Special Procedures:

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• Special Procedures
• TBI, Total Skin and Intraoperative Radiation
  Therapy

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Total Body Irradiation

• TBI and other large fields, such as total
  lymphoid irradiation(TLI) and total abdominal
  irradiation(TAI) play an important role in
  cytoreductive regimes for bone marrow transplants.

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TBI

• Three main purposes
• Immunosuppression to allow grafting of donor
  marrow.
• Eradication of malignant cells.
• Eradication of cell populations with genetic
  disorders.

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Advantages over chemotherapy

• There is no sparing of sanctuary site like the
  testis.
• The dose is fairly homogeneous and does not
  depend on the blood supply.
• There is no cross resistance with other agents.
• Dose distribution can be adjusted by boosting or
  blocking certain areas.

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Diseases where it is used for bone marrow
transplants.

• Malignant
• ALL
• AML
• CML
• NHL
• Multiple myeloma
• Pediatric solid tumors
• Neuroblastoma
• Ewings sarcoma.
• Small cell lung
• Testicular ca.

• Non malignant
• Immune disorders
• Aplastic anemia
• Genetic disorders
• Osteoporosis
• Thrombocytopenia
• Fanconis anemia

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Physical principles

• Immobilization
• Standing or lying down
• Low dose rate
• Lung and eye shields
• Boosting (electrons)

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technique

• Treatment unit
• Conventional megavoltage equipment used
• Beam energy
• All mega OK, but with higher energies there is
  better dose homogeneity.
• Dose prescription point
• Location of point depends on technique. Dose
  should be /- 10 of prescription point dose.

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Side effects

• Nausea and vomiting

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Doses

• Fractionated versus single fraction
• Hyperfractionation
• 130 to 150 cGy in 10 fractions in 5 days.
• Memorial Sloan Kettering treats 3x per day

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Total skin irradiation

• Is a technique that aims to treat all of the
  patients skin, while sparing other organs.
• Skin is superficial, so electrons are suitable.
• Patient population is very small, so this is done
  at only a very few centers.

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Problems

• The skin shape is irregular so it is difficult to
  get an even dose.
• Therefore the goal is to aim at as even a dose as
  possible without harming the patient.
• X-ray contamination of electron beams.

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Diseases

• Mycosis fungoides
• Kaposis sarcoma
• 4000cGy in 20 fractions is required for extensive
  malignant skin disease.

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Techniques

• Large fields (Stanford)
• Rotational (McGill)

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Scattering

• Electrons are scattered by an aluminum mirror and
  the air.

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Scattering

• Electrons are scattered by a lucite scattering
  plate placed between the gantry and patient.

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Summary

• TSI is used in the treatment of certain skin
  diseases.
• Offered only at a very few sites.
• Has been practiced since the 1950s.
• Requires a large electron field with a reasonably
  uniform dose and an output high enough so that
  the treatments are not too long.
• Boosts are usually needed for areas that are
  underdosed such as the soles of feet, perineum

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Intraoperative radiation therapy

• The total dose delivered to a tumor is limited by
  the critical structures surrounding the tumor.
• Intraoperative radiation allows a single dose to
  be delivered to the tumor at the time of surgery.
• Direct visualization and moving critical
  structures out of the way allows a large dose to
  be delivered safely.

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Advantages

• Exclusion of dose limiting structures
• Reduction of post op. radiation
• Immediate targeting of at risk areas
• Treatment of previously irradiated areas
• Elimination of time between surgery and RT

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History

• Used almost immediately after x-rays were
  discovered.
• Interest dropped after megavoltage machines were
  in use.
• Interest shown again in the 1970s to prevent
  bowel effects after high total doses to abdomen.

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Equipment

• Electron beam is most commonly used.
• Orthovoltage
• Linear accelerators are modified.
• Cones are used
• Periscopes may be used.

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Technique

• Multidisciplinary team is needed
• Radiation oncologist consults on any potential
  candidate.
• At time of surgery, a sterile cone is placed, the
  depth determined and information relayed to
  physicist for calculation.
• Incisions are temporarily closed and patient
  transferred for treatment.

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Technique

• Patient is transported under anesthesia,
  transferred to treatment couch and redraped.
• Incision is reopened and machine is docked to
  cone.
• 1000 to 2000 cGy is delivered, depending on the
  area and volume.
• The energy of electrons depends on the depth to
  be treated.

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Typical sites

• Colorectal
• Pancreatic
• Gastric
• Extrahepatic biliary
• Soft tissue sarcomas
• Gynecologic
• Bladder
• HN

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Results

• Trials show improvement in local control.
• IORT is standard practice for gastric ca. in
  Japan.
• Survival depends on site.