Radiology module 2
deterministic effect
- above the threshold, those effects in which the severity of the damage in the tissue increases with dose - example: radiation-induced cataracts on the lens of the eyes.
factors that contribute to candidiasis
- hyposalivation resulting from radiation damage to the salivary glands - tissue damage caused by radiation - induced oral mucositis - dietary impairment - inability to maintain good oral hygene
xerostomia treatment
-radioprotectant medication (as amifostine (Ethyol) -saliva substitues and mouth rinses (hyetellose, hyprolose, or carmellose) -Other ways to stimulate the salivary glands, such as sucking on sugar-free candy or chewing sugarless gum Patients should be advised to visit dentist at least 2 weeks before starting radiation treatment and may be placed on fluoride supplements to control dental caries
In what two ways is radiation therapy used?
1. to cure cancer -destroy tumors that have not spread to other parts of the body -reduce the risk that cancer will return after surgery or chemo 2. to reduce symptoms - shrink tumors affecting quality of life -alleviate pain by reducing size of tumor
how long after radiation therapy do taste receptors recover and become functional?
6-8 weeks zinc sulfate supplements have been reported to help
biological effects of ionizing radiation may be divided into which two categories?
Direct and indirect
developmental effects of radiation on fetus per stage of development
First 2 weeks: Embryonic death and miscarriage From 3rd to 8th week: Congenital malformations, Miscarriage From 9th week until birth: Mental retardation, microcephaly, stunting of growth.
early effects of ionizing radiation
Following a whole body high dose exposure to ionizing radiation, greater than 100 rad within a few hours or days, there is nausea, vomiting and diarrhea during a period called the prodromal period
nervous syndrome
Grater than 5000 rad, the central nervous system syndrome will manifest.
gastrointestinal syndrome
If the dose is greater than 1000 rad but less than 5000 rad, the gastrointestinal syndrome will manifest
hematologic syndrome
If the dose is greater than 200 rad but less than 1000 rad, the hematologic syndrome will manifest
late radiation effects
If the dose is not enough to produce illness, the person is not in danger of a manifest illness; however, there is a high risk of disorders that are collectively called late radiation effects.
what is the decay pattern in radiation caries
Incisal edges, cusp tips and cervical areas are the involved surfaces. The lesion begins as diffuse demineralization that encircles the tooth and causes it to break off at the gingival margin. Black lesions are also common.
in which phase are cells most resistant?
Late S phase
in which phase are cells most radiosensitive?
M and G2
chronic or late complications of radiation therapy of the oral cavity after therapy has ended.
Mucosal fibrosis and atrophy. Decreased saliva secretion and xerostomia Accelerated dental caries related to compromised saliva secretion. Infections (primarily candidiasis). Tissue necrosis (soft tissue necrosis and osteonecrosis). Taste dysfunction (dysgeusia/ageusia). Muscular and cutaneous fibrosis. Dysphagia
acute complications of radiotherapy in the oral cavity
Oropharyngeal mucositis Sialadenitis and xerostomia. Infections (primarily candidiasis). Taste dysfunction.
latent period
Shortly thereafter the symptoms diminish and there is no outward evidence of radiation sickness
T/F younger patients tend to develop oral mucositis more often than older patients and heal more rapidly too.
T. This appears to be due to the more rapid rate of basal cell turnover noted in children.
The stages of the cell cycle are important to us for mainly two reasons:
The cell's stage is one of the determining factors of radio-sensitivity During metaphase of mitosis chromosomal damage can be evaluated
what are the radiographic characteristics of osteoradionecrosis
The radiographic appearance is similar to osteomyelitis Is common in the posterior mandible The borders are ill defined in the periphery Presents resorption of bony cortex The affected area presents sclerotic bone appearance
How does radiosensitivity of living tissue vary?
The stem cells are radiosensitive The more mature a cell is, the more resistant to radiation it is. The younger tissues and organs are, the more radiosensitive they are When the level of metabolic activity is high, radiosensitivity is also high As the proliferation rate for cells and the growth rate for tissues increase, the radiosensitivity is also increased.
mucositis
a general term referring to the inflammatory reaction and ulcerative lesions of the mouth and oropharynx that occur secondary to RT and certain chemotherapy agents. is probably the most common, debilitating complication of cancer treatments, particularly chemotherapy and radiation pain, nutritional problems as a result of inability to eat, and increased risk of infection due to open sores in the mucosa The atrophic changes in the epithelium of the oral membrane usually occur at a total dose level of 1600 to 2200 cGy when radiation is administered at a rate of 200 cGy per day
radiation therapist
administers the daily radiation under the doctor's prescription and supervision
benefits of fractioning over using a single large dose
allows more tumor destruction, allows time for cells of normal tissue to repair
teratogen
an agent that causes congenital birth defects, ionizing radiation is one of the most potent teratogens ( effect dependent on stage of embryonic development more than radiation source)
what is the primary mechanism of biological damage to macro molecules from ionizing radiation?
