Review of medical accelerators L G Sukhikh 30000

Review of medical accelerators L. G. Sukhikh

30000 Accelerators in the world Courtesy R. Baily 2

Accelerators in medicine 1. Accelerators for treatment 2. Accelerators for radiopharmaceuticals production 3. Indirect use (e. g. sterilization) 3

Radiation sterilization • E. g. syringes sterilization 4 BINP, Novosibirsk

Radiopharmaceutical production • Pharmaceuticals for nuclear diagnostics: gamma and positron emitters: F-18, N-15, Tc-99 etc. • Pharmaceuticals for nuclear treatment: beta emitters P-32, Sr-89, etc. 5

PET 6

Particle accelerators: Cyclotron • In a cyclotron the heavy particles (protons, ions) are accelerated along a spiral trajectory guided inside two evacuated half-cylindrical electrodes (dees) by a uniform magnetic field produced between the pole pieces of a large magnet (1 T). 7

Fluorine-18 production 8

Fluorine-18 production Proton energies 11 -18 Me. V Currents 50 -300 u. A 9

Radionuclides for nuclear therapy 10

RADIATION THERAPY 11

Radiation treatment - radiotherapy • >95% of radiation therapy is used for cancer treatment 12

Radiation • • Ionizing radiation is DANGEROUS! 1 Gy (J/kg) per whole body – radiation disease 7 Gy per whole body – 95% lethal result in a few weeks 20 -25 Gy per whole body – lethal result in 30 min 13

Radiobiology • Radiation kills cells mainly via DNA damage 14

Tumour control probability • TCP and NTCP vs. dose • Minimal complications of normal tissues and organs are desired 15 B point – 35 -70 Gy •

Typical medical accelerator For a radiotherapist Black box Dose distribution 16

Dose in water 17

ELECTRON MACHINES 18

Particle accelerators: Betatron • • Betatron is a cyclic induction accelerator in which the electrons are made to circulate in a toroidal vacuum chamber (doughnut) that is placed into a gap between two magnet poles. Conceptually, the betatron may be considered an analog of a transformer: – Primary current is the alternating current exciting the magnet. – Secondary current is the electron current circulating in the doughnut. 19

Particle accelerators: Betatron • Betatrons were used for external RT in 70 -th, 80 -th Finland Great Britain 20

Particle accelerators: Betatron • Betatrons now are used only for Intraoperative radiotherapy with Me. V electron beams 21

Particle accelerators: Betatron • Betatrons now are used only for Intraoperative radiotherapy with Me. V electron beams 22

LINACS • Medical linacs accelerate electrons to kinetic energies from 4 to 25 Me. V using microwave radiofrequency fields: – 103 MHz : L band – 2856 MHz: S band – 104 MHz: X band • In a linac the electrons are accelerated following straight trajectories in special evacuated structures called accelerating waveguides. 23

LINACS • During the past 40 years medical linacs have gone through five distinct generations, each one increasingly more sophisticated: (1) (2) (3) (4) (5) Low energy x rays (4 -6 MV) Medium energy x rays (10 -15 MV) and electrons High energy x rays (18 -25 MV) and electrons Computer controlled dual energy linac with electrons combined with intensity modulation 24

LINACS • Linacs are usually mounted isocentrically and the operational systems are distributed over five major and distinct sections of the machine: – Gantry stand support – Modulator – Patient support assembly – Control console 25

LINACS: configuration • In the simplest and most practical configuration: – Electron source and the x-ray target form part of the accelerating waveguide and are aligned directly with the linac isocentre obviating the need for a beam transport system. – Since the target is embedded into the waveguide, this linac type cannot produce electron beams. 26

Configuration of modern linacs 27

LINACS: configuration • For both electrons and photons (Varian): 28

LINACS: configuration Alpha 29

Configuration of modern linacs Typical modern dual energy linac, incorporating imaging system and electronic portal imaging device (EPID), Elekta, Stockholm 30

Configuration of modern linacs Typical modern dual energy linac, with on board imaging system and an electronic portal imaging device (EPID), Varian, Palo Alto, CA, USA 31

Configuration of modern linacs 32

Electron beam transport Three systems for electron beam bending have been developed: 90 o bending 270 o bending 112. 5 o (slalom) bending 33

Clinical X-ray beam 34

Clinical X-ray beam • Typical electron pulses arriving on the x-ray target of a linac. Typical values: Pulse height: 50 m. A s Pulse duration: 2 Repetition rate: 100 Hz • Period: 104 s The target is insulated from ground, acts as a Faraday cup, and allows measurement of the electron charge striking the target. 35

Clinical electron beam 36

Multileaf collimator 37

Conventional EBRT Rectangular shape 38

3 D-CRT 39

IMRT and VMAT 40

PROTON MACHINES 41

Dose depth distribution 42

Spread of Bragg peak Tumour Proton energy 70 -250 Me. V 43

Pencil beam scanning 44

Single scattering 45

Uniform scanning (wobbling) 46

Intensity modulation pencil beam Fast intensity modulation is needed (easier with CW isochronous cyclotrons) 47

Main blocks Accelerator Energy selection Beam transport Gantry 48 Courtesy M. Schippers

Building 49

Accelerator 1. Cyclotron: fixed energy, energy modulation is needed, CW 2. Synchrotron: variable energy, complexity 50

Energy degrader (PSI) 51

Gantry 52

Main manufactures Germany (RP) USA (PT) GE, USA (RP) USA (PT) Japan (RP+PT) Canada (RP) C 235 Canada (RP) Belgium (RP+PT) 53

Conclusions 1. Roughly 35% of accelerator are used for medical purposes, mainly radiotherapy. 2. Electron linacs are the main “working horses” that are developed in the direction of precise dose delivery 3. Proton therapy is widely developed but still to expensive and complicated, mostly because of beam transport and delivery. 54

Thank you for your Attention! 55