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hybrid Compton-PET imaging for ion-range monitoring in hadron therapy

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J. Balibrea-Correa¹, J. Lerendegui-Marco¹, V. Babiano-Suarez¹, C. Domingo-Pardo¹, I. Ladarescu¹, A. Tarifeño-Saldivia¹,P. Torres-Sánchez¹,

M. Pallàs⁴,B.Brusasco⁴,C. Guerrero^2,3, T. Rodríguez-González^2,3, M. C. Jiménez-Ramos³, B. Fernández-Martínez^2,3,J. M. Quesada²

¹ IFIC (CSIC-University of Valencia), Paterna, 46980 Spain ² University of Seville, Seville, 41012 Spain ³ Centro Nacional de Aceleradores (U. Sevilla, CSIC, Junta de Andalucía), Sevilla, 41092 Spain. ⁴ Universitat Politècnica de Catalunya, Barcelona, Spain.

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We acknowledge funding from AEI/MCIN PDC2021-12536-C21 & ERC-CoG HYMNS Grant Agreement Nr. 681740

This work was supported by grant ICJ220-045122-I funded by MCIN/AEI/10.13039/501100011033 and by European Union NextGeneration EU/PRTR.

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XVI CPAN days 19-21 de Noviembre de 2024

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• Introduction

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• Overview of the Hybrid PGI/PET experiments:
• Pilot experiment @ CNA: 18 MeV, “manually” pulsed
• PoC experiment @ HIT: clinical energy & intensity, pulsed beam structure (synchrotron)
• Experiment @ WPE (IBA-ProteusPlus)
• Experiment @ Reading (IBA-ProteusOne)

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• Summary and conclusions

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Phys. Med. Biol. 58 (2013) R131–R160

Hadron-therapy is a incipient technique with multiple benefits over the traditional radiotherapy:

• Target very precisely the tumor area and large LET.
• Minimize damage into neighbouring tissues.

Potential benefits can be improved because of large safety margins due to hadron range unreliability:

• Anatomical changes.
• Patient setup errors.
• Uncertainty of charged particles stopping power.

Safety margins can be lowered using an online ion-range verification (3.5% +3 mm)

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PGI & PET hadron-monitoring

Phys. Med. Biol. 59 (2014) 7089

Main techniques for hadron range verification:

• Prompt Gamma-ray monitoring using Compton Cameras or collimated detection systems.

Measures the prompt ɣ-rays during the irradiation (4.4 MeV…):

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✔ High spatial correlation.

❌ Harsh measurement conditions.

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• In-vivo PET using clinical machines just after the patient irradiation.

Measures the activity of β⁺ emitters produced during irradiations

(¹¹C, ¹³N,¹⁵O…):

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✔ Low background measurements.

❌ Biological wash-out.

• And many others:
• Proton-acustic
• Count Rate variations.

NIM A 591 (2008) 282–286

2021 IEEE Nuclear Science Symposium and Medical Imaging Conference (NSS/MIC)

A.C. Kraan et al. / Physica Medica xxx (2014) 1-11

Phys. Med. Biol. 59 (2014) 7089

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Overcome individual limitations from both imaging techniques by complementary information

New perspectives of in vivo ion beam treatment verification:

• Prompt Gamma Imaging most promising for quasi real-time monitoring
• PET offers intrinsic tomographic and functional imaging modality.

NIM A 953 (2020) 163228

CNA pilot experiment (2020)

• Experimental setup made of 2 Compton Imagers (CI).
• Simplified problem with p @ 18 MeV and small phantoms:
• PGI: Thick C target
• PET: Thin material + ⁺e converter
• Beam duty cycle optimized for PGI and long lived-isotopes:
• Delivery (in-spill): ~200s.
• Waiting time (off-spill): ~200s.

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PoC experiment @ HIT (2021)

Heidelberg Ion Therapy (HIT) driven by a linac-synchrotron:

• Pencil beam of p, ⍺ & C-ion (55/155/155/275 MeV)
• Minimal clinical current
• Beam duty cycle optimized for PGI and “short”-lived PET isotopes: in-spill/off-spill: ~60/300 ms.

Experimental setup made of 4 CI:

• Large PGI-PET FoV (PET ~200x200m²) covering the full p, ⍺ & C-ion track
• Phantoms:
• Small graphite for PGI/PET validation
• Large PE phantoms sensitivity

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The hybrid PGI/PET technique is validated at 55 MeV protons!

• PET in-spill:

Large e⁺ & ɣ-rays production reducing sensitivity:

Still there are differences between displaced distributions!

• PET off-spill:

Only long-lived isotopes contributions:

Clean shape with differences in displacements of 0.5 mm!

The setup is sensitive to 0.5 mm in PET in-beam off-spill!

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- At 155 MeV and for clinically relevant intensity (10⁸ p/spot) even with four large Compton imagers the spatial PGI sensitivity is of

<20mm.

- Therefore, at high beam energy in-beam off-spill PET provides a superior information.

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Experiment @ WPE (2024)

Isochronous Normal Conducting Cyclotron (IBA-ProteusPlus) as the 10 planned for Spain:

• Only p @ 100 and 125 MeV in clinical operation (minimum current).
• Duty cycle of 400 ms/~1-2s

Experimental setup made of 4 CI in the optimized configuration:

• PGI/PET FoV (PET ~100x100x100m³) focus on p Bragg peak.
• Large PE phantoms

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• Hybrid PGI/PET may provide an added value for ion-range verification owing to complementary information:
• PGI most promising technique for quasi-real monitoring.
• PET offers tomographic and functional imaging.
• The technique can be fully exploited with pulsed beams.
• 1st Pilot Experiment @ CNA (2020) 2 Compton imagers at 20 MeV p (subclinical energies and intensities)
• Excellent performance for both PET and PGI, sub-mm sensitivity to range-shifts
• Experiment @ HIT (2021) 4 Compton imagers with large efficiency, 55/155/155/275 MeV p ⍺ C (1st test at clinical energies and intensities with a suitable pulsed machine - synchrotron)
• Excellent performance of hybrid PET-PGI at 55 MeV
• Superior PET performance at 155 MeV, 275 MeV for p ⍺ C
• Experiment @ WPE (2024) 4 Compton imagers in cross-config at 100/120 MeV p
• Validation of hybrid PET-PGI at conventional cyclotron machines for PT (synchronous sc-cyclotron / Proteus Plus)
• Good performance PET-PGI at 100 MeV with a pseudo-pulsed beam structure
• Analysis in progress for higher beam energy
• Experiment @ Reading (2024) 4 CC with “small” FoV 100/120 MeV p
• Validation of hybrid PET-PGI at conventional cyclotrons for PT (isochronous cyclotrons / Proteus One)
• Analysis in progress

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Thank you very much for your attention!