Radiobiologia

Question 1

Atom

Answer 1

The word “atom” derives from the Greek word “atomos,” which means indivisible; an atom was the smallest indivisible component of matter according to some philosophers in Ancient Greece [1]. However, we now know that atoms are actually composed of subatomic particles: protons and neutrons in the nucleus of the atom, and electrons orbiting that nucleus´ The diameter of an atom is about 10−8 cm, whereas the diameter of the atomic nucleus is 10−13 cm.

Question 2

Electron

Answer 2

negative charged particles orbiting the nucleus The mass of an electron is 9.109 3826(16) × 10−31 kg. The electrical charge of an electron is −1.602 176 53(14) × 10−19 C.

Question 3

Protons

Answer 3

Positively charged particles. Mass = 1,839 times grater than the one of an electron. Protons and neutrons form the nucleus of an atom, and so these particles are also called nucleons.

Question 4

Neutrons

Answer 4

Uncharged (neutral) particles. The mass of a neutron s very slightly larger that that of a proton. Protons and neutrons form the nucleus of an atom, and so these particles are also called nucleons.

Question 5

Mass number of the ATOM

Answer 5

The total number of protons and neutrons in a nucleus (p+n) is termed the mass number of that atom, symbolyzed by A.

Question 6

Atomic number

Answer 6

The total number of protons is called the atomic number and is symbolized by Z.

Question 7

Neutron Number

Answer 7

Total number of neutrons is called the neutron number, and is symbolized by N.

Question 8

A=Z+N

Answer 8

NUCLIDE FORMAT

Question 9

NUCLIDE

Answer 9

if an atom is expressed in the form A/Z(X), it is called a nuclide

Question 10

RADIONUCLIDE

Answer 10

f the atom is expressed in the form A/Z(X) and is radioactive, it is called a radionuclide.

Question 11

RADIATION

Answer 11

The propagation of energy from a radiative source to another medium is termed radiation. This transmission of energy can take the form of particulate radiation or electromagnetic radiation (i.e., electromagnetic waves). The various forms of radiation originating from atoms, which include (among others) visible light, X-rays and g-rays, are grouped together under the terms “electromagnetic radiation” [1] or “the electromagnetic spectrum” [1, 2]. Radio waves, which have the longest wavelengths and thus the lowest frequencies and energies of the various types of electromagnetic radiation, are located at tone end of the electromagnetic spectrum, whereas X-rays and g-rays, which have the highest frequencies and energies, are situated at the other end of this spectrum.

Question 12

PHOTON

Answer 12

If the smallest unit of an element is considered to be its atoms, the photon is the smallest unit of electromagnetic radiation • Photons have no mass.

Question 13

ELECTROMAGNETIC RADIATION

Answer 13

• It propagates in a straight line. • It travels at the speed of light (nearly 300,000 km/s). • It transfers energy to the medium through which it passes, and the amount of energy transferred correlates positively with the frequency and negatively with the wavelength of the radiation. • The energy of the radiation decreases as it passes through a material, due to absorption and scattering, and this decrease in energy is negatively correlated with the square of the distance traveled through the material.

Question 14

Types of nonionizing electromagnetic radiation

Answer 14

• Radio waves • Microwaves • Infrared light • Visible light • Ultraviolet light

Question 15

NONIONIZING RADIATION

Answer 15

A type of low-energy radiation that does not have enough energy to remove an electron (negative particle) from an atom or molecule. Non-ionizing radiation includes visible, infrared, and ultraviolet light; microwaves; radio waves; and radiofrequency energy from cell phones. Most types of non-ionizing radiation have not been found to cause cancer. Electromagnetic radiation can also be subdivided into ionizing and nonionizing radiations. Nonionizing radiations have wavelengths of ³10−7 m. Nonionizing radiations have energies of <12 electron volts (eV); 12 eV is considered to be the lowest energy that an ionizing radiation can possess

