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The Future of Brachytherapy
Alex Rijnders Europe Hospitals Brussels, Belgium
[email protected] Sarajevo, May 21, 2014
Brachytherapy = application of sealed sources inside or in close proximity of tissue
Important milestones
Early 1900s: use of Radium for BT
1930s: Manchester System
End 1950s: artificial isotopes (60Co – 137Cs)
1960s: 192Ir wire sources – Manual afterloading techniques – Paris System
1970s-1990s: Remote Afterloading Devices
2000s: Imaging Assisted Brachytherapy
2010s: Improved dose calculation algorithms
Temporary Implants LDR
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24
Hours
Dose
Rate
PDR
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24
Dose
Rate
Low Dose Rate: v Continuous
irradiation v 0.40 – 2 Gy/h
Pulsed Dose Rate: v mimic low dose rate v short pulses, same
average dose rate
High Dose Rate: v >0.2 Gy/min v One/a few fractions
LDR
PDR
HDR
HDR
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24
Dose
Rate
Current/Future Developments
n Sources - Isotopes n Afterloaders / applications n Use of modern imaging techniques/tools n Dose calculation (TPS) n Recommendations for registration and reporting n Uniformity and accessibility of basic dosimetrical
data (ESTRO-Braphyqs / AAPM) n …
• Long Half Life
=> Economical use (! Radioactive waste !)
• High Specific activity: activity per unit of mass
=> physical size of source (2mm catheters)
• Low mean energy of radiation
=> less penetration in tissue
• Small half value layer in lead or concrete
=> radiation protection
Ideal source/isotope
Physical properties of nuclides
λ=ln2 / T½
Isotope Average photon energy* Half-life T½ Half value
layer in lead Treatment room wall
Cobalt-60 Co-60 1,25 MeV 5,26 years 12 mm (Concrete) typical values
Caesium-137 Cs-137 662 KeV 30,1 years 6,5 mm
Iridium-192 Ir-192 380 KeV 73,8 days 3,0 mm (40 cm)
Ytterbium-169 Yb-169 93 KeV 32,0 days 0,23 mm
Thulium-170 Tu-170 66 KeV 128.6 days 0,17 mm (12 cm)
Iodine-125 I-125 28 KeV 59,4 days 0,025 mm (4.5 cm)
Palladium-103 Pd-103 21 KeV 17,0 days 0,01 mm (1 cm)
Caesium-131 Cs-131 30 KeV 9,7 days - * Approximate values, depending on the source make and filtration
⇒ Radioprotection:
Ø Reduced Mean Energy (<= 100 KeV)
Ø Yb-169, Tu-170, I-125, Pd-103
⇒ Increased half-life (source exchange)
Ø Co-60
« New » Isotopes
Electronic BT sources
Cost differences ? Clinical results ?
Bx Source
Advantages
Disadvantages
radionuclide Well established therapeutic use
Well established calibration procedures Fixed photon spectrum and half-life High specific activity, small size
Fixed dosimetry properties Radioactive waste concerns Regular source shipments due to decay
electronic User-adjustable dose rate (on/off) User-adjustable dosimetric properties Lessened radiological exposure to staff
Unproven clinical application Output variability amongst sources Typically larger in size
X-ray source tip detail
Miniature x-ray source inserted into a flexible cooling catheter § High vacuum x-ray tube technology § 50 kV max. operating potential § Water cooled § Fully disposable device
X-Ray Tube HV Cable Cooling connections
HV connection
miniature x-ray source
Example: Xoft Inc.
Might be interesting in the field of the Mammosite technique, accelerated partial breast irradiation….
Permanent Implants
Radioactive sources remain in the patient and decay v Relative short half life v Low energy (radiation
protection)
Permanent Implant 125I
0.00
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0.20
0.30
0.40
0.50
0.60
0.70
0.80
0.90
1.00
0 30 60 90 120 150 180
Days
Dos
e R
ate
0.000
0.100
0.200
0.300
0.400
0.500
0.600
0.700
0.800
0.900
1.000
Tota
l Dos
e
Permanent Implants
e.g., for prostate, brain
these sources should combine a short half life with low energy:
=> patient should be able to continue life as usual
Examples:
I-125 (60 days; 28 keV)
Pd-103 (17 days; 21 keV)
Sources for Permanent Implants:
Requirements for design of seed products
• Visibility
• isotropic dose distribution
• stability in production
• reliability of source delivery, short delivery time
• smaller packaging, customized, take back procedure of remainder of radionuclide material, metal tubes, etc
Visibility of seeds
• X-Ray: the seed needs a marker
• US: hollow, air cavity; surface reflection(?)
• CT: small scattering effects
• MR: -
Cross-Sectional drawings of sources with a Rod, Wire, or Cylinder internal core design; (a) Amersham 6711 OncoSeed, (b) Syncor PharmaSeed, (c) UroMed Symmetra, (d)SourceTech Medical 125Implant, (e) Med-Tec I-Plant, (f) International Brachytherapy, Inc. InterSource125, (g) Best Medical Model 2301 (h) Amersham 6702, (i) UroCor ProstaSeed, (j)Imagyn IsoSTAR, (k) Mentor's IoGold, (l) DraxImage BrachySeed.
