Ionoacoustic range monitoring for proton therapy W. Assmann Faculty - - PowerPoint PPT Presentation

▶
ionoacoustic range monitoring for proton therapy
SMART_READER_LITE
LIVE PREVIEW

Ionoacoustic range monitoring for proton therapy W. Assmann Faculty - - PowerPoint PPT Presentation

Feb 22, 2024 136 likes •515 views

Ionoacoustic range monitoring for proton therapy W. Assmann Faculty of Physics Department for Medical Physics, Ludwig-Maximilians-Universitt Mnchen, Germany Overview Radiation therapy with ions: special features Range uncertainty:

slide-1
SLIDE 1
  • W. Assmann

Faculty of Physics – Department for Medical Physics, Ludwig-Maximilians-Universität München, Germany

Ionoacoustic range monitoring for proton therapy

slide-2
SLIDE 2

Overview

  • Radiation therapy with ions: special features
  • Range uncertainty: problem and present solutions
  • New (old) approach: Ionoacoustics (thermoacoustics with ions)
  • Experimental tests at 20 MeV
  • Simulations with k-Wave
  • First experiments around 200 MeV
slide-3
SLIDE 3

Ion beam therapy

Advantages of particle therapy

  • Finite range of ions
  • Maximum dose deposition

at end of range (Bragg Peak, BP)  highly conformal irradiation

  • Minimum dose in healty tissue

Dose distribution: photons vs. ions

Skull base tumor Wilson, R.R., “Radiological use of fast protons”, Radiology 47, 487-91 (1946)

slide-4
SLIDE 4

Photon vs Proton

+ maximal dose in tumor + minimal dose in healthy tissue

  • expensive technology
  • very sensitive to

range uncertainty

Dose delivery photons protons

+ conformal dose distribution (with advanced IMRT techniques) + less sensitive to range uncertainty

  • dose bath of healthy tissue
  • limitation of tumor dose
slide-5
SLIDE 5

Range uncertainty

Reasons: Calibration errors CT/HU to ion stopping power, CT artefacts, patient and tumor movement, anatomical changes, positioning error, … Example: Prostate tumor - planning CT vs. situation on irradiation day-N

 in-vivo range verification with ≈1 mm resolution

slide-6
SLIDE 6

Range uncertainty

Example: Prostate tumor

(b-c) optimal anterior dose delivery sparing best healthy tissue and organs-at-risk, but needs in-vivo range verification with ≤ 1 mm resolution at present (a) suboptimal lateral dose delivery with larger dose deposition in healthy tissue (femoral heads, hip replacements!)

  • S. Tang et al., Int J Rad Oncol Biol Phys, 83(1), 408 (2012)

in the future

slide-7
SLIDE 7

Range verification

Presently under development: Nuclear Imaging Techniques

  • online PET (Positron Emission Tomography) GSI, HIT
  • Prompt gamma imaging (Compton camera) IBA
  • K. Parodi, PhD thesis, 2004

Problem:

both methods complex and indirect methods, costly and bulky equipment, 1 millimeter resolution?? Example:

  • ffline

PET imaging

measurement simulation

slide-8
SLIDE 8

Ionoacoustic effect

Stopping of ions causes local heating and pressure wave:

*

thermal confinement: stress confinement:

t ion pulse < t therm diffusion (here > 100 ms) t ion pulse < t stress propagation (vs ~ 1.5 mm/ms)

slide-9
SLIDE 9

Ionoacoustics

But: 1 Gy dose  0.25 mK DT  2 mbar Dp very weak effect! usable? General thermoacoustic equation for acoustic wave propogation : in thermal confinement: „Heating function“

slide-10
SLIDE 10

New approach but old idea …

Sulak et al, NIM 161 (1979), 203-217 see also: G.A. Askariyan et al, NIM 164 (1979), 267-278 50 ms/div 100 ms spill time

slide-11
SLIDE 11
  • Y. Hayakawa et al, Rad. Onc. Invest., 3, (1995), 42-45

(weak) US signal detected, but no progress since then…

Hydrophone Hepatic cancer treatment

New approach but old idea …

proton beam

slide-12
SLIDE 12

New approach but old idea …

slide-13
SLIDE 13

Time for new attempt?