Question 16

IONIZING RADIATION

Answer 16

Ionizing (high-energy) radiation has the ability to remove electrons from atoms; i.e., to ionize the atoms. Ionizing radiation can be electromagnetic or particulate radiation

Question 17

ELECTROMAGNETIC INONIZING RADIATION

Answer 17

Z-RAYS γ-rays

Question 18

PARTICULATE IONIZING RADIATION

Answer 18

α particles Electron (β)particles Neutron Proton Π Meson Heavy ions

Question 19

Electromagnetic Radiation

Answer 19

The electromagnetic spectrum comprises all types of electromagnetic radiation, ranging from radio waves (low energy, long wavelength, low frequency) to ionizing radiations (high energy, short wavelength, high frequency)

Question 20

ELECTROMAGNETIC RADIATION IONIZATION

Answer 20

Electrons are knocked out of their atomic and molecular orbits (a process known as ionization) when high-energy radiation interacts with matter [8]. Those electrons produce secondary electrons during their passage through the material. A mean of energy of 33.85 eV is transferred during the ionization process, which in atomic and molecular terms is a highly significant amount of energy. When high-energy photons are used clinically, the resulting secondary electrons, which have an average energy of 60 eV per destructive event, are transferred to cellular molecules.

Question 21

X-Rays

Answer 21

X-rays are a type of electromagnetic radiation with wavelengths of 10–0.01 nm, frequencies of 30–30,000 pHz (1015 Hz), and typical photon energies of 100 eV–100 keV X-rays are generally produced in either X-ray tubes or linacs. X-ray tubes are the main source of X-rays in laboratory instruments. In such a tube, a focused electron beam is accelerated under high voltage within a glass vacuum tube impacts a fixed or rotating target. When the electrons approach target atoms, Coulomb interactions with the nuclei cause the electrons to be suddenly deflected from their previous paths and slowed. During this braking process, energy in the form of X-rays is produced in a continuous spectrum (→ bremsstrahlung X-rays). High-energy electrons hit inner orbital electrons and knock them out of the atom during the ionization process. Free electrons from outer orbits then fill the empty spaces in the inner orbitals, and X-rays with energies that are characteristic of the target are produced (→ characteristic X-rays) ( X-rays were discovered by the German physicist Wilhelm Conrad Roentgen in \95 [9]. The hot cathode Roentgen tube, which was developed by William David Coolidge in 1913, is a pressured (to 10−3 mmHg) glass tube consisting of anode and cathode layers between which a high-energy (106 –108 V) potential is applied (Fig. 1.5a, b). Electrons produced by thermionic emission in the cathode are accelerated towards the anode by the potential. They thus hit the anode, which is a metal with high melting temperature. X-rays are produced by the sudden deceleration of these electrons due to Coulomb interactions with nuclei in the anode (this sudden deceleration of fast-moving electrons is known as bremsstrahlung; Fig. 1.6). The energy and the wavelength of the X-rays depend on the atomic number of the target (anode) metal, as well as the velocity and the kinetic energy of the electrons. This process is used to produce medical radiation in diagnostic X-ray units, linear accelerators (linacs), and betatrons.

Question 22

Gamma (g) Rays

Answer 22

Gamma rays are physically identical to X-rays, but they are emitted from atomic nuclei (intranuclearly). An unstable atomic nucleus sheds its excess energy in the form of either an intranuclear electron (e−) (beta particle) or a helium nucleus (an “alpha particle”) (Fig. 1.8). If it still possesses excess energy after that, gamma rays are emitted in order to reach its steady state (Fig. 1.9).

Question 23

Gamma Emission

Answer 23

A nucleus is not always fully stable (i.e., at its basal energy level) just after it decays; sometimes, the nucleus will be in a semi-stable state instead (Fig. 1.14). The excess energy carried by the nucleus is then emitted as gamma radiation. There is no change in the atomic or mass number of the nucleus after this decay, so it is termed an “isomeric” decay. The half-lives of gamma radiation sources are much shorter than sources of other types of decay, and are generally less than 10−9 s. However, there are some gamma radiation sources with half-lives of hours or even years. Gamma energy spectra are not continuous

Question 24

Isotope

Answer 24

Atoms with the same atomic number but different mass numbers are called isotopes

Question 25

Isotone.

