Volume 5 Number 2 Summer 99

Master List Volume 5 Number 2 Summer 1999

IN THIS ISSUE Malignant Melanoma Breast Cancer
FAQs
Nuclear Medicine

Nuclear Medicine at University Hospital
by Michael Zinsmeister, MD

Patient with a malignant melanoma lesions of the right back. Delayed images reveal a single right acillary lymph node. No groin lymph nodes are observed.

Malignant melanoma and breast cancer are two commonly encountered malignancies whose incidence has increased in recent years. Commonly, the treatments for these cancers can be extensive and may be disfiguring. For a select group of patients, the surgical approach to these two cancers has recently become more conservative. Therefore, innovative radiologic studies are being performed to help the surgeon plan these limited cancer procedures. Specifically, cutaneous and intramammary lymphoscintigraphy are being performed to allow the surgeon to identify the areas in the body that have a higher likelihood for harboring additional cancerous tissue.

Malignant Melanoma

The objective of the limited surgical procedure is to reduce the potential morbidity and complications attendant with an extensive regional lymph node dissection. In addition to local resection of the primary lesion, regional lymph node dissection was performed to reduce the risk of potential recurrence. This current limited surgical approach is termed the sentinel lymph node theory. Melanoma is particularly well suited to this novel approach because it has been extensively documented that the mode of metastasis of melanoma is nearly uniformly through the lymphatic system to the regional lymph nodes drained by the primary lesion. Radiologic procedures, especially the scintigraphic evaluation, are uniquely suited for the minimally invasive identification of these strategic lymph nodes. After the lymph node(s) are identified with the assistance of the nuclear medicine Anger (gamma) camera, it (they) are marked on the patient's skin in the nuclear medicine suite. This allows rapid surgical identification and potentially reduces the time of the operative procedure. Also, the surgeon is assisted by the use of a small, hand-held gamma probe. This is a device similar to the larger gamma camera, except images are not produced; its objective is to identify small accumulations of localized radioactivity in the desired lymph node. A small incision is made, the tissue containing the radioactive lymph node is excised, and it is evaluated pathologically for evidence of malignant cells. Decisions on the need for additional surgical intervention are based upon the analysis of the sentinel lymph node(s).

Technically, the procedure of cutaneous lymphoscintigraphy is simple. No patient preparation is required. The area of the lesion is cleaned and draped. The radionuclide used is commonly one of three types: sulfur colloid, filtered sulfur colloid, or human serum albumin. Other effective agents have been successfully used, but are unavailable in the United States. Usually, filtered sulfur colloid is used. It has been observed that the filtered compound migrates in the lymphatic channels more rapidly than the larger non-filtered colloidal particles. This can potentially reduce imaging time requirements.

Multiple small intradermal injections are made with a small-bore needle. The injections are ideally made to surround the lesion; this affords the best possibility to observe all of the surrounding potential drained nodes. Subsequently, the patient is positioned under the gamma camera and sequential images are produced. Imaging continues until a focal accumulation of radiocolloid is observed separate from the lesion injection site. The time required is variable, but a sentinel node is observed in the large majority of patients within 30 &endash; 45 minutes. Though infrequent, non-migration of the colloid has been documented. Such an event can be superceded by intraoperative cutaneous color dye injection; this is an alternative lymphatic mapping method, which is also useful. The skin overlying the radioactive lymph node is marked for rapid identification.

Breast Cancer

The procedure for regional lymph node identification is similar to that for melanoma except that for non-palpable breast lesions, ultrasound guided localization is performed. The patient's mammographic study is initially used to localize the region in the breast for evaluation. The ultrasound probe is used to identify the lesion or the site from which the excisional specimen had been removed. A small postoperative fluid collection is frequently present at the procedure site. The overlying skin is cleaned and draped. The radiocolloid is deposited about the lesion, as in the melanoma evaluation. The patient is subsequently returned to the nuclear medicine suite for imaging. Commonly, a draining regional lymph node is rapidly identified. Often, one to two hour delayed images are required to observe a regional lymph node. Alternatively, if the breast lesion is palpable, the tissues surrounding the lesion can be directly injected, as in the melanoma evaluation, but the injections are intramammary. Additionally, new data is being reported that intradermal injections, similar to that performed for melanoma patients, may also accurately identify the sentinel regional lymph nodes; this variation in the lymphoscintigraphic evaluation of the breast is under investigation. The skin overlying the observed, usually axillary, lymph node is marked, thus facilitating quick intraoperative identification.

