Lecture Series for Radiation Oncologist

1. Dr. Lokesh Viswanath M.D
Professor, Dept of Radiation Oncology
Kidwai Memorial Institute of Oncology
AROI KC July 2016 : Lecture no 4 (Rad Onc)

2.  The goal of radiotherapy is to deliver a prescribed dose
of radiation to the Target while sparing surrounding
healthy tissues to the largest extent possible

3. RT Planning for Breast Cancer
 As treatment techniques become more complex - - - >
Plan evaluation >> >>> cumbersome
 Interaction with the Radn Physcist at various steps
 There is loss of clinical feeling of the adequacy of
treatment plan - Virtual
Need for Plan Evaluation :
 to find optimal radiotherapy machine settings to
deliver desired dose distribution, these settings are
patient specific
 To assess the target coverage and normal tissue sparing

4. Plan Evaluation Process
 After contouring
 The Physics team works on the RT plan
 Rad Onc – Plan evaluation and supervision at various
steps

5. Iterative & interactive Process
 Initial beam arrangement
 Primarily based on clinical experience:
 CW : MT:LT
 CW + Ax&SC : MT:LT + AP
 BCRT : MT:LT
 BCRT+ Ax&CS : MT:LT + AP
 Post AB : MT:LT + AP + PA
 Use of BEV displays
 Beam orientation – feasibility
 MLC settings
 Block apertures : Cardia + electrons for under-dosed zones
 Review of dose distributions generated
 Multilevel 2D display (isodose lines superimposed on CT images)
 Color wash (superimposed)
 DVH
 Modification of beam arrangements based on above parameters
2F
3F
FIF
>5F (Tangential / every 300)
non Coplanar
Rotational (complete/limited)

7.  Rooms eye view – REV
 To Display dose cloud along the rendered PTVs & OAR
 Hot & cold spots
 Skin view -> beam aperture projection on the skin of virtual
patient. Suggest : autocontour bone – 3D skeletal View with
skin
 Plan approval
 Planned dose distribution – approve (Uniform dose delivery
to TV)
 +7% to – 5% of the prescribed dose with dose to critical
structure below tolerance level
 Constrains of absolute Max dose, Median dose & volumes
specified
 Evidence based Dose volume constrains : Target & OAR
(document reason for non compliance)

8. Dose reporting and dose prescription:
ICRU reference point
 Location
 Clinically relevant / unambiguous
 where it can be accurately determined
 In a region where there is no steep gradient
 Generally - Centre of PTV / intersection point
 Single spatial reporting : dose volume reporting
TV Point dose ( Grid assigned to single voxel)
Past Min Dose Max Dose
ICRU 83 Near Minimum Dose
(D98%)
Near maximum Dose (D2%) Median Dose
(D50%)
For serial
like organ /
structures
Maximum Dose > single
calculation point Dmax or D
0%
D2% to be
reported

9. Dose homogenity
 Dose coverage of PTV to be kept within specific limit +7%
& -5% of the prescribed dose
 If the degree of desired homogeneity cannot be achieved :
 Radiation Oncologist
 to decide weather the dose heterogenity is acceptable
 Part of PTV with high risk CTV /GTV– higher dose here might be
advantageous
 Slight under dose of PTV is acceptable – particularly if it is in close
proximity to OAR
 Check single Fraction coverage of PTV in absolute dose mode >
evaluate hot & cold zones> change dose per fraction if necessary
 Freedom to prescribe parameters in his or her own way or current
practice

10. IMRT plan evaluation
 Complex
 Unconventional
 Dose distribution > highly conformal
 Dose
 Dose volume parameters
 Min Dose
 Max Dose
 Min Dose to specified fractional volume
 Volume structure receiving a specified dose or higher
 D98% or D near Minimum – dose to at least 98% of PTV
 Corresponding D2% - dose received by the most heavily
irradiated 2% of PTV

11. DVH : Differential /cumulative
 Do not provide any spatial information
 DVH complements > spatial dose distribution tool
(isodose)

12. Designing beam
 Beam orientation > is it possible to setup – clinical
judgment , test for clearance between
gantry/patient/couch
 hard copy:: Evaluate for geometric accuracy of plan
output . (note - issues with CT simulation artifacts)
 Note
 grid size (effect on dose distribution)
 Bin size (effect on DVH)

13. QA - supervision
 Plan review> approve > sign &date
 Beam normalization – isocentre (shift to suitable
location in case of non tissue medium/under or near
MLC)
 MU to realize the dose prescription (independent
check/hand calculation/independent computer
calculation).
 IMRT additional check – review optimization
parameters, min gap size, min MU/seg, max dose in
/out of target
 Phantom measurements, Machine – point dose and
spatial distribution

14. Observe patient setup
 MLC setting
 Block fabrication / mounting
 Review portal images
 Wedge / compensator alignments
Verification Simulation
 EPID
 u/s Video surfacing
 Static KV imaging
 KV CBCT
 MV helical CBCTT
 MV CBCT

15. Issues with Respiratory motion
Respiratory Gating: Introducing
Systematic error in our favour

16. RT for Breast Cancer
 Challenges
 Large difference in tissue thickness in RT field : IMRT
 Close proximity to Lung / Apex & Heart
 Target motion during breathing
 RT field – skin boundary – tissue / air
 Significant inhomogenity
 Most planning system (inverse) cannot handle skin
flash appropriately

17. Setup uncertanities
 Breathing motion
 Breast tissue – mobile (portion of breast tissue may
move out of skin line)
 IMRT : Solution
 Expand PTV & optimize coverage of entire PTV
 Portion of PTV in air > add virtual tissue / manually open
certain imrt segments to take care of skin flash
 Interest in IMRT (FIF)
 Left Ca Br
 spare myocardium from high dose region
 improve PTV coverage

