1 / 29

LCSC - 01

LCSC - 01. Monte Carlo Simulation of Radiation Transport, for Stereotactic Radio Surgery. Per Kjäll Elekta Instrument AB 2001-10-25. LCSC - 01. Agenda:. Background Leksell GammaKnife Monte-Carlo Simulation Parallel approaches. LCSC - 01. Photon tracks. LCSC - 01. LCSC - 01.

candace-coffey
Download Presentation

LCSC - 01

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. LCSC - 01 Monte Carlo Simulation of Radiation Transport, for Stereotactic Radio Surgery Per Kjäll Elekta Instrument AB 2001-10-25

  2. LCSC - 01 Agenda: • Background • Leksell GammaKnife • Monte-Carlo Simulation • Parallel approaches

  3. LCSC - 01 Photon tracks

  4. LCSC - 01

  5. LCSC - 01 Definition of Dose (the dose at any point in V) E = Expectation Value of energy imparted in the volume V m = Mass in the volume V The dose is distributed and deposited by the electrons D = E/m [Gy  J/kg]

  6. LCSC - 01 The effects of Radiation Clinical effect: LD50 for whole body irradiation is 10 Gy. Thermal effect: A dose of 10 Gy absorbed in tissue is equivalent to a temperature increase of approximately 0.002 degrees C

  7. LCSC - 01 Direct Action Path lengths for electrons in the range 0.01 - 1.0 MeV in water is 0.003 mm - 4 mm. diameter of a cell  0.01 mm diameter of cell nucleus  0.001 mm Action must occur within the DNA. Increased dose = increased likelihood of interaction with the DNA. LET = Linear Energy Transfer

  8. LCSC - 01 Order of Events 1. Diagnosis 2. Acquiring diagnostical/anatomical images 3. Determining the required dose 4. Simulation of dose delivery 5. Dose delivery 6. Dose verification

  9. LCSC - 01 Simulation of dose delivery (Measurement in vivo is difficult/impossible) Models • Empirical / Semiempirical / Phenomenological • Analytical • Stochastic simulation Accuracy = f( time, clinical information needed, clinical reality, …)

  10. LCSC - 01 Ideal situation after dose delivery

  11. LCSC - 01 Real situation

  12. LCSC - 01 A few, highly shaped (dynamical) beams Strategies: I

  13. LCSC - 01 Strategies: II Multiple, narrow, converging simple beams

  14. LCSC - 01 • Discrepancy dependent on • Positioning / movement • Radiation delivery • Equipment (status) • Simulation of treatment • Clinical data • Radiation modality used Total Accuracy

  15. LCSC - 01 The Clinical Balance Damage to healthy tissue Tumourcidal Effect

  16. LCSC - 01 Leksell Gamma Knife

  17. LCSC - 01 Leksell Gamma Knife Automatic Positioning System Cobalt-60 sources Beam channel Helmet with collimators Shielding Helmet supports Plastic cover Treatment couch with mattress Protection panels Shielding doors Helmet in treatment position

  18. LCSC - 01 Leksell Gamma Knife

  19. LCSC - 01 • 4 different collimators (helmets): 4,8,14 & 18 mm • 201 narrow beams intersecting in one point • Sources (Co-60) fixed, i.e. not moving. • Patient rigidly (invasively) fixed to the treatment unit

  20. LCSC - 01

  21. LCSC - 01 • Dose is a function of: • Tissue in, and around, the beam path and the target • Location of target • Type of radiation (spectrum) • Intensity • Irradiation Time Dose Simulation (revisited) Ideal Simulation Characteristics: Fast, accurate, simple and requiring a minimum of clinical data.

  22. LCSC - 01 The tracks are stocastically generated: i.e.the path lengths, the types and the details of the interactions undergone are all sampled from the physical models (distributions) describing these interactions. Monte Carlo Simulation A “good” random number generator is needed. My PC: 250 histories/s Real source: 1012 photons/s One history is the sum total of all effects caused by one photon; such as generation of secondary particles and their energy deposition.

  23. LCSC - 01 Random Number Generators, some remarks Or, rather “Pseudo” Random Number Generators, since the computer algorithms generating the sequences are strictly deterministic. The same seed will genrate the same sequence of “random” numbers. An important “quality” of a Generator is a small correlation between the values in the sequence. The sequence of numbers generated by a random number generator is periodic. The longer the period, the better. For example, the RAND-function in FORTRAN 77 produces 32-bit floating point numbers uniformly distributed between 0 and 1, and with a period of the order of 1018. Two radiation transport runs with the same seeds and the same number of particles will produce two sets of identical histories. Running the random number generator through a sequence longer than its period will duplicate histories. No new information is obtained.

  24. LCSC - 01 What will we use MCS for? Treatment planning Radiation protection/safety “Dynamical” dose delivery Dose to other parts of the body (radiation milieu) Design of effective beam shaping

  25. LCSC - 01 Treatment Planning Phase-space information: Energy, direction, type, history

  26. LCSC - 01 Treatment Planning And then some numbers: Loading the phase space file with 10 million particles per channel (100 days on my PC !), and using 28 bytes per particle, results in a phase space file of approx. 50-100 GB. The clinical data set (MR / Voxels): 100 slices x 0.5MB/slice => 50 MB. “Releasing” the particles in the phase space file is estimated to require approx. 100 days on my PC. Desired calculation time …. 1 second/shot !

  27. LCSC - 01 Design of effective beam shaping Requirement: A final dose distribution with a set of desired characteristics. Approx. Calculation time on my PC is 3 weeks. Size of data set, < 50 MB.

  28. LCSC - 01 Radiation milieu Effects due to changes to shielding? Dose to various parts of the body ? Data set size can be huge! Calc. time, ..,? Phase space surfaces

  29. LCSC - 01 Parallel computation Random number generators for parallel computation (the Leapfrog Method). Cluster architecture: Using available PC-network Dedicated cluster Buying computer time (NSC)

More Related