Radioisotopes and dose rates used for brachytherapy
This is the seminar about different radioisotopes used in brachytherapy beginning from radium to iradium and different dose rates, low dose rate, high dose rate used in brachytherapy. The significance of different dose rates and its radiobiology along with the clinical results.
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Radioisotopes and dose rates used for brachytherapy
1. Moderator : Dr. A. S.Oinam
Presented By : Dr. Subhash Thakur
3rd year JR, Department of Radiotherapy
PGIMER, Chandigarh, India
Presented On : 18/08/2018a
Radioisotopes and Dose Rates
Used For Brachytherapy
2. RADIOISOTOPES
An unstable form of element that emit radiation to
transform into stable form
These are mostly artificially produced in research
reactor or accelerators by exposing the target material
to particles such as neutron or protons.eg.
Co59 + neutron = Co60
3. Brachytherapy
Definition:
It is a method of treatment in which sealed
radioactive source are used to deliver
radiation at a short distance by various
methods.
Brachytherapy developed largely through the use
of sealed radium and radon sources.
In the 1950s, alternative artificially produced
nuclides became available.
Gradually radium and radon were replaced with
137Cs, 192Ir, 60Co, 198Au, and 125I sources
4. Properties of brachytherapy
sources and radionucleides
Clinical utility of any radionuclide depends on
Half life
Radiation output per unit activity
Specific activity (Ci/gm)
Photon energy
Whereas
Methods of producing radionuclide, its physical
and chemical properties determine its cost
effectiveness and toxicity
5. Some Terms which will be used
frequently :
Radioisotopes
Brachytherapy
Activity
Half life
Specific activity
Air Kerma
Reference air Kerma rate
Exposure rate
Exposure rate constant
6. IMPORTANT DEFINITIONS
Radioactivity:
No. of disintegrations per unit time (sec ,min,hrs.)
expressed in curies
• 1 curie (ci)=3.7x1010 disintegration /sec
• 1 Bequerel (Bq) =1 disintegration / sec.
(S.I.unit)
Half life(T1/2):
“The time required for a radioactive isotope to
lose half of its original activity .”
Half Value layer (HVL):
The thickness of the specified substance that
when introduced into the path of radiation
coming from source, reduces the exposure rate
7. Kerma (dEtr/dm)
Where dEtr is the sum of initial kinetic energy
of all the charged ionizing particles released by
uncharged particles in a material of mass dm.
Unit : J/Kg
Air Kerma Strength
Air kerma strength is defined the product of air
kerma rate in free space and the square of
distance of the calibration point for the source
center along the perpendicular bisector.
Unit : J m2/kg-hr
8. REFERENCE AIR KERMA RATE (RAKR)
“the kerma rate to air, in air, at a reference distance of 1
m,corrected for air attenuation and scattering”.
µGy/ h at 1 m LDR
µGy /s at 1 m and mGy /h at 1 m HDR
9. TOTAL REFERENCE AIR KERMA
There are steep dose gradients in the region of the
sources, so that specifying a treatment in terms of
the dose at a point is not recommended.
TRAK IS THE SUM OF THE PRODUCTS OF RAKR
AND THE DURATION OF THE APPLICATION FOR
EACH SOURCE
independent of the source geometry and
proportional to the integral dose to the patient.
compare treatments within one centre or between
different centres and to explain possible differences
in the delivered dose or in the treatment volume
dimensions.
useful index for radiation protection of personnel
11. Radioisotopes in
Brachytherapy
Radium
1. Discovered by Madam
Curie in 1898
2. Naturally occuring
radionucleide
3. Complex decay
scheme
4. 1st used in 1906 in
clinics, led to Radiation
Necrosis due to
intense beta ray dose
from the Radium
5. 1920 : successful
filtration of the beta
rays was achieved
12. Radium
Cascade of transformation of one daughter product
to another ending with stable isotope of Lead206
13. RADIUM-226
88Ra226 →
86Rn222 + 4He2
H
1. Gamma Energy 0.184 -2.54 MeV (avg. energy -0.83
MeV)
2. Beta Energy 0.07 - 3.25 MeV
3. Half life 1600 years
4. Specific activity 0.97 Ci /gm
5. HVL 12mm of Pb.
6. Exposure Rate Const. 8.25 Rcm2/mg-hr
7. Spectrum wide range of 49 gamma rays
8. Encapsulation 0.5 mm Platinum.
9. Physical form Tubes, Needles
14. Radium sources are
specified by (a) active
length, the distance
between the ends of the
radioactive material;
(b) physical length, the
distance between the
actual ends of the source;
(c)activity or strength of
source, milligrams of
radium content;
(d) filtration, transverse
thickness of the capsule
wall, usually expressed in
terms of millimeters of
platinum.
15. WHY RADIUM IS NOT USED NOW A
DAYS
Daughter products, RADON is an alpha emitter.
It is a Gas which is soluble in tissue.
Not easily detected by a visual check
can escape through hairline crack in the radium
capsule
Radium and its daughter products may become
deposited more or less permanently in the bone if
ruptured within patients body
Radiation protection for these sources requires large
thicknesses of lead, which can cause problems when it
comes to:
Transporting sources in heavy containers.
Using very heavy protective screens around the
patient.
The need for a heavy rectal shield in applicators used
for gynecological treatment.
Sources of higher activity are bulky and not suitable for
16. Properties of the Ideal
Brachytherapy Source.
Ideal radionuclide should produce a single gamma ray
spectrum with energy of around 0.5 MeV.
acceptable half life
Cheap and easily produced
Preferably solid
Stable solid decay products
High specific activity
Closest to the ideal radionuclide for LDR at present time is
Cesium 137
17. Radium Substitutes
The first sources to be used as alternatives to
radium were
Cobalt-60,
Gold-198,
Cesium-137 and
Iridium-192.
18.
19. Cesium
discovered in the late 1930s by Glenn Seaborg and
Margaret Melhase
Product of nuclear fission
• Gamma Energy - 0.662 MeV.
• Beta Energy - 0.5-1.17 MeV
• Half life - 30 yrs
• Specific activity - 10 Ci/gm.
• HVL - 5.5 mm of Pb
• Exposure Rate Const - 3.26 R cm 2/mCi-hr.
• Spectrum- Single Gamma ray with beta rays
• Encapsulation - 0.5 mm of Pt.
• Physical form- Needles, microspheres, powder
• 2% annual reduction in source activity occurs
20. Source specification
insoluble powders or ceramic microspheres,
labeled with 137Cs, and doubly encapsulated in
stainless steel needles and tubes.
21.
22. Cobalt 60
Properties of Cobalt 60
Production : by neutron activation of the stable
isotope cobalt-59
Half Life : 5.27 years
Decay Scheme : 27Co60
28 Ni60 + -1 β + γ
Beta energies : 0.318 MeV
Photon energies : 1.17 MeV and 1.33 MeV
Beta filtration : typical source wall thickness
Half value layer in lead : 10 mm
23. Form of source Co60
Cobalt brachytherapy sources are usually
fabricated in the form of needle
An alloy wire composed of 45% cobalt & 55%
nickel, so called cobanic
Encapsulated in a sheath of platinum of stainless
steel
Because cobalt tends to be corrosive, it is usually
nickel plated;
encapsulation with 0.1 mm to 0.2 mm platinum-
equivalent is necessary to filter the b-particles.
24. Iridium192
Used for HDR brachytherapy
Properties of Iridium192
Production : by neutron activation of the stable
isotope Iridium191
Half Life : 73.83 days
Decay Scheme : 77Ir192
78Pt192 + -1e0
+ γ
Beta energies : 0.079-0.672 MeV
Photon energies : 0.2 – 1.06 MeV
Beta filtration : 0.1 Platinum
Half value layer in lead : 4.5 mm
25. Most common form of source : wire in 1 m length
coils, wire consists of an active iridio platinum
core, 0.1 mm thick, encased in a sheath of
platinum, 0.1 mm thick
26. iridium seeds
seeds are 3 mm long and
0.5 mm in diameter
Made up of 30% Ir + 70%
Pt surrounded by 0.2 mm
thick stainless wall
pure iridium is very hard
and brittle, and is difficult
to fabricate.
27. GOLD198
Au 197 + 0
1n → Au198 +Υ
• Gamma Energy: 0.412 MeV
• Beta Energy 0.69 MeV.
• Half Life 2.7 days
• HVL : 2.5 mm Pb
• Exposure rate const. : 2.38 Rcm2/mCi–
hr
• Physical form: seed
• Used for permanent implant
• Gold seeds of size 2.5 mm long & 0.8 mm
diameter
28. Advantages of Gold over
others
The average photon energy of gold is 0.406 Mev,
making the radiation protection requirements
much easier and cheaper to implant than those of
Ra226 , Rn, Co or Cs
Very short half life so useful for permanent
implants
29. IODINE125
• Xe124 +
0n1 → Xe125 → I 125
• Allen Reid and Albert keston discovered I125 in 1946
• Gamma Energy - 0.028 MeV (avg).
• Beta Energy- None
• Half life - 59.4days
• Specific activity - 1739 Ci/gm
• HVL - 0.025 mm OF Pb
• Spectrum - Three gamma rays
• Exposure rate const. - 1.46 Rcm2/mCi–hr
• Encapsulation - 0.5 mm titanium
• Physical form- seed
• Used for permanent interstitial implants.
30. 125I decays by electron capture to an excited state of
125Te which decays to ground state releasing
35.5keV .
IODINE FROM FM KHAN
31. The high specific activity of I125 enables the
production of miniature sources sufficient activity
for use in both permanent and temporary
implants
The main current application field of I125 is
permanent interstitial implant for prostate
cancer
32. Palladium103
46Pd102 + 0n1 →
46Pd103
• Gamma Energy : 0.021 MeV (avg)
• Beta Energy: None
• Half life : 17days
• Specific activity 7448 Ci/gm
• HVL : 0.008 mm of Pb
• Encapsulation : Titanium
• Exposure rate constant: 1.48 Rcm2/mCi–hr.
• 103Pd decays by electron capture (20-23 keV x
rays)
33. Pd103 has been introduced as replacement for
I125 sources for permanent implant
Its short half life of 17 days makes Pd103 only
appropriate for permanent implants
Its short half life and high specific activity enables
dose delivery at initial dose rate higher than that
of I125
This feature is beneficial when used for rapidly
proliferating tumors
34. Advantages of one over
another
Cs over Radium
Reduced amout of shielding is required and absence of
gaseous daughter product
Cs over Cobalt
Longer half life of 30.07 years compared with 5.27 years
of Co, which enables the clinical use of Cs source over a
long period of time
Low production cost
Smaller amount of shielding required
Disadvantages of Cs
Lowest specific activity, doesnot allow the production of
miniature sources of very high activity for HDR remote
controlled loading BT
Thus appropriate only for LDR
35. Cobalt over Cs
Due to high specific activity, Co is appropriate for
fabrication of small high activity source
Cobalt over Radium
Cobalt wires can be bent to conform to the shape of
tumor
No danger of leakages or breakages
cobalt over iridium
Half life of cobalt is much more than of iridium, hence it
need not to be replaced as frequently as iridium
25 source exchanges are required for 192Ir for one
exchange of a 60Co source
THOUGH INTEGRAL DOSE IS HIGHER IN CO60
36. Types of Brachytherapy……
Depending on source loading pattern:
Preloaded: inserting needles/tubes containing
radioactive material directly into the tumor
After loaded: first, the non-radioactive tubes
inserted into tumor
Manual: Ir192 wires, sources manipulated into applicator by
means of forceps & hand-held tools
Computerized remote controlled after loaded: consists of
pneumatically or motor-driven source transport system
37. Preloading pattern
Advantage:
Loose & flexible system(can be inserted even
in distorted cervix)
Excellent clinical result
Cheap
Long term results with least morbidity (due to
LDR)
Disadvantages:
Hasty application -Improper geometry in dose
distribution
Loose system – high chance of slipping of
applicators – improper geometry
Application needed special instruments to
maintain distance.
Radiation hazard
38. After loading pattern
MANUAL AFTERLOADING
Advantages
1. Circumvents radiation protection problems of preloading
2. Allows better applicator placement and verification prior
to source placement.
3. Radiation hazard can be minimized in the OT / bystanders
as patient loaded in ward.
4. Advantages of preloading remain.
Disadvantages:
specialized applicators are required.
39. REMOTE AFTERLOADING
Advantages :
1. No radiation hazard
2. Accurate applicator placement
-ideal geometry maintained
-dose homogeneity achieved
-better dose distribution
3. Information on source positions available
4. Individualization & optimization of treatment possible
5. Higher precision , better control
6. Decreased treatment time- opd treatment possible
7. Chances of source loss nil .
Disadvantages :
1. costly
40. Different dose rates used for
brachytherapy
treatment dose rates fall into these categories:
Ultra LDR : 001 to 0.3 Gy/hr : dose rate used in
permanent implants with I125 and Pd103
LDR : 0.4 to 2 Gy/hr, compatible with conventional
manual or automatic after loading technique
MDR : 2 – 12 Gy/hr, can also be delivered by manual or
automatic afterloading, although the latter is far more
frequent
HDR : >12 Gy/hr and only automatic afterloading can
be used because of the high source activity
PDR : pulses of 1 to 3 Gy/hr, delivers the dose in a
large number of small fractions with short intervals
Permanent Implants : deliver a high total dose (eg.
41. Sources for LDR intracavitary
brachytherapy
Active length should be 1.3 to 1.5 cm
Half Life should be 5 to 10 years working life
without variation in prescription dose rates
Average photon energy : 60 to 100 keV
Sources : Radium226 and Cesium137
42. Sources for permanent Interstitial
Brachytherapy
2 Basic approach
1. Classical LDR permanent brachytherapy
Radon 222
Au 198 seeds
HALF LIFE : FEW DAYS
High energy photons
Patient must be confined to the hospital until the
source strength decays to safe level (10 days)
43. 2. ULDR brachytherapy
Larger lives but low energy emitters – Pd103 and I125
Patients tissue or thin lead foils are sufficient to
limit exposure to negligible levels
No need to hospitalize patients solely for radiation
protection
During the implant procedure, decreased radiation
exposure to O.T. persons
44. Sources for HDR brachytherapy
Uses high intensity source to deliver discrete
fractions ranging from 3 to 10 Gy
A remote after loading device must be used
Radio-nuclide with high specific activity (Ci/gm) is
needed so that treatment dose rates of at least 12
Gy/hr can be achieved.
A miniature source no longer than 1 mm
diameter and 4 mm length with an exposure rate
of 1 R/sec at 1cm is required.
45. The radiobiology of
brachytherapy
Brachy : not only short treatment distance but
also short treatment time
Short overall treatment time, compared to EBRT
minimizes tumor repopulation in rapidly growing
tumors
Short overall treatment time in brachytherapy are
likely to contribute significantly to clinical efficacy
for tumor sites like cervix, head and neck and
lung where long overall treatment time is
associated with reduced local control.
46. Radiobiology of the brachytherapy
and Dose Rate Effect
The biological effects of radiotherapy depends on
Dose distribution
Treated volume
Dose rate
Fractionation and
Treatment duration
However these are of different importance in
determining the outcome of EBRT and of
brachytherapy
47. Radiobiological difference between
EBRT and brachytherapy
Factors EBRT Brachytherapy
Volume treated Large Very small
Dose homogenity -5 to +7% acceptable Very inhomogenous
Volume effect
relationship
>tolerance dose, not
well toleraable
Very high doses
tolerated well
Time dose factors Small daily fractions of
few seconds/minutes
Continuous deliver and
short treatment
48. Radiobiological Mechanisms
The bilogical damage inflicted by irradiation of
human cells can be divided into three consecutive
steps :
Physical phase : short initial phase, excitation of
electrons and ionisation, energy deposition phase
Chemical Phase : ionized and excited atoms
interact directly or indirectly through the formation of
free radicals to the breakage of chemical bonds.
Biological Phase : Longer phase, seconds to years,
cells reaction to inflicted chemical damage, specific
repair enzymes successfully repair the majority of
DNA lesions, however few may not repair and lead
to cell death.
Early reactions
Late reactions
49. Radiobiology – LDR Vs HDR
In terms of 4Rs
Repair :
LDR : allows time for sublethal damage repair in
normal tisues
HDR : short treatment time prohibits this repair
Reassortment :
LDR : theoretic advantage of an improved result
HDR : ---
Only shown in vitro, but in vivo the effect of
reassortment has not been shown to give a true
advantage, possibly due to disruption of the
mechanism of cell cycle in cancer cells
50. Repopulation
LDR & PDR : probably prevents repopulation during
treatment
HDR : short treatment time, so no issue of
repopulation
Reoxygenation :
2 types of hypoxia : chromic and transient
LDR : transient hypoxia may correct during
treatment time
HDR : not possible
If brachytherapy is fractionated, tumor shrinkage
and re-oxygenation of areas of chroni hypoxia may
occur between insertions
51. Biophysical Modeling of
Brachytherapy
In 1970s, before the diffrential response of early
and late responding tissues was understood, the
most widespread approach for designing
alternative fractionation schedule was Nominal
Standard dose equation (NSD)
This equation was based on data from early
responding tissues and it didn’t account for
diffrential response to fraction size/dose rate of
early Vs Late effects
52. Linear Quadratic Model
Distinguishes between early and late response
Based on mechanistic notion and how cells are
killed by radiation
After several decades of investigation and use,
LQ model have been well supported by clinical
experience and outcome date
53. Mechanistic basis of LQ model
In this approach radiotherapeutic response is
primarily related to cell survival
Cell killing is the dominant determinant of
radiotherapeutic response both for early and late
responding end points
S(D)=e-αD-βD2
54. The Linear Quadratic Model
Type A damages:
Two Critical Target within a cell are
simultaneously damaged (hit) in a
single radiation interaction event
leading to cell death
Type B damages:
Two critical Target are damaged in
separate events, after which the
damaged sites interacts to produce
cell death
Sub Lethal damages:
The damages which are not so
effective for lethality of cell
55. Linear component related to single
track events,
Quadratic component related to
interaction of multi-track events
low dose radiation
single track events predominate and
are far apart in time to produce any
significant double track events. The
curve is straight with no shoulder.
high dose radiation
Multiple track events predominate.
Survival curve bends and becomes
curved.
dose
E
f
f
e
c
t
e-
e-
e-
Linear
EαD
Quadratic
EαD2
Basis of LQ model
56. The Linear Quadratic Model
Sparsely
ionizing
particles
Densely
ionizing
particles
βD2
αD
α/β
4 8 12
The expression for cell survival curve by this model
P (survival) or SF = exp (-αd -βd2)
2 components of cell killing:
Type A damages –
Cell Killing proportional to dose D
i.e E, effect proportional to D
Type B damages –
Cell Killing proportional to the
square of the dose D2.
i.e E, effect proportional to D2
Fowler (1989)
57. Low Dose Rate continuous
Brachytherapy
BED = D [1+g. R /(α/β)]
Where
Total dose = D = Dose Rate x Time = R.T
g = incomplete repair factor
g = (2/µT).[1-(1/µT).{1-exp(-µT)}]
and µ = 0.693/t1/2
58. Use of LQ model in Brachytherapy
quantifing the rationale for LDR
Lowering the dose rate generally reduces
radiobilogical damage.
For high dose rates, the dose reduction needed
to match the late effects is larger than the dose
reduction needed to match tumor control
For any selected dose, increasing the dose rate
will increase late effects much more than it will
increase tumor control
Conversly
Decreasing dose rate will decrease late effects
much more than it will decrease tumor control
Thus the therapeutic ratio increases as the dose
rate decreases
59. Use of LQ model in Brachytherapy
quantifing the rationale for LDR
60. High Dose Rate Brachytherapy
BED = D [1+d/(α/β)]
Where
D = n.d
n = no. of fractions
d = dose per fraction
DNA Repairs doesn’t occurred in a short period of time
of 10 min.
DNA repairs occurs between two successive fractions
only
Bur for well spaced fraction >>12 hrs, Correction for
incomplete Repairs is not required
61. Radiobiological principles involved in
moving from LDR to HDR
This is the
case for
cervical
brachythera
py because
bladder and
rectum are
generally
some
significant
distance
from
implant
62. Brachytherapy for prostate cancer
Optimized dose protraction for
prostate cancer Brachytherapy
Prostate tumors contain unusually small fractions
of cycling cells
Low α/β ratio
So they behave like late responding
normal tissues
63. Ca prostate : Brachytherapy
Radiobiological Basis
α/β value for prostate cancer is similar to that for
surrounding late responding normal tissue, HDR could be
employed to match conventional fractionated regimen with
respect to tumor control and late sequalae while reducing
early urinary sequalae
The α/β value for grade 2 or higher late rectal toxicity is
4.8 and this value is larger than of the prostate tumor α/β
ratio
This suggests that HDR prostate Brachytherapy might
actually improve the therapeutic outcomes of prostate cancr
Brachytheapy
64. Advantages of HDR Over LDR
Radiation Protection
After loading
No source preparation and transportation
Only one source, there is no risk of losing a radioactive
source
Short treatment times
Less discomfort to patient
Low risk of applicator movement during therapy
Treat large no of patients
Smaller diameter
Reduced dilation of cetvix
After loading
Treatement dose optimization Possible
65. Disadvantages of HDR over LDR
Radiobilogic
Short treatment times : no sublethal damage repair,
no reassortment , redistribution and reoxygenation
Limited experience
The economic disadvantages
Costly remote after loaders
Required shielded room and more labor intensive
Greater potential Risk
High specific activity source used, if machine
malfunctions or there is calculation error, there is
very short time to detect and correct errors
66. Difference between LDR & HDR
brachytherapy treatment Planning
HDR BT differs from LDR BT in 3 Ways :-
1st difference : time Course
The patient waits in the treatment position during the treatment
plan generation in HDR while
Treatment plan generation performed with the patient
elsewhere in LDR
2nd difference : quantities involved with dose calculation
HDR : one source strength and many different dwell times
LDR : input – source strength input by user, many sources
In both case, dose calculation algorithm uses the
product of source strength and time at a given location
3rd difference : role of quantities as input or output
LDR : input : source strength and treatment duration
HDR : reverse process start with dose pattern disingned and
working backward to the dwell time distributing necessary to
achieve that dose
67. Conversion from Low to High Dose
rate Brachytherapy
Biggest questions : How many fractions to use
???
What dose/fraction ????
Increasing the number of fractions increases
therapeutic ratio but each additional fraction
brings
Costs for departmental resources and
Inconvenience to patient
So Most regimens use 5 or 6 #s if applicator
insertions involved and 8 -12 #s if applicators can
be left in place
68. Dose/# ????
BEDHDR = BEDLDR
calculate dose/#
α/β : comes into play again
If normal tissue toxicity is kept constant, α/β = 3
If tumor cure is kept constant then α/β = 10 (or value
of particular type of tumor)
If late complications are to be kept constant then α/β=2
For intracavitary applications, normal tissue can be
kept away from the applicator, which allow us to
calculate dose based on equivalent tumor control
69. Experimental Results
In vitro studies in sixties have shown that there is an
effect of dose rate on cell survival
This effect differs with cell type
The dose needed for 1% survival is roughly 1.5-3
times higher at 1 Gy/hr than it is at 1 Gy/min
70. Pulse Dose Rate (PDR)
Combined physical advantage of HDR BT and
radiobiological advantage of LDR BT
PDR BT was proposed and introduced as a
method to replace continuous LDR
advantages of PDR brachytherapy compared with
LDR
full radiation protection for caregivers
no source preparation necessary
no extensive source inventory, that is, only one
iridium-192 source per afterloader to be replaced
every 2 or 3 months
71. Compared with HDR
brachytherapy,
PDR offers similar quality of dose distribution, and
similar treatment procedure and technical
verification, both being stepping source
technologies
Clinical results : Ca Cervix
source
72. Most Studies
Local control : 80-90%
Overall survival : 4 yrs for 55% Patients
Low incidence of gr II GI and GU late toxicity
Disadvantage of PDR
PDR delivered by stepping source might
behave more like HDR than LDR,
Especially for tissues with a substantial
component of repair of very short T1/2
73. 1990-1992, 180 patients, St IIB-III
All patients received EBRT@ 45 Gy/25#/4.5 weeks
Divided into two arms
Dose reduction arm (30%) – 2450 cGy to Pt A
Dose reduction arm (12.5%) – 3060 cGy to Pt A
Vs
Previously treated IIB and III patients with LDR
(55-65 cGy/hr)
74. MDR – 30 : results were comparable to LDR group, so
this group was retained
MDR – 12.5 : discontinued due to increased morbidity
So, decided to evaluate dose reduction between LDR
and MDR 30
20% dose reduction was decided upon
1st : MDR –30 2nd : MDR – 20
75. Summary
No statistical difference in local control between
LDR, MDR – 30, MDR -20 and MDR – 12.5
However significant increase in late complications
with MDR -12.5 and higher trend seen with MDR -
20
So its important to know the absolute dose received
by critical organs _ rectum and bladder
76. Clinical Results : LDR, MDR and
HDR brachytherapy
Many clinical data have been accumulated over
the years in brachytherapy, but very few
randomized trials.
These retrospective studies help to better
understand the biological background of
brachytherapy and devise the rules that can be
followed in clinical practise.
77. Results of HDR Vs LDR
Cervical Cancer
LDR brachytherapy : experience > 100 years
It is very important to critically analyze how the
results obtained with HDR Brachytherapy which
has a much shorter history to be compared with
LDR
Meta Analysis By Orton et al, 56 institutes
HDR : 17068 patients
LDR : 5666 patients
5 year survival date was available for 6639 HDR
patients and 3365 LDR patientsStage HDR LDR
I 82.7% 82.4%
II 66.6% 66.8%
III 47.2% 42.6%
78. 1999, Pertreit and Peracy, Literature review
5619 patients with HDR treatment
5 year pelvic control rates were 91% for stage I, 82% for
stage II and 71% for Stage III Patients
5 years OS was similar to previous metaanalysis
4 Randomised Studies by
Shigematu et al
Hareyama et al
Patel et al and recently
Teshima et al (2004) from thailand
Which all of them have showed no difference in OS,
RFS or Pelvic Control and
No statistical difference in complication rates for rectum,
bladder or small Bowel
79. Total no of patients = 423, EBRT @ 45 Gy/20# f/b
Two groups
LDR group : 220 pts, dose rate @ 55cGy/hr to 90
cGy/hr, dose 35 Gy in single inserrtion with Cs137
HDR group : 203 patients, radionucleide Co60 , dose
8.5 to 9.5 Gy to point A, 2 sessions
80. Results
Patients with complete response after completion
of treatment : 90 % LDR Vs 89 % HDR
Recurrence cervical : 9 % LDR Vs 10 % HDR
Parametrial : 12% LDR Vs 11% HDR, at last f/u,
end of 5 yrs
Overall control of disease : 72% with LDR and
72% with HDR
81. Ca Prostate
Permanent implantation of I125 or Pd103 is the
most common type of prostate Brachytherapy
However several centers have used HDR
Brachytherapy as a boost to EBRT with
encouraging results
Potential advantage of HDR Brachytherapy in
prostate cancer is the theoretical consideration
that prostate cancer cells behave more like late
reacting tissues with low α/β , they should therefore
respond more favourably to HDR fractions rather than
LDR Brachytherapy
82. Galalae et al, 611 patients treated at 3 institutes
with EBRT followed by Brachytherapy for
localized prostate cancer
Five year biochemical control :
Low risk 96%
Intermediate risk 88%
High Risk 69%
85. Carcinoma Breast
EBRT is standard radiation modality after
Lumpectomy
Over the past decade, increasing use of
Brachytherapy as the sole modality of treatment
to decrease the treatment time from 6 weeks to
about 5 days
ABS recommends : 34 Gy/10# to CTV when HDR
Brachytherapy is used as the sole modality
Data on use of HDR as boost is very limited
86. Polgar et al, 207 patients with stage I and stage II
patients
All patients underwent BCS f/b WBRT
Two arms :
No further treatment
Radiation boost by either 16 Gy of electrons or HDR
BT12 to 14 Gy
52 patients with HDR Boost
5 year local tumor control was 91.4%
And excellent to good cosmesis : 88.5%
Same results were obtained with electron
irradiation
87. Esophageal Carcinoma
Brachytherapy is relatively simple to perform
because a single catheter is used for treatment
Largest diameter applicator should be used to
minimize the mucosal dose relative to dose at
depth
ABS recommends : HDR dose of 10 Gy in 2 #,
prescribed at 1cm from source to boost 50Gy of
EBRT
88. Sur et al, 1992, 50 patients with squamous cell
carcinoma
One arm : EBRT alone
Another arm : EBRT + HDBT
(12Gy/2#)
12 month survival 44% Vs
78%
Relief of dysphagia at 6 months 53.5% Vs
90.5%
89. For medically inoperable patients with submucosal
esophageal cancer, EBRT with ILBT is an attractive
approach
Ishikawa et al, 5 year cause specific survival to be
86% with EBRT and ILBT and 62% with EBRT alone
In pallilative setting to relieve dysphagia HDBT is
more defined
Sur et al, 50 Patients, EBRT @ 35 Gy/15#,
1st arm : kept on f/u
2nd arm : 12 Gy/2# HDR
6 month relief of dysphagia : 84% Vs 13%
1 year survival : 69% Vs 16%
90. Head and Neck Cancers
Head and Neck area doesnot tolerate high dose
per fraction
Nasopharynx : Easily accessed by intracavitary
HDR applicator
Lovenderg et al, have shown patients most suitable
for HDR BT boost are tghose with T1 and T2 lesion
following 60 to 70 Gy of EBRT
HDR of 18 Gy/6 # are delivered by special
nasopharynx applicator
T3, T4 : better suited to be boosted by IMRT
91. HDR Brachytherapy as salvage in
H&N Cancer
Loco-regional recurrence is the primary pattern of
failure in H&N caners despite of advancement in
surgery, concurrent CCT and EBRT
Surgical Treatment is the preferred treatment,
however it is not possible in all cases
EBRT is as effective as salvage treatment but
with high toxicity
HDR BT has been used in previously irradiated
patients, initial results appear to be comparable to
other modalities
92. Conclusion
Beginning of brachytherapy started with the
discovery of Radium.
With the improvement in specific activity of
sources the era of HDR came along with the
decreased radiation exposure to the persons
involved .
Though theoritically , LDR is radio biologically
better than HDR , clinical trials have shown the
result of HDR as good as LDR .
SOURCE CERTIFICATE
Form of the source
CAPSULE
SOURCE PELLET
INTRACAVITARY :
low melting point;
Earlier sources made from caesium chloride or caesium sulphate: SOLUBLE IN WATER.
In the case of point sources or small capsule sources, the caesiu
Pls give source certificate
Why activity difference is there in co and iridium
Electron capture what is advantage of iodine over gold in permanent implant