Previous irradiation technique “passive scattering” irradiation of whole tumor volume at once  diffuse local dose deposition  small ionoacoustic signal amplitude  complex range information Advanced irradiation technique “active scanning” irradiation of tumor volume by single beam spots  highly localized dose deposition  enhanced ionoacoustic signal amplitude  direct range information Additionally: synchro-cyclotrons now available with higher pulse intensity

slide-14
SLIDE 14

Test experiment

MLL Tandem accelerator (Garching):

protons, 20 MeV ≈ 4 mm range in water  sharp BP (≈ 300 mm FWHM)  Pulse rise time: 3 ns Pulse width variation: 1 ns – 1 ms Pulse rate variation: 1 kHz - 2.5 MHz  ideal conditions for ionoacoustic test experiment MC– Simulation (Geant4)

Range verification with sub-mm spatial resolution?

  • W. Assmann et al., Med.Phys. 42, 567 (2015)
slide-15
SLIDE 15

The setup

slide-16
SLIDE 16

Test experiment

Experimental setup:

  • Water phantom
  • PZT detector, 1 – 10 MHz

remotely controlled (scan)

  • US detector array (tomography)

Model focus fc [MHz] US resolution [mm] V-303* spherical 1 1000 V-382* planar 3.5 300 V-311* spherical 10 100 array cylindrical 5 220

* immersion transducers (Videoscan) Olympus

slide-17
SLIDE 17

The sound of protons

10 MHz Transducer, 16 averages

20 MeV protons, 280 ns pulse width, 63 dB amplifier 2.106 p per pulse  4.1013 eV total energy deposition (ca 2 Gy)

slide-18
SLIDE 18

Ionoacoustic signal

BP Entrance window BP-reflection R W Speed of sound: 1520 m/s (H2O, 35 ⁰C)

  • r 1.52 mm/ms

1 Bragg Peak (BP) 2 Entrance window (W) 3 Reflection (R) 1 2 3

slide-19
SLIDE 19

Reproducibility & resolution

z-scan

20 mm Repetition in 200 um steps Reproducibility of BP position (10 MHz) Signal integration Frequency dependence

Space resolution in US: 1 MHz: 1.0 mm 10 MHz: 0.10 mm

slide-20
SLIDE 20

Vacuum window Kapton Titanium Titanium Proton energy [MeV]

20 20 21

Geant4 simulation [mm] 4040 +- 30 4070 +- 30 4450 +- 30 Experiment [mm] Bragg peak – foil Bragg peak – reflection 3990 +- 40 4020 +- 20 4090 +- 40 4060 +- 20 4490 +- 40 4460 +- 20 Difference simulation – exp [mm]

  • 50
  • 20

+20

  • 10

+40 +10

Bragg peak position

Uncertainty of Geant4 simulation: beam path geometry mean excitation energy

slide-21
SLIDE 21

Range no absorber Geant4 [mm] 4060 Measurement [mm] 4040 +- 30 0.52 mm Al Geant4 [mm] 3000 Measurement [mm] 3020 +- 30

Range shift accuracy

20 MeV protons

Range shift with Al absorber:

DGeant4: 1060 mm Dmeas: 1020 mm

slide-22
SLIDE 22

2D Bragg peak image

EBT2 film MC-simulation, Geant4 Measurement, 10 MHz Transducer

x-y-scan EBT2 A B B A A B

no absorber Al absorber

slide-23
SLIDE 23

Tomography

Real-time tomography with 64-channel transducer-array

3-dim reconstruction of US waves US detector setup

  • S. Kellnberger et al., to be published
slide-24
SLIDE 24

Image

reconstruction

x (mm) z (mm)

