Brachytherapy in Carcinoma Cervix

BRACHYTHERAPY IN
CA CERVIX
Dr RAJSREE RAJAN

INTRODUCTION - BRACHYTHERAPY
• Brachytherapy is the delivery of radiation therapy using
sealed sources that are placed as close as possible to the
site to be treated.
• The very term ‘brachytherapy’ means ‘near treatment’.
• It has been described as the first form of conformal
radiation therapy
• Allows delivery of a well focused and high levels of
absorbed dose to the tumor
• It has a rapid absorbed-dose fall-off allows OARS to
be spared
Brachytherapy treats a smaller volume with an
extremely heterogeneous dose distribution.
The average dose within the target volume is
usually far higher than the prescribed dose at the
reference isodose on the periphery of the
implant.
This is tolerated due to the volume–effect
relationship: very small normal tissue volumes
(eg 1–2 cm3) can tolerate very high doses that
larger volumes would not tolerate.

INDICATIONS IN CA CERVIX
1. Stage IB - IV tumours of the cervix [In combination with EBRT]

• Intracavitary brachytherapy is recommended if there is no residual disease, or residual
disease at the cervix or limited to the medial parametrium and/or upper vagina.
• It primarily consists of placement of an applicator in uterine and vaginal cavities in the
vicinity of target tissues (residual disease, uterus, parametrium, adjacent vaginal mucosa)
by using uterine tandem and various vaginal source carriers such as
ring/ovoids/cylinders.
• Interstitial brachytherapy is recommended in vault cancers with residual disease at vault
with significant disease in the parametrium at the time of BT

Intracavitary Use sources that are
loaded within body
cavities
Ex: Uterine [Ca
Cervix] and
Vaginal ICRT
Interstitial Surgically implanted
small radioactive
sources directly into
the target tissue.
Ex: Interstitial
implants
[Radioactive
needles]
Classification of Brachytherapy
1.Based on Implantation technique
TEMPORARY
- Implants are placed in the tumour/adjacent tissue
- The implant is left in the patient for a specified time to
deliver the prescribed dose
- Delivers MDR/LDR/HDR treatments
- Source is removed once prescribed dose is given
- Ex: All intracavitary implants are temporary implants
2.Based on means of controlling the dose delivered

1 Low dose rate 0.4-2Gy/hour Tx time: 24 – 144
hours
Patient is treated IP
Repair of SLD
More effective in
normal tissues than
malignant tissues
2 Medium dose rate 2-12Gy/hour
3 High dose rate >12Gy/hour or >0.2Gy/min
Modern remote after loaders
0.12Gy/s[430Gy/hr] at a
distance of 1cm
Tx time is only few
minutes
Fractionated BT
OPD basis
Heavily shielded
vaults
Uses remote after
loading systems
As dose rate
increases treatment
has to be fractionated
to allow SLDR
3.Based on Dose Rate

PRELOADING AFTERLOADING
Applicator is preloaded with sources
and inserted into the tumour
Two types
- Manual AL
- Remote AL
Disadvantages:
- Radiation hazard very high
- Increased chance of loss of sources
Manual AL: Implanting non-radioactive
tubes or intracavitary applicators into
the patient, and sources will be
manipulated into the applicators by
means of forceps/tools.
RemoteAL: Pneumatically driven source
transport system which robotically
transports radioactive material between
shielded safe and treatment applicator
that allows elimination in radiation
exposure
4.Based on Source loading technology

SEALED SOURCE
Fully encapsulated
Encapsulation prevents radioactive material from leaking out of the
source and absorbs non penetrating radiation [beta rays, alpha rays and
low energy photons] which otherwise gives rise to high surface dose and
no contribution to therapeutic effect.
Used in LDR/MDR/HDR/PDR
5. Type of source

INTRACAVITARY RADIATION THERAPY

BRACHYTHERAPY SYSTEMS
• Intracavitary brachytherapy for cervical carcinoma was impacted by the development of various
“systems” that attempted to combine empirical, systematic, and scientific approaches.
• A brachytherapy dosimetric system consists of a set of rules for the arrangement of a specific set of
radioactive sources in order to deliver a prescribed dose to a designated point or volume of interest.
• The three basic systems developed during the first half of the last century were:
• Stockholm system (1910)
• Paris method (1919)
• Manchester system (Paterson, 1938).
• A combination of the Paris method and the Manchester system evolved as the
• MD Anderson system (Fletcher et al., 1953).

1. THE STOCKHOLM SYSTEM
• Began in 1910
• It was based on a fractionated course of
radiotherapy delivery using 226Ra sources
over a period of 1 month
• Usually, 2- 3 applications were used
• Each application : 20–30 h.
• Applicator: Intravaginal plate applicator
[lead], and an intrauterine tube [flexible
rubber].
• The Stockholm system advocated an unequal
loading for the uterine and vaginal radium
sources.

• In this system, in order to deliver the prescribed radiation dose,
• 30–90 mg of radium was placed inside the uterus
• 60–80 mg sources were placed inside the vagina.
• Usually, a total “dose” of 6500–7100 mg-h was prescribed for the
treatment of a cervical cancer patient, from which 4500 mg-h was
contributed by the vaginal applicator and the remainder by the
intrauterine tube.

2. THE PARIS SYSTEM
• Institute of Radium of Paris [1919]
• Described by Regaud.
• It prescribed a fixed product of source mass and dur-
ation (in units of mg h) for a given tumor volume
based on the premise that—for any given geometric
arrangement of specified sources—absorbed dose at
any point is directly proportional to the product of
source strength and implant duration.
• Regaud believed that better results were obtained
with small amounts of radium acting over a long
time because more cells would be irradiated during
mitosis.
• The sources were left in place for a minimum of 120
h to deliver from 7200 mg h to 8000 mg h, with the
source activity equally divided between the uterus
and vagina with 3600 mg h to 4000 mg h each.

