Biological Effects of Radiology

Question 1

interactions of xrays with matter

Answer 1

incident xray => beam attenuated (reduced in intensity) c through interactions with tissue => remnant beam strikes receptor to create image

Question 2

attenuation

Answer 2

1) individual photons in the beam can be absorbed by atoms in the tissues
- cease to exist after absorption interactions
2) scattered out the beam with tissue atoms
- theyll move in a different direction
3) absorption
- more likely in bone
4)scattering
- more likely in soft tissue

Question 3

percent of interactions

Answer 3

1) 9% no interaction
2) 7% coherent scattering
3) 27% photoelectric absorption
4) 57% compton scattering

Question 4

photoelectric absorption

Answer 4

1) incident photon interacts with electron in inner orbital
2) atom is ionized and inner electron is ejected
- photoelectron
3) travels short distance before it gives up energy through secondary ionization

Question 5

characteristic radiation

Answer 5

1) released when the electron deficiency is filled
2) low energy absorbed by the patient, not contribute to image degradation

Question 6

radiographic contrast

Answer 6

1) differential absorption in various tissues and objects (restorations)
2) probability of photoelectric absorption in bone is 6.5x greater than in equal thickness of soft tissue
3) different degrees of radiopacities on the image is due to differential photoelectric absorption of photons in those structures

Question 7

compton scatter

Answer 7

1) incident photon collides with outer orbital electron
2) the outer orbital electron receives some kinetic energy from the photon and recoils
3) ionization
4) path of incident photon is deflected and scattered in a new direction
- additional ionizations at tissue sites outsize the circumference of the incident beam
5) we dont like it
- more radiation exposure
- degrades image contrast
6) independent of atomic #

Question 8

coherent scatter

Answer 8

1) low energy incident photon interacts with a whole atom
2) momentarily excited and the incident photon ceases to exist
3) excited atom returns to the ground state and generates another photon with the same energy as incident photon
- but at a different angle
4) insignificant bio effects and image degradation

Question 9

biological effects of ionization radiation

Answer 9

1) direct actions
2) indirect actions
3) both yield unstable free radicals

Question 10

direct actions

Answer 10

1) photon directly interacts with and ionized a biological macromolecule
2) secondary electrons may also interact

Question 11

indirect actions

Answer 11

1) photons and secondary electrons interact with water
2) 2/3 of the biological damage due to hydroxyl radical

Question 12

double strand breaks

Answer 12

1) detrimental event for cell killing, tumors, and inheritable effects
2) repair mechanisms is very ERROR prone
- nonhomologous end joining and homologous recombination
3) most important

Question 13

damage clusters

Answer 13

1) though to be critial lesions, responsible or cell killing ,carcinogenesis, and heritible effects
2) can be causes by a single xray photon

Question 14

DNA aberrations

Answer 14

1) occur due to failure of chromosome to rejoin
2) chromosome aberration
- DNA strand break occurs prior to chromosomal duplication
- the break is replicated
3) chromatid aberration
- DNA strand break occurs after
- only in one sister chromatic
–
basically, cause cell death OR tumor induction and heritable effects

Question 15

stochastic effects

Answer 15

1) no dose threshold
2) diagnostic radiation place at risk
- but either you have it or not
3) sublethal DNA changes
- ex. survives with mutation
4) type of cell damaged has effect on the manifestation
- germ cell = heritable
- cell growth cell = carcinogenesis

Question 16

deterministic effects

Answer 16

1) manifest only when radiation dose exceeds a certain threshold
2) once past threshold, pretty much everyone will have the effect

Question 17

stochastic effects are though to occur without a dose threshold

Answer 17

1) a single xray photon has the potential
2) smallest dose COULD cause heritable effect or cancer
4) but the probability increases with dose

Question 18

radiation induced cancer

Answer 18

1) clinically and histologically indistinguishable from other cancers
2) certain tissues are more sensitive to it
3) long latent period between radiation exposure and cancer
- years to decades
4) higher in children than adults
- 3x

Question 19

main radiation induced cancers

Answer 19

1) leukemia
- exposed bone marrow to radiation
- highest risk in children up to 7
2) thyroid chancer
- highest risk in children
- females 2-3x more susceptible
3) salivary gland tumors
- incidence of both benign and malignant tumors is increased in patients treated with H&N radiation and atomic bomb survivors

