Contact microscopy, enables us to visualize the detailed internal structure of biological cells. Exposure of biological specimen mounted on X-ray or UV sensitive materials to soft X-ray or UV introduces chemical damage to the materials, and the damage distribution due to the absorption of the X-rays or the UV by the specimen reveals as relief on the surface of the material after development process. The relief can be visualized with an AFM at high resolution of ~100 nm. We have applied the contact microscopy technique to high-resolution neutron-induced alpha-autoradiography for boron imaging in boron neutron capture therapy (BNCT). In BNCT, energetic alpha/lithium particles (range ~ single cell) from boron-neutron reactions introduce lethal damage to tumor cells selectively through thermal neutron irradiation with tumor-accumulating boron compounds. To understand the mechanism of drug delivery of those boron compounds is significant to evaluate the efficacy of BNCT. In the new technique, we can visualize those alpha/lithium particle tracks as etch pits and contact X-ray/UV microscopic image of tumor cells as relief on the surface of CR-39 plastic track detectors after etching process. Achievable resolution was ~100 nm with AFM readout, so that we can perform the boron imaging at subcellular scale.
The cytotoxic effect of boron neutron capture therapy (BNCT) is due to the nuclear reaction between <SUP>10</SUP>B and thermal neutrons. Recently, polyethylene glycol (PEG) has attracted attention due to its ability to avoid uptake by reticulo- endothelial systems, and to accumulate in the tumor cells. We prepared boronated PEG-binding bovine serum Albumin (BSA). Prompt g-ray spectrometry showed that 250.0 +/- 4.9 ppm <SUP>10</SUP>B atoms were found to conjugate to PEG-BSA. <SUP>10</SUP>B concentrations in AsPC-1, human pancreatic cancer cells obtained 0, 9, 24 hrs after incubation with <SUP>10</SUP>B- PEG-BSA were 0, 4.97 +/- 0.49, and 13.01 +/- 1.74 ppm respectively. It is said that the <SUP>10</SUP>B concentrations between 15 and 30 ppm are necessary for effective boron neutron-capture therapy. These data indicated that the <SUP>10</SUP>B-PEG-BSA were getting close to the lowest acceptable limit of 15 ppm, and when using Na<SUB>2</SUB><SUP>10</SUP>B<SUB>20</SUB>H<SUB>18</SUB> and increasing the <SUP>10</SUP>B binding site of the BSA, we could increase the <SUP>10</SUP>B uptake levels in the tumors for BNCT.