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Unit 20 Assignment 5
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Unit 20 Medical Physics Techniques Assignment 5 (P M D)
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Laura LatkovaRadiotherapy
Radiation therapy is a treatment that uses ionizing radiation to damage DNA of malignant
cells. This causes cellular death. By this cancer cells are removed.
This cancer treatment is done by LINAC machine or linear accelerator which is operated by
radiation therapist. Medical dosimetrist prescribes how the dose is delivered and radiation
oncologist prescribes the volume and dose of radiation. Inside LINAC, microwaves are used
to accelerate electrons or photons which then at high speed collide with target metal. This
produces high energy x rays which can be customised into shape of exact tumour which
needs to be removed.
As the x ray beam is higher energy the penetrating is deeper so there is less reduction of
dose with depth. Also as the beam is moved away from axis, the dose isn’t absorbed as it
should be so the dose delivered decreases.
Beam of x rays that is applied to tumour is customised, shaped to suit every individual
tumour of patients. This is done with compensators and wedges.
Compensators are specifically made for each individual to suit the shape and size of
tumour. This allows correct dose and distribution of radiation.
Wedges can lower the intensity of the beam in specific areas.
There are two types of therapy a patient can have by changing how the beam is used-
multiple (therapy uses separate beam of x rays from different location at the same time)
and rotational (therapy uses a beam which is pointed at the tumour during a rotation
around it. Both ways are healthier because they cause less damage to normal tissue around
the tumour.
Types of radiotherapy done by LINAC
Megavoltage radiotherapy produces very high energy x rays which are over 1000 keV. It is
the highest possible X ray therapy done and they are used for treatment of tumours deep
inside body.
Superficial radiotherapy only produces 36- 60 keV. This low energy x rays cannot penetrate
the tissue into depth therefore this therapy is used for treating skin cancer mainly.
Orthovoltage radiotherapy is used for treating tumours however it is useful only for tumours
which are from 4-6 cm under the skin as its x rays are medium energy 200- 500 keV.
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