3. THE MANCHESTER SYSTEM
• 1938
• Tod and Meredith
• The widely used Fletcher-Suit applicator system, the Fletcher
loadings, and the point A and B reference points are all
derived from the Manchester system.
The Classical Manchester System
The original Manchester applicator system consisted of
a rubber intrauterine tandem and two vaginal “ovoids,”
whose ellipsoidal shape was designed to conform to the
isodose curves arising from 226Ra tubes placed along
their long axes.
The applicators were designed for use with 226Ra tubes
2.2 cm long with 1-mm platinum filtration and an active
length between 1 and 1.5 cm.
The small, medium, and large ovoid minimum
diameters were 2, 2.5, and 3 cm, respectively, and are
the same as Fletcher’s small, medium, and large
colpostats.
The preloaded ovoids contained no shielding and relied
on extensive anterior and posterior packing to spare
bladder and rectal tissue.

• This system was the first to use applicators and loadings designed to satisfy specific
dosimetric constraints
• It was the first system to use a radiation field quantity, exposure at point A, rather
than mg-h, to specify treatment.

The reference point A (Fig.) originally
was defined as the point “2 cm lateral
to the centre of the uterine canal and 2
cm from the mucous membrane of the
lateral fornix in the plane of the
uterus.”
This seemingly arbitrary definition
reflected the system developers’ view
that “radiation necrosis is not the
result of direct effects of radiation on
the bladder and rectum, but high dose
effects in the area in medial edge of
the broad ligament where the uterine
vessels cross the ureter.”
They believed the radiation tolerance
of this area, termed the paracervical
triangle, to be the limiting factor in the
treatment of cervical cancer and used
point A exposure to represent its
average dose. *Point p is used by the Mallinckrodt institute of Radiology System to specify
minimum dose to the pelvic lymph nodes. It is located 2 cm superior to the
lateral fornix and 6 cm lateral to the patient’s midline.

• In current practice, point A dose is used to approximate the average or
minimum dose to the tumor.
• Point B, defined to be 5 cm from the patient’s midline at the same level as
point A, was intended to quantify the dose delivered to the obturator
lymph nodes.
• The Manchester ovoid dimensions and applicator loadings were designed
to ensure that the point A dose rate, about 0.52 Gy/hour in modern units,
remained constant for all allowed applicator loadings and combinations.
• The design also ensured that the vaginal loading contribution to point A
was limited to 40% of the total dose.
• Small, medium, and large ovoids were loaded with 17.5, 20, and 22.5 mg of
radium, respectively, to compensate for the greater source-to-point A
treatment distances with the larger ovoids.
• Medium (4 cm long) and long (6 cm) tandems were loaded, os to fundus,
with source trains consisting of 10- and 15-mg sources and 10-, 10-, and 15-
mg sources, respectively, whereas the short tandem (used for cervical
stump cancer) was loaded with a single 20-mg radium tube.

• In contrast to the Paris and Stockholm systems, which prescribed a fixed number of milligram-hours,
equivalent Manchester treatment regimens can deliver from 8,400 to 11,200 mg-h—a variation of
33%.
• As the size of an intracavitary application (i.e., colpostat diameter and tandem length) increases, the
penetration or “lateral throw-off” of the dose distribution increases.
• As colpostat diameter increases from 2 to 3 cm, the vaginal surface dose decreases by 35% relative to
the dose 2 cm from the applicator surface; this is simply a consequence of increasing the source-to-
surface distance.
• Similarly, increasing the tandem length increases the point B contribution relative to the uterine
cavity surface dose; the radioactivity near the ends of the long tandem contributes little to the surface
dose (because of inverse-square law), whereas each tandem segment makes roughly equal
contributions to points remote from the applicator.
• These physical principles underlie the practice of using the largest colpostats and longest tandem
that the patient’s anatomy can accommodate.

Point A was defined as 2 cm from the mucous membrane of
the lateral fornix in the axis of the uterus and 2 cm lateral to
the central canal of the uterus.
Point A was thought to correlate anatomically with the point where the
ureter and uterine artery cross and the tolerance of these structures is
the main limiting factor in the irradiation of the uterine cervix.
Point B was located 5 cm from midline at the level of Point A
and was thought to correspond to the location of the obturator
lymph nodes.
The fixed Points A and B were selected on the assumption that the
absorbed dose in the para-cervical triangle, and not the actual absorbed
dose to the bladder, rectum, or vagina, determined normal tissue
tolerance.
The paracervical triangle was described as a pyramidal-
shaped area with its base resting on the lateral vaginal
fornices and its apex curving around with the anteverted
uterus.

4.THE FLETCHER SUIT APPLICATOR SYSTEM
• The Fletcher system was established at M.D. Anderson Hospital in the 1940s and
the applicator was subsequently developed in 1953.
• The Fletcher applicator system adhered to the basic Manchester design while
incorporating many improvements including internal shielding.
• These shields are located on the medial aspects of the anterior and posterior
colpostat faces and consist of 180-degree and 150-degree disk-shaped 3- to 5-mm-
thick tungsten sectors to shield the rectum and bladder.
• The cylindrical colpostat body has a diameter of 2 cm that can be increased to 2.5
and 3 cm by use of small and large slip-on plastic caps, thereby retaining the
Manchester ovoid dimensions.
• Afterloading capability was added to the Fletcher applicator by Suit et al.
• The Fletcher loadings—15, 20, and 25 mg for small, medium, and large
colpostats, respectively—are similar to those of the Manchester system, whereas
tandem loadings are identical to their Manchester counterparts.
• Because of the similarity of Fletcher loadings (55 to 85 mg) to the Manchester
loadings, point A dose rates are nearly independent of applicator dimensions.
• The shielded Fletcher colpostat was designed to reduce dose to the bladder
trigone and the anterior rectal wall without decreasing irradiation to the
uterosacral and broad ligaments, thereby reducing the need for the extensive
vaginal packing characteristic of Manchester insertions

• When the effects of the intrauterine tandem and the
contralateral colpostat are included, applicator
shielding reduces midline rectal and bladder doses by
21% to 34% relative to conventional treatment-
planning calculations, which ignore shielding.
• Modern versions of the shielded Fletcher colpostat for
LDR BT include the LDR 3M Fletcher-Suit-Delclos
(FSD).
• For HDR BT, the Fletcher- Williamson applicator
duplicates the original Fletcher shielding
configuration.
The isodose curves (C) in the coronal plane 10 mm from the
posterior face of the applicator and (D) in the transverse
plane of the colpostat for a 72 μGy × m 2 × h−1 137 cs tube.

