Gallium scan

Source: Wikipedia, the free encyclopedia.
Gallium-67 scan
SynonymsGallium imaging
ICD-10-PCSC?1?LZZ (planar) C?2?LZZ (tomographic)
ICD-9-CM92.18
OPS-301 code3-70c
MedlinePlus003450

A gallium scan is a type of

gamma emission of gallium-67 is imaged by a gamma camera, while the positron emission of gallium-68 is imaged by positron emission tomography
(PET).

Gallium salts are taken up by tumors, inflammation, and both acute and chronic infection,[3][4] allowing these pathological processes to be imaged. Gallium is particularly useful in imaging osteomyelitis that involves the spine, and in imaging older and chronic infections that may be the cause of a fever of unknown origin.[5][6]

Gallium-68 DOTA scans are increasingly replacing octreotide scans (a type of

neuroendocrine tumors and pancreatic cancer.[7][8]

Gallium citrate scan

Gallium scan showing panda (A) and lambda (B) patterns, considered specific for sarcoidosis in the absence of histological confirmation

In the past, the gallium scan was the

fludeoxyglucose (FDG).[9][10] Gallium imaging is still used to image inflammation and chronic
infections, and it still sometimes locates unsuspected tumors as it is taken up by many kinds of cancer cells in amounts that exceed those of normal tissues. Thus, an increased uptake of gallium-67 may indicate a new or old infection, an inflammatory focus from any cause, or a cancerous tumor.

It has been suggested that gallium imaging may become an obsolete technique, with

fludeoxyglucose PET imaging in the future.[11]

In infections, the gallium scan has an advantage over indium leukocyte imaging in imaging

pelvic infections. Both the gallium scan and indium leukocyte imaging may be used to image fever of unknown origin (elevated temperature without an explanation). However, the indium leukocyte scan will image only the 25% of such cases which are caused by acute infections, while gallium will also localize to other sources of fever, such as chronic infections and tumors.[12][13]

Mechanism

The body generally handles Ga3+ as though it were

bacterial siderophores, inflammatory proteins, and cell-membranes in neutrophils, both living and dead.[15]

Lactoferrin is contained within leukocytes. Gallium may bind to lactoferrin and be transported to sites of inflammation, or binds to lactoferrin released during bacterial

leukopenic patients with bacterial infection (here it attaches directly to bacterial proteins, and leukocytes are not needed).[17] Uptake is thought to be associated with a range of tumour properties including transferring receptors, anaerobic tumor metabolism and tumor perfusion and vascular permeability.[18][19]

Common indications

Note that all of these conditions are also seen in PET scans using the gallium-68.

Technique

The main (67Ga) technique uses

computed tomography
(CT) scan using either fusion software or SPECT/CT hybrid cameras to superimpose both physiological image-information from the gallium scan, and anatomical information from the CT scan.

A common injection dose is around 150 megabecquerels.[25] Imaging should not usually be sooner than 24 hours as high background at this time produces false negatives. Forty-eight-hour whole body images are appropriate. Delayed imaging can be obtained even 1 week or longer after injection if bowel is confounding. SPECT can be performed as needed. Oral laxatives or enemas can be given before imaging to reduce bowel activity and reduce dose to large bowel; however, the usefulness of bowel preparation is controversial.[24]

10% to 25% of the dose of gallium-67 is excreted within 24 hours after injection (the majority of which is excreted through the kidneys). After 24 hours the principal excretory pathway is colon.[24] The "target organ" (organ that receives the largest radiation dose in the average scan) is the colon (large bowel).[23]

In a normal scan, uptake of gallium is seen in wide range of locations which do not indicate a positive finding. These typically include soft tissues,

nasopharyngeal and lacrimal glands, breasts (particularly in lactation or pregnancy), normally healing wounds, kidneys, bladder and colon.[26]

Gallium PSMA scan

See also: PSMA scan
CT scan (left) and gallium PSMA PET scan (right) of patient with prostate cancer metastases in the bones

The positron emitting isotope, 68Ga, can be used to target

MRI or CT scans.[27]

In December 2020, the U.S. Food and Drug Administration (FDA) approved 68Ga PSMA-11 for medical use in the United States.[28][29] It is indicated for positron emission tomography (PET) of prostate specific membrane antigen (PSMA) positive lesions in men with prostate cancer.[30][29] It is manufactured by the UCLA Biomedical Cyclotron Facility.[29] The FDA approved 68Ga PSMA-11 based on evidence from two clinical trials (Trial 1/NCT0336847 identical to NCT02919111 and Trial 2/NCT02940262 identical to NCT02918357) of male participants with prostate cancer.[29] Some participants were recently diagnosed with the prostate cancer.[29] Other participants were treated before, but there was suspicion that the cancer was spreading because of rising prostate specific antigen or PSA.[29] The trials were conducted at two sites in the United States.[29]

The FDA considers 68Ga PSMA-11 to be a first-in-class medication.[31]

Common indications

Gallium PSMA scanning is recommended primarily in cases of biochemical recurrence of prostate cancer, particularly for patients with low PSA values, and in patients with high risk disease where metastases are considered likely.[32][33]

Technique

An

megabecquerels of 68Ga PSMA-11 per kilogram of bodyweight is recommended. Imaging should commence approximately 60 minutes after administration with an acquisition from mid-thigh to the base of the skull.[32][34]

Gallium DOTA scans

68Ga

therapy.[37][38]

In June 2016, Netspot (kit for the preparation of gallium Ga-68 dotatate injection) was approved for medical use in the United States.[39][40]

In August 2019, 68Ga edotreotide injection (68Ga DOTATOC) was approved for medical use in the United States for use with PET imaging for the localization of somatostatin receptor positive neuroendocrine tumors (NETs) in adults and children.[41][42][43]

The U.S. Food and Drug Administration (FDA) approved 68Ga edotreotide (DOTATOC) based on evidence from three clinical trials (Trial 1/NCT#1619865, Trial 2/NCT#1869725, Trial 3/NCT#2441062) of 334 known or suspected neuro-endocrine tumors.[42] The trials were conducted in the United States.[42]

Gallium (68Ga) oxodotreotide was approved for medical use in Canada as Netspot in July 2019,[44] and as Netvision in May 2022.[45]

Radiochemistry of gallium-67

Gallium-67 citrate is produced by a cyclotron. Charged particle bombardment of enriched Zn-68 is used to produce gallium-67. The gallium-67 is then complexed with citric acid to form gallium citrate. The half-life of gallium-67 is 78 hours.

keV (39% abundance), followed by 185 keV (21%) and 300 keV (17%).[47]: 64  For imaging, multiple gamma camera energy windows are used, typically centred around 93 and 184 keV or 93, 184, and 296 keV.[24]

Radiochemistry of gallium-68

See also: Gallium-68 generator

zinc-68 through a low energy cyclotron. Use of a generator means a supply of 68Ga can be produced easily with minimal infrastructure, for example at sites without a cyclotron
, commonly used to produce other PET isotopes. It decays by positron emission and electron capture into zinc-68.[48] Maximum energy of positron emission is at 1.9 MeV.[47]: 65 

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