Leksell Gamma Knife Flashcards
What is stereotactic irradiation (surgery)?
Refers to the delivery of radiation using stereotactic (accurate positioning of probes inside the brain or other parts of the body, based on three-dimensional diagrams) principles.
Delivery of a high dose radiation to small region usually within a well-immobilized system that conforms closely to the 3D shape of the target volume while ensuring rapid fall-off to the surrounding normal tissues
What is ablative doses?
Ablation radiation: highly focused radiation treatment that gives an intense dose of radiation concentrated on a tumor, while limiting the dose to the surrounding organs
Utilizes 3D coordinate system with the highest possible accuracy/precision using a single of few fractions
Conventional radiation therapy: Breast Cancer
Breast cancer
30-35 fractions, 1.8 Gy/fraction → 60-66 Gy
Conventional radiation therapy: Prostate cancer
Prostate cancer
35-45 fractions, 1.8 Gy/fraction → 75 Gy
Conventional radiation therapy: Lung cancer
Lung cancer
25-35 fractions, 1.8-2.0 Gy/fraction → 50-60 Gy
What does stereotactic regimen typically consist of?
1-5 treatment sessions, each with a high dose per fraction, usually between 8-24 Gy (hypofractionated)
What is Stereotactic Radiosurgery (SRS)?
Single, LARGE fraction
Intracranial
(GK delivers this*)
What is Stereotactic Body Radiotherapy (SBRT)?
1-5 large fractions
Extracranial (big, blue, body bags in room E)
Who invented Stereotactic Radiosurgery?
Professor Lars Leksell in 1950’s in Stockholm, Sweden
With Elekta, developed the Leksell Gamma Knife
Current model used it Gamma Knife Icon
Fun fact (not so fun fact)
Suddam Hussein had his own Leksell Gamma Knife in his bunker.
Brain cancer? Or was the 40 Cobalt sources in GK used to make weapons?
GK Indicators: Benign Brain Tumors
Benign: not cancer, no threat to host UNLESS in the cranium as it can push on vital brain regions
- Meningioma (lining of brain)
- Acoustic Neuroma/Schwannoma
- Pituitary Tumor
- Chordoma
- Craniopharyngioma
Vascular Disorders: AVM (arteriovenous malformation)
GK Indications: Malignant Brain Tumors
- GBM
- Astrocytoma
- Oligodendroglioma
Metastatic Disease: Lung and Breast most common
Functional Disorders: Trigeminal Neuralgia
When is GK an option?
Kind of tumor
Rule of thumb: no larger than 35 mm in diameter
Pressing on critical structure and producing symptoms (does NOT help mass effects)
Age and health of patient
How good are alternatives
Patient’s preferance
Top 3 NMH Indications Treated
- Brain mets
- Glomus
- Glial Tumors
Top 3 NMH Metastatic Population
- Lung
- Breast
- Others
The Physics and Basic Principles of GK
GK uses Cobalt-60 as radiation source which undergoes beta decay; as part of decay process, gamma rays are emitted
- Recall, x-rays and gamma rays are exactly the same except their origin
Inside GK unit there are 192-201 Co-60 sources
Dose distribution is modified by using combination of isocenters and positions, using different collimators, and different dwell times, and highly sophisticated treatment planning
GK operates on principles of stereotaxy to achieve high level of precision
GK Radiosurgery
Delivery of single, high dose radiation to a small and critically located intracranial volume though the intact skull
192 narrow, pencil like beams intersecting in one focal point
Cobalt Delivery Systems
4 C Collimator System (where head/helmet goes)
Sector system (the inside portion)
Treatment Procedure [for frame]
- Frame Fixation (frame vs. frameless)
- Diagnostic imaging
- Treatment planning
- Treatment
- Frame Fixation
Patient fixation
Establish spatial reference for the planning phase
Fiducial box and measurements
- Diagnostic Imaging
MRI, CT Scan, Angiogram with frame on
Coordinate frame provides optimal stereotactic localization
Digital image transfer to Leksell Gamma Plan
- Treatment Planning
Leksell Gamma Plan provides:
- Surgical precision (hence gamma KNIFE)
- User-friendly software dedicated for GK Surgery
- Fast creation for optimal treatment plan
- Treatment Planning - Leksell Gamma Plan
- Tailor made surgical planning
- Real time dose calculation
- Integrated dose plan optimization
- Full 2D/3D image and dose display
- Treatment Planning - Gamma Knife Dosing
Based upon indication treated, size, location and critical structures
- Bigger volumes = smaller dose
- Pinpoint doses to critical structures
Acoustic Neuroma → 1200 cGy/ 50%
AVM → 1600 cGy - 2000 cGy/ 50%
Meningioma → 1600 cGy/ 50%
Metastatic Disease → 1600 - 2400 cGy/ 50%
Trigeminal Neuralgia → 8160 cGy/ 100 %
- Treatment
Delivery of Cobalt Radiation
Automatic Treatment (Redundant safety and verification systems)
Patient communication (Audio-Visual system)
Follow-up
Biological effect of GK:
- Damages to DNA of the tumor cells
- AVMs – cause blood vessels to thicken and close off
- Minimal damage to surrounding tissue
Effects of treatment will occur over a period of time
Follow up imaging
- Depends on what was treated
- Typically MRI in 3 months
Patient Care Considerations Post Frame-Based GK
- Band-aids
- Slight bleeding at pin sites
- Headache
- Swelling above the eyes
- Ice packs
- Elevate head
- Possible Steroid (Decadron)
- Radiation Necrosis
Treatment Procedure [frameless]
- Diagnostic imaging
- Simulation (mask-making)
- Treatment planning
- Treatment(s)
- Diagnostic Imaging
MRI – typically morning of simulation or within the week prior to simulation
- Simulation
Headrest/Mask (20 min in oven, 20 minutes to shape/cool)
Patient comfort
- Table height
- Music
- Ativan if claustrophobic
Reference CBCT
Test HDMM
- Treatment Planning
Physics will fuse reference CBCT with MRI
Same planning process as frame-based (Gamma Plan)
- Treatment(s)
Daily CBCT prior to treatment
- Match current CBCT with reference CBCT
- Review of dosimetry prior to starting treatment
- Adjust table positioning/shots based on positioning
1-5 fractions
Monitor motion entire treatment (1 mm or 1.5 mm tolerance)
3-month follow-up with MRI
Frame vs. Frameless
Influencing factors:
- Location of lesion(s)
- Number of lesions
- Treatment time
- Patient preference/status
Advantages of GK?
- Accuracy
- Faster recovery to normal life vs. Surgery & WBRT
- One time treatment
- Reduced costs per patient
- No intensive and minimal post-operative care
- Few support staff required
Disadvantages of GK?
- Size limitation
- Invasive frame application
- Does not treat whole brain
- Not an immediate response
- Cobalt Sources
- Half life of 5.26 years and thus needs to be replaced
