and protection
X- ray has harmful effects on the cells, tissues, and the whole body. That’s why for operator and patient the amount of radiation absorbed by their bodies must be as small as possible.All the living subjects in our body composed of (atoms) these atoms arranged together in a particular fashion known as (molecules) each atoms has electrical stability (number of - ve charge equal to the number of + ve one) and when X- ray photon strikes a – ve electron in the atom of living subjects (tissues) it displace the electron leaving the atom electrically unbalance so the atom ionized such process called (ionization), now this ionized atom has a strong tendency to seek its stability by accepting a –ve electron from some where else and by doing so a new chemical is form and the cell of which the atoms and molecules are parts can be altered. So basic effects of ionization are:-X-ray photon Ionization interacts Excitation with tissue Break bonds
Chemical changes
Biological changesX-ray photons interact with Ionization Free radical formation water in cells x-ray photons
H2O H+ H+ H2O OH- O- H2O OH- H+ OH-
IONIZATION
Free radicals Combine Toxins such ( as H2O2)
1. Direct effect: - Those effects occurred in specific area of the body where all exposed cells in this area are altered directly by ionization process and death occurred at the time of mitotic cell division. 2. Indirect effect:- It happened in several ways where new chemicals result from process of ionization are incompatible with body tissues example conversion of water to H2O2 which cause cellular dysfunction also X- radiation can alter the chemical composition of hormones, enzymes and other body secretions make them partially or to tally ineffective such indirect effects depend on the amount of exposure to X- ray.
Tissue variability: - Body tissues differ in their susceptibility to ionizing radiation. * The following tissue and organs are listed in order to their susceptibility to X-ray:- 1. Blood forming tissues and reproductive cells. 2. Young bone glandular tissue and epithelium of alimentary canal. 3. Skin and muscles 4. Nerve tissue and adult bone.
Latent period:- Is a period of time interpose between exposure to X-Ray and clinical symptoms. Such period varies with the dose. So the more is sever dose the shorter is the latent period some time the latent period is as long as 25 years for some minimum doses. * Radiation to genetic tissues:- The effect of ionizing radiation is on the (genes) of reproductive cells. The number of gene alterations in one generation which are passed to the next generation can be increased by further exposure to X-ray and the [altered gene] appears to be recessive in character.
* Radiation of somatic tissues:- These tissues include all the cells of the body other than reproductive cells now the effect of ionizing radiation on these tissues include ((alteration or destruction)) of particular cells.
* Protection of patients from x-ray:- this done by several ways:- 1. By using faster films (film speed) because the faster the film the less is the amount of radiation required to produce a radiographic image so it need less exposure time. 2. Collimation: - This done by collimating device to prevent the un necessary beam divergence. 3. filtration:- In order to absorb be the long wave length X-ray photons (soft radiation) which have no diagnostic value.
4. Exposure and developing techniques: In order to prevent exposure of patient to much more radiation, we should know the exposure time for each segment of the jaw. So for anterior teeth the exposure time is 0.36 seconds for premolars is 0.40 seconds while for molars is 0.50 seconds if higher kV. Technique is used its possible to use a constant exposure time for whole dentition. * Exposure time required for child and old people may have be decreased as much as 50% while exposure time required for dense and thick objects may have to be doubled. Some time when we use excessive long exposure time we have to decrease the developing time to get acceptable quality of radiographic image
5. Distance and kV:- the purpose of using cylinders and cones in the X-ray machine is to [limit the path for X-ray] so X-ray beam hit only the examined area we have 2 types of cone:- open end cone and pointed closed cone the last one is contraindicated now because it cause greater radiation dose exposed to the patient with a lot of scattered radiation while in open type cone we have 2 cone length (8and 16 inches) the long cone mean increase tube film distance and when use higher kV. With this cone we reduce the radiation dose absorbed by skin surface but increase the deep radiation absorption and this is useful in therapeutic purpose.
6. Film placement and angulation:- This is important to prevent retakes and get a radiograph with best diagnostic in formation.7. Lined cylinder: - Sometime lining the open cylinder by sheet of lead foil with 0.2 – 0.3 mm thickness result in elimination of scattered radiation.
8. Protective apron: - Sheet of lead used to cover chest and reproductive areas of the patient so must be used in pregnant and young adult.
It is estimated that a typical full-mouth intraoral examination, using D-speed film and round collimation, gives the patient the equivalent of 7 days of environmental background exposure. In contrast, by using F-speed film and rectangular collimation for a full-mouth exam, the patient receives the equivalent of 1.2 days of background exposure . A typical panoramic examination gives the equivalent of about one day; and the usual 4-film (D-speed film) bite-wing study (round collimation), the equivalent of 7 hours or approximately three tenths of a day. Note that other common procedures in medical radiology deliver much larger doses to the patient than dental X-ray studies.
Protection of the operator Operator received secondary radiation and generally workers in X-ray clinic should not received more than 5 rem of whole body radiation each year.
To minimize the exposure the operator:- 1. position:- Operator must stand behind the patient because the head of the patient will absorb scattered radiation operator must stand with an angle of 90 - 135˚ to the radiation beam because in this area we have less scattered radiation.2. Distance: - The intensity of radiation inversely proportional to the distance (inverse square law) so it's recommended for him to stand 6 feet away from the source of X-ray radiation.3. Barrier:- It interpose between the source of radiation and the operator it is the most effective method of providing safety to the operator and barrier is made of 2mm of lead , steel , concert ,or barium plaster of 1/16 inch.
X-ray tube head Primary beam
Patient 90 Degree (6 feet) Radiographer135 Degree
* Film badgesThey consist of:- A. Blue plastic frame containing a variety of metal filters and a small radiographic film which exposed to X-ray.B. It provide a permanent record of the dose received and it used for 1 – 3 months before being processed.
Monitoring devices. A Personal monitoring film badge. B Personal monitoring TLD badge. C lonization bleeper. D TLD extremity monitor.