Squeezing the proton. towards small proton therapy systems. Roelf Slopsema. M.Sc. / UF Health Proton Therapy Institute

Transcription

1 Squeezing the proton towards small proton therapy systems Roelf Slopsema. M.Sc. / UF Health Proton Therapy Institute

2 Disclosures I worked as an R&D physicist for IBA from 2002 until 2004 I have received a research grant from IBA in 2007 I have performed paid consultancy work for MevIon in 2013 I work at a center that has IBA equipment I like protons I am not a PhD

3 Learning objectives After this presentation you.. know what proton therapy is. have an overview of the historical development of proton accelerators and proton therapy... have an understanding of the different factors driving the development of smaller PT systems. know the different technologies applied to make PT systems smaller. have an idea of the small proton therapy systems available now, in the near future, and in the distant future

4 Overview what is proton therapy? technical challenges of proton therapy systems history of proton accelerators and PT systems rationale for smaller PT systems technology for smaller PT systems o limited-angle gantry o superconducting cyclotrons o linear accelerators o laser-accelerated protons current status and outlook for the future

5 What is proton therapy? (1) Proton therapy (PT) = type of radiotherapy that uses highenergy protons to irradiate diseased tissue The process through which high-energy protons loose energy while traversing matter results in a distinct depth dose distribution called the Bragg peak The penetration depth of the Bragg peak can controlled with the entrance energy, allowing for complete sparing of structures distal to the target

6 PT depth dose distribution

7 PT delivery techniques Several different delivery techniques are applied in PT: 3D conformal proton therapy : using a block (aperture) and range compensator to conform the dose to the target passive scattering uniform scanning Spot scanning : using many, scanned, small beams of varying energy to paint in the target (allows for IMPT)

8 PT dose distribution 3D conformal XT IMRT 3D conformal PT

9 PT dose distribution

10 Technical challenges of PT delivery (1) Energy loss in coulomb interactions with shell electrons for electrons 1 or protons 2 : E k : kinetic energy E 0 : rest energy electrons: E 0 = MeV protons: E 0 = MeV 10 MeV electrons: =0.93 1/ 2 = MeV protons: =0.14 1/ 2 = MeV protons: =0.93 1/ 2 = MeV/cm 2.0 MeV/cm 2.1 MeV/cm At same kinetic energy protons lose much more energy than electrons because of higher mass. 1: Moeller cross section ; 2 Bethe equation (

11 Technical challenges of PT delivery (2) Range: de/dx R CSDA You need large proton energy to get sufficient range in the body. 2.5 cm (EYE) : Ek 55 MeV 16 cm (BRAIN): Ek 160 MeV 32 cm (ABDOMEN): Ek 230 MeV Note: Compared to electrons, protons scatter little allowing deep penetration with little lateral deflection around the initial beam direction.

12 Technical challenges of PT delivery (3) Magnetic rigidity of a charged particle charge 1, rest energy E 0, kinetic energy E k : High E 0 and E k results in high BR For example, bending a 250 MeV proton with a 1.5 T field results in a bending radius of 1.6 m, requiring a 2.5 m long magnetic field for a 90 bend

13 Technical challenges of PT delivery (4) 1. You need high proton energy to achieve sufficient range inside the patient large accelerator 2. The high proton kinetic and rest energy results in large magnetic rigidity large bending radii / large magnets 3. Clinical applications require beam delivery from different angles with respect to patient large gantry structures

14 Invention of the cyclotron invented in 1931 by Lawrence & Livingstone Noble prize in inch, 80 kev 4.5-inch cyclotron Ernest Lawrence

15 1931 / 11 inch cyclotron / protons to 1 MeV

16 1937 / 37 inch cyclotron / deutrons to 8 MeV

17 "He creates and destroys."

18 1939 / 60 inch cyclotron / deutrons to 16 MeV "I must confess that one reason we have undertaken this biological work is that we thereby have been able to get financial support for all of the work in the laboratory. As you know, it is much easier to get funds for medical research." Lawrence to Niels Bohr, 1935

19 Atomic explosion over Hiroshima.

20 1946 / 184 inch synchrocyclotron / protons to 340 MeV

21 Evolution of accelerator energy

22 Birth of proton therapy Robert Wilson: Higher-energy machines are now under construction, however, and the ions from them will in general be energetic enough to have a range in tissue comparable to body dimensions. It must have occurred to many people that the particles themselves now become of considerable therapeutic interest. Radiological Use of Fast Protons, R.R. Wilson, Radiology 47(1946),

23 Birth of proton therapy 1954 first patient treated with protons at Berkeley Radiation Laboratory irradiation to destroy the pituitary gland in patients with hormone-sensitive metastatic breast cancer Robert Stone and John Lawrence, Ernest's brother, treat a patient with neutrons from the 60-inch cyclotron.

