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Angelica Perez-Andujar University of Puerto Rico, Mayagüez Campus

Fermi National Accelerator Laboratory Neutron Therapy Facility. Experimental Analysis of Wedge Factors for Neutron Therapy. Angelica Perez-Andujar University of Puerto Rico, Mayagüez Campus. Outline. NEUTRON THERAPY AND TREATMENT PLANNING THE USE OF TEFLON WEDGE FILTERS

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Angelica Perez-Andujar University of Puerto Rico, Mayagüez Campus

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  1. Fermi National Accelerator Laboratory Neutron Therapy Facility Experimental Analysis of Wedge Factors for Neutron Therapy Angelica Perez-Andujar University of Puerto Rico, Mayagüez Campus

  2. Outline • NEUTRON THERAPY AND TREATMENT PLANNING • THE USE OF TEFLON WEDGE FILTERS • WEDGE FACTOR MEASUREMENTS • RESULTS • CONCLUSION • RECOMMENDATIONS

  3. Dose Distribution • An isodose chart presents the percent of dose that is going to be delivered at an specific depth at the body. • The dose distribution is presented as isodose curves.

  4. Teflon Wedge Filter

  5. Wedge Effect on the Isodose Curves • Wedges tilts the isodose curves. no wedge 60 º wedge 45º wedge

  6. h l w  Wedges Characteristics Teflon wedge filter without aluminum mount • Each wedge has a physical angle that tilts the dose that the patient is going to received.

  7. What other changes can wedges produce? • They absorb some beam What can be done to ensure the delivery of the correct amount of dose? • A wedge factor could be calculated. What is a wedge factor? • The wedge factor is the ratio of the dose delivered with and without wedge. • If the wedge factor is known it is possible to calculate the amount of beam necessary to deliver the desired dose. More about Wedge Filters

  8. Experimental Setup Isoplane Heavy Concrete Shielding Wall Polyethylene Phantom Transmission Chamber Neutrons Linac Protons Isocenter Beryllium Target Collimator SDD= 109cm SAD=190cm

  9. Ionization Chamber in the Phantom Spokas Thimble Chamber

  10. Collimators

  11. Wedges and Collimators Used • Not all wedges were used for all collimators. • Wedges 1 and 3 do not cover the big collimator aperture. • Wedge 2 and 4 absorb more beam than necessary when small collimators are used.

  12. T + 273.15 1013.25 x TPCOR= P 295.15 (Normalized Charge x TPCOR)wedge Wedge Factor = (Normalized Charge x TPCOR )nowedge Wedge Factor Calculations • The amount of charge received by the ionization chamber at the phantom was normalized to the one received at the transmission chamber. • The normalized charge is multiplied by a temperature-pressure correction factor. • The wedge factor is given by: • The wedge factors obtained were compared with the ones that were calculated years ago

  13. Wedge Factor vs. Depth

  14. Wedge Factor vs. Square Root of Collimator Aperture

  15. Conclusions and Recommendations Conclusions • The wedge factor is a function of the collimator size and the depth in the phantom. • It increases as depth and collimator size increase. • The relationship between depth and collimator size is not linear it suggests a curvature as depth increases. Recommendations • New measurements have to be made. • It is necessary to use a tissue equivalent material phantom. • Measurements need to be performed with longer beam exposure. • An improved phantom positioning system should be developed.

  16. Acknowledgements • Thomas Kroc • Arlene Lennox • Gordon Holmblad • Ruth DeJerld • Marc Austin • Miguel Morales • All my new friends • SIST Program • you

  17. Questions ?

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