Total body irradiation

2. 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
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3. 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.
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4. TBI
Conditioning (Preparative)
Regimen
To suppress the patient’s immune
system from rejecting the stem cells.
To eliminate the cancer
TBI CHEMO
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5. Stem Cell Sources
 Bone Marrow
 Blood
 Umbilical Cord
 Fetal Liver
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6. 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.
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7. 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
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8. 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.

9. 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)
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10. TBI treatment techniques are carried out
with:
Dedicated irradiators
Collimator Removal
Maximum Field Size
Extended SSD of 230 cm.
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11. Dedicated Irradiators
Two linear accelerators
two parallel-opposed
Beams simultaneously
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12. Modified Conventional Megavoltage
Radiotherapy Equipment
Treatment at extended source-surface distance (SSD)
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13. Modified Conventional Megavoltage
Radiotherapy Equipment
Treatment with a translational beam.
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14. Modified Conventional Megavoltage
Radiotherapy Equipment
Sweeping beam technique
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What about PDDs. Are they remain same as for stationary or will change????

15. Direct horizontal, long SSD Head rotation
 Half body, adjacent direct fields
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16. 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

17. Commissioning of Total Body
Irradiation Procedure
Machine absolute calibration (large fields)
Beam profiles
Percentage depth doses or tissue-phantom ratios
Monitor unit calculation
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18. 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)
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19. 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

21. 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)

22. 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?????

23. 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???

24. Block Shielding The Heart

25. 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)

26. AP/PA VS BILATERAL
Opinions ( audiences)
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27. 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 =
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28. Schematic Diagram
A B C
D
E F G
H
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29. 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

30. 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

31. 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

32. Oncology
Special thanks to
Dr. Sherali Hussein and sir Zaka
Thank you for listening
QUERIES????
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