INTRACAVITARY BRACHYTHERAPY REPORTING AND DOSE
SPECIFICATION
1985 2016

The ICRU38 introduced the concept of reference
volume enclosed by the reference isodose surface for
reporting and comparing intracavitary treatments
performed in different centers regardless of the
applicator system, insertion technique, and method of
treatment prescription used.
Specifically, ICRU Report No. 38 recommended that
the reference volume be taken as the 60-Gy isodose
surface, resulting from the addition of dose
contributions from any external-beam whole-pelvis
irradiation and all intracavitary insertions.
The ICRU proposed that this pear- shaped reference
volume (Fig.) be described in terms of its three
orthogonal maximal dimensions: height (dh ), width
(dw), and thickness (dt ), measured in the oblique
coronal and sagittal planes containing the intrauterine
sources.

1.The bladder reference point:
• A Foley catheter is used, and
the balloon is filled with 7 cm3
of radio-opaque fluid.
• The catheter is pulled
downwards to bring the
balloon against the urethra.
• On the lateral radiograph, the
reference point is obtained on
an antero-posterior line drawn
through the centre of the
balloon. The reference point is
taken on this line at the
posterior surface of the
balloon.
• On the frontal radiograph, the
reference point is taken at the
center of the balloon.
• Following figures illustrates the bladder and rectal reference
points recommended by the ICRU.

2.The point of reference for the rectal dose:
On the lateral radiograph, an anteroposterior
line is drawn from the lower end of the
intrauterine source (or from the middle of the
intravaginal sources).
The point is located on this line 5 mm behind
the posterior vaginal wall.
The posterior vaginal wall is visualized,
depending upon the technique, by means of an
intravaginal mould or by opacification of the
vaginal cavity with a radio-opaque gauze used
for the packing.
On the AP radiograph, this reference point is at
the lower end of the intrauterine source or at the
middle of the intravaginal source(s).

3.The lymphatic trapezoid of Fletcher
• A line is drawn from the junction of S1-S2 to
the top of the symphysis
• Then a line is drawn from the middle of that
line to the middle of the anterior aspect of
L4 .
• A trapezoid is constructed in a plane
passing through the transverse line in the
pelvic brim plane and the midpoint of the
anterior aspect of the body of L4.
• A point 6 cm lateral to the midline at the
inferior end of this figure is used to give an
estimate of the dose rate to mid-external
iliac lymph nodes (labeled R. EXT and L.
EXT for right and left external, respectively).
• At the top of the trapezoid, points 2 cm
lateral to the midline at the level of L4 are
used to estimate the dose to the low para-
aortic area (labeled R. PARA and L. PARA).
• The midpoint of a line connecting these two
points is used to estimate the dose to the
low common (labeled R. COM and L. COM)
iliac lymph nodes.

4.The pelvic-wall reference point
• Visualized on an AP and a lateral radiograph
and related to fixed bony structures.
• This point is intended to be representative of
the absorbed dose at the distal part of the
parametrium and at the obturator lymph
nodes.
• On an AP radiograph, the pelvic-wall reference
point is intersected by the following two lines:
a horizontal line tangential to the highest point
of the acetabulum, a vertical line tangential to
the inner aspect of the acetabulum.
• On a lateral radiograph, the highest points of
the right and left acetabulum, in the cranio-
caudal direction, are joined and the lateral
projection of the pelvic-wall reference point is
located at the mid-distance of these points.

The revised definition of point A
• It references its location to the
cervical os (tandem collar,
proximal aspect of the most caudal
tandem source, or a gold seed
implanted in the cervix) rather
than to the lateral fornix.
• Thus, the revised point A
definition does not have the
physical significance of the
classical quantity.

1. TANDEM AND RING APPLICATOR (MODIFIED STOCKHOLM TECHNIQUE)
• The ring applicator, an adaptation of the Stockholm tandem-and-box
technique
• The vaginal ring is perpendicular and fixed to the rigid tandem and rests
against the cervix, secured by gauze packing.
• The metal ring is covered by a plastic cap, which places the vaginal mucosa
0.6 cm from the source path.
• The classical Stockholm loading patterns can be reproduced.
• The short distance from the ring to the vaginal mucosa can result in very
high surface absorbed doses in small areas.
• The ring- tandem angle can push absorbed dose closer to the bladder or
rectum depending on the angle chosen.

• Referred to as a fixed applicator
• Because the tandem is fixed in the middle of the ring, making for a predictable geometry.
• It is ideal for patients with shallow or obliterated vaginal fornices and with non-bulky disease, but
also allows for larger tumors.
• Its predictable geometry makes it a popular alternative to tandem and ovoids.
• With the PDR and HDR applications, there are dwell locations all around the ring where the moving
source will stop and dwell to deliver absorbed dose, which can be activated as needed.

2. TANDEM AND OVOID APPLICATOR (MODIFIED MANCHESTER TECHNIQUE)
• The contemporary Manchester applicators physically
mimic the classical models, with the same ovoid
diameters, but with more tandem lengths and angles
available, and a clamp to hold the ovoids and tandem in
a fixed relationship.
• The whole applicator is stabilized and secured in
contact with the cervix and the vaginal fornices by
gauze packing.
• The ovoids are angled at 400 to the vaginal axis
• Preferable in barrel shaped cervix

3.TANDEM AND OVOID APPLICATOR (MODIFIED FLETCHER TECHNIQUE)
• 1960s
• Used for afterloading (Fletcher-Suit applicator)
• The ovoids are 2.0 cm, 2.5 cm, and 3.0 cm in diameter with and
without shielding.
• The mini-ovoids have a diameter of 1.6 cm and a flat medial
surface. The mini-ovoids, unlike the standard Fletcher ovoids, do
not have shielding, and this—together with their smaller
diameter—produces a higher vaginal surface absorbed dose than
regular ovoids and the potential for higher absorbed doses to the
rectum and bladder.
• Ovoids should fit snugly in the lateral fornix and the largest size
accommodated should be used.

