WK 10- CLINICAL USE OF RADIOTHERAPY AND DIAGNOSTIC IMAGING

Question 1

What is the action of ionizing radiation

Answer 1

Transfer of energy that results in damage caused to an atom→ creating a free radical (free electron) to dispatch and damage DNA

Question 2

What are the two different mechanisms used in radiotherapy

Answer 2

Usage of photons and electrons

Question 3

How does radiation kill cells

Answer 3

free electrons will cause damage through dislodging and cause bases to break- cause double stranded breaks that are hard to fix- will causes cells to undergo apoptosis

Question 4

How do photons work in radiotherapy

Answer 4

photons are essentially just visible light particles that are able to travel in a straight line into the body, causing damage on entry, depositing max energy a few mm under the skin, and then causing damage on exit

Question 5

How do electrons work in radiotherapy

Answer 5

Electrons are small light particles that scatter easily and only leave an entry dose (damage only on entry)-> most damage is done superficially as this is where highest dose is delivered

Question 6

What causes the drop in energy once particles (both photon and electrons) are inside skin

Answer 6

inverse square law and loss of energy through transfer into cells is responsible for the gradual decline in energy once particles are in skin

Question 7

what is the inverse square law- how can we utilise it to gain protection from radiation

Answer 7

Law states that doubling distance from the source will decrease your risk of exposure/risk of harm by 4

Question 8

What is the isocentre

Answer 8

This is where the highest dose of energy emitted will land- want middle of the tumour to be here to gain maximum therapeutic effects

Question 9

What is the major aim of radiation

Answer 9

To deliver high radiation doses to the tumour to gain therapeutic effects, but deliver low level radiation to peripheral tissues to minimise collateral damage to healthy tissue

Question 10

What are the 4 factors that influence use of radiation in cancer treatment

Answer 10

1. Patient needs= is the radiation for symptom control or is it curative
2. Tumour factors= the type of tumour, size of tumour, location
3. Tolerance doses= doses high enough to kill tumour, but not to damage surrounding tissue
4. Efficiency

Question 11

Why is accuracy so important when delivering radiotherapy

Answer 11

Accuracy in terms of geographic (hitting the right locations) and dosimetric (machine callibration-dosage) are important in ensuring effective treatment of the tumour, but minimising the impact on surrounding healthy tissues (eg. if go over tolerance in spinal cord, toxicities can result and cause paraplegia)

Question 12

How can positioning of a patient - give 2 examples

Answer 12

Important to allow the radiation to work in different angles to target different locations-> eg. raising arms to gain access to under arms, using a belly board to shift the small intestine and allow view of spinal cord etc.

Question 13

Between X-ray and CT scan, which would be most effective in assessing patients pre-radiation and why

Answer 13

X-Rays would only show bony anatomy and limited soft tissus, whilst CT scans allow you to accurately see soft tissue structures and tailor the treatment towards the patients anatomy-> aids in accuracy of treatment (eg. use oblique rays)

Question 14

Why is having a margin in radiotherapy use important

Answer 14

• margin of normally 5-8mm
  a) cancer is often well circumscribed so a margin would allow for cancer projections to also be treated
  b) patient may breathe/wriggle during treatment- tumour may move slightly but remain within the margin being treated

Question 15

What is meant by treatment verification- how is this done

Answer 15

Verification- through using the same fraction everyday, using the exact same positioning, have the same external set up and even using imaging devices to ensure accurate set up of internal anatomy- allows the lasers to hit the isocentre of the tumour every single treatment, aiding in efficacy
-this is often done by tattooing a small dot where the lasers should hit

Question 16

What are examples of early radiation toxicity

Answer 16

Damage to rapidly dividing tissue: Denudation of mucosa, skin (rapidly proliferating tissues), Erythema, Desquamation (dry/moist), Alopecia, Inflammation, eg cystitis, proctitis, oesophagitis, cytopaenia

• Occurs at moderate doses (usually week 2-3)
• Almost always completely reversible, heals spontaneously within 4 weeks of completion

Question 17

What are examples of late radiation toxicity

Answer 17

Occur at least 6 months after treatment

• Fibrosis/microvascular damage to non-proliferating tissues, Induration, Telangiectasia, Atrophy, Hyper-or hypopigmentation, Necrosis, Loss of function, Glomerulonephritis → renal failure, Oesophagealstenosis → dysphagia
• Minimally reversible –scarring (Hyperbaric O2 may help)

Question 18

What is radiation-induced malignancy

Answer 18

As radiation is being use to damage cellular DNA, damage of previously healthy cells can potentially cause cancer- very rare and less of an issue when treating malignancy, more related to radiation exposure

Question 19

What does the degree of acceptable toxicity for treatments depend on

Answer 19

Depends on whether the treatment intent is;
palliative: minimise any toxicity that impacts on QOL or takes considerable amount of time
or curative: accept more short term toxicity

Question 20

Why would palliative treatment be at a higher dose/fraction

Answer 20

Allows patient to receive higher doses in a shorter period of time to allow for effective results, but also allows patients to spend their last few months/years with family

Question 21

What are the 5 R’s of radiobiology

Answer 21

1. Radiosensitivity
2. Reoxygenation
3. Repopulation
4. Repair
5. Redistribution

Question 22

What is the main reason for fractionating radiation

Answer 22

Fractionating is spreading a course of radiotherapy over days/weeks-> allows normal tissues to repair much of the radiation damage, increases the tolerability by patients and increases efficacy

