Particle accelerators in medicine!

Transcription

1 Particle accelerators in medicine! Fundamental tools to produce radiation for!! >" Diagnostics (previous lecture)! >" Therapy (this lecture)!! Cancer radiation therapy is based on accelerators:!! >" Conventional radiation therapy (electron linacs)! >" Hadrontherapy (proton and ion cyclotrons and synchrotrons)!!! 0!

2 Cells and their scales >" Cell: µm >" Cell nucleus: 3-10 µm >" DNA: " Pitch :! 3 nm " diameter :! 3 nm " Total length:! 3 m What is the relation between the dimensions of DNA and ionization? 1!

3 Absorbed dose Volume dv Mass dm Radiation source D = de dm Distance d >" de : average sum of all the energies imparted to dv minus the energy leaving dv >" Units: J / kg or Gy (gray) >" Typical radiation therapy: 2 Gy x fractions (60-80 Gy) >" This sets the scale of the beam current! 2!

4 Radiation therapy with cobalt sources >" Advantages: " Higher energy than X-rays, easy to install, no maintenance >" Disadvantages: " Half-life 5.27 years (the source has to be periodically replaced; radioactive waste issues) " The treatment time depends on the age of the source " Relatively low energy (high dose to the skin) Cobalt-60 apparatus (! 1 MeV gammas) Produced in reactors by slow neutrons First treatments in 1951 Now obsolete Cobalt source 2000

5 Betatrons: first electron accelerators for cancer radiation therapy >" Electron circular accelerators " Based on the induction of an electric accelerating field by a varying magnetic field >" Higher energies with respect to 60 Co sources >" Complex to operate for daily medical use Medical betatron mounted on a rotating gantry! Energy: MeV! In the seventies, about 200 installed! Now obsolete!

6 The betatron! Electron source! Target! Vacuum! chamber! Stable orbit! Gamma-Rays! Magnet poles! Target! Stability range! Stable orbit! Electron source! Exercise: calculate the time variation of the magnetic field on the orbit as a function of the average magnetic field produced by the magnet! Maximum energy #300 MeV due to losses by photon radiation! 5!

7 Electron linac mounted on a gantry "About installed in the world "6-20 MeV electron linacs produce gamma rays by Bremsstrahlung "Today: 20'000 patients/year treated every 10 million inhabitants 6!

8 Electron linacs >" 3 GHz cavities 1 inch = 2.54 cm >" Traveling wave principle (electrons are already relativistic at 500 kev) >" Gradient about 10 MeV / m 7!

9 Tomotherapy " The accelerator rotates and the patient is moved (spiral pattern) during irradiation " The intensity is modulated through the use of a multi-leaf collimator " CT imaging is integrated in the apparatus 8!

10 Can we do better? 2 X-ray beams 9 X-ray beams (IMRT) Question for physicists: Are there better radiations to attack the tumor and spare at best the healthy tissues? Answer : BEAMS OF CHARGED HADRONS 9!

11 The basic concept of hadrontherapy Fundamental physics Particle identification L3 at LEP Medical applications Cancer hadrontherapy 10!

12 The Bragg peak Straggling and multiple scattering Fragmentation 11!

13 Single beam comparison X rays Protons or ions 12!

14 IMRT and protons Tumour between the eyes 9 X ray beams 1 proton beam 13!

15 A very interesting and still actual paper >" Bob Wilson was student of Lawrence in Berkley >" Studied the shielding for the new cyclotron! re-discovered the Bragg peak >" Interdisciplinary environment = new ideas! >" 1946: he suggested the use of protons and charged hadrons to better distribute the dose of radiation in cancer therapy >" At that time: no imaging and no powerful enough accelerators " hadrontharpy was just a dream " R.R. Wilson, Radiology, 47 (1946) !

16 The beginning of hadronthearpy: Berkeley, 1954 >" 1954: first patient treated with the Berkley 340 MeV proton cyclotron!! >" First clinical trial: irradiation of the pituitary gland in 26 patients with metastatic breast cancer C.A. Tobias, J.H. Lawrence et al., Cancer Research 18 (1958) !

17 The basic figures of hadrontherapy Protons 200 MeV 1 na 27 cm Tumor target Carbon ions 4800 MeV 0.1 na Beam of hadrons slowing down in matter >" Bragg peak " Better conformity of the dose to the target # Healthy tissue sparing >" Hadrons are charged " Can be magnetically driven # Beam scanning for dose distribution >" Heavy ions " Higher biological effectiveness # Cure of radio-resistant tumors 16!

18 The Spread Out Bragg Peak (SOBP) >" A tumor is much larger (few cm) than the Bragg peak (few mm) >" Particles of different energies have to be used >" Many Bragg peaks have to be superimposed with the right weights to obtain a flat dose distribution (Spread Out Bragg Peak SOBP) Accelerator:! -" Small energy spread! -" Energy variations! -" Intensity variations! -" and if the target is moving?! 17!

19 Lateral penumbra " and biological effects! >" Lateral scattering is a very important feature (lateral penumbra) >" For carbon ions the biological effects strongly depend on the penetration depth and corrections have to be taken into account 18!

20 Proton-therapy: two main kind of treatments "" Treatment of eye-melanoma #" Shallow tumor #" About 65 MeV of energy are needed #" Relatively small cyclotrons #" Very high local control #" Many centers in operation #" ex. Catania, Nice, PSI OPTIS 2 at PSI! "" Treatment of deep seated tumors #" Energies up to about 250 MeV are used #" Much larger infrastructure 19!

