Advanced Quality Assurance
instrumentation for radiotherapy:
the experience at Centre for MedicalRadiation Physics
Marco Petasecca, PhD

Japan 2015, 28 September, 2015 KEK

Wollongong

CENTRE FOR MEDICAL RADIATIONPHYSICS

Technology
SOLUTIONS

Excellence in
EDUCATION

Partnerships in

BUSINESSResearch Areas- Radiotherapy and Instrumentation
 External Beam Radiotherapy
 Brachytherapy
 Proton Therapy
 Heavy Ion Therapy
 Microbeam Radiotherapy- Medical Imaging
 PET CT
 ProtonCT Volumetric dosimetry reconstruction- Radiobiology and Dosimetry
 Personnel monitoring Micro and Nano dosimetry- High Energy Physics
 Radiation detector optimisation and rad damage



Semiconductor Dosimetry in Proton Therapy◦ LomaLinda Cancer Centre (US) Dose Magnifying Glass (DMG)

1D Si High Spatial Resolution Beam Energy reconstruction◦ HIMAC (Japan)
 Serial DMG

Dosimetry in SRT with motion compensation◦ Royal North Shore Hospital (Sydney – AUSTRALIA) MagicPlate 512
 Serial DMG

Conclusion

Advanced radiotherapy techniques such as SRT (SBRT,SRS), Proton and Heavy Ion therapy produce:◦ high dose modulation and tight gradients◦ Strong hypo-fractionation with small or none margin of error◦ Conformality requires organ motion compensation  interplay
effects

Difficulties in the dosimetric verification of these newcomplex treatment methods using existing dosimeters
has led to the need for a new generation of fast
responding real time dosimeters with sub-millimetre
accuracy Most of them are spin off from HEP radiation detectors
designed for fundamental research.
Dose Magnifying Glass (DMG)•The DMG is a silicon strip detector–••

Designed and developed at CMRP

Real time and high spatial resolution
Each diode provides sensitive area
20 x 2000 μm2 and 200 μm pitch,mounted on 375μm thick p-type
SubstrateAuthors:••CMRP: J. Wong, I. Fuduli, M. Newall, M. Petasecca, M.
Lerch, S. Guatelli, A. Rosenfeld,
Loma Linda university: A. Wroe and R. SchulteThe Data Acquisition System (DAS)•Very large scale integration application
specific integration circuit (VLSI ASIC)
known as; TERA.

Connected to a field programmable gatearray (FPGA) with universal serial bus (USB)interface to a personal computer (PC).

The detector isoperated inpassive mode.

The TERA DAS consists of a current to frequency converter anddigital counter enabling continuous integration and readout of
the response from 256 channels during acquisition [5].

Setup at LMCC
••
•••
•

The DMG is positioned horizontally in front of the nozzle
Measures simultaneously profile and depth dose in a water phantom
Waterproof
Automatic stager for depth scanning
127or 157 MeV protons
20 mm diameter proton beam, comparison with a commercial PTW diode, PTW Markus
Parallel-Plate Ionization Chamber and Monte CarloResults – PDD 127 MeVMax discrepancy 2.6%

Submitted to PMB – Aug 2015

Results – PDD 157 MeV

Max discrepancy 2.7%

Submitted to PMB – Aug 2015

Results – Profiles 127 and 157 MeV

Beam Energy reconstruction in C-12 RT at HIMAC
introducing Serial DMG•Common Axisof Detection

The ‘sDMG’ is a silicon strip detector
comprised of[3]:Form factor

Linear, 50.8mm

Channels

256

Isolation

p-stop

Strip area

20 x 2000 μm2

Pitch

200 μmSubstrate typep-type silicon

Substrate thickness

375 μmResistivity

10 ΩcmPre-irradiation

4 MradFigure – Serial Dose Magnifying Glass (sDMG) [3].Experimental Methodology•Experiments conducted at HIMAC, Chiba, Japan. The detector is irradiated by;– C-12 ion beam,– Energy 290 MeV/u (E’) and– 10x10cm2 square field•

Placed inside a PMMA phantom, the detector is setup in configurations:
1. Detection axis aligned parallel to beam direction
2. Detection axis aligned perpendicular to beam direction

Experimental Methodology – Depth Profile•

The detection axis is aligned parallel to thedirection of the C-12 beam.

•C-12 ion beam, energy 290 MeV/u and 10x10cm2square field.

– PBP (pristine Bragg peak)– SOBP (spread-out Bragg peak, 60mmwidth in water)•Depth Dose Profiles: PBP measurements conductedwith increasing depth in PMMA (+/- 1mm).

•Dose-rate: SOBP measurements
conducted with depth in PMMA
86mm for various dose-rates.

DataAcquisition
SystemsDMG
detector inPMMA

C-12 beamExperimental Methodology – Lateral Profile••

The detection axis is aligned perpendicular to the direction of theC-12 beam.
SOPB (60mm width in water) C-12 ion beam, energy 290 MeV/u
and 10x10cm2 square field.

Penumbral Study:• Measurements conducted with increasing depth in PMMA (+/1mm).

DataAcquisition
SystemsDMG
detector inPMMA

C-12 beamResults: Pristine Bragg Peak - Measurement•

Result processed with generated equalisation vector.

Absolute Depth (mm)- Larger straggling effect in silicon?
- Radiation damage creates artefacts?

Results: Energy Reconstruction•

Propose method of independent beam energy verification.

•Calculation of E0 (residual energy of beam, at surface of PMMA phantom) from PBP
measurements.

Results: Energy Reconstruction - MCMonte-Carlo Simulation:Geant4 9.6.p01•

Physics activated:
––•

EM:–
G4EmStandardPhysics_option3
Hadronic:-QGSP_BIC_HP• Binary intra-nuclear
cascade model + precompound model +nuclear de-excitation +High precision models forneutrons with Energy<20MeV

Geometry:– Cuts in the air: 10cm
– Cuts in the phantom:
0.1mm

Detailed experimental geometry:

Results: Energy Reconstruction
1.

Measurement of location of PBP in silicon detector (at known depth in PMMA).

2. Energy (E1) upon entrance to silicon is backcalculated from measurement of PBP.
3. Location of PBP (projected range withoutsilicon + depth) in PMMA is determined fromE1.

4. Residual Energy (E0) at entrance to PMMA
phantom calculated from location of PBP in
PMMA (without silicon)

Workflow Diagram

DepthSi

E1DPMMA

E0

Results: Energy Reconstruction

Depth in
PMMA (mm),(+/- 1 mm)

Measured Peak Locationin Silicon (mm), (+/0.4mm)

Reconstructed Energy, E1(MeV/u), (+/-3MeV/u)

Simulated Energy(MeV/u),(+/-0.1%)

Reconstructed ResidualEnergy, E0, (MeV/u), (+/3MeV/u)

Percentage Differenceto Monte-Carlo (%)

102

19.4

118

1212791.62

8927.2143147277

1.25

6442.1

186

190

277

0.93

5448.7203206

2781.30•

E0 determined by Monte-Carlo simulation to be 275 MeV/u +/- 0.01%,•E0 determined by reconstruction to be (278 +/- 1) MeV/u

Results: Penumbral Study•

SOPB (60mm width in water) delivered for depths in PMMA; 60mm, 80mm, 100mm, 120mm and130mm.

Results: Dose-Rate dependence•

Investigated dose-rate dependence ofdetector under irradiation by SOBP (width60mm in water).

•Region of SOBP detector is exposed to,high-LET particles•

Detector placed at 86mm in PMMA
phantom, response of individual channels
examined for varying dose-rates:
Dose-Rates(Gy/min)

4.000
0.400
0.040
0.004

Results: Dose-Rate Dependence

Pre-irradiation dose

Future Work

Pristine Bragg Peak results demonstrated:
Prolonged Exposure → Radiation Damage

•Necessitates implementation of radiation harder substrate

Penumbral study and Pristine Bragg Peak results
established feasibility of high spatial resolution silicondetector.
But, necessitates simultaneous measurement ofdepth dose profile and beam profile•

Thus, future studies will utilise DUO:
 a two dimensional detector for high resolution
profiling, enabling simultaneous readout of X and Yprofiles

Stereotactic RT and motion tracking compensation study
using MP512
Designed and developed at CMRP, MP512 is a 2D array:•Monolithic silicon:– 512 diodes in a square array– Sensitive volume ~ 0.5 x 0.5 x 0.1 mm3– Diode separation – 2 mm
– Size – 52 x 52 mm2•

Readout Electronics:– Custom design multi-channel electrometer– Pulse-by-Pulse acquisition

Dosimetric Characterisation of MP512: OF – PDD in 6MV
photon beams•MP512 compared to various
dosimeters for varying field size.
Condition

ValueSource

Linear Accelerator

Type6MV photon

Dose delivered

100 MU

Field Size•…

Source to surface
distance

90 cm

Depth

10 cm

For field sizes < 1x1cm2 MP512 over
responds <4%, for greater field sizes,results agree within +/- 1%.
Figure – Normalised output factor
measurements of 6MV beam for a variety ofdetectors (Aldosari et. al. 2014)

Combining Small Field dosimetry andMotion Tracking• Characterize the performance of a high spatial
andresolution detector for QA ofNeedtemporal
Realisation
Source:Linear Accelerator

treatmentsthat dynamically track the tumour
HexaMotion

Motion Platform:
Motion:Patient Lung trace

Motion Tracking:Calypsomotion.
Detector:
MP512

Adaptive Strategy: Dynamic MLC

Dynamic Characterisation of MP512
MotionTracking
Array

Radiofrequency
Transponder
Beacons

DataAcquisition
System+Y+X
MotionPlatform

MP512
Detector
plane

StaticMotion+X+Y

Motion+Tracking

2loaded
Motionplatformwithpatientlungtrace,→of motion
tracking
systemand MLC
tracking• •Introduction
MLC
defined1x1cmsquare
field clinicaldeliveredto stationary
detectordetectorMotion
movingthroughout
beam delivery→ WithMotion
throughout
beam delivery
to movingsystem →Motion+Tracking
WithoutDynamic Characterisation of MP512
Without Motion – 1x1cm2 field size

Dynamic Characterisation by MP512
With Motion – 1x1cm2 field size

With Motion and MLC Tracking - 1x1cm2 field size

sDMG – FS 1x1cm2

Results: Beam Profiles• Comparison of results from MP512 to EBT3 film for three experimental cases for field size
1x1cm2.
2

Y-profiles – 1x1cm

Without Motion

With Motion

With Motion and MLC tracking

Figure – Normalised profile comparison, MP512 with EBT3 film ()• The average uncertainty for EBT3 film is +/-1.9%, for M512 is +/-2%, induced by the RFfrom Calypso

Results: Beam Profiles• Comparison of results from MP512 to EBT3 film for three experimental cases for field size
1x1cm2.
2X-profiles – 1x1cm

Without Motion

With Motion

With Motion and MLC tracking

Figure – Normalised profile comparison, MP512 with EBT3 film ()MLC used to produce enhanced
dynamic wedge to generate anintensity modulated dose profileIntegral profile along y-axis iscompared for cases:◦ Without Motion◦ With Motion◦ With Motion + Tracking

M512

Detailed timing information
6 MV Linac 10x10 cm field 600 MU/min

Beam On

Transient phaseTiming analysis of motion/interplay effect

Motion compensation
algorithm/tracking software
generates a lag in time (200 ms)
 tracking cannot cope with fasttransient components

Integral profiles cannot display
which is the phenomenon which
creates the dose discrepancy

25TH – 30TH JANUARYHOBART, TASMANIA