Plus-Hex CLINICAL
Anecdotally , cats with long-term FHT (> 18 months ) and cats with higher TT4 levels have an increased risk of requiring a second RAI dose . Cats with a high-normal or just above normal TT4 are more likely to become hypothyroid after RAIT . Cats with very high TT4 should ideally have scintigraphy and biopsy of the thyroid mass prior to treatment , to determine the presence of any malignant cells .
Determining the dose of RAI
While there are specific formulas for calculating RAI doses ( usually requiring scintigraphy ), the experience of the treating VS is invaluable in determining an appropriate dose for individual cats . The VS at this clinic has been licensed to treat cats with RAI for over 15 years . She considers the cat ' s TT4 , other pathology results , length of illness and response to any previous medical management , as well as its overall health and scintigraphy and biopsy results . She compares these with data on cats previously treated with RAI and their response to treatment . The cat ' s bodyweight has no effect in determining the dose of iodine-131 ( I-131 ). RAIT can be administered by subcutaneous injection or as a capsule given orally ; this clinic uses the latter form .
Preparing for admission
Once all testing is complete and discussions with the client have occurred , the primary VS sends the cat ' s history to the referral VS . Following discussions between the referral VS , the primary VS and the client , including the provision of substantial written material ( emailed by the referral VS and available on the clinic ' s website ), a decision is made about the suitability of RAIT for the cat .
One week prior to admission , the RAI capsule for each cat is ordered from the Australian Nuclear Science and Technology Organisation ( ANSTO ) in Sydney . At this point , clients pay for the capsule , which is prepared specifically for their cat .
The hospital and treatment room
The only veterinary service offered by this clinic is RAIT for cats with FHT . Monitoring before and after treatment is provided by the primary VS . The clinic is not continously staffed ; the VS assesses and tends to the cats for 15 minutes each morning and another staff member tends to them each afternoon / evening .
A maximum of four cats are treated in any given week ; the actual number of cats depends on their collective RAI dose . All cats are admitted on the same day ( Thursday ) and the majority are discharged the following Thursday . Cats are housed in fibreglass cages with clear Perspex fronts to guard against urine spraying . There are ventilation holes in the roof and above / below the Perspex front . Cage dimensions are 1.5 m long , 0.75 m wide and 0.95 m high ( Figure 1 ).
Because this clinic is a stand-alone facility with minimal staff presence , cages are not required to be lead-lined . This was determined by the radiation protection report calculations that were required prior to a radiation management licence being issued for the site . However , lead-lined cages are likely to be a requirement in a larger , multi-speciality centre with a significantly higher and prolonged human presence .
It is essential that clients are fully aware of the treatment process and the potential outcomes and risks . Clients who choose RAIT for their cat are usually highly invested in the cat ' s welfare , both financially and emotionally , and are concerned about the outcome of treatment and the separation of their cat from the family . Owing to the risks involved , visits are not permitted during the isolation period , but clients of this clinic receive daily updates via text message and photos of their cat to help them through the separation process .
This clinic advises that cats receiving initial dietary management ( e . g . Hill ' s Prescription Diet y / d ) cease this diet 4 weeks prior to RAIT . ( Precisely when ( and if ) to withdraw this diet is not known [ 1 ] .) For cats initially treated with carbimazole or methimazole , these medications are ceased 1 week prior to RAIT ( or 2 weeks prior , for those that have received long-term medical management ). By ceasing any prior treatment , the abnormal thyroid tissue can ‘ flare up ’, which results in a more efficient uptake of I-131 by the abnormal cells .
Figure 1 . The cats ' housing during the isolation period contains a sleeping box to hide in and upper levels to explore .
Volume 38 ( 5 ) • October 2023
43