• The Henschke tandem and ovoid applicator was
initially unshielded but later modified with rectal and
bladder shielding
• It consists of hemi-spheroidal ovoids, with the ovoids
and tandem fixed together.
• Sources in the ovoids are parallel to the sources in the
uterine tandem.
• The Henschke applicator can be easier to insert into
shallow vaginal fornices in comparison to
ovoids/colpostats

4.THE TANDEM AND CYLINDER APPLICATORS
• The plastic cylinders vary in diameter from 2.0 cm to 4.0 cm and
have varying lengths and curvatures to accommodate varying
vaginal sizes.
• Also called central vaginal surface applicator [CVS]
• Used in patients with :
• 1. narrow vaginas/upper vaginal stenosis
• 2. Lower vaginal spread of disease

• The major limitation of tandem-cylinder ICBT application is compromise in the dose to the
medial parametrium by virtue of poor lateral throw off of the isodose distribution and
higher doses to organs at risk.
• Additionally, a higher rate of complications can occur due to the increased length of vagina
treated and the proximity of rectum and bladder to the high-dose area.
• Packing cannot be used with cylinders as this would displace the targeted vaginal walls from
the necessary absorbed dose

5.TANDEM AND MOLD APPLICATOR
• Developed at Institut Gustave-Roussy in Paris.
• This process involves fabrication of applicators made from vaginal molds of each patient
• The first step in the preparation of the applicator is the vaginal impression.
• The second step consists of acrylic molded applicator fabrication.
• Vaginal catheters are located on each side of the cervical limits for cervical cancers.
• The position of the vaginal catheters, which is determined by the radiation oncologist, is
drawn according to the tumor extensions.
• These catheters are fixed in place in the applicator.
• One hole is made at the level of the cervical os for the uterine-tube insertion and different
holes are made in the applicator, allowing daily vaginal irrigation and vaginal-mucosal
herniation, which prevent mold displacement.
• The source position is adapted to the tumor topography.
With this technique, no packing is necessary, as the mold
itself expands the vaginal walls.
In this technique, a customized vaginal applicator is made
for each patient from a cervico-vaginal impression.

• These traditional implant systems that arose early in the 20th century were developed to guide the radiation
oncologist in arranging and positioning radium needles within the surgically identified target volume.
• Nomograms and classical system lookup tables were used to prescribe dose and to optimize the implant
geometry.
All interstitial implant systems consist of the following components:
• 1. Distribution rules: Given a target volume, the distribution rules determine how to distribute the
radioactive sources and applicators in and around the target volume.
• 2. Dose specification and implant optimization criteria: definition of prescribed dose.
• 3. Dose calculation aids: These devices are used to estimate the source strengths required to achieve the
prescribed dose rate as defined by the system for source arrangements satisfying its distribution rules. Older
systems (Manchester and Quimby) use tables that give dose delivered as function of treatment volume. The
Paris system makes use of computerized treatment planning to relate absorbed dose to source strength and
treatment time.

• The Manchester System
• The Manchester system was developed in the 1930s and often is called the Paterson-Parker (P-P)
system.
• The use of nonuniform distribution of the radioactivity was recommended to achieve a uniform
dose distribution
• The Manchester dosimetry system for interstitial implants was based on the use of radium sources.
• It consisted of sets of dosage tables to calculate the amount of radium required and sets of distribution
rules to determine how the radioactive material was to be distributed.
• The tables gave the product of the amount of radium (in mg) and the time (in hours) needed to give
1000 roentgens to the treated surface.
• The rules, known as Paterson–Parker Rules, were given for planar moulds, sandwich moulds, cylinder
moulds, planar implants, and volume implants.

Planar implants
• The sources were implanted in a single plane and the dosimetry specified
on a parallel plane, 5 mm from the source’s plane.
• The implanted plane is divided into the periphery and the area.
• Sources are arranged as uniformly as possible on each of these categories,
the proportion depending on the area.
• Distances between sources should not exceed 10 mm.
• The distribution rules for planar implants are laid out in Table.
• A common arrangement for a planar implant is for a row of parallel needles
with the ends 'crossed' by needles at right angles.
• If an end is 'uncrossed' 10% should be deducted from the area when
reading from the table for each uncrossed end.
• For a two-plane implant, planes should be parallel and the average area of
the two planes is used for table reading purposes.
• The total activity should be divided between the planes.
• The dose mid-way between the planes will be low by 10%–30% depending
on the separation and area.

Volume implants
• For volume implants, the implanted volume is
divided into the 'rind' and the 'core’.
• The activity determined from the table is divided
into eight parts, and distributed as laid out in
Table.
• Sources should be spaced as evenly as possible on
each surface and within the volume, with not
more than 10–15 mm between needles.
• A correction is made for 'elongation' when the
volume dimensions are unequal.
• A correction is made for uncrossed ends (–7.5%
per uncrossed end).

Quimby System
• When the Manchester system was developed, the 0.66 and 0.33 mg Ra/cm radium sources were not
available in the United States.
• Therefore, the Quimby system was developed at Memorial Hospital in New York City based on one
linear source activity of 226Ra sources that was available in the United States.
• This system was mostly concentrated on planar implants.
• Similar to the Manchester system, tabulated data have been generated to provide the total source
strength in terms of milligram-hours to provide 1000 cGy to the prescription point, for a uniform
distribution of the source activity.
• The dose specification is in terms of the minimum dose, which occurs in the actual implanted region.
• However, unlike the Manchester system, a higher dose rate (60– 70 cGy/h versus 40 cGy/h) has been
used with the Quimby system for patient treatments. In addition, dose homogeneity is not a factor in
this system.

