OverviewIntroductionPhysical considerationsTBI Techniques and EquipmentIrradiation techniquesDosimetric considerationsDosimetric challengesAAPM #17 RecommendationsCommissioningTest of TBI Dosimetry ProtocolReferences Summary

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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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TBIConditioning (Preparative)

RegimenTo suppress the patient’s immune

system from rejecting the stem cells.To eliminate the cancer

TBI CHEMO

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Stem Cell Sources

Bone Marrow Blood Umbilical Cord Fetal Liver

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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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Diseases Treated by Bone Marrow Transplantation

Aplastic anemiaThalassemiaSickle cell anemiaImmunodeficiency

disordersAcute myelogenous

leukemiaMyelodysplastic

syndromeMultiple myeloma

Armitage, NEJM 1994

Acute lymphocytic leukemia

Chronic myelogenous leukemia

Chronic lymphocytic leukemia

Non-Hodgkin’s lymphoma

Hodgkin’s disease

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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 sessionTotal nodal irradiation, with a typical nodal dose of 40

Gy delivered in 20 fractions.

TBI Techniques and EquipmentProtocolAvailable EquipmentBeam Energy (depends upon patients thickness and

tissue lateral effect)Maximum Field sizeTreatment Distance (extended SSD)Dose RatePatient DimensionsShielding (Lungs, kidneys, brain etc)

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TBI treatment techniques are carried out with:

Dedicated irradiatorsCollimator RemovalMaximum Field SizeExtended SSD of 230 cm.

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Dedicated IrradiatorsTwo linear acceleratorstwo parallel-opposed Beams simultaneously

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Modified Conventional Megavoltage Radiotherapy Equipment

Treatment at extended source-surface distance (SSD)

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Modified Conventional Megavoltage Radiotherapy Equipment

Treatment with a translational beam.

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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????

Direct horizontal, long SSD Head rotation

Half body, adjacent direct fields

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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

Commissioning of Total Body Irradiation Procedure

Machine absolute calibration (large fields)Beam profilesPercentage depth doses or tissue-phantom ratiosMonitor unit calculation

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AAPM RecommendationsAAPM TG21 Liquid water PhantomPolystyrene, 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

effectsDose calibration(FS, Compensators etc.

consideration)ramahunzai

AAPM RecommendationsCentral ray data (PDDs, TMRs, TPRs) with full scattering

conditionsTest 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

conditionsInhomogeneity corrections (lungs, bones

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Methods Of Bone Dose DeterminationBones are blood forming organsenergy absorption of radiation is a two-stage processKerma Absorbed doseElectronic equilibrium (lacking at the interface)Mathematical relationship

Need to know the spectrum of energy at bone locationCo-60 High energy Linacs(bones = muscles)

Problems of Dosimetry for TBIPhantom size Irradiation of ionization chamber cableNon-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?????

Problems of Dosimetry for TBILarge variation of diode reading i.e. lack of diode

sensitivityAttenuation coefficients changes for Linac????

(due to primary beam photon spectrumMaking of customized compensators???

Block Shielding The Heart

Test of Total Body Irradiation Dosimetry Protocol

Complete assurance of required dose rate from medical physicist.

ICRU criteria fulfillment. TBI irradiation ‘dry runs’ ?????Anthropomorphic phantomTLD measurements of films (verification of uniform dose

distribution)Use od detectors(TLD, Diodes, ionization chambers)(but concerns are there in using these devices)

AP/PA VS BILATERAL Opinions ( audiences)

Pre-treatment set up

Separation (cm)

Head(bolus)

Neck(bolus)

Nipple level

Umbilicus MidThigh

Knees(bolus)

Mid Calf(bolus)

Ankles(bolus)

A B C D E F G H

superior inclination of the couch =

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Schematic Diagram

A B C

D

E F G H

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Dose prescription pointThe TBI dose is prescribed to a point inside

the bodyMidpoint at the level of the umbilicusPrescribed dose must be within ±10% of the

prescribed point doseUniformity of dose is achieved with the use

of bolus or compensators

SummaryTBI is one of the way along with chemo to suppress

immunosuppression.There are lot of treatment techniques, protocolsCommissioning of data is playing key roleSeveral recommendations of AAPM Report-17Dosimetric problems are thereOunce TBI starts a fully commissioned back is very

importantBecause of highly irregular shapes, achievement of uniform

dose distribution is the major concernDry tests must satisfy the protocol we are following

ReferencesThe Physical aspects of total body and half body

photon irradiation (AAPM Report NO. 17)The Physics of Radiation Therapy, Faiz M. KHANRadiation Oncology Physics: A Handbook for

Teachers and Students, IAEA, Vienna, 2007TBI 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

Oncology

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