an indirect interaction that begins with the radiolysis of water
examples of chromatid aberrations
anaphase bridge, isochromatid deletion, paracentric inversion.
when does osteoradionecrosis happen?
at least 3 months after the delivery of the radiation therapy, dose above 50 Gy cause irreversible damage.
internal radiation therapy
brachytherapy or seed implants - involves placing radioactive sources inside the patient. This places radiation sources close to the tumor so large doses can hit the cancer cells. It allows minimal radiation exposure to normal tissue. The radioactive sources can be thin wires, ribbons, capsules or seeds
what are the most important concerns considered to be late effects of low dose ionizing radiation
carcinogenesis and genetic effects
candidiasis
colonization of yeast on damaged tissue
common chromosomal abberations
deletion, duplication, inversion and trisomy
external beam radiation
delivers radiation using a linear accelerator
stochastic effects
effects in which the severity of the damage is not dose related but the probability of occurrence increases with dose. there is no threshold. example: cancer
The initial interaction between ionizing radiation and matter occurs at the level of the _______ within the first 10^-13 seconds after exposure
electron
medical radiation physicist
ensures that complex treatment plans are properly tailored for each patient
how does mucositis present? clinical manifestation.
erythema, ulceration, or a spotted or confluent pseudomembrane over the irradiated tissue resulting from aggravated hyperemia and edema
In what tow ways can radiation be delivered?
external beam radiation internal radiation therapy
late effects of radiation
from 6 months -years examples: cataracts, second malignancies
bone that has been irradiated is ___________ and __________________.
hypo-cellular and hypo-vascular
osteoradionecrosis
inflammatory condition of bone that occurs after the bone has been exposed to therapeutic doses of radiation usually given for head and neck radiotherapy
radiolysis of water
ionization of water molecules causes them to split, a cascade of chemical transformation that result in the formation of free radicals
classic triad of radiation effects on the embryo
lethal effects, congenital malformation, growth effects
chronic hyperplastic candidiasis
leukoplakia like plaques the do not wipe away
what are the phases of the cell cycle for mammalian cells
mitosis, GI, DNA synthetic phase (S), G2
Sulfhydryls
natural radio-protectors tend to be at their highest levels in S phase and lowest near mitosis.
xerostomia
occurs when salivary glands do not make enough saliva to keep the mouth moist
chromatid aberrations:
occurs when the dose of radiation is given later in interphase, after the DNA material has doubled and the chromosomes consist of two strands of chromatin (G2 and late S)
clinical manifestations and symptoms of osteoradionecrosis
pain swelling reduced mobility of the jaw drainage exposed bone in the maxilla and/or mandible bone destruction
late effects of ionizing radiation
potential effects of low dose ionizing radiation primarily from scatter
Law of bergonie and tribondeau
radiosensitivity is a function of metabolic state of the tissue irradiated
pseudomembranous candidiasis
removable white plaques with erythematous base
early effects of radiation
resolve during irradiation first 3-4 months examples: skin and gut reactions, bone marrow depletion
chromosomal aberrations
result if a cell is irradiated early in interphase before the chromosome material has been duplicated ( in G1 or early S phase)
what are the effects of radiation on a fetus during the period of organogenesis
skeletal and CNS disorders
radiation therapy
the art of using ionizing radiation to destroy malignant tumors while being able to minimize damage to normal tissue
What is the most sensitive part of the nucleus?
the chromosomes
radiation oncologist
the doctor who oversees the radiation therapy treatments
direct effect
the initial ionization event occurs on a particular sensitive molecular structure such as DNA
Indirect effect
the initial ionizing event occurs on a noncritical molecule such as water, that transfers the energy of ionization to the target molecule
threshold dose
the minimum dose of radiation that produces a detectable biological effect
which type of salivary gland cell is most damaged by radiation therapy?
the ones that produce serous saliva, leaving behind thick and sticky saliva
Radiobiology
the study of the effects of ionizing radiation on living organisms
radiation caries
tooth decay that results from radiation-induced xerostomia
dosimetrist
works with the radiation oncologist and medical physicist to calculate the proper dose of radiation given to the tumor. - employs a 3-D computer model to calculate exactly where and how to distribute the radiation.
