Brachytherapy.ar

BRACHYTHERAPY
RAJA BABU CH
OMEGA HOSPITALS
HYDERABAD

INTRODUCTION
 BRACHYTHERAPY is a method of treament in wchich
sealed radioactive sources are used to deliver at a short distane
 The sources are placed directly into the treatment volume or near
the treatment volume.
 The word brachy originates from the greek word ‘Brachus’
meaning ‘SHORT’
 Radium was discovered in Paris in 1898 by Marie and Pierre
Curie and with in a few years the first successful brachyterapy
treatment was reported

The first successful brachytherapy treatments were performed soon after Marie
and Pierre Curie’s discovery of radium in 1898. This picture shows how radium
(226Ra) surface applicators were used for the treatment of skin cancer.

Advantages
 High radiation dose can be delivered locally to the
tumor with rapid dose fall-off in the surrounding normal
tissues due to the inversesquare law.
 Improved localized dose delivery to the target
Disadvantage
 Accessibility of tumour volume and its size

IDEAL PROPERTIES
 The optimum gamma ray emission should be high enough to avoid
increased energy deposition in bone,whilst at the same time be
low enough to minimize protection requirements
 The optimum energy should be in the range of 0.2 to 0.4 MeV
 Should Preferably be no gaseous disintegration product, which
may be released if any break occurs due to pressure build up with
in the encapsulation
 Should have high specific activity to make the physical size of the
source as small as possible
 Preferably monoenergetic

 Half life : 1600 Yrs
 Energy : 0.83 MeV
Disadvantage :
 Its daughter product Radon is a highly toxic gas
 The maximum gamma energy is about 2.45 MeV, wchich demands
more shielding
 The maximum beta energy is about 3.2MeV,wchich necessitates
heavy filtration results in bulky sources
 HVL in water : 10.6cm
 HVL in Lead : 12 mm
Ra-226*

CO-60
 Half life : 5.26 Yrs
Disadvantage :
 High gamma energy(1.17 &1.33),which necessitates thicker
shielding
 Now it has been discontinued
 HVL in water : 10.8 cm
 HVL in Lead : 11.0 mm

CS-137
 Half life : 30 Yrs
Advantage :
 Medium gamma energy
 It requires less sheilding

IR-192
 Half life : 73.8 d
Advantage :
 Low gamma energy and high specific activity
Disadvantage :
 Short half life

IR-192 SOURCE
SCHEMATIC
 It has a core diameter of
either 0.3 or 0.1mm,
sheathed in pure platinum
of 0.1 mm thick to form an
outer diameter of 0.5 mm
or 0.3 mm

AU-198
Advantage :
 Used for permanent implants and replaced Rn-222

I-125
Advantage :
 Low enery photon,which requires less shielding
Disadvantage :
 Dosimetry more complex

Pd-103
 Half life : 17 d
Advantage :
 Having shorter half life than that of I-125,May provide biological
advantage in permanent implants

Radio nuclide Half life Energy (MeV) HVL in Water
(Cm)
HVL in Lead
(mm)
Cs-137 30Yrs 0.662 8.2 5.5
IR-192 73.8d 0.38 6.3 2.5
Co-60 5.26Yrs 1.25 10.8 11.0
Au-198 2.7d 0.412 7.0 2.5
I-125 60d 0.028 2.0 0.025
Pd-103 17d 0.021 1.0 0.008

Source strength specification provides three
functions
 Standard means for describing quantities of emitted
radiation
 Allows for computational dosimetry
 Serves as prescription parameter in brachytherapy

 Historically, the quantity used for specifying the strength of radium was
the mass of the radioactive material.
 The conventional unit was milligram or gram
 Subsequently, a new quantity ,Activity, with the special unit Curie,
was introduced
 Curie was originally defined as “that quantity of radon in equilibrium
with 1gm of radium”
 Now curie was modified to “the quantity of radioactive nuclide that
emits 3.7 × 1010 dps”
 Special unit for activity is becquerel (Bq), which is equivalent to 1 dps

SPECIFIC GAMMA RAY CONSTANT
 Specific Gamma Ray Constant is defined as the exposure
rate per unit activity at 1cm distance from a source
Unit : R hr-1 mCi-1 at 1 cm
 The activity of the source is not easy to measure practically
because of the absorption of gamma rays in source itself
and with in the sheath.
 For this reason the term Apparent activity was introduced
by the IAEA and ICRU

APPARENT ACTIVITY
 The activity of a hypothetical unfiltered point source of
the same radionuclide which will give the same exposure
rate in air at the same distance on the transverse axis of
the given sealed source
 The distance being large enough for the atual source to
be considered as a point source
 It takes account the effect of self absorption and source
encapsulation on the radiation output

EXPOSURE RATE CONSTANT
 exposure rate constant is like specific gamma ray constant but it
defined for unshielded point source
 Defined as the exposure rate per unit activity at 1cm distance from a
source
 The difference between two that is the specific gamma ray constant
includes exposure contribution due to only the primary gamma
emission whereas exposure rate constant includes, apart from
primary gamma emission, the contribution due to characteristics
X-rays
(Γx) = (d2.X)/A
Unit : R hr-1 mCi-1 at 1 cm

AIR KERMA RATE CONSTANT
 With the introduction of SI units, exposure rate constant was
replaced by Air kerma rate constant, based on air kerma
rate at a reference distance. Using the relation between
exposure rate and air kerma rate equation,
Kair = X.(W/e) / (1-g)
then AKRC (Γk)= (d2.Kair)/A
 Air kerma rate constant is defined as the air kerma rate at a distance
d(m) from a source of activity A(MBq)
Unit : μGy.m 2 / h.MBq

Radio nuclide Exp.Rate const. AKRC
(R.cm2 hr-1 mCi-1) (μGy.m 2 / h.MBq)
Cs-137 3.26 0.077
Ir-192 4.69 0.111
Co-60 13.07 0.308
Au-198 2.38 0.056
I-125 1.46 0.034
Pd-103 1.48 0.035
Ra-226* 8.25 0.195

REFERENCE AIR KERMA RATE
 which is defined by the ICRU as the air kerma rate
in air at a reference distance of 1 m, corrected for
air attenuation and scattering.
 Unit : μGy / h
 The term m2 not included in the unit , that is
presumption that it is inherent in the defination itself

AIR-KERMA STRENGTH
 AAPM,However ,felt that it is important to have the
distance explicit in the unit.
 It is defined as the air kerma rate in free space at
distance d(m) from the source in the plane normal to
and bisecting the long axis of the source
 Unit : μGy m2 / h

AFTERLOADING TECHNIQUES
Pre(hot) loading technique
Afterloading techniques
- manual Afterloading
- remote Afterloading

PRE LOADING TECHNIQUE
 The applicator is pre-loaded with
sources and inserted into the tumour
Disadvantage :
 The radiation hazard is very high
 Probability of loss of the sources also
maximum

MANUAL AFTERLOADING
 In afterloading technique, hollow
applicators are first inserted into
the lesion of interest, sources are
introduced afterwards using a
safer device
 The main advantage of this
technique is less exposure to staff
 Improved applicator placement

REMOTE AFTERLOADING
 Remote Afterloading is Cancer treatment with
radioactive sources controlled from a distance
Advantages :
 Reduced radiation exposure to staff
 Reduced possibility of human error
 Improved applicator placement

REMOTE AFTERLOADING UNITS
LDR (<2Gy/h )
MDR (2-12Gy/h)
HDR (>12 Gy/h)

LDR UNITS
 Low dose rate (<2Gy/h)
Ex : selectron LDR/MDR
 It employs Cs-137 source peliets of 2.5 dia
 Maximum activity permitted is 40mCi / peliet
 A maximum of 36 active peliets and 6 channels
are provided
Disadvantage :
 Duration of irradiation is of the order of several
hours or even day

HDR UNITS
 High dose rate (>12Gy/h)
 First commercially available HDR Ir-192 Remote
Afterloader GammaMed l in 1964
 Single dwell position

HDR REMOTE AFTERLOADERS
Neucletron Varisource Gammamed Plus

 All three units employ high activity ( ~10 Ci ) Ir-198
stepping forword source
 Source can be programmed to irradiate from any
desired position for the pre-set time
 Advantages :
 exposure time is short.
 Outpatient treatment possible
 The sources are withdrawn every time someone enters
the room

HDR DEVICE COMPARISON
MicroSelectron Varisource Gammamed
Company Nucletron Varian Varian
Channels Up to 18 Up to 20 Up to 24
Treatment PLATO BrachyVisio Abacus
planning Oncentra
Source size 0.9 mm dia 0.59 mm D 0.9 mm D
4.5 mm long 5 mm long 4.5 mm long

SURFACE MOULD THERAPY
 SURFACE MOULD THERAPY is used for treating superficial lesions
by keeping the source very close to the skin surface
EX : lip, ear...etc.
 Radioactive sources are mounted on the mould and the mould in turn is
placed on the surface to be treated,thus keeping the constant separation
from the plan of sources
 Distance between source and skin depends upon the depth below the
surface to be irradiated. { 0.5 or 1 cm generally used}

 Surface applicator with
irregular distribution of
radium on the
applicator surface
(Murdoch, Brussels
1933)

INTERSTITIAL THERAPY
 In interstitial therapy, sources are directly implanted into the tumour
tissue
EX : Breast,Head and Neck
 Permanent implants : is a one
sources left in the patient forever
- patient discharged with implant
in place
 Temporary implants : is one
which sorces are removed after
a pre-set time
Implant removed before patient
is discharged from hospital

INTRALUMINAL BRACHYTHERAPY
 Sources are inserted into
natural body cavities, lumen
sheped
EX : bile duct carcinomas,
endobronchil carcinoma

INTRACAVITY BRACHYTERAPY
 Sorces are inserted into
natural cavities of the
body by using the
applicators
 Most widespread of intra-
cavity terapy has been
in the treatment of female
gynaecological
EX : uterine cervix

CERVIX APPLICATORS
 Consists of a central tube,
called the tandem and
lateral ovoids
 The applicators consists
tandems,with curvature of
15, 30, 40 degree angles

VAGINAL AND RECTAL
APPLICATORS
 The Applicator Set is used to
treat cancer of the vagina or
rectum.
 The set offers a variety of
cylinder diameters that
maintain an optimal distance
between the source and the
layers of tissue to be
treated.

INTRALUMINAL CATHETER
 Suitable diameter catheters of various lengths are avilable
for treating intraluminal disease such as endobrochial
carcinoma

NEXT SESSION
 DOSIMETRY
 OTHERTECHNIQUES IN BT
 QA OF BT

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