Radiation Therapy Techniques and Treatment Planning for Breast Cancer

1. Radiotherapy Breast Cancer
Medical Physicist / Mohamed Ali Morsy
ph_moh_ali@yahoo.com
(+20- 01001700467)

2. Breast cancer is the most common cancer, and the
second most common cause of cancer
related death in females

3. Anatomy of the breast

4. • A pectoralis major
muscle
• B axillary lymph
nodes: levels I
• C axillary lymph
nodes: levels II
• D axillary lymph
nodes: levels III
• E supraclavicular
lymph nodes
• F internal mammary
lymph nodes

5. Treatment Planning
OBJECTIVE :
• Deliver uniform dose distribution throughout target volume
• ensure adequate tumor coverage
• minimize doses to normal tissue

6. TECHNIQUE FOR RADIOTHERAPY
Positioning
Immobilization
Simulation
Target Volume
Treatment Planning
Dose & Fractionation
Set Up Verification
Sequelae Of Radiotherapy

7. Positioning & Immobilization
most crucial parts of RT treatment for
 accurate delivery of a prescribed radiation dose
sparing surrounding critical tissues
primary goal:
other benefits :
1) can reduce time for daily set up.
2) make patient feel more secure & less apprehensive.
3) help to stabilize relationship between external skin marks & internal structures
1) reproducibility of position
2) reduce positioning errors

8. TREATMENT POSITION
Supine
Prone
Older techniques
 Lateral
 erect
• Most important aspect of positioning - patient comfort & reproducibility.

9. Positioning devices
• Breast board
• Wing board

10. Breast Board
breast board is an inclined plane with
fixed angle positions
the ant. chest wall slopes downward
from mid chest to neck
brings the chest wall parallel to
treatment couch
the inclination is limited to a 10–15°
angle for 70 cm, and 17.5–20° for
larger 85 cm aperture ct scanners

11. • Several adjustable features to allow for the manipulation of
patients arms, wrists, head & shoulders.
• make chest wall surface horizontal,
• brings arms out of the way of lateral beams..
• Thermoplastic breast support can be added for
immobilization of large pendulous breast
• Constructed of carbon fiber which has lower attenuation
levels permitting maximum beam penetration.
Advantages of breast board

12. Wing board
 Simpler positioning device
 Can be used in narrow bore gantry
 Chest wall slope cannot be corrected
 Need other techniques for reducing dose to heart and field
matching

13. Other treatment positions
• Prone
• Requires patient to climb onto a
prone board, lie on the stomach &
rest the arms over the head.
• The i/l breast gravitates through a
hole in the breast board & c/l breast
is pushed away against an angled
platform to avoid the radiation
beams

14. Prone breast board
System includes:
Prone board
Face cushion
15 Degree Contralateral Wedge
Handles

15. advantages

16. A systematic review of methods to immobilise breast tissue during adjuvant breast irradiation
Sheffield Hallam University Research Archive

17. Simulation
• Where available, CT scanning has become standard for
planning breast radiotherapy
• Scar & drain sites identified with radiopaque markers.
• field borders are chosen & radiopaque wires are placed
• Radiopaque wires is also placed encircling breast tissue
• CT data are acquired superiorly from neck and inferiorly up to diaphragm
• Slice thickness should be sufficient (usually 5 mm) but dependent on agreed local
CT protocols
• Three reference tattoos are placed on the central slice and in right & left sides so
that measurements can be made to subsequent beam centres

18. Supine:
• Most patients are treated in the supine position, with the arm/s abducted and face turned
to the C/L side
• breast tilt boards with armrests used for positioning
• immobilization devices (e.g., Alpha cradle, plastic moulds) can be used
patient immobilized for breast irradiation on a slant board with custom mold

19. POSITION OF ARMS
• The preferred arm position is bilateral arms to be abducted 90 degrees or greater & externally
rotated
• Arm elevation required to facilitate tangential fields across the chest wall without irradiating the
arm.
• Advantages of raising both arms vs only the I/L arm
• Factors deciding the angle of arm elevation
i) Ability to elevate without discomfort.
ii) No/Minimal skin folds in the Supraclavicular region.
iii) Ability to move the patient through the CT aperture.
i. patient is more comfortable and relaxed
ii. position is more symmetrical and easily reproducible with lesser chances of rotation of the torso
iii. more precise matching of the previously irradiated field if c/l breast requires radiation in future

20. Position of head:
• rigid head holder or a neck rest can be used to
stabilize & position head
• also elevate the chin to minimize neck skin folds
within the SCF field

21. Treatment planning
• Conventional
• Three-Dimensional Conformal
• Intensity-Modulated Radiation
Therapy

22. 2D based planning

23. Conventional planning
• positioning & immobilization
• Technique
• field borders
• simulation: fluoroscopy or ct based
• Setting medial & lateral tangential beams
• beam modification
• field matching

24. POSITIONING
• Breast board
• Supine with anterior chest wall
parallel to couch
• Arms overhead and comfortable
• If 2 field: patient looks straight
• If 3- field technique: turn the
head to the opposite side to be
treated.

25. TECHNIQUE for WBRT
• Two tangential fields are used.
• Additional fields for SCF, IMC, & post. Axillary may be used

26. Field borders For tangential fields
• Upper border –
• when supra clavicular field used - 2nd ICS (angle of Louis)
When SCF not irradiated – head of clavicle
• Medial border – at or 1cm away from midline
• Lateral border – 2-3cm beyond all palpable breast tissue – mid
axillary line
• Lower border – 2cm below inframammary fold
• Borders can be modified in order to
• cover entire breast tissue,
• to include nodal volumes and scar marks DO NOT MISS THE TARGET VOLUME

28. Beam Modification Devices in breast
radiotherapy
 Wedges
 Compensators
 Bolus
WBRT uses tangential field technique; however, dose
distribution is complicated because of
 irregularities in the chest-wall contour
 varying thickness of the underlying lung tissue.
Therefore beam modification is required to improve dose
planning target volume (PTV) should be within the 95% and
107% isodose for homogenous dose distribution

29. Wedge Filters
• beam modifying device
• causes progressive decrease in intensity across the beam, resulting in
tilting the isodose curves from their normal positions.
• Degree of the tilt depends upon the slope of the wedge filter.
• Wedges Are Used As Compensators In Breast Radiotherapy.
• Dose uniformity within the breast tissue can be improved
• Preferred in the lateral tangential field than the medial
.

30. Higher dose to the
apex without
wedges
Wedges alter dose distribution only in the transverse direction
and not in the sagittal direction of the bitangential fields.

31. Alignment of the Tangential Beam with the Chest Wall Contour
• following can be used to make the posterior edge of tangential beam
follow chest contour
Rotating Collimators,
Breast Board:
Multileaf Collimation.

32. Sloping surface of chest wall • Due to the obliquity of the anterior chest wall,
the tangential fields require collimation so as to
reduce the amount of lung irradiated.
Rotating Collimators: collimator of the tangential beam may be rotated

33. The need for collimation can be eliminated if the
upper torso is elevated so as to make the chest wall
horizontal.
This is done by BREAST BOARD
However in a collimated field, junction matching
between the bitangential fields and the anterior SCF
field becomes problematic resulting in hot/cold
spots.

35. consists of two banks of tungsten leaves, situated
within the path of the treatment beam, which
individually move under computer control
Can be moved automatically independent of each
other to generate a field of any shape
multileaf collimator (MLC)

36. Selection of appropriate energy
X-ray energies of 4 to 6 MV are preferred
Photon energies >6 MV underdose superficial tissues beneath the skin surface
If tangential field separation is >22 cm :significant dose inhomogeneity in the breast
So higher-energy photons (10 to 18 MV) can be used to deliver a portion of the
breast radiation (approximately 50%) as determined with treatment planning to
maintain the inhomogeneity throughout the entire breast to between 93 and 105%.
IMRT techniques such as field-in-field or dynamic multileaf collimators (MLCs)
may be utilized to reduce dose inhomogeneity

37. Dose of radiation
Perez & Brady's Principles and Practice of Radiation Oncology, chapter 56, p1089
Whole breast radiotherapy/chest wall irradiation
• Conventional Dose
• 50 Gy in 25 daily fractions given in 5 weeks
• Hypofractionated dose schedule
• 40 Gy in 15 daily fractions of 2.67 Gy given in 3 weeks.
• 42.5 Gy in 16 daily frac ons of 2.66 Gy given in 31⁄2 weeks.
Breast boost irradiation to Tumour bed
• 16 Gy in 8 daily fractions given in 1.5 weeks.
• 10 Gy in 5 daily fractions given in 1 week
Lymph node irradiation
• 50 Gy in 25 daily fractions given in 5 weeks
• 40 Gy in 15 daily fractions of 2.67 Gy given in 3 weeks.

