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TBI

Total Body Irradiation (TBI) is given
to prepare (condition) the patient’s body for bone marrow or stem cell transplant.
It is a special radio therapeutic technique
that delivers to a patient’s whole body, a
uniform dose within (+/-)10% of the
prescribed dose.

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TBI

  1. 1. Total Body Irradiation By Aparna P M.Sc.Radiation Physics University of Calicut
  2. 2. Contents * Definition * Technical aspects of TBI * Clinical TBI categories * Beam energy * Tissue lateral effect * Normal tissue shielding * Patient positioning methods * Port films for TBI * In vivo dosimetry * Side effects of TBI
  3. 3. T B I Total Body Irradiation (TBI) is given to prepare (condition) the patient’s body for bone marrow or stem cell transplant. It is given to the entire body of the patient.
  4. 4. Which is used in the treatment of diseases such as; * Leukemia * Aplastic anemia * Lymphoma * Multiple myeloma etc….
  5. 5. Purpose of TBI Before Transplant To destroy cancer cells in areas not easily reached by chemotherapy. These are the nervous system, bones, skin, and testes in men.
  6. 6. To decrease the response of immune system. If a patient is getting bone marrow or Stem cells from a donor, his/her body may see these as foreign and hence try to destroy. To prevent this destruction TBI is given.  To create space for the new marrow to grow (engraft).
  7. 7. Technical aspects of TBI TBI is a special radio therapeutic technique that delivers to a patient’s whole body, a uniform dose within (+/-)10% of the prescribed dose. Megavoltage photon beams , either Co-60 Gamma rays or Megavoltage X-rays are used for this purpose.
  8. 8. The beams are either stationary, with field sizes of the order of (70 × 200) cm^2 encompass- -ing the whole patient. or Moving, with smaller field sizes, in some sort of translational or rotational motion to cover the whole patient within the radiation beam.
  9. 9. Clinical TBI categories Depending on the specific clinical situation , TBI techniques are divided into the following four categories: 1:High dose TBI, with dose delivery in a single session or in up to six fractions of 200 cGy each in three days (total dose 1200 cGy); 2: Low dose TBI, with dose delivery in 10–15 fractions of 10–15 cGy each;
  10. 10. 3: Half-body irradiation, with a dose of 8 Gy delivered to the upper or lower half body in a single session; 4:Total nodal irradiation, with a typical nodal dose of 40 Gy delivered in 20 fractions.
  11. 11. BEAM ENERGY  The choice of photon beam energy is dictated by patient thickness and the Specification of dose homogeneity.  In addition to the thickness variation along the axis of the patient, the patient diameter along the path of beam also affects dose uniformity depending upon beam energy.
  12. 12. The thicker the patient, the higher is the beam energy required to produce acceptable dose uniformity for parallel-opposed fields.
  13. 13. Tissue Lateral Effect A term tissue lateral effect has been used to describe the situation in which lower energy or a thicker patient is treated with parallel-opposed beams can give rise to an excessively higher dose to the subcutaneous tissues compared with the midpoint dose.
  14. 14. For patients of thickness greater than 35 cm, energies higher than 6 MV should be used to minimize the tissue lateral effect.
  15. 15. Dose prescription point The TBI dose is prescribed to a point inside the body, referred to as the dose prescription point (usually at the midpoint at the level of the umbilicus).
  16. 16. The TBI procedure must deliver the prescribed dose to this point and should maintain the dose throughout the body within ±10% of the prescribed dose. Uniformity of dose is achieved with the use of bolus or compensators.
  17. 17. Normal Tissue Shielding Shielding of normal tissues must be carefully Considered in TBI because shielding may potentially reduce the dose to the target volume (ie;bone marrow cells, leukemic cells, and circulating stem cells). Despite this concern, there are situations in which partial shielding of critical tissues, including the lungs, kidneys, eyes (lens), and brain, is considered.
  18. 18. During TBI care should be taken to reduce dose to the underlying normal lung tissue. This is done with the use of customized lung blocks fabricated with low melting point alloy known as Cerrobend. These are carefully placed over the lungs at the time of treatment. Lung Blocks used to reduce dose to lung
  19. 19. Patient Positioning methods 1 : AP/PA 2 : Bilateral 3 : Translational couch
