overview of brachytherapy principals

1. PRINCIPALS
OF
BRACHYTHERAPY
Presenter :-
Dr. Shashank bansal
PGT Radiotherapy
Dr.B.Boroah Cancer Institute

2. DEFINITION
 Derives from the Greek word ‘brachy’ – meaning short-distance
Brachytherapy involves placing small radiation sources internally, either
into or immediately next to the tumor in a geometrical fashion , allowing
precise radiation dose delivery (1)
1) Stewart AJ & Jones B. In Devlin Brachytherapy: Applications and techniques. 2007.

3. HISTORY
 1896 :- Radioactivity was described by Becquerel
 1898 :- Marie curie extracted radium from pitchblende ore
 1901 :- Danlos and Bloc performed first radium implant
 1931 :- The term brachytherapy proposed first time by Forsell
 1940-1950 :- Brachytherapy rules were developed and followed
 1953 :- Aterloading technique first introduced by Henschke in New
York – removed hazard of radiation exposure. Also Ir-192 used first
time by Henschke
 1953 :- LDR brachytherapy became the gold standard
 1968 :- HDR brachytherapy was introduced
 1970s :- Brachytherapy is established as a safe and effective
standard of care for many gynecological cancers

4. ADVANTAGES
 High dose of radiation is delivered to tumor in short time.So
biologically very effective
 Normal tissue spared due to rapid dose fall off
 Better tumor control
 Radiation morbidity minimal
 Acute reactions appear when treatment is over; so no
treatment breaks. Also radiation reactions localized &
manageable
 Treatment time short – reduces risk of tumor repopulation
 Therapeutic ratio high

5. DISADVANTAGES
 Invasive procedure
 Radiation hazard due to radioisotopes (in olden days due to
preloading techniques, now risk decreased )
 General anesthesia required
 Dose inhomogeneity is higher than EBRT (but acceptable if
rules followed)
 Because of greater conformity, small errors in source
placement can lead to extreme changes from the intended
dose distribution

6. TYPES OF BRACHYTHERAPY
 Classification
 Based on Duration of implant
 Based on Source position
 Based on Source loading pattern
 Based on Dose rate

7. TYPES OF BRACHYTHERAPY
 Classification
 Based on Duration of implant
 Based on Source placement
 Based on source loading pattern
 Based on Dose rate

8. DURATION OF IMPLANT
 Temporary- Dose is delivered over a short period of time
and the sources are removed after the prescribed dose has
been reached. The specific treatment duration will depend on
many different factors, including the required rate of dose
delivery and the type, size and location of the cancer. Eg :-
Cs137, Ir192
 Permanent- also known as seed implantation, involves placing
small LDR radioactive seeds or pellets (about the size of a grain of rice) in
the tumor or treatment site and leaving them there permanently to
gradually decay. Eg :- I125 ,Pd103, Au198

9. SEED ANATOMY

13. TYPES OF BRACHYTHERAPY
 Classification
 Based on Duration of implant
 Based on Source placement
 Based on Source loading pattern
 Based on Dose rate

14.  Interstitial - the sources are placed directly in the target
tissue of the affected site, such as the prostate or breast.
 Contact - involves placement of the radiation source in a
space next to the target tissue.
 Intracavitary – Consists of positioning applicators bearing radioactive sources
into the body cavity in close proximity to target tissue eg :- Cervix
 Intraluminal – Consists of inserting single line source into a body lumen to treat
its surface &adjacent tissue.
 Surface (Mould) – (Plesiocurie/Mould therapy) Consists of an applicator
containing array of radioactive sources designed to deliver a uniform dose
distribution to skin/mucosal surface.
 Intravascular – Inserting a single line source to Blood vessels to treat the
layers of blood vessel

15. Interstitial Breast Implant Interstitial Implant in soft tissue
sarcoma

16. Martinez Universal Perineal
Interstitial Template (MUPIT)
Syed-Neblett template

17. Esophageal Brachytherapy Applicator @ BBCI

18. Intracavitary Applicators @ BBCI

19. TYPES OF BRACHYTHERAPY
 Classification
 Based on Duration of implant
 Based on Source placement
 Based on Source loading pattern
 Based on Dose rate

20.  Pre-loading :- Inserting needles/tubes containing radioactive material directly
into the tumor
 After-loading :- First, the non-radioactive tubes inserted into tumor
 Manual After Loading :- Ir192 wires, sources manipulated into applicator by means of forceps
& hand-held tools
 Remote After Loading :- consists of pneumatically or motor-driven source transport system

21. PRELOADING (PROS & CONS)
 Advantage:
 – Loose & flexible system(can be inserted even in distorted cervix)
 – Excellent clinical result
 – Cheap
 – Long term results with least morbidity (due toLDR)
 • 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
 – Optimization not possible

22. AFTER LOADING (MANUAL)
 Advantages
 Circumvents radiation protection problems of preloading
 Allows better applicator placement and verification prior to source placement.
 Radiation hazard can be minimized in the OT/bystanders as patient loaded
in ward.
 Advantages of preloading remain as practised at LDR.
 Disadvantages:
 specialized applicators are required.

