Archive for August, 2008

Acne Vulgaris: an Understanding

Acne is chronic inflammatory disease of pilosebaceous glands. It is mainly characterized by seborrhea, formation of comedones, papules and pustules. Less commonly symptom like nodules, deep pustules and in some cases scarring is seen.

Four factors are involved in pathogenesis (1) Seborrhea (increase sebum production) (2) Hyper cornification of pilosebaseous duct (3) Colonization of pilosebaseous duct by P. acne (propionobacterium acne) and (4) Inflammation.

Natural History:

The problem of acne usually starts in adolescence and in many case resolve spontaneously by mid twenties. Regarding acne, different studies show different data. In one USA study, prevalence of acne in mid teens was virtually 100%. But only 20% needed medical intervention. If the acne is mild it is called physiological acne. In females acne develop earlier than males, may be due to earlier onset of puberty. Prepubertal acne is very uncommon. In fact acne can be the first sign of puberty.

Acne resolve spontaneously but slowly in mid twenties. But in a significant proportion acne persists beyond mid twenty (25 years of age). In some countries like Denmark there is a reduction in cases of acne which may be due to use of oral contraceptives. But in many countries acne cases are increasing along with mean age of acne, which is going in the mid twenties. Factors which causes resolution of acne are not clearly understood; studies on acne are also inconclusive and due to improved management prevalence and severity of acne has reduced.

Genetic factors:

Many studies has shown that genetic factors influence acne. In a study it was seen that boys with acne had parents with acne were 45% and boys without acne had parents with acne were only 8%.

Twin studies also confirm the effects of genetic factor on acne. Comedone numbers also similar in monozygotic twins but not in dizygotic twins. Patients with persistent acne have strong family history of persistent acne. But in adolescence acne there is no or insignificant history of persistent acne. There is decrease incidence of acne in patients with atopic dermatitis may be due to less sebum production in patients with atopic dermatitis.

Racial studies provide an interesting insight of genetic and environmental factor in acne. Acne in African Americans is less than white Americans but Black Americans have more severe acne than the Japanese. In Canada acne is less among Inuits, who eat a diet rich in fish. But when they adopt western diet with more saturated fat there is marked increase in acne. Same type of changes has been observed among the Japanese who settled in Hawaii and eat American style.

The Global Magnitude of the Problem of Cancer

Cancer afflict all the communities throughout the world. At present more than 11 million people are diagnosed with cancer and more than 7 million people die due to cancer every year, throughout the world. More than 30 million people are living with cancer at present. In term of incidence, the most common cancers are Lung cancer (12.3% of all cancer), breast cancer (10.4%) and colorectal cancer (9.4%). In terms of death from cancer the most common cancers is Lung cancer (17.8% of all deaths due to cancer).

For a disease, the relationship of incidence to mortality rate is an indication of prognosis. Similar incidence and mortality rate is indication of essentially fatal condition. That is why lung cancer accounts for most deaths from cancer (1.1 million) in the world annually, because its incidence and mortality rate is similar and it is invariably associated with poor prognosis. On the other hand for breast cancer appropriate management can be effective in avoiding fatal out come. That is why although it is second in term of incidence but in terms of mortality it is ranked 5^th .

The most important feature of the distribution of cancers between sexes is the predominance of lung cancer among males. Stomach, esophagus and bladder cancers are also common among males. Usually the difference in distribution between the sexes is attributed to the difference in exposure to the causative agents rather than difference in susceptibility. For example cancers of pancreas, colorectal cancer has insignificant sex difference. So, the incidence and mortality due to cancer is not effected by sex.

Burden of cancer in different countries is different from other countries due to difference in distribution . The total cancer burden is highest in the developed countries, due to high incidence of cancer associated with smoking and western lifestyle, i.e. cancer of lung , prostate and breast. On the other hand 25% of the cancers in the developing countries are due to infectious agents e.g. Liver cancer (hepatitis B), Stomach cancer (Helicobacter pylori), and cervical cancer (Human papilloma viruse). In western countries like USA recently there is a decline of incidence and mortality due to cancer. This is due to reduction in smoking prevalence, improvement in early defection techniques and advances in cancer therapy.

