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Total body irradiation

Total body irradiation

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Total body irradiation

  1. 1. Overview Introduction Physical considerations TBI Techniques and Equipment Irradiation techniques Dosimetric considerations Dosimetric challenges AAPM #17 Recommendations Commissioning Test of TBI Dosimetry Protocol References Summary ramahunzai
  2. 2. TOTAL BODY IRRADIATION “Total body irradiation (TBI) is a special radio therapeutic technique that delivers to a patient’s whole body a dose uniform to within 10% of the prescribed dose.” Megavoltage photon beams (Cobalt-60 & linacs) used for this purpose. ramahunzai
  3. 3. TBI Conditioning (Preparative) Regimen To suppress the patient’s immune system from rejecting the stem cells. To eliminate the cancer TBI CHEMO ramahunzai
  4. 4. Stem Cell Sources  Bone Marrow  Blood  Umbilical Cord  Fetal Liver ramahunzai
  5. 5. HISTORY OF STEM CELL TRANSPLANTATION  Turn of the 20th century  The idea that a small number of cells in the marrow  Stem cells”, might be responsible for the development of all blood cells.  Marrow injury exposure to atomic weapons.  Spread of nuclear technology and weapons, studies of bone marrow transplantation were initiated. ramahunzai
  6. 6. Diseases Treated by Bone Marrow Transplantation Aplastic anemia Thalassemia Sickle cell anemia Immunodeficiency disorders Acute myelogenous leukemia Myelodysplastic syndrome Multiple myeloma Armitage, NEJM 1994  Acute lymphocytic leukemia  Chronic myelogenous leukemia  Chronic lymphocytic leukemia  Non-Hodgkin’s lymphoma  Hodgkin’s disease ramahunzai
  7. 7. Clinical Total Body Irradiation Categories High dose TBI single session or 6 fractions of 200 cGy)  Low dose TBI 10–15 fractions of 10–15 cGy each;  Half-body irradiation 8 Gy delivered to the upper or lower half body in a single session Total nodal irradiation, with a typical nodal dose of 40 Gy delivered in 20 fractions.
  8. 8. TBI Techniques and Equipment Protocol Available Equipment Beam Energy (depends upon patients thickness and tissue lateral effect) Maximum Field size Treatment Distance (extended SSD) Dose Rate Patient Dimensions Shielding (Lungs, kidneys, brain etc) ramahunzai
  9. 9. TBI treatment techniques are carried out with: Dedicated irradiators Collimator Removal Maximum Field Size Extended SSD of 230 cm. ramahunzai
  10. 10. Dedicated Irradiators Two linear accelerators two parallel-opposed Beams simultaneously ramahunzai
  11. 11. Modified Conventional Megavoltage Radiotherapy Equipment Treatment at extended source-surface distance (SSD) ramahunzai
  12. 12. Modified Conventional Megavoltage Radiotherapy Equipment Treatment with a translational beam. ramahunzai
  13. 13. Modified Conventional Megavoltage Radiotherapy Equipment Sweeping beam technique ramahunzai What about PDDs. Are they remain same as for stationary or will change????
  14. 14. Direct horizontal, long SSD Head rotation  Half body, adjacent direct fields ramahunzai
  15. 15. Commissioning of Total Body Irradiation Procedure Need for commissioning TBI? Dose rate at Treatment SSDT Nominal PDD and TMR may not be appropriate at SSDT If SSDT is greater than 130 cm, absolute dose rate calibration necessary
  16. 16. Commissioning of Total Body Irradiation Procedure Machine absolute calibration (large fields) Beam profiles Percentage depth doses or tissue-phantom ratios Monitor unit calculation ramahunzai
  17. 17. AAPM Recommendations AAPM TG21 Liquid water Phantom Polystyrene, acrylics etc. (need correction factor) Recommended phantom size 30x30x30cm3 ????? Higher energy beam recommended for uniform dose distribution(excluding build up region) AP/PA preferred Dosimeter response E independent cable effects Dose calibration(FS, Compensators etc. consideration) ramahunzai
  18. 18. AAPM Recommendations Central ray data (PDDs, TMRs, TPRs) with full scattering conditions Test of inverse sq. law (deviation must be within 2%) Beam profiles (along CAX, both parallel and perpendicular planes along CAX) Attenuation data measurement under treatment conditions Inhomogeneity corrections (lungs, bones
  19. 19. Methods Of Bone Dose Determination Bones are blood forming organs energy absorption of radiation is a two-stage process Kerma Absorbed dose Electronic equilibrium (lacking at the interface) Mathematical relationship Need to know the spectrum of energy at bone location Co-60 High energy Linacs(bones = muscles)
  20. 20. Problems of Dosimetry for TBI Phantom size  Irradiation of ionization chamber cable Non-application of inverse square lay. Unreliability of monitor chambers for long time irradiation. TAR, TMR and TPR becomes distance dependent????? Lacking of output factors if shielding is there?????
  21. 21. Problems of Dosimetry for TBI Large variation of diode reading i.e. lack of diode sensitivity Attenuation coefficients changes for Linac???? (due to primary beam photon spectrum Making of customized compensators???
  22. 22. Block Shielding The Heart
  23. 23. Test of Total Body Irradiation Dosimetry Protocol Complete assurance of required dose rate from medical physicist. ICRU criteria fulfillment. TBI irradiation ‘dry runs’ ????? Anthropomorphic phantom TLD measurements of films (verification of uniform dose distribution) Use od detectors(TLD, Diodes, ionization chambers) (but concerns are there in using these devices)
  24. 24. AP/PA VS BILATERAL Opinions ( audiences)        
  25. 25. Pre-treatment set up Separation (cm) Head (bolus) Neck (bolus) Nipple level Umbilicus Mid Thigh Knees (bolus) Mid Calf (bolus) Ankles (bolus) A B C D E F G H superior inclination of the couch = ramahunzai
  26. 26. Schematic Diagram A B C D E F G H ramahunzai
  27. 27. Dose prescription point The TBI dose is prescribed to a point inside the body Midpoint at the level of the umbilicus Prescribed dose must be within ±10% of the prescribed point dose Uniformity of dose is achieved with the use of bolus or compensators
  28. 28. Summary TBI is one of the way along with chemo to suppress immunosuppression. There are lot of treatment techniques, protocols Commissioning of data is playing key role Several recommendations of AAPM Report-17 Dosimetric problems are there Ounce TBI starts a fully commissioned back is very important Because of highly irregular shapes, achievement of uniform dose distribution is the major concern Dry tests must satisfy the protocol we are following
  29. 29. References The Physical aspects of total body and half body photon irradiation (AAPM Report NO. 17) The Physics of Radiation Therapy, Faiz M. KHAN Radiation Oncology Physics: A Handbook for Teachers and Students, IAEA, Vienna, 2007 TBI with a sweeping cobalt beam by Dr. Sherali hussein PhD, F.C.C.P.M and El-Khatib PhD, F.C.C.P.M Google books
  30. 30. Oncology Special thanks to Dr. Sherali Hussein and sir Zaka Thank you for listening QUERIES???? ramahunzai

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