Using 131I labeled antibody (Bexxar) to NHL cell site to treat Non-Hodgkins lymphoma
Thyroid Diseases Treatable with 131I-NaI
- hyperthyroidism (Graves disease)
- toxic nodular goiter (Plummerís disease)
- thyroid carcinoma (ranked in order of likelihood of 131I uptake)
the other two types of thyroid cancer, medullary and anaplastic, are not treatable with I-131
The decay scheme below indicates that there are 14 gammas and 6 betas emitted from I-131. Therefore, True or False, 14/20 of the tissue damage is attributable to gammas and 6/20 to betas.
False for 2 reasons:
1. The LET (Linear Transfer Rate) for betas is much higher than for gammas; consequently they confer a much higher radiation dose
2. The fractions 14/20 and 6/20 imply that the % abundance of each of these 20 emissions is exactly 5%, which is not possible. In fact the % abundances vary from a fraction of 1% to almost 85%.
Correct answer is that ~90% of tissue damage is attributable to beta particles.
|procedure||dose (mCi)||route of administration|
|raiu & scan, substernal||0.100||oral|
|total body mets survey||5-10||oral|
|toxic nodular goiter||25||oral|
|thyroid Ca therapy||75-225||oral|
Radiation Dosimetry of 131I- NaI
Following oral administration of 10 mCi dose of 131I-NaI for treatment of hyperthyroidism, 90% of dose to tissue is achieved by b- emissions. For a hyperthyroid patient treated with I-131:
Tissue absorbed radiation dose (rads/10 mCi of I-131) Thyroid 11,000 Testes 9.2 Ovaries 9.3 Whole body 16.0
Dose Determination for Therapy in Graves Disease
Measure % uptake; estimate mass of thyroid (g)
Dose = 60-100 uCi/g x mass (g) x 100% % uptake
: since 60-100 uCi /g is a wide range, it is difficult to determine the appropriate factor for an individual patient. Use of this formula often results in incorrect estimate of the required dose, resulting in over- or under-dosing of patient.
A standard dose of 131I NaI is given orally to all patients
(8 mCi to females, 10 mCi to males); these doses may be modified a litle based on %RAIU
Advantage: adequately treats 85% of all Graves disease patients with 1 treatment.
Disadvantage: of the 15% who are refractory, 10% require a second administration of 131I; the other 5% require a third dose of 131I.
of hyperthyroid patients to treatment with 131I sodium iodide
Long-term Side Effect
As indicated in the following graph, the rate of hypothyroidism after the first year is 3%/year for all patients treated with 131I sodium iodide for Graves disease. They are treated with synthroid daily for the rest of their lives.
Rate of Induction of Hypothyroidism Following Therapy with 131I-NaI
1. Keep your distance to minimize personal radiation dose
2. Patient is assigned a private room
3. Everyone involved with patient must wear film badge
4. Gloves must be used by patient to handle telephone, bed controls
5. Housekeeping not allowed in room until room is released by RSO
6. No visitors allowed for at least 24 hr
7. No bed baths
8. Patient must stay in bed unless instructed otherwise
9. Absorbent pads taped to floor from toilet to bed
10. Patient must use disposable items for food service
11. Diagnostic blood samples taken by Nuclear Medicine
12. If patient dies, attending physician must be notified immediately
13. Room must be surveyed by RSO prior to release for next use.
14. Every participant in therapy must have thyroid counted 24 hr post dose
Patient Release Criteria
For Some Agreement States...Reading <5 mR/hr at 1 meter from patientís chest, which is equivalent to a body burden <30 mCi of 131I.
For NRC States*...Reading <7 mR/hr at 1 meter from patientís chest, which is equivalent to a body burden <33 mCi of 131I.
Note: NRC is no longer requiring hospitalization for 131I therapy
- Bexxar Lymphoma Therapy
- 131I lableled antibody to NHL cell site
- 5 mci scan dose first
- Determine body t1/2
- Use data from dosimetry study to determine therapy dose
- Average dpse 75 mci 131I antibody