Brachytherapy Final

DR. MANOJ KUMAR B
MODERATOR:PROF. S.C. SHARMA
DEPTT. OF RADIOTHERAPY AND ONCOLOGY
PGIMER,CHANDIGARH
BRACHYTHERAPY PRINCIPLE AND METHODS

BRACHYTHERAPY
Type of radiation treatment in which radioactive sources are arranged in such a fashion that radiation is delivered to the tumor at a short distance by interstitial, intracavitary or surface application.

CLINICAL ADVANTAGES
High biological efficacy
Rapid dose fall-off
High tolerance
Tolerable acute intense reaction
Decreased risk of tumor population
High control rate
Better cosmesis
Minimal radiation morbidity
Day care procedure

LIMITATIONS & DISADVANTAGES
Difficult for inaccessible regions
Limited for small tumors (T 1 _T 2 )
Invasive procedures, require GA
Higher dose inhomogeneity
Greater conformation –small errors in placement of sources lead to extreme changes from the intended dose distribution
Radioactive hazards (not now)
Costly

SELECTION CRITERIA
Easily accessible lesions
Early stage diseases (Ideal implant ≤ 5 cm)
Well localized tumor to organ of origin
No nodal or distant metastases
No local infections or inflammation
Favorable histology- mod. diff. i.e. SCC
Non DM / HTN
Proliferative/ ulcerative lesions preferred

INDICATIONS
RADICAL RADIATION
Skin malignancies- BCC, SCC
Head & neck cancers
Ca cx
Ca prostate
BOOST AFTER EXT.RT±CCT
Head & neck cancers
Ca Breast
Esophagus
Anal canal

INDICATIONS...
PERIOPERTIVE
STS
Ca Breast
POSTOP
Ca Endometrium
Ca cx
Ca Breast
PALLIATIVE
Bronchogenic Ca
Biliary duct malignancy
Ca Esophagus
Recurrent tumors
BENIGN
Keloids / Pterygium
OTHERS
Endovascular/Rad. stent

CLASSIFICATION Classification Schemes Positioning of Radionuclide Dose rate of irradiation Duration of irradiation Loading pattern

CLASSIFICATION
SURGICAL APPROACH / POSITIONING
SOURCE IN TUMOR
INTERSTITIAL
INTRACAVITARY
INTRALUMINAL
ENDOVASCULAR
SOURCE IN CONTACT BUT SUPERFICIAL
SURFACE BRACHYTHERAPY/ MOULAGE
DURATION OF IRRADIATION
TEMPORARY-Cs 137 ,Ir 192
PERMANENT-I 125 ,Au 198

DOSE RATE(ICRU 38)
LOW DOSE RATE (LDR)
0.4-2 Gy/hr
Bed confinement
LDR A/L : Cs 137
MEDIUM DOSE RATE (MDR)
2-12 Gy/hr
HIGH DOSE RATE (HDR)
> 12 Gy/hr
ULTRA LOW DOSE RATE
0.01-0.3 Gy/hr
ROUGHLY
LDR – 10 Gy/day
MDR -10 Gy/hr
HDR – 10 Gy/min

ADVANTAGES
LDR
HDR
Predictable clinical effects
Superior radiobiological role
Less morbidity, control is best
Well practised since long
Minimum intersession variability in dose distribution
SHORT T/T TIME
Geometry well maintained
Better patient compliance / comfort
Day care procedure
OPTIMIZATION
NO RADIATION HAZARDS
SMALL APPLICATOR
Less tissue trauma
Better packing

MDR BRACHYTHERAPY
ADVANTAGES
Comparative shorter T/T time
One time treatment can be used
Patient convenience
Radio biologically acceptable nearer to LDR Brachytherapy
DISADVANTAGES
Late complications increases if correction not done

SOURCE LOADING TECHNIQUE
PRELOADING SYSTEM
Live sources
ADVANTAGES
Clinical results are best
Affordable
Long term results with lesser morbidities
DISADVANTAGES
Radiation hazards
Special instruments
Difficult application / hasty
Geometry not maintained
? Optimization

AFTER LOADING TECHNIQUE
MANUAL
Avoids radiation protection issue of preloading
Better applicator placement
Verification prior to source placement
Min. radiation hazard
Advantages of preloading
REMOTE CONTROLLED
No radiation hazard
Accurate placement
Geometry maintained
Better dose distribution
Highly precise
Short T/T time
Day care procedure
Mainly used for HDR