3D  2D

slide-25
SLIDE 25

Pulse length variation

25 30 35 40

  • 2
  • 1.5
  • 1
  • 0.5

0.5 time (µs) amplitude (mV) 25 30 35 40

  • 6
  • 4
  • 2

2 4 time (µs) amplitude (mV) 25 30 35 40

  • 4
  • 2

2 4 time (µs) amplitude (mV)

50 ns 200 ns 500 ns 1000 ns

25 30 35 40

  • 6
  • 4
  • 2

2 4 time (µs) amplitude (mV)

Note: inverting preamp

slide-26
SLIDE 26

Bragg peak width

p2p

peak to peak distance (p2p) of Bragg peak signal saturates for short pulse durations (i.e. in stress confinement)

 saturation value corresponds to Bragg peak width (steepest gradients)

Point detector approximation

slide-27
SLIDE 27

Entrance window width

10 MHz critical dimension lc and stress confinement time ts

  • Bragg peak:

lc = 230 mm, ts = 150 ns

  • entrance window:

lc = 50 mm, ts = 30 ns  detector frequency and size limited

slide-28
SLIDE 28

Acoustic simulations

k-Wave program

B.E. Treeby, B.T. Cox, J Biomed Opt 15 (2010)

  • Matlab toolbox for time-domain

modelling of acoustic wave propagation

  • Solving of the coupled first order

acoustic wave equation by k-space pseudospectral method

Input

slide-29
SLIDE 29

k-Wave input

Source term:

  • Geant4 dose distribution
  • Proton pulse time profile

Grid size:

  • Space: 30 – 60 mm
  • Time: 10 ns

Air Water Kapton foil US detector Bragg curve

slide-30
SLIDE 30

Example

simulation vs exp

slide-31
SLIDE 31

Conclusion from 20 MeV test experiments

  • submillimeter range accuracy
  • frequency independent
  • lowest detectable signal:

104 p per pulse  1012 eV (corresponding to 0.1 Gy)

  • beam modulation demonstrated

 lock-in technique to improve SNR

  • Bragg peak width at clinical energies
  • f 120 – 230 MeV: 5 - 20 mm
  • ionoacoustic frequencies ≈ 200 kHz
  • soft tissue attenuation

(50x water, but 200 kHz!)

  • tissue inhomogeneity and patient noise
  • position resolution at 200 kHz??

1 μsec pulse with 3.5 MHz modulation

Proof-of-Principle: Clinical Application:

slide-32
SLIDE 32

First test at clinical energies

Ionoacoustic experiment at the IBA 230 MeV synchro-cyclotron (Nice, France)

Note: 1024 averages

slide-33
SLIDE 33

Preliminary results…

Geant4 simulation DE = 1 MeV DE = 81 MeV

Energy (range) variation

See also: K.C. Jones at al., Experimental observation of acoustic emissions generated by a pulsed proton beam from a hospital-based clinical cyclotron, Med Phys 42 (2015) 7090.

slide-34
SLIDE 34

Grand goal

Transrectal ultrasonography of prostate tumor tissue

Corregistration of ultrasound imaging with ionoacoustic Bragg peak signal!?

prostate tumor expected ionoacoustic signal Main problem: ionoacoustic signal to noise ratio

slide-35
SLIDE 35

Thanks to …..

IBMI, Helmholtz-Zentrum München

  • S. Kellnberger, M. Omar, V. Ntziachristos

Universität der Bundeswehr München

  • M. Moser, C. Greubel, G. Dollinger

LMU München, Department for Medical Physics

  • A. Edlich, S. Lehrack, A. Maaß, S. Reinhardt,
  • J. Schreiber, P. Thirolf, K. Parodi

IBA, Ion Beam Applications SA, Belgium

  • F. Vander Stappen, D. Bertrand, D. Prieels

 Recent review: K. Parodi and W. Assmann, Mod Phys Lett A 30, 17 (2015) 1540025

slide-36
SLIDE 36

Finally… Thank you for your attention