24 Development of proton therapy 1957 : results from Berkeley duplicated in Uppsala, Sweden 1961: Harvard Cyclotron facility starts PT 1990: first hospital-based PT system opens at Loma Linda University, CA 2001 : PT starts at MGH : an additional 10 large, hospital-based PT centers are opened in the U.S. (I.U., M.D. Anderson, UF, Upenn, Hampton Uni., ) 2013 onwards: introduction of smaller, one-room PT systems

25 IBA cyclotron: 230 MeV, 220 tons

26 IBA gantry: 38 feet tall by 35 feet wide, >200,000 pounds

27 Five-room proton therapy center as installed at Scripps (San Diego, CA) / proton-therapy

28 Rationale for smaller systems

29 Rationale for smaller systems High cost of PT equipment limits widespread adaptation of proton therapy. Linear accelerator: $2.8 million ( ) 1 5-room PT system: $144 million 2 1 Modern Healthcare / ECRI Institute Technology Price Index July 2013 ( 2

30 Rationale for smaller systems smaller systems can reduce cost by.. reducing foot print of building eliminating need for construction of dedicated building/room reduction in #components making PT available for smaller centers (one room) or as extra modality in existing centers (economy of scale) make proton therapy more compatible with conventional forms of RT

31 Technical challenges of PT delivery (4) 1. You need high proton energy to achieve sufficient range inside the patient large accelerator 2. The high proton kinetic and rest energy results in large magnetic rigidity large bending radii / large magnets 3. Clinical applications require beam delivery from different angles with respect to patient large gantry structures

32 Approaches to smaller PT systems 1. Limit the number of treatment rooms 2. Reduce the foot print of the building (land/shielding) accelerator under gantry accelerator on gantry reduce required shielding (proton absorption / degradation) 3. Shrink the size of the accelerator superconducting cyclotron linear accelerator with very high potential gradient laser-accelerated protons 4. Shrink the size of gantry structure / beamline short gantries limited-angle gantries / fixed beam line

33 Limit the number of treatment rooms IBA Proteus system with four rooms IBA Proteus system with one room Take a multi-room facility and strip away all tx rooms except one... smaller, but not very cost effective

34 Reducing foot print - cyclo under room Sumitomo PT system: single gantry double-decker small vault foot print: 16mx20m

35 Shrink size gantry Sumitomo short gantry

36 Shrink size gantry few fixed angles IBA inclined beam line: two fixed beam lines (90 and 30deg) limited-angle gantry that rotates just nozzle (not beam line) robotic positioner often in centers with additional full gantry rooms

37 Shrink size gantry limited angle MevIon S250: 180 degrees IBA Proteus One : 220 degrees

38 Reducing foot print shrinking beamline degrader IBA Proteus One: incorporate energy-selection system into gantry move scanning magnets from nozzle to gantry conventional to superconducting cyclotron limited-angle gantry energy-selection system scanning magnets

39 Reducing foot print IBA Proteus One

40 Shrink size accelerator superconducting cyclo First some cyclo basics. Revolution period: T = 2πm/B But for relativistic energies: m = γm 0 T increases with energy To compensate for mass increase with radius you need to either. decrease RF frequency with radius > synchrocyclotron increase magnetic field with radius > isochronous cyclotron

41 Shrink size accelerator superconducting cyclo some more cyclo basics. Isochronous cyclotron continuous beam (~100 MHz) increasing magnetic field causes vertical defocusing > need for complex magnet shape Synchrocyclotron pulsed beam structure (khz region) lower RF power simpler magnet design (weak focusing) IBA C230 isochronous cyclotron earliest cyclotrons used for PT were synchrocyclotrons later commercial cyclotrons are isochronous

42 Shrink size accelerator superconducting cyclo superconductivity allows increase of magnetic field above levels obtainable with conventional electromagnets (several T) higher magnetic field results in smaller bending radius (at same energy) r = mv/b But, increased magnetic field makes vertical focusing difficult saturated poles > limit on field gradient between hills/valleys limit in spiral design To account for this you either stay with an isochronous cyclotron, but limit the magnetic field increase use a synchrocyclotron design allowing for higher magnetic fields

43 Shrink size accelerator superconducting cyclo Varian SC isochronous cyclotron MevIon TriNiobium Core SC synchrocyclotron IBA S2C2 SC synchrocyclotron

44 Shrink size accelerator superconducting cyclo Comparison of normal and superconducting cyclotrons used for proton therapy Manufact. Model Superconducting Type Energy [MeV] Weight [tons] Diam. [m] Peak B [T] IBA C230 NO isochronous Varian YES isochronous <4 MevIon S250 YES synchro ~9 IBA S2C2 YES synchro 230 < ~6.6 /

45 Reducing foot print - cyclo on gantry MevIon S250 system

46 Shrink size accelerator proton linacs Issues with proton linear accelerators. long or high field gradients needed protons move at relatively low speed (up to of 60% of speed of light) > large variation in speed along accelerator Potential benefits. variable energy without degrader (neutrons, shielding) fast energy change light: no need for (heavy) magnets in accelerator Different approaches. long cavity-coupled linac dielectric wall accelerator

