy (surgical resection of both lobes – right and left – of the gland and of the isthmus – the tissue that links them) associated or not to one or several nodal resections.

 

As organized for all malignant diseases, the therapeutic approach, to be used for these patients, is discussed, case by case, in multidisciplinary oncology consultations. These are attended by physicians trained in different specialties – among which Nuclear Medicine – who might be involved in the future therapeutic medical care of the patients.

 

There are two main characteristics for the treatment and monitoring of these cancers.
In most cases, the thyroid cells – should they be normal or cancerous – capture iodine, and – benign (normal) or malignant (cancerous) – release a substance in the blood, i.e. a protein called thyroglobulin (Tg).
 

In 20 to 30% of the cases, the patients’ blood unfortunately also contains ‘antibodies’ directed against that protein, which make hazardous the diagnosis value of its measure.

 

Why is a radioactive iodine treatment by Iodine-131 used in those cases ?

There are several reasons to administer an Iodine-131 treatment to thyroid cancer patients :
- the tissue resection at the neck level is very rarely total (some parts of the thyroid are too adjacent to structures that should be preserved) and there is always a risk to have cancerous cells in these not removed tissues;

- some thyroid tissue can sometimes be found in unusual areas;
- cancer sometimes goes beyond the thyroid borders and invades the surrounding tissues;
- the nodes were not removed during the thyroidectomy and can be the seat of metastatic cells;
- all the nodes were not removed and some of the removed one were affected…. with the risk for the others to be affected as well;
- some cancers (some types more than others) can metastasize to other organs.

 

However, the cells of these cancers called ‘well differentiated’ still have the ability to capture iodine, wherever their location within the body. By giving Iodine-131 to these patients, we bring into cells a radio-element that will kill them. Actually, Iodine-131 emits a beta radiation, electrons that will destruct those cells.

 

Nevertheless, Iodine-131 also emits a gamma radiation that can be detected. After having administered Iodine-131 to patients, an imaging of all the body areas affected by the disease (of all localizations said ‘secondary’, the metastases in nodes or in others organs) that captured the radioactive iodine can be obtained. Their localization in precise sites can thus lead – in some cases, to targeted second-intention therapeutic interventions (external radiation, new intervention for exeresis, etc.).

When these imaging (which are limited; sometimes, they can not to detect a or various cells “hidden” in some places) only shows the thyroid remnants that the surgeon could not remove at the neck level, the destruction of these remnants with iodine-131 puts patients in a situation where in their blood, the thyroglobuline secreted by cells cannot be (has no more to be) detectable. If thyroglobuline is still present in the following blood tests, it is the sign that malignant thyroid cells are developing somewhere else – possibly at distance from the primary tumour.

 

What does a radio-iodine treatment involve ?

• Radioprotection measures !
  The amount of radioactive iodine atoms is high. Patients that receive iodine-131 are thus ‘radioactive’ (i.e. they emit large quantities of gamma radiations) as long as their body contains iodine. So, there is to protect the others from being exposed to these gamma radiations while it is intense.
  Moreover, only a part of that radioactive iodine stays fixed within the patient’s body. The major part (which won’t be fixed by thyroid cells) will be eliminated through the urine, but radioactivity is also present in saliva, faeces, nasal secretions, sweat (mammary glandular secretions, milk of breastfeeding women). Elimination time can vary; the peak occurs in urine within 48 hours following the taking of the radioiodine caps. However, during all the elimination time of the iodine, the patient is said ‘contaminating’; in other words, he can release radioactive iodine through urine, saliva, … That iodine can thus irradiate people that would be contaminated or, more seriously, can penetrate within these people’s body and accumulate in their thyroid.
   
  
• From 2 to 4 days in hospital (sometimes – but seldom – more) !
  In our clinical practice, these patients are thus admitted to hospital in a ‘metabolic chamber’. These chambers can be easily decontaminated and patient’s faeces and urine are collected and stored in special tanks in which iodine has the time to disappear (the quantity of emitted iodine-131 and radiations decreases with time; it is reduced by half every 8 days) before being evacuated through public sewers. (For a virtual visit of a metabolic chamber: click here).
  The patient stays isolated as long as he is radioactive (i.e. as he emits gamma radiations above a certain quantity).
  That hospitalization requires some constraints which are explained in the booklets given to patients during the consultation that precedes the admittance.
   
  
• Some precautions when going back home !
  In our clinical practice, an imaging of the iodine-131 distribution within patient’s body is made when they leave hospital. These imaging (see example) show 2 things :
  - the organs that are still contamination sources depending whether radioactivity is still present in urine, faeces, saliva, … when patients go back home;
  - if patients are contaminated.
  Patients are thus given instructions to follow; these are adapted to each patient for their home return.
  

  If the measured radiation quantity at a distance of one meter from the patient has dropped under a certain level when he leaves hospital, the areas that fixed the radioactive iodine are still radioactive near the person. Thus, some precautions have to be kept.
   

• A minimal follow-up !
  Finally, patients are invited to come back to hospital 4 days after they left. We will then check the radiation quantity that they still emit and will make another imaging of the iodine-131 distribution within the body. These images sometimes also show pathological iodine-fixing sources that were not detected on the images made when the patient left. From these images, we will also draw information that allow us to assess and predict the effect of the treatment.
  According to the results of these measures and images, patients will be given adapted radioprotection instructions to follow. In some cases, they will be asked to come back again to hospital for a check-up.

- For a virtual visit of a metabolic chamber: click here

 

- For a more physiopathological approach of thyroid cancers and of their iodine-131 treatments: click here
(Text published in 2006 in the “Journal du Réseau Cancer de l’ULB”)

 

Person in charge : Pr Patrick Flamen

Updating : March 2008