SABR/SBRT

Question 1

Define the term stereotactic (general).

Answer 1

incredibly precise treatment.

Question 2

In general what is stereotactic radiation?

Answer 2

High precision image guided dose delivery to a target (1mm and 1* accuracy for field placement)
Usually requires intra-fraction motion management (where applicable).
Highly conformal dose - with steep dose gradient

Question 3

Define SBRT (Stereotactic Body Radiotherapy).

Answer 3

SBRT- USED FOR DOSE ESCALATION (targets in close proximity to OAR - E.G. spine, prostate). Stereotactic radiation that occurs extracranially.
Typically 1-5 fractions, may be up to 8. Usually more than or equal to 8Gy per fraction.
Highly conformal treatment with steep dose gradients.
Intra-fraction motion management is essential.

Question 4

Define SABR (Stereotactic Ablative Body Radiotherapy).

Answer 4

SABR is for ABLATION rather than dose escalation - treats a larger area than SBRT in order to destroy tumour and some surrounding tissue.
Ablation is often used if the patient is awaiting a transplant.
Used in sites such as lung, liver and kidneys.
Typically 1-5 fractions may be up to 8.
Usually more than or equal to 8Gy per fraction.
Highly conformal with steep dose gradient.

Question 5

Define SRS (Stereotactic radiosurgery)

Answer 5

Single fraction
Generally refers to intracranial treatment. (can be given to some extra-cranial sites).
12Gy -90Gy.

Question 6

Define SRS (stereotactic radiotherapy)

Answer 6

Only intra-cranial.
For larger lesions not suitable for SRS.
Used for post operative cavities. 
Fractionated, typically 2-5 fractions 
Lower BEDs than SRS.

Question 7

Compare the dose fractionation of conventional RT to stereotactic RT.

Answer 7

Conventional RT: 1.8–2.4 Gy per day, 15 – 40 fractions over 3 – 8 weeks. This allows for: normal cell repair, re-population after RT, re-distribution in cell cycle, re-oxygenation, radiosensitivity.

Stereotactic: More than 8Gy per day, 1-5 fractions, 1-2 weeks. Allows for: Less normal tissue irradiated, Anti–tumour effects such as injured vasculature and anti-tumour immunity

Question 8

What can stereotactic RT treat?

Answer 8

Primary and secondary disease
< 5cm max dimension
Non-malignant conditions e.g. Spinal Cord AVM, meningioma
For dose escalation
For ablation
Applied to tumours considered radioresistant

Question 9

What is Oligometastasis?

Answer 9

An intermediate state of ‘metastasis’ between localised disease and widespread metastasis. Important because patients with limited number of metastasis can now be cured.

Question 10

What are patient performance indications for stereotacitc treatments?

Answer 10

ECOG performance status 0-2.
Life expectancy > 6 months (3 months for liver).
Low metastatic burden (≤ 5mets, < 5 cm in dimension).

Question 11

What are contra-indications for stereotactic RT?

Answer 11

Prior RT
Unable to lie flat for prolonged period
Cannot receive chemo 1 – 4 weeks pre or post SBRT (depending on site for treatment)
Severe connective tissue disease or scleroderma
Claustrophobia
Mental status prevents of patient compliance

Question 12

Define immobilie, stabilise and positioning?

Answer 12

Immobilise:  prevent (something or 
someone) from moving or operating as 
normal 
Stablise: make or become unlikely to 
change, fail, or decline 
Positioning: put or arrange (someone/
something) in a particular place or way

Question 13

(MOTION MANAGEMENT) What are causes of internal motion in a patient and how are they managed?

Answer 13

Skeletal/muscular (i.e. the patient) 
    – mitigate through stabilisation
Respiratory motion 
    – evaluate with 4DCT, manage with compression (i.e. compression belt or compression plate), breath hold (i.e. DIBH, end expiratory breath hold [EEBH]) or gating. 
Cardiac motion
Peristalsis 
   – manage with compression belt/plate
Bladder and bowel filling and emptying 
  – manage with protocols, enemas, medications, catheterisation

Question 14

What are the sources of error in a patient?

Answer 14

•Position
•Immobilisation – choice of equipment
•Organ motion 
     –Respiration
     –Cardiac function
     – Peristaltic activity
     – Organ filling/emptying
•Correct use of immobilisation equipment

Question 15

What important factors should be considered relating to CT acquisition for stereotactic patients?

Answer 15

•Maximum 2 mm slices
• Scan limits should include Organs at Risk where DVH constraints are set e.g. whole of lungs with margin according to TPS guidelines
•Scan limits should be increased by 10 –15 cm sup/inf if non-coplanar beams are to be used
•4DCT (check recon for artefacts)
•Contrast –in particular if the target is near subclavian vessels (accurate delineation very important)
• Long scanning session with multiple scans required
•DIBH –scan twice to assess BREATH HOLD variability
–Patients will require a coaching session prior to CT depending on departmental approach

Question 16

What is the 4DCT scan primarily used for?

Answer 16

To capture an ITV (internal target volume). This volume takes into consideration full movements of the CTV on all planes
It is important to check the 4DCT scan for errors in binning or mismatches in tumour trajectory.

Question 17

What are IGRT requirements for stereotactic patients.

Answer 17

• All treatments require Pre-fraction CBCT
• RO must be present for all treatments and is responsible for approving all CBCT moves.
• Initial image registration is to be made utilising large clip box to exclude gross error; clip box is subsequently reduced to the region of interest for final image verification as determined by RO
• Pre-fraction CBCT translations > 1mm are actioned by RO.
• Pre-fraction CBCT rotations < 3˚ are accepted*
• Intrafraction CBCT and post-fraction also taken depending on technique, treatment duration, tumour motion and OAR proximity.

Question 18

Why is IGRT important for stereotactic patients?

Answer 18

• To ensure that the patient is within 1mm and 1 degree to what was planned.
  We are dealing with very steep dose gradients so the patient moving 1mm can change the dose by 3Gy
  May be treating in close proximity to OAR, thus ensuring accurate setup is important
  Dose from IMRT and VMAT is affected by geographical displacement (patient movement) more than separation or changes to patient contour (i.e. weightloss).

Question 19

What are some challenges to IGRT?

Answer 19

The patient (pain control, position has to be stable and reproducible). 
Efficiency in set up, IGRT and treatment delivery ( the patient is spending a longer time on the bed with all the CBCT scans being taken = greater chance of movement).