Question 20

breast cancer

Answer 20

1) female breast tissue is highly sensitive to radiation induced cancer
2) linear relationship between risk and dose
3) higher risk before 20

Question 21

brain and nervous system cancer

Answer 21

1) in utero and to therapeutic doses in childhood and adulthood show higher incidence of malignant and benign tumors
2) association between intracranial meningiomas and previous radiography

Question 22

risk and age

Answer 22

1) risk for younger patients

Question 23

heritable effects of radiation

Answer 23

1) result from DNA damage in germ cells
2) information from atomic bomb survivors
- no significant adverse outcomes in the offspring of the survivors
3) it is possible that damage occurs at low frequence

Question 24

deterministic effects

Answer 24

1) need threshold dose to manifest
- higher the dose, more severe the effect
2) the dose from diagnostic radiation is less than threshold dose

Question 25

general rule of organ sensitivity

Answer 25

1) rapidly dividing cells are more radiosensitive
2) post mitotic specialized cells are more radioresistant
3) relevant exceptions (due to death by apoptosis instead of mitotic deth
- lymphocytes are more sensitive
- serous acini of salivary glands are as well

Question 26

deterministic radiation effects on embryos and fetuses

Answer 26

1)embryos and fetuses are mroe sensitive
2) preimplantation (0-9 days)
- 100 mGy (14,000x higher than the fetal dose)
- embryonic death
3) 8-25 weeks
- 0.3 Gy (42,000x higher than fetal dose)
- microcephaly and mental retardation

Question 27

radiotherapy involving oral cavity

Answer 27

1) H&N is administered by fractions
-greater tumor destruction
- increases cellular repair
- increase mean oxygen tension in the tumor
- helps generate free radicals to kill cancer cells
2) 2Gy is delivered daily for a weekly exposure of 10 Gy until a total of 60-70 Gy

Question 28

oral complications for H&N radiation therapy

Answer 28

1) any changes that last 2 years, pose lifelong risks

Question 29

mucositis`

Answer 29

1) discomfort is most severe at the end of therapy
2) typically heals after 2 months
3) lasting effects: fibrotic underlying CT, which can cause ulcerations
4) ulcerations may represent tumor recurrence
- biopsy

Question 30

taste buds

Answer 30

1) loss of taste 2-3 weeks of radiotherapy
2) decreases by factor of 1000-10000 during the treatment
3) typically bitter and acid
- posterior 2/3
4) salt and sweet
- anterior 1/3
5) reversible in about 2-4 months

Question 31

salivary glands

Answer 31

1) 50% reduction in salivary flow in the first week of radiation therapy
2) parotid > radiosensitive than submandibular
3) xerostomia results from a loss of saliva production

Question 32

radiation caries

Answer 32

1) radiation induced xerostomia
2) widespread lesions at buccal, occlusal, incisal, and palatal
- more common
3) more likely to have PA inflammation and disease

Question 33

tooth development

Answer 33

1) effect depends on stage of tooth development
2) early development may destroy tooth bud
3) or later, arrested development
4) eruptive mechanism is relatively radiation resistant
5) failure to form tooth, root, or dwarfed teeth

Question 34

osteoradionecrosis

Answer 34

1) damage to vasculature of periosteum and cortical bone
2) this is devitalized area of irradiated bone
- 5-7% incidence for conventional radiotherapy, IMRT, and brachytherapy
3) unlikely when dose <60 Gy
4) can develop anytime after the therapy
- often 6-12 mo
5) mandible is more susceptible due to lower vascularity

Question 35

osteoradionecrosis features

Answer 35

1) widening of PDL
2) lytic changes (radiolucent areas of bone destruction)
3) sequestrations (necrotic bone)
4) fractures

Question 36

to minimize risk of ORN

Answer 36

1) prior
- restore carious teeth
- implement oral hygiene
- consider extracting teeth with severe caries and periodontal bone loss
2) post
- monitor for disease
- minimize surgical trauma
- adjust dentures to avoid dental sores

Question 37

musculature

Answer 37

1) the muscles of mastication may experience contracture and trismus due to inflammation and fibrosis
2) masseter or pterygoid are commonly affected
3) progressive restricted mouth opening 2 mo after completion of radiation therapy