- •Control points to Charter 7
- •Factors that influence on organ or tissue response to radiation.
- •Radiosensitivity of a cell.
- •Differentiation.
- •Categories of cell populations.
- •5. Terms “vim”, “dim”, Multipotential Connective Tissue Cells, “rpm”, “fpm”.
- •6. Tissue organization (compartments).
- •9. Clonogenic assays. In Situ Assays.
- •7. Normal tissue damage.
- •8. Categories of arrays of damaged tissue; criteria necessary to value tissue effect.
- •10. Transplantation Assays. Functional Assays.
- •11. Lethality.
- •12. Shapes of survival curves.
10. Transplantation Assays. Functional Assays.
Transplantation Assays
The assays of clonogenic survival in bone marrow and thyroid and mammary glands require that the irradiated tissue be removed from the animal and a single cell suspension be made and then injected into another animal. This technique is best illustrated by the bone marrow colony-forming units (CFUs) assay developed by Till and McCulloch: (1) animals are irradiated to the whole body with a range of doses, (2) bone marrow is removed from their legs, and (3) single cell suspensions are made, various amounts of which are injected into previously irradiated syngeneic recipient animals. (The recipient animals must be previously irradiated so that all their bone marrow cells are destroyed, allowing the cells of the donor mice to grow.) These donor cells colonize the bone marrow and spleen, forming visible colonies in the latter. The spleen is removed 9 days later and the number of colonies counted, each of which is assumed to have arisen from the injection of one surviving cell. The number of colonies after each dose is counted; the proportion of cells surviving calculated and plotted as a function of dose. Similar assays are available for thyroid and mammary glands.
Functional Assays
Functional analysis is used to understand of the responses of late responding normal tissues to radiation. These functional endpoints meet the criteria that damage must increase as a function of dose. Such data produce dose response curves rather than cell survival curves, and although they tell little about the survival of the underlying putative target cells, they do allow comparison of tissue responses to radiation. Most of these are based on either the physiology of the organ (e.g., breathing rate measurements after lung irradiation, frequency of urination after bladder irradiation), whereas others rely on scoring visible changes in the organ that occur after irradiation (e.g., acute skin reactions consisting of hair loss, erythema, and desquamation).
11. Lethality.
The single most often used nonclonogenic assay for quantifying damage in normal tissues is lethality. In these studies the number of animals dead after localized irradiation of a specific organ is quantified as a function of dose and dose response curves are then constructed.
The lethal dose that kills 50% of the animals, LD50 is obtained for different normal tissues, allowing comparisons of the dose for this same effect (called isoeffect) between tissues.
The LD50 for a given tissue is further defined by the time when deaths occur. Based on the assumption that cell division is necessary for radiation damage to be expressed, deaths would occur quickly after irradiation of the intestine (by irradiating the whole abdomen), but much more slowly after irradiation of the lungs, reflecting the differences in turnover times of the critical cells in these two tissues.
12. Shapes of survival curves.
It has been suggested that not only do acutely and late responding normal tissues express their damage at vastly different times, but that their survival curves for the "target" cells are also different. The shapes of the survival curves for the two classes of tissue differ, and that the curve for late responding normal tissues is "curvier" than that for acutely responding normal tissues.