This document provides an overview of different brachytherapy systems that have been developed over time for delivering radiation internally or close to the surface of the body. It describes several early systems from the 1930s-1960s including the Paterson-Parker system, Quimby system, Paris system, and Manchester system. It also covers the Stockholm, Paris, and Manchester methods for intracavitary cervical cancer treatment. Later sections discuss the Paris system improvements, computer planning systems, and the current International Commission on Radiation Units and Measurements reporting system.
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Aim of the work
1.Investigate the physical properties of electron beams
at different beam energies.
2.Evaluate the accuracy of dose calculated by
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different field configurations.
Dosimetric Evaluation of High Energy Electron Beams Applied in RadiotherapyAYMAN G. STOHY
Electron-beam therapy: is used to treat superficial tumors at a standard 100 cm source-to-surface distance (SSD). Characteristics of electron beams from an Elekta PreciseTM linear accelerator are presented at a nominal SSD of 100 cm. However, certain clinical situations require the use of an extended SSD. The effects of extended source-to-surface distance (SSD) on the electron beam dose profiles were evaluated for various electron beam energies 6, 8, 10,12 and 15 MeV and the accuracy of various output correction methods was analyzed on an Elekta PreciseTM linear accelerator using a radiation field analyzer (RFA). Effective SSDs was evaluated for field sizes ranging from 6×6, 10×10, 14×14 and 20×20 cm2 for various energies.
Aim of the work
1.Investigate the physical properties of electron beams
at different beam energies.
2.Evaluate the accuracy of dose calculated by
Treatment Planning System (TPS) and measured for
different field configurations.
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2. SYSTEMS OF BRACHY:-OUTLINE
Systems of implant
dosimetry
Systems of intracavitary
therapy
Paterson Parker system
Quimby System
Paris system
Computer System
Stockholm system
Paris system
Manchester system
International commission on
radiation units and
measurements system
3. 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.
High radiation dose to the tumour.
Rapid dose fall off in the surrounding normal tissue.
4. PATERSON-PARKER SYSTEM
Developed by Ralston Paterson (radiation oncologist)
and Herbert Parker (physicist) in the 1930s
Aim: To deliver a uniform dose(within 10%) to a plane
or volume.
Non - uniform distribution of sources
5. PLANAR IMPLANT
Technique used: When tumour spread is under the skin / lesion can be
sandwiched between parallel planes of implant.
Effectively irradiate tissues of 1 cm thickness (0.5 cm on either side).
Reference dose plane is 0.5 cm from source plane.
The dose at 0.5 cm is the minimum dose throughout the 1 cm thick
slab.
The high spots immediately surrounding each source are assumed to
be tolerated by tissues and its presence is ignored.
7. PLANAR IMPLANT
Distribution laws:
-------------------------------------------------------------------------
Area Fraction of Activity on
(cm2) Periphery Center
-------------------------------------------------------------------------
< 25 2/3 1/3
25-100 1/2 1/2
> 100 1/3 2/3
8. PLANAR IMPLANT
Needles spacing: not more than 1 cm. from each
other or from the crossing ends.
For uncrossed ends: effective area has to be
reduced by 10% for each uncrossed ends. Fig.B
effective area is 0.9 x b x c and for Fig. C, it is 0.8 x
b x d
9. PLANAR IMPLANT
Multiplanar implant:
Planes should be parallel to each other.
Two plane implant: 1.5/2.0/2.5 cm.
Separation is more than 1.0 cm between the planes then
Plane Separation Multiplication Factor
1.5 1.25
2.0 1.40
2.5 1.50
10. VOLUME IMPLANT
When the lesion > 2.5 cm thick.
Two plane implant leads to low dose region midway
between the planes.
Tumours are implanted using 3D shapes:
Sphere
Cuboid
Cylinder.
11. VOLUME IMPLANT
Volume is divided into two parts: rind and core.