INTERSTITIAL BRACHYTHERAPY
Sealed Radioactive sources directly implanted into the tumor in a geometric fashion
First suggested by Alexander Graham Bell
ADVANTAGES
Higher local dose in shorter time
Rapid dose fall
Better tumor control
Lesser radiation morbidities
Superior cosmetics
Functional preservation of organs

INTERSTITIAL BRACHYTHERAPY…
DISADVANTAGES
Radiation hazards in older days
Costly
Not applicable to inaccessible areas
INTENTION OF TREATMENT
Always RADICAL
As radical brachytherapy alone (smaller lesions)
Local boost in combination with EBRT (larger lesion)
NEVER USED FOR PALLIATION

SELECTION CRITERIA
Easily accessible lesions, at least from one side
Early stage disease
T 1 -T 2 and sometimes early T 3
Ideally total size of implant ≤ 5 cm
Non DM /HTN
No local infection
Proliferative and ulcerative lesions preferred

CLINICAL APPLICATIONS
Head & neck tumors
Early stage oropharyngeal cancers
Ca breast- Boost /PBI
Ca prostate
Soft tissue sarcoma
Gynecologic malignancies
Ca anal canal and rectum
Ca lung and pancreas

TYPES OF INTERSTITIAL IMPLANTS ACCORDING TO SIZE/LOCATION/PROXIMITY OF TUMOR TO NORMAL STRUCTURES
TEMPORARY
Radioactive sources removed after desirable dose has been delivered
Rigid stainless steel needles/flexible Teflon / nylon guides/plastic tubes
Preloaded/After loaded
PERMANENT
Preloaded – rigid needle eg. Ra 226 ,Cs 137
After loaded – Manual/ Remote
Advantages
Flexibility of implant design
Reduction of radiation exposure levels resulting in more accurate placement of needles and guides

SYSTEMS OF IMPLANT DOSIMETRY
OBJECTIVES OF TREATMENT PLANNING
To determine the distribution & type of radiation sources to provide optimum dose distribution
To provide complete dose distribution in irradiated volume
SYSTEM USED
Paterson-Parker (Manchester) system
Quimby system (Memorial) system
Paris system – Pierquin, Chassagne , Dutreix and Marinello
Computer System

SYSTEMS OF IMPLANT DOSIMETRY
These system designed during times when computers were not available for routine planning
Extensive table & elaborate rules of source distribution were devised to facilitate the process of manual treatment planning
These systems differ in rule of implantation, definition of dose uniformity & method used in reference dose specification

RULES OF INT.IMPLANT SYSTEM 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

COMPONENTS-CLASSICAL SYSTEM
DISTRIBUTION RULES : given a target volume, distribution rules determine how to distribute RA sources & applicators in & around target volume
DOSE SPECIFICATION & IMPLANT OPTIMIZATION CRITERIA : Each system has a definition of prescribed dose
Above 2 criteria determine dose homogeneity, normal tissue sparing, no. of catheters implanted & margins around target
DOSE CALCULATION AIDS : Older systems used tables that give dose delivered per mg Ra-Eq-hr as a function of treatment volume or area
Recent Paris system uses computerized treatment planning to relate absorbed dose to source strength & treatment time

PRINCIPLE-MANCHESTER SYSTEM FEATURES DOSE & DOSE RATE 6000-8000 R in 6-8 days (1000 R/day; 40 R/hr) UNIT / USE OF RADIUM mg Ra hr – defined as amount of radium to give specified dose in 1 hr DOSE SPECIFICATION CRITERA Effective minimum dose 10% above absolute minimum dose LINEAR ACTIVITY Variable: 0.66 and 0.33 mg RaEq/cm

QUIMBY SYSTEM
Developed by Edith Quimby et al
Dose 5000-6000 R in 3-4 days
Equal linear intensity (mg RaEq/cm) needles distributed uniformly (fixed spacing) in each implant, although spacing selected in 1-2 cm range acc. to implant size
Quimby tables (Nomogram ) give mg RaEq-hr to deliver stated exposure of 1000 R as function of T.V. or area (5000-6000 R over 3-4 days; 60-70 R/hour)
No clear description of rules for distributing Ra needles
Crossing recommended; peripheral needles placed on or beyond T.V. boundaries
Dose specification criteria inconsistent
NOT RECOMMENDED FOR CLINICAL USE

PARIS SYSTEM- PRINCIPLES
RADIOACTVE SOURCES
Rectilinear/parallel -arrangement so that centers are located in the same plane which is perpendicular to the direction of sources- CENTRAL PLANE
Equidistant
Linear activity-uniform and identical
Source geometries
Linear- single-plane implants
Squares/Equilateral triangles- two plane implants

