stato dell'arte della brachiterapia: le applicazioni ......stato dell'arte della...
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Stato dell'arte della brachiterapia:
le applicazioni cliniche più moderne
e gli argomenti di ricerca più attuali
Seminario – 31 Maggio 2018
e gli argomenti di ricerca più attuali
Mauro Carrara - [email protected]
La brachiterapia all’Istituto Nazionale dei Tumori di Milano
2008 2009 2010 2011 2012 2013 2014
Treatment planning of cervix
cancer on MR images
La brachiterapia all’Istituto Nazionale dei Tumori di Milano
2008 2009 2010 2011 2012
from LDR to HDR (Nucletron Microselectron)
TRUS-guided real-time
treatment planning facility
for prostate HDR
brachytherapy
More than 50 years
traddition with BT
2013 2014
La brachiterapia all’Istituto Nazionale dei Tumori di Milano
Calcolo della dose model-based
Co-60 vs Ir-192
Brachiterapia dinamica/modulataBrachiterapia dinamica/modulata
Nuove sorgenti radioattive
IGABT e MRI planning
Calcolo della dose model-basedCalcolo della dose model-based
Dose calculation: AAPM TG – 43 algorithm
The formalism of dose calculation in brachytherapy is defined in AAPM TG-43
publication and in its subsequent update(s).
( ) ( )( ) ( )ϑ
ϑϑϑ ,)(
,
,,
00
rFrgrG
rGSrD K ⋅⋅
⋅Λ⋅=&
TG-43 Algorithm
Dose calculation: AAPM TG Dose calculation: TG-43 algorithm limitations
D.
In some specific cases, these approximations are
not negligible.
HOMOGENEOUS
MEDIUMINFINITE
MEDIUM
Based on the photon energy range, clinical applications for which the current
dose calculation standard would lead to significant deviations
Dose calculation with TG-43: important approximationsDose calculation: AAPM TG – 43 algorithmDose calculation: TG-43 algorithm limitations
� Accepted clinical dose parameters can be over- or under-
estimated by at least 5% and by as much as factor of 10 in numerous
situations
Dose calculation: from analytical-based to model-based
Shift form TG-43 algorithm to heterogeneity correction
software
Analitical-based
dose calcultation
Model-based dose
calculation
algorithm (MBDCA)
Two commercially available systems:
Advanced Collapsed cone Engine (ACE) by Elekta
Dose calculation: from analytical-based to model-based
Model-based dose
calculation
algorithm (MBDCA)
Advanced Collapsed cone Engine (ACE) by Elekta
� Point kernel superposition method
Acuros BrachyVision by Varian
� grid-based numerical method, directly solves a
discretized version of the linear Boltzmann transport
equation
Model-based dose calculation: AAPM TG – 186 reportDose calculation: AAPM TG – 43 algorithmDose calculation: MBDCA vs TG-43
Dose calculation: MBDCA Commissioning
The output of MBDCA is highly dependent on how
imaging and applicator structure information is
obtained and used by the algorithm.
Model-based dose
calculation
algorithm (MBDCA)
obtained and used by the algorithm.
MBDCAs for all their advantages can lead to large
center-to-center dose-calculation variations if specific
guidance is not provided.
Accurate commissioning of MBDCA is important
Dose calculation: MBDCA Commissioning – in phantom calculations
MBDCA should fall back to TG-43 in well controlled conditions
full scatter - homogeneous water
1° level verification:
Dose calculation: MBDCA Commissioning – in phantom measurements
2° level verification:
Deviations >10% between
homogeneous medium
calculations (TG-43) and
MBDCA (confirmed by
dosimetry)
Model-based dose calculation: AAPM TG – 186 reportDose calculation: AAPM TG – 43 algorithmDose calculation: MBDCA Commissioning – in phantom measurements
2° level verification:
� AAPM/ESTRO/ABS working group: Brachytherapy Source Registry with validated
digital cases including reference dose calculations
http://rpc.mdanderson.org/RPC/BrachySeeds/Source_Registry.htm
Model-based dose calculation: AAPM TG – 186 reportDose calculation: AAPM TG – 43 algorithmDose calculation: MBDCA Commissioning – Brachytherapy Source Registry
2° level verification:
Verification of MBDCA with Monte Carlo calculations… Not easily stustanible for
clinical physicists
Dose calculation: MBDCA Commissioning – Brachytherapy Source Registry
Supports uniform commissioning procedures and direct comparisons among
treatmet planning systems for Ir-192 brachytherapy
Co-60 vs Ir-192Co-60 vs Ir-192
Radionuclide Half-life Photon Energy (MeV) Half-value Layer (mm lead)
