Download The Evolution of Stereotactic Radiosurgery

Stereotactic Radiosurgery (SRS)
王怡振(Yizhen Wang), Medical Physicist
Mississauga Halton/Central West
Regional Cancer Program
Trillium Health Partners
Definition of Stereotactic
Radiosurgery (SRS)
“A single high dose of radiation, stereotactically directed to
an intra-cranial region of interest. May be from X-ray,
gamma ray, protons or heavy particles.”
-Lars Leksell, 1951
High dose of “ablative” radiation delivered to a target
localized in 3-dimensions with overall end to end precision
on the order of 1-2 mm delivered over 1-5 treatments
- Present
The Evolution of SRS
Courtesy of Dr. Timothy D. Solberg et al. Historical Development of Stereotactic Ablative Radiotherapy
The invention of Stereotactic technique
Stereotaxis: Method of
locating points in brain
using an external 3D frame.
-Concept originated with
Robert Clarke (engineer,
physiologist and surgeon) in
1895.
-First device built by Clarke
and Victor Horsley
(neurosurgeon) in 1905.
-First experiment in 1906.
Fig a. original frame by
Clarke and Horsley
Fig c. Leksell frame
Courtesy of Dr. Timothy D. Solberg et al. Historical Development of Stereotactic Ablative Radiotherapy
The invention of stereotactic
radiosurgery (SRS)
• 1947, Ernest Speigel and Henry Wycis performed first successful human
cranial stereotactic surgery. (Temple university, Philladelphia)
• 1949, Lars Leksell built his first stereotactic frame.
• 1951, Leksell would use his frame to target narrow radiation beams.
• 1955, Leksell and Bjore Larsson treated SRS patients using 280 KV X-ray.
(Uppsala, Sweden)
• Late 1950s and 1960s, Uppsala group, Berkeley group (CA) and Cambridge
group (MA) used proton facilities for physics research to treat SRS patients.
• 1967, Leksell, Larsson, Lidén and Walstam built “Gamma Knife I”.
• 1980, Leksell and Jernberg developed CT compatible frame
Gamma Knife Development
Gamma
Knife I:
U Gamma
knife:
- 179 60Co
sources
-rectangle
collimator
- 201 60 Co
sources
- Cone
collimator
Model B:
Model 4C:
- Simpler
source
change
-Allow 3D
planning
- More
efficient
helmet
change
Courtesy of Dr. Timothy D. Solberg et al. Historical Development of Stereotactic Ablative Radiotherapy
Gamma Knife Development
Leksell Gamma Knife Perfexion
• 8 independent sectors.
24 60Co sources/each sector
• 4, 8, and 16 mm collimators can
be combined within each sector.
Automatic collimator adjustment.
Linac Based SRS Techniques- Early Development
1982, Derechinsky and Betti. Buenos Aris, Argentina
Linac Based SRS Techniques- Early Development
Linac Based SRS Techniques- Early Development
1986, McGill SRS system. Montreal, QC
Modern Dedicated SRS Machines
- Cyberknife
110 beam angles
Modern Dedicated SRS Machines
- Novalis
Modern Dedicated SRS Machines
- Varian EDGE
Flattening Filter Free (FFF) mode up to 2400 MU/min
HD-MLC
PerfectpitchTM couch
VisionRT for patient setup
and real time tracking
Comparison of Various Techniques
• Gamma Knife:
- high accuracy (submillimeter)
- for cranial disease only
- cone collimation better for circular target
- source change & radiation safety concern
• Cyberknife:
- high accuracy (submillimeter)
- SRS/SBRT
- cone collimation (MLC under development)
- long treatment time
• Linac:
- Deliver all types of radiation treatment
- capable of conforming to all target shapes (cone & MLC)
- less cost
- accuracy at a few millimeters.
Clinical Aspects of SRS
What SRS Treats
• Malignant tumor: Brain metastases, Glioma,
Glioblastoma (GBM), Astrocytoma, Oligodendroglioma
• Benign tumor: meningioma, schwannoma, pituitary
adenoma, acoustic neuroma,
• Functional disorder or other benign conditions:
trigeminal neuralgia, arteriovenous malformations
(AVM), Epilepsy, Parkinson’s Disease
Brain Metastases
• Most commonly
grey/white junction
• 80% in cerebrum, 15%
in cerebellum, 5% in
brain stem
• Multi sites more
often.
The Sources (Primary Cancers) of Brain
Metastases
Lymphoma
GI cancers
Neuroblastoma
Head and neck cancer
Melanoma
Osteosarcoma
GU cancers
Breast cancer
Lung cancer
0%
10%
20%
30%
Chart created based on Memorial Sloan-Kettering study
40%
50%
60%
Clinical Indication for Brain Mets
• RTOG 90-05, as an example:
- ≤ 2.0 cm, 24 Gy
- 2.1-3.0 cm, 18 Gy
- 3.1- 4.0 cm, 15 Gy
• Less dose -> higher local recurrence
Higher dose -> more toxicities (nausea, vomiting,
dizziness, seizure, headaches)
Outcome of SRS
Studies from RTOG (95-08), EORTC (22952-26001) and MD Anderson
reveal:
• Radiation can reduce the risk of recurrence
• SRS produce similar results as surgery+WBRT in terms of local
control
• WBRT provide better control on distant intracranial recurrence
compared to SRS
• SRS has much better neurocognitive outcome compared to WBRT
• SRS/WBRT has little impact on total survival rate
Technique Requirements for SRS
1. Reliable patient immobilization
Headrings
Relocatable frame based masks
2. Accurate target localization
CT localizer: Z = ?
