Total Body Irradiation

Diseases where BMT used

• Leukemia, aplastic Anemia, Fanconi’s Anemia, Epidermolysis bulosa, osetpetrosis, leukencephalopathy, Hurlers syndrome, sickle cell anemia

Allogeneic

• from donor

• healthy donor marrow regenerates in place of eradicated marrow

• donor lymphocytes show a anti-tumor effect

Autologous

• from patient

• infused marrow from patient

• may have residual malignant cells

  • can try to purge

  • no lymphocyte anti-tumor effect

Steps

1. Eradicate native bone marrow

2. immunosuppression to avoid rejection

3. minimal toxicity to healthy tissues

   *conditioning determined by disease, type of donor, etc.

Common dose scheules

• 200 cGy 1 fraction

• 1320 cGy 8 fractions

• 300 cGy in 1 fraction

• 400 cGy in 2 fractions

Common complications

• intersitial pneumonitis

  • dose rate dependent

  • up to 20% of patient develop

• infection

• infertility

• endocrine anomalies

• nausea

• muted growth

Dosimetric goal

within 10% of prescribed dose to whole body

Most common techniques

Bilateral reclining and Anterior-Posterior standing

may use lung compensations

both use a beam spoiler

beam spoiler

to increase dose at superficial depth

Bilateral reclining

• patient is semi-recombent, at extended distance

• TBI copensators for head/neck, legs, and lungs

Anterior- Posterior standing

• patient on TBI stand at extended distance

most important factor in devliery

beam energy

higher energy = more uniform dose

distance dependence

greater distance = more uniform dose

Simulation

• NOT CT based

• Calipers and meterstick measurements used

• need position of hte stsrt of the leg compensator

• also need a chest x-ray or chest CT -to determine if a lung compensator is needed

Reclining TBI Measurements

• thickness: head, neck, shoulder, mid mediastinum, umbilicus, pelvis, knees and ankle

• length: shoulder-to-top of had, iliac crest-to-knee, ilic crest-to-heel, and foot

Calculations needed

• monitor units

• dose rate

• compensator thickness

  • head/neck and legs based on caliper measurements

  • lun compensator based on chest x-ray or chest CT

• compensator length

Monitor Unit Calculation

• TMR calculation with extended distance

SAD factor

• corrects fro inverse square effect

• must be verified during commissioning

  • room geometry may cause it to be invalid

  • floors, walls, etc. can cause extra scatter

STF

• spoiler-tray factor

Sc

• Collimator scatter factor

• use 40×40 cm factor

Sp

• Phantom Scatter factor

• assume 30×30 cm for whole body

k

calibration factor = 1 cGy/MU

Tissue Deficit (TD)

• how mush tissue to missing for given

• TD = Lref - L

• Lref = thickness at prescription point

• L = thickness at given site

TD for lung

Aluminum compensator thickness

• density of Al is 2.7 g/cm3

• higher density limits physical dimensions

Compensator thickenss formula

Thickness ratio

t = 0.7

accounts for loss of beam intesnity due to out of field scatter from TBI compensators

large magnification factor

• compensators on tray near source (72 cm)

• patient at extended distance (410 cm)

• M = 0.182

Energy

bilateral: high energy usually used

AP: low energy (6 MV)

Comepensators

Bilateral: head/ neck, legs, cometimes lungs

AP: always lungs

AP vs. Bilateral

• AP

  • comps close to patient

  • measure lung on sagittal

• Bilateral

  • comps far from patient

  • measure lng on coronal

Beam blocking

• sometime block sensitive organs

• like lungs, kidneys, ovaries, testes, thymus

• lung blocking requires electron boost beams to chest wall under block

ovary blocking

• 5 HVL block in front of one

• surgeon moves ovary and marks location

Thymus blocking

• blocked with 5 HVL for Fanconi’s anemia

• accelerate immune system recovery

• contour on contrast enhanced CT
  generate a block with 1 cm expension

Pediatric Patients

• standing not possible for sedated

• bilateral still possible

• move monitor and pumps out of beam

• AP - performed laying on floor

Verification

• in-vivo measurements to verify dose

Commissioning TBI

• verify TMR ratios at TBI distance in solid water

• inverse square at TBI distance

• STF at TBI distance

• Verify in a RANDO phantom

Total Marrow irradiation

• improved therapeutic ratio - higher bone marrow dose, lower normal tissue

• patient position more complex

  • over 1 hour per treatment

  • high expense of resources

  • field matching in 1 or more locations

TBI with VMAT

• takes longer to plan since have more beam matching

• but will limit lung dose to < 8 to 10 GY to reduce idiopathic pneumonitis syndrome (IPS)

dose rate

-dependence on dose rate with toxicity

proven for kidneys, working on thyroid