Answer 25

Atoms with the same number of neutrons, but different numbers of protons are called isotones

Question 26

Isobar.

Answer 26

Atoms with the same number of nucleons but different numbers of protons are called isobars

Question 27

Isomer.

Answer 27

Atoms with the same atomic and mass numbers but which are in different energy states are called nuclear isomers

Question 28

Ionizing Particulate Radiation

Answer 28

Electrons, protons, alpha particles, neutrons, pi mesons and heavy ions are all forms of ionizing particulate radiation [19]. Electrons are the particles that are generally used in routine clinics. Other particles are only used in specific clinics worldwide. Electrons, due to their negative charge and low mass, can be accelerated to high energies in linacs or betatrons.

Question 29

INTERACTION OF RADIATION WITH MATTER

Answer 29

Radiation is scattered and absorbed when it passes through tissue [19, 20]. The intensities of monoenergetic X-rays or gamma rays attenuate exponentially within tissues. In other words, the intensity of radiation constantly decreases as it propagates within tissues. This decrease depends on the type of tissue and its thickness. If the wavelength stays constant, the intensity of the radiation passing through a tissue can be calculated by the following formula:

Question 30

I = I0 .e−mt

Answer 30

I = intensity of outgoing radiation beam I0 = intensity of incoming radiation beam m = absorption coefficient (which is positively correlated with the fourth power of the atomic number of the penetrated tissue, and the third power of the wavelength of the radiation) t = tissue thickness As seen in the above formula, the intensity of the radiation decreases exponentially with the absorbent thickness, and the intensity of the outgoing radiation depends on the tissue absorption coefficient and its thickness.

Question 31

Photoelectric Effect def

Answer 31

also known as hertz effect. To define it simply, when any electromagnetic radiation reaches a surface (generally a metallic surface), it transfers its energy to the electrons of that surface, which are then scattered. At the atomic level, the incoming radiation knocks an electron from an inner atomic orbital, propelling it from the atom

Question 32

Photoelectric Effect

Answer 32

This is the basic interaction in diagnostic radiology. It is dominant at energies of less than 35 kV, and in atoms with high atomic numbers (Z). Since the atomic number of bone is higher than that of soft tissue, bone absorbs more radiation than soft tissue. This absorption difference is the basis of diagnostic radiology. This effect also explains why metals with high atomic numbers (e.g., lead) are used to absorb low-energy X-rays and gamma rays.

Question 33

laws of photoelectric effect

Answer 33

1. photoelectrons are ejected by a metal surface when the frequency of incident radiation becomes equal or greater than the work funcion of the metal.

2, the number of photoelectrons emitted per second is directly proportional to the intensity of incident radiation.

3. the maxium energy of photoelectrons do not depends on the intensity of incident light but relies on the frecuency of light.

Question 34

compton effect def

Answer 34

In the Compton effect, a photon collides with an electron in an outer orbital, and the photon and electron are scattered in different directions (where q is the angle between the directions) [21]. The energy of the incoming photon is transferred to the electron in the form of kinetic energy. The scattered electron also interacts with the outer orbital electrons of other atoms. After the interaction, the photon has a lower energy than it did beforehand (Fig. 1.20).

Question 35

Compton Effect

Answer 35

This is the main mechanism for the absorption of ionizing radiation in radiotherapy. It is the dominant effect across a wide spectrum of energies, such as 35 kV–50 MV. It has no dependency on the atomic number (Z) of the absorbent material, but it does depend on the electron density of the material. The absorption of incoming radiation is the same for bone and soft tissues.

Question 36

Pair Production def

Answer 36

This is a relatively rare effect. In it, a photon transforms into an electron and a positron near a nucleus (Fig. 1.22) [21]. The electron sheds all of its energy by the absorption processes explained above. On the other hand, the positron propagates through the medium ionizing atoms until its energy has dropped to such a low level that it pulls a free electron close enough to combine with it, in a process called annihilation. This annihilation causes the appearance of a pair of photon moving in opposite directions, and each with 0.511 MeV of energy. These annihilation photons are absorbed through either photoelectric or Compton events.

Question 37

Pair Production

Answer 37

The threshold photon energy level for pair production is 1.02 MeV; below this, pair production will not occur. The probability of pair production occurring increases as Z increases. Pair production is more frequently observed than the Compton effect at energies of more than 10 MeV (Fig. 1.23).

Question 38

The measured quantities associated with ionizing radiation can be briefly summarized as follows

Answer 38

Source → activity units The first interaction point → kinetic energy released in matter (kerma) Matter → absorbed dose

Question 39

Radioactivity.

Answer 39

This is the transition of an unstable nucleus to a steady state through the emission of particulate or electromagnetic radiation from the nucleus.

Question 40

Curie (Ci).

Answer 40

This is an activity of 3.7 × 1010 disintegrations per second.

Question 41

Becquerel (Bq).

Answer 41

This is an activity of one disintegration per second. 1 Ci = 33.7 × 1010 Bq 1 Bq = 2.7 × 10−11 Ci

Question 42

Activity unit.

Answer 42

This is the number of spontaneous nuclear disintegrations (N) per unit time (t) (A = N/t), as measured in becquerels (Bq). Note that an older system of units, the curie (Ci), is also often encountered.

Question 43

Kerma (kinetic energy released in the medium).

Answer 43

This is the sum of the initial kinetic energies of all of the charged particles liberated by uncharged ionizing radiation (neutrons, protons) in a sample of matter divided by the mass of the sample. The kerma is measured in the same units as absorbed dose (Gy).

Question 44

reference air kerma

Answer 44

is used to define the visible activity. It is the dose delivered in one hour to air one meter away from a source with an activity of 1 MBq. Its units are 1 mGy–1. m2 = 1 cGy. h−1. cm2.

Question 45

Absorbed dose

Answer 45

The basic quantity associated with radiation measurement in radiotherapy is the absorbed dose. This defines the amount of energy absorbed from a radiation beam per unit mass of absorbent material. It is measured in grays (Gy), although an older unit, the rad, is also still used.

Question 46

Rad

Answer 46

This is the amount of radiation that causes one erg (of energy) to be absorbed per gram of irradiated material (rad = radiation absorbed dose). 1 rad = 100 erg/g.

Question 47

Gray (Gy).

Answer 47

This is the amount of radiation amount that cause one joule to be absorbed per kilogram of irradiated material. 1 Gy = 1 J/kg. 1 Gy = 100 cGy = 100 Rad.

Question 48

Exposure.

Answer 48

This is the amount of ionization produced by photons in air. Since it is impossible to directly measure the absorbed dose in tissue, the measurement of radiation is performed in air. The exposure is the amount of radiation required to liberate a positive or negative charge of one electrostatic unit of charge (esu) in 1 cm3 of dry air at standard temperature and pressure (this corresponds to the generation of approximately 2.08 × 109 ion pairs). It is measured in coulombs per kilogram (C/kg), although the old unit of the roentgen (R) is also commonly encountered.

Question 49

Roentgen (R).

Answer 49

In normal air conditions (0°C and 760 mmHg pressure), this is the amount of X-radiation or gamma radiation that produces 2.58 × 10−4 coulombs of electrical charge (in the form of ions) in one kilogram of air. The roentgen and C/kg are only used for photonic radiation (X-rays and gamma rays), not for particulate radiation. The energies of therapeutic or diagnostic gamma rays and X-rays are in the kilovolt (kV) or megavolt (MV) range, while the energies of therapeutic electrons are in the megaelectronvolt (MeV) range.