Patient with cancer in the right breast was injected at the site of the tumor. Delayed images revealed 2 lymph nodes in the right axilla.

The resurgence in the use of a previously infrequently used scintigraphic technique has the potential to assist in the surgical management of two aggressive cancers. Further study is being performed and additional modifications to this technique will be made as scientific data becomes available. The cutaneous and intramammary lymphoscintigraphy procedures described here afford many advantages, including their minimally invasive nature, speed, and observed reliability.

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FAQS - Frequently Asked Questions

Injection was performed at the site of the left breast cancer lesion. Delayed left lateral images reveal a single observed left acillary lymph node.

Q: What is nuclear medicine?

Nuclear medicine is the subspecialty of radiology dealing with the use, application, and imaging of radioactive materials. Most frequently, these radioactive compounds, collectively termed radionuclides or nuclides, are administered intravenously. In contrast to other radiologic examinations, which are directed toward the anatomic and structural evaluation of the body, nuclear medicine focuses primarily on the physiology and function of the target organ or region of interest; anatomy is usually not the primary objective because the spatial resolution of radionuclide examinations is limited.

Q: Is there a significant radiation exposure related to nuclear medicine procedures?

The amount of radiation exposure received by the patient in a routine radionuclide examination is comparable to that of conventional radiologic examinations. The exposure is distributed differently throughout the body depending upon the type of examination performed. For example, hepatobiliary examinations ("HIDA scans") deposit the majority of the absorbed radiation in the liver, hepatobiliary tract, and the bowel, whereas ventilation/perfusion scans deposit most of the acquired dose at the lungs and the trachea. However, in all cases, the radionuclide dose is calculated to limit radiation exposure while providing important and radiologically diagnostic data. No expected adverse effects will be observed due to the radiation dose received to the person undergoing the examination.

Q: Is there any preparation needed for nuclear medicine procedures?

Generally, minimal preparation is needed, but this depends upon the type of radionuclide examination. For example, radionuclide bone scans, renal scans, thyroid imaging scans, parathyroid scans, and ventilation/perfusion (V/Q) scans require no pretest patient preparation. At least four-hour pretest fasting is requested prior to radionuclide hepatobiliary scans ("HIDA scans"). This is to attempt to improve the ability to visualize the gallbladder. Morning NPO status is requested for most radionuclide cardiac perfusion scans. Depending upon the clinical concern and type of thyroid radionuclide examination, a period for withholding the oral thyroid hormone is required. To learn of the exact pretest requirement of any radionuclide examination, contact any of the nuclear medicine staff. They will direct you to the appropriate nuclear medicine physician or radiologist.

Q: What is the risk of a "contrast reaction" in a nuclear medicine examination?

This is a frequently asked and reasonable question, especially in persons who have previously had "reactions" to iodinated contrast media. However, the material injected for radionuclide examinations is completely unrelated to the iodinated contrast utilized for CT scans, arthrograms, and myelograms. The material given, most frequently intravenously, is a small amount of a compound, which is usually composed of a specific radioactive isotope and a specific ligand or chelate, linked together. The specific test and organ of interest determine the ligand/chelate and the nuclide used. It is extraordinarily rare and unexpected for a person to develop signs or symptoms commonly attributed to allergic or anaphylactic reactions sometimes elicited during or after the use of iodinated contrast agents.

Q: What if the patient is of child bearing age or pregnant?