Paris system
• The Paris system was developed for use in determining the dose distributions around iridium-192 wire
implants.
• It is based on a set of implant rules and then specifies how dose calculations are to be made.
• The system aimed to give low dose rate treatments, typically of 0.5 Gy h–1 to the prescribed reference
dose.
• The placement rules achieve a good even distribution of dose.

Basic principles of the Paris system
• The active sources should be straight and parallel.
• Unlike the Manchester interstitial system, no crossing
sources at the end of the implant are used.
• Ideally, sources should be of equal length and of equal
linear activity.
• They should be placed in a regular geometric pattern with
equal separation between them.
• The separation may vary between 5 mm and 20 mm,
depending on the number of sources, their activity, and the
geometry of the implant.
• If the separation is less than 5 mm it is difficult to implant
the sources in a precise regular manner, and so the dose
will be uneven, and if the separation is over 20 mm then the
high dose volume surrounding each source will be large,
resulting in a greater risk of necrosis.
In cross-section, the implants should have one of three
geometrical arrangements.
The simplest is a single plane implant, with the wires
regularly spaced.
To treat thicker tumours a multiple plane arrangement will
be required. This can either be a triangular pattern, or a
rectangular or square pattern.

Paris system calculation
• The dosimetry is calculated on the central plane.
• The central plane is defined as a plane
perpendicular to the sources midway along the
sources (Fig).
• For an iridium wire implant where the sources are
not of equal length the central plane should be
placed as close to the mean mid-length of the wires
as possible, where the dose rate between the wires
due to their length contribution will be at its
maximum.

Basal dose points
• The basal points are defined on the central plane and are
located at the points of minimum dose rate between the wires.
The arithmetic mean of all the basal dose rates is used to
calculate the basal dose rate for the implant as a whole.
• The basal points can be defined geometrically. For a single
plane, the minimum dose will be midway between each pair of
wires.
• For a triangular arrangement of wires the basal dose rates are
calculated at the centre of gravity (centroid) of each triangle (the
intersection of perpendicular bisectors of the sides of the
triangles), and for a square geometrical arrangement the basal
dose rates are calculated at the centre of each square.
Reference dose rate
• The reference dose rate of the implant is defined as 85% of the
mean basal dose rate.
• the treatment volume is defined as the volume enclosed by the
85% reference isodose.

Dimensions covered by the treated
volume
• As the isodoses will 'pull in' between
the wires it is necessary to allow
extra coverage to give sufficient
margins for the treatment.
• The length of the treated volume is
approximately 0.65 times the length
of the sources.
• Hence for a particular target volume
length, the sources should be about
20–30% longer, at each end, than the
target volume (Fig. 3.3a).

• TG43 U1 formalism which is now used in commercial planning
systems.
• TG43 U1 is based on measured or measurable quantities (TLD or
Monte Carlo generated) produced by a source in a water equivalent
medium.

ICRU 58 Recommendations
• The ICRU had set guidelines for reporting in Interstitial
brachytherapy in the report Dose and Volume Specification for
Reporting Interstitial Therapy (ICRU 1997).
• In this ICRU 58 report, parameters are recommended for
reporting, which are closely related to those of the Paris system.
• The recommendations cover the following items: description of
volumes; description of sources; description of technique, source
pattern, and time pattern; total reference air kerma; and
description of dose and dose distribution, prescribed dose,
minimum target dose (MTD), mean central dose (MCD), and high
and low dose regions.

• INTERSTITIAL BRACHYTHERAPY APPLICATORS

INTERSTITIAL APPLICATORS WITH AND WITHOUT A TANDEM AND
COLPOSTATS
Interstitial implantation is helpful in patients with
1. Bulky infiltrative extensive disease
2. Anatomical unfavourable topography [asymmetrical tumor
growth narrow vagina or an obliterated endo-cervical canal]
3. Vaginal spread of disease
4. Recurrent disease.
Prefabricated perineal templates are available, through which
needles are inserted and after- loaded and allows for a predictable
distribution of needles across the entire perineum.
TRUS is used to guide insertion of the applicator
Free-hand interstitial implantation is also used selectively for small
volume vaginal and parametrial disease.
.

1.MUPIT
• The MUPIT (Martinez Universal
Perineal Interstitial Template)
accommodates implantation of multiple
pelvic-perineal malignancies.

2. SYED NEBLETT
• The Syed-Neblett is a commercially available template system
• These are particularly suited for treatment of extensive vaginal
disease as they are combined intracavitary and interstitial systems.
• The vaginal obturators that accompany the template are used to
treat the vaginal surface, and the vaginal obturator needles can be
strategically loaded to encompass disease from the fornices to the
introitus.
• Along with the intracavitary uterine tandem, the obturator needles
can also be advanced directly into the cervix as an interstitial
application and can be essential in delivering high absorbed doses
to the cervix thereby preventing a central low-dose region,
especially in those circumstances in which an intra-uterine tandem
cannot be inserted.
• The tandem can extend absorbed dose superiorly throughout the
uterine cavity, provide additional absorbed dose to the parametria,
and increase the absorbed dose centrally in the implant where it is
most needed

3. VIENNA APPLICATOR
• This is a modified ring applicator with holes
in the ring for needle guidance parallel to the
uterine tandem and the ring fixed to the cervix
through the tandem and vaginal packing.
• The Vienna applicator is used for treating
parametrial residual disease after CTRT with
unfavourable topography
• Additional absorbed dose in residual disease
can be provided with the addition of a
number of needles implanted in those parts of
the lateral tumor extension not covered by the
intracavitary pear-shaped absorbed-dose
pattern.

4. VIENNA II
• A “Vienna II” applicator has been suggested for distal
parametrial disease with an add-on to the ring,
providing holes for additional oblique needles.

5.UTRECHT APPLICATOR
• There are also modified ovoid applicators (Utrecht
applicator) using needles that are guided through
holes in the ovoids, enabling better coverage of
disease in the parametrium
• These applicators can be used to extend and improve
lateral and superior coverage of the target volume by
approximately 10 mm.

