Development of a new prompt gamma ray detection system for full 3D proton range verification
Costanza, P. Taylor, Michael J
Costanza, P.
Taylor, Michael J
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Abstract
Purpose or Objective
The ability to determine proton range in 3D is well suited
for spot-scanning systems and for detecting non-uniform
anatomical changes. In range verification via prompt
gamma (PG) detection range is determined through the
reconstruction of the origin of PG-rays emitted from
nuclear de-excitations following proton bombardment. We
report the first results of a new PG-based 3D range
verification technique.
Material and Methods
Our technique utilises the 2.741-6.128 MeV (p, 16O) PG
rays, emitted in cascade. Within the limitation of
spectroscopy detector/electronic systems, these rays are
effectively emitted simultaneously in time and position.
When protons impinge tissues several 2.741-6.128 MeV PGray
couples are produced. Their detection, coupled with a
reconstruction algorithm, allows the identification of the
common emission point. The maximum intensity of the PGray
distribution is located few millimeters prior to the
Bragg peak. For a beam passing through tissues with
constant oxygen concentration, the beam range can be
determined from the emission points of all detected
couples.
The detection system is comprised of 16 LaBr3(Ce)
detectors, in a symmetrical design. To determine the PGray PGray
emission positions, the information recorded by each
detector is fed into an in-house built reconstruction
algorithm.
Results
The position reconstruction capability of the system was
investigated by means of Geant4 simulations. The
spectrometer, with a 8 cm internal radius, has been
modelled with realistic energy/temporal resolution.
Figure 1 shows the detector/algorithm performance when
a clinical 180 MeV beam impinges a water phantom. An
excellent agreement is observed between the algorithmreconstructed
PG-rays emission positions (blue curve), the
phantom-scored PG-rays emission positions (red curve) and
the dose distribution (black curve). The PG-ray origin is
determined from the width of the detected peak with a σ
of 4.17 mm. Subsequently a 175 and a 177.5 MeV proton
beam were shot on the same phantom. The phantom is
modelled so that the spectrometer centre coincides with
the Bragg peak for a 180 MeV beam; this translates into a
range undershoot of 5 and 10 mm. Figure 2 depicts the
algorithm-reconstructed PG-rays emission positions for the
175 (purple curve) and 177.5 MeV (green curve) beams.
The same plot for a 180 MeV beam is shown for comparison
(blue curve). The σ is 4.31 and 5.47 mm for a 5 and 10 mm
undershoot, respectively.
Conclusion
A new technique for proton range verification was
developed; it allows to determine the range of a 180 MeV
beam to within 4.17 mm. With a 10 mm undershoot the
range was still reconstructed to within 6 mm. These
uncertainties are lower than the ones fed into robust
planning or the margins used in proton treatment planning. Next stage is to test the technique for a beam passing
through different tissues. Developments are ongoing to
construct a spectrometer prototype. The ultimate goal is
a clinically compliant system for on-line, real-time range
verification.
Description
Date
2020
Publisher
Collections
Keywords
Type
Meetings and Proceedings
Citation
Costanza P, Mackay RI, Kirkby KJ, Taylor MJ. PO-1728: Development of a new prompt gamma ray detection system for full 3D proton range verification. Radiotherapy and Oncology . 2020 Nov;152:S957–8.