intraoperative implants
TRANSCRIPT
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IntraIntra--operative radiation operative radiation therapy (IORT)therapy (IORT)
Gilad Cohen, M.S. and Marco Zaider, Ph.D.Department of Medical Physics
MSKCC, New York
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IORT refers to a single-fraction treatment delivered to a surgically
exposed area
• Electron beam (not discussed here)
• High dose-rate (HDR) Ir-192 afterloader
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Advantages:Advantages:• The treatment is performed at the time of
surgery, when the target area (the tumor bed) is exposed and the applicator can be placed directly over the target
• Organs at risk may be retracted and shielded as necessary
• The applicator can be used in virtually any anatomic location (e.g. treatment of colorectal malignancies where the tumor bed is often inaccessible to the cones of a linac based system)
• Avoids cold spots and hot spots often encountered when using the electron beam approach due to angle of beam incidence and field matching
• Convenience and cost effectiveness
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Afterloading devices:Afterloading devices:
• Gammamed (Varian Medical Systems, Inc)
• VariSource (Varian Medical Systems, Inc)
• Nucletron, BV
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The Harrison-Anderson-Mick applicator(has FDA 510K approval)(has FDA 510K approval)
• 130-cm source guides embedded at 1-cm spacing in 8-mm thick silastic rubber
• 5 mm from the center of catheter to front, and 3 mm to back (to gain flexibility)
• 2 to 24 catheters• 22-cm long (can treat up to 20x23 cm2)• Prescription point 1 cm away from source
plane (0.5 cm from the surface)
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Mick Radionuclear Instruments, Mt. Vernon, NY
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Modified breast HAM (Mick Radionuclear Instruments)
Tungsten shield
2-cm total thickness
Prescription at 2 cm from the source plane
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IORT prescription:
• Physicist takes oral (rather than written prescription)
• Prescription details should be repeated by physicist and confirmed by physician
• Prescription includes: number of channels (width), length (number of stopping positions), dose and prescription point(s).
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Treatment planning: Prescription / worksheetTreatment planning: Prescription / worksheet
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IORT Dose specificationIORT Dose specification
ually, homogeneous dose is desired throughout the treatment
ea.
ose ranges between 15 - 20 Gy at 5 mm in tissue
ower dose for pediatric cases: 7.5 -12.5 Gy
ower dose also used if IORT is combined w/ EBRT: 10 -12.5 Gy
reast IORT: 20 Gy at 1 cm in tissue
gher dose prescription has been reported in the literature (30 Gy
r biliary / hepatic treatments)
ccasionally, non-uniform dose and irregular treatment geometry
ay be specified
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Treatment planning: Standard GeometryTreatment planning: Standard Geometry
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Treatment planning: Standard PlaneTreatment planning: Standard Plane
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Treatment planning: Breast IORTTreatment planning: Breast IORT
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Treatment planning: Breast IORTTreatment planning: Breast IORT
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QA ConsiderationsQA Considerations
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Applicator QAApplicator QA
Prior to sterilization: catheter length and integrity, labelsAfter treatment: applicator integrityInsure that sterilization does not damage the applicator
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1 Ch# <19
Confirm Pt ID, Rx dose, tx site, etc
Input treatment parameters
1 Ch# >20 2 Ch
no no> 2 Ch
no
yes
vaginalcylinder
yes
bronchialcatheter
yes
GYN ring& tandem
yes
HAMIORT
Reconstruct geometry and calculate dose to reference point(s)
QA: Computer Assisted Independent Dose QA: Computer Assisted Independent Dose Calculation and VerificationCalculation and Verification
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QA: Classical systems (Manchester)QA: Classical systems (Manchester)
2 2( ) 1 0.5 ,0.510. ( ) 0.5K
eff
D Gy hS M A ElongationFactt h h
⎡ ⎤⎛ ⎞ ⎛ ⎞= ⎢ ⎥⎜ ⎟ ⎜ ⎟⎝ ⎠ ⎝ ⎠⎢ ⎥⎣ ⎦
where:where:1/ 2
ln(2)1/ 2 1
ln(2)
tT
effTt e
−⎡ ⎤= −⎢ ⎥
⎢ ⎥⎣ ⎦
The total air kerma strength, SThe total air kerma strength, SKK, needed to deliver dose D at distance h , needed to deliver dose D at distance h over time t is given by: over time t is given by:
and in the case of HDR, the nominal treatment time (s):and in the case of HDR, the nominal treatment time (s):2 2
3/ 40.50.0659 ,0.5 exp(0.05[ 1] )0.5hT M A E
h⎡ ⎤⎛ ⎞ ⎛ ⎞= −⎢ ⎥⎜ ⎟ ⎜ ⎟
⎝ ⎠ ⎝ ⎠⎢ ⎥⎣ ⎦
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Other precautions:Other precautions:
Remote monitoring of patient and anesthesia equipmentOR stuff remain scrubbed during treatment in case of emergencyIn case of emergency the patient can not leave the OR; instead, a shielded enclosure should be provided for the afterloader and source
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Personnel requirementsPersonnel requirements
Physician, Therapist, and two Physicists
Be aware of the unpredictable timing of IORT
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How much it costs:
Initial investment:Initial investment:
shielding (with assoc. structure) 250K
after-loader 200K
planning software 30-50K
applicators (capital investment) up to 25K ea
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Running costs:
source change + PMI $12K quarterly
HAM applicator ~$100. / chWith an average of five channels / treatment and one IORT procedure / week, cost /procedure excluding initial investment is roughly $1500.