Radiation Physics and Engineering
A peer-reviewed journal published by K. N. Toosi University of Technology

Monte Carlo optimization of collimator length for a parallel-hole prompt gamma camera in proton beam range verification

Document Type : Research Article

Authors

Sharareh Gharib
Payvand Taherparvar

Department of Physics, Faculty of Sciences, University of Guilan, Rasht, Guilan, Iran

https://doi.org/10.22034/rpe.2026.576834.1346
Abstract
This study aimed to optimize the collimator length for a parallel-hole prompt gamma camera dedicated to real-time proton beam range verification, achieving an optimal balance between detection sensitivity and spatial accuracy for clinical application. Comprehensive Monte Carlo simulations were conducted using the GATE platform with the QGSP_BIC_HP_EMZ physics list. A cylindrical PMMA phantom was irradiated with a 90 MeV monoenergetic proton beam, and a PG camera model consisting of an LSO scintillator coupled with a lead parallel-hole collimator was simulated. Collimator length was systematically varied from 4 to 8 cm, and detected PG events were analyzed within a 4.2-6.3 MeV energy window. System performance was evaluated using sensitivity (total detected counts) and spatial accuracy (Δ), defined as the absolute difference between true and reconstructed depth of maximum PG emission. The simulated energy spectrum exhibited characteristic photopeaks from carbon and oxygen, and a strong spatial correlation was confirmed between the distal edge of the Bragg peak and the PG emission maximum. Increasing collimator length decreased sensitivity but generally improved spatial accuracy. The optimal trade-off was achieved with a 7 cm collimator, yielding the best spatial accuracy of Δ = 2 mm. This study identifies 7 cm as the optimal collimator length for a parallel-hole PG camera, achieving spatial accuracy comparable to more complex slit- or pinhole-based systems. The findings provide a quantitative design framework and underscore the critical importance of balancing geometric resolution with sufficient count statistics for precise and timely clinical range verification.

Highlights

  • Optimized collimator length for a parallel-hole prompt gamma camera in proton therapy using GATE code.
  • Evaluated trade-off between detection sensitivity and spatial accuracy for collimator lengths of 4-8 cm.
  • Spatial accuracy comparable to more complex slit- or pinhole-based systems.
  • Demonstrates that sufficient count statistics are as critical as geometric resolution for clinical range verification.

Keywords

Proton therapy
Prompt gamma imaging
Range verification
Monte Carlo simulation
Collimator optimization
GATE simulation

Copyright
RPE is licensed under a Creative Commons Attribution-NonCommercial 4.0 International License (CC BY-NC 4.0).

Conflict of Interest
The authors declare no potential conflict of interest regarding the publication of this work‎.

Funding
‎The authors declare that no funds‎, ‎grants‎, ‎or other financial support were received during the preparation of this manuscript‎.

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Radiation Physics and Engineering
Volume 7, Issue 4
Autumn 2026
Pages 67-73

  • Receive Date 19 February 2026
  • Revise Date 08 August 2026
  • Accept Date 11 September 2026

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