Question 50

C/kg

Answer 50

In normal air conditions, this is the amount of radiation that produces one coulomb of electrical charge (in the form of ions) in one kilogram of air. The roentgen and C/kg are only used for photonic radiation (X-rays and gamma rays), not for particulate radiation. The energies of therapeutic or diagnostic gamma rays and X-rays are in the kilovolt (kV) or megavolt (MV) range, while the energies of therapeutic electrons are in the megaelectronvolt (MeV) range.

Question 51

Integral dose.

Answer 51

This is the total energy absorbed in the treated volume (in J = kg × Gy).

Question 52

Equivalent dose.

Answer 52

Since different radiations have different harmful effects on human tissues, the basic dosimetric unit of absorbed dose (→ Gy) is not sufficient for studies of radiation protection. Thus, the absorbed dose in tissue must be multiplied by a radiationweighting factor that depends on the type of radiation employed. The resulting dose is called the equivalent dose, and it is measured in sieverts (Sv), although an older unit, the rem (roentgen equivalent man), is often used too.

Question 53

H = D×WR

Answer 53

H = equivalent dose (Sv) WR = radiation-weighting factor (no unit) D = dose (Gy) 1 Sv = 1 J/kg = 100 rem

Question 54

CANCER DEF

Answer 54

Cancer is a group of diseases involving abnormal cell growth with the potential to invade or spread to other parts of the body.[2][8] These contrast with benign tumors, which do not spread. Possible signs and symptoms include a lump, abnormal bleeding, prolonged cough, unexplained weight loss, and a change in bowel movements.[1] While these symptoms may indicate cancer, they can also have other causes.[1] Over 100 types of cancers affect humans.

Question 55

FUNDAMENTAL OF CANCER

Answer 55

CANCER IS A DISEASE CAUSED WHEN CELLS DIVIDE UNCONTROLLABLY AND SPREAD INTO SURROUNDING TISSUES.

Question 56

WHAT CAUSES CANCER?

Answer 56

CANCER IS CAUSED BY CHANGES TO DNA. MOST CANCER-CAUSING DNA CHANGES OCCUR IN SECTIONS OF DNA CALLED GENES. THESE CHANGES ARE ALSO CALLED GENETIC CHANGES.

Question 57

WHAT ARE ONCOGENES?

Answer 57

A DNA CHANGES CAN CAUSE GENES INVOLVED IN NORMAL CELL GROWTH TO BECOME ONCOGENES. UNLIKE NORMAL GENES, ONCOGENES CANNOT BE TURNED OFF, SO THEY CAUSE UNCONTROLLED CELL GROWTH.

Question 58

WHAT A TUMOR SUPRESSOR GENES?

Answer 58

IN NORMAL CELLS, TUMOR SUPRESSOR GENES PREVENT CANCER BY SLOWING OR STOPPING CELL GROWTH. DNA CHANGES THAT INACTIVATE TUMOR SUPRESSOR GENES CAN LEAD TO UNCONTROLLED CELL GROWTH AND CANCER

Question 59

WHAT IS THE TUMOR MICROENVIRONMENT?

Answer 59

WITHIN A TUMOR, CANCER CELLS ARE SURROUNDED BY A VARIETY OF INMUNE CELLS, FIBROBLAST, MOLECULES, AND BLOOD VESSELS- WHAT´S KNOWN AS THE TUMOR MICROENVIRONMENT. CANCER CELLS CAN CHANGE THE MICROENVIRONMENT, WHICH IN TURN CAN AFFECT HOW CANCER GROWS AND SPREADS.

Question 60

HOW DOES THE INMUNE SYSTEM INTERACT WITH CANCER

Answer 60

INMUNE SYSTEM CELLS CAN DETECT AND ATTACK CANNCER CELLS. BUT SOME CANCER CELLS CAN AVOID DETECTION OR THWART AN ATTACK. SOME CANCER TREATMENTS CAN HELP THE IMMUNE SYSTEM BETTER DETECT AND KILL CANCER CELLS.

Question 61

HOW DO GENETIC CHANGES AFFECT CANCER TREATMENT

Answer 61

EACH PEARSONS CANCER HAS A UNIQUE COMBINATION OF GENETIC CHANGES. SPECIFIC GENETIC CHANGES MAY MAKE A PERSON´S CANCER MORE OR LESS LIKLEY TO RESPOND TO CERTAIN TREATMETN.

Question 62

WHAT CAUSES GENETIC CHANGES?

Answer 62

GENETIC CHANGES THAT CAUSE CANCER CAN BE INHERITED OR ARISE FROM CERTAIN ENVIROMENTAL EXPOSURES. GENETIC CHANGES CAN ALSO HAPPEN BECAUS OF ERRORS THAT OCCUR AS CELLS DIVIDE.

Question 63

HOW DOES AGE RELATE TO CANCER?

Answer 63

MOST OFTEN, CANCER-CAUSINGE GENETIC CHANGES ACCUMULATE SLOWLY AS A PERSONS AGES, LEADING TO A HIGHER RISK OF CANCER LATER IN LIFE.

Question 64

WHAT IS METASTASIS?

Answer 64

CANCER CELLS CAN BREAK AWAY FROM THE ORIGINAL TUMOR AND TRAVEL TRHOUG THE BLOOD OR LYMPH SYSTEM TO DISTANT LOCATIONS IN THE BODY, WHERE THEY EXIT THE VESSELS TO FORM ADDITIONAL TUMORS. THIS IS CALLED METASTAISS.

Question 65

Tissue Changes that Are Not Cancer

Answer 65

Hyperplasia occurs when cells within a tissue divide faster than normal and extra cells build up, or proliferate. However, the cells and the way the tissue is organized look normal under a microscope. Hyperplasia can be caused by several factors or conditions, including chronic irritation.

Dysplasia is a more serious condition than hyperplasia. In dysplasia, there is also a buildup of extra cells. But the cells look abnormal and there are changes in how the tissue is organized. In general, the more abnormal the cells and tissue look, the greater the chance that cancer will form.

Some types of dysplasia may need to be monitored or treated. An example of dysplasia is an abnormal mole (called a dysplastic nevus) that forms on the skin. A dysplastic nevus can turn into melanoma, although most do not.

An even more serious condition is carcinoma in situ. Although it is sometimes called cancer, carcinoma in situ is not cancer because the abnormal cells do not spread beyond the original tissue. That is, they do not invade nearby tissue the way that cancer cells do. But, because some carcinomas in situ may become cancer, they are usually treated.

Question 66

CARCINOMA

Answer 66

Carcinomas are the most common type of cancer. They are formed by epithelial cells, which are the cells that cover the inside and outside surfaces of the body. There are many types of epithelial cells, which often have a column-like shape when viewed under a microscope.

Carcinomas that begin in different epithelial cell types have specific names:

Adenocarcinoma is a cancer that forms in epithelial cells that produce fluids or mucus. Tissues with this type of epithelial cell are sometimes called glandular tissues. Most cancers of the breast, colon, and prostate are adenocarcinomas.

Basal cell carcinoma is a cancer that begins in the lower or basal (base) layer of the epidermis, which is a person’s outer layer of skin.

Squamous cell carcinoma is a cancer that forms in squamous cells, which are epithelial cells that lie just beneath the outer surface of the skin. Squamous cells also line many other organs, including the stomach, intestines, lungs, bladder, and kidneys. Squamous cells look flat, like fish scales, when viewed under a microscope. Squamous cell carcinomas are sometimes called epidermoid carcinomas.

Transitional cell carcinoma is a cancer that forms in a type of epithelial tissue called transitional epithelium, or urothelium. This tissue, which is made up of many layers of epithelial cells that can get bigger and smaller, is found in the linings of the bladder, ureters, and part of the kidneys (renal pelvis), and a few other organs. Some cancers of the bladder, ureters, and kidneys are transitional cell carcinomas.