All female patients of childbearing age are questioned as to their pregnancy status. If pregnancy status proves to be uncertain or possibly positive, we request a pretest pregnancy test for female patients scheduled to receive radioactive iodine I-131, except in cases of hysterectomy or bilateral tubal ligation. Pregnant patients for whom an examination is still crucial pose a special problem. It is preferable if a different radiologic or imaging examination can be performed. If not, such as in the case of suspected pulmonary thromboembolus in a gravid patient, the radionuclide examination can be performed with dosage alterations prescribed by the nuclear medicine physician or the radiologist.

Q: What if the patient is breast-feeding?

The time that breast-feeding should be delayed after radionuclide administration depends upon the physical decay properties of the specific nuclide given. For the majority of radionuclide examinations, only 8 to 12 hours post administration is required before breast-feeding can resume normally. It is important for the patient to express the breast milk as per their routine and discard that milk. Only for the nuclides indium-111, gallium-67, and iodine-131 are different recommendations made. Breast-feeding should be terminated for 3 weeks after the administration of indium-111 or gallium-67; unfortunately, iodine-131 requires the termination of breast-feeding after dose administration for that child. Breast feeding for any subsequent birth can resume normally. This strict requirement is related to the potentially high radiation dose to the infant's thyroid, which is particularly sensitive and the long physical half-life of iodine-131.

Q: How much time is required for a nuclear medicine examination?

As above, the time requirements depend upon the test being performed. Commonly, this may require only 10 &endash; 20 minutes as for a conventional ventilation/perfusion scan. Alternatively, a whole body gallium scan usually requires a delay of four days from the day of nuclide injection to the day of imaging, sometimes with an additional one or two days being needed to fully complete the examination. The actual time needed to acquire the image of the patient usually lasts approximately 20 &endash; 40 minutes. The majority of examinations require between 2 &endash; 4 hours after dose administration before imaging is performed.

Q: Are there any special precautions patients should take after having their examinations?

No. The radiation dose given is of a size small enough to allow virtually all patients to be released after the completion of imaging and no special requirements are asked of the patients. The only common and frequent exception is for patients being imaged with iodine-131 with the history of thyroid cancer or hyperthyroidism. For the hyperthyroid patients, the precautions are given to the patient in written form and the patient is only requested to follow simple precautions for 3 &endash; 4 days. Also, the patient is directly counseled prior to the administration of the radioactive dose. For patients being treated with iodine-131 for thyroid cancer, all will be given their iodine dose after they have been admitted to the hospital; the duration of the hospital stay is usually 2 &endash; 3 days.

