SBRT/SABR Flashcards
Define sterotactic
- high precision image guided dose delivery (1mm, 1 degree)
- highly conformal dose with steep dose drop off
- intrafraction motion management
What is SBRT?
- sterotactic body radiotherapy
- dose escalation for targets close to OAR (extracranial e.g. spine, prostate)
- 1 to 5 #
- > 8Gy per fraction
What is SABR?
- sterotactic ablative body radiotherapy
- for ablation (extracranial e.g. liver, lung, renal)
- 1 to 5 #
- > 8Gy per fraction
What is SRS?
- sterotacitc radiosurgery
- historically intracranial but can be extracranial
- single fraction
- 12 to 90+ Gy per fraction
- can use gamma, cyber or linac
What is SRT?
- stereotactic radiotherapy
- for large cranial lesions not suited for SRS (e.g. post operative cavities)
- 2 to 5 #
- lower BED then SRS
What does conventional dose fractionation allow?
- normal cell repair
- re-population after RT
- re-distribution in cell cycle
- re-oxygenation
- radiosensitivity
What does SBRT dose fractionation do?
- less dose to normal tissue irradiated
- anti-tumour effects not predicted by classsic radiobiology
What is the patient performance criteria for SBRT?
- performance status 0-2
- life expectancy >6months (>3 months for liver)
- low metastatic burden (>5 mets, >5cm diameter)
What are the contra-indications for SBRT?
- 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
What are the planning principles?
- image fusion
- increased no. beams
- non-coplanar
- small to no margin for beam penumbra
- highly conformal
- inhomogenous dose distribution
What are the simulation considerations?
- increased immobilisation
- 4DCT
- breath hold
What body areas move?
- skeletal/muscle: stabilisation
- respiratory (lungs, ribs, abdomen): 4DCT, breath hold or gating
- cardiac: remains
- peristalsis: compression
- bladder and bowel: preparation or catherisation
What are the sources of error (non-patient)?
- 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
What lung tumours are considered for SBRT?
- inoperable
- central tumour
- > 5cm diamter
- no tissue diagnosis
- T3 tumour with chest wall invasion
What is the interfraction interval?
- 40 hrs
What is dose fractionation for lung?
- ITV is >1.5cm from ribs: 54Gy in 3#
- ITV is <1.5cm from ribs: 48Gy in 4#
What spine patients are considered?
- oligometastatic disease
- 1 to 2 vertebrae
What is the dose fractionation for spine?
- 20 in 1#
- 24 to 28Gy in 2#
- 24 to 30Gy in 3#
What is the CT aquisition for spine?
- 2mm slice
- MRI registration
- scan limits to include all OAR
What liver patients are considered for SBRT?
- unsuitable for surgery
- treat up to 5 lesions if mets
- 3 lesions if HCC
- treat with end exhale breath hold
What is the dose fractionation for liver?
- 48Gy in 3#
- 60Gy in 6#
What is the CT aquisition for liver?
- hi-definition contrast CT in exhale breath hold
- contrast phase: HCC arterial (30 secs) and mets venous (60secs)
What are the dose fractionation for prostate?
- 35 to 40Gy in 5#
- need spacer betwene rectum and prostate
What is the plan evaluation?
- OAR goals
- PTV coverage
- min dose to GTV and CTV
- dose fall off
- hotspot
- check R50 and D2cm
What is R50?
- 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
What is the gradient index?
- 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
What is D2cm?
- the dose at any point 2cm from the PTV