In USA there is no nationwide cancer registry. So the incidence of cancer is estimated on the basis of the National Cancer Institute’s Surveillance, Epidemiology and End Results (SEER) database and also from population data from the U.S. Census Bureau. 1.445 million new cases of cancer (766,860 men, 678,060 women) were diagnosed and 559,650 persons (289,550 men, 270,100 women) died from cancer in 2007. Cancer incidence has been declining in USA by about 2% each year since 1992.

Cancer is the second leading cause of death behind heart disease. Under age 85 years cancer has overtaken heart disease as the number one cause of death.

Cancer control (Secondary prevention)

Secondary prevention comprises the following measures:

(1) Cancer registration:

Cancer registration is a sine qua non for any cancer control programme. It provides a base for planning the necessary services and for assessment of the magnitude of the problem of cancer. Cancer registries are of two types: hospital-based and population based registries.

(a) Hospital-based registries: The hospital-based registry includes all patients treated by a particular institution, both inpatients and out patients. Registries collect data as recommended by WHO in the “WHO Handbook for Standardized Cancer Registers”. If follow-up is long-term, hospital-based registries can be of considerable value in the evaluation of diagnostic and treatment programmes and also for research. Since hospital population will always be a selected population, the use of hospital-based registries for epidemiological purposes is limited.

(b) Population-based registries: The best thing to do is to set up a “hospital-based cancer registry” and extend it to a “population-based cancer registry”. 2-7 million is the optimum size of base population for population based registry. The aim is to cover the complete cancer situation in a given geographic area. The data from such registries alone can provide the incidence rate of cancer and serve as a useful tool for initiating epidemiological enquiries into causes of cancer, surveillance of time trends and planning and evaluation of operational activities in all main areas of cancer control.

(2) Early detection of cases:

Cancer screening is the main weapon for early detection of cancer at a pre-invasive (in situ) or pre malignant (cancerous) stage. Effective screening programmes have been developed for cervical cancer (Papanicolaou smear, known as pap smear), breast cancer (mammography) and oral cancer. Like primary prevention, early diagnosis has to be conducted on a large scale. But it is possible to increase the efficiency of screening programmes by focusing on high-risk groups. but there is no point in detecting cancer at an early stage unless facilities for treatment and after care are available. Early detection programmes will require mobilization of all available resources and development of a cancer infrastructure starting at the level of primary health care, ending with complex cancer centers or institutions at state or national levels (tertiary health care).

(3) Treatment:

Treatment facilities should be available to all cancer patients. Some of the cancers are amenable to surgical removal, while some others respond favorably to radiation or chemotherapy or combination of both. Since most of the known methods of treatment have only complementary effect on the ultimate outcome of the patient, multi-modality approach to cancer control has become a standard practice in cancer centers. In the developed countries cancer treatment is geared to high technology. For those who are beyond the curable stage, the goal must be to provide pain relief. A largely neglected problem in cancer care is the management of pain. The WHO has developed guidelines on relief of cancer pain “Freedom from cancer pain” is now considered a right for cancer patients.

Cancer control (Primary Prevention)

Cancer control consists of a series of measures based on present medical knowledge in the fields of prevention, early detection through screening and population education, diagnosis, treatment, after care and rehabilitation, aimed at reducing the number of new cases, increasing the number of “cures” and reducing the invalidism due to cancer.

The basic approach to the control of cancer is through primary prevention and secondary prevention. It is estimated that at least one third of all cancers are preventable. If we analyze the causes of cancer it is seen that environmental factors are the most important in causation of cancer which are modifiable. Genetic factors which are not modifiable are responsible in small number of cases of cancer.

Primary prevention:

Cancer prevention till recently was mainly concerned with the early diagnosis of the disease (secondary prevention), preferably at a precancerous stage. Advancing knowledge has increased our understanding of causative factors of some cancers and it is now possible to control these factors in the general population as well as in particular occupational groups through population education and legislation.. They include the following:

