VERT SESSION (RANDOM STUFF)

Question 1

what are the two types of radiation produced in the linac treatment head and describe what they are.

Answer 1

1. characteristic - produced when an incident electron knocks out an electron from the tungsten atom
2. Bremsstrahlung - produced when electrons are slowed down, ion the process they release x-rays

Question 2

what are the 3 planes of the body

Answer 2

1. transverse - perpendicular to the sagittal and coronal planes.
2. coronal - vertical plane running side to side splits the body into anterior and posterior
3. sagittal - vertical plane running from head to toe splits the body into left and right.

Question 3

describe image guided radiotherapy

Answer 3

using a ct scanner to get an image whilst the patient is on the couch to compare to the planning ct - ensures patient is in the right position.

Question 4

what is the inverse square law

Answer 4

if we increase the distance from the focal spot the dose will decrease

Question 5

What technique harnesses the inverse square law and when is it used?

Answer 5

extended-beam delivery technique - used in total body irradiation for lymphoma and bone marrow transplants.

Question 6

what is the isodose and how does you calculate it

Answer 6

high dose to the skin but 100% of the dose is deposited around 1.5cm below the skin.

calculate: energy/4

linac energy normally 6-10MV so 6-10/4

Question 7

describe parallel opposed pair, what are the limitations of this. When is it used?

Answer 7

using two beams to get a homogenous dose throughout the patient. The treatment is very high dose to the tumour and surrounding structures = high side effects so it is only used for palliative patients.

Question 8

what is intensity-modulated radiotherapy what are the benefits and limitations

Answer 8

using multiple beams and different points. Has amazing dosimetry giving high dose to the tumour but minimal dosage to surrounding structures. A limitation is the static movement is very time consuming and the patient must move halfway through treatment

Question 9

what is voluted arc therapy

Answer 9

uses multiple beams similar to IMRT but the beam is always being modulated by multi-leaf collimation which allows for an effective dose

Question 10

define tolerance dose

Answer 10

the amount of radiation an organ can tolerate. If only one part of the organ is being treatment the tolerance can increase

Question 11

define isocenter

Answer 11

1. where the lasers intersect
2. 1m from the treatment head
3. the point in space which the gantry rotates around
4. 9/10 where the dose is prescribed from

Question 12

what is patient separation

Answer 12

the distance between the tissues can cause problems in head and neck patients as less photons are attenuated due to width of the head so normally experience side effects on skin compared to pelvic patients