**7. Radioimmunoscintigraphy**

It is well known that mammography provides a high sensitivity at the cost of relatively low specificity. Therefore, breast cancer diagnosis requires an adjunctive test to mammography that can increase diagnostic specificity while maintaining a high positive predictive value. Although sestamibi imaging has been introduced as an adjunctive test to mammography, it fails to provide the necessary sensitivity, specificity and predictive values for nonpalpable

Breast Cancer: Radioimmunoscintigraphy and Radioimmunotherapy 179

The most common radionuclides in nuclear medicine are 99mTc, 123I, 67Ga and 111In. Lower energy γ-rays are readily absorbed in tissues and therefore less useful for external imaging. On the other hand, highest energy γ-rays cause to decrease the sensitivity of imaging system (Berghammeret al., 2001). Technetium-99m is so far the most commonly used radionuclide in nuclear medicine (Hamoudeh et al., 2008). This is due to the highly interesting physical properties of 99mTc which is advantageous for both effective imaging and patient safety perspectives. Its properties include short half-life (6 h), gamma energy at 140 keV with practically no alpha or beta emissions and latent chemical properties, facilitating thereby the labeling of several types of kits for versatile diagnostic applications and readily available and inexpensive (it is derived as a column elute from a 99Mo/99mTc generator) (Verhaar et al., 2000). It is most often used with smaller antibody forms such as Fab, scFv, diabodies and nanobodies. The gamma-ray emitting radionuclides are commonly used in gamma camera and single photon emission tomography (SPECT). Other groups of diagnostically used radionuclides are ß+ emitters such as 11C, 18F, 13N and 15O (Hamoudeh et al., 2008). The positron emitting radionuclides are used in positron emission tomography (PET). The positive electron travels only a short distance through the tissues and interacts with a free or loosely bound negative electron. The outcome of this interaction is two photons, consisting each of 511

keV energy and being given off in opposite directions (Boswell & Brechbiel, 2007).

computed tomography (SPECT) and positron emission tomography (PET).

Imaging systems in nclear medicine include gamma camera, single photon emission

Gamma camera is a one-headed, variable-angle diagnostic instrument that is used to image gamma radiation emitting radioisotopes, a technique known as scintigraphy. Gamma camera consists of a scintillation crystal, optically coupled to an array of photomultiplier

Single photon emission computed tomography (SPECT) is a sensitive nuclear imaging technique that provides a 3D spatial distribution of single-photon emitting radionuclide within the body (Gomes et al., 2010). Multiple 2D images, also called projections, are acquired from multiple angles around the patient and subsequently reconstructed using the reconstruction imaging methods to generate cross-sectional images of the internal distribution of the injected molecules (Wernick, & Aarsvold,2004). Because of the isotropic emission of γ-rays, a geometric collimation is needed to restrict the travelling direction of the emitted γ-rays from the body, through the use of lead collimators. In clinical systems, collimators typically have many parallel holes that produce no magnification. The photons that travel in other directions than those specified by the aperture of collimator are absorbed and do not contribute to the image, which reduces the detection efficiency and sensitivity of SPECT as compared to PET (Madsen, 2007). SPECT have several advantages including (1) whole body imaging, (2) quantitative molecular imaging and (3) can be combined with CT for preparing anatomical information. The disadvantages of this method are radiation exposure, low spatial resoulation (0.3-1 mm,

**7.1 Radionuclides for imaging** 

**7.2 Imaging systems in nuclear medicine** 

tubes which converts the γ-rays into electric signals.

12-15 mm3) and long acquisition time (Pysz et al., 2010).

**7.2.2 Single photon emission tomography** 

**7.2.1 Gamma camera** 

lesions, thus resulting in a relatively high false-positive rate in patient population. Several strategies have been developed over the past two decades for earlier and more accurate diagnosis of disease and to evaluate response to therapy. One of the novel approaches for specific detection of cancers is the use of monoclonal antibodies conjugated with radionuclides so-called radioimmunoscintigraphy (is also called radioimmunodetection, radioimmunoimaging and radioimmunodiagnosis) (Salouti, et al., 2006). In this method, a radio-isotope labeled antibody is administered to a patient with cancer. Once localized to the tumor tissue, the radioisotope (and hence the sites of malignancy) can be detected with a nuclear medicine imaging system like gamma camera. The summery of history for RIS has been shown in table 1. The efficacy of this technique depends on antigen expression on tumor cells compared to normal tissues. Affinity, specificity, pharmacokinethics, properties of the radionuclide and imaging technique have influence on the efficacy of radioimmunoscintigraphy. The potential clinical applications of RIS are (1) evaluation of patients with suspected breast cancer, (2) locoregional staging of newly discovered breast cancer, (3) detection of distant metastases using whole body scintigraphy and (4) evaluation of tumor response to therapy (Berghammer et al., 2001).


Table 1. The summery of history for radioimmunoscintigraphy.
