Stato dell'arte della brachiterapia: le applicazioni ......Stato dell'arte della brachiterapia: le...

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


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

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


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


� 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


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


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



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


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



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


Attività specifica: attività di uno specifico radionuclide

per unità di massa Unita’ di misura: Bq/g


SK = Aapp ΓAKR


• Less source exchanges required for 60-Co


• 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)


• Higher investment for radioprotection and radiation safety with 60-Co (e.g.,

shielding of treatment room and treatment unit)


• 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


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


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


400 %

150 %

100 %

90 %

50 %


90 %


300 %

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