The document discusses intensity modulated radiation therapy (IMRT) and its advantages over conventional radiotherapy. It describes how IMRT uses non-uniform beam intensities to optimize dose distribution and improve tumor targeting while sparing nearby healthy tissues. Treatment planning for IMRT involves determining optimal fluence profiles for multiple beams and inverse planning. Key benefits of IMRT include better tissue sparing to reduce side effects and potentially higher doses to more effectively treat tumors.

2. Conventional to Conformal
2D Conventional Radiotherapy
3D Conformal Radiotherapy
Intensity Modulation
IMRT – Definition and Principle
Conventional Radiotherapy vs. IMRT
Benefits to the Patient
Clinical Implementation of IMRT
IMRT – Treatment Planning
Different IMRT Techniques
IMRT with Multileaf Collimator
IMRT Quality Assurance Program
Draw Backs of IMRT
Risk of IMRT

3. Conventional Radiotherapy

4. Conformal Radiotherapy

5. Intensity Modulated Radiotherapy (IMRT)

6. Conventional Radiotherapy
Conventional to Conformal

7. Conventional to Conformal Conformal Radiotherapy without Intensity Modulation (CRT)

8. Conventional to Conformal
Conformal Radiotherapy with Intensity Modulation (IMRT)

9. It is based on standardized treatment techniques applied to classes of patients thought to be similar
X-ray simulator and 2D computer treatment planning system are used
This process is limited to generating dose distributions in a single, or a few planes of the patient’s target volume
2D Conventional Radiotherapy

10. It is based on standardized treatment techniques applied to classes of patients thought to be similar
X-ray simulator and 2D computer treatment planning system are used
This process is limited to generating dose distributions in a single, or a few planes of the patient’s target volume Testing the Modulex 2D Radiation Treatment Planning System, circa 1980
2D Conventional Radiotherapy

11. 2D Conventional Radiotherapy It is based on standardized treatment techniques applied to classes of patients thought to be similar X-ray simulator and 2D computer treatment planning system are used This process is limited to generating dose distributions in a single, or a few planes of the patient’s target volume
Testing the Modulex 2D Radiation Treatment Planning System, circa 1980

12. 2D Conventional Radiotherapy
2D transmission images of human body provided unprecedented imagery of bony landmarks, allowing radiologists to deduce the location of internal organs
Additional blocks placed daily to match marks on the patient’s skin
Using planar radiographs, radiologists planned cancer treatments by collimating rectangular fields encompassing the presumed tumor location

13. 2D Conventional Radiotherapy
2D transmission images of human body provided unprecedented imagery of bony landmarks, allowing radiologists to deduce the location of internal organs
Additional blocks placed daily to match marks on the patient’s skin
Using planar radiographs, radiologists planned cancer treatments by collimating rectangular fields encompassing the presumed tumor location

14. 2D Conventional Radiotherapy
2D transmission images of human body provided unprecedented imagery of bony landmarks, allowing radiologists to deduce the location of internal organs
Additional blocks placed daily to match marks on the patient’s skin
Using planar radiographs, radiologists planned cancer treatments by collimating rectangular fields encompassing the presumed tumor location

15. 3D Conformal Radiotherapy
It allows to increase the doses of radiation delivered to the tumor without increasing damage to nearby tissues.
Before treatment is begun, digital images of the individual’s target are prepared and compiled into virtual 3D models of how the target will “look” to the accelerator from all angles.
Then the accelerator shapes the beam to match those “beam’s eye views” (insets), thus reducing the amount of radiation hitting the organs at risk or other unintended targets.

16. 3D Conformal Radiotherapy
It allows to increase the doses of radiation delivered to the tumor without increasing damage to nearby tissues.
Before treatment is begun, digital images of the individual’s target are prepared and compiled into virtual 3D models of how the target will “look” to the accelerator from all angles.
Then the accelerator shapes the beam to match those “beam’s eye views” (insets), thus reducing the amount of radiation hitting the organs at risk or other unintended targets.

17. 3D Conformal Radiotherapy
It allows to increase the doses of radiation delivered to the tumor without increasing damage to nearby tissues.
Before treatment is begun, digital images of the individual’s target are prepared and compiled into virtual 3D models of how the target will “look” to the accelerator from all angles.
Then the accelerator shapes the beam to match those “beam’s eye views” (insets), thus reducing the amount of radiation hitting the organs at risk or other unintended targets.

