Nuclear: Non-PET for Cancer

Question 1

What is the most commonly used radiotracer for somatostatin receptor imaging?

Answer 1

In-111 Pentetreotide (octreotide)

Note: This can only bind 2 of the 5 types of somatostatin receptors (but these 2 are the ones that cancers usually have).

Question 2

How is In-111 produced?

Answer 2

Cyclotron

Question 3

What is the half life of In-111?

Answer 3

67 hours

Question 4

What are the photopeaks for In-111?

Answer 4

• 173 keV
• 247 keV

Question 5

In-111 Pentetreotide

Answer 5

Normal early distribution at 4 hours (usually there is some bowel activity on later distribution at 24 hours)

Question 6

In-111 Pentetreotide

Answer 6

Meningioma

Question 7

MIBG is an analog of ____

Answer 7

Norepinephrine (which is why it is taken up by adrenergic tissue)

Question 8

MIBG is a first line radiotracer for which tumors?

Answer 8

• Pheochromocytoma
• Paraganglioma
• Neuroblastoma

Question 9

Is MIBG better with I-123 or I-131?

Answer 9

I-123 (better image quality)

Note: I-131 is cheaper and has a longer half life (allowing for more delayed images).

Question 10

What needs to be given to a pt prior to a MIBG scan?

Answer 10

Lugol’s iodine or perchlorate (AKA super saturated potassium iodine)

Note: This is needed to block the thyroid (to prevent unintended thyroid radiation from unbound I-123 or I-131).

Question 11

What went wrong with this MIBG scan?

Answer 11

The pt didn’t take the Lugol’s iodine so the thyroid wasn’t blocked (and has now been unnecessarily irradiated)

Question 12

Best study to look for neuroblastoma bone mets

Answer 12

MIBG

Note: MIBG is superior to MDP bone scan.

Question 13

MIBG

Answer 13

Bone metastases

Note: You should not see bone on MIBG.

Question 14

What medications need to be stopped before an MIBG scan?

Answer 14

• Calcium-channel blockers
• Labetolol (other beta blockers are fine)
• Reserpine
• Tricyclic antidepressants
• Sympathomimetics

Question 15

MIBG

Answer 15

Brown fat

Note: Brown fat (which has sympathetic innervation) can show up on MIBG studies just like in FDG PET studies.

Question 16

What precautions should you take before performing an ocretotide study for suspected insulinoma?

Answer 16

Have D50 on hand to administer in case of hypoglycemia (octreotide can precipitate hypoglycemia in pts with an insulinoma)

Note: Some practices administer an IV solution with glucose before and during the administration of octreotide for this reason.

Question 17

How long before an octreotide scan should you stop taking octreotide (if on octreotide therapy)

Answer 17

3 days prior to the study

Question 18

Octreotide is better than MIBG for most neuroendocrine tumors, except…

Answer 18

• Pheochromocytoma (except for the 10% that are malignant)
• Neuroblastoma

Question 19

Best nuclear study for carcinoid

Answer 19

Octreotide (sensitivity 80-90%)

Note: MIBG sensitivity is 50-70%.

Question 20

Best nuclear study for insulinoma

Answer 20

Octreotide, but its still shit (only 30% sensitivity)

Note: Insulinoma are usually benign.

Question 21

Best nuclear study for gastrinoma

Answer 21

Octreotide (sensitivity 85%)

Note: Gastrinomas are usually malignant.

Question 22

Best nuclear study for non-functional islet cell tumors

Answer 22

FDG PET

Note: MIBG and octreotide are both crap because these have no function and no receptors.

Question 23

Best nuclear study for pheochromocytomas

Answer 23

Non-malignant/adrenal (90%): MIBG

Malignant/extra-adrenal (10%): Octreotide

Question 24

Best nuclear study for paraganglioma

Answer 24

Octreotide (sensitivity 95%)

Question 25

Best nuclear study for medullary thyroid cancer

Answer 25

Octreotide (sensitivity 50-80%)

Note: MIBG sensitivity is ~30%. If octreotide is negative, FDG PET is the next step.

Question 26

Best nuclear study for neuroblastoma

Answer 26

MIBG (sensitivity 95%)

Note: Octreotide sensitivity is 64%.

Question 27

Critical organ for In-111 WBC

Answer 27

Spleen

Question 28

Critical organ for In-111 octreotide

Answer 28

Spleen

Question 29

Critical organ for In-111 PSMA (AKA ProstaScint, AKA Capromab Pendetide)

Answer 29

Liver

Question 30

Indication for In-111 PSMA study

Answer 30

History of prostate cancer and rising PSA levels but negative bone scan

Note: The purpose of the study is to look for soft tissue metastases outside the prostate bed (don’t obsess over the surgical bed, which will likely be irradiated regardless, the important point is to identify distant mets).

Question 31

Is In-111 PSMA good for identifying all prostate cancer mets?

Answer 31

No, only soft tissue mets (it cannot localize to bone mets, which is why you need to do a bone scan seperately)

Question 32

What radiotracer is used for sentinel lymph node detection?

Answer 32

10-100 nm Tc99m sulfur colloid

Question 33

Indication for sentinel node mapping in pts with melanoma

Answer 33

If the melanoma is between 1 mm and 4 mm deep

Note: If less than 1 mm you are safe; if more than 4 mm there are likely already distant metastases.

Question 34

Where should you inject radiotracer for sentinel node mapping of melanoma?

Answer 34

Intradermal injections in 4 spots around the lesion

Question 35

How often does breast cancer drain to an internal mammary lymph node?

Answer 35

3%

Question 36

What are standard particle sized for Tc-99m sulfur colloid?

Answer 36

Lymphoscintigraphy: < 0.2 micros (< 200 nm)
VQ scan: 10-100 microns (10,000-100,000 nm)
Liver/spleen: Unfiltered (all sizes)

Question 37

How do you perform breast specific gamma imaging?

Answer 37

20-30 mCi Tc-99m Sestamibi in the contralateral arm, then image 20 min later

Note: This is supposedly 90% sensitive for breast cancer (which will be ~6x hotter than background tissue). If you want to image both breasts, you should inject into the foot.

Question 38

When should breast specific gamma imaging be done in the menstrual cycle?

Answer 38

Mid-cycle in premenopausal women

Question 39

Common causes of false positives on breast specific gamma imaging

Answer 39

• Fibroadenoma
• Fibrocystic change
• Inflammation

Question 40

Common causes of false negatives on breast specific gamma imaging

Answer 40

• Small cancers (<1 cm)
• Deep cancer
• Cancer located in the medial breast
• Cancers overlapping with cardiac activity

Question 41

Is it normal for lymph nodes to take up sestamibi on breast specific gamma imaging?

Answer 41

No, think metastases

Question 42

What radiotracer is used for breast specific gamma imaging?

Answer 42

Tc-99m Sestamibi