Download Introduction to Lymphatic Mapping

Introduction to Lymphatic Mapping
Introduction to Lymphatic Mapping
Cancer Staging
When a patient is given the diagnosis of cancer, one of the first questions to be answered is whether the
cancer has spread from the primary site (breast, colon, lung, etc.), or if it is still contained in that area.
The answer to that question will have implications in the prognosis of the patient and the treatment
prescribed. Determining whether a tumor has spread, or evaluating the extent of the cancer throughout
the body, is called “staging.” There are multiple ways to analyze whether the tumor has spread, or
“metastasized” from the primary site. The size of the tumor, for example, might give clues as to the
likelihood of metastasis. But for most solid tumors, the most powerful indicator of metastatic spread is
the presence or absence of cancer cells in the regional lymph nodes.
The lymphatic system can be thought of as a secondary circulatory system (the primary circulatory
system being the arterial-venous system). The lymphatic system collects fluid which escapes from the
cells, arteries, and veins, and returns the fluid, called “lymph”, back to the heart. The lymph nodes serve
as filters in the lymphatic system, that filter any foreign bodies from the lymph before it returns to the
heart. These foreign bodies may be bacteria, viruses, etc., or even cancer cells.
As tumors secrete fluid, and also shed cells (metastasize), the lymphatic system is a likely reservoir for
those fluids and cancer cells to deposit. Thus, if the lymph nodes in the area of the tumor can be localized,
surgically removed, and evaluated by pathology to determine if there are any cancer cells trapped there,
the extent of the spread of the cancer can be determined. This is the most common method used to gain
cancer staging information.
Axillary Lymph Node Dissection (ALND)
The technique of surgically removing the lymph nodes
in the area of the tumor is a traumatic procedure,
however. It is performed under anesthesia, and
associated with a high degree of post-operative
complications. Typical complications include the
following:
Rate
Complication
40%
Acute Lymphedema – the accumulation of
lymphatic fluid in the tissues, causing swelling.
This condition subsides over time.
5%
40%
Chronic
Lymphedema – a prolonged
permanent condition of lymphedema.
Paresthesia of arm – loss of sensation or
movement due to nerve damage.
10%
Seroma formation – a pocket of serum, caused
by lymphatic drainage into an excision cavity. A
Seroma must be surgically drained.
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Introduction to Lymphatic Mapping
Sentinel Lymph Node Biopsy (SLNB)
First reported in 1977, a revised method of obtaining this staging information has been developed, and
has gained broad acceptance in the surgical community. This method involves localization of the lymph
node that is first in the lymph node chain to receive lymphatic drainage from a primary tumor site. This
first draining node is referred to as the “sentinel” lymph node (SLN), and it has been found to be a highly
accurate indicator of the metastatic involvement of the entire lymph node basin in which it is situated. In
short, if the Sentinel Node doesn’t contain cancer, then the rest of the lymph nodes are also negative for
cancer. What this means is that instead of removing all of the lymph nodes (10-15) in the lymphatic basin
in the area of the tumor, only the Sentinel Node is necessary to remove.
The localization, excision, and pathologic evaluation of the sentinel node for the purpose of gaining
cancer staging information is called “Sentinel Lymph Node Biopsy, or “Intraoperative Lymphatic
Mapping” (ILM). In theory, the histology of SLN should be highly predictive of the remainder of the
lymphatic basin, a theory which has been proven clinically for melanoma and breast cancer. This
procedure is beneficial in that it replaces full nodal dissection for a majority of patients, thus avoiding the
complications associated with it. Typically in a full axillary dissection, 10-25 nodes are removed and
analyzed. With SLNB, 1-3 sentinel nodes will be excised and analyzed, thereby greatly reducing or
eliminating
the
complications
associated
with
full
dissection.
The first technique investigated to localize the SLN involved the injection of a blue dye, Lyphazurin 1%
blue dye, around the tumor site. The dye flows into the lymphatic basin which receives lymphatic
drainage from the tumor, and the nodes are stained blue. The surgeon then proceeds to carefully dissect
the nodal basin, and visually identify blue-stained lymphatic vessels. These lymphatic vessels are
followed to the SLN, the first blue node in the lymphatic chain from the tumor. The SLN is then excised,
and its histologic status is determined by pathology. Although this method has been used successfully by
several researchers, its success varies with the experience level of the surgeon, and can result in a
procedure which approaches the invasive level of a full dissection of the nodal basin. Success rates in
finding the SLN by the blue dye technique alone vary from 65% to 93%.
The second technique introduced a radiocolloid (Tc99m Sulfur Colloid) as the agent injected around the
tumor. This radioactive tracer flows into the lymphatics in the same manner as the blue dye, and deposits
into the SLN. The advantage to this method is that a gamma detection probe is utilized to detect and
mark the SLN at the skin (pre-incision) and also intra-operatively. This method allows a small incision to
be used, unlike the blue dye, when visual search for nodes is necessary. Once localized, the SLN is
excised and its histologic status determined.
It has been documented that the best results in SLN
identification are obtained when the radiocolloid and blue
dye are used together. Since there is a chance that some
of the nodes will stain blue, but not be “hot” by
radiocolloid, or may be “hot” but not blue, many surgeons
find that the use of both agents increases their incidence of
correctly identifying the SLN.
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Introduction to Lymphatic Mapping
Nuclear Medicine 101
Nuclear Medicine is a scientific and clinical discipline of medicine which utilizes radiopharmaceuticals,
chemical substances which contain a radioactive component (radionuclide) within its structure and are
suitable for human use. These radiopharmaceuticals are used in the diagnosis and/or treatment of disease.
In the detection of disease, nuclear medicine technologists administer radiopharmaceuticals to patients
and obtain images of the bio-distribution of these tracers. The images are captured by scintillation
detectors, commonly called gamma cameras.
Unlike an X-ray or CT scan, in which X-rays are transmitted through the patient to the film plate, nuclear
medicine images are formed by the radiation emanating from the patient after the injection of the
radiopharmaceutical. The gamma camera captures the emitted radiation, and the resulting images
describe the organs in which the tracer has localized. Nuclear medicine is unique in that the obtained
information describes the function of organs, while the other imaging modalities (X-ray, CT, MRI,
Ultrasound, etc.) only depict the physical structure of organs. These functional studies are interpreted by
a radiologist. A radiologist who has achieved certification in nuclear medicine is called a nuclear
medicine physician.
85-90% of all nuclear medicine procedures utilize Technetium-99m (Tc99m) as the radioactive
component of their associated radiopharmaceuticals. Tc99m is considered an optimum tracer for most
procedures due to its half life (6 hrs), which is short enough to limit exposure to the patient, yet long
enough to permit flexible scan scheduling. Another advantage is its gamma energy (140 keV), which is
energetic enough to penetrate tissue, yet readily captured by the camera detector.
The preparation of radiopharmaceuticals involves combining Tc99m with a chemical “carrier” which
dictates which organs the tracer will localize to. The nuclear medicine staff typically will be responsible
for procurement, preparation and injection of the radiopharmaceutical (Tc99m Sulfur Colloid) as well as
any lymphoscintigraphy (imaging of the lymphatic flow).
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Introduction to Lymphatic Mapping
Principles of Radioactive Decay
Radioactive decay is the spontaneous process by which an unstable atomic nucleus transforms into
another, more stable nucleus. During this transition, the unstable nucleus emits particles and/or gamma
rays. These photons, or “gamma rays”, have characteristic energies, measured in keV, or kilo electron
volts.
Each radionuclide can be
identified by its peak energy.
The illustration on the right
shows the 140 keV gamma
ray given off by Tc99m. In
this example, we see that
Tc99m emits the majority of
its gamma rays around the
140 keV energy level. We
also note that there are a
significant
number
of
radioactive counts falling in
the 40-120 keV range. These
counts represent “scattered”
gamma rays, which are those
protons which have lost
some of their original 140
keV energy due to collisions
with tissue before leaving
the body.
All radionuclides also have a
characteristic
lifetime,
measured in half-lives. A
half-life is defined as the
time
required
for
a
radionuclide to decay to half
its initial activity level.
Radionuclides are identified by these two criteria. For Example, Technetium 99 (Tc99m) is the radio
nuclide used in the SLNB procedure, as well as most Nuclear Medicine scans. Its characteristics can be
described by the energy of its emitted gamma rays (140 keV), as well as its half-life (6-hours). These two
defining characteristics make Tc99 an ideal radionuclide for diagnostic scanning, since its energy level is
high enough to be detected outside the body, and its half-life is short enough to spare the patient excessive
radiation exposure.
44 Hunt Street, Watertown, MA 02472 I Phone: 617.668.6900 I Fax: 617.926.9743 [email protected] I www.dynasilproducts.com
Introduction to Lymphatic Mapping
Glossary
ALND
Axillary Lymph Node Dissection, the removal of all the lymph nodes in the axillary
region, as part of breast cancer treatment
Colloid
A suspension of particles in a carrier medium (liquid)
Ex vivo
Outside the body
FDG-18
Flourine-18 De-oxyglucose
Formalin
Preservative fluid used to store pathologic specimens
Gamma
A form of radiation. Other forms include microwave, radio wave, and light
Half-life
The length of time required for radioactive material to decay to ½ it’s initial activity
In situ
In place
Interparenchymal
Between the essential and distinctive tissue of an organ or an abnormal growth as
distinguished from its supportive framework
Intradermal
Within or between the layers of skin
keV
Kilo electron volts, unit of measurement of gamma ray energy
Lymph-edema
The accumulation of lymphatic fluid in the tissues, causes swelling
Lymphoscintigraphy
Nuclear medicine imaging of lymphatic drainage
mCi
Millicurie, unit of measurement of radiation, 1/1000 curie
Micron
1/1000 mm, sulfur colloid particles range in size from .05-1.0 micron
nm
Nanometer, 1/1000 micron
Parenchyma
The functioning tissue of an organ
Paresthesia
Lack of sensation, can be caused by nerve damage during axillary dissection
PET
Positron Emission Tomography
Photopeak
The graphical representation of the energy of the gamma emissions of a radionuclide
Radiocolloid
A colloid tagged with a radionuclide for the purpose of diagnostic imaging
Radionuclide
The radioactive form of an element
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Introduction to Lymphatic Mapping
Radiopharmaceutical
A tracer used in nuclear medicine, composed of a radioactive component tagged to a
chemical component which localizes to the organ of interest
Scintillation
Production of light photons by a crystal
Seroma
A pocket of serum, caused by lymphatic drainage into an excision cavity. Must be
surgically aspirated
SLN
Sentinel Lymph Node, The first lymph node to receive lymphatic drainage from a
tumor
Staging
Determining the extent of tumor spread
Subdermal
Under the skin (injection)
TC-99m
Technetium-99
uCi
Microcurie, 1/1000 mCi
VAT
Video Assisted Technique
44 Hunt Street, Watertown, MA 02472 I Phone: 617.668.6900 I Fax: 617.926.9743 [email protected] I www.dynasilproducts.com