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.

1. Total Body Irradiation
By
Aparna P
M.Sc.Radiation Physics
University of Calicut

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. 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. Which is used in the treatment of
diseases such as;
* Leukemia
* Aplastic anemia
* Lymphoma
* Multiple myeloma etc….

6. 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.

7. 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).

8. 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.

9. 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.

10. 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;

11. 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.

12. 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.

13. The thicker the patient, the higher is the
beam energy required to produce acceptable
dose uniformity for parallel-opposed fields.

14. 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.

15. For patients of thickness greater than 35
cm, energies higher than 6 MV should be
used to minimize the tissue lateral effect.

16. 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).

17. 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.

18. 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.

19. 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

20. Patient Positioning methods
1 : AP/PA
2 : Bilateral
3 : Translational couch

21. 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.

22. 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.

23. This technique requires an SSD in excess
of 3m to encompass the patient within
the large beams.
Distances from source to patient

24. 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.

25. Bilateral
technique
This technique involves left and right lateral
opposing fields with the patient treated in a
semi seated position (fig.).

26. 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.

27. The patient set-up is recorded in terms of
distances measured b/n external body land
mark as shown in fig.

28. 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.

30. 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.

31. Disadvantage:
This technique suffers from poor
dose uniformity and does not allow
for effective shielding of lungs and
kidneys.

32. Comparison

33. 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 .

34. 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.

35. 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.

36. 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.

37. 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.

38. 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.

39. 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.

40. 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.

41. 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.

42. Reference
F.M Khan-Physics of radiation therapy
Hand book-theory and practice
ICRU Report 17
Wikipedia

43. THANK YOU……