1. Control of tobacco and alcohol consumption: Primary prevention offers the greatest hope for reducing the number of tobacco induced (tobacco related) and alcohol related cancer deaths. It has been estimated that control of tobacco smoking alone would reduce the total burden of cancer by over a million cancers each year globally. Some countries (e.g. Norway) have adopted ambitious programmes to eradicate tobacco smoking by the year 2000, which has given encouraging results.
2. Personal hygiene: Improvements in personal hygiene may lead t declines in the incidence of certain types of cancer, e. g. cancer cervix. Women with good personal hygiene have very low incidence of cervical cancer.
3. Radiation: Special efforts should be made reduce the amount of radiation (including medical radiation) received by each individual (patients, medical professionals, workers at nuclear reactors) to a minimum without reducing the benefits.
4. Occupational exposures :The occupational aspects of cancer are frequently neglected. Measures to protect workers from exposure to industrial carcinogens should be enforced in industries.
5. Immunization: In the case of primary liver cancer, immunization against hepatitis B virus prevent people from hepatocellular carcinoma (liver cancer).
6. Foods, drugs and cosmetics: These should be tested for carcinogens and legislation should be available to make these less harmful.
7. Air pollution: Control of air pollution is another preventive measure which can prevent lung cancer and many respiratory problems.
8. Avoidance of sun: Non melanoma skin cancers (basal cell and squamous cell) are induced by cumulative exposure to ultraviolet (UV) radiation. Reduction of sun exposure through use of protective clothing and changing patterns of outdoor activities can reduce skin cancer risk among Caucasians. Sunburns, in childhood and adolescence, are associated with increased risk of melanoma in adulthood. Sunscreens decrease the risk of actinic keratoses, the precursor to squamous cell skin cancer, but it may increase risk of melanoma. Sunscreens prevent burning, but this may encourage more prolonged exposure to the sun and may not filter out wavelengths of energy that cause melanoma.
9. Energy balance: Risk of cancer increases as BMI (body mass index) increases over 25 kg/m². Obesity increases risks for cancers of the colon, breast (female postmenopausal), endometrium, kidney (renal cell), and esophagus, although causality is not established. Relative risks of colon cancer are increased in obesity by 1.5–2.0 fold for men and 1.2–1.5 fold for women. Obese postmenopausal women have a 30–50% increased risk of breast cancer. A hypothesis for the association is that adipose tissue serves as a depot for aromatase (an enzyme) that facilitates estrogen production. Adiposity is also associated with poorer survival and increased risk of recurrence after treatment.
10. Treatment of precancerous lesions: Early detection and prompt treatment of precancerous lesions such as cervical tears, intestinal polyposis, warts, chronic gastritis, chronic cervicitis, and adenomata is one of the cornerstones of cancer prevention.
11. Screening for Cancer: Screening for cancer is one of the measure to prevent cancer. In the developed countries some of the cancer screening are compulsory e.g. screening for cervical cancer (Papanicolou smear known as pap smear) has virtually eradicated cervical cancer. But due to absence of this type of screening and poor personal hygiene in developing countries cervical cancer is still one of the commonest cancers in these countries.
12. Legislation: Legislation has also a role in primary prevention. The solution to cancer control problems is not to be found in research laboratories, but in legislatures. For example, legislation to control known environmental carcinogens (e.g. tobacco, alcohol, air pollution) is inadequate or only moderately enforced in a number of countries.
13. Cancer education: An important area of primary prevention is cancer education of general population. It should be directed at “high risk” groups. The aim of cancer education is to motivate people to seek early diagnosis and early treatment and also learn how to prevent cancer by changing lifestyle and food habits etc. Cancer organizations in many countries remind the public of the early warning signs (“danger signals”) of cancer. These are:

• A lump or hard area in the breast.

• A persistent cough or hoarseness.

• A change in a wart or mole.

• Excessive loss of blood during menstrual period or loss of blood outside the usual menstrual period.

• Blood loss from any natural orifice.

• A swelling or sore that do not heal.

• Unexplained loss of weight.

There is no doubt that the possibilities for primary prevention are many. Since primary prevention is directed at large population groups (e.g., high risk groups, school children, occupational groups, youth organizations) the cost can be high and programmes difficult to conduct . Primary prevention, although a hopeful approach, is still in its early stages. Major risk factors have been identified for a small number of cancers only and far more research is needed in that direction.

Causes of cancer

Cancer is a chronic disease. As with any other chronic diseases, cancer has a multifactorial etiology (cause). Carcinogens are the substances which can cause cancer to humans.

