Clinical tests of hyper-sensitivity to low doses of ionizing radiation

2 Gy fractionated dose of ionizing radiation applied daily for 5 days is the conventional way to treat malignant cancers (total dose 40-70 Gy). Fractionated doses below 1 Gy were until recently not used even in unconventional radiotherapy schemes. On the basis of the shape of the initial fragment of the survival curves drawn according to the linear-quadratic model (LQ) commonly used in radiotherapy, 0.1-1 Gy doses were regarded as ineffective. However, since 1993 when Marples and Joiner discovered hyper-sensitivity to low doses of ionizing radiation <0.5 Gy (HRS, low-dose hyper-radiosensitivity), opinions on biologic effects of low radiation doses in radiotherapy have changed. The HRS effect means that low dose of radiation may kill a larger percentage of cells than the percentage predicted by the LQ model. An increased resistance to radiation observed for doses above that level is referred to as increased radioresistance (IRR).

A debate on potential usefulness of the HRS effect for clinical treatment of oncology patients has been going on since its discovery. Common opinion is that lower doses are relatively more efficient (per dose unit) than conventional ones (2 Gy), because they do not activate DNA repair mechanisms in the irradiated cells, and in effect the cells more often die. Both in vitro and in vivo research have also shown that low fractionated doses ≤ 0.5 Gy may increase citostatic effects of chemotherapeutic preparations. On the basis of those results some clinical tests of low-dose (0.2–0.8 Gy) fractionated radiotherapy (LDFRT) combined with chemotherapy have been run in groups of patients suffering some advanced forms of malignant cancers.

The HRS mechanism will be discussed and the results of the so-far done clinical tests will be presented during the seminar.

NCBJ bus leaves to Świerk at 10.25 am from entrance gate to the Hoża 69 premises in Warsaw.

All interested persons are invited
L. Dobrzyński