Chronic lymphatic leukemia (CLL) was formerly considered to be a non-radiogenic form of cancer. Non-Hodgkin Lymphomas (NHL) were supposed to be very rare after radiation exposure. These historical estimations were based on the early observations of the Japanese A-bomb survivors. In contrast to these conclusions, increasing rates of CLL and NHL were found in the last decades in nuclear workers and liquidators of Chernobyl, i.e. in cases of low dose chronic exposure. Estimating the dose response, the authors generally refer to the bone marrow as the corresponding target organ which often leads to surprisingly high-risk figures for the radiation effect. We recently investigated three cases of people suffering from B-lymphocyte proliferation (two CLLs and one lymphoma) who were involved in the decontamination of nuclear establishments, because Germany decided to go out of nuclear energy, and they started tearing down the plants. The men worked in the same enterprise, were exposed to external doses of 46, 108 and 116 mSv, and had certainly inhaled alpha emitters such as uranium and plutonium isotopes. In the 1980s, radiation hematologists stated that the bone marrow should not be considered as the relevant target of B-cell lymphomas and CLL of B-cell type because the effect results in a proliferation of mature B lymphocytes which mainly occur outside the bone marrow. Therefore, the diseases may be induced in the whole pool of B lymphocytes including all peripheral locations also comprising lymph nodes and lymphatic organs. Our impression is that CLL and NHL are initiated predominantly at workplaces where the possibility of open radioactivity exists: in uranium mines, uranium and radium processing facilities, nuclear facilities, and consequently in liquidators. Several studies involving animals and humans have shown that incorporated radionuclides such as uranium, thorium, and plutonium concentrate in the lymph nodes leading to higher radiation doses to the lymphocytes than are provided in other tissues. This effect is explained by the immunological reaction of macrophages functioning as scavengers of particles such as materials emitting alpha-radiation. These cells circulating via the lymph vessels are stored in the stationary lymph nodes. If the target organ for dosimetry must be seen in all mature B lymphocytes in the body, this will be valid for all kinds of external and internal exposures. Except in cases of homogeneous whole-body exposure, any dose estimation will be extremely unsafe or – as in our examples – not possible. These limitations must be considered when planning the radiation protection strategies for nuclear workers and adequate evaluation in compensation cases.

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