Heintz BH, Wallace RE, Hevezi JM. Comparison of I-125 sources used for permanent interstitial implants. Med Phys 2001 Apr;28(4):671-82
Seeds:
Special presentations of seeds
“Rapidstrand®” seed ribbon technique with
the 125I sources connected in a suture
“Isocord®”: comparable technique with the 125I sources connected in a bio-absorbable suture
And there are many more …
New presentation: SourceLink (Bard)
New isotope: Cs-131 (IsoRay)
- Short half-life (9.7 days) may provide radiobiological advantage for some prostate cancers - γ-ray emitter with highest peaks from 29 to 34 keV - Clinical protocol developed in Texas Cancer Center by Prestidge et al. - A Phase II Study on the use of Cs-131 for localized prostatic carcinoma at the New York Prostate Institute
E. Lief, AAPM Brachytherapy School, 2005
New Seeds: Optiseed (IBt)
Courtesy of M. Gaelens, IBt
New Seeds: Optiseed (IBt)
Courtesy of M. Gaelens, IBt
HDR and PDR afterloaders
192Ir stepping source, HDR or PDR
Example of tip of a high dose rate (HDR) source, Ir-192,welded to the end of a drive cable
Ir-192 source HDR afterloader
Advantage of HDR technology
n One single source (costs) n Half life 74 days => usable for 3-4
months (costs) n Afterloader system => radiation
protection n Stepping source technology allows dose
optimisation => optimisation algorithms n Short irradiation time (10-15 minutes)
Degrees of freedom in HDR BT
{ t }
{ r }
Dose shaping with HDR and PDR machines
Advanced Optimisation Technology (example :SWIFTTM)
Advanced Optimisation Technology (example :SWIFTTM)
Cartridges and Drive Wire
Compose element
Shielding
seedSelectron®
Activity measurement and
check on seed spacer composition
Developments in seed delivery
No seed manipulation: no human mistakes in preparation and delivery
Calibration of drive wire at start of seed delivery
Check on activity of individual seeds
Check on seed spacer combinations just before insertion
Image guided brachytherapy
• Slow introduction of new imaging modalities into this field:
X-ray, CT (spiral, multislice), MR (open, 0.5T), US (PET)
• It seems to follow external beam technology, at a slower pace
• Guided brachytherapy, why not? Robotic techniques?
MOTIVATION
Apply also to modern
brachytherapy
Apply also to (modern)
brachytherapy
• ‘Modern Radiotherapy’ seems to be driven by significant developments in EBT
– 3D Conformal Radiotherapy – Stereotactic Radiotherapy: High Precision – Intensity Modulated Radiotherapy: Dose Shaping – Imaging for GTV/PTV, OAR (structure segmentation) – Computerized treatment plan optimization – Image guided RT
From Poetter et al
=> Evaluate potential of Brachytherapy based on modern technology
3D Treatment Planning Prostate BT
D 90 V 100 V 150
CTV, Urethra, Rectum
- CT - MRI - US - PET - Functional… => the role of ‘imaging’
in RT increases rapidly ➨ Better understanding of anatomy
➨ Better understanding of pathology
➨ More appropriate contouring
Multi modality Imaging
MRI guided single needle implant method
University Medical Center Utrecht, M. Moerland, M. van den Bosch, M. Moman, M. van Vulpen, J. Lagendijk.
University Medical Center Utrecht, M. Moerland, M. van den Bosch, M. Moman, M. van Vulpen, J. Lagendijk.
UROBotics, USA
MRI-Guided Robotic Brachytherapy of the Prostate
BT Dose Calculation: TG43
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θθ
θθ rr
r
rkr Fg
GGSD •••Λ•=
TG-43 Concept • Calculate (Monte-Carlo) and measure the
dose distribution around a source • Parameterize TG-43 parameters to fit to the
measurements
TG-43 parameters
(TG-43 Algorithm)-1
Experimental setup
TG-43 Concept • Calculate (Monte-Carlo) and measure the dose
distribution around a source => GUIDELINES • Parameterize TG-43 parameters to fit to the
measurements => CONSENSUS DATASETS
TG-43 parameters
TG-43 Algorithm
experimental
patient
Limitations of TG43 algorithm
n Line source ó cylindrical source n Homogeneous “water” patient (energy-tissues) n Full scatter patient (skin dose 15-20% overestimated) n Transit dose (for afterloaders) n Intersource effect (6% effect on peripheral dose) n Applicators n Shielding
New algorithms
n Monte Carlo –… n Varian: BrachyVision Acuros n Nucletron/Elekta : Collapsed Cone
n AAPM TG-186: “Model-based Dose Calculation in BT: status and clinical requirements for implementation beyond TG-43”
Training in Brachytherapy
n As treatment techniques and delivery systems become more complex
n Need for better formed/trained staff n ! Few centres specialised in “ high end
BT “ (certainly in Western Europe)
Brachytherapie ó Teletherapie
Investments
€ 300.000 € 2.400.000
(+ € 13.000 / source) (+ maintenance) Workload ++ Workload +++
CONCLUSIONS
Continuous Development in BT
Collaboration at international level eg AAPM / GEC-ESTRO
Brachytherapy continues to merit its place along external beam radiotherapy
Credits: Jack Venselaar, Rien Moerland, Dimos Baltas