18. PROBLEMS OF RESPIRATION
MOTION DURING RADIOTHERAPY
 A. Image acquisition limitations
 B. Treatment planning limitations
 C. Radiation delivery limitations

20. RT delivery limitations
 Delivery in the presence of Intrafraction Organ
motion
 Results
 in deviation between intended dose and dose actually
delivered
 Averaging/smearing of RT dose over the path of motion
 Motion artifact > dose variation >20% single filed
 Care during Hypofractionated RT

21. Recognize the effect of Respiratory
motion on CT simulation for RT
planning
 Image artifacts : planning CT / CBCT
 Artifact
 significant & unpredictable
 Difficulty in Tumor visualization
 Uncorrected > lead to uncertainties in
 Target visualization
 Beam placement
 Compromise overall effectiveness of treatment
 Scan speed
 Slow – T – smeared
 Faster - T – position and shape captured in arbitary

22. Ways to compensate for motion: to
minimize its impact on treatment
integrity
 >> 4 D imaging
 > 4D target delineation
 Increasing planning margin
 Abdominal compression (forced shallow breathing)
 Respiratory gating
 Real time tumour tracking

23. Motion artifact
4D CT

24. Respiratory Gating
 2 main approaches
 Internal
 e.g. RTRT – implanted marker. (Precise, real-
time localization during RT) – fluroscopic
imaging
 External
 External respiratory surrogates
 Markers on abdominal/Thx surface
 Compression belt
 Spirometer signals

25.  The location of the infrared camera at the foot of the
couch for tracking the marker block in the RPM
system.
 4D Imaging : 4DCT

26. Respiration phase Tagged image
acquisition – multiple data sets

27. Methods used in the management
of respiration motion
 Respiratory gated techniques.
 Breath-hold techniques.
 Forced shallow breathing methods.
 Real-time tumor tracking methods.

29. O
N
O
F
F

30. RPM Light weight plas tic box with 2-6 passive infrared markers
 Patients abd wall xipisternum
 Monitor – charge coupled device video camera (Imaging & Treatment room)
 Surrogate signals of surface motion (amplitude / phase gated)
 RPM during CT simulation to acquire pt geometry in gating window and to setup
gating window
 Major strength:
 Non invasive
 Easy to use
 Well tolerated
 Technique
 Breath hold
 Deep inspiratory breath hold
 Patients ability for breath hold >15sec , repeatedly
 Breathing coaching: any monitoring technique can be used
 Surface marker
 Spirometer
 ABC device
 RPM
 Align RT

32. ABC

33. ABC

34. Patient A

35. Free Breathing

36. As the patient inspires: observe air entry anterior
to cardia . Separation of cardia and chest wall >
8mm. Also not the change in shape of the
mediastinum / cardia

37. Free breathig & DIBH: note the separation
achieved between the cardia and chest wall

38. Note the portion and
volume of chest wall
that would have got
irradiated during free
breathing

39. Note the portion of cardia
exposed in the tangential field
during conventional 3 D CRT
Plan in free breathing

40. Note the exclusion/sparing of
cardia in the tangential field
during conventional 3 D CRT -
Field in Field IMRT Plan in Deep
Inspiratory Breath Hold

41. Limited Tangential zone Rapid Arc with

42. FIF 3DCRT (Tangential Fields) v/s Rapid Arc

49. Results
Free Breathing DIBH
SD + SD +
Lt Lung
(V20)
25.91 cc 1.6 16.4 cc 1.9
Heart
Dose
Mean 8.1Gy 1.5 2.9 Gy 1.06
Maximum 50.6 Gy 1.6 31.44 Gy 13.3

50. Tumor tracking
 Most ideal
 Most technologically intense
 Real time tumour localization
 Dynamicallly / seamlessly integration :
 Fast processing & relay of info
 Corresponding repositioning of beam
 Motion freezing methods
 Real time 3D position information
 Marker less
 Marker guided
 Implantable transponders

51. Real time video guided IMRT
 Camera – capture full fram 3D surface image through
single snapshot
 Patient setup parameters determined
semiautomatically
 IMRT leaf segments are modified in real time
 System compensated for changes in surface topology
by changing treatment plan rather than adjusting
position

52. Thank you

53. Interactive Secession for Students

54. Technical issues
 Patient position
 Arm abducted
 >90 0 - Ax Ly – overlap humeral head
 < 90 0
 Large pendulous breast
 Supine
 Lateral
 Prone

55. MT : LT
 Separation:
 > 22cms > dose in-homogenity > less cosmetic result
 Use 10-18Mv (50%)
 Maintain in-homogenity between 93 % - 105%
 Use Degrader to modify buildup in beams
 Use simple IMRT (FIF) or DMLC
 Alignment of Tangential
 CW contour / slope :
 Pt positioned - Slope
 Collimator rotation
 Beam splitter
 MLC
 SC field : Tangent Superior edge remains true vertical

56. RT – CW+RN
 Technically challenging
 Field matching – difficulties
 Anatomic variations between patients
 Lack of clear evidence – superiority of any single
approach
Field matching
 SC & CW : just below clavicular head
 Single isocentre technique
 CW & IMN – match line (hot /cold)

57. CLD
CLD Ipsilateral lung
1.5 cms 6%
2.5 cms 16%
3.5cms 26%

58. Special attention to minimizing
volume of heart irradiated
 Cardiac sequelae : even small amount of heart in field
can affect cardiac function
 Solutions
 Field Placements
 Cardiac Block
 3DCRT / IMRT
 DIBH

59. Thank You