P3 topic 3 Flashcards
what are the side effects of palliative radiotherapy?
tiredness, sickness, feeling very sore
when does palliative radiotherapy cause sickness?
if there has been treatment to the stomach, abdomen or brain
when does palliative radiotherapy cause the patient to feel sore?
following treatment to the lung, head or neck
what are patients often prescribed to control sickness?
they are often prescribed anti-emetic drugs
what’s a problem with radiotherapy?
not all cancers respond well to it
why does radiotherapy cause damage to cells?
the radiation ionises the atoms in the cells
What does external radiotherapy work well for?
treating cancer cells in a localised area of the body
what is a benefit of external radiotherapy?
patients can have external radiotherapy for more than one area of the body at the same time
how regularly can patients have external radiotherapy?
patients can have 1 or 2 treatments or up to 10 short treatments given over 2 weeks
what are the different types of internal radiotherapy?
an injection, a radioactive metal implant inserted into the patient’s body, drink or capsule containing radioactive materials
what are injections of radioactive substances usually used for?
to treat widespread cancer in the bones
where is the radioactive metal implant put inside the body?
very close to the cancer- these are sometimes in the form of wires
what are patients told after being treated with radioactive materials?
they are often allowed to go home, but to to steer clear of children or pregnant women
what can also be used in the
treatment of cancer?
an intense beam of fast moving neutrons
how can neutrons ionise atoms?
they have no charge, but because they have a large speed and mass they have enormous amounts of kinetic energy and can ionise atoms- they can produce 5 times more ionisation than x rays and beta particles
how are intense neutrons beams produced?
by bombarding berylium with protons from a particle accelerator
how is the neutron beam used?
it’s pointed at the tumour with the help of lasers and is able to stop the growth of the tumour or possibly destroy it completely
palliative radiotherapy
treatment to shrink a cancer or slow down its growth- it doesn’t aim to cure the cancer completely and uses either external or internal radiation
medical radioactive tracer
a radioactive substance that is either injected into or swallowed by a patient
tracers
they are absorbed differently by different tissues in the body; a radiation detecter can produced an image showing the distribution of the radioactive substance
what are radioactive tracers?
either beta or gamma emitters with short half lives
Iodine-131
beta; half life of 8.1 days; used to monitor passage of fluid through the kidney
Technetium-99
gamma; half life of 6 hours; used to monitor blood flow in the brain or lungs, growth of bones; blood circulation in the heart
Xenon-133
gamma; half life of 2.3 days; used to monitor the function of the lungs
how does iodine-131 work?
a healthy kidney will pass the iodine through to the bladder; if there is a blockage, the iodine builds up in the kidney and can be detected
why does the radioactive tracer need to have a suitable half-life?
it can’t be so short that there is no time to see the effect, but it can’t be too long so the tracer does not exist for too long in the body
what are PET scanners used to monitor?
activity of the brain; spread of cancer through the body; flow of blood through organs such as the heart
what are radioactive isotopes (beta-plus emitters) first produced in?
a cyclotron
radiopharmaceutical
a substance produced by tagging radioactive isotopes to natural chemicals in the body such as glucose, ammonia and water- it’s injected into the patient
what will happen when the radiopharmaceutical is injected into the body?
it will go to areas which use the natural chemical
what is fluorine-18 tagged to?
glucose to produce fluorodeoxyglucose (FDG)- cancers use glucose differently from normal tissues so the FDG will reveal cancerous tissues
what do the radioactive isotopes used include?
carbon-11, nitrogen-13, oxygen-15 and fluorine-18 which have short half lives
what does a PET detect to work?
the gamma rays produced by the annihilation of positrons (emitted by radioactive isotopes) and electrons
why are PET scanners very expensive?
they also require a cyclotron to produce the radiopharmaceuticals
how many PET scanners are there around the world?
only about 150- mostly in the developed world- USA, Europe and Japan
what can ionising radiation do?
damage body tissue- cells may mutate, die or fail to reproduce themselves
effects of radiation damage
skin burns, nausea, destruction of bone marrow, hair loss, sterility, cancers, changes to genetic material
how are people who work with ionising radiation protected?
keeping the distance between workers and source of radiation as large as possible, keeping exposure time to a min, using shielding such as lead-lined aprons or concrete walls; wearing dosimeters
dosimeters
radiation-sensitive film within a holder- the film goes darker when exposed to increasing amounts of radiation
what are the three types of damage causes to cells by ionising radiation?
cells become damaged then repair themselves and operate normally; cells become damaged then repair themselves but function abnormally, such as failing to reproduce themselves or reproducing at an uncontrolled rate- this is the main cause of cancers; cells become so damaged they die
what does the amount of damage caused by the radiation depend on?
the dose received; the parts of the body exposed; the nature of the radiation- alpha particles are easily stopped by the skin, so do not present a serious problem until the source gets inside the body
which parts of the body are most susceptible to radiation?
rapidly dividing cells (such as blood cells and hair follicles)
equivalent dose
the effective biological damage to human tissue by ionising radiation is known as the equivalent dose
what is the equivalent dose measured in?
Sieverts (Sv)
what happens the higher the equivalent dose?
the greater the chance of biological damage
what’s the max radiation dose a day that causes no actuate symptoms?
up to 0.25 Sv a day
when does the radiation dose begin to cause acute symptoms?
between 0.25 Sv and 1 Sv a day can cause nausea, loss of appetite and damage to bone marrow
what is the maximum permissible dose for medical personnel a year?
20 mSv per year, averaged over 5 years, with a max of 50 mSv in any one year
what are patients always given?
the smallest dose of radiation needed for their treatment
equivalent dose of dental x ray
0.0005 mSv
equivalent dose of full body CAT scan
15 mSv
equivalent dose of fluoroscopy
5 mSv
estimated max dose to residents of Fukushima following nuclear accident in 2011
68 mSv
quarks
tiny particles which make up all matter
who was the quark model proposed by?
independently by both Murray Gell-Mann and George Zweig in 1964
what are quarks?
fundamental particles- they cannot be subdivided into smaller particles
fundamental particles
electrons, positrons and quarks
charge of up quark
+ two thirds e
charge of down quark
-a third e
what do both experiment and theory show?
that it’s impossible to isolate quarks
what are the quarks that make up a neutron?
one up quark and two down quarks
what are the quarks that make up a proton?
two up quarks and one down quark
how big is a quark compared to a proton or a neutron?
80 times smaller
beta minus decay and quarks
a down quark in a neutron changes into an up quark and an electron, the electron is emitted as a beta-minus particle so the neutron now has two up quarks and one down quark, so is now a proton
beta plus decay and quarks
an up quark in a proton changes into a down quark and a positron; the positron is emitted as a beta-plus particle so the proton now has 2 down quarks and one up quark so is now a neutron
how might a proton in the nucleus change?
through beta-plus decay into a neutron and a positron
what can happen to a neutron on its own?
it can decay to release an electron- the half-life of a free neutron is about 11 minutes
N-Z curve
a graph if the number of neutrons against the number of protons for all known nuclei
where do the stable nuclei lie?
on a curve starting from the origin with slightly increasing gradient (black line on graph)
what do stable nuclei with atomic numbers less than 20 have?
equal numbers of neutrons and protons
what do most stable nuclei have?
more neutrons than protons
what are unstable nuclei above the stability curve?
neutron rich- those below are neutron poor
what are the protons and the neutrons in the nucleus held together by?
a strong nuclear force, which has to overcome the repulsion between the positively charged protons
how does a neutron rich nucleus decay?
it has too many neutrons to be stable and decays by emitting a beta-minus (electron)- a neutron changes into a proton and an electron- this brings the nucleus closer to the stability curve
how does a neutron poor nucleus decay?
it has too many protons to be stable and decays by emitting a beta-plus (positron)- a proton changes into a neutron and a positron- this brings the nucleus closer to the stability curve
what decays by emitting alpha particles?
unstable nuclei with a high atomic number (above 82) decay by emitting alpha particles- this has little effect on the nucleus’ position relative to the stability curve
what also happens during beta plus decay?
a nucleus also emits a neutrino- neutrinos have no charge and a negligible mass, so they don’t interact with matter and are therefore very difficult to detect
what is the mass of a neutrino?
one billionth of the mass of a proton
when was the existence of neutrinos predicted?
by Wolfgang Pauli in 1930, but they are only discovered 26 years later
what links the universe and neutrinos?
the universe is believed to be saturated with neutrinos
what does an alpha particle contain?
2 protons and 2 neutrons
what may an unstable nucleus of heavier atoms do?
emit alpha particles and transmute into a new daughter nucleus
what do done lighter nuclei do?
emit beta particles which are fast moving electrons
what happens in beta minus decay?
a neutron inside the nucleus changes into a proton and an electron; the electron is emitted as a beta particle and the proton remains in the nucleus
gamma decay
gamma rays are often emitted following alpha or beta emission to reduce surplus energy; gamma rays have no charge and so there is no change to the structure of the nucleus- the nucleus undergoes some rearrangement to get to a lower energy state
what type of decay do some proton rich nuclei undergo?
positron (beta plus decay)
beta plus decay
a positron removes a positive charge from the nucleus- a proton changes into a positron
what are all materials made up of?
atoms
isotopes
nuclei which have the same number of protons, but differing numbers of neutrons
mass of an electron
0.00055
what do some heavier isotopes emit to become stable?
neutrons
positron
the same mass as an electron but it has a positive charge of 1.6 X 10 -19- it’s the antiparticle to an electron
alpha
helium nucleus; 2+ charge; strongly ionising; stopped by paper, skin or 6cm air
beta
electron; 1-; weakly ionising, stopped by a few mm of aluminium
gamma
short wavelength EM radiation; no charge; very weakly ionising, significantly absorbed by a few cm of lead, or a few m of concrete
neutron
no charge; does not interacting with matter
beta-plus
positron; 1+; a positron interacts strongly with an electron to produce gamma rays
what are radioactive materials used in?
the treatment and diagnosis of cancer
what can ionising radiations do?
damage living cells, so exposure is kept to a minimum
what do radiographers and other people who work with ionising radiation need to do?
wear protective clothing, usually made of lead- they also wear dosimeters to record the amount of radiation exposure