PARIS SYSTEM FEATURES DOSE AND DOSE RATE 6000 -7000 cGy in 3-11 days DOSE PRESCRIPTION POINT Average of the minimum doses in the region defined by the source REFERENCE DOSE & DOSE GRADIENT 85 % of the BASAL DOSE 15 % between the Reference dose and the Basal dose RA SOURCE PLACEMENT Reference isodose volume covers the treated volume

PERMANENT IMPLANTS
ADVANTAGES
DISADVANTAGES
Less accessible sites
Cont. ultra low dose rate>Max biological effectiveness
Better tissue heal
Better effect in slow and radio resistant tumors
Improved mobility
Environmental issue
Dosimetric uncertainties > Later part of T/T becomes less effective
Source displacement
Large tumor > Difficult procedure and geometry
Radio biologically less effective for rapidly proliferating tumors

COMPUTER SYSTEM
Implant system evolved through use of computers
Implantation rules: Sources of uniform strength
Spaced uniformly (1-1.5 cm), larger spacing for larger implants to cover entire T.V.
Active length 30-40% longer than Target length as ends uncrossed
T.V.: sufficient safety margins; peripheral sources implanted on outer surface
Dose specified by isodose surface that surrounds target
Whole planning with help of computers

COMPUTER DOSIMETRY
Possible to preplan implants & complete isodose distribution corresponding to final source distribution
Rapid & fast; helps modify implant
Isodose patterns can be magnified & superimposed on implant radiograph
Localization of sources:
Orthogonal Imaging method
Stereo-shift method
CT
Dose Calculation:
No. of milligrams or millicurie in implant
Location of each source with respect to dose calculation point
Type of isotope being used
Filtration of the encapsulation

COMPUTER DOSIMTERY
Dose Computation:
Dose calculation Formalisms’ (AAPM TG 43 algorithm)
Use Sievert Integral directly
Precalculated dose tables
For Radium & other long lived sources: Dose rates in form of isodose curves
For Iridium & relatively short lived implants: Computer calculates cumulative dose with decay correction

Oral Cavity:
LIP:
Indications: T1-2N0 Lesions
T.V.: All visible & palpable tumour with 5-10 mm margin
Dose: 50-70Gy in 5-7 days LDR
Technique:
Rigid afterloading needles maintained in place by Template
Classical plastic tubes
Spacers to decrease dose to gingiva, teeth & other lip

CLINICAL APPLICATIONS…
Buccal Mucosa:
Indications:
Brachytherapy alone indicated for small (<4cm), well-defined lesions in anterior 2/3 rd
As boost after EBRT for larger lesions
T.V.: GTV + margins
Dose: Alone 65-70 Gy
Boost 25-30 Gy
Technique: Guide Gutter Technique: Lesion < 2cm
Plastic tube technique : For other lesions

Oral Tongue:
Indications: T1 N0, T2 N0 < 3cm lesion
T.V.: GTV + 5 mm margin
Dose: Alone:60-65 Gy LDR
Boost 20-25 Gy after EBRT dose of 45-50 Gy
Techniques: Guide-gutter technique
AP X-ray

Floor of Mouth :
Indications: T1-2N0 lesions, ≥ 5 mm away from mandible
Dose: Techniques same as for Tongue implants
Complication: Osteoradionecrosis:5-15%
Oropharynx:
Indications: Ca BOT , soft palate, tonsillar fossa & vallecula usually as boost after EBRT
Lesions < 5 cm (after EBRT)
T.V.: GTV + 10 mm margin
Dose: Tonsillar fossa-25-30 Gy; BOT 30-35 Gy
Technique: Classical Plastic Loop technique

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
Moderator: Prof. S. C. Sharma 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.

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

Prostate:
Indications
Brachytherapy as monotherapy:
Stage T1-2a & Gleason score 2-6 & PSA ≤ 10 ng/ml
As boost after EBRT
Stage T2b, T2c or Gleason score 7-10 or PSA > 10 ng/ml
For brachytherapy, Prostate size < 50 cc
Exclusion criteria:
Life expectancy < 5 yrs
Large or poorly healed TURP defect
Distant Mets or operative risk
T.V.: Whole prostate within capsule + 2-3 mm margin
Methods: Permanent Implant (I 125 or Pd 103 ) or
Temporary Implant (Ir 192 )

Technique for Permanent implant
Retropubic approach with I 125 seeds- Disappointing results
Modern technique: Transperineal Approach
TRUS guided
Two step approach
Volume study of prostate
Computer planning
Seed positioning
Coverage check -USG & Flouroscopy
Check Cystoscopy
Post-implant image based dosimetry