1. Environmental factors: Environmental factors are responsible for at least 90 per cent of all human cancers. The major environmental factors identified include the following:

a. Tobacco: Tobacco in various forms of usage (e.g. smoking, chewing, sniffing) is the major environmental cause of cancers of lungs, larynx, mouth, pharynx, esophagus, bladder, pancreas and also kidney. It has been estimated that cigarette smoking is responsible for more than one million premature deaths every year throughout the world in the form of cancer, respiratory problems and also in many other way. There is hardly any organ system which is not affected adversely due to cigarette smoking.

b. Alcohol: Excessive intake of alcoholic beverages is associated with esophageal and liver cancer. Some recent studies have suggested that beer consumption may be associated with rectal cancer. It is estimated that alcohol contribute to about 3 per cent of all cancer deaths in the world.

c. Diet: Dietary factors are also related to cancer. Smoked fish and meat is related to stomach cancer (consumption of smoked fish causes cancer), less intake of dietary fiber can cause intestinal cancer, excessive beef consumption can lead to bowel cancer and a high fat diet can lead to breast cancer. A variety of other dietary factors such as food additives and contaminants are also blamed to be carcinogenic. Diet rich in vitamins, minerals and antioxidants reduce the incidence of cancer.

d. Occupational exposures: These include exposure to benzene, cadmium, chromium, arsenic, asbestos, polycyclic hydrocarbons, vinyl chloride, etc. Many others remain to identified. The risk of occupational exposure is considerably increased if the individuals also smoke cigarettes. Occupational exposures are reported to account for 15 per cent of all human cancers. Occupation like road construction and handling of coal tar causes cancer of skin. Chimney sweepers are prone to develop prostate cancer.

e. Viruses : An intensive search for a viral origin of human cancers revealed that hepatitis B virus can cause hepatocellular carcinoma (liver cancer). The Epstein-Barr virus (EBV) is associated with 2 human malignancies, Burkitt’s lymphoma and nasopharyngeal carcinoma. Cytomegalovirus (CMV) is a suspected oncogenic agent of classical Kaposi’s sarcoma. Human papilloma virus (HPV) is the main suspect of cancer cervix. Main causative agent of cervical cancer is most likely a virus, due to the fact that it is almost non existence among Christian nuns who are not engaged in sexual intercourse. Whereas the incidence is very high among females with multiple sex partners. Hodgkin’s disease is also believed to be of viral origin. The human T-cell leukemia virus is associated with adult T-cell leukemia/lymphoma in United States and southern part of Japan .

f. Parasites: Parasitic infections can also increase the risk of cancer. Schistosmiasis in Middle East causes carcinoma of the urinary bladder.

g. Others: There are numerous other environmental factors such as sunlight, aeration, air and water pollution, medications (e.g. estrogen) and pesticides which are suspected to be related to cause cancer. Exposure to sun can cause skin cancer in white people, that is why skin cancer is most commonly seen in Australia and New Zealand.

h. Customs, habit and life styles: Customs, habits and lifestyles of people may be associated with an increased risk for certain cancers. The familiar examples are the demonstrated association between smoking and lung cancer, tobacco and betel chewing and oral cancer etc. Kangri cancer is seen in Kashmir. This is due to holding an earthen pot full of burning coal, in front of abdomen during winter months to keep the body warm. The skin around umbilicus is exposed to constant heat, which causes skin cancer.

2. Genetic factors: Genetic influences have long been suspected . For example, retinoblastoma occurs in children of the same parent. Certain people are more likely to develop cancer (leukaemia) than normal children. However, genetic factors are less conspicuous and more difficult to identify. There is probably a complex interrelationship between hereditary susceptibility and environmental carcinogenic stimuli in the causation of a number of cancers.

Cancer: a General understanding

Cancer can be regarded as a group of most serious diseases which are characterized by (1) abnormal growth of cells without control. (2) ability to invade nearby tissues and even to distant organs, by local invasion, through lymphatic system and blood. (3) the eventual death of patient it the tumor (cancer) has progressed beyond the stage when it can be successfully removed by surgery . Cancer can occur at any site of the body and it can involve any type of cells.

If cancer occurs in a tissue, the cells of the tissue starts growing abnormally fast. But the cells can not mature and because cells are not mature they cannot perform the function for which they are present in the body. For example if there is cancer of liver (hepatocellular carcinoma) the cancerous liver cells cannot perform functions of liver, but they consume the nutrition and due to large number and fast growing they consume large number of calories. This is the reason of weight loss in cancer. These immature cells keeps growing in number without any function and may spread to nearby tissues or to a distant site through blood. One cancerous cell is enough for spread to distant organ which keep growing very fast.

Cancer can be categorized into the following major categories:

1. Caremomas :They arise from epithelial cells which is the cell lining the surface of various organs like mouth, uterus, intestines, stomach, inner side of nose etc, This type may arise from skin also from skin epithelium .
2. Sarcomas :They arise from various cells which constitute connective tissues like bone, fat, fibrous tissues, bran tissue etc.
3. Lymphomas, myelomas and leukemias (blood cancer) arise from the cells of immune system as well as from bone marrow. Blood cancer or leukemia arise from bone marrow, because blood cells are formed in bone marrow.

In blood cancer (leukemia) white blood cells, whose main function is to fight with the invading microorganisms (bacteria, virus, fungus etc), starts growing abnormally rapidly in bone marrow but they are not mature. Because of immaturity they can not perform their primary function, which is to fight with invading microorganisms. And patient eventually die due to infection.

The term primary (cancer) tumor means cancer in the organ of origin, but secondary (cancer) tumor means the cancer which has spread to distant organ or to regional lymph nodes. When cancer cells multiply and reach a critical size cancer can be clinically evident as mass or ulcer in the particular area. Some time primary tumor can not be detected or found, but the secondary tumor became the main cancer. In this type of cases the primary tumor shrinks due some reason and become undetectable.

Effects of Heat on Humans

Effects of Heat: There are 14 documented disorders which can be due to excess exposure to heat. Some of the common and important disorders are discussed below:

1. Heat stroke: Also known as sunstroke. This is due to failure of heat regulating mechanism of human body . The main feature of heat stroke is very high body temperature of about 110 degree Fahrenheit(43⁰ Centigrade). High temperature is accompanied by convulsion, delirium and partial or complete loss of consciousness. Skin is usually dry and hot. Sweating is absent or very scanty. Death rate is high (about 40%) even it quick medical attention is provided. Treatment of heat stroke consists of rapidly cooling the body in ice water till rectal temperature falls blow 102 degree Fahrenheit. Rectal temperature should be continuously monitored. It indicate the progress of treatment as well as guard against hypothermia, that may occur if cooling is continued for very long . Further treatment of heat stroke is supportive & symptomatic. The patient should be hospitalized for several days, till temperature control & regulatory mechanism become stable.
2. Heat Hyperpyrexia: This is due to impairment of heat regulating mechanism of human body. It generally have temperature above 106 degree Fahrenheit. It may be seen before heat stroke /sun stroke.
3. Heat exhaustion: It is not because of failure of heat regulating mechanism ,unlike heat stroke and heat hyperpyrexia. It is less severe than heat stroke and due to imbalance or inadequate replacement of water and salts lost by perspiration due to excess heat. Body temperature may be normal or slightly higher but generally do not cross 102 degree Fahrenheit. It is seen after several days of high temperature. Symptoms of heat exhaustion are dizziness, weakness, and fatigue. Elderly people with heat exhaustion may require hospitalization. Treatment is correction of fluid and electrolyte imbalance.
4. Heat cramps: It is seen in people engaged in heavy work and muscular activity at high temperature and humidity, mainly those who are not adopted to muscular activities at high temperature and humidity. Heat cramp is due to loss of sodium and chlorides in blood and it causes painful and spasmodic contraction of skeletal muscles.
5. Heat syncope: Heat syncope is quite common problem . In typical form of heat syncope, person standing in sun suddenly become pale, his blood pressure falls and he collapses. Body temperature is normal. This is due to pooling of blood in legs due to dilatation of blood vessels in legs. This results in reduced venous return to heart and fall in blood pressure and lack of blood supply in brain. The treatment is very simple. The patient is made to lie down in shade with the head slightly down . Patient recovers in 5 to 10 minutes. This type of problem is very common in soldiers standing in sun for parade.

Preventive Measures: The effects of heat can be prevented by following measures.

• Replacement of water : People working under high temperature and humidity should encouraged to drink lots of cool water. In hot climate a person requires about one liter of water per hour during physical work and a sedentary worker need half liter of water. There is no need of extra salt in water because sweat contain very less salt, contrary to popular belief that extra salt is required. But if a person is not acclimatized he should take extra salt for first 10 days.

