neutron dose for igpt
DESCRIPTION
Monte Carlo study on secondary neutrons in x-ray imaging equipment for real time image guided proton therapy : Preliminary resultsTRANSCRIPT
Monte Carlo study on secondary neutrons in x-ray imaging equipment
for real time image guided proton therapy : Preliminary results
Department of Radiation Oncology
Samsung Medical Center
Jin Sung Kim, Ph.D ([email protected])
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
Contents• SMC Proton Introduction
• Image Guided Proton Therapy @ SMC
• Neutron
• Motivation
• MCNP simulation geometry, parameters
• Results
• Conclusion
Full Proton Scanning Proton Therapy
2 Fully 360 Rotating Gantries with PBS1 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
Real -Time Image Guided Proton Therapy
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)
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)
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.
MotivationQuadrupole
magnet
Wobblingmagnet
Dose monitor2D monitor
MLC
Block
He gas duct
Quadrupole magnet
Wobblingmagnet
Dose monitor2D monitor Dose monitor
2D monitor
Quadrupole magnet
Scanningmagnet
Scatterer
Ridge filter
MLC
Block
Compensator Block
Wobbling(scattering) Scanning ScanningMultiPurpose
Nozzle (G1)PBS dedicatedNozzle (G2)
Motivation & Questions about neutrons
Nozzle Type MLC Compensator Block No
Multi-Purpose Nozzle
WobblingO O X MW1
Multi-Purpose Nozzle
WobblingO O O MW2Multi-
Purpose Nozzle
Scanning
O X X MS1
Multi-Purpose Nozzle
ScanningO X O MS2
PBSDedicated
Nozzle
ScanningX X X PS1PBS
Dedicated Nozzle
Scanning
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!
Monte Carlo SimulationMC Code MCNPX 2.5, Mesh tally(type3)
GeometryMLC, 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 detectorCalculation Points 20, 40, 60cm distance from isocenter
MC Calculation Results
(mSv/Gy) MW1 MW2 MS1 MS2 PS1 PS2
X-ray Tube
Detector
Isocenter
20cm
40cm
60cm
0.194 0.188 0.081 0.080 0.078 0.078
0.593 0.572 0.058 0.058 0.131 0.131
27.505 27.328 6.398 6.405 6.555 6.916
3.463 3.130 0.392 0.351 0.492 0.417
3.085 3.235 0.222 0.205 0.492 0.363
1.788 1.764 0.168 0.173 0.404 0.363
Neutron Dose Table
Nozzle Type MLC Compensator Block No
Multi-Purpose Nozzle
WobblingO O X MW1
Multi-Purpose Nozzle
WobblingO O O MW2Multi-
Purpose Nozzle
Scanning
O X X MS1
Multi-Purpose Nozzle
ScanningO X O MS2
PBSDedicated
Nozzle
ScanningX X X PS1PBS
Dedicated Nozzle
Scanning
X X O PS2
0.01
0.10
1.00
10.00
100.00
Isocenter 20cm 40cm 60cm
MW1MW2MS1MS2PS1PS2
Neutron Dose as a function of distance
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?
(mSv/Gy)
MW1 MW2MS1 MS2PS1 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.
MW1 MW2MS1 MS2PS1 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.
Although it is not validated with real measured data, It looks possible to estimate relatively effect with various options
Wobbling vs Scanning
at isocenter
0
10.0
20.0
30.027.51 27.33
6.40 6.41 6.566.92
MW1MW2 MS1 MS2 PS1 PS2
Neutron Dose at isocenter
1. Neutron dose using wobbling is 4 times higher than scanning!
2. MLC and Block have a small difference at isocenter.
Block effect
MLC effect on Scanning
Nozzle Type MLC Compensator Block No
Multi-Purpose Nozzle
WobblingO O X MW1
Multi-Purpose Nozzle
WobblingO O O MW2Multi-
Purpose Nozzle
Scanning
O X X MS1
Multi-Purpose Nozzle
ScanningO X O MS2
PBSDedicated
Nozzle
ScanningX X X PS1PBS
Dedicated Nozzle
Scanning
X X O PS2
(mSv/Gy)
Neutron dose at x-ray equipments
0
0.15
0.30
0.45
0.60
0.194
0.593
0.188
0.572
0.081 0.0580.080 0.0580.078
0.131
0.078
0.131
X-ray TubeDetector
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!
Neutron Dose at x-ray imaging machineNozzle Type MLC Compensator Block No
Multi-Purpose Nozzle
WobblingO O X MW1
Multi-Purpose Nozzle
Wobbling
O O O MW2Multi-Purpose Nozzle
Scanning
O X X MS1
Multi-Purpose Nozzle
ScanningO X O MS2
PBSDedicated Nozzle
Scanning
X X X PS1PBSDedicated Nozzle
Scanning
X X O PS2
(mSv/Gy)
Conclusion (1)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.
27.51
0.19
0.59
27.33
0.19
0.57
6.40
0.08
0.06
6.41
0.08
0.06
6.56
0.08
0.13
6.92
0.08
0.13
IsocenterX-ray Tube
Detector
MW1 MW2 MS1 MS2 PS1 PS2
(mSv/Gy)
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.
