described about brachytherapy reference volumes, different reference points and brachytherapy systems

1. ICRU 38
Presenter: Dr. Masthan Basha
Moderator: Dr. Pranabandhu Das

2. INTRODUCTION
• Brachytherapy is a method of treatment in which sealed
radioactive sources are used to deliver radiation at a short
distance by interstitial, intracavitary, or surface application.
• Advantage:
• A high radiation dose can be delivered locally to the tumor
with rapid dose falloff in the surrounding normal tissue

3. HISTORICAL SYSTEMS
• Based on clinical experience
• Stockholm system
• Paris system
• Manchester system
• "system" denotes a set of rules taking into account the source
strengths, geometry and method of application in order to
obtain suitable dose distributions over the volume(s) to be
treated

4. Stockholm system
• The intrauterine rod-shaped applicator is loaded
with 53-88 mg radium (74 mg ).
• The vaginal applicator consists of a flat box
containing 60-80 mg radium (70 mg )
• Classically, the two applicators are not fixed to
each other, but fixed or semi-fixed combinations
also developed
• The vaginal applicator is held against the cervix
and lateral fornices by careful and systematic
gauze packing.
• Typically 2or3 applications are given with 3-week
intervals
• Each application lasting for 27-30 hours.
• Modifications of the Stockholm method, using
larger amounts of radium, allow for application
times of 10-18 hours at each treatment.

5. PARIS SYSTEM
• Typical radium application for a
treatment of cervix carcinoma
consisting of: 3 individualized
vaginal sources (one in each
lateral fornix and one central in
front of the cervical os), 1
intrauterine source made of 3
radium tubes (in so called
tandem position).
• Possible variations of the Paris
system include:
• 2 vaginal sources (or only one) in
case of a narrow vaginal cavity;
• only 2 intrauterine radium tubes
(or only one) in case of short
uterus.

6. • In both systems, applications have been reported in terms of
"mg-h" (milligram hours), i.e., the product of the total mass or
radium contained in the sources (in mg) and of the duration of
the application (in hours).

7. Manchester System
• The Manchester system is one of the oldest
and the most extensively used systems in
the world.
• It is characterized by doses to four points:
point A, point B, a bladder point, and a
rectum point.
• The duration of the implant is based on the
dose rate calculated at point A
• Point A is defined as a point 2 cm lateral to
the central canal of the uterus and 2 cm up
from the mucous membrane of the lateral
fornix, in the axis of the uterus.
• Point B is defined as being in the transverse
axis through points A, 5 cm from the
midline.

8. MANCHESTER SYSTEM
• In clinical practice, dose calculations are often made from
radiographs and point A is taken 2 cm up from the flange of the
intrauterine source and 2 cm lateral from the central canal . Point B
is defined to be 3 cm lateral to point A.
• Ideally, point A represents the location where the uterine vessels
cross the ureter.
• It is believed that the tolerance of these structures is the main
limiting factor in the irradiation of the uterine cervix.

9. • The critics point out the following limitations of point A:
• (a) it relates to the position of the sources and not to a specific
anatomic structure
• (b) dose to point A is very sensitive to the position of the ovoid
sources relative to the tandem sources, which should not be the
determining factor in deciding on implant duration
• (c) depending on the size of the cervix, point A may lie inside the
tumor or outside the tumor . Thus, dose prescription at point A
could risk underdosage of large cervical cancers or overdosage of
small ones.

10. ICRU 38
• The International Commission on Radiation Units and
Measurements (ICRU) has recommended a system of dose
specification that relates the dose distribution to the target volume,
instead of the dose to a specific point .
• The dose is prescribed as the value of an isodose surface that just
surrounds the target volume.

11. • Description of the Technique
• Total reference air kerma
• Description of the reference volume
• Absorbed dose at reference points
• Time-dose pattern
Data for Reporting Intracavitary Therapy

12. • Applicator type
• Source type, source strength and arrangement.
• Loading technique
Description of the Technique

15. Total Reference Air Kerma
• Previously when radium was used , the product of the "quantity of
radioactive material" and the duration of the treatment given
(mg·h)
• New radioactive sources are specified in terms of "reference air
kerma rate".
• The reference air kerma rate of a source is the kerma rate to air, in
air, at a reference distance of 1 meter, corrected for air attenuation
and scattering.
• For this purpose this quantity is expressed in μGy-m²/hr at one
metre.
• The total reference air kerma is the sum of the products of the
reference air kerma rate and the duration of the application for
each source.