38. Doses To Heart & Lung By Tangential Fields
• The amount of lung included in the irradiated volume is greatly
influenced by the portals used.
• Various parameters are used to determine he amount of lung & heart in
tangential field

39. • CLD: perpendicular distance from the posterior tangential field edge to the posterior part of
the anterior chest wall at the center of the field
• MLD: maximum perpendicular distance from the posterior tangential field edge to the
posterior part of the anterior chest wall
Central lung distance marked on the digitally reconstructed radiograph (a) and on
the central axial slice (b)

40. Central lung distance
• Best predictor of %age of ipsilateral lung vol.
treated by tangential fields
CLD (cm) % of lung
irradiated
1.5 cm 6%
2.5 cm 16%
3.5 cm 26%
Usually up to 2 to 3 cm of underlying lung
may be included in the tangential portals
Radiation pneumonitis risk <2% with CLD<3 cm.
Risk upto 10% with CLD 4-4.5 cm.

41. To prevent excess volume of lung irradiated, the divergence of the deep
margins is matched.
2 ways
- angle the central axes slightly more than 180⁰
- half beam block technique.
In very large breasts, bitangentials are unable to cover the target volume
without significantly increasing the volume of OARs irradiated.
MATCHING DIVERGENCE OF PHOTON BEAM

42. angle the central axes slightly more than 180⁰

43. half beam block technique.
By moving one of the independent jaws to midline, a half
beam block can be created.
This forms a non-divergent field edge centrally.
The half beam block functions is easier to set up (less
movements of the couch/gantry)

44. Dose to heart can be minimized by
Median tangential breast port
Cardiac block & electron field
breath hold
gating
When the CLD is >3 cm, in treatment of
the left breast, a significant volume of
heart will also be irradiated
MAXIMUM HEART DISTANCE: maximum perpendicular distance from the
posterior tangential field edge to the heart border

45. Three-Dimensional Conformal Radiation Therapy
• Standard opposed tangential fields with appropriate use of wedges to
optimize dose homogeneity remains the most commonly employed
method for delivery of whole-breast irradiation
• 3DCRT may improve dose to target volume & reduction in dose to
normal tissues & critical organs
• Better cosmetic results
• Less dose to heart and lung

46. 3-Dimensional planning
• Simulation
• Plain CT scan of 5mm
slice thickness is taken
from the neck to just
below diaphragm.
• Contouring
• Field set up

47. Field arrangement:
Two tangential fields for breast
Add some wedges
– Usually 15° for breast tangential fields

48. Tangential fields : Why ???
Gantry angles –minimize irradiated lung volume
Field arrangement:

49. IMRT Breast:
• Dosimetric advantages:
(1) better dose homogeneity for whole breast RT
(2) better coverage of tumor cavity
(3) feasibility of SIB
(4) Decrease dose to the critical organs
(5) Left sided tumors- decrease heart dose
Disadvantages:
- May increase the volume of tissue exposed to lower doses of radiation.
- May increase the risk of second malignancies

50. • Reduces the hotspots specially in
the superior and inframammary
portions of the breast.
Increases homogenity
Manifests clinically into decrease
in moist desqumation in these
areas.

52. INVERSE PLANNING
Inverse planning is a technique using a computer program to
automatically achieve a treatment plan which has an optimal merit.
target doses & OAR constraints are set
Then, an optimisation program is run to find the treatment plan which
best matches all the input criteria.
IMRT PLANNING: forward vs inverse

53. Forward planning IMRT: Field within Field
• Advancement to conventional 3DCRT
• In this technique a pair of conventional open tangential fields is produced first
• MLCs are used to shape the fields & spare OARs
• Wedge angle & relative weight of beams optimized to produce plan
• To ovoid hotspots and large doses to OAR & to obtain a homogenous dose
distribution (range 95-107%) the dose delivered with open fields is reduced to 90-
93% of total dose
• new tangential beam with same gantry & wedge angles are designed for remaining
dose
• The new reduced field are shaped to exclude areas receiving more than 105% of
dose.
• The other approach is to delineate regions of non uniform dose by contouring
isodose lines

54. Forward planned IMRT (field-in-field) is preferred
• Breast dosimetry can be significantly improved
• Better cosmetic outcomes
• simple method
• Less MU
• Less scatter
• Decreased planning time
• Decreased treatment time

55. Forward plan IMRT

58. The FIF plan improved dose homogeneity,
conformity and uniformity within the whole
breast tissue in comparison with the TWB plan.
The FIF plan also reduced the lung or heart
volume receiving radiation doses that can in
duce radiation-related late toxicities. The FIF
plan is a simple and clinically useful technique
for whole breast irradiation.