  20. 20. AP/PA Technique This technique consist of irradiating antereo-posteriorly by parallel opposed fields with patient in standing position. The TBI Stand facilitates treatments of patients in a standing position.
  21. 21. Standing allows shielding of certain critical organs (eg:lungs) from photons and boosting {giving extra dose of radiation to specific areas of body} of superficial tissues with electrons in the shadow of the blocks. eg:Dose to the lungs can be reduced using lung blocks of about 1HVT and the chest wall under the blocks can be boosted with electrons of appropriate energy.
  22. 22. This technique requires an SSD in excess of 3m to encompass the patient within the large beams. Distances from source to patient
  23. 23. Disadvantage The sickness and fatigue associated with chemo therapy makes it difficult for many patients to hold a standing position resulting in poor reproducibility set up.
  24. 24. Bilateral technique This technique involves left and right lateral opposing fields with the patient treated in a semi seated position (fig.).
  25. 25. This positioning helps to overcome the limitations of treatment room dimensions to an extent and is more comfortable to patient. Arms are positioned laterally such that arms shadow the lungs.
  26. 26. The patient set-up is recorded in terms of distances measured b/n external body land mark as shown in fig.
  27. 27. Sagital laser light installed in the ceiling measures the source-to-body axis distance. Laser light also helps to position the patient’s sagital axis at right angles to the beam’s central axis.
  28. 28. Lateral body thickness along the patient axis varies considerably in the bilateral TBI. To achieve the dose uniformity with ~+10% along the sagital axis, compensators are designed for head and neck, lungs and legs.
  29. 29. Disadvantage: This technique suffers from poor dose uniformity and does not allow for effective shielding of lungs and kidneys.
  30. 30. Comparison
  31. 31. Translational Couch Technique A translational couch technique (Fig.) is utilized in which patient rests on a couch in supine position and is transported horizontally through a vertical beam. This technique presents a special challenge regarding dosimetry due to the moving beam dose delivery .
  32. 32. Port films for TBI  Port films for TBI can be obtained by attaching a channel to the wall of treatment room ,so that a series of films could be mounted for obtaining 3 portal image as a single exposure.  Standard radiation therapy cassettes (lead screens) were used for the filming.
  33. 33. Port films are commonly used to check the positioning of a lung compensator ,and are essential for guaranteeing that adequate margin is achieved at all points around the patient’s body.
  34. 34. In Vivo Patient Dosimetry Treatment planning for TBI can stress the capabilities of any Treatment Planning System. This is because the sizes and depths of the fields used for TBI often exceed the limits employed in TPS.
  35. 35. Therefore Point measurements for verifying the dose prescription and distribution should be done. This is called In Vivo dosimetry. For these measurements, TLDs and diodes(eg.Si) are used.
  36. 36. Method: The TLD capsule or chips surrounded by suitable build up bolus, may be placed on the patient skin at different locations and measure the dose. TLD results are then compared with expected doses calculated by summing entrance and exit doses at the location of the TLDs.  An overall dose uniformity of (+/-)10% is acceptable.
  37. 37. Diode is taped in place over the umbilicus calculation point. Blocks are Suspended on bar in front of patient and knee gate is used to help patient Maintain posture.
  38. 38. Side effects of TBI: Most common side effects are; Head ache Nausea and Vomiting Fatigue Hair loss Bone marrow suppression(low blood counts ) etc. These will go away over time.
  39. 39. TBI can cause long term side effects, which occur months or years after transplant; Clouding of lungs and eye(cataracts) A small risk of developing a second cancer Underactive thyroid Inflammation of lungs etc.
  40. 40. Reference F.M Khan-Physics of radiation therapy Hand book-theory and practice ICRU Report 17 Wikipedia
  41. 41. THANK YOU……

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Total Body Irradiation (TBI) is given to prepare (condition) the patient’s body for bone marrow or stem cell transplant. It is a special radio therapeutic technique that delivers to a patient’s whole body, a uniform dose within (+/-)10% of the prescribed dose.

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