A 62-year-old Japanese man with hepatitis B virus-related liver cirrhosis revealed alpha-fetoprotein (AFP) elevation. Dynamic computed tomography, taken at this time, showed a liver tumor in the anterior segment. As the patient refused any further medical treatment, he was observed in an outpatient clinic. The size of the tumor reduced and the serum level of AFP decreased gradually without any treatment. Twelve months after the initial diagnosis, the tumor could not be detected by computed tomography (CT) scan, and the level of AFP had declined to the normal range. Blood supply is essential for tumor growth and an arterioportal shunt near the tumor may change the dynamics of blood flow to the tumor. The shunt found in this patient was thought to be one of the causative factors leading to regression, but it could not be denied that immunological mechanisms may have played an important role in the spontaneous regression of hepatocellular carcinoma.

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Particle size distribution of activity was investigated with an impactor for airborne particles released from a pneumatic irradiation system of a research reactor. Airborne radioactivity released from the pneumatic tube of the reactor was identified as 24Na, 38Cl, and 56Mn and various fission products of which origin was uranium impurity in aluminum used in the part of the pneumatic tube. The AMAD (activity median aerodynamic diameter) of 24Na and 56Mn that were produced through (n,γ) reactions was ca. 1 μm, while that of fission products was ca. 0.4 μm. It was suggested that radioactive particles of ca. 1 μm were due to activation of aluminum dust in the pneumatic tube, and that the particles of ca. 0.4 μm were formed by attachment of recoiled fission products to radiation-induced airborne particles.

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