47 Proton Linacs - LIGHT LIGHT = Linac Image Guided Hadron Technology Spin-off from LHC project (R&D facility at CERN) LIGHT components: Radio-frequency quadrupole injector (4.5 MeV) Side-couple drift tube linac (35 MeV) Cavity-Coupled linacs (10 accelerators > 230 MeV) Potential benefits 1 lower shielding requirements (no absorbers for energy modulation) fast energy changes (2-3 ms) (modular) (more compact) (lower cost) We estimate that the cost of a LIGHT facility will be in the region of US$40m vs. US$ m for those using cyclotrons or synchrotrons

48 Linear accelerators- LIGHT

49 Proton Linacs Dielectric wall accelerator Principles of dielectric wall accelerator developed at Lawrence Livermore National Laboratory uses fast switched high voltage transmission lines to generate pulsed electric fields on the inside of a high gradient insulating (HGI) acceleration tube high electric field gradients are achieved by the use of alternating dielectric insulators and conductors and short pulse times use of laser-controlled switching to fire acceleration in phase with proton propagation and energy DWAs are expected to reach acceleration gradients around 100 MV/m STATUS OF THE DIELECTRIC WALL ACCELERATOR, G. Caporaso et al, Proceedings of PAC09, Vancouver, BC, Canada

50 Proton Linacs Dielectric wall accelerator AAPM presentation, R. Mackie, Dielectric wall accelerator and distal edge tracking proton therapy system

51 Proton Linacs Dielectric wall accelerator AAPM presentation, R. Mackie, Dielectric wall accelerator and distal edge tracking proton therapy system

52 Proton Linacs TomoTherapy PT system proton arc therapy using distal edge tracking

53 Proton Linacs CPAC system CPAC = Compact Particle Acceleration Corporation using dielectric wall technology /

54 Shrink accelerator laser-accelerated protons Principles of laser accelerated protons Target Normal Sheath Acceleration (TNSA) ultra-intense laser pulse hits thin foil >10 19 W/cm 2 plasma plume created in focal region laser accelerates plasma electrons electrons exit on other side creating strong electric field TV/m protons (ion) are pulled out and accelerated under the influence of created electric field

55 Shrink accelerator laser-accelerated protons

56 Shrink accelerator laser-accelerated protons Characteristics current experimental systems maximum proton energy of 70 MeV for a 100 TeraWatt laser development of PetaWatt lasers underway enough for clinical PT energies high power requires pulsed lasers 10 Hz repetition for ultra-short pulses (50 fs) few pulses per minute for long pulses (700 fs) biology experiments have been performed Proton Accelerators, M. Schippers, in Proton Therapy Physics, Ed. H. Paganetti, 2012 / A compact solution for ion beam therapy with laser accelerated protons, U. Masood et al, Appl. Phys. B (2014) 117:41-52

57 Shrink accelerator laser-accelerated protons Benefits of laser-accelerated protons. no need for accelerator no/less need of particle transport (mirrors instead of magnets) Challenges of laser-accelerated protons. laser power and maximum energy need W/cm 2 to get 200 MeV protons energy spread loss of bragg peak ultra-short pulsed beam extreme instantaneous dose rates Gy/s (biology/dosimetry) Proton Accelerators, M. Schippers, in Proton Therapy Physics, Ed. H. Paganetti, 2012 / A compact solution for ion beam therapy with laser accelerated protons, U. Masood et al, Appl. Phys. B (2014) 117:41-52

58 PT system with laser-accelerated protons Our proposed design for laser-driven beams results in a substantial reduction in size by a factor of 2-3, and hence weight, compared to the most compact conventional Ion Beam Therapy gantry systems. A compact solution for ion beam therapy with laser accelerated protons, U. Masood et al, Appl. Phys. B (2014) 117:41-52

59 Current status and outlook Currently most PT centers are large, multi-room facilities Recently the first one-room systems have started operation and several more are under construction

60 Operational Research-facility PT systems 12

61 Operational Multi-room hospital-based systems (IBA Proteus, Varian ProBeam, Hitachi ProBeat) 27

62 Operational Multi-functional one-room systems (MevIon S250, Proteus One) 2

63 Under construction / Planned 0 Research-facility based systems Multi-room hospital-based systems (Proteus, Varian, Hitachi ProBeat) One-room systems (MevIon S250, Proteus One, single gantry)

64 Current status and outlook Currently most PT centers are large, multi-room facilities Recently the first one-room systems have started operation and several more are under construction Several new technologies (laser-accelerated protons, LINACS) are interesting, but are likely not ready for clinical application in the next 5-10 years How much these new technologies will reduce the cost of PT systems, remains to be seen The continued growth of proton therapy will depend on both. the results of the effort of cost reduction and the clinical outcome of PT politics

65 You never know, the next break through in proton delivery might be just around the corner Thank you for your attention.