23. Manual After Loading

24.  Advantages :
 No radiation hazard
 Accurate applicator placement
 -ideal geometry maintained
 -dose homogeneity achieved
 -better dose distribution
 Information on source positions available
 Individualization & optimization of treatment possible
 Higher precision , better control
 Decreased treatment time- opd treatment possible
 Chances of source loss nil .
 Disadvantages :
 Costly
AFTER LOADING (REMOTE)

26. HDR Microselectron Rmote Afterloading unit @ BBCI (using Ir192 source )

27. Emergency
button
Hand cranks if
everything else fails
Safe, holding the active
source and a dummy source
Optopair to verify
source position
Indexer face
with 18
source
channels
Transfer
tube
connector
Stepper motor
with shaft encoder (additional
DC motor available for source
retraction in case of failure)
Indexer
Radiation monitor

28. Remote After Loading Treatment Console Room @ BBCI

29. APPLICATORS
HENSCHKE
MANCHESTER

30. TYPES OF BRACHYTHERAPY
 Classification
 Based on Duration of implant
 Based on Source placement
 Based on Source loading pattern
 Based on Dose rate

31.  Low-dose rate(LDR)- Emit radiation at a rate of 0.4–2 Gy/hour.
 Medium-dose rate (MDR)- characterized by a medium rate of dose
delivery, ranging between 2-12 Gy/hour.
 High-dose rate (HDR)-when the rate of dose delivery exceeds
12 Gy/h.
 Pulsed-dose rate (PDR) - involves short pulses of radiation, typically
once an hour, to simulate the overall rate and effectiveness of LDR
treatment. (1ci)
 Ultra low dose rate - Dose range 0.03 to 0.3 Gy/Hr

32. HDR V/S LDR
 Advantages :-
 Radiation protection
 Allows shorter treatments times
 HDR sources are of smaller diameter than the cesium sources that are
used for intracavitary LDR ,hence reduced need of Anaesthesia
 HDR makes treatment dose distribution optimization possible
 Disadvantage
 Radiobiological
 Limited experience
 The economic disadvantage
 Greater potential risks

33. Remote After Loading HDR unit With connectors

34. Layout of Brachytherapy Facility

35. KEY ELEMENT
 Obsolete or historical
 226Ra, 222Rn
 • Currently used sealed sources
 137 Cs, 192Ir, 60Co, 125I, 103Pd,198Au, 90Sr.
 • Developmental sealed sources
 241Am, 169Yb, 252Cf,145Sm.

36. IDEAL ISOTOPE
 Easily available & Cost effective
 Gamma ray energy high enough to avoid increased energy deposition in bone & low
enough to minimise radiation protection requirements
 Preferably monoenergetic: Optimum 300 KeV to 400 KeV(max=600 kev)
 Absence of charged particle emission or it should be easily screened (Beta energy
as low as possible: filtration)
 Half life such that correction for decay during treatment is minimal
 – Moderate (few years) T1/2 for removable implants
 – Shorter T1/2 for permanent implants
 Moderate gamma ray constant (determines activity & output) &also determine
shielding required.

37.  No daughter product; No gaseous disintegration product to prevent physical damage
to source and to avoid source contamination
 High Specific Activity (Ci/gm) to allow fabrication of smaller sources & to achieve
higher output (adequate photon yield)
 Material available is insoluble & non-toxic form
 Sources can be made in different shapes & sizes: Tubes, needle, wire, rod, beads
etc.
 Should withstand sterilization process
 Disposable without radiation hazard to environment
 Isotropic: same magnitude in all directions around the source
 No self attenuation

38. SOURCE IN USE

40. NEW IN MARKET

41. PATIENT SELECTION
 Small size tumors (3 – 5 cm)
 Depth of penetration/thickness < 1.5 – 2 cm
 Histology: moderately radiosensitive tumors (ca squamous cell) ; some
adenocarcinomas
 Early stage (localized to organ)
 No nodal/distant metastasis
 Location : accessible site with relatively maintained anatomy
 Absence of local infection & inflammation

42. RULES OF THE GAME
Interstitial
• Manchester
• Quimby
• Paris
• Memorial
Intracavitary
• Manchester
• Paris
• Stockholm
Surface/Mould
• Manchester
Objectives:-
•To determine the distribution & type of radiation sources to provide optimum dose
distribution
•To provide complete dose distribution in irradiated volume
Components :-
•Distribution rules
•Dose specification and optimization
•Dose calculation aid

43. PARAMETERS MANCHESTER QUIMBY PARIS COMPUTER
Linear strength Variable Constant Constant Constant
Source
distribution
Planar implant:(periphery)
Area <25 cm- 2/3 Ra;
25-100 cm- ½ Ra; >100 cm-
1/3
Volume
implant::Cylinder:belt-4
parts,core-2,end-1
Sphere:shell-6,core-2
Cube :each side-1,core-2
Uniform
Uniform
Uniform
Line sources
parallel
planes
Uniform
Line sources
Parallel or
cylinderic
volumes
Spacing line
source
Constant approx. 1 cm apart
from each other or from
crossing ends
Same as
Manchester
Constant,
Selective
Separation 8-
15 mm
Constant
Selective
Crossing needles Required to enhance dose at
implant ends
Same Crossing
needles not
used;active
length 30-
40% longer
Crossing
needles not
used;active
length 30-40%
longer