18. 3D CRT : Treatment Planning Process
Imaging Data Aquisition
To accurately delineate target volume and normal structures
CT is the most commonly used procedure, even other modalities offer special advantages in imaging certain types of tumors and locations
CT
MRI
PET
SPECT

19. 3D CRT : Treatment Planning Process
Image Registration
It is a process of correlating different image data sets to identify corresponding structures or regions Image fusion is the seamless mixing up of two image sets of the same patient; it may be
-Two different image modalities
-Same modality in which image sets are taken at different point of time

20. 3D CRT : Treatment Planning Process
It refers to slice-by-slice delineation of anatomic regions of interest
The segmented regions can be rendered in different and can be viewed in beam’s eye view (BEV) configuration or in other planes using digital reconstructed radiographs

21. 3D CRT : Treatment Planning Process
Designing beam aperture is aided by the BEV capability of the 3D treatment planning system

22. 3D CRT : Treatment Planning Process
Combination of multileaf collimators and independent jaws provides almost unlimited capability of designing multiple fields of any shape
Targets and critical structures can be viewed in the BEV configuration individually for each field

23. 3D CRT : Treatment Planning Process
An optimal plan should deliver tumoricidal dose to the entire tumor and spare all the normal tissues.
Isodose Curves and Surfaces
Dose distributions of competing plans are evaluated by viewing isodose curves in individual slices, orthogonal planes or 3D isodose surfaces

24. 3D CRT : Treatment Planning Process
Dose Volume Histograms (DVHs)
Display of dose distribution in the form of isodose curves or surfaces is useful because their anatomic location and extent.
This information is supplemented by dose volume histograms (DVHs).
DVH summarizes the entire dose distribution into a single curve for each anatomic structure of interest.

25. 3D CRT : Treatment Planning Process
Electronic Portal Imaging (EPI)
Patient position at the time of treatment should be verifiable via electronic portal imaging (EPI)
Tools should exist to quantify discrepancies between treatment position and planned position and to evaluate consequences and make corrections

26. 3D CRT

27. Intensity Modulation
•Conventional radiotherapy treatments are delivered with radiation beams that are of uniform intensity across the field (within the flatness specification limits)
•Wedges or compensators are used to modify the intensity profile to offset contour in irregularities and produce more uniform composite dose distributions such as in techniques using wedges
•This process of changing beam intensity profile to meet the goals of a composite plan is called intensity modulation

28. Intensity Modulation
•Conventional radiotherapy treatments are delivered with radiation beams that are of uniform intensity across the field (within the flatness specification limits)
•Wedges or compensators are used to modify the intensity profile to offset contour in irregularities and produce more uniform composite dose distributions such as in techniques using wedges
•This process of changing beam intensity profile to meet the goals of a composite plan is called intensity modulation

29. Intensity Modulation
•Conventional radiotherapy treatments are delivered with radiation beams that are of uniform intensity across the field (within the flatness specification limits)
•Wedges or compensators are used to modify the intensity profile to offset contour in irregularities and produce more uniform composite dose distributions such as in techniques using wedges
•This process of changing beam intensity profile to meet the goals of a composite plan is called

30. IMRT refers to a radiation therapy technique in which nonuniform fluence is delivered to the patient from any given position of the treatment beam to optimize the composite dose distribution
Definition and Principle of IMRT

31. The fluence files thus generated are electronically transmitted to the linear accelerator, which is computer controlled, to deliver intensity modulated beams (IMBs) as calculated
IMRT refers to a radiation therapy technique in which nonuniform fluence is delivered to the patient from any given position of the treatment beam to optimize the composite dose distribution
The optimal fluence profiles for a given set of beam directions are determined through
Definition and Principle of IMRT

32. Definition and Principle of IMRT
The fluence files thus generated are electronically transmitted to the linear accelerator, which is computer controlled, to deliver intensity modulated beams (IMBs) as calculated
IMRT refers to a radiation therapy technique in which nonuniform fluence is delivered to the patient from any given position of the treatment beam to optimize the composite dose distribution
The optimal fluence profiles for a given set of beam directions are determined through inverse planning

33. IMRT is especially useful when
the target volume has a concavity in its surface
and/or
closely juxtaposes OARs
Definition and Principle of IMRT
IMRT is an approach to conformal therapy that not only conforms (high) dose to the target volume
but also
conforms (low) dose to sensitive structures

34. IMRT is especially useful when
the target volume has a concavity in its surface
and/or
closely juxtaposes OARs
Definition and Principle of IMRT
IMRT is an approach to conformal therapy that not only conforms (high) dose to the target volume
but also
conforms (low) dose to sensitive structures

35. Definition and Principle of IMRT
A breast cancer, metastatic to T7, previously treated with a full course of spinal radiation. The patient continued with severe pain in the thoracic spine and was referred for palliative radiation. She was to receive 18 Gy in nine fractions to the target volume shown on the above. The delivered dose distribution is shown to the below. Note the achievement of a concave high-dose volume and protection of the spinal cord. (From Carol 1997a.)

36. Conventional Radiotherapy vs. IMRT
Conventional Radiotherapy
“Blocks” are used to shape the beam to the target and to avoid dose from areas outside the target
FIELD 1
Normal Tissue
Tumor

37. Conventional Radiotherapy
Conventional Radiotherapy vs. IMRT

38. Conventional Radiotherapy
FIELD 2
Conventional Radiotherapy vs. IMRT

39. Conventional Radiotherapy
Conventional Radiotherapy vs. IMRT

40. Conventional Radiotherapy
FIELD 3
Conventional Radiotherapy vs. IMRT

41. Conventional Radiotherapy
Conventional Radiotherapy vs. IMRT

42. IMRT
Intensity of radiation is varied across the beam depending on the shape of the target and the presence of sensitive structures within its envelope
FIELD 1
Conventional Radiotherapy vs. IMRT
Normal Tissue
Tumor

43. IMRT
Conventional Radiotherapy vs. IMRT

44. IMRT
FIELD 2
Conventional Radiotherapy vs. IMRT

45. IMRT
Conventional Radiotherapy vs. IMRT

46. IMRT
FIELD 3
Conventional Radiotherapy vs. IMRT

47. IMRT
Conventional Radiotherapy vs. IMRT

48. Tumor and Normal tissues are irradiated with UNIFORM DOSE..!
Conventional Radiotherapy
IMRT
Tumor and Normal tissues are irradiated with MODULATED INTENSITY BEAMS..!
TARGET
Conventional Radiotherapy vs. IMRT

49. Benefits to the Patient
Better normal tissue sparing – Less toxicity
Possibly higher dose to the target – Higher chance of cure
More dose in a fraction – Fewer fractions

50. Clinical implementation of IMRT requires two systems, they are :
1.A treatment planning computer system that can calculate nonuniform fluence maps for multiple beams directed from different directions to maximize dose to the target volume while minimizing dose to the critical normal structures
2.A system of delivering the nonuniform fluence as planned
Clinical Implementation of IMRT

51. IMRT Treatment Planning Divides each beam into a large number of beamlets Determines optimum setting of their fluences or weights The optimization process involves inverse planning in which beamlet weights or intensities are adjusted to satisfy predefined dose distribution criteria for the composite plan

52. IMRT Treatment Planning Once the tumor and OAR are contoured, the treatment planner must take a decision on the number, energy and direction of treatment beams

53. It is common practice to select a fixed set of five, seven or nine equally spaced non opposing coplanar beams
IMRT Treatment Planning
A large number of beams (e.g. nine vs. five) may produce a more conformal plan

54. For deep seated targets, the dose to both PTV and OAR does not depend significantly on the number of beams and energy. Instead, the main difference occurs in regions far from the PTV.
In these regions, the dose is significantly increased for both a smaller number of beams and for lower energy.
Nine beams or more, the energy dependence far from the PTV was negligible
∴ for a five field plan, one may want to consider using higher energy beams (15 MV), but if one prefers to use nine fields, then a 6 MV beam could be used with the same result.
IMRT Treatment Planning

55. For deep seated targets, the dose to both PTV and OAR does not depend significantly on the number of beams and energy. Instead, the main difference occurs in regions far from the PTV.
In these regions, the dose is significantly increased for both a smaller number of beams and for lower energy.
Nine beams or more, the energy dependence far from the PTV was negligible
∴ for a five field plan, one may want to consider using higher energy beams (15 MV), but if one prefers to use nine fields, then a 6 MV beam could be used with the same result.
IMRT Treatment Planning

56. For deep seated targets, the dose to both PTV and OAR does not depend significantly on the number of beams and energy. Instead, the main difference occurs in regions far from the PTV. In these regions, the dose is significantly increased for both a smaller number of beams and for lower energy. Nine beams or more, the energy dependence far from the PTV was negligible ∴ for a five field plan, one may want to consider using higher energy beams (15 MV), but if one prefers to use nine fields, then a 6 MV beam could be used with the same result.
IMRT Treatment Planning

57. For deep seated targets, the dose to both PTV and OAR does not depend significantly on the number of beams and energy. Instead, the main difference occurs in regions far from the PTV.
In these regions, the dose is significantly increased for both a smaller number of beams and for lower energy.
Nine beams or more, the energy dependence far from the PTV was negligible
∴ for a five field plan, one may want to consider using higher energy beams (15 MV), but if one prefers to use nine fields, then a 6 MV beam could be used with the same result.
IMRT Treatment Planning

58. The dose gradient away from the PTV for a nine field IMRT plan is less steep than is achieved with a well-designed static field (conventional) plan
If a high gradient is required at a certain critical interface, then careful selection of beam angles is important
In a typical plan, the use of noncoplanar beam orientations resulted in a 15 – 25 % decrease in dose to the hottest portion of the rectum compared with coplanar beam orientations
A seven field noncoplanar IMRT technique produced increased bladder sparing compared with standard field arrangements
IMRT Treatment Planning

59. The dose gradient away from the PTV for a nine field IMRT plan is less steep than is achieved with a well-designed static field (conventional) plan
If a high gradient is required at a certain critical interface, then careful selection of beam angles is important
In a typical plan, the use of noncoplanar beam orientations resulted in a 15 – 25 % decrease in dose to the hottest portion of the rectum compared with coplanar beam orientations
A seven field noncoplanar IMRT technique produced increased bladder sparing compared with standard field arrangements
IMRT Treatment Planning

60. The dose gradient away from the PTV for a nine field IMRT plan is less steep than is achieved with a well-designed static field (conventional) plan If a high gradient is required at a certain critical interface, then careful selection of beam angles is important In a typical plan, the use of noncoplanar beam orientations resulted in a 15 – 25 % decrease in dose to the hottest portion of the rectum compared with coplanar beam orientations A seven field noncoplanar IMRT technique produced increased bladder sparing compared with standard field arrangements
IMRT Treatment Planning

61. The dose gradient away from the PTV for a nine field IMRT plan is less steep than is achieved with a well-designed static field (conventional) plan
If a high gradient is required at a certain critical interface, then careful selection of beam angles is important
In a typical plan, the use of noncoplanar beam orientations resulted in a 15 – 25 % decrease in dose to the hottest portion of the rectum compared with coplanar beam orientations
A seven field noncoplanar IMRT technique produced increased bladder sparing compared with standard field arrangements
IMRT Treatment Planning

62. Different IMRT Techniques

63. Different IMRT Techniques

64. IMRT with Multileaf Collimator Material of Multileaf Collimator : Tungsten alloy
•Highest density
•Hard
•Simple to fashion
•Reasonably inexpensive
•Low coefficient of thermal expansion

65. IMRT with Multileaf Collimator It is a technique to construct IMBs using a sequence of static MLC shaped fields in which the shape changes between the delivery of quanta of fluence
Multiple Static Field (MSF) Technique or
Static Multileaf Colliator (SMLC) Technique or
Step & Shoot Technique

66. IMRT with Multileaf Collimator
Dynamic Multileaf Collimator (DMLC) Technique
The leaves may define changing shapes with the radiation ON

67. IMRT Quality Assurance Program
Frequency
Procedure
Tolerance
Before first treatment
Individual field verification, plan verification
3% (point dose), other per clinical significance
Daily
Dose to a test point in each IMRT field
3%
Weekly
Static field vs Sliding window field dose distribution as a function of gantry and collimator angles
3% in dose delivery

68. IMRT Quality Assurance Program
Frequency
Procedure
Tolerance
Annualy
All commissioning procedures :
Stability of leaf speed,
Leaf acceleration and deceleration,
MLC transmission,
Leaf Position accuracy,
Static field vs Sliding window field dose distribution as a function of gantry and collimator angles,
Standard plan verification
3% in dose delivery, other per clinical significance

69. Draw Backs of IMRT
•More complexity
•Need for new (and more accurate) equipment
•More need for QA
•Longer treatment times
•Higher risk of geographical miss

70. Risk of IMRT
There is an increased risk secondary malignancies in patients treated with beam energies of >10 MV owing to a higher neutron dose. However, the degree of neutron production depends on the specific IMRT plan parameters, including the number segments and monitor units (MUs).
Moreover, the importance of considering secondary malignancies from IMRT treatments for any energy beam has been raised, especially for pediatric cases. These aspects require further investigation and scrutiny.

71. References
1.Steve Webb : “Intensity- Modulated Radiation Therapy” (2001)
2.Arno J. Mundt. MD, John C. Roeske. PhD: “Intensity Modulated Radiation Therapy – A Clinical Perspective” (2005)
3.Faiz M. Khan : “Treatment Planning in Radiation Oncology” (2nd Ed)
4.Faiz M. Khan : “Physics of Radiation Therapy” (4th Ed)