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Q: What is nuclear medicine?	Nuclear medicine is the subspecialty of radiology dealing with the use, application, and imaging of radioactive materials. Most frequently, these radioactive compounds, collectively termed radionuclides or nuclides, are administered intravenously. In contrast to other radiologic examinations, which are directed toward the anatomic and structural evaluation of the body, nuclear medicine focuses primarily on the physiology and function of the target organ or region of interest; anatomy is usually not the primary objective because the spatial resolution of radionuclide examinations is limited.
Q: Is there a significant radiation exposure related to nuclear medicine procedures?	The amount of radiation exposure received by the patient in a routine radionuclide examination is comparable to that of conventional radiologic examinations. The exposure is distributed differently throughout the body depending upon the type of examination performed. For example, hepatobiliary examinations ("HIDA scans") deposit the majority of the absorbed radiation in the liver, hepatobiliary tract, and the bowel, whereas ventilation/perfusion scans deposit most of the acquired dose at the lungs and the trachea. However, in all cases, the radionuclide dose is calculated to limit radiation exposure while providing important and radiologically diagnostic data. No expected adverse effects will be observed due to the radiation dose received to the person undergoing the examination.
Q: Is there any preparation needed for nuclear medicine procedures?	Generally, minimal preparation is needed, but this depends upon the type of radionuclide examination. For example, radionuclide bone scans, renal scans, thyroid imaging scans, parathyroid scans, and ventilation/perfusion (V/Q) scans require no pretest patient preparation. At least four-hour pretest fasting is requested prior to radionuclide hepatobiliary scans ("HIDA scans"). This is to attempt to improve the ability to visualize the gallbladder. Morning NPO status is requested for most radionuclide cardiac perfusion scans. Depending upon the clinical concern and type of thyroid radionuclide examination, a period for withholding the oral thyroid hormone is required. To learn of the exact pretest requirement of any radionuclide examination, contact any of the nuclear medicine staff. They will direct you to the appropriate nuclear medicine physician or radiologist.
Q: What is the risk of a "contrast reaction" in a nuclear medicine examination?	This is a frequently asked and reasonable question, especially in persons who have previously had "reactions" to iodinated contrast media. However, the material injected for radionuclide examinations is completely unrelated to the iodinated contrast utilized for CT scans, arthrograms, and myelograms. The material given, most frequently intravenously, is a small amount of a compound, which is usually composed of a specific radioactive isotope and a specific ligand or chelate, linked together. The specific test and organ of interest determine the ligand/chelate and the nuclide used. It is extraordinarily rare and unexpected for a person to develop signs or symptoms commonly attributed to allergic or anaphylactic reactions sometimes elicited during or after the use of iodinated contrast agents.
Q: What if the patient is of child bearing age or pregnant?	All female patients of childbearing age are questioned as to their pregnancy status. If pregnancy status proves to be uncertain or possibly positive, we request a pretest pregnancy test for female patients scheduled to receive radioactive iodine I-131, except in cases of hysterectomy or bilateral tubal ligation. Pregnant patients for whom an examination is still crucial pose a special problem. It is preferable if a different radiologic or imaging examination can be performed. If not, such as in the case of suspected pulmonary thromboembolus in a gravid patient, the radionuclide examination can be performed with dosage alterations prescribed by the nuclear medicine physician or the radiologist.
Q: What if the patient is breast-feeding?	The time that breast-feeding should be delayed after radionuclide administration depends upon the physical decay properties of the specific nuclide given. For the majority of radionuclide examinations, only 8 to 12 hours post administration is required before breast-feeding can resume normally. It is important for the patient to express the breast milk as per their routine and discard that milk. Only for the nuclides indium-111, gallium-67, and iodine-131 are different recommendations made. Breast-feeding should be terminated for 3 weeks after the administration of indium-111 or gallium-67; unfortunately, iodine-131 requires the termination of breast-feeding after dose administration for that child. Breast feeding for any subsequent birth can resume normally. This strict requirement is related to the potentially high radiation dose to the infant's thyroid, which is particularly sensitive and the long physical half-life of iodine-131.
Q: How much time is required for a nuclear medicine examination?	As above, the time requirements depend upon the test being performed. Commonly, this may require only 10 &endash; 20 minutes as for a conventional ventilation/perfusion scan. Alternatively, a whole body gallium scan usually requires a delay of four days from the day of nuclide injection to the day of imaging, sometimes with an additional one or two days being needed to fully complete the examination. The actual time needed to acquire the image of the patient usually lasts approximately 20 &endash; 40 minutes. The majority of examinations require between 2 &endash; 4 hours after dose administration before imaging is performed.
Q: Are there any special precautions patients should take after having their examinations?	No. The radiation dose given is of a size small enough to allow virtually all patients to be released after the completion of imaging and no special requirements are asked of the patients. The only common and frequent exception is for patients being imaged with iodine-131 with the history of thyroid cancer or hyperthyroidism. For the hyperthyroid patients, the precautions are given to the patient in written form and the patient is only requested to follow simple precautions for 3 &endash; 4 days. Also, the patient is directly counseled prior to the administration of the radioactive dose. For patients being treated with iodine-131 for thyroid cancer, all will be given their iodine dose after they have been admitted to the hospital; the duration of the hospital stay is usually 2 &endash; 3 days.