New modalities

Question 1

What are examples of high LET RT?

Answer 1

Alpha particles, neutrons

Question 2

When is neutron therapy most effective?

Answer 2

Salivary gland tumours

Question 3

Neutron therapy is useful in tumours with what characteristics?

Answer 3

o Large proportion hypoxic cells
o Tumours that do not re-oxygenate
o Tumours with broad shouldered dose-survival curves
o Slowly proliferating tumours

Question 4

What happens in high LET RT with regards to fractionation?

Answer 4

LRNT are not spared by fractionation of high LET RT and so use hypofractionation

Question 5

What is hadron therapy?

Answer 5

Subatomic particles e.g. protons (low LET), neutrons and carbons

Question 6

How does boron neutron capture therapy work?

Answer 6

• Thermal neutrons normally produce little radiobiological effect in normal tissue but can interact with boron containing drugs which preferentially localise to tumour to produce short range, densely ionising alpha particles.
• Potential use in:
  o GBM where BBB is disrupted in the tumour
  o Tumours which metabolise boron compounds e.g. melanoma
  o Any tumour that could have a MAB prepared
• The therapy itself is less demanding as it is only given 1 or 2 times
• Tabletop neutron generators more popular and cheaper

Question 7

How does proton beam therapy work?

Answer 7

• Low LET so good penetration
• Don’t deposit much energy until they slow down, this creates a delayed Bragg peak which can be utilised to minimise normal tissue effects by determining the Bragg peak to be in the centre of the tumour

Question 8

When is proton beam therapy useful?

Answer 8

Choroidal tumours and paediatrics

Question 9

What is FLASH RT?

Answer 9

• Ultra-high dose rate
• Normal = 3-4Gy / minute
• Flash = 100Gy/ second
• Normal tissue toxicity limited