Question 23

What cells, and tumours, are most sensitive to radiation (radiosensitive)

Answer 23

Tumours: small cell, lymphoma, seminoma

Normal cells: hair follicles, epithelium

Question 24

What cells, and tumours are most resistant to radiation (radiosensitive)

Answer 24

Tumours: renal, melanoma, pancreas, GBM

Normal cells: Connective tissue, conjunctiva

Question 25

What is reoxygenation and why is it important in treatment (fractionating)

Answer 25

Oxygens is required to make radiation-induced DNA damage permanent-> hypoxic cells are therefore significantly more resistant-> fractionating treatment allows time for hypoxic cells to become oxic (and sensitive to radiation- allows outside layers to peel off and for radiation to reach the core)

Question 26

What is repopulation- how does it affect reatment

Answer 26

Cells begin to increase their ability to rapidly repopulate after being treated with radiation → keep treatment short otherwise it becomes useless as the cells only begin to repopulate quicker/waste the Gy

Question 27

How does ability of tumour cells to self-repair impact on treatment

Answer 27

Tumour cells have faulty DNA repair mechanisms→ Less able to repair radiation induced DNA damage when compared to healthy cells with repair mechanisms

Question 28

What does redistribution refer to - how does it relate to treatment

Answer 28

-Some stages of cell cycle are more radiosensitive than others
→G2/M most sensitive → Least sensitive in S / G0
-Fractionating treatment increases chance of hitting a cell during sensitive phase

Question 29

If a patient was in palliative care, what dosages/fractions would they be given

Answer 29

• 8Gy/1#, 20Gy/5#, 30Gy/10#
• Higher dose = more substantial, longer durable effect but more scaring/late toxicity-> often doesn’t matter if the patient is going to die soon anyway because they may not experience the toxicities
• Accelerate treatment by giving larger dose per fraction- allow time to be spent with family/friends/at home

Question 30

If a patient was in palliative care, what dosages/fractions would they be given

Answer 30

Most schedules give 2Gy/day, 5 days per week

• Total dose 50-78Gy
• Dose usually approaches highest tolerable dose for area- allow for some short term toxicities

Question 31

What are the 3 major modalities of cancer treatment

Answer 31

Surgery (most important- but on its own isn’t often curative) / Chemotherapy / Radiotherapy
-often used in combination

Question 32

What is neoadjuvant treatment

Answer 32

Using radiotherapy before surgery in the removal of tumours-> aids in shrinking size and aiding resection, also allows you to reduce the chance of cancer recurring/reduces toxicities

Question 33

What is primary treatment

Answer 33

Concurrent chemoradiotherapy (combine chemo and radiation)→ allows patients to often keep their anatomy through reducing need for surgering

Question 34

What is adjuvant therapy

Answer 34

Chemotherapy after surgery-> reduces risk of recurrence (if the risk is high)

Question 35

Which has a higher radiation exposure rate- diagnostic or therapeutic radiation

Answer 35

Therapeutic- comes from multiple radiation sources- gives blurred image

Question 36

How does a CT scan work

Answer 36

• single source radiation that fans out in one plane and is caught by the detector
• allows you to get more information (especially about soft tissue)
• images are reconstructed in different planes

Question 37

How does a bone scan work

Answer 37

Tracers are taken up by osteoblasts, shows area of bone turnover-> high bone turnover= metastasis

Question 38

How does a PET scan work

Answer 38

Glucose labelled with 18-F/tracer taken up by metabolically active tissues (includes brain, heart, tumour), excreted in urine (so goes to kidney and bladder)-> )→ causes positrons to be emitted→ where there are a lot of positrons moving-highlights metabolic activity

Question 39

Where does the PMSA tracer go/what does it stand for

Answer 39

PSMA (prostate specific membrane antigen→ only goes to prostate cells/salivary cells)

Question 40

What kinds of cancers are PET scans not as effective in

Answer 40

Slow growing cancers- eg. prostate cancers

Question 41

What are 2 imaging techniques that do not use radiation

Answer 41

MRI, Ultrasound

Question 42

How does an ultrasound work

Answer 42

Emits sound waves that can be picked up by a detector

-allows you to get outlines of organs

Question 43

How does an MRI work

Answer 43

uses very strong magnetic field to align atoms-> causes energy emission that can be formed into an image

Question 44

What are the 3 main principles of radiation safety

Answer 44

Time, distance, shielding

-safest way to use radiation is to not use it-> look for other alternatives

Question 45

What factors of ‘time’ contribute to radiation safety

Answer 45

• Minimise time exposed
• Shorter, simpler treatments
• Operate as quickly as possible (eg image intensifier)
• Fewer X-ray / scan requests

Question 46

What concept of ‘distance’ contribute to radiation safety

Answer 46

Inverse square law: Doubling distance from radiation source decreases exposure by factor of 4 (step back)

Question 47

What factors of ‘screening’ contribute to radiation safety

Answer 47

Type of shielding depends on photon energy
-Low energy: paper / foil (eg UV)
-Intermediate energy: lead glass
-High energy: lead / concrete
→ creating a maze can artificially create distance; need to increase distance between radiation and staff, but want to minimise the time taken to get to patient (in cases of emergency)