• Clothing: The cloth used should be loose fitting and of light color

• Regulation of work: Duration of work at hot and humid condition should be reduced. There should be periods of rest in between intense work. If symptoms of effect of heat like headache, dizziness appear the worker should be removed to a cooler place and adequate treatment given.

• Protective Devices: protective goggles, helmets and shields should be used where practicable.

• Proper ventilation should be provided and air-conditioning done where practicable.

Effects of Radiation on Humans

The biological effects of radiation on human can be divided into two groups, somatic effects and genetic effects.

(1) Somatic effects: A dose of 600 to 700 roentgen is invariably fatal in humans and a dose of 400 to 500 roentgen can kill up to 50% of people. Those who are not killed, also suffer from severe damage and radiation sickness. If a person is exposed to 25 to 50 roentgen of radiation it effects white blood cells (corpuscles) and produce lassitude and softening of the muscles. Somatic effects of radiation can be immediate and delayed. Immediate effects are radiation sickness and acute radiation syndrome. Delayed effects take time to develop and can take from few weeks to few years to develop. Delayed effects of radiation are mainly leukemia (blood cancer), malignant tumors ( cancer) shortening of life and fetal developmental abnormalities.

(2) Genetic effects: Somatic effects are seen during ones lifetime of the person exposed to ionizing radiation genetic effects generally manifest in the life of off-spring . Genetic effects of radiation are mainly due to point mutation and chromosomal mutation. Chromosomal mutation generally is involved with sterility and point mutation effects the genes .

Protection from Radiation: The amount of radiation received from outer space is about 0.1rad per year and at present it is not considered a hazard. The additional permissible dose from man made sources is about 5rad per year. Out of all the man made sources x-ray constitute the greatest hazard. In routine fluoroscopy a dose of 4rad is delivered to a part in one minute, which means unnecessary x-ray examination should be avoided, mainly in pregnant woman an children.

There is requirement of adequate control & surveillance of x-ray installations, protection of workers, improvement of techniques to reduce dose of radiation.

Effective protective measures include use of lead shields, and lead rubber aprons by radiographers .Lead aprons of 0.5mm thickness of lead reduces the intensity of scattered x-rays up to 90% and all workers should use them who are associated with x-rays. Worker also should wear a dosimeter or a film badge that shows accumulated exposure to radiation. Besides all the above periodic medical cheek up, regular working hours & recreation should be provided to the health workers who are exposed to x-rays.

Radiation hygiene is one of the latest branch of hygiene. International agencies like WHO(World Health Organization), IAEA(International Atomic Energy Agency) and International Commission on Radiological Protection (ICRP) are active in the field of radiation hygiene. The ICRP has recommended that the genetic dose to the whole population from man made sources (other than natural sources) should not exceed 5rems per year over period of 30 years. Many countries in the world have adopted the ICRP recommendation . The main concern is to promote peaceful use of atomic energy with out any problem on heath.

There is growing concern throughout the world in recent times for codes of practice for the safe operation of nuclear power plants and safe disposals of nuclear waste which is generated from nuclear power plants.

Types of radiation

Ionizing radiation is the radiation which can penetrate tissues and deposit its energy within them. They are of three types of electromagnetic radiation: alpha particles, beta particles (electron) and protons.

Alpha particles are 10 times more harmful than X-rays, beta particles or gamma rays but they have very little penetrating force. But they are dangerous it enters the body by inhalation or wound. X-rays & gamma rays are of short wave length and can penetrate deep.

Alpha particles can penetrate 4cm in air, 0.05mm in tissue and no penetration in lead. Beta particles can penetrate 6 to 300cm in air, 0.06-4mm in tissue and 0.005 to0.3 mm in lead. Gamma rays can penetrate 400 meters in air, 50cm in tissue and 40mm in lead. X-rays can penetrate 120-240 meters in air 15 to 30cm in tissue and 0.3 mm in lead.

“Non ionizing radiation” in compare to ionizing radiation have longer electro magnetic wave length. As the wave length becomes longer the energy of the electro magnetic wave decreases. So all the non-ionizing radiation have lesser energy than ionizing radiation. In order of increasing wave length that means lesser energy, non ionizing radiation include ultraviolet rays (UV), visible light, infrared rays, microwave radiation and radio frequency radiation.

Units of Radiation

The activity of radioactive material is the number of nuclear disintegration per unit of time. The unit of radioactive activity is Becquerel(Bq). 1 Bq is equal to one disintegration per second. Formerly unit of radiation was curie (Ci).

