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Neutron dose for IGPT

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

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Neutron dose for IGPT

  1. 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. 2. Contents • SMC Proton Introduction • Image Guided Proton Therapy @ SMC • • Motivation • Neutron MCNP simulation geometry, parameters • Results • Conclusion
  3. 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. 4. Real -Time Image Guided Proton Therapy
  5. 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. 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. 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. 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. 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. 10. MC Calculation Results
  11. 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. 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. 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. 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. 15. Wobbling vs Scanning at isocenter
  16. 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. 17. Neutron dose at x-ray equipments
  18. 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. 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. 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. 21. Thank you for attention! jinsung.k@gmail.com twitter@jinsungk

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