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Planning > SBRT/SABR > Flashcards

SBRT/SABR Flashcards

1
Q

Define sterotactic

A
  • high precision image guided dose delivery (1mm, 1 degree)
  • highly conformal dose with steep dose drop off
  • intrafraction motion management
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2
Q

What is SBRT?

A
  • sterotactic body radiotherapy
  • dose escalation for targets close to OAR (extracranial e.g. spine, prostate)
  • 1 to 5 #
  • > 8Gy per fraction
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3
Q

What is SABR?

A
  • sterotactic ablative body radiotherapy
  • for ablation (extracranial e.g. liver, lung, renal)
  • 1 to 5 #
  • > 8Gy per fraction
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4
Q

What is SRS?

A
  • sterotacitc radiosurgery
  • historically intracranial but can be extracranial
  • single fraction
  • 12 to 90+ Gy per fraction
  • can use gamma, cyber or linac
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5
Q

What is SRT?

A
  • stereotactic radiotherapy
  • for large cranial lesions not suited for SRS (e.g. post operative cavities)
  • 2 to 5 #
  • lower BED then SRS
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6
Q

What does conventional dose fractionation allow?

A
  • normal cell repair
  • re-population after RT
  • re-distribution in cell cycle
  • re-oxygenation
  • radiosensitivity
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7
Q

What does SBRT dose fractionation do?

A
  • less dose to normal tissue irradiated

- anti-tumour effects not predicted by classsic radiobiology

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8
Q

What is the patient performance criteria for SBRT?

A
  • performance status 0-2
  • life expectancy >6months (>3 months for liver)
  • low metastatic burden (>5 mets, >5cm diameter)
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9
Q

What are the contra-indications for SBRT?

A
  • prior RT
  • unable to lie flat
  • cannot receieve chemo 1-4 weeks pre and post
  • sever connective tissue disease or scleroderma
  • claustrophobia
  • mental status prohibitve of patient compliance
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10
Q

What are the planning principles?

A
  • image fusion
  • increased no. beams
  • non-coplanar
  • small to no margin for beam penumbra
  • highly conformal
  • inhomogenous dose distribution
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11
Q

What are the simulation considerations?

A
  • increased immobilisation
  • 4DCT
  • breath hold
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12
Q

What body areas move?

A
  • skeletal/muscle: stabilisation
  • respiratory (lungs, ribs, abdomen): 4DCT, breath hold or gating
  • cardiac: remains
  • peristalsis: compression
  • bladder and bowel: preparation or catherisation
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13
Q

What are the sources of error (non-patient)?

A
  • image resolution (size of structures)
  • accuracey of image fusion
  • accuracey of target delineation
  • accuracey of mechanical isocentre
  • accuracey of treatment isocentre
  • resolution of couch position
  • resolution of infared camera
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14
Q

What lung tumours are considered for SBRT?

A
  • inoperable
  • central tumour
  • > 5cm diamter
  • no tissue diagnosis
  • T3 tumour with chest wall invasion
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15
Q

What is the interfraction interval?

A
  • 40 hrs
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16
Q

What is dose fractionation for lung?

A
  • ITV is >1.5cm from ribs: 54Gy in 3#

- ITV is <1.5cm from ribs: 48Gy in 4#

17
Q

What spine patients are considered?

A
  • oligometastatic disease

- 1 to 2 vertebrae

18
Q

What is the dose fractionation for spine?

A
  • 20 in 1#
  • 24 to 28Gy in 2#
  • 24 to 30Gy in 3#
19
Q

What is the CT aquisition for spine?

A
  • 2mm slice
  • MRI registration
  • scan limits to include all OAR
20
Q

What liver patients are considered for SBRT?

A
  • unsuitable for surgery
  • treat up to 5 lesions if mets
  • 3 lesions if HCC
  • treat with end exhale breath hold
21
Q

What is the dose fractionation for liver?

A
  • 48Gy in 3#

- 60Gy in 6#

22
Q

What is the CT aquisition for liver?

A
  • hi-definition contrast CT in exhale breath hold

- contrast phase: HCC arterial (30 secs) and mets venous (60secs)

23
Q

What are the dose fractionation for prostate?

A
  • 35 to 40Gy in 5#

- need spacer betwene rectum and prostate

24
Q

What is the plan evaluation?

A
  • OAR goals
  • PTV coverage
  • min dose to GTV and CTV
  • dose fall off
  • hotspot
  • check R50 and D2cm
25
Q

What is R50?

A
  • ratio of the volume covered by the isodose representing 50% of the prescription dose to the volume of the PTV
  • function of the size of the PTV - smaller for larger PTV
26
Q

What is the gradient index?

A
  • the ratio of the volume of half the prescription isodose to the volume of the prescription isodose
  • differentiates plans with similar conformality but with different dose gradients
27
Q

What is D2cm?

A
  • the dose at any point 2cm from the PTV

Planning (8 decks)

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