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A Range Verification Method for Proton Therapy
using a Photon Counting Detector
Jin Sung Kim1, Su Jung An2,3, Yong Hyun Chung2,3*
1Department
of Radiation Oncology, Samsung Medical Center, Seoul, 135-710, Korea
2Department of Radiological Science, College of Health Science, Yonsei University, Wonju, 220-710, Korea
3Institute of Health Science, Yonsei University, Wonju, 220-710, Korea
C. Simulation setup for in-beam PET imaging
INTRODUCTION
•
In the past few decades, proton radiotherapy has evolved into a widely practiced modality for cancer treatment.
• The main advantage of proton beam is its capability to irradiate a highly conformal dose distribution in a given
target volume, due to its unique interaction and energy deposition.
• The deposited dose reaches a maximum called the Bragg peak beyond which it sharply falls to zero.
• Owing to the typically steep dose gradient at the distal edge of each individual proton beam, however,
uncertainties in treatment planning and treatment delivery can have a significant influence on the delivered 3D
•The detector system consists of two opposing parallel-planes of CZT detectors to measure proton range
verification.(figure1(c))
•To verify proper detection of annihilation gamma , several thickness of CZT crystals were used. (Table 1)
•The distance between the detector heads was fixed at 20 cm.
•Using phase space file as input, e+ sources were emitted from PMMA phantom using particle filter in
GATE 6 actor toolkit.
•The 2D image of positron emitting radionuclide in the phantom was acquired by plotting the coincidence
counts per opposing detector pixel pair.
dose distribution.
• This study presents the results of the vary first multi-modality imaging system for X-ray and gamma-ray
coincidence imaging using a single CdZnTe detector to measure proton range verification.
RESULTS
• The detector system consists of two parallel planes of detectors and an X-ray generator.
• An X-ray image is acquired using one detector for the verification of 2-dimensional anatomical structure of the
A. Generation of positron emitting radio-nuclides
patient.
• 110 and 140 MeV proton beams, cylindrical tissue phantom, and two rectangular CdZnTe detectors were
modeled, and the imaging performance of this system was evaluated using GATE simulation
• The results showed the potential benefits of a X-ray/gamma-ray imaging with a single detector for range
Dose
Relative counts of total nuclei
verification in proton therapy
MATERIALS & METHODS
Relative counts
a. 110MeV
Dose
Relative counts of total nuclei
b. 140MeV
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Normalized dose
• Image registration is intrinsic because the X-ray and gamma ray images are acquired in the same geometry.
Relative counts
proton penetration.
• Figure 2 shows the simulated Bragg curve and spatial distribution of the positron emitting nuclei along
the depth direction for 110 and 140 MeV proton beams.
• This distribution shows a nearly flat plateau, dropping to zero in close proximity to the Bragg peak.
• The systematic distance between the 50% level of the total activity and dose maximum in PMMA was
observed as about 6 mm.
• This results were subsequently used as the source distribution on the PET simulation.
Normalized dose
• The paired gamma rays from the annihilation are imaged with two modules to determine the maximum range of
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Depth position (mm)
Figure 2.The total isotope distribution from GATE6 simulation
B. X-ray imaging with CZT photon counting detector
a. PMMA phantom
c. Coincidence imaging
b. X-ray imaging
• Figure 3 shows the spectral x-ray image of the PMMA phantom with CZT photon
counting detector.
• 1 mm-thick CZT detector is usable for x-ray imaging to see anatomical structure of
the object.
Figure 1. Schematic diagram of a simulation setup
Table 1. Thickness of CZT detector used in simulation
Figure 3. Simulated X-ray image using CZT photon counting detector
Thickness of CZT detector
C. In-beam PET imaging with parallel-planes of CZT detector
DETECTOR A
1 mm CZT + 5 mm CZT
DETECTOR B
1 mm CZT + 10 mm CZT
DETECTOR C
1 mm CZT + 15 mm CZT
A. Generation of positron emitting radio-nuclides
• GATE(Version 6.0) was used to simulate the generation of positron emitting radio-nuclides by proton irradiation
• The simulated 2D images of positron emitting radionuclides in the phantom were illustrated in Figure 4
for 110 and 140 MeV proton beams.
• The results demonstrate the better image quality from a thicker detector.
• Simulation has proven that the proton therapy dose distribution could be imaged by CZT pair detectors.
Thickness of CZT
detector
110 MeV
PET image
PET + radiography image
140 MeV
PET image
PET + radiography image
DETECTOR A
in PMMA cylindrical phantom with a height of 20 cm and a diameter of 15 cm.
• Cylindrical phantom contains 5 balls (Aluminum, Glass, Spinebone, PVC, Water) that were arranged as shown
(1 mm CZT + 5 mm CZT)
in figure 1(a).
• Two monoenergetic pencil-like proton beam were used.
(energy: 110 and 140 MeV; FWHM: ~10 mm; intensity : 1 x 108 p/s)
• The passage of protons through the phantom was simulated through physical interactions and the distribution of
DETECTOR B
(1 mm CZT + 10 mm CZT)
generated positron emitting isotopes was calculated.
• GATE V6 allows the user to record so-called phase-space files containing the essential properties of the
simulated particles at a given geometric level.
• The properties of
C11,
O15,
C10
particles in the phantom are stored in a phase-space file.
• This output file can then be used as an input file in subsequent PET simulations.
B. Simulation setup for X-ray imaging
•
DETECTOR C
(1 mm CZT + 15 mm CZT)
Figure 4. in-beam PET image using CZT detector
DISCUSSION & CONCLUSION
The detector system consists of an X-ray generator and one CZT detector module for 2-D X-ray imaging.
(figure1 (b))
• Date acquisition was performed using an 1 mm-thick CZT detector and a PMMA phantom same as in section A.
• X-ray system has a source to detector distance of 68.5 cm, maximum fan angle of the x-ray beam of 17°, and
magnification factor of 1.17.
• The spectral X-ray system using a photon counting CZT detector consists of 0.5 x 0.5 mm2 pixel and 400 x 400
array of pixels.
• X-ray spectrum of 120 kVp tube voltage was generated in SRS-78 program.
• The x-ray beam quality was 7 mm Al equivalent half value layer(HVL).
• The proton range verification with x-ray imaging using single CZT detector, as described in this paper could be a
simple tool for accurate in vivo range verifications in proton therapy.
• According to our simulations, it is achievable to use two CZT detectors system, which have different thickness
for positron emitting radionuclides.
• Although 1 mm thickness CZT system was enough for x-ray imaging to see anatomical anatomy of phantom,
additional 15 mm thickness CZT detector was required to measure proton distribution.
• Based on this work, we will proceed with investigation of this method for our clinical practice and the next step
will be finding a suitable detector and design.
• This study also presented the potential feasibility about 3D volume measurement for proton dose distribution
using PET/CBCT system with single detector system.