Dose:
I 125 : 145 Gy as sole RT
100-110 Gy as boost to 40-50 Gy EBRT
Pd 103 : 125 Gy as sole RT
90-100 Gy as boost to 40-50 Gy EBRT
Temporary Implants with Ir 192 (LDR or HDR):
Procedure same as above; lesser no. of plastic catheters required (8-15)
Dose:
LDR 30-35 Gy seeds left for 3 days(Boost to 45 Gy EBRT)
HDR 20-25 Gy, 4-6 Gy/#(Boost to 45 Gy EBRT)

Soft tissue Sarcomas (using Ir 192 or I 125 )
Indications:
As sole postop RT:
completely resected intermediate or high grade tumours of extremity or superficial trunk with -ve margins
As boost to postop EBRT:
Intermediate or high grade sarcoma with +/- margins
Postop pts with small lesions & +ve/uncertain margins
Deep lesions
Low grade sarcomas
T.V.: GTV + 2-5 cm margin
GTV based on preop MRI & clinical findings
Dose: LDR (Ir seeds or wires) as sole treatment 45-50 Gy in 4-6 days
As boost to 45-50 Gy EBRT: 15-25 Gy in 2-3 days

Technique:
Usually performed at time of surgery
Basic or sealed end temporary implant technique

Brain: Permanent or temporary (using I 125 or Ir 192 seeds/wires )
Indications:
As boost to EBRT or recurrence
Anaplastic astrocytoma or GBM, unifocal, well cicumscribed, peripheral lesions & < 5 cm in diameter
T.V.: Contrast enhancing area on MRI +/- 5mm margin
Dose: LDR 50-60 Gy, 0.4-0.5 Gy/hr
Technique: Planning CT/MRI done

Ca Anorectum
Indications: As boost to EBRT/ChemoRT
If T.V. doesnot exceeds 1/2 circumference, 5 mm thick, 5 cm long i.e. T1-2 & small T3 lesions
T1N0 adenocarcinoma of rectum 3-10 cm above anus
T.V.: Visible palpable tumor+5 mm
Dose: LDR 15-20 Gy at 0.3-0.6 Gy/hr
Technique: Guide needle technique with template

Gynecological Tumors ( Ir 192 LDR or HDR)
Indications:
Ca Cervix
Ca Endometrium
Postop local recurrence
Ca Vagina & Vulva
Radical BT in select early lesions (T1-2N0)
Boost after EBRT in large lesions (T2-3N1)
Technique:
Guide-gutter technique
Blind plastic tube implant
(transperineal technique)
Plastic or guide needles

CLINICAL APPLICATION – CA CX
ABS Recommendations
Bulky primary disease
Prior hysterectomy-inability to place tandem
Post hysterectomy
vault recc./cut-through hysterectomy/cervical stump presentation
Extesive parametrial involvement
Distorted anatomy
Narrow vagina & fornices
Extensive / Distal vaginal wall involvement
Re-irradiation after recurrences
Prior course of RT to area of interest

PERINEAL IMPLANTS
Martinez Universal Perineal Interstitial Template (MUPIT ) Syed-Neblett template

Dose:
Radical BT:
LDR: 55-60 Gy @ 50-90 cGy/hr
HDR: 3.5 Gy/#@ 2#/day/12-16#
Boost
LDR: 15-25 Gy , 50-90 cGy/hr
HDR: as above, no. of # depend upon EBRT doses

Other sites:
Lung: Permanent perioperative BT, I 125 seeds, Au 198 Grains
Persistent or recurrent ds after EBRT or residual ds after surgery
Pancreas: Permanent perioperative BT, I 125 seeds
Locally advanced unresectable ds
Penis & Urethra:

INTRACAVITARY APPLICATION
Radioactive sources are placed in a existing cavity usually inside a predefined applicator with special geometry
Uses:
Cervix
Endometrium
Vagina
Maxilla
Nasopharynx

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

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/#)

DRAWBACKS OF PARIS AND STOCKHOLM SYSTEMS
Long treatment time
Discomfort to the patient
No dose prescription

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

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 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

LOADING OF APPLICATORS
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
APPLICATORS

LOADING PATTERN TUBE TYPE LENGTH TUBES RADIUM (mg) UNITS (FUNDUS to CX) LOADING TUBES (mg) LARGE 6 3 35 6-4-4 15-10-10 MEDIUM 4 2 25 6-4 15-10 SMALL 2 1 20 8 20 VAGINAL OVOIDS TUBES RADIUM (mg) UNITS LOADING TUBES(mg) LARGE 3 22.5 9 10-10-5 or 20/25 MEDIUM 2 20 8 20 SMALL 1 17.5 7 10-5-5 or 20/15