226Ra 1600 years 0.047 - 2.45 (0.83 ave) 8
222Rn 3.83 days 0.047 - 2.45 (0.83 ave) 8
60Co 5.26 years 1.17, 1.33 11
Characteristics of the main brachytherapy source:
La scelta di una sorgente radioattiva
Co 5.26 years 1.17, 1.33 11
137Cs 30.0 years 0.662 5.5
192Ir 74.2 days 0.136 - 1.06 (0.38 ave) 2.5
198Au 2.7 days 0.412 2.5
125I 60.2 days 0.028 ave 0.025
103Pd 17.0 days 0.021 ave 0.008
Radionuclide Half-life Photon Energy (MeV) Half-value Layer (mm lead)
226Ra 1600 years 0.047 - 2.45 (0.83 ave) 8
222Rn 3.83 days 0.047 - 2.45 (0.83 ave) 8
60Co 5.26 years 1.17, 1.33 11
137Cs 30.0 years 0.662 5.5
La scelta di una sorgente radioattiva
Characteristics of the main brachytherapy source:
137Cs 30.0 years 0.662 5.5
192Ir 74.2 days 0.136 - 1.06 (0.38 ave) 2.5
198Au 2.7 days 0.412 2.5
125I 60.2 days 0.028 ave 0.025
103Pd 17.0 days 0.021 ave 0.008
• Very low energy - therefore shielding is easy and radiation from an implant
is easily absorbed in the patient: permanent implants are possible
• Mostly used in the form of seeds
• Not suited for gynecology
Radionuclide Half-life Photon Energy (MeV) Half-value Layer (mm lead)
226Ra 1600 years 0.047 - 2.45 (0.83 ave) 8
222Rn 3.83 days 0.047 - 2.45 (0.83 ave) 8
60Co 5.26 years 1.17, 1.33 11
137Cs 30.0 years 0.662 5.5
La scelta di una sorgente radioattiva
Characteristics of the main brachytherapy source:
137Cs 30.0 years 0.662 5.5
192Ir 74.2 days 0.136 - 1.06 (0.38 ave) 2.5
198Au 2.7 days 0.412 2.5
125I 60.2 days 0.028 ave 0.025
103Pd 17.0 days 0.021 ave 0.008
• Higher energies � deeper radiation penetration
• suited for gynecology
Cobalt 60
• New recent alternative to 192-Ir
• Long half life of 5.27 years
Ir-192 versus Co-60 HDR sources
• Sources must be replaced every 2-5 years
(or after about 100.000 transfer cycles)
Cobalt 60
Ir-192 versus Co-60 HDR sources
Attività specifica: attività di uno specifico radionuclide
per unità di massa Unita’ di misura: Bq/g
Ir-192 versus Co-60 HDR sources
SK = Aapp ΓAKR
Ir-192 versus Co-60 HDR sources
Ir-192 versus Co-60 HDR sources
• Less source exchanges required for 60-Co
Ir-192 versus Co-60 HDR sources
• The aimed source strength for 60-Co can be achieved with lower activity (1
GBq of 60-Co is equivalent to 2.77 GBq of 192-Ir)
Ir-192 versus Co-60 HDR sources
• Higher investment for radioprotection and radiation safety with 60-Co (e.g.,
shielding of treatment room and treatment unit)
Ir-192 versus Co-60 HDR sources
• Sources typically supplied by the manufacturers have initial activities of 10 Ci
(192-Ir) and 2 Ci (60-Co); treatment time 1.8 times shorter for 192-Ir
Ir-192Co-60
Ir-192 versus Co-60 HDR sources
Ir-192
Ir-192 versus Co-60 HDR sources
Co-60
Ir-192 data
( ):,ϑrF“Funzione di anisotropia”: corregge per l’assorbimento della
radiazione da parte della sorgente stessa e della capsula di
rivestimento
Dose calculation: AAPM TG – 43 algorithm
60-Co and 192-Ir sources of identical shape and construction show
practically identical dose distributions despite definite differences in physical
characteristics.
Tissue dependent differences in absorption as result of the different mean
Ir-192 versus Co-60 HDR sources
Tissue dependent differences in absorption as result of the different mean
energies of 375 keV and 1.25 MeV can be neglected.
Minimal differences between dose distributions of the two nuclides in
clinical application.
Brachiterapia dinamica/modulataBrachiterapia dinamica/modulata
Dose delivery: Direction-Modulated Brachytherapy
Dose delivery: Interstitial rotating shield brachytherapy
et al
Dose delivery: grooved-shielding applicator
et al
Dose delivery: dynamic modulated brachytherapy
Image Guided Adaptive Brachytherapy(IGABT) e MRI planning(IGABT) e MRI planning
intracavitary
Choice of applicators
Intracavitary + interstitial
“Venezia”
Choice of applicators
Image Guided Adaptive Brachytherapy (IGABT)
GTV 1
GTV 2
GTV 3
GTV 4
GTV D
GTV 1
Tumour volume regression on MRI images
GTV 4
GTV2
Example 2: MRI planning, IC+IS application
Example 2: MRI planning, IC+IS application
Example 2: MRI planning, IC+IS application
400 %
150 %
100 %
90 %
50 %
Example 2: MRI planning, IC+IS application
Example 2: MRI planning, IC+IS application
Example 2: MRI planning, IC+IS application
90 %
Example 2: MRI planning, IC+IS application
300 %