14. Respiratory challenges in radiotherapy

Question 1

What are ‘organs at risk’?

Answer 1

Any organ which impacts how to treat a tumour.

Question 2

What are parallel organs?

Answer 2

When damage to part of the lung does not stop the whole lung working (no clinical toxicity). Too much can reduce overall function though.
This organ has volume dosed constraints

Question 3

What are serial organs?

Answer 3

When vital structures are in a sequence so if one part is damaged the whole function is affected.
This organ has fixed dose constraints.

Question 4

What happens is too much normal lung gets radiation?

Answer 4

Radiation pneumonitis (inflammation of the lungs)
Reduced lung function

Question 5

What are the radiotherapy techniques used to reduced dose to other lung?

Answer 5

1. Intensity Modulated Radiotherapy (IMRT)
2. Volumated Modulated Arc Therapy (VMAT)
3. Lateral Beam Arrangement

Question 6

What are the challenges in dose calculation?

Answer 6

Lung is mostly air, which changes how radiation behaves.
Heterogenous tissue: lungs are a mix of air and soft tissue so dose calculations are less predictable.
Electron scatter: Radiation behaves differently in air-filled tissue compared to dense tissues like muscle.
Range uncertainty: The actual dose received by the tumour can vary slightly from the planned dose.

Question 7

What happens when you breathe in relation to lung tumours?

Answer 7

Lungs and nearby organs move up to 2-3cm with normal breathing.

Question 8

What strategies are used in radiotherapy to manage respiratory motion?

Answer 8

Breath hold techniques
Respiratory Gating (tracking tumour position and delivering radiation only at specific phases of the breathing cycle.)
Four dimensional (4D) CT planning (Accounting for motion in treatment planning)