Sphere: rind → shell/surface,
Cuboid: rind → six faces,
Cyl: rind → belt &2 ends
Total amount of radium activity is divided into eight equal
parts:
Sphere: Shell – 6 parts, core - 2 parts
Cylinder: Belt - 4 parts, core - 2 parts, each end - 1 part
Cuboid : Each side 1 part, core 2 parts
12. VOLUME IMPLANT
Needles should be placed as uniformly as possible, not
more than 1 cm apart.
At least 8 needles in the belt and 4 in the core.
Target volume effectively treated is reduced by 7.5% for
each uncrossed end.
13.
14. Manchester system
Dose and dose rate:- 6,000 R to 8,000 R in 6-8 days
(1,000 R/day; 40 R/h)
Linear activity Variable:- 0.66 and 0.33 mg Ra Eq/cm
15. QUIMBY SYSTEM
Quimby System (1932)
Developed by Edith Quimby at New York Memorial Hospital.
Uniform distribution of sources of equal linear activity
Results:
Non uniform distribution
Hot spots in central region
Planar Implant:
Quimby table gives the mg.hrs required to deliver 1000R at the central
plane.
Stated dose is the max. dose in the plane of implant
Volume Implant:
Stated dose is the min. dose within the implanted volume.
16. MEMORIAL SYSTEM
Extension of the Quimby System
Based on computer generated dose
distributions
Uniform source strength spaced 1 cm. apart
Tables are generated to provide information
of mg- hrs required to deliver 1000 rads at 0.5
cm from the source plane for planar implant.
17. PARIS SYSTEM
Developed in early 1960s by Pierquin, Dutreix
and Marinello.
Sources of uniform activity
Placed parallel and equidistant
Square or triangular pattern for volume implant
Source spacing varies between 8-15 mm for
short implant and 15-22 mm for long implants
For target thickness < 12 mm, single plane
implant and for > 12 mm, double plane implant.
18. Basal Dose Rate (BD), is defined as the arithmetic mean of the
local minimum doses midway through an array of equally spaced
implants . For double plane implants, the basal dose rate is the
dose rate in the central cross-sectional plane at the intersection
of perpendicular bisectors projected from the side of the
triangle for triangular arrangement and at the geometric
centre for square arrangements.
Reference Dose Rate (RD) is equal to 85% BD and is the dose
rate used for dose prescription.
Ref. Dose Rate (RD) = 0.85 x BD
19.
20. Paris system
Dose and dose rate:- 6,000 cGy to 7,000 cGy in 3-11
days (25 cGy/h to 90 cGy/h)
Linear activity Constant:- 4-14 µGy · m2 · h-1/cm
22. COMPUTER SYSTEM
Source of uniform strength are implanted.
Spaced uniformly (e.g. 1.0 to 1.5cm) with larger spacing
for larger implant size.
Cover the entire target volume.
Result of uniform activity source :- ‘’HOTTER’’ in
middle than periphery (as in Quimby & Paris system)
23. COMPUTER SYSTEM
Dose specified at isodose surface that is just
surrounding the target .
Better to implant a larger volume, then to select a
lower value of isodose curve to increase the coverage.
Active length of line source should be suitably longer (
≈ 40% longer) then the length of target volume due to
uncrossed ends.
24. COMPUTER SYSTEM:- Advantages
Older dosimetry system are based on idealized implants
conforming to certain distribution rule which are
seldom realised.
In Computer system possible to preplan complete
isodose distribution corresponding to final source
distribution.
Rapid turnaround time.
Isodose curve may be generated in any arbitrary plane.
Isodose pattern can be magnified & superimposed on an
implant radiograph for viewing distribution in relation to
patients anatomy.
25. INTRACAVITARY BRACHYTHERAPY
Three methods were developed between 1910 &
1938 for treatment of carcinoma cervix by
intracavitary brachytherapy.
1. Stockholm Method : 1914
2. Paris Method : 1919
3. Manchester System: 1938
26. 26
STOCKHOLM METHOD
Fractionated course of radiation
delivered over a period of one month.
Three insertions each of 22 hours
separated by 1-3 weeks.