21 The Loma Linda University Medical Center (LLUMC) " " " " Near Los Angeles! First hospital-based proton-therapy centre, built in 1993! ~160/sessions a day! ~1000 patients/year! 20!

22 What do we need to treat deep seated tumors with protons? 21!

23 Accelerators for hadrontherapy " Proton therapy: 4-5 m diameter cyclotrons and 6-8 m diameter synchrotrons! " Carbon ions: meter diameter synchrotrons! 22!

24 Cyclotrons an example IBA PT proton cyclotron E = 230 MeV B max = 3 T (Saturated field) Ø = 4 m 200 tons 23!

25 Cyclotrons energy selection system PSI Carbon wedge degrader MeV 5 mm $Range in 50 ms Collimator Degrader Diagnostics 24!

26 Synchrotrons principle layout Injector linac with energies of some MeV/u: $ v ~ 10% c Magnetic rigidity: p $ 2,26 Tm C $ 6,6 Tm With ~ 50% fill factor for dipoles: p $ Ø Sync ~ 6 m C $ Ø Sync ~ 18 m 25!

27 Synchrotrons cyclic operation mode Theory 1 st HIT design Hysteresis compensation. Implementation Linac injector (7 MeV/u) necessary! 26!

28 Comparison: Cyclotrons vs. Synchrotrons Persisting cw beam Discontinuous dc beam Fixed A/Q Variable A/Q Passive energy variation Active energy variation

29 Proton therapy in Switzerland: PROSCAN at PSI Cyclotron Experiment OPTIS 2 Gantry 2 Gantry 1 " Superconducting 250 MeV proton cyclotron " New proton gantry for advanced scanning 28!

30 Carbon ions: HIT in Heidelberg! " 25 m diameter synchrotron! " Injectors: Source + RFQ + Linac! " 2 fixed beams + 1 gantry! " First patient in 2009! " Now about 1500 patients treated! 29!

31 Dose distribution: a gantry for proton therapy 30!

32 Dose distribution: passive spreading Primary beam! PTV! Double scattering technique >" Primary energy: determines the depth of the SOBP! >" Range shifter: determines the width of the SOBP! >" Scatterers: produce a transversally flat beam over the surface! >" Collimator: shapes the beams in the transverse plane according to PTV! >" Compensator (or bolus): shapes the beam in depth according to PTV! 31!

33 Dose distribution: raster scanning New technique developed at GSI 32!

34 Spot scanning at PSI Superposition of discrete spots! SAMBA Strip Accurate Monitor for Beam Applications Measurement of a spot U direction (magnet) 33!

35 Time profile of the clinical beam Total Intensity SPOTS Average flat-top current 0.2 na Time 5 ms 34!

36 Gantry / Active Pencil beam scanning!! $ Bring vaccum as close as possible to nozzle monitors and the nozzle as close as possible to the target volume!

37 HIT Ion Beam Gantry!! 45 dipoles Scanner! magnets! 90 dipole Position accuracy: Dipoles +/- 2mm Quadrupoles +/- 0.5 mm Treatment! room! MT Mechatronics

38 Comparison: Proton vs. Ion Gantry!! Total Weights: PSI Gantry II ~ 220 to HIT Gantry ~ 670 to

39 Present of hadrontherapy >" Proton-therapy! " > patients treated (but only 3% using scanning)! " > 20 hospital based centers! " Many centers under constructions and in project phase!! >" Carbon ion therapy! " > patients treated (mainly in Japan)! " 6 centers in operation (4 in Japan and 2 in Europe)! " Several projects! " Clinical trials! More information on: 38!

40 The future of hadrontherapy >" Two main driving forces! " Improve the local control and minimize secondary effects! " Reduce costs, size and complexity! >" There is a lot to do on! " Accelerators! " Gantries! " Dose distribution systems (moving organs)! " Imaging! "! As a summary on hadrontherapy you can read:! U. Amaldi and S. Braccini, Present challenges in hadrontherapy techniques,! Eur. Phys. J. Plus (2011) 126: 70.! 39!

41 Cyclotrons, synchrotrons, linacs or!? " Cyclotrons and synchrotrons are commercially available! " Linacs present some advantages and are today a research issue!! 40!

42 A linac for proton therapy >" Ideal situation: high frequency spots of variable energy and direction " Tracking of the moving organ >" One possible solution: fast cycling linear accelerators 20 of these modules compose the full linac Accelerating cavities U. Amaldi, S. Braccini and P. Puggioni, RAST2 (2009)

43 Patients and treatment rooms U. Amaldi, S. Braccini et al., Nucl. Instr. Meth. A 620 (2010) 563! Single room facilities: future of proton-therapy?! 42!

44 Compact superconducting synchrocyclotron " 250 MeV, 15 tons synchrocyclotron mounted on its gantry! " 10 T superconducting magnet!! " First full system constructed! " Waiting for the first patient! Courtesy Mevion Medical Systems 43!

45 A turning linac? a dream?! Patent US B2 and EP B1! TUrning LInac for Proton-therapy (TULIP)! " 24 MeV cyclotron: injector (+ radioisotope production)! " Advanced spot scanning (moving organ tacking)! " On-line proton radiography! 44!

46 References! >" CERN Accelerator School, Small Accelerators, CERN ! >" CERN Accelerator School, Cyclotrons, Linacs and their applications, CERN 96-02! 45!