total body irradiation
TRANSCRIPT
OverviewIntroductionPhysical considerationsTBI Techniques and EquipmentIrradiation techniquesDosimetric considerationsDosimetric challengesAAPM #17 RecommendationsCommissioningTest of TBI Dosimetry ProtocolReferences Summary
ramahunzai
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
TBIConditioning (Preparative)
RegimenTo suppress the patient’s immune
system from rejecting the stem cells.To eliminate the cancer
TBI CHEMO
ramahunzai
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
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
ramahunzai
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)
ramahunzai
TBI treatment techniques are carried out with:
Dedicated irradiatorsCollimator RemovalMaximum Field SizeExtended SSD of 230 cm.
ramahunzai
Modified Conventional Megavoltage Radiotherapy Equipment
Treatment at extended source-surface distance (SSD)
ramahunzai
Modified Conventional Megavoltage Radiotherapy Equipment
Treatment with a translational beam.
ramahunzai
Modified Conventional Megavoltage Radiotherapy Equipment
Sweeping beam technique
ramahunzai
What about PDDs. Are they remain same as for stationary or will change????
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
ramahunzai
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
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???
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)
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 =
ramahunzai
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