Target Volume Localisation Flashcards
What are the main stages in the patient pathway? (9 marks)
Pre-planning stages: immobilise patient, create virtual representation and localise the tumour.
Planning: selects number of beams and geometry, optimise the plan, determine the amount of dose required/MUs
Post-planning: independently verify the dose, verify the set-up, record details of treatment, deliver the treatment.
What is the aim of immobilisation and give different types? (7 marks)
Aims: ensure the patient is in the correct position that is reproducible. Ideally the patient will also be as comfortable as possible as this will assist with reproducibility. Need low attenuation and artefacts. Should be easy to produce.
Types of immobilisation: restraint- thermoplastic shells for head and neck treatments, support - breast boards, vac bags, invasive - stereotactic frames for steoretactic treatments such as GammaKnife.
What is the aim of tumour localisation and what methods, and modalities, can be used to achieve this? (7 marks)
Aim: to determine the position and size of the GTV and CTV.
Modalities/methods: palpitation, CT, MRI, US, PET-CT, etc.
What are the pros and cons of CT representation? (6 marks)
Cons: exposure of patient to risks from ionising radiation, soft tissue contrast is worse compared to MR.
Pros: relatively cheap compared to MR, provides electron density map, is used readily by most TPS systems, relatively good resolution and free from distortion effects (unlike MR)
What are the pros and cons of MRI for RT imaging? (5 marks)
Cons: expensive, need to convert MRI data into suitable format (might not be usable for all TPS), prone to geometric distortion, no correlation with e density, no signal from bone.
Pros: no dose, great soft tissue visualisation, able to differentiate pathology,
What are the two main challenges with MR? (4 marks)
Need to correct for geometric distortions.
Need to develop an imaging method suitable for integration with TPS systems.
What are the pros and cons of PET-CT? (3 marks)
Pros: can see function with PET and structure with CT
Cons: Expensive, compromise quality of both, requires iimage interpretation.
