Organisation of the Body
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| Scale of cancer | Number one fear of British people
More that 200 type each with different causes, symptoms and treatments
Breast, lung, prostate and bowl cancers make up over half of cases
Male incidence rates have rise by 23% compared to 43% in women
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| Grade of tumours | Differentiation is incomplete to some extent
Described in terms of tumour grade
Grade I - well differentiated
Grade III - poorly differentiated
Has prognostic value
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| Stage of tumours | Described on the TNM scale (tumour size 1-4, lymph node involvement 0-3 and metastasis 0 or 1 )
Or on an overall scale of 1 (small localised) to 4 (metastasis)
Has prognostic value and often determines course of therapy
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| Survival rates of tumours | Different cancers have different clinical outcomes
Judged by survival or progression free survival
Early stage cancers have the best prognosis whilst late stage cancers have the worst
Linked to treatment options
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| Treatment options for cancers | Surgery 49% - can cure local cancers by removing the tumour
Radiotherapy 40% - large contribution
Chemotherapy 11% - relatively little use except in certain tumour types
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| Outcomes of DNA damage | Detected by damage sensors e.g. ATM
Can lead to cell cycle arrest, DNA repair or apoptosis
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| Ionising radiation | High energy low frequency wavelengths
Can ionise material
E.g. UV, X-ray and Gamma
Triggers a free radical cascade starting with water in molecular tissues
This generates DNA damage by many mechanisms
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| Iodine - 131 | A radioactive isotope of iodine used to treat thyroid cancer and hyper-thyroidism (Grave's disease)
Thyroid is a natural scavenger of iodine, so it concentrates in the thyroid gland
Repurposed for other purposes e.g. target CD20 receptors on B cells
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| Brachytherapy | Directly implanting metallic pellets into a patient
A radioactive material releases ionising radiation directly into the tumour
E.g. Iridium - half life 74 days
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| Radiotherapy Treatment | 60% of patients receive this (alone or alongside chemo/surgery)
High energy X rays delivered with a linear accelerator
Localised against the tumour to avoid normal tissue
Patient is immobilised
Planning CT performed
Can be palliative or curative
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| Linear accelerator | Electrons accelerated using synchronised microwaves and a voltage gradient
X-rays produced by electrons striking a metal target
Energy of x-rays dependant on electron energy
Isocentric set up - machine rotates around the tumour
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| The Compton effect | Ionisation of water forces out electrons
The scattered photons then have an increased wavelength
Electron has a lower wavelength - depth of the effect is pronounced -
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| Distribution of dose | The peak delivery is around 2 1/2 cm depth
At greater depths the ionising potential is lost
Changing voltage has very little effect
Due to Compton effect
Limits therapeutic potential
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| Organs at risk | Many structures in the body are radiosensitive
E.g. heart, lungs, spinal cord
Dosage to these areas must be limited to prevent damage
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| Beam modification - multi leaf collimation | Lead plates that can be adjusted to shape the x-ray beam
The radiotherapy fields can be conformed to the shape of the tumour
Enables shielding of some surrounding normal tissue
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| Wedges | Thick end absorbs the beam more that the thin part
Alters dose distribution of the beam
Steepness of the wedge determines the change in beam characteristic
Dynamic wedges more common than manual wedges
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| Gross tumour volume | Extent of disease detectable by imaging or other clinical methods
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| Clinical target volume | Contains the GTV and surrounding areas considered likely to contain subclinical disease e.g. adjacent tissues, lymph nodes
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| Planning Target volume | Contains the CTV and a margin to allow for physiological and technical variations
Accounts for limitations in imaging and motion
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| Immobilisation | Treatment must be delivered to the intended area otherwise the tumour is missed and normal tissue inadvertently irradiated
Need to be able to place patient in a position where they will remain still
Precisely matched to patient anatomy
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| What does the level of immobilisation depend on | How much the organ moves e.g. lung tumours
Level of importance of immobility e.g. radiosurgery of brain tumours
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| Planning CT | Patient undergoes a CT wearing any immobilising structures
They are in the same position as they will be for the radiation - markers are placed on the patient to ensure the same position is used each time
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| 3D conformal radiotherapy - Planning | Patients scanned in treatment position
Set up is identical to treatment room
Tattoo made on skin which is then covered with radio-opaque marker for visualisation on CT
Correlation between marker and CT images
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| 3D conformal radiotherapy - process | Involves a high dose of radiotherapy to patients with curable disease
3 or more intersecting beams
Enables precise decisions to be made regarding treatment volumes
Homogenous dose across tumour
Beams can be aligned, shaped and wedged
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| Work plan of radiotherapy | Oncologist plans treatment
Each Ct slice outlines tumour and organs
Grow to PTV
Decide on dose and tell physicists what tolerances will be accepted by tissues
Physicists optimise beam arrangements
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| Stereotactic radiotherapy | Beams delivered from many directions
Lots of beams provide low dose from each direction to give a highly specific higher dose
Limits dosage to surrounding tissue
SABR (A-ablative) at non-cranial sites
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| Intensity modulated radiotherapy | Using varying intensities of hundreds of small radiation beams produce dose distributions that are more precise compared to 3DCRT
Difference in physics
Allows irradiation of local lymph nodes
Lowers exposure to surrounding tissue
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