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© 2018 IBA SA
Topical Workshop on Medical Accelerator Design and Diagnostics, Darmstadt, 11.12.2018
Integration of Prompt Gamma based Range Verification in a Proton Therapy System
Dr. Johannes Petzoldt
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Content
Range Uncertainties
Prompt Gamma Range Verification
Integration in Medical Environment – Needs and Problems
Requirements and Considerations for PG Systems
Examples of Integration of PG range verification
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Range Uncertainties in Proton Therapy
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Radiation Therapy – Protons vs Photons
Radiation therapy is one of the cornerstones for cancer treatment Photons: exponential decrease of dose
Protons: finite range and Bragg peak → spare normal tissue
Spread-Out-Bragg-Peak (SOBP) → overlay of mono energetic proton beams
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Tumor
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Range Uncertainties – How to reduce them?
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Intrinsic: conversion of HU to SPR (±2%)
Daily errors: patient setup, tumor shrinkage, anatomical changes…
Safety margins to compensate uncertainties → more dose to healthy tissue
Penetration depth / cm
D /
Dm
ax
Tissue Air TumorTissue Tumor
Protonbeam
Schaffner and Pedroni, Phys Med Biol 43 (1998)
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Prompt Gamma based Range Verification
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Prompt Gamma Rays as Range Probe
7Deposited doseFiedler et al. NSS 2011
Prompt gamma emission
Verburg et al., PMB 58 L37, 2013
Nuclear reactions between tissue and proton
Excited nucleus
Emission of prompt photons (τ << ns)
Characteristic lines, high energies (2-7 MeV)
Spatial correlation to dose deposition
Different concepts for translating PG signal to proton range
Kelleter et al., Physica Medica 34 7, 2017
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Example 1: Knife-edge slit camera
8Depth / a.u.
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ose
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pt G
am
ma E
mis
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n / a
.u.
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0.25
0.50
0.75
1.00
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0.50
0.75
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5 10 15 200
PG emission due to proton beam → collimator to project image of the emission on detector
Spatially resolved detector along beam path → 1D measurement (“PG profile”)
Shift in proton range = shift in PG profile
Simple concept, heavy collimator necessary
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Example 1: Knife-edge slit camera
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Tungsten collimator
LYSO crystals
SiPM readout
Analogue readout electronics
= PG Camera
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Example 2: Prompt Gamma Timing
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Proton transit time depends on range (higher range → longer transit time)
Scintillation detector in time-of-flight setup
PG emission time along particle track = PGT spectrum
Higher proton range = longer PG emission time
No collimation necessary, small footprint
CeBr3 detectors with digital readout electronics
Courtesy of C. Golnik
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Integration of PG Range Verification in a Clinical Treatment Facility
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Integration – What do we need to consider?
12
Integration
How to bring prototype from the lab to the treatment room
Connection into existing systems
Proof-of-Concept vs Product?
Define User Requirements Positioning accuracy and reproducibility etc.
Concept vs Reality Small problems like gravity etc.
Medical Environment Patient & staff safety!
Regulations (documentation and certification)
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Integration of PG Prototypes
13
Be aware
Certification necessary in case clinical device is changed
Impact on clinical workflow (e.g. increased time)
Limited space in treatment room
Cost efficient solution (development + hardware cost)
Requirements of PG systems
High position accuracy (<1 mm) -> error source
Usable for all gantry angles (360° rotation)
Usable for all treatment indications
Certification
$$$
Footprint
Positioning
Accuracy
All gantry
angles
All treatment
indications
Setup time
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Integration of knife-edge slit camera
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Example 1: Knife-edge slit camera
15
Positioning
Accuracy
$
All gantry
angles
Footprint
PG Trolley 1st generation
Movable solution, no change to PTS
Alignment with laser system
Rotation of camera
Used during patient treatment
Rather low position accuracy
All treatment
indications
Setup time
Certification
Yes
Low
High
No
Richter et al. 2016, Rad. Oncol.
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Example 1: Knife-edge slit camera
16
Positioning
Accuracy
$$All gantry
angles
Footprint
PG Trolley 2nd generation
Under the treatment couch
Docking holes in floor – pins on trolley
Calibration using X-ray and beam
Only horizontal fields possible
First patient 16/11/2018!
Setup time
Certification
Yes
Low
High
No
All treatment
indications
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Integration of Prompt Gamma Timing
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Positioning
AccuracyAll gantry
angles
Footprint
All treatment
indications
Setup time
Certification
Example 2: Prompt Gamma Timing
18
PGT Snout
Connected to nozzle, 8 PGT detectors
High position accuracy
“Real” integration in proton therapy system
High development effort due to regulations
First phantom measurements planned Q2/2019
Yes
Low
High
No
$$$
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Summary
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Integration necessary to obtain patient data
(Re-)Movable systems (trolleys) feasible without certification
Trade-off between different requirements
Further steps to “real” integration
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Thank you!This project has received funding from the European Union’s Horizon 2020
research and innovation programme under the Marie Sklodowska-Curie grant agreement No 675265, OMA – Optimization of Medical Accelerators.
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