The Future of Brachytherapy. Alex Rijnders Europe Hospitals Brussels, Belgium

Transcription

1 The Future of Brachytherapy Alex Rijnders Europe Hospitals Brussels, Belgium Sarajevo, May 21, 2014

2 Brachytherapy = application of sealed sources inside or in close proximity of tissue

3 Important milestones Early 1900s: use of Radium for BT 1930s: Manchester System End 1950s: artificial isotopes ( 60 Co 137 Cs) 1960s: 192 Ir wire sources Manual afterloading techniques Paris System 1970s-1990s: Remote Afterloading Devices 2000s: Imaging Assisted Brachytherapy 2010s: Improved dose calculation algorithms

4 Temporary Implants LDR Low Dose Rate: v Continuous irradiation v Gy/h Dose Rate Hours LDR PDR Pulsed Dose Rate: v mimic low dose rate v short pulses, same average dose rate Dose Rate PDR HDR High Dose Rate: v >0.2 Gy/min v One/a few fractions Dose Rate HDR

5 Current/Future Developments n n n n n n n Sources - Isotopes Afterloaders / applications Use of modern imaging techniques/tools Dose calculation (TPS) Recommendations for registration and reporting Uniformity and accessibility of basic dosimetrical data (ESTRO-Braphyqs / AAPM)

6 Ideal source/isotope 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

7 Physical properties of nuclides 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 KeV 30,1 years 6,5 mm Iridium-192 Ir KeV 73,8 days 3,0 mm (40 cm) Ytterbium-169 Yb KeV 32,0 days 0,23 mm Thulium-170 Tu KeV days 0,17 mm (12 cm) Iodine-125 I KeV 59,4 days 0,025 mm (4.5 cm) Palladium-103 Pd KeV 17,0 days 0,01 mm (1 cm) Caesium-131 Cs KeV 9,7 days - * Approximate values, depending on the source make and filtration λ=ln2 / T½

8 «New» Isotopes Radioprotection: Ø Reduced Mean Energy (<= 100 KeV) Ø Yb-169, Tu-170, I-125, Pd-103 Increased half-life (source exchange) Ø Co-60

9 Electronic BT sources Bx Source Advantages Disadvantages radionuclide Well established therapeutic use Well established calibration procedures Fixed photon spectrum and half-life High specific activity, small size electronic User-adjustable dose rate (on/off) User-adjustable dosimetric properties Lessened radiological exposure to staff Fixed dosimetry properties Radioactive waste concerns Regular source shipments due to decay Unproven clinical application Output variability amongst sources Typically larger in size Cost differences? Clinical results?

10 Example: Xoft Inc. 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 HV connection miniature x-ray source Cooling connections X-Ray Tube HV Cable X-ray source tip detail

11 Might be interesting in the field of the Mammosite technique, accelerated partial breast irradiation.

12 Permanent Implants Permanent Implant 125 I Radioactive sources remain in the patient and decay v Relative short half life v Low energy (radiation protection) Dose Rate Days Total Dose

13 Permanent Implants e.g., for prostate, brain these sources should combine a short half life with low energy: Examples: => patient should be able to continue life as usual I-125 (60 days; 28 kev) Pd-103 (17 days; 21 kev)

14 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

15 Visibility of seeds X-Ray: the seed needs a marker US: hollow, air cavity; surface reflection(?) CT: small scattering effects MR: -

16 Seeds: 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

17 Special presentations of seeds Rapidstrand seed ribbon technique with the 125 I sources connected in a suture Isocord : comparable technique with the 125 I sources connected in a bio-absorbable suture And there are many more

18 New presentation: SourceLink (Bard)

19 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

20 New Seeds: Optiseed (IBt) Courtesy of M. Gaelens, IBt

21 New Seeds: Optiseed (IBt) Courtesy of M. Gaelens, IBt

22 HDR and PDR afterloaders 192 Ir stepping source, HDR or PDR

23 Ir-192 source HDR afterloader Example of tip of a high dose rate (HDR) source, Ir-192,welded to the end of a drive cable

24 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)

25 Degrees of freedom in HDR BT { r } { t }

26 Dose shaping with HDR and PDR machines

27 Advanced Optimisation Technology (example :SWIFT TM)

28 Advanced Optimisation Technology (example :SWIFT TM)

29 Developments in seed delivery seedselectron Cartridges and Drive Wire Activity measurement and check on seed spacer composition Shielding Compose element 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

30 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?

31 MOTIVATION From Poetter et al Modern Radiotherapy seems to be driven by significant developments in EBT 3D Conformal Radiotherapy Stereotactic Radiotherapy: High Precision Intensity Modulated Radiotherapy: Dose Shaping Apply also to (modern) brachytherapy Imaging for GTV/PTV, OAR (structure segmentation) Computerized treatment plan optimization Image guided RT => Evaluate potential of Brachytherapy based on modern technology Apply also to modern brachytherapy

32 3D Treatment Planning Prostate BT D 90 V 100 V 150 CTV, Urethra, Rectum

33 Multi modality Imaging - CT - MRI - US - PET - Functional => the role of imaging in RT increases rapidly Better understanding of anatomy Better understanding of pathology More appropriate contouring

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35 MRI guided single needle implant method University Medical Center Utrecht, M. Moerland, M. van den Bosch, M. Moman, M. van Vulpen, J. Lagendijk.

36 University Medical Center Utrecht, M. Moerland, M. van den Bosch, M. Moman, M. van Vulpen, J. Lagendijk.

37 MRI-Guided Robotic Brachytherapy of the Prostate UROBotics, USA

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39 BT Dose Calculation: TG43. D ( r, θ ) = S k Λ G G ( r, θ ) ( r 0, θ 0 ) g ( r) F ( r, θ )

40 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 Algorithm) -1 Experimental setup TG-43 parameters

41 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 experimental TG-43 parameters patient TG-43 Algorithm

42 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

43 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

44 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)

45 Investments Brachytherapie ó Teletherapie ( / source) (+ maintenance) Workload ++ Workload +++

46 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