ABSTRACT
In biomedicine, cancer-related screening, diagnostic workup, image-guided biopsy and therapy delivery, and all X-ray sources such as simulators, linear accelerators, and computed tomography (CT) scanners generate broadband radiation. High-energy radiation doses are needed for sufšcient tissue penetration, and higher exposure is needed for linear absorption. Hainfeld et al. (2004) found that irradiation with gold nanoparticles embedded in the malignant tumor is more effective than direct irradiation.Since X-rays interact more efšciently with high-Z elements, the nanoparticles are made of heavy high-Z elements that are not abundant in living tissues such as C, O, and Fe. They are also chosen to be nontoxic after injecting into the body and designed with antigens that seek out antibodies produced in the tumor. Some of the high-Z elements in medical applications are bromine, iodine, gadolinium, platinum, and gold, which are used in compounds that do not react unfavorably in the body. High-energy irradiating X-rays interact mainly with heavy elements, while lighter elements remain inactive because of low absorptivity. The typical size of ananoparticlevaries from afew nanometers to afew tens of nanometers and hence can penetratevascular cells of typical sizes <30 nm or so. The high-energy X-rays have an additional advantage that they can penetrate the tissue before much loss of energy and reach the embedded nanoparticles.