GUIDELINES
Largest possible ovoid
Lesser dose to mucosa
Longest possible tandem (not > 6 cm)
Better lateral throwoff
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

INTRACAVITARY APPLICATORS
MANCHESTER
PGI

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

ICRU REPORT NO.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

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

CERVICAL BRACHYTHERAPY

ABS.DOSE AT REFERENCE POINTS
BLADDER POINT
RECTAL POINT
LYMPHATIC TRAPEZOID OF FLETCHER
LOW PA, LOW COMM.ILIAC LN & MID EXT ILIAC LNs
PELVIC WALL POINTS
DISTAL PART OF PARAMETRIUM & OBTURATOR LNs

DOSE SCHEDULE
LDR (<200cgy/hr)
35-40 Gy at point A
MDR (200-1200cgy/hr)
35 Gy LDR EQUIVALENT at point A
HDR(>1200cgy/hr)
9 Gy in 2 #
6.8Gy in 3# at point A

EXTERNAL RT WITH BRACHYTHERAPY
Brachytherapy can follow external irradiation
SIMULTANEOUS
Stage I - II with very minimal parametriun involvement
HDR -5 sessions (9gy /#/ 5, 1week apart)
40 Gy by XRT simultaneously
SANDWICH
Stage I-II
MDR 40 Gy LDR eq.—› XRT 40 Gy —› MDR 35 Gy LDR eq.
In both above cases a MIDLINE SHIELD is used

POST OP/ VAULT BRACHYTHERAPY
Vault RT
No residual disease
8500 cGy at 5mm from the surface of the vault
2 sessions 1 week apart
Residual disease
CTV of 2 cm given to gross tumor and the prescription of 8500cgy encompassing the whole CTV is made
2 sessions 1 week apart
Mostly after XRT

POST OP BRACHYTHERAPY
CONTRAINDICATIONS
Vaginal wall involvement ( middle- lower 13)
Heavy parametrium infiltration
VVF or VRF
Inadequate space
Medical contraindications
Metastatic disease
Supplementary radiation 2000 cGy 10# 2 weeks

SURFACE MOULDS
Radiation is delivered by arranging RA sources over the surface of tumor
Types
Planar
Circular
Square
Rectangular
Line source
Cylinder

INDICATIONS
Superficial /Accessible tumors
Skin ca
Post mastectomy recurrence
Oral tumor
hard palate ,alveolus
Penile carcinoma

CIRCULAR MOULDS
Amount of radium used is obtained from the table for a particular treating distance
Circular arrangement is the best
Space between the needles (end) should not be more than H

SQUARE MOULDS
An arrangement is considered to be linear if the distance between the active end of the sources does not exceed the height
Length of the side of the square is less than twice the height
No further radium is placed in the center

RECTANGULAR MOULDS
The dividing lines or bars are placed parallel to the longer side
Elongation correction factor: Increase the reading in milligrams hour by a given factor
This factor is proportional to the ratio of the sides of the rectangle
1.5:1 = 2.5%
2:1 = 5%
3:1 = 9%
4:1 = 12%

CIRCULAR MOULDS
CURVED SURFACES
COAXIAL RINGS
Irregular area
Curved surfaces: convex, concave
The smaller area is used for calculation of radium dose and implant rules
Cylinder mould: Amount of radium is 30D 2
DISTRIBUION RULES
In case of coaxial rings radium is placed at a distance equal to 2H

INTRALUMINAL BRACHYTHERAPY
Radioactive source is passed through a tube and passed into a hollow lumen
Sites
Esophagus
Bronchus : Bronchogenic carcinoma
Definitive : T 1 -T 2 tumors
Palliative
Dyspnea
Cough
Atelectasis
Biliary tract

RADIOBIOLOGY
Biological effects depend on
Dose prescribed
Treated volume
Dose rate
Fractionation
Treatment duration
Heterogeneous dose distribution
Higher average dose
Short treatment

RADIOBIOLOGY – 4 Rs
Repair
Reassortment / redistribution
Repopulation
Reoxygenation

RADIOBIOLOGY- LDR
Repair of Sublethal damage
Most significant- 1 Gy/min and 0.3 Gy /h
DNA repair
Dynamic process
Special kinetics
Simple exponential kinetics
Reassortment - slow and imp. <1 Gy/min
Repopulation-slowest and significant
Reoxygenation - relative slow process may be a disadvantage

LDR AND HDR
LDR vs HDR
EFