What are the acquisition protocols for breast cancer lymphoscintigraphy (sentinel lymph node mapping)?

Updated: Dec 13, 2018
  • Author: Durre Sabih, MBBS, MSc, FRCP(Edin); Chief Editor: Mahan Mathur, MD  more...
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Answer

Answer

Imaging techniques must be meticulous and of a high standard. The camera should be equipped with a low-energy, high-resolution collimator and should be peaked at 140 KeV with a 20% window centered over the peak. Shielding of the injection site is usually not needed. A small magnification (1.35) is often used.

Imaging times for the various injection techniques are given in the table below.

Table. Acquisition Protocols and Imaging Times for Various Injection Types (Open Table in a new window)

 

Computer Matrix

Dynamic Phase

Static Phase

Intradermal

128 x 128 x 16 (dynamic) or highest available

256 x 256 x 16 (static) or highest available

20 seconds for 15-20 minutes

20 minutes, 2-3 hours, 12-24 hours (immediately prior to surgery)

Subcutaneous

256 x 256 x 16 (static) or highest available

 

20-30 minutes, 2 hours, 4-6 hours, prior to surgery

Peritumoral or intratumoral

256 x 256 x 16 (static) or highest available

 

20-30 minutes, 2 hours, 4-6 hours, prior to surgery

An anterior oblique view with a 30-degree lateral tilt is used. If a dual-head camera is used, simultaneous lateral images are also acquired.

Transmission images, radioactive markers to identify the nipple, and flexible line sources to outline the breast contour may be used to provide additional anatomical localization.

Once a sentinel node is identified, a radioactive marker is moved over skin while the patient is under the gamma camera detector, keeping the sentinel node in the field of view. With real-time imaging mode, the marker is moved until the two sources coincide (the marker and sentinel node). This area is marked with waterproof ink.

It is useful to add late images before the patient is taken for surgery to ensure that the sentinel node identified is indeed retaining the radiopharmaceutical and also to see if subsequent tier nodes have appeared.


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