2. Accurate target localization
CT:
Good Geometry
integrity,
e- density information,
but limited soft tissue
contrast.
Good for treatment
planning
MRI:
Geometry distortion,
no e- density
information, but
excellent soft tissue
contrast.
Good for target
delineation
2. Accurate target localization
Target positioner
3. Dose conformal to target.
3. Dose conformal to target.
Micro multileaf collimators (Micro MLC):
-Attached to or built-in a Linac
- While projecting at isocenter, 14 leaf pairs of 3 mm width, 6 leaf pairs
of 4.5 mm width, and 6 leaf pairs of 5.5 mm width.
-Can conform to any shape
3. Dose conformal to target.
Conical cone collimator:
-Better for spherical or oval targets
-Sharp penumbra
Safety events involving radiosurgery
Courtesy of Dr. Kelly Younge
• SRS involves extremely small fields and very
high doses
• Very little opportunity to correct mistakes
• Some incidents have been highly publicized:
• Incorrect calibration of accelerator output
– 77 patients in Florida, 145 patients in Toulouse,
France, 152 patients in Springfield, MO
– 25-100% overdoses in these patients
• Lesson: use the right detector, and use more
than one
• Backup jaws set incorrectly
– A Pinpoint Beam Strays Invisibly, Harming Instead
of Healing, W. Bogdanich and K. Rebelo, NYT, Dec.
28, 2010
• These patients received an SRS dose to a significant
area of normal brain
• Multiple
people were
treated this
way before
the mistake
was realized
Commissioning of SRS
• Dosimetry (small field dosimetry very challenging)
• Mechanicals
• Imaging
• IGRT
• Margin design
• Secondary dosimetry check system
• End-2-end tests
• External audit
Commissioning: Dosimetry

PDDs, profiles, output factors
Commissioning: Dosimetry
• Multiple detectors to ensure accuracy:
Micro ionization
chamber
Film
Stereotactic
Diode or Electron
Diode
Edge Diode
Diamond dosimeter Liquid ion chamber
Commissioning: Dosimetry
Detector selection:
•Need to select dosimeters with high resolution
•Use at least two types of detectors to verify with each other
•Ion chambers: volume ≤ ~0.01 cc (cc01, A16)
•Diodes: unshielded diodes (SRS diodes, electron diodes)
•Radiochromic film: Handling process dependent, better for
verification only.
Commissioning: Dosimetry
PDD measurement:
•Follow TPS’ requirement (e.g. depth > 30cm, F.S.
covers clinical need), verify 10x10 PDD
•Can use micro IC at vertical orientation (chamber
parallel to beam)
•Diodes
Commissioning: Dosimetry
Profile measurement:
• Air-filled ion chamber too large
• Use diodes
• Verify with Film
Commissioning: Dosimetry
Commissioning: Dosimetry
IAEA/AAPM Working Group’s Recommendation (and
upcoming TG-155*):
Reference
dosimetry:
Corrects for differences between the conditions of field size,
geometry, phantom material, and beam quality
Output
factor:
Accounts for
detector
response
difference
Alfonso, et al. "A new formalism for reference dosimetry of small and non-standard fields,"Med Phys 35, 51795186 (2008)
*TG-155: Small fields and non-equilibrium condition photon beam dosimetry
Commissioning: Dosimetry
Commissioning: Dosimetry
Commissioning: Dosimetry
Absolute dose machine calibration:
• Use standard ion chamber
• Calibrated at reference field size (not always
10x10).
Commissioning: Dosimetry
Dosimetry verification of TPS configured
• Deliver a set of fields and/or plans and
perform measurements. Measurement and
calculation should agree.
Commissioning: Mechanicals
• Linac mechanical/radiation isocenter: ≤1mm
• Couch position accuracy: ≤1mm
• Collimator position accuracy:
- cone alignment
- MLC position accuracy (fence test)
• Laser alignment: Winston Lutz (WL) test
(<1mm)
Commissioning: Mechanicals
Winston Lutz (WL) test (cone or MLC)
Commissioning: Imaging
•
CT imaging:
- good geometry integrity
- for reference image, simulation, planning,
- prefer thin slice(<), axial scan, with contrast
•
MRI imaging:
- good soft tissue contrast
- use for target delineation
- need T1, T2, Axial, Sagittal, Coronal, 3D T1 with contrast most useful
•
Angiogram:
- orthogonal X-rays, for Arteriovenous Malformation (AVM, 动静脉畸形)
Commissioning: Imaging
CT imaging
Commissioning: Imaging
MRI imaging
Commissioning: Imaging
MRI imaging: T1 weighted, before and after contrast
Commissioning: Imaging
MRI imaging: T2 weighted,
Commissioning: Imaging
CT/MRI image fusion
Commissioning: Imaging
Angiogram
Angiogram/CT registration
Commissioning: IGRT
• Dedicated IGRT system
• Cone beam CT (CBCT)
• On board orthobonal X-rays
Need to determine the accuracy of the imaging system
Commissioning: IGRT
Dedicated IGRT system
•
Mounted on floor and
ceiling
•
Submillimeter accuracy
•
Realtime imaging at any
couch angle
ExacTrac®
Commissioning: IGRT
CBCT/OBI
• Accuracy up to 1 mm
• Only at couch = 0
Commissioning: Margin Design
Need to include:
•
•
•
•
•
Size of mechanical and radiation isocenters
CT/MRI slice thickness
Image registration
Contouring accuracy
Patient setup accuracy (IGRT accuracy if imaging
used as primary target positioning)
Commissioning: Secondary dosimetry
check system
• Commercial monitor unit (MU) calculation
software
• Hand MU calculation table or spreadsheet (not for
IMRT or VMAT)
• Patient specific QA measurement (IMRT or Vmat)
Commissioning: End-to-end tests
• Localization/positioning end-to-end test: hidden target
Curtesy: Dr. Kelly Younge
Commissioning: End-to-end tests
Dosimetry end-to-end test:
• follow clinical procedure using clinical mode and R&V system
• measuring with film (plus ion chamber if possible)
Curtesy: Dr. Kelly Younge
Commissioning: External Audit
Perform external audit and/or invite external physicist with
experience to review the program, if possible.
SRS phantom from IROC, MD Anderson, Houston
SRS Planning and Evaluation
Techniques available:
•Non-coplaner arcs
•McGill dynamic arc
•Static beams
•IMRT
•Vmat
SRS Planning and Evaluation
Cone planning:
• Sharp penumbra but can be tricky
• on GK, CK and maybe Linac, prefer spherical target
SRS Planning and Evaluation
Conformal index:
CI= Rx dose Volume/ PTV, Range: 0 - ∞, ideally 1. but,
2
V
PTV ( D )
Paddick Index: CI Paddick 
VPTVVTotal ( D )
Range: 0 – 1, ideally 1
RTOG wants CI <2, dose homegeneity index, DHI = Max
Dose/Rx dose <2. For most cases better indices are
achievable.
Quality Assurance of SRS Program
Equipment QA:
•Daily QA
– Winston-Lutz test (mechanical / rad isocenter)
– Verification imaging isocenter
•Monthly
– Winston-Lutz
– Couch position
•Annual
– End-to-end test (including Localization/dosimetry)
Patient/Process QA: Apply checklist
Quality Assurance of SRS Program: Daily QA
From AAPM TG-142
Quality Assurance of SRS Program: Daily QA
From Astro white paper, “Quality and safety consideration in SRS/SBRT”
Quality Assurance of SRS Program: Daily QA
From Astro white paper, “Quality and safety consideration in SRS/SBRT”
Quality Assurance of SRS Program: Monthly QA
From AAPM TG-142
Quality Assurance of SRS Program: Monthly QA
From Astro white paper, “Quality and safety consideration in SRS/SBRT”
Quality Assurance of SRS Program: Annual QA
From AAPM TG-142
Quality Assurance of SRS Program: Annual QA
From Astro white paper, “Quality and safety consideration in SRS/SBRT”
Quality Assurance of SRS Program: Patient QA
From Astro white paper, “Quality and safety consideration in SRS/SBRT”
Quality Assurance of SRS Program: Patient QA
Checklist Example
From Astro white paper, “Quality and safety consideration in SRS/SBRT”
Quality Assurance of SRS Program: Patient QA
Checklist Example
From Astro white paper, “Quality and safety consideration in SRS/SBRT”
Quality Assurance of SRS Program: Patient QA
Checklist Example
From Astro white paper, “Quality and safety consideration in SRS/SBRT”
Quality Assurance of SRS Program: Patient QA
Checklist Example
From Astro white paper, “Quality and safety consideration in SRS/SBRT”
Quality Assurance of SRS Program: Patient QA
Checklist Example
From Astro white paper, “Quality and safety consideration in SRS/SBRT”
Quality Assurance of SRS Program: Patient QA
Checklist Example
From Astro white paper, “Quality and safety consideration in SRS/SBRT”
References:
• “Stereotactic Radiosurgery”, Dr. Michael Schell, et al. AAPM TG-42
(report 54)
• “ Quality and Safety Considerations in Stereotactic Radiosurgery and
Stereotactic Body Radiation Therapy”, Dr. Timothy D. Solberg, et al.
Practical Radiation Oncology: August 2011. (Astro white paper)
• “Stereotactic body radiation therapy”, Dr. Stanley Benedict, et al. The
report of AAPM Task Group 101
• “Small fields and non-equilibrium condition photon beam dosimetry”,
AAPM TG-155 (in progress)
• “Intracranial stereotactic positioning systems”, AAPM TG-68
• “Use of MRI in treatment planning and stereotactic procedures”, AAPM
TG-117 (in progress)