Monte Carlo study on secondary neutrons in x-ray imaging equipment for real time image guided proton therapy : Preliminary results

1. Monte Carlo study on secondary neutrons
in x-ray imaging equipment
for real time image guided proton therapy
: Preliminary results
Jin Sung Kim, Ph.D (jinsung.k@gmail.com)
Jung Suk Shin, Kwangzoo Chung, Eunheak Shin
Hye Young Kim, Sung Hwan Ahn, Sang Gyu Ju, Sang Hoon Jung
Youngyih Han, Hee Chul Park, Doo Ho Choi
Department of Radiation Oncology
Samsung Medical Center

2. Contents
• SMC Proton Introduction
•
Image Guided Proton Therapy @ SMC
•
•
Motivation
• Neutron
MCNP simulation geometry, parameters
• Results
• Conclusion

3. Full Proton Scanning Proton Therapy
2 Fully 360 Rotating Gantries with PBS
1 Scanning dedicated nozzle + 1 Multipurpose nozzle
MultiLeaf Collimator (MLC) for Patient-Specific Treatment
4D Respiratory Gating Proton Therapy
Cone-Beam CT Image Guided RT
Automatic Positioning using Robotic Couch
SMC Proton Therapy Center

4. Real -Time Image Guided Proton Therapy

5. Why neutron?
Hall EJ. Intensity-modulated radiation therapy, protons, and the risk of second cancers.
Int J Radiat Oncol Biol Phys. 2006 May 1;65(1):1-7. (558 citation)

6. Why neutron?
Shin D, Yoon M, Kwak J, Shin J, Lee SB, Park SY, Park S, Kim DY, Cho
KH. Secondary neutron doses for several beam configurations for
proton therapy. Int J Radiat Oncol Biol Phys. 2009 May 1;74(1):260-5.
Hall EJ. Intensity-modulated radiation therapy, protons, and the risk of second cancers.
Int J Radiat Oncol Biol Phys. 2006 May 1;65(1):1-7. (558 citation)

7. Motivation
Quadrupole
magnet
Quadrupole
magnet
Quadrupole
magnet
Wobbling
magnet
Wobbling
magnet
Scanning
magnet
Scatterer
Ridge filter
He gas duct
Dose monitor
2D monitor
Dose monitor
2D monitor
MLC
Compensator
MLC
Block
Block
Wobbling
(scattering)
Dose monitor
2D monitor
Block
MultiPurpose
Nozzle (G1)
Scanning
PBS dedicated
Nozzle (G2)
Scanning

8. Motivation & Questions about neutrons
Nozzle
Type
MLC Compensator
Block
No
MultiPurpose
Nozzle
PBS
Dedicated
Nozzle
Scanning
O
X
MW1
O
O
O
MW2
O
Wobbling
O
X
X
MS1
O
X
O
MS2
X
X
X
PS1
X
X
O
PS2
Q1. How big the difference between Wobbling vs Scanning?
Q2. What’s MLC effect on scanning treatment?
Q3. What’s block’s neutron effect to reduce proton penumbra?
at isocenter, x-ray tube and x-ray detector for IGPT!

9. Monte Carlo Simulation
MC Code
MCNPX 2.5, Mesh tally(type3)
Geometry
MLC, Compensator, Block, Flatness monitor,
Dose monitor, Ridge filter, Satterer, Profile
monitor
Proton Energy
230 MeV
SOBP
10 cm
Field Size
15 x 15 cm
Water
Phantom
30 x 30 x 40 cm
Calculation
Points
Isocenter, X-ray tube, X-ray detector
20, 40, 60cm distance from isocenter

10. MC Calculation Results

11. Neutron Dose Table
(mSv/Gy)
MW1
MW2
MS1
MS2
PS1
PS2
X-ray Tube
0.194
0.188
0.081
0.080
0.078
0.078
Detector
0.593
0.572
0.058
0.058
0.131
0.131
Isocenter
27.505
27.328
6.398
6.405
6.555
6.916
20cm
3.463
3.130
0.392
0.351
0.492
0.417
40cm
3.085
3.235
0.222
0.205
0.492
0.363
60cm
1.788
1.764
0.168
0.173
0.404
0.363

12. Neutron Dose as a function of distance
100.00
Nozzle
Type
(mSv/Gy)
Block
No
O
10.00
Scanning
PBS
Dedicated
Nozzle
1.00
0.10
20cm
40cm
60cm
X
MW1
O
O
O
MW2
X
X
MS1
O
X
O
MS2
X
X
X
PS1
X
MultiPurpose
Nozzle
O
O
Wobbling
0.01
Isocenter
MLC Compensator
X
O
PS2
MW1
MW2
MS1
MS2
PS1
PS2
Neutron dose equivalent per therapeutic dose (H/D) as a function of distance from the field edge.
Can we use this MCNP results without real measurement?

13. MW1
MS1
PS1
MW2
MS2
PS2
Zheng Y, Newhauser W, Fontenot J, Taddei P, Mohan R. Monte Carlo study of neutron dose equivalent
during passive scattering proton therapy. Phys Med Biol. 2007 Aug 7;52(15):4481-96.

14. Although it is not validated with real measured data,
It looks possible to estimate relatively effect with various options
MW1
MS1
PS1
MW2
MS2
PS2
Zacharatou Jarlskog C, Paganetti H. Risk of developing second cancer from neutron dose in proton therapy as
function of field characteristics, organ, and patient age. Int J Radiat Oncol Biol Phys. 2008 Sep 1;72(1):228-35.

15. Wobbling vs Scanning
at isocenter

16. Nozzle
Neutron Dose at isocenter
Type
MultiPurpose
Nozzle
(mSv/Gy)
Scanning
PBS
Dedicated
Nozzle
30.0
27.51
27.33
Compensator
Block
No
O
O
X
MW1
O
O
O
MW2
O
Wobbling
MLC
X
X
MS1
O
X
O
MS2
X
X
X
PS1
X
X
O
PS2
MLC effect on Scanning
20.0
Block effect
10.0
6.40
0
MW1
MW2
MS1
6.41
MS2
6.56
PS1
6.92
PS2
1. Neutron dose using wobbling is 4 times higher than scanning!
2. MLC and Block have a small difference at isocenter.

17. Neutron dose
at x-ray equipments

18. (mSv/Gy)
0.60
Neutron Dose at x-ray imaging machine
0.593
Nozzle
Type
MLC
Compensator
Block
No
O
O
X
MW1
O
O
O
MW2
O
X
X
MS1
O
X
O
MS2
X
X
X
PS1
X
X
O
0.572
PS2
Wobbling
0.45
MultiPurpose
Nozzle
Scanning
PBS
Dedicate
d Nozzle
0.30
0.194
0.188
0.131
0.15
0.081
0.080
0.078
0.078
0.058
0
0.131
0.058
Detector
X-ray Tube
MW1
MW2
MS1
MS2
PS1
PS2
Neutron dose using wobbling is higher than scanning.
Detector dose is relatively higher than X-ray tube
Neutron dose using scanning is reduced with MLC at imaging detector!

19. Conclusion (1)
(mSv/Gy)
27.51
27.33
Q1. How big the difference between Wobbling vs Scanning?
- ND wobbling much higher (4 more) than scanning
Q2. What’s MLC effect on scanning treatment?
- Scanning treatment of Multipurpose nozzle show smaller
neutron dose than PBS dedicated nozzle at detector
- MLC is absorbing neutron in Multipurpose nozzle.
- We need to add some neutron absorber on PBS nozzle
Q3. What’s block’s neutron effect to reduce proton penumbra?
- No significant effect on scanning treatment.
6.40
6.41
6.56
6.92
0.59
0.19
Isocenter
0.19
0.08
0.08
0.08
0.08
MW2
0.06
0.06
0.13
0.13
Detector
X-ray Tube
MW1
0.57
MS1
MS2
PS1
PS2

20. Conclusion (2)
•
We successfully calculate neutron dose distribution for 2 different
nozzle of proton therapy machine at samsung medical center using
MCNPX.
•
The world’s 1st neutron dose of imaging equipment (x-ray tube,
detector) was calculated for real-time image guide proton therapy
with 6 different options varying wobbling, scanning, MLC, block.
•
Neutron dose measurement and validation of monte-carlo simulation
should be performed after all installation of proton therapy machine
at samsung medical center.
•
Further calculations and measurements to reduce secondary neutron
dose to imaging detector and patient using neutron-absorbing
material (ex. SWX207HD5 or other boron containing materials) are
required according to the ALARA principle for image guided proton
therapy.

21. Thank you for attention!
jinsung.k@gmail.com
twitter@jinsungk