4. Neutron activation in medicine

NAA is used in different applications in medicine and has made inroads in the newer areas.

Trace elements have important bearing on the physiological and biochemical processes, and relative abundance and balance of different elements in trace quantities strongly influence the occurrence and advancement of many diseases. Estimation of trace element concentration in breast cancer, skin cancer, colorectal cancer, dysfunction and malignancy of thyroid gland has been done using neutron activation followed by high-resolution gamma spectrometric studies. NAA is one of the preferred choices for trace- and ultra-trace-level quantitative estimation as it is a highly accurate, precise and reproducible method even for measurements to the ppm and ppb level.

Concentration of Ca, Cu, Co, I, Mg, Se, Fe, Zn, Hg, Ba and Cr at the trace level in the malignant tissues of colorectal cancer was determined through NAA by H. Arriola et al. [26]. The study was carried out for patients from Mexican population. The results were compared with those obtained for normal tissues in the same population. It was observed that the amount of Co, Fe, I and Ba changes due to incidence of colorectal cancer.

NAA was used to estimate the concentration of Al, K, Na, CI, Rb, Co, Sc, Mn, Mg, Se, Zn, Cs, Fe and Cr in the patients of breast cancer in Sudanese population (Ammar Mubark Ebrahim A M, 2003) [27]. Though the number of patients studied was only 80, it was found that the amount of Al, Mg, Cr, Mn, Se and Zn is higher in the malignant tissues compared to the normal tissue. In this work the author has observed variation in the levels of K, Na, Fe, Co, Sc, Rb and Cs but to a much lesser extent.

Rees et al. [28] have used INAA to detect and measure the arsenic content in the toenail of the skin cancer patients. Tissues from both basal skin carcinoma (BCS) and squamous cell carcinoma (SCC) were examined from the patients of non-melanoma skin cancer.

Zaichick and Zaichick [29] have studied the changes in trace element concentration in the cancerous human prostate gland. They have used INAA to measure the concentration of 43 trace elements and compared the results for malignant, benign hypertrophic and normal prostate. Of the 43 elements measured, concentration of 33 elements in the malignant prostate is higher than that in the benign hypertrophic tissue. For the elements Co, Hg, Rb, Sc, Se and Zn, a reverse trend was observed. When compared with the normal tissue, lower contents of Sc, Se, Zn, Rb and Cd were detected in the malignant prostate.

Zaichick et al. [30] have studied the role of trace elements in the induction and advancement of thyroid cancer. Contents of 11 elements, namely, Sc, Se, Zn, Co, Cr, Fe, Hg, I, Rb, Sb and Ag were determined in malignant and non-malignant thyroid nodules as well as in the nonaffected paranodular thyroid tissue. Measured concentration of the elements mentioned was compared with the reference standard material H-4 of the International Atomic Energy Agency (IAEA). The results of this study showed that the level of Ag, Co, Hg, I and Rb is higher in the paranodular tissue. Selenium deficiency was also reported in this work for malignant thyroid. Zaichick and Zaichick [31] also studied the influence of different elements in the functional behaviour of thyroid and their dependence on sex and age.

Neutron activation analysis through monitoring of the delayed gamma radiation (DGNA) in combination with dual-energy X-ray absorption was used by Aloia et al. [32] to estimate the total body calcium. For the same population, the results obtained by the two methods vary more than 20%.

Gamma ray imaging plays a significant role in the pharmaceutical industry in development and progress of a drug delivery system. The standard form of radiolabelling of the drug molecules is done using some of the most commonly used medically important radioisotopes, like 99mTc or 111In. But for complex drug molecules, radiolabel is produced through in situ neutron activation [33].

NSECT or neutron-stimulated emission computed tomography is one of the most advanced imaging techniques employed to study the isotope distribution in biological tissue [2, 34]. The method depends on irradiation of the sample by fast neutrons. The gamma rays emitted in the nuclear reaction induced in the isotopes in the tissue under study are monitored to construct tomographic images of each section of the sample. Though the instrumentation is expensive, high sensitivity of the technique has rendered it suitable to be used for cancer staging, detection of breast cancer.

Another important advancement in the realm of nuclear medicine is the early diagnosis of breast cancer with the help of the fast neutrons. Multiple pencil beams are developed to carry out NAA of the breast tissue. Since the oxygen content of the cancer tissue is different from that in the normal tissue, differential femto-oximetry is used in the diagnosis of the malignant tissue [3]. With the advancement in beam profile variation, the technique may be used for diagnosis of other types of cancer.
