BRACHYTHERAPY

1. BRACHYTHERAPY: PHYSICAL AND
CLINICAL ASPECTS
Seema Sharma
Medical physicist

2. BRACHYTHERAPY: PHYSICAL AND CLINICAL ASPECTS

17. Intracavitary brachytherapy
• Three systems:
• Paris system
• Stockholm system
• Manchester system

18. Historical systemsHistorical systems
PriorPrior toto availabilityavailability
ofof computerizedcomputerized
dosedose calculation,calculation, thethe
dosedose waswas prescribedprescribed
accordingaccording toto
systemssystems whichwhich werewere
linkedlinked toto particularparticular
applicatorapplicator designdesign
e.g.e.g. Paris systemParis system

19. Paris Technique
• It makes use of small quantities of Radium
applied for fairly long period of about 5 days.
• The total application amounting to about
8000mg hrs.
• A part of Radium is applied in uterine canal &
the rest is divided in to two halves & placed in
two colpostats.

20. Stockholm Technique
• Originally devised by Forsell & Heyman.
• The technique is based on repeated treatments
with fairly large amount of Radium for a
relatively shorter time.
• These applicators are permanently loaded with 53
to 88 mg of Radium & are so designed that the
dose rate at 2cm from the centre of applicator is
about 75R/hr.

21. Stockholm Technique
• The vaginal applicators most of which are
permanently loaded, vary in shape & size &
contain 60 – 80 mg Ra.
• The time of treatment generally was about
27hrs, at each of two sittings , 3 weeks apart.
• Multiple small sources, called Heyman
capsules.

22. STOCKHOLM SYSTEM PARIS SYSTEM

23. Stockholm & Paris Technique
• In Stockholm Technique & Paris Technique,
the treatment was specified in terms of mg hrs
of Radium .
• When the intracavitary therapy is combined
with external beam therapy, this form of dose
specification is not adequate to describe the
overall treatment.

24. Manchester System
• Paris system was modified by Manchester group,
known as Manchester system.
• The Manchester group analysed Paris system
from a physical point of view so that the dose at
points in pelvis could be expressed in Roentgens.
• The main feature of Manchester System is the
selection of reference point in pelvic cavity for
dose specifications.

25. Manchester System (criteria for
selection of reference point)
• Anatomically comparable from patient to
patient.
• Not highly sensitive to small & clinically
insignificant alterations in applicator position.
• Allows for correlation of dosage & clinical
effects.

26. Manchester system
• Point A definitions:
• corresponds to the paracervical
triangle in the medial edge of the
broad ligament where the uterine
vessels cross the ureter.

27. Point A and Isodose Shape
• Point A was first introduced in
the Manchester dosimetric
system
• The isodose line is pear shaped
(dotted line)

28. Original definition of point A
• Original definition: draw a line connecting the superior aspects
of the vaginal ovoids and measuring 2 cm superior along the
tandem and then 2 cm perpendicular to this. (weakness: failure
of localization radiographs to show the surface of the ovoids'
caps)

29. Revised definition of point A
• Revised definition #1: 2 cm above the external
cervical os and 2 cm lateral to midline
• Revised definition #2 (1953, Tod & Meredith):
2 cm above the distal end of the lowest source
in the tandem and 2 cm lateral to the tandem
• Common variation: use flange at cervical os

30. Point B
• Point B - 5 cm lateral from the midline at the
same level as Point A
• This point was near the obturator lymph node
& gave an indication of lateral throw-off dose.

31. Manchester Applicator
• The Manchester applicators consisted of a
rubber tandem and two ellipsoid "ovoids" with
diameters 2, 2.5, and 3 cm.
• No shielding in ovoids, so needed generous
packing anteriorly and posteriorly.

32. Manchester Applicator
• Tandem of variable length and angles
• Ovoids of different sizes and shapes

33. ICRT APPLICATOR SET
LDR HDR

34. VariablesVariables StockholmStockholm ParisParis ManchesterManchester
Year ofYear of ForsellForsell 19141914 Regaud1926Regaud1926 Todd 1938Todd 1938
ApplicatorApplicator Tandem + VaginalTandem + Vaginal
boxbox
Tandem + ovoidsTandem + ovoids
(cork & spring)(cork & spring)
Tandem + ovoidsTandem + ovoids
(spacer, washer.(spacer, washer.
loose system)loose system)
Rad.nucliRad.nucli RadiumRadium RadiumRadium RadiumRadium
AmountAmount
(Ra(Ra eqeq))
TT--5353--8888
VV--6060--8080
TT--3030--4545
OO--2020--4545
TT--2020--3535
OO--3030--5050
Number ofNumber of
insertioninsertion
22--3, 3 wks apart3, 3 wks apart singlesingle 11--2, wk apart2, wk apart
DurationDuration 2727--30 hrs30 hrs 66--8 days8 days 72 hrs72 hrs
Pt A and BPt A and B NilNil NilNil YesYes
Tot doseTot dose 8000 R8000 R 7000 R7000 R 8000 R8000 R
Dose rateDose rate HDRHDR LDRLDR LDRLDR
LoadingLoading PreloadedPreloaded PreloadedPreloaded PreloadedPreloaded
INTRACAVITARY SYSTEMS - COMPARISON

