18. Thyroid treatment Flashcards
When is the Iodine 131 treatment used?
To treat thyroid cancer, following a thyroidectomy.
To move any remaining thyroid tissue/metastases.
What is the physical half-life of Iodine-131?
8 days
What is the mean beta energy of Iodine-131?
192 keV
What is the average beta path length in tissue of Iodine-131?
0.4 mm
What is maximum beta path length in tissue of Iodine-131?
2 mm
What is the principal gamma activity of Iodine-131?
364 keV
What is the major site of iodine absorption in the body?
Thyroid tissue
How is the Iodine-131 treatment carried out?
- Capsule containing radioactive I-131 ingested.
- Iodine molecules absorbed through wall of stomach into blood stream.
- Any residual thyroid cells take up the I-131.
- Beta particles destroy the thyroid cells.
Timeline
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How is Iodine-131 administered?
Test the I-131 prior to administration (assay).
Tube screws into capsule holder at bottom of lead pot.
Hold tube at top to minimise finger dose.
What are the immediate side effects of the I131 treatment
Swelling, tenderness of salivary gland - sialadenitis
Dry mouth - Xerostomia
Loss of taste
Neck swelling/Oedema
Nausea
What are the delayed side effects of the I131 treatment?
Chronic sialadentis with xerostomia
Leukaemia
Secondary malignancy
What radioactive bodily fluids can cause contamination?
Saliva, vomit, tears, sputum, perspiration, blood, faeces, urine.
What is the primary route of radioactive excretion?
urinary tract, 50-60% activity excreted in urine in first 24 hours.
What precautions should be taken when a radioactive patient suffers from urinary incontinence?
Change pad immediately in aware of urine as there is the potential for skin doses from contact with pads.
How are radioactive patients with catheter bags dealt with?
Bags must be regularly emptied to reduce external dose to patient.
Use glove to minimise contamination risk.
How long should radioactive patients stay in isolation?
Until activity has dropped below 800MBq
How do you determine the residual activity of the I131 treatment in a patient?
Monitor patient 1 hour post administration (ask them not to use toilet before this , if possible)
Assume all administered activity in within patient
Monitor at least daily after this (ensuring distance from patient is constant)
If monitoring count rate
Residual activity = (𝑐𝑢𝑟𝑟𝑒𝑛𝑡 𝑐𝑜𝑢𝑛𝑡𝑠)/(𝑖𝑛𝑖𝑡𝑖𝑎𝑙 𝑐𝑜𝑢𝑛𝑡𝑠) x administered activity
(similar calculation can be used based on ratio of dose rates)
When and why are patients imaged post-ablation?
Typically 3-7 days post administration.
To identify residual thyroid tissue and metastases.
How is whole body imaging and SPECT completed?
What restrictions are given to patient who have had the I131 treatment when they go home?
Limit contact with adults at home, sleeping arrangements.
Limit contact with adults outside the home (public transport, work, social life.)
Minimise contact with children.
Generally lasts for about 7 days.
What consideration should be taken following an I131’s patient discharge?
Females should avoid conception for 6 months.
Males should avoid conception for 4 months.
Patients should try to be distant in long travel journeys.
Airports may have sensitive radiation scanners triggered by patient, so patient needs to be issued with letter to explain situation.
What should a letter to the GP following an I131 treatment contain?
- Inform of treatment
- Restrictions on blood tests, urine collection, surgery.
- Warn about restrictions if the patient dies.
- Give appropriate dates + contact details.
When should staff dose be considered to ensure safety when dealing with the I131 treatment?
Considerations should be taken when:
1. Administering capsule
2. Scanning the patient
3. Cleaning the cubicle after use
4. Pregnant staff
How does the I131 treatment work?
Beta particles destroy the cells while gamma rays can be used for imaging.
