Imaging with MIBG

  1. Anatomy and Physiology
  2. Pheochromocytoma is a neuroectodermal vascular tumor of the chromaffin tissue usually found in the adrenal medulla, however it can be found ectopically
  3. Development
    1. Excess chromaffin tissue is found in children (considered normal)
    2. At the age of 3, these sites usually regress and are usually found in the adrenal gland
    3. Extra-adrenal sites include the sympathetic ganglia and carotid bodies (abnormal)
    4. Other sites can form any between the base of the skull to the bladder (abnormal)
  4. Usually occurs in the adult population (90%), put can also found in children
  5. Physiology
    1. Tumors produce catecholamines which are epinephrine and norepinephrine
    2. Epinephrine secreting tumors are usually found in the adrenal gland
    3. Norepinephrine maybe secreted by tumors in the adrenal gland or at extra-adrenal tumor sites
    4. Characteristics of this hyper-secretion (norepinephrine and epinephrine) cause intermittent hypertension
    5. Tumor are usually non malignant and can also be found in children
    6. Indication of tumor includes catecholamine metabolites found in urine
  6. Neuroblastoma are malignant tumors
    1. Primary occurs from the adrenal gland or sympathetic nervous system specifically ganglia located in the abdomen (~67%)
    2. Primary tumor may also arise form chest, neck, pelvis, or spinal cord (~33%)
    3. Usually occurs in the pediatric population below the age of 10, with over 1/2 occurring before the age of 2
    4. In the US there are approximately 650 cases per year
  7. Diagnosing the disease
    1. Imaging the disease in with nuclear medicine or CT is usually for the purpose of location not for diagnosis
    2. CT is usually the method for finding the disease. However, when CT is equivocal or when there is a concern of tumors located outside the adrenals then the use of MIBG becomes necessary
    3. Note – tumor can be found between the bladder and the base of the skull
  8. Imaging with MIBG
    1. MIBG is iobenguane or meta-iodobenzylguanidine
    2. It can be tagged to 131I or 123I
    3. Contraindicating for this procedure includes: cocaine, Ca-blockers, decongestants, anti-psychotics, catecholamine, reserpine, and a list all drug interactions
    4. Lugol's solution should be administrated daily, one day prior and up to one week post injection to block the thyroid
    5. Dose
      1. 131I 500 to 1000 μCi or
      2. 123I - 3 to 10 mCi of 123I-MIBG
      3. Pediatric dose will be less, however, the minimum recommended does is 0.135 mCi of 131I-MIBG
      4. Pediatric dose for 123I-MIBG suggest 0.14 mCi/kg
        5. Organ 131I - rad/ dose 123I - rad/mCi dose
        Adrenal 0.8 0.059
        Kidneys 0.3 0.048
        Urinary Bladder Wall 2.8 0.311
        Pancreas 0.4 0.056

      5. Imaging with of 131I-MIBG
        1. Planar or whole body to include head to mid-thigh
        2. Scan speed should be as low as 6 cm/minute and static images should be at least 15 minutes per view
        3. images can be done at 24, 48, and 72 hours
      6. Imaging with 123I-MIBG
        1. Same views as above
        2. Scan speed may be increased slightly and well as a reduction in time for static images
        3. Six and 24 hour images should be taken
        4. SPECT may also be considered - 64 matrix, 360 degrees, sample every 3 to 6 degrees, and 30 to 45 second per stop (literature does not indicate how many head the camera has)
      7. In addition, renal imaging with DTPA is recommended for localization of the kidneys (where are the adrenal glands located?)

Normal findings

  1. Faint visualization of adrenal medulla and occurs in 16% of studies
  2. Maximum liver uptake occurs within 24 hours
  3. Urine excretion is seen in 60% cases of patient for up to 24 hours
  4. Large bowel uptake is noted in 20% of patients
  5. Salivary glands will visualize
  6. Higher concentrations of activity is seen in the heart (why?)

Abnormal

  1. Abnormal uptake in the adrenal medulla
  2. Uptake outside the adrenal glands is defined as extra-adrenal sites
  3. Tumors in the bladder can be missed and is do to normal bladder activity
  4. Sensitivity for pheochromocytomas is between 85 to 90 percent

Example

  1. Compare the two MIBG exams and note that it is exam of using both iodines. Can you appreciate the difference? Is one better than the other?
  2. In 131I-MIBG the patient has a Pheochromocytoma in the left adrenal. http://en.wikipedia.org/wiki/Iobenguane
  3. 123I-MIBG is a different patient that also has a pheochromocytoma located in the left adrenal. http://gamma.wustl.edu/newtfh/general/combined/submitted_130879.html
  4. Should you see thyroid uptake? What does this anomaly indicate?
Application of therapy
  1. 131I-MIBG if given in a large enough dose case be used to treat paragangliomas and pheochromocytomas.
    1. Candidate for treatment
      1. Children older than 12 years of age
      2. Tumors that cannot be surgically removed
      3. Spreading to other parts of the body
    2. Clinical study completed by Pryma, DA, et al. treated neuroendocrine tumors
      1. ~500 mCi per dose (18.5 GBq) given IV
      2. Of 68 patients approximately 92% has a partial response and stabilized the disease within 12 months
      3. Adverse reaction were nausea, myelosuppression, and fatigue
      4. There was no hyperactive response to the medication

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Reference

Efficacy and Safety of High-Specific-Activity I-131 MIBG Therapy in Patients with Advanced Pheochromocytoma or Paraganglioma by Pyrma, DA, et al., JNM 2018

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