45. CLINICAL DEMO !!!

46. Breast
Indications: Boost after BCS & EBRT
 Postoperative interstitial irradiation alone of
the primary tumor site after BCS in selected
low risk T1 and small T2N0 (PBI)
 Chest wall recurrences
As sole modality As Boost to EBRT
Patient choice: cannot come for 5-6 wks treatment :
 Distance
 Lack of time
Close, positive or unknown margins
Elderly, frail, poor health patient EIC
Large breasts: unacceptable toxicity Younger patients
Deep tumour in large breast
Irregularly thick target vol.

47.  T.V.: Primary Tumor site + 2-3 cm margin
 Dose: As Boost: 10-20 Gy LDR
 AS PBI: 45-50 Gy in 4-5 days LDR (30-70 cGy/hour)
 34 Gy/10#, 2# per day HDR
 Technique:
 Localization of PTV: Surgical clips (at least 6)
 USG, CT or MRI localization, Intraop USG
 During primary surgery
 Guide needle technique or
 Plastic tube technique using Template
 Double plane implant
 Skin to source distance: Minimum 5 mm

49. INTRACAVITARY
 MANCHESTER SYSTEM
 To define the treatment in terms of dose to a point.
 Criteria of the point:
 Anatomically comparable
 Position
 where the dosage is not highly sensitive to small alteration in applicator position
 Allows correlation of the dose levels with the clinical effects
 To design a set of applicators and their loading which would give the same
dose rate irrespective of the combination of applicators used
 To formulate a set of rules regarding the activity, relationship and
positioning of the radium sources in the uterine tumors and the vaginal
ovoids , for the desired dose rate

50. 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 fornix
POINT B
 Rate of dose fall-off laterally
 Imp. Calculating total dose-Combined with EBRT
 Proximity to important OBTURATOR LNs
 Same level as point A but 5 cm from midline
 Dose ~20-25 % of the dose at point A

52. MIND IT !!
In order that point A receives same dosage rate no matter which ovoid combination is used ,it is
necessary to have different radium loading for each applicator size
Dose rate 57.5 R/hr to point A
Not more than 1/3 dose to point A must be delivered from vaginal radium
 Largest possible ovoid should be used to reduce dose to mucosa
 Longest possible tandem (not > 6 cm)
 Better lateral throw off
 Smaller dose to mucosa
 Dose to point A- 8000R
 Dose to uterus wall -30,000R
 Dose to vaginal mucosa-20,000R
 Dose to recto-vaginal septum- 6750 R
 Dose limitation
 BLADDER <80 Gy
 RECTUM <75 Gy

53. IDEAL APPLICATION
 Tandem
 1/3 of the way between S1 –S2 and the symphysis pubis
 Midway between the bladder and S1 -S2
 Bisect the ovoids
 Marker seeds should be placed in the cervix
 Ovoids
 against the cervix (marker seeds)
 Largest
 Separated by 0.5-1.0 mm
 Axis of the tandem-central
 Bladder and rectum -should be packed away from the implant

54. PARIS SYSTEM
 Single application of radium
 Two cork colpostats (cylinder) and an intrauterine tube
 Delivers a dose of 7000- 8000 mg-hrs of radium over a period of five
days(45R/hr) (5500mg/hr
 Equal amount of radium used in the uterus and the vagina
 Intrauterine sources
 3 radioactive sources, with source strengths in the ratio of 1:1:0.5
 colpostats
 sources with the same strength as the topmost uterine source

55. STOCKHOLM SYSTEM
 Fractionated course of radiation delivered over a period of one month.
 Usually 2-3 applications, each for a period of 20- 30 hours (repeated 3weekly)
 Intravaginal boxes -lead 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 or
2500mg/hr/#)

56. DRAWBACKS OF STOCKHOLM AND PARIS SYSTEM
 Long treatment time
 Discomfort to the patient
 No dose prescription

57. ICRU 38
DOSIMETRIC INFORMATION FOR REPORTING
 Complete description
 Technique
 Time-dose pattern
 Treatment prescription
 Total Reference Air Kerma
 Dose description
 Prescription points/surface
 Reference dose in central plane
 Mean central /peripheral dose
 Volumes: Treated/ point A/ reference volume
 Dose to Organs at Risk : bladder, rectum

58.  REFERENCE VOLUME
 Dimensions of the volume included in the corresponding isodose
 The recommended dose 60 Gy
 TREATED VOLUME
 Pear and Banana shape
 Received the dose appropriate to achieve the purpose of the treatment, e.g., tumor
eradication or palliation, within the limits of acceptable complications
 IRRADIATED VOLUME
 Volumes surrounding the Treated Volume
 Encompassed by a lower isodose to be specified, e.g., 90 – 50% of the dose
defining the Treated Volume
 Reporting irradiated volumes may be useful for interpretation of side effects outside

59. CLINICAL DEMO !!!

60. THANKS