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Division of Medical Radiation Physics
BRACHYTHERAPY
Dario Terribilini
Dario Terribilini, Ph.D. SSRMP
Div. of Med. Radiation Physics
Inselspital - University of Berne
CH-3010 Berne
Switzerland
Phone: +41 31 632 1898
Fax: +41 31 632 2676
Email: [email protected]
www.ams.unibe.ch www.insel.ch
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http://www.estro.org/estroactivities/Pages/
GEC-BRACHYTHERAPYCOMMITTEEACTIVITY.aspx
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http://www.estro-education.org/publications/
Documents/GEC ESTRO Handbook of Brachytherapy.html
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http://www-naweb.iaea.org/nahu/dmrp/
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Table of Contents
• Introduction
• Photon/Beta Source Characteristics
• Dose distribution around sources
• Dose calculation procedures
• Dose specification and reporting
• Quality Controls (Physical parameters)
• Inaccuracies
• (Clinical use and dosimetry systems)
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Tiefe
Do
sis
Photonen (perkutane Therapie)
Protonen
Introduction
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Tiefe
Do
sis
Photonen (perkutane Therapie)
Protonen
Introduction
Photonen (Brachtherapie)
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Miniature X-Ray sources (50 kV)
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Gynecological applications, rectum
HNO, lip, eyelid, mamma, rectum, prostate
or eye cornea
Bronchus, oesophagus, HNO
Single catheter or flabs
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Pulsed dose rate (PDR): Simulation of a low dose rate
(LDR) treatment (50-100cGy/h) by a series of short dose
pulses separated by intervals of 1 hour to several hours
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Introduction
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Introduction
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Introduction
Electronic X-Ray Source
• 50 kV, 0.3 mA, 15 W
• Water cooled
• Can be used as
HDR source
Rivard et al, Med Phys. 33(11), 2006
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Photon Source Characteristics
Radionuclides Photons
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Dose distribution around sources – Point Source
Air
Air
Measurement: ( )
Source
XXX
d
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Dose distribution around sources – Point Source
Wasser
Air
Source
XXX
d
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Dose distribution around sources – Point Source
Wasser
Water
Source
XXX
d
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Dose distribution around sources – Point Source
Wasser
Water
Source
correction due to Bremsstrahlung
XXX
d
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is
1is
p
Dose calculation procedures – Point Sources
2s
4s
3s
1s
isipspspspspp tsDtsDtsDtsDtsDD )()()()()(4321 4321
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t is the thickness of the source capsule
is the attenuation coefficient for photon in the source capsule
material
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Dose distributions around sources
The calculation process according
to the Sievert-integration procedure
considers the dose at a point near
the source as the summation of
point-source contributions. An
elongated source is then divided
into a series of infinitesimal source
elements.
This method is accurate to within
2%–8% for 137Cs sources but is
less accurate at low- and
intermediate-photon energies e.g.,
less than 0.4 MeV.
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is
1is
p
Dose calculation procedures – Point Sources
2s
4s
3s
1s
isipspspspspp tsDtsDtsDtsDtsDD )()()()()(4321 4321
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is
1is
p
Dose calculation procedures – Line Sources
2s
4s
3s
1s
isipspspspspp tsDtsDtsDtsDtsDD )()()()()(4321 4321
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AAPM TG 43 algorithm – Formalismus
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is
1is
p
Dose calculation procedures – Point Sources
2s
4s
3s
1s
isipspspspspp tsDtsDtsDtsDtsDD )()()()()(4321 4321
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is
1is
p
Dose calculation procedures – Line Sources
2s
4s
3s
1s
isipspspspspp tsDtsDtsDtsDtsDD )()()()()(4321 4321
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is
1is
p
Dose calculation procedures – AAPM TG 43
2s
4s
3s
1s
isipspspspspp tsDtsDtsDtsDtsDD )()()()()(4321 4321
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AAPM TG 43 algorithm – Assumptions & Limitations
• Dose calculation in water
– no material heterogeneities within the body
– no applicators
– no shieldings
– no source interplay
• Infinite patient
– no phantom size effect
• Azimuthal symmetry
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AAPM TG 43 algorithm – Limitations
Rivard et al., Med Phys. 36, 2009.
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Alternative Approaches
The goal is to take
• patient inhomogeneities
• patient shape
• source interplays
• effects of applicators and shieldings
into account which are ignored by the AAPM TG 43
protocol
Analytical Models (Convolution/Superposition, CC)
Full Monte Carlo Simulations
Deterministic solutions of the transport equations
(LBTE)
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(Manchester System for gynecological applications, ect)
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…for LDR!
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References on dose specification & reporting
• ICRU 38 (1985): Dose and Volume Specification for Reporting
Intracavitary Therapy in Gynaecology
• ICRU 58 (1997): Dose and Volume Specification for Reporting
Interstitial Therapy
• American Brachytherapy Society (ABS) Recommendations for
Transperineal Permaent Brachytherapy of Prostate Cancer (IJROBP
1999)
• SGSMP-Bericht 18 (1996): Dosis- und Volumenspezifikationen zur
Dokumentation in der Brachytherapie
• http://www.estro-education.org/publications/Documents/GEC ESTRO
Handbook of Brachytherapy.html
Reporting in Brachytherapy: Dose and Volume Specification
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Quality Control procedures of afterloading
equipment and implants – Phisical parameters HDR / PDR,
Remote
afterloading
MDR / LDR,
Remote
afterloading
LDR,
manual
afterloading
Permanent
Implant
Source calibration X X X X
Radioactive decay X X X
Source position accuracy X X
Linear uniformity of (wire) sources X X
Source length X X
Source identification X X
Length of treatment tubes X
Transit time effect X X
Timer consistency & linearity X X
Grid calibration X
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Baltas (Bern, 2007)
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Baltas (Bern, 2007)
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Baltas (Bern, 2007)
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Baltas (Bern, 2007)
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Thank you
…Questions?
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Seelentag, 2009
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If the tandem displaces the central canal,
point A moves with the canal, but point B
remains fixed at 5 cm from the midline.
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