The potency of radiation is measured in three ways. Roentgen: It is the unit of exposure. . It is the amount of radiation absorbed in air at a given point, that is the number of ions produced in one ml of air . Rad: It is the unit of absorbed dose of radiation, that is the amount of radioactive energy absorbed per gram of tissue in humans or in any material. 1mrad (milliard ) is equal to 0.001rad of radiation. Rem: This is the product of absorbed dose and modifying factors, that means the effects of modifying factors are deducted from absorbed dose and we get the rem. Due to high speed and high penetrating power of x-rays and gamma rays the rem and rad of these are equal. This means the entire dose which is absorbed and modifying factors have no effect.

The above radiation units (roentgen, rad & rem) have been replaced by the new SI units (International System of Units). They are of three types

(1) Coulomb per kilogram(c/kg)has replaced Roentgen unit. 1 roentgen unit is equal to 2.58×10⁴ C/kg. This is the unit for exposure.

(2) Gray(GY): It has replaced rad. It is the unit of dose of ionizing radiation that imparts 1 joule of energy to one kilogram of absorbed material. 1rad is equal to 0.01Grey (GY).

(3) Sievert (sv) has replaced rem. It is the unit of dose equivalent. 1 seivert (Sv) is equal to 100rem.

Dose equivalent(H): The concept of dose equivalent has been introduced due to the fact that all types of radiation do not produce same biological effect per unit of energy absorbed. The dose equivalent (H) of seivert, which is equal to the absorbed dose (D) of grays, multiplied by a quality factor Q, which depends upon the density of ionizing radiation produced in the tissue by the radiation.

H = DQ

The quality factor (Q) of X-ray, gamma ray and electron is equal to 1 (one), whereas for a particle it is 20. From this fact it is clear that particles like ? rays are 20 times more harmful than X-ray or gamma ray.

Radiation: a Discussion

Radiation is a part of man’s environment. Man is exposed from two sources of radiation natural and man made.

Natural sources of radiation are cosmic rays internal rays like carbon-14 and Potassium-40, atmospheric and terrestrial. Man made sources of radiation are medical & dental X-rays, radioisotopes for treatment of killer disease like cancer, radioactive fall out from nuclear explosions. Miscellaneous man made radioactive sources are television sets, radioactive dial matches, luminous markers, isotope tagged products. They are too small a source of radiation to be significant at present.

Natural sources:

Man is exposed to radiation throughout life continuously. Cosmic rays originate in outer space and become weak as they pass through atmosphere. Generally a person is exposed to about 35mrad of radiation a year. At higher attitude of about 20 km cosmic radiation becomes important. A commercial jet pilot receives about 300mrad of radiation a year compare to normal 35mrad.

Terrestrial radiation: Radioactive elements like thorium, uranium, radium and radioactive isotopes are present in man’s environment e.g. soil, rocks, buildings. Man derives about 50mrad of radiation from terrestrial sources. Some areas like Kerala in India, rock formations contain uranium, where radiation exposure may be as high as 2000mrad per year. Radiation from radioactive gases like radon contribute about 2mrad of radiation per year.

Internal radiation: Man is exposed to internal radiation from radioactive materials stored in body tissues. These include minute quantities of uranium, thorium, radioactive isotopes of carbon(C14), Potassium(K40), strontium(Sr90). From these sources radiation is about 25mrad per year but it may be as high as 70 to 80. it is estimated that a person is exposed to about 0.1rad of radiation per year from natural sources.

Man made sources:

Man is exposed to man made sources of radiation in addition to natural sources.

X-ray: this is the largest source of man made radiation. Two groups of people are exposed to X-ray radiation, patients and radiologists & radio technicians and radiotherapists. When optimum radiographic techniques are used a single X-ray film can give more than 0.02rad.

Radioactive fallout:

Nuclear explosions release tremendous amount of energy in the form of heat, light, radiation and also it releases many radioactive substances like carbon (C14), iodine (I 131), cesium (Cs 137) and strontium (Sr 90). Cesium and strontium are very important because they are released in large quantities and their half lives are 30 years and 28 years respectively. They float for few years and due to air current the particles are distributed throughout the world. Miscellaneous sources contribute too small am out of radiation to be important.