16. • Total Reference Air Kerma (TRAK)
TRAK= Σ si . Ti
• Si = Reference air kerma rate for each source.
• ti = Irradiation time for each source.
• This quantity is analogous to mg-h.

17. DESCRIPTION OF THE REFERENCE
VOLUME

18. Definition of Target Volume for Only
Intracavitary Treatment

19. Definition of Target and Treatment Volumes for
Only Intracavitary Treatment

20. Definition of Target and Treatment Volumes for
Combined Intra cavitary and External Beam
Treatment

21. • The reference volume is defined as the volume enclosed by the
reference isodose surface.
• In order to facilitate intercomparisons between radiotherapy
centers, it is necessary to agree upon a reference dose level
• The value of this isodose surface, based on the Paris experience , is
set at 60 Gy for classical low dose rate therapy.
• The prescription isodose value of 60 Gy includes the dose
contribution from the external beam.
• So, isodose surface value for only intracavitary brachytherapy : 60
Gy– EBRT dose
• Ex: 60Gy- 40 Gy = 20 Gy
Description of the Reference Volume

22. • The reference volume for the intracavitary part of the treatment is
pear shaped with its longest axis coincident with the intrauterine
source.
• This reference volume is defined by means of three dimensions
• (i) the height (dh) is the maximum dimension along the intrauterine
source and is measured in the oblique frontal plane containing the
intrauterine source
• (ii) the width (dw) is the maximum dimension perpendicular to the
intrauterine source and is measured in the same oblique frontal
plane.
• (iii) the thickness (d t ) is the -maximum dimension perpendicular to
the intrauterine source and is measured in the oblique sagittal
plane containing the intrauterine source.
• The reference volume is approximated by (dh × dw × dt) cm3.

23. Determination of the Reference
Volume

24. • Bladder Point
• Rectal Point
• Lymphatic Trapezoid of Fletcher
• Pelvic Wall Points
Absorbed Dose at Reference Points

25. Bladder Point
• The bladder point is localized by using a Foley catheter, with the
balloon filled with 7 cc of a radiopaque fluid.
• The catheter is then pulled downwards to bring the balloon against
the urethra
• On the lateral radiograph, the bladder point is obtained on a line
drawn anteroposteriorly through the center of the balloon, at the
posterior surface
• On the frontal radiograph, the bladder point is marked at the center
of the balloon

30. • Points corresponding to the following nodes:
• Mid-external iliac lymph nodes
• Low common iliac nodes
• Low para aortic nodes
Lymphatic Trapezoid of Fletcher

33. Time Dose Pattern
• Dose rate and duration of the application should be stated.
• When more than one application is performed, the duration of each
as well as the time interval(s) between them.
• Similarly, when external beam therapy and intracavitary therapy are
combined, the time-dose schedule of the whole treatment should
be reported.

34. Conclusion & Final Recommendations
• 1) Any method of specification will be meaningful only to the extent
that the treatment technique has been completely described
• 2)The total reference air kerma should be stated. For a given
method of application the doses delivered at the different tissues or
organs are directly proportional to the total reference air kerma.
• 3)It is recommended that the reference volume be described in
terms of the height, width and thickness of the volume enclosed in
the 60 Gy isodose surface for cervix-carcinoma treatment by low
dose rates. For higher dose rates a dose level lower than 60 Gy has
to be selected.

35. • 4)The absorbed dose at reference points in organs at risk (rectum,
bladder) should be determined (computed or measured) and
expressed in well-codified ways to provide additional safety limits.In
addition, the absorbed dose(s) at reference point(s) related to bony
structures (lymphatic trapezoid and pelvic-wall reference points)
should also be reported.
• 5) the time-dose pattern should be completely specified.

37. THANK U