fundamentals of radiobiology, biological effects of radiation - part 2

deterministic effects occur when:

enough cells in an organ and tissue are killed or prevented from functioning normally

the threshold for deterministic effects is..

the level where symptoms will appear in 1% of those exposed

above the threshold, the severity of the effect increases with dose. the curve will plateau when the effect is so severe that the organ/tissue is no longer viable

the threshold dose varies with:

• organ affected

• confounding factors such as:
  health
  age
  smoking

threshold doses for deterministic effects

systemic effects may be…

morphological and/or functional

according to radiosensitivity laws (bergonie and tribondeau), the most radiosensitive cells are…

from the basal stratum of the epidermis

skin reactions

hair loss

temporary hair loss can occur approx. 3 weeks after exposure of 2-5 Gy, with regrowth beginning approx. 2 months later (complete regrowth in 6-12 months)

the [1] of the eye is very radiosensitive and surrounded by [2]

1- lens

2- highly radiosensitive cuboid cells

there are 2 basic effects from radiation damage to the eye:

cataractogenic radiation damage starts at…

the anterior surface

(lens of the eye) radiation damage results in

aberrant crystalline protein folding and dysregulation of lens cell morphology

[1] was thought to be the only typical lesion related to radiation damage to the lens but recent data suggest that radiation induced opacities can be found in the [2] as well

1- posterior subcapsular (PSC) opacification

2- the lens cortex

reproductive organs - testes. the testes contain both radiosensitive cell populations [1] and radioresistant cell populations [2]

1- spermatogonia

2- mature spermatozoa

the primary effect on the male is temporary [1] or permanent sterility [2]

1- acute doses of 2.5 Gy

2- 6 Gy

reproductive organs - ovaries. the [1] within ovarian follicles are radiosensitive. the [2] are the most radiosensitive, then [3], with the [4] being the least radiosensitive

1- ova

2- intermediate follicles

3- mature follicles

4- small follicles

reduces fertility can occur after exposure to ionizing radiation [1]. permanent sterility can occur after doses of greater than [2]

1- 1.5 Gy

2- 3 Gy

the [1] is one of the main organs affected by irradiation injury

1- hematopoietic system

exposure to radiation can cause [1] and [2] due to the [3] that can self-renew and differentiate into all types of blood cells

1- acute myelosuppression

2- long-term hematopoietic injury

3- direct or indirect damage of hematopoietic stem cells (HSCs)

there are 3 kinds of effects from antenatal exposure:

1- lethality

2- congenital anomalies

3- large delay effects (cancer and hereditary effects)

lethal effects can be induced by [1] before or immediately after [2]

1- 0.1 Gy or less

2- implantation of the embryo into the uterine wall

an embryo is a few non-specialized cells:

[1] if a few cells are killed…

[2] if too many cells are damaged

1- the remaining embryonic cells replace the cells lost (within a few cell divisions) with no adverse effects

2- the embryo fails to implant and is resorbed

it is likely a potential pregnancy would not be identified

effects of antenatal exposure - congenital anomalies

intellectual disability

• ICRP notes that intellectual disability can be induced by radiation (iq score < 100)

• can occur during the most radiosensitive period (8-25 weeks)

• reduction in iq of 25 points per Gy

• there is no known link with down syndrome

effects of antenatal exposure - congenital anomalies

8-15 weeks vs 15-25 weeks

8-15 → severe intellectual disability with a risk factor of 0.4/Sv

15-25 → severe intellectual disability with a risk factor of 0.1/Sv

effects of antenatal exposure - large delay effects

both somatic effects and genetic effects can occur as a result of antenatal exposure

acute radiation syndrome (radiation poisoning) is..

a combination of clinical syndromes occurring in stages, hours to weeks after exposure as injury to various tissues and organs is expressed

ARS occurs if the exposure:

1- is acute

2- involves the whole body or a large portion of it

whole body response (to acute radiation syndrome). steps:

1- prodromic (onset of disease)

2- latency

3- manifestation

what is the lethal dose 50/30?

the dose which would cause the death of 50% of the population in 30 days

its value is about 2-3 Gy for humans for whole body radiation

timescale of radiation damage

1- delayed tissue reactions from exposure are seen within:

• weeks, e.g. skin erythema

• years, e.g. cataracts

• decades, e.g. cardiovascular disease

2- cancer induction is a late effect:

occurs years or decades after mutation

3- heritable effects is also a late effect:

• have not been seen in children of irradiated parents

• have been observed in plant/animal studies

• will require further research using sensitive dna based methods

time of events leading up to radiation effects