© 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

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

2

Range Uncertainties in Proton Therapy

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

4

Tumor

Range Uncertainties – How to reduce them?

5

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)

Prompt Gamma based Range Verification

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

Example 1: Knife-edge slit camera

8Depth / a.u.

No

rma

lize

d D

ose

/ a

.u. P

rom

pt G

am

ma E

mis

sio

n / a

.u.

0

0.25

0.50

0.75

1.00

0

0.50

0.75

1.00

0.25

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

Example 1: Knife-edge slit camera

9

Tungsten collimator

LYSO crystals

SiPM readout

Analogue readout electronics

= PG Camera

Example 2: Prompt Gamma Timing

10

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

Integration of PG Range Verification in a Clinical Treatment Facility

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)

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

Integration of knife-edge slit camera

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.

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

Integration of Prompt Gamma Timing

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

$$$

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

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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