35. Brachytherapy Recommendations in
Cancer of the Cervix
• ICRU 38
• ABS
• Gyn GEC ESTRO

36. ICRU 38 Treatment Reporting
• Description of the technique used
• Total reference air kerma (cGy @ 1m)
• Reference volume
– Usually at Isodose with Dtotal of 60Gy, must specify
otherwise
• Dtotal = DEBRT + DBT
– Shape (pear) and dimensions
• Absorbed dose at reference point
– Bladder
– Rectum
– Lymphatic trapezoid
– Pelvic wall reference point

37. • The rectal dose should be 80% or less of the
Point A dose
• Prescribed 8 Gy to point A in two applications
after external RT.
• Vaginal contribution to Point A was limited to
40% of the total dose
Treatment specificationsTreatment specifications

38. Weakness of point A
• Wide variation in Point A with respect to the
ovoids.
• Point A often occurs in a high-gradient region
of the isodose distribution. Therefore, minor
differences in position can result in large
differences in dose.

39. Consequences of tilt in uterine tube
• Point A is a geometric point .
• The uterus does not always conform to the
geometry assumed in the calculation & may
be pushed or pulled by disease so that no
longer lies in midline of the body.
• Then dose to L & R point A will not be equal,
but computer controlled dwell positions &
dwell time can correct this non uniformity.

40. ICRU 38: Bladder and Rectal
Dose Points
• Bladder point is located at the center of the posterior surface of the
bladder Foley balloon
• Rectal point is located directly posterior to the lower end of the
intrauterine source, 0.5cm behind the posterior vaginal wall

41. ICRU 38: Reference Volume
• Reference volume covered by 60 Gy isodose surface
• Critical dimensions: Height (dh), width (dw) and thickness
(dt)

42. ICRU 38: Guidance on combination ofICRU 38: Guidance on combination of
brachytherapy and external beambrachytherapy and external beam
dosesdoses
Often brachytherapyOften brachytherapy
is just given as ais just given as a
boost to externalboost to external
beam radiotherapybeam radiotherapy
If both are plannedIf both are planned
from CT scans thefrom CT scans the
dose can also bedose can also be
overlaid in manyoverlaid in many
treatment planningtreatment planning
systemssystems

43. Draw a line connecting the mid dwell position of the ovoids. From
the intersection of this line with the tandem move superiorly along
the tandem 2 cm plus the radius of the ovoids and then 2 cm
perpendicular to the tandem in the lateral direction
POINT H
AmericanAmerican
Brachytherapy SocietyBrachytherapy Society
(ABS)(ABS)

44. ABS bladder & rectum point
• ABS recommendation for bladder & rectum
point is same as in ICRU 38.

45. BT Planning for Cervix
• Source localization
– 2 radiographs (orthogonal)
• Computer dose calculation
• Dose
– Point A
– ICRU 38
• Optimization
– Dose points
– Dose volume - shape

46. SIMULATION
Markers
Markers Orthogonal radiographs

47. PLANNING
Plato TPS
ICRT isodose curves

48. OVOID ISODOSE CURVES

49. Microselectron HDR
Selectron LDR
Microselectron PDR

50. BRACHYTHERAPY DOSE RATES
LDRLDR-- 0.40.4--2 Gy/hr2 Gy/hr
MDRMDR-- 22--12 Gy/hr12 Gy/hr
HDRHDR-- > 12Gy/hr> 12Gy/hr

51. PreloadingPreloading
AfterAfter--loadingloading
--Manual afterloadingManual afterloading
--Remote afterloadingRemote afterloading
BRACHYTHERAPY LOADING

52. Computer planning
Dose distributions
AP and lateral radiograph

53. Volumes – GYN GEC ESTRO
• HR CTV
– Macroscopic + residual macroscopic tumor,
includes
• Whole cervix
• Extracervical tumor extension
– Dose as high as possible, aim to eradicate
• IR CTV
– Initial macroscopic extent of tumor + margins
(case by case, limited by OAR)
– Dose to cure microscopic disease (>60Gy)

