reference - F M KHAN

1. CELL SURVIVAL CURVE
Presented by – Moderated by –
Dr. Pushpendra Kumar Patel Dr. V. B. Rathore
Dept. of radiation oncology Dept. of radiation
oncology
RCC Raipur RCC Raipur

2. Cell Survival Curve
• It describes relationship between radiation dose
and the fraction of cells that “survive” that dose.
• This is mainly used to assess biological
effectiveness of radiation.
• The shape of cell survival curve tells us the
radiosensitivity , repair and recovering ability of
the cell. The shape of the curve gets altered if the
conditions are changed.

3.  To understand it better, we need to know about
a few basic things e.g.
1.Cell Death
2.Estimation of Survival / Plating Efficiency.
3.Nature of Cell killing etc.

4. Cell Death
Cell death can have different meanings:
 loss of a specific function (Functional death)-
differentiated cells (nerve,muscle, secretory cells)
 loss of the ability to divide - proliferating cells such as stem
cells in hematopoietic system or intestinal epithelium
loss of reproductive integrity - “reproductive death”

5. Mechanism of cell death
Apoptosis
Mitotic
Bystander effect
Autophagic death

6. Apoptosis
 It is a Greek word that means programmed cell death.
 Apoptosis occurs in normal cell and can be induced in tumour cell by
irradiation.
 In the case of tumor cell it is cell type dependent.
 Apoptosis occurs in particular in certain cell lines after low dose of
radiation , eg. Lymphocyte, serous salivary glands ,certain cells in
testis and intestinal crypts.

7. Mitotic death
 Reproductive cell death is a result of mitotic catastrophe,
which can occur in the first few cell division after
irradiation.
 The mitotic death is the most common radiation induced
cell death and it is due chromosomal aberrations.
 The irradiated cells may undergo cell cycle and they may
die in the first or second mitotic cycle , while attempting
division.

8. Bystander effect
 When a population of cell is irradiate , the cells surrounding
the irradiated cell population are also affected and this
effect is called radiation – induced bystander effect (RIBE).
 This effect is true for α , proton and soft x-rays.
 Laboratory study with low –LET radiation reveals that the
irradiated cells secrete molecules/chemicals which are
capable of killing cells.

9. Autophagic cell death
 Autophagy is a self digestive process that uses lysosomal
degradation of long –lived proteins and organelles to
maintain cellular mechanism of cells.
 Chemotherapeutic agents and radiotherapy can induce
autophagy and autophagic cell death.

13. Relevant Dose
 100 Gy --
destroys cell function in non-proliferating systems (for
example: nerve, muscle cells)
 2 Gy --
mean lethal dose for loss of proliferative capacity for
proliferating cells

14. Survival
 Conversely - “Survival” means retention of reproductive
integrity.
 the capacity for sustained proliferation in cells that
proliferate.

15.  Proof of reproductive integrity - the capability of a
single cell to grow into a large colony, visible to the
naked eye.
 A surviving cell that has retained its reproductive
integrity and is able to proliferate indefinitely is said to
be clonogenic

16. Estimating Survival
In order to determine the surviving fraction, we must know
the plating efficiency.
PE is the percentage of cells (in control batch) that grow
into colonies.
(in other words, those cells that survive the plating
Process)

17. Derivation of Survival Curves
1) Cells have been taken
from stock culture and
placed in seed dishes.
2) Then irradiated (0 Gy
to 6 Gy)and allowed to
grow into colonies for
1-2 weeks’
3) Colonies have been
counted for survival
data
Always will have a control
batch to determine PE.

18. • 100 cells are seeded into an
unirradiated culture, and 10
colonies are formed, then the
PE is 10%.
• If there are 5 colonies after
a 450 cGy dose of radiation,
. Thus, the SF of 450 cGy
is 0.5%.

19. Quantization of cell killing
 A dose of radiation that
introduces an average of one
lethal event per cell leaves
37% still viable is called D0
dose.
 Cell killing follows exponential
relationship. A dose which
reduces cell survival to 50%
will, if repeated, reduce
survival to 25%, and similarly
to 12.5% from a third
exposure.
 This means Surviving fraction
never becomes zero.

20.  A straight line results when cell
survival (from a series of equal dose
fractions) is plotted on a logarithmic
scale as a function of dose on linear
scale.
 The slope of such a semi-logarithmic
dose curve could be described by the
D0, the dose to reduce survival to 37%,
D50, the dose to reduce survival to
50%, the D10, the dose to reduce
survival to 10%.
 D0 usually lies between 1 and 2 Gy
 D10= 2.3 x D0

21. Survival Curve Shape
general shapes of survival curves for mammalian cells exposed to radiation –
Initial portion has a shoulder
and terminal portion become
straight line.
 In low dose region ,some
dose of radiation goes
waste.
 Terminal portion follow
exponential relationship
means same dose increment
result into equal reduction in
surviving fraction.

22. Mammalian Cell Survival Curve
 Shoulder Region
Shows accumulation of SUBLETHAL
DAMAGE.
 The larger the shoulder
region, the more dose will
initally be needed to kill the
same proportion of cells.
 Beyond the shoulder region
The D0 dose, or the inverse of
the slop of the curve, indicates
the relative radiosensitivity.
The smaller the D0 dose, the
greater the radiosensitivity.

23. Survival Curve Features
 Simple to describe qualitatively
 Difficulty lies in explaining underlying biophysical events
 Many models have been proposed
 Steepness of curve represent the radiosensitiveness.

24.  The shape pf the survival curve varies with linear energy transfer
(LET) of the radiation.
 At high LETs, such as alpha particals or low energy neutrons , the
curve is a straight line.
 For sparsely ionizing radiation (low lets) such as x rays the curve starts
out straight with a finite initial slope; that is surviving fraction is
aexponential of the dose.