COMBINED INTRACAVITARY AND INTERSTITIAL BRACHYTHERAPY
• Combined intracavitary and interstitial brachytherapy is recommended if the residual disease at the cervix extends into
the parametrium beyond the medial third at the time of BT.
• The principle of ICIS application includes insertion of interstitial needles/tubes in addition to the standard ICBT procedure.
• The needles/tubes are inserted through the array of holes in the ovoids/ring into the medial parametrium, in parallel
direction to the tandem.
• Usually, 4/5 cm length of needle is inserted into the parametrium from the surface of the vaginal applicators (ovoid/ring).
• Commonly used applicators include the Vienna applicator, Utrecht applicator, Venezia applicator or Tandem with
perineal template (Syed-Neblett or MUPIT).
• The interstitial needles in desired positions are inserted to a depth of around 4-5 cm from the surface of the ring/ ovoid.
• Needle channels should be numbered preferably in clock-wise direction.

BRACHYTHERAPY PROCEDURE STEPS
Timing of Brachytherapy
• Brachytherapy insertions are performed according to the volume of disease
present.
• In some patients with small-volume disease, brachytherapy might be possible
from the beginning or can be used early during the course of external-beam
irradiation and chemotherapy.
• Patients with more bulky and extensive disease require the completion of 5
weeks of concurrent external-beam and chemotherapy, producing sufficient
disease regression to facilitate optimal applicator geometry in relation to target
and organs at risk.

• Figure 1 and 2 show an example of a clinical
drawing which can be utilized for disease
mapping and objective documentation in
terms of extent of disease involving cervical
lips, vagina, parametrium, etc., with different
color codes/patterns and measurements in
various directions.
• The clinical drawing has been adopted and
modified based on the (EMBRACE) research
protocol and (Gyn GEC-ESTRO) guidelines
and ICRU 89 recommendations
• This drawing should be utilized for
documentation of disease at diagnosis, and at
the time of each brachytherapy session.

PATIENT PREPARATION
• Most patients will have had preceding external beam
radiotherapy and so attention to
• electrolyte balance with control of gastrointestinal symptoms
with appropriate antidiarrhea medication, diet and fluid
replacement is important.
• Many patients with cancer of the cervix have low-grade
anaemia and there is good evidence that this impedes the
response to treatment.
• While the role of transfusion is not clear before brachytherapy
their haemoglobin should be assessed and maintained above
11.5 g/dl.
• Patients other than those treated with outpatient HDR
techniques are at increased risk of thromboembolism while
immobile with applicators in situ and should be on
prophylactic measures.
All patients should undergo a
Complete blood count
Renal function tests,
Liver functions,
Coagulation Parameters,
Chest radiograph
As part of the assessment of general
status and fitness for therapy
Shaving
Antiseptic vaginal douches

ANAESTHESIA
• For brachytherapy to be optimal, patients must have proper
sedation and analgesia to facilitate applicator placement and
treatment planning. It allows cervical canal dilatation and
adequate relaxation of the pelvic floor and vaginal muscles for
adequate vaginal packing and a reproducible brachytherapy
application at every fraction.
• Various options available – General anaesthesia, Conscious
sedation [iv fentanyl and midazolam] , Regional anaesthesia
[spinal].
• Insertions can take place in an operating room or departmental
brachytherapy suite.
• To begin the process, the patient is evaluated for anaesthesia
options prior to the actual procedure. Once cleared, the
procedures can begin.

Brachytherapy procedure
1. The patient is placed in the lithotomy position and
the vulval area cleaned with antiseptic.
2. Examination under anaesthetic should be
performed both per vaginum and per rectum to
assess the clinical extent of tumour and any
extension into the vagina or parametrial tissues.

3. A bladder catheter is inserted, and a vaginal and
perineal preparation performed. The foleys bulb is
inflated with 7cc of radiopaque dye if Xray based
or normal saline if planned for CT/ MR-based
dosimetry. The bladder is filled with 150ml of
distilled water [facilitate the ultrasound imaging]. The
catheter should be pulled down so that the bulb rests
against the trigone of the bladder.
4. The endo-cervical canal is localized, measured, and
dilated and a tandem inserted with a given length
(flange) and angle.

• The cervix should be identified using a
speculum and grasped with Volsellum
forceps.
• It may be difficult in the case of an
advanced tumour where there is extensive
necrotic tumour tissue replacing the cervix
and it may only be possible to retain
adjacent vaginal tissue.
• The cervical canal should be identified
using a blunt uterine probe, which is
passed into the uterine cavity and the
length of the cavity can at this point be
measured.

• Having identified the cervical canal this should
be dilated with appropriate dilators.
•
Using the dilator, the uterine cavity size can be
checked, and the intrauterine tube chosen.
• At this point, it is also necessary to assess the
vaginal size for the appropriate vaginal
applicator to be chosen.
•
The dilator should then be replaced by the
intrauterine tube followed by the vaginal source.
5. Ultrasound guidance is useful, especially if
there is difficulty finding the canal or if there
is concern over perforation and also confirms
version of the uterus

6. The largest diameter ovoids that will
fit through and fill appropriately is
chosen
7. The colpostats are pushed against the
lateral vaginal fornices.
8. The applicator is clamped together.

9. Then insertion of vaginal packing to fix the
applicator against the cervix and push away
the bladder and rectum as much as possible.
10. A rectal retractor can be used in addition to
packing.
11. A T bandage is used to fix the applicator for
HDR systems and for LDR/MDR and PDR
systems, an anchoring corset is often used.
12. A rectal catheter is inserted for image contrast
.

13. The patient is carefully taken from the
dorsal lithotomy position and insertion
stirrups into the legs-down position.
14. An external fixation device, such as a
perineal bar, is used by some to limit
applicator movement.
15. Localization imaging is then performed.

