Stereotactic Treatment Definitions And Literature Overview

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Stereotactic Treatment Definitions And Literature Overview

Transcript Of Stereotactic Treatment Definitions And Literature Overview

STEREOTACTIC TREATMENT DEFINITIONS AND LITERATURE
OVERVIEW

Doracy P. Fontenla, Ph.D. Associate Professor_AECOM
Associate Chief Physicist NSUH-LIJ Health Systems



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Radiosurgery Definitions
Stereotactic/ Stereotaxy : Clinical procedure
based on reference markers to precisely locate a target within 3D-boundaries. Combine the use of a stereotatic apparatus & radiation beams
Two modalities: Stereotactic Radiosurgery - SRS
or
Stereotactic Radiotherapy - SRT



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STEREOTACTIC RADIOSURGERY (SRS)
A “non-invasive” technique Delivers of a single high dose of radiation Limited, well-defined small intracranial target
volumes Avoids nearby normal tissue and critical structures Minimize the dose to the adjacent brain tissue
STEREOTACTIC RADIOTHERAPY (SRT)
Employs same stereotactic techniques used for SRS Refers to delivering collimated beams of radiation in multiple fractions, to a stereotactically located target.



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SRS-SRT
Two way process: • Accurate shape definition and location of
lesion and adjacent neuro-anatomy, from MRI, CT,CTA, Radiografic films, using stereotatic frame.
• Accurately delivery of a very conformal plan.



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• SRS first developed by Leksell (late 1940’s) using orthovoltage X-Rays.
• Employed Heavy charged particles from cyclotrons.
• Gamma rays Gamma Knife (201 60Co sources)
• Megavoltage X-rays from linacs (4 to 18 MV)
• First 3D treatment :Megavoltage unit, April 1948 (Kerst,1975)
• First combined used of X-ray unit & stereotatic frame: Leksel, 1950



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• High Doses (16 Gy to 22 Gy, generally prescribed to the 80% or 90%)
• Delivered in 1 fraction
• Mandate very rigorous, thorough and methodical QA.
• Written detailed procedures is mandatory.



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Achievable uncertanties in SRS(*)

CT slice Thickness 1mm

Stereotatic Frame

1 mm

Isocenter Alignment

1 mm

CT Image resolution

1.7 mm

Tissue Motion 1.0 mm

3mm
1 mm 1 mm 3.2 mm 1 mm

Angio (Pt. identification)

0.3 mm

0.3 mm

Std. Dev. of Pos. 2.4 mm
Uncertainty
(*) AAPM Report No 54:Stereotatic Radiosurgery

3.7 mm



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Linac Based

VS

(Xknife/Brainlab)

•Collimator sizes: 4 to 45 mm in 2.5 mm steps •Conformal SRS: with jaws/circles or MMLC; IMRT.
• Extra-cranial: head and neck; body localization: spine, prostate, lung, liver
•Tx Room can be used for other Tx modalities.

Radioactive Source (Co) Gamma Knife
•Collimator sizes: 4,8,14,18 mm
•Conformality is only attained through multiple isocenters •No extra-cranial targets possible
•Requires dedicated Tx. Room.



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Gamma Knife



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Stereotactic Radiosurgery -Linac Based
• A “non-invasive “ technique to deliver a single high dose of radiation, to limited, well-defined target volumes, while avoiding nearby normal tissue and critical structures.



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DpfSrsDoseRadiationStereotatic Frame