Intra-vaginal boxes Silver or gold
Intrauterine tube -flexible rubber
Unequal loading
30 - 90 mg of radium in uterus
60 - 80 mg in vagina
Total prescribed dose -6500-7100 mg Ra
4500 mg Ra contributed by the
vaginal box
Dose rate-110R/hr
27. 27
PARIS METHOD
Devised by Claudine Regaud & Antone Lacassagne.
Single application of radium for 120 hours.
Two cork colpostats (cylinder) with 13.3 mg radium in each and
an intrauterine tube of silk rubber containing 33.3 mg of radium.
Delivers a dose of 5500 mg-hrs of radium over a period of five
days at dose rate of 45R/h.
28. 28
The historical 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).
29. 29
DRAWBACKS OF PARIS AND STOCKHOLM
SYSTEMS
Long treatment time
Discomfort to the patient
No dose prescription
30. 30
MANCHESTER SYSTEM
Developed by Todd & Meredith in 1938
NEED:
1. Recognized that unique dosage system was
necessary.
2. Defined the treatment in terms of dose to a point.
3. Stressed the importance of constant dose rate.
4. Introduced reproducible technique which could
aim at better tumour control and less radiation
morbidity.
5. Defined point A and point B.
31. POINT A
PARACERVICAL TRIANGLE where initial lesion of
radiation necrosis occurs
Area in the medial edge of broad ligament where the
uterine vessel cross over the ureter
The point A: fixed point 2cm lateral to the center of
uterine canal and 2 cm above from the mucosa of the
lateral vaginal fornix
Revised point A: 2 cm superior from lower end of
central radium tube(external cervical os) and 2 cm
lateral from uterine canal(1953).
32.
33. 33
POINT B
Same level as point A but 5 cm from
midline
Proximity to obturator LNs
Dose ~15-20 % of the dose at point A
POINT H
A line connecting middle of sources in
vaginal ovoids on A-P radiograph and
move 2 cm plus the radius of ovoid
superiorly along the tandem from
intersection of this line with intrauterine
source line and then 2 cm lateral on either
side of the tandem (IJROBP.48(1),201-
11,2000).
34. 34
POINT P:
Used by Mallinckrodt Institute of Radiology
System to specify minimum dose to pelvic lymph
nodes.
It is 6 cm to Rt and Lt of patient midline in same
plane as of classical point A.
35. Localisation of bladder and rectum performed using
radiographs with contrast media in the bladder and
rectum.
Maximum dose to bladder and rectum should be, as
far as possible, less than the dose to point A(80% or
less of the dose to point A).
37. The ICRU introduced the concept of reference volume
enclosed by the reference isodose surface for
reporting, communicating and comparing
intracavitary treatments performed in different
centers regardless of the applicator system, insertion
technique, and method of treatment prescription
used.
38. 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.
39. The ICRU proposed that a pear-shaped reference
volume 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.
40.
41. DATA NEEDED FOR REPORTING
ICRU
Description of the technique used.
Total reference Air Kerma
Description of the Reference Volume – 60 Gys.
Dimensions of the reference volume.
Absorbed dose at reference points
Bladder point
Rectal point
Lymphatic trapezoid of fletcher
Pelvic wall points
Time dose pattern
42. 42
BLADDER POINT
Frontal radiograph:- Center of the balloon
Lateral radiograph:- At the posterior surface on a
line drawn anteroposteriorly through the center of
the balloon.
43. 43
RECTAL POINT
Frontal radiograph:- Mid point of ovoid sources or lower end
of intrauterine source
Lateral radiograph:-Line drawn from the middle of ovoid
sources, 0.5cm behind the posterior vaginal wall.
45. Pelvic wall points
AP X-ray:- At the intersection of a horizontal tangent
to superior aspect of acetabulum and a vertical line
touching the medial aspect of acetabulum
Lateral view:- Highest middistance points of the right
and left acetabulum.
46. Time dose pattern
Duration and time sequence of the implant should be
recorded.