• Verification imaging is a vital component of the
procedure.
• As a minimum this should be anteroposterior and
lateral orthogonal X-ray films with a magnification
marker;
• Ideally CT imaging will be undertaken and where
MR is available then the soft tissue definition is
undoubtedly superior with MRI.
• Where HDR is used, then imaging is essential
before each fraction.

IDEAL APPLICATION
1. The tandem should bisect the ovoids on AP and lateral
images
2. On lateral images, ovoids should not be displaced down
from the flange and should be symmetric or overlap one
another
3. The tandem should be ½ - 1/3rd the distance between the
Symphysis Pubis and sacral promontory [equidistant
between bladder and rectosigmoid]
4. Superior tip of tandem should be located below the sacral
promontory within the pelvis
5. Radio-opaque packing should be placed anterior and
posterior to the ovoids and superior packing indicates
unwanted inferior displacement of applicator.

As GTV and CTV for BT change significantly
during treatment, time frame for assessment
of GTV and CTV for BT is specified in this
report:
At time of diagnosis GTVD, CTVD and at time
of BT GTVB, CTVB.
Furthermore, CTV for BT is defined related
to risk for recurrence:
High risk CTV and intermediate risk CTV.

MRI BASED PLANNING
Gross tumor volume at time of
brachytherapy (BT)
• Includes macroscopic tumor
extension at time of BT as detected
by clinical examination
• As visualized on MRI: high signal
intensity mass(es) (FSE, T2) in the
cervix/corpus, parametria, vagina,
bladder, and rectum.
High-risk CTV for BT
• Encompasses macroscopic
tumor burden [GTV]
• Whole cervix and extra-
cervical tumor extension at
time of BT.
• Residual tissue(s) as defined by
palpable indurations and/or
residual gray zones in the
parametria, uterine corpus,
vagina or rectum, and bladder
on MRI.
Intermediate-risk CTV
• Microscopic tumor load, with a
safety margin of 5–15 mm.
• In AP direction, up to 5 mm
• In CC directions margin of 10
mm [Os sup, vagina inferiorly]
• In lateral direction, a 10 mm
margin into both parametria,.
• In case of endocervical or
lateral macroscopic tumor
growth, an additional margin
of 5 mm is applied, into the
direction of potential spread.

• BRACHYTHERAPY DOSE , PLANNING ,
DELIVERY

Brachytherapy therapy dose prescription
• The prescription depends on the EBRT and BT schedules.
• The combined EBRT and brachytherapy dose is generally expressed in terms of equivalent dose at 2 Gy
per fraction (EQD2) assuming α/β of 10 Gy for tumor and 3 Gy for OARs.
• Currently, a minimum dose of 75 Gy (range: 75-85 Gy) EQD2 to point A depending on the stage, or a
minimum dose of 85 Gy (range: 85-90 Gy) EQD2 to target (CTVHR D90) should be delivered.
• Dose constraints (measured as EQD2) for the ICRU bladder point and ICRU recto-vaginal point
(previously known as ICRU rectal point) are 95 Gy and 65-70 Gy, respectively.
• Similarly, in 3D planning 2 cm3 doses for bladder and rectum should be restricted to less than 95 Gy and
75 Gy, respectively.

• Various HDR fractionation regimens have been used for cervical cancer brachytherapy.
• It is recommended to limit the dose per fraction to less than or equal to 7 Gy.
• Overall treatment time [OTT] for the combination of EBRT ± concurrent CT and fractionated HDR BT
should not exceed 8 weeks [less than 56 days].
• When an interstitial template is used for delivering boost doses, the most commonly used dose
prescription is 4 Gy per fraction for 4-6 fractions (16-24 Gy) prescribed to the reference isodose volume
depending on residual disease burden, OARs’ doses and institutional practice .

Treatment Planning
Low Dose Rate Treatment Planning
• The prescription to point A and B
• Selecting the loadings for LDR intracavitary placement and specifying dose is an important aspect of treatment
planning.
• In order to achieve the appropriate dose rate, 35- to 40-mg Ra eq, or approximately 5- to 6-mg Ra eq per cm are
placed in a 6- to 8-cm tandem.
• The most typical superior to inferior tandem loading is generally 15/10/10 mg Ra eq.
• Ovoid loading is generally based on diameter and the presence of shielding, and, on average, a loading of 10 to 20 mg
Ra Eq results in a vaginal surface dose rate of between 70 to 100 cGy per hour.
• The cumulative vaginal surface dose should be limited to 120 to 140 Gy.
• The dose rate is typically between 40 to 45 cGy per hour to Point A with the FSD system, and the total dose to Point A
is usually 40 to 45 Gy in two 48-hour implants.
• The classical goal was to achieve 6,500 mg Ra hours.
• This equated to a point A cumulative dose of >80 Gy.

High Dose Rate Fractionation and Treatment Planning
• The HDR optimization of sources results in an approximation of LDR dosimetry.
• The biological effect (particularly to normal tissues) of a nominal dose of radiation will be significantly greater when it
is given with HDR as compared with LDR brachytherapy, and this depends on the fraction size.
• This factor leads to the need for increasing fraction numbers when using HDR versus LDR therapy.
• To select an HDR schedule that may be comparable with LDR treatment, it is helpful to consider the fractionation and
dose-rate effects and, specifically, applications of the linear quadratic (LQ) model used to describe these effects.
• The LQ model has been used to describe a biologically effective dose (BED), given as
• BED = total dose [1+ (dose per fraction (α/β)]
• where α/β describes the varying influence of fraction size on radiation effects in different tumors and normal tissues.
• This is then converted to the EQD2 using BED/1.2 for the α/β = 10 for tumor.

• The use of the LQ equation allows one to calculate and approximate the biological equivalency
of HDR-based to traditional LDR-based dosing.
• Using the LQ equation, tumor doses of 80 to 85 Gy to point A in LDR equivalent would result
in BEDs of 96 to 102 Gy10.
• Conservatively, accounting for late-responding normal tissue tolerances, LDR equivalent doses
of 70 Gy to the rectum and 75 Gy to the bladder correspond to BED 120 Gy3 and 125 Gy3,
respectively.

• The starting point for HDR loading schemes attempt to
recapitulate the familiar and symmetrical “pear-shaped” dose
distribution typically used in LDR brachytherapy.
• This isodose distribution can be obtained by designating a
series of dose points surrounding the tandem and colpostat and
using the dosimetry program to calculate source dwell times in
each source location to create the desired dose distribution
(inverse planning).
• After creating a standard plan, this plan should be “optimized”
to allow sculpting of the dose away from normal tissues and to
optimize coverage of the CTV as seen on CT or MRI.
• The physician may specify the relative weight of each selected
dwell position in the brachytherapy apparatus.

STEPS IN HDR BRACHY PLANNING
• Physician will delineate a target volume (a CTV) and critical structure
contours for planning
• Catheter is reconstructed on the CT for each channel in the applicator,
typically starting at the tip end of the applicator.
• The catheter should be reconstructed sufficiently beyond the area to be
treated.
• The length of each catheter must be defined for the planning system to
properly index the channel position.
• Source dwell position are activated, spaced 5 to 10 mm apart depending on
the type of applicator used.
• The treatment plan is typically normalized to a set of points.
• ● These points will receive on average 100% of the prescribed dose.
• ● The dwell times for all active positions remain equal after normalization.
• The plan can also be optimized.
• Optimization adjusts the dwell times such that the dose at each normalization
point is closer to 100% of the prescribed dose, with the average dose among
all points still equal to the prescribed dose.

Applicator reconstruction
• Applicator reconstruction is the process of defining all the
source channels on the brachytherapy planning images.
• Errors in applicator reconstruction can lead to geometric
and dosimetric uncertainties.
• Hence applicator commissioning is a prerequisite for
minimizing errors during the applicator reconstruction
process.
• The applicator commissioning includes verification of the
• (i) applicator geometry using phantom scans or technical
drawings,
• (ii) source path and dwell positions by autoradiography or
imaging of the source inside the applicator.
The applicator reconstruction can be classified into two types:
1.Direct digitization when the source channels or marker wires are
visible in the images.
2.Library-based digitization in which fixed-geometry applicators are
merged with the patient images based on fusion of reference points or
by direct positioning of the applicator shape into the images
according to visible structures of the applicator, such as parts of the
source path or the outer surface of the applicator.

SOURCE LOADING PATTERNS, PLANNING AND OPTIMIZATION
• The standard loading pattern for uterine and vaginal sources is essentially derived from radium loading
of the Manchester system.
• With the advent of miniature sources (192Ir), after loading techniques and stepping source technology,
the source loading can be simulated to that of radium loading used in the Manchester system so as to
achieve a standard pear-shaped distribution.
• An example of loading patterns for standard intracavitary BT application (tandem-ovoids/ring)
commonly used is given in Table.

HDR brachytherapy is usually performed with single-stepping source after loaders.
These after- loaders contain a small, mostly 192Ir, source mounted at the end of a flexible steel wire, which
is transported under computer control in previously implanted applicators.
The machine is programmed to position the source at predefined positions—the so- called dwell positions—
in the applicators.
The time the source spends at each dwell position—the so-called dwell time—can freely be chosen.
This enables optimization of the dose distribution by optimization of the dwell times over all dwell
positions in the implant.
So catheter-based optimization techniques are :
• Dose point optimization
• Geometric optimization

• Plan evaluation and documentation of various
DVH parameters should be based on GEC
ESTRO/ICRU 89 recommendations.

Reporting
• BT prescription reporting
should be as per ICRU 89
recommendations. Minimum
standards (level 1) for
reporting are detailed in Table
4.

TREATMENT TOXICITY
• Most acute side effects are controllable
with supportive care
• The frequency of late complications
requiring hospitalization or surgical
interventions ranges from 5 to 14%.
•
• Most complications occur within the first 5
years; however, a low risk of urinary
complications persists over a 25- year
period.
• Vaginal side-effects are predominantly related
to stenosis and shortening of the vagina, which
can be prevented to some degree by the use of
vaginal dilators.
• Rectal complications includes rectal frequency
and bleeding due to telangiectasia (<5%).
Rectal complications mean time to being 2–3
years.
• Bladder side-effects will include frequency and
haematuria from bladder telangiectasia.
Occasionally, urethral stricture may also
develop requiring dilatation [<5%]. Bladder
problems developing on average a year or two
later.

Brachytherapy procedure related complications:
•
1. Perforation: Perforation during BT is commonly seen as a false passage through the fornices,
missing the uterine canal or perforation through the wall of the uterus or cavity. These are often
missed on orthogonal X-ray-based planning imaging, and reported literature suggests up to 15%
perforation rates. These can be prevented using real-time ultrasonography (transabdominal US) intra-
operatively during the BT procedure.
• 2. Bleeding: Bleeding from the tumor or procedure related injury is encountered during the
procedure or removal of the BT application. In the majority of situations, the bleeding can be arrested
with conservative management including vaginal gauze packing and antifibrinolytics (tranexamic
acid). If there is considerable blood loss, replacement is done by blood transfusions. If the bleeding is
due to a vaginal tear, repair by suturing should be done under anesthesia.
• 3. Vaginal injuries: Vaginal injuries in the form of mucosal abrasions and tears related to the
procedure may be seen. The treatment includes repair of the tear by suturing, avoiding BT treatments
for 7-10 days and antibiotic therapy.
• 4. Bladder/rectal/bowel injuries: These are very rare and may require specialist surgeon care.

Follow-up
• After the completion of planned therapy, response evaluation is usually done after 3-4 months.
• Patients with residual disease at the 1st follow-up undergo close follow-up over the next 2-3
months.
• Patients with a complete response are reviewed every 3-4 monthly for the first 2 years and 6
monthly until at least 5 years and annually thereafter.
• Follow-up evaluation includes general and pelvic examination, imaging when indicated and
investigations to document and manage late toxicities if any.

Brachytherapy in Carcinoma Cervix

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