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Змістto pay attention to importance of deontological, ethics moments of radiotherapy of oncological patients l
V. Plan and organizatio of practical lesson
L = ii-iii
5.2.2. Basic stage
Radiation effects on living tissue
Organ Dose Weighting Factors
6.1. Place of conducting of lesson
6.3. Materials of control of base (initial level) preparation of students
Methodical Instruction of practical lesson № 1
Theme: Radio-activity and dose. Dosimetry of ionizing radiation: units and methods of determination of radio-activity and dose of radiation. Structure of radiometers and dosimeters.
I. Actuality of theme:
In connection with a practical necessity to get quantitative and qualitative description of ionizing radiations there is a branch of sciense - dosimetry.
By means the dosimetry solves such a basic questions:
1. Searching the source of radiation, determinations of kind, quantities and energies of radiation.
2. Determination of level of influencing of radiation on an object, that is exposed to the rays.
3. Control of protective facilities and devices, that are used for providing of radiation safety of auxiliary personnel and patients.
ІІ. Training purpose:
2.1. A student must know:
2.2 To Be Able:
ІІІ. Educational purpose:
IV. Intersubject integration.
5.1. Duration of lesson - 2 hours.
5.2. Stages of lesson (table):
5.2.1. Preparatory stage:
At the beginning of lesson a teacher acquaints students with the basic tasks of lesson, plan. For the control of initial level of knowledges of students to each of them the list of tests is offered. The analysis of basic properties of ionizing radiation is conducted.
Radiation dosimetry is the calculation of absorbed dose in matter and tissue resulting from the exposure to ionizing radiation. It is a scientific subspecialty in the fields of health physics and medical physics that is focused on the calculation of internal and external doses from ionizing radiation.
Dose is reported in gray (Gy) for matter or sieverts (Sv) for biological tissue, where 1 Gy or 1 Sv is equal to 1 joule per kilogram. Non-SI units are still prevalent as well, where dose is often reported in rads and dose equivalent in rems. By definition, 1 Gy = 100 rad and 1 Sv = 100 rem.
The distinction between absorbed dose (Gy) and dose equivalent (Sv) is based upon the biological effects of the radiation in question and the tissue and organism irradiated. For different types of radiation, the same absorbed dose (measured in Gy) may have very different biological consequences. Therefore, a radiation weighting factor (denoted wr) and tissue/organ weighting factor (WT) have been established, which compare the relative biological effects of various types of radiation and the susceptibility of different organs.
By definition, the weighting factor for the whole body is 1, such that 1 Gy of radiation delivered to the whole body (i.e. an evenly distributed 1 joule of energy deposited per kilogram of body) is equal to one Sievert (for photons with a radiation weighting factor of 1, see below). Therefore, the weighting factors for each organ must sum to 1 as the unit Gray is defined per kilogram and is therefore a local effect. As the table below shows, 1 Gray delivered to the gonads is equivalent to 0.25 Gy to the whole body - in this case, the actual energy deposited to the gonads, being small, would also be small.
Radiation dose refers to the amount of energy deposited in matter and/or biological effects of radiation, and should not be confused with the unit of radioactive activity (becquerel, Bq). Exposure to a radioactive source will give a dose which is dependent on the activity, time of exposure, energy of the radiation emitted, distance from the source and shielding. The equivalent dose is then dependent upon the weighting factors above. Dose is a measure of deposited dose, and therefore can never go down - removal of a radioactive source can only reduce the rate of increase of absorbed dose, never the total absorbed dose.
The worldwide average background dose for a human being is about 3.5 mSv per year , mostly from cosmic radiation and natural isotopes in the earth. The largest single source of radiation exposure to the general public is naturally-occurring radon gas, which comprises approximately 55% of the annual background dose. It is estimated that radon is responsible for 10% of lung cancers in the United States.
There are several ways of measuring doses from ionizing radiation. Workers who come in contact with radioactive substances or may be exposed to radiation routinely carry personal dosimeters. In the United States, these dosimeters usually contain materials that can be used in thermoluminescent dosimetry (TLD) or optically stimulated luminescence (OSL). Outside the United States, the most widely-used type of personal dosimeter is the film badge dosimeter, which uses photographic emulsions that are sensitive to ionizing radiation. The equipment used in radiotherapy (linear particle accelerator in external beam therapy) is routinely calibrated using ionization chambers.
Because the human body is approximately 70% water and has an overall density close to 1 g/cm3, dose measurement is usually calculated and calibrated as dose to water. National standards laboratories suh as the NPL provide calibration factors for ionization chambers and other measurement devices to convert from the instrument's readout to absorbed dose. The standards laboratories operate a Primary Standard, which is normally calibrated by absolute calorimetry, the warming of substances when they absorb energy. A user sends their Secondary Standard to the laboratory, where it is exposed to a known amount of radiation (derived from the Primary Standard) and a factor is issued to convert the instrument's reading to that dose. The user may then use their Secondary Standard to derive calibration factors for other instruments they use, which then become Tertiary Standards, or field instruments. The NPL in the UK operates a graphite-calorimeter for absolute photon dosimetry. Graphite is used instead of water as its specific heat capacity is one-sixth that of water and therefore the temperature rises in graphite are 6 times more than the equivalent in water and measurements are more accurate. Significant problems exist in insulating the graphite from the laboratory in order to measure the tiny temperature changes. A lethal dose of radiation to a human is approximately 10-20 Gy. This is 10-20 joules per kg. A 1 cm3 piece of graphite weighing 2 grams would therefore absorb around 20-40 mJ. With a specific heat capacity of around 700 Jkg-1K-1, this equates to a temperature rise of just 20 mK.
5.3. Control questions to the theme of lesson:
5.4. Final stage.
The control of solution of tasks and eventual level of knowledges is conducted by their verification and raising of questions of practical direction. Rating of mastering the material of theme is depends on theoretical knowledges, practical skills, independent work of studrnt.
In a result a teacher considers typical errors which are assumed by students at implementation of self-education work and assigns to a next lesson. A teacher sets the homework, recommends literature after the theme of the following lesson^: basic and additional.
VІ. Materials for the methodical providing of employment.
VІ. Materials for the methodical providing of lesson.
^ class room, department of radial therapy.
6.2. Material providing of lesson:
^ to the test of task.
Tests for determination of initial level of knowledges
1. What is unit of radioactivity?
а) coulomb/ kg;
2. What is “sievert”?
а) unit of expositive dose;
б) unit of secondary radiation;
в) unit of effective dose;
г) unit of equivalent dose;
3. What is a unit of absorbed dose?
a ) roentgen;
б) coulomb /cg;
4. For scintillation dosimets it is nessasory to have:
а) vacuum photocells;
в) photoelectronic multipliers;
5. What limit of effective dose inherent to the personnel of category A at the radiation of all body?
а) 20 mSv/ year;
б) 150 mSv/ year;
в) 30 mSv/ year;
г) 15 mSv/ year;
д) 5 mSv/ year.
6 To the category of patients of BD patients belongs patients with:
а) the lung cancer;
б) the cirrhosis of liver;
в) the metastases of breast cancer;
7 Correlations between two doses
а) 100 Gy= 1 rad;
б) 0 Gy= 1 rad;
в) 1 Gy= 10 rad;
д) 1 Gy= 100 rad;
9. Correlations between two doses
а) 1 Sv= 100 ber;
б) 1 Sv= 10 ber;
в) 100 Sv= 1 ber;
д) 1000 Sv= 1 ber.
10. Most penetrating power or ionizing radiation:
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