54. GYN GEC ESTRO – 3D Planning
• Source localization
– MRI (preferred over CT)
• Volume delineation
– GTV, HR CTV, IR CTV
– Organ at Risk – bladder, rectum, sigmoid, vagina
• Computer dose calculation
• Dose
– Point A
– ICRU 38 – only bladder and rectum
– D100, D90 for GTV, HR CTV, IR CTV
– D0.1cc, D1cc, D2cc for OARs if volumes are delineated
– D5cc, D10cc for OAR if walls are contoured
• Optimization
– Dose points
– Dose volume
• Shape
• DVH

55. Volumes – GYN GEC ESTRO
• GTV, HR CTV and IR CTV delineation for responsive disease,
after EBT and chemotherapy
(IR CTV = HR CTV + 10mm margin)

56. Volumes – GYN GEC ESTRO
• GTV changes during the course of EBT and BT,
delineate GTV and CTVs everytime

58. Applicator placement
• Applicator position is also important if the PTV
is going to be covered
• Therefore the use of US to guide the
applicator into position is being used more.

59. CT or MRI
• CT shows only limited anatomy, but is easier
to access for the majority of departments.
• MRI has better definition, however is not
available to all.

62. Dose Volume Histogram (DVH) – Tumor
Volumes
• D100, D90 – minimum dose delivered to 100%, 90% of respective volumes, D90
being more stable.
• V(60 GyEQD) and V100 – Volume that receive 60 GyEQD and 100% of total dose,
respectively. V(D GyEQD) is preferred for intercomparison purpose

63. Dose Volume Histogram (DVH) – OAR
Volumes
DD2cc2cc, D, D1cc1cc, D, D0.1cc0.1cc –– minimum dose delivered to 2, 1, and 0.1 cmminimum dose delivered to 2, 1, and 0.1 cm33,,
respectively.respectively.

64. Disadvantages of 2D
• There is missing information when using 2D
film based dosimetry
– Soft tissue: uterus, cervix, vagina and the tumour
– Organs at risk: bladder, rectum, sigmoid and small
bowel

65. Advantages of 3D
• GTV – CTV approach may provide a better option to
gynaecological brachytherapy.
• Shaping the dose distribution to surround tumour,
rather than specified to a point.
• The organs are best imaged by CT/MR – their
proximity and Isodose curves can be shaped to
reduce their dose.
• Therefore image guided brachytherapy is more
precise.

66. 3D and 2D Planning Comparison
• Source localization
– 2 radiographs
(orthogonal)
• Computer dose calculation
• Dose
– Point A
– ICRU 38
• Optimization
– Dose points
– Dose volume - shape
Source localizationSource localization
–– MRI (preferred over CT)MRI (preferred over CT)
Volume delineationVolume delineation
–– GTV, HR CTV, IR CTVGTV, HR CTV, IR CTV
–– Organ at RiskOrgan at Risk –– bladder, rectum,bladder, rectum,
sigmoid, vaginasigmoid, vagina
Computer dose calculationComputer dose calculation
DoseDose
–– Point APoint A
–– ICRU 38ICRU 38 –– only bladder and rectumonly bladder and rectum
–– D100, D90 for GTV, HR CTV, IR CTVD100, D90 for GTV, HR CTV, IR CTV
–– DD0.1cc0.1cc, D, D1cc1cc, D, D2cc2cc for OARs if volumesfor OARs if volumes
are delineatedare delineated
–– DD5cc5cc, D, D10cc10cc for OAR if walls arefor OAR if walls are
contouredcontoured
OptimizationOptimization
–– Dose pointsDose points
–– Dose volumeDose volume
ShapeShape
DVHDVH

67. Major Differences
2D planning2D planning 3D planning3D planning
Total dose (EBT + BT)Total dose (EBT + BT) Use physical doseUse physical dose Use biologically weightedUse biologically weighted
dosedose
Dose prescriptionDose prescription point Apoint A target volumetarget volume
VolumesVolumes only describe tumoronly describe tumor
volumesvolumes
tumor and OARtumor and OAR
volumesvolumes
CTV splits into HRCTV splits into HR
CTV, IR CTV, LR CTVCTV, IR CTV, LR CTV
Reference volumeReference volume 60 Gy isodose volume60 Gy isodose volume 60 Gy isodose volume60 Gy isodose volume
Dose optimizationDose optimization base on dose points,base on dose points,
isodose shapeisodose shape
base on dose points,base on dose points,
isodose shape andisodose shape and
coverage, DVHcoverage, DVH
Dose reportingDose reporting Point A, bladder, rectum,Point A, bladder, rectum,
shape ref isodoseshape ref isodose
Same as in 2D + otherSame as in 2D + other
volumes specsvolumes specs

68. Implementation – infrastructure
requirements
• Availability of imaging CT/MRI
• Compatible applicator (costs)
• 3D Planning system
• Trained personnel
– Clinician
– Physics
– Radiographers
• Additional costs

69. COCLUSION
• ICRT implant geometry will not be the same for each
session so re planning has to be done for each
session.
• Image based (CT/MR) brachytherapy planning was
found to be superior in delineating accurate tumor &
organ at risk volumes.
• With the help of CT & MR we will be able to escalate
the dose to the target without increasing dose to
bladder & rectum beyond tolerance level .
• Inverse planning in brachytherapy is also can be
done.

70. AIM OF ICRU 58
• Aim is to develop a common language which is
based on existing concepts.
• To retain consistency as much as possible in
dose volume specification for external &
brachytherapy.

71. Dose prescription and reporting in
interstitial brachytherapy
• ICRU report 58 (1995)
• Recommendations based on
the so called ‘Paris’ system
• 3D nature of the implant
considered

72. VOLUMES & PLANES
Definitions of GTV(gross tumor volume) , CTV(clinical
target volume) & PTV(planning target volume) are
identical to the definition given for EBRT in ICRU
Report 50.
Treated volume is that, volume of tissue based on
implant which is encompassed by an isodose surface
selected ,this isodose should entirely encompass the
CTV.

73. CENTRAL PLANE
• Central plane is that in which the source lines
are straight, parallel, of equal length & with
centers which lie in plane to the direction of
the source lines.

74. Description of dose distribution
• In brachytherapy, dose distribution is non
homogeneous & includes steep dose gradients &
region of high dose surrounding each source.
• 1.) the region of plateau dose are equidistant between
adjacent sources, for sources of identical linear activity.
They are regions of local minimum doses.
• 2.) variation in dose between different plateau can be
used to describe the dose uniformity of implant.

75. Minimum target dose (MTD)
• The minimum target dose is the isodose
surface corresponding to minimum target
dose.
• MTD defines the treatment volume & should
entirely encompass the CTV.
• MTD is known in some American centers as
minimum peripheral dose.

76. Mean central dose (MCD)
• MCD is taken to be the arithmetic mean of the
local minimum doses between sources, in the
central plane, or in central planes if there are
more than one.

77. In radiotherapy practice:
• Volumes vary significantly
from patient to patient
• No homogenous dose
distribution
Dose
profiles
Line
sources

78. HIGH DOSE & LOW DOSE VOLUME
• Volume encompassed by the
isodose corresponding to
150% of the MCD around the
sources in any plane parallel
to the central plane.
• It is volume within the CTV,
encompassed by an isodose
corresponding to 90% of the
prescribed dose.

79. Idea:
• Use minimum dose
between linear
sources
• Prescribe dose to 85%
of Dm

80. ICRU 58: Dose prescription
• Assume implant of line
sources in parallel - this
could also be the
catheters for a stepping
HDR source
• Calculate dose
distribution in plane
orthogonal to the source
lines
• Calculate dose between
lines

81. ICRU 58: Dose prescription
• The calculation points are
always in the
‘geometrical’ centre
between line sources
• Prescribe to 85% of the
mean of these point doses
• This works only if the
differences between the
dose at different points is
not too large

82. ICRU 58: dose prescription
• System can be extended
to any number of sources
and is equally applicable
to surface moulds
• In practice relatively easy
to do

83. Works in 2D and
3D
From ICRU report 58
• The concept can also be
extended to line
sources of different
length

84. ICRU 58:
Guidance on
reporting
• System of
priorities
• Similar tables
exist for other
interstitial
implant types

85. In practice one needs to report
at a minimum:
• Dose to target and possible critical
structure
• Description of implant (sources,
techniques)
• Dose time pattern

86. 5. Treatment verification
• Most importantly: verification of the
implant geometry
– typically two orthogonal X Rays with markers in
the applicators/catheters
– used as input for planning of individual
patients

87. Patient flow in brachytherapy
Treatment decision
Ideal plan - determines source number
and location
Implant of sources or applicators in theatre
Treatment plan
Localization of sources or
applicators(typically using X Rays)
Commence treatment
Verification

88. Interstitial Brachy therapy in Carcinoma cervix

89. Ant. Radiograph Lat. Radiograph

90. Advantage of interstitial approach
Advantage of interstitial approach
ICB + Interstitial brachytherapy

91. Graphical Optimization TechniqueGraphical Optimization Technique

92. Three Dimensional Dose Distribution with MUPITThree Dimensional Dose Distribution with MUPIT

93. MUPIT IMPLANT IN CA CERVIX

94. PERINEAL INTERSTITIAL
BRACHYTHERAPY

95. Breast implants
• Typically a boost
• Often utilizes templates to improve source
positioning
• Catheters or needles