Question 67

SARCOMA

Answer 67

Sarcomas are cancers that form in bone and soft tissues, including muscle, fat, blood vessels, lymph vessels, and fibrous tissue (such as tendons and ligaments).

Osteosarcoma is the most common cancer of bone. The most common types of soft tissue sarcoma are leiomyosarcoma, Kaposi sarcoma, malignant fibrous histiocytoma, liposarcoma, and dermatofibrosarcoma protuberans.

Question 68

Leukemia

Answer 68

Cancers that begin in the blood-forming tissue of the bone marrow are called leukemias. These cancers do not form solid tumors. Instead, large numbers of abnormal white blood cells (leukemia cells and leukemic blast cells) build up in the blood and bone marrow, crowding out normal blood cells. The low level of normal blood cells can make it harder for the body to get oxygen to its tissues, control bleeding, or fight infections.

There are four common types of leukemia, which are grouped based on how quickly the disease gets worse (acute or chronic) and on the type of blood cell the cancer starts in (lymphoblastic or myeloid).

Question 69

Lymphoma

Answer 69

Lymphoma is cancer that begins in lymphocytes (T cells or B cells). These are disease-fighting white blood cells that are part of the immune system. In lymphoma, abnormal lymphocytes build up in lymph nodes and lymph vessels, as well as in other organs of the body.

There are two main types of lymphoma:

Hodgkin lymphoma – People with this disease have abnormal lymphocytes that are called Reed-Sternberg cells. These cells usually form from B cells.

Non-Hodgkin lymphoma – This is a large group of cancers that start in lymphocytes. The cancers can grow quickly or slowly and can form from B cells or T cells.

Question 70

Multiple Myeloma

Answer 70

Multiple myeloma is cancer that begins in plasma cells, another type of immune cell. The abnormal plasma cells, called myeloma cells, build up in the bone marrow and form tumors in bones all through the body. Multiple myeloma is also called plasma cell myeloma and Kahler disease.

Question 71

Melanoma

Answer 71

Melanoma is cancer that begins in cells that become melanocytes, which are specialized cells that make melanin (the pigment that gives skin its color). Most melanomas form on the skin, but melanomas can also form in other pigmented tissues, such as the eye.

Question 72

Brain and Spinal Cord Tumors

Answer 72

There are different types of brain and spinal cord tumors. These tumors are named based on the type of cell in which they formed and where the tumor first formed in the central nervous system. For example, an astrocytic tumor begins in star-shaped brain cells called astrocytes, which help keep nerve cells healthy. Brain tumors can be benign (not cancer) or malignant (cancer).

Question 73

Other Types of Tumors

Answer 73

Germ Cell Tumors

Germ cell tumors are a type of tumor that begins in the cells that give rise to sperm or eggs. These tumors can occur almost anywhere in the body and can be either benign or malignant.

Our page of cancers by body location/system includes a list of germ cell tumors with links to more information.

Neuroendocrine Tumors

Neuroendocrine tumors form from cells that release hormones into the blood in response to a signal from the nervous system. These tumors, which may make higher-than-normal amounts of hormones, can cause many different symptoms. Neuroendocrine tumors may be benign or malignant.

Our definition of neuroendocrine tumors has more information.

Carcinoid Tumors

Carcinoid tumors are a type of neuroendocrine tumor. They are slow-growing tumors that are usually found in the gastrointestinal system (most often in the rectum and small intestine). Carcinoid tumors may spread to the liver or other sites in the body, and they may secrete substances such as serotonin or prostaglandins, causing carcinoid syndrome.

Question 74

RADIOTHERPHY

Answer 74

The use of high-energy radiation from x-rays, gamma rays, neutrons, protons, and other sources to kill cancer cells and shrink tumors. Radiation may come from a machine outside the body (external-beam radiation therapy), or it may come from radioactive material placed in the body near cancer cells (internal radiation therapy or brachytherapy). Systemic radiation therapy uses a radioactive substance, such as a radiolabeled monoclonal antibody, that travels in the blood to tissues throughout the body. Also called irradiation and radiotherapy.