Session 5 - Radiotherapy Flashcards
What is a major issue with radiation therapy?
Potentially carcinogenic
Give two local controls used in current cancer treratment
Surgery
Radiotherapy
Give two systemic controls used in current cancer treatment
Chemotherapy
Immunotherapy
Give three palliative controls used in current cancer treatment
Radiotherapy
Chemotherapy
Immunotherapy
What percentage of cancer patients undergo radiotherapy at some point?
50%
Give three types of radiotherapy
External beam
Brachytherapy
Unsealed sources
What is the objective of radiotherapy
To maximise dose to tumour
Minimise dose to normal tissue
What does the process by which radiation is absorbed in a cell depend on?
Energy of the photons
Chemical composition of the absorbing material
What is the comptom process?
High energy photons ionise atoms in a tissue and proceed through it at a reduced energy level. Many fast electrons are produced which will go on and ionise other atoms of the absorber and produce a deflected/scattered photon of reduced energy.
This process is independent of atomic number of absorbing species and thus avoids practicioner having to avoid tissues with differing tissue density.
An example of this process is found in radiotherapy.
What is the photoelectric process?
Low energy photons will ionise atoms and produce fast electrons but will in themselves be entirely absorbed. This varies rapidly with the atomic number.
An example of this process is found in diagnostic x-rays.
What are the two methods by which ionising radiation acts to kill cells?
Directly
Indirectly
What is the directly acting method by which ionising radiation kills cells?
– If the atoms of the target molecule (DNA) are ionised this is a diret effect. This cannot be modified by sensitisers and protectors
What is the indirectly acting method by which ionising radiation kills cells?
If the radiation interacts with other molecules (H20) to produce free radicals that migrate to DNA. This accounts for 2/3 of cellular damage and is modified by sensitizers and protectors.
What is the principle target of ionising radiation in radiotherapy?
DNA of cancer cells
Why is DNA the primary target in radiotherapy?
Only needs to damage a few essential genes to induce apotposis
Chemically, what are three things radiation can do to DNA to damage, and give two examples of each
Base damage • Thymine Glycols • 8-Hydroxyguanine Sugar damage • Abasic sites • Strand break lesions Strand breaks • Single strand breaks • Double strand breaks
Why are double strand breaks critical cell killing leasions
. Double strand break repair is error-prone in mammalian systems. Misrepaired Double Strand Breaks are the principle lesions of radiation mutation and visible chromosomal aberration formation.
What is therapeutic gain?
The dose at which you can attain tumour control AND acceptable damage to normal tissue
How is therapeutic gain achieved? (2 ways)
Fractionation
Multi-Beam Conformal Radiotherapy
What is fractionation?
Fractionation of the radiation dose (splitting of the total dose into many single doses) produces, in most cases, better tumour control for a given level of normal tissue toxicity than does administration of a single large dose.
Fractionation spares normal tissue by allowing for damage repair between doses.
What is the issue with tumour hypoxia in cancer, and how does fractionation overcome this?
Proteins produced in hypoxia, such as Hif-1 and CA IX, can cause radioresistance. Fractionation allows radiotherapy to overcome this resistance by spreading out the doses over time in order to allow the previously hypoxic cells to become oxic and vulnerable to radiation.
What is multiple beam radiotherapy?
Allows the radiologist to superimpose the x-ray dose over the tumour bearing region – allowing a high dose to hit the tumour volume with sparing of adjacent tissues.
This combined with a multi-leaf collimator allows the radiologist to shape the x-ray beam to the tumour shape, in order to allow a high dose region to fit the tumour volume, with greater sparing of adjacent tissue.
What is protonic therapy?
A form of radiotherapy which presents energy “peak” once it reaches target tissue, before dropping off rapidly.
Allows targeted irradiation of tumour and minimal damage to surrounding tissue.
What is an issue with protonic therapy?
Tumours rarely fall neatly into braggpeak, and therefore multiple proton beams must be used in order to facilitate effective treatment
What are the advantages of protonic therapy?
, the lack of soft tissue damage surrounding the tumour is still significant enough to warrant its use on the treatment of tumours in vulnerable locations, such as the brain.
What is a universal carcinogen?
Radiation
Induces cancer in most tissue of most species of all ages, as a result of all penetrating nature.
How many cancer deaths result directly from radiotherapy?
3680/year
Outline nuclear medicine imaging
- Radiopharmaceuticals are taken internally, by intravenous injection or via injection.
- External detectors (gamma cameras) capture and form images from the radiation emitted by the radiopharmaceuticals
- Differ from other tests in that they show the physiological function of the system being investigated. Generally more organ or tissue specific than those in conventional radiology imaging, which focus on a particular section of the body.
- Can be used for whole body bone scans in evaluation of bone related pathology
Give three uses of nuclear medicine imaging
analyze kidney function.
visualize heart blood flow and function.
scan lungs for respiratory and blood flow problems.
identify inflammation in the gallbladder.
evaluate bones for fractures, infection, arthritis and tumours.
determine the presence or spread of cancer in various parts of the body.
identify bleeding into the bowel.
locate the presence of infection.
measure thyroid function to detect an overactive or underactive thyroid.
investigate abnormalities in the brain, such as seizures, memory loss
and abnormalities in blood flow.
localize the lymph nodes before surgery in patients with breast cancer or
melanoma.
What is a PET scan?
A nuclear medicine imaging technique that produces a three-dimensional image or picture of functional processes in the body. The system detects pairs of gamma rays emitted indirectly by a positron-emitting radionuclide which is introduced intot hebody on a biologically active molecule. 3-d images of tracer conc within body are then constructed by computer analysis. In modern scanner 3-d imaging is often accomplished with the aid of a CT X-ray scan performed on the patient during the same session, in the same machine.
If the biologically active molecule chosen for PET is FDG, an analogue of glucose, the conc of tracer imaged give tissue metabolic activity n terms of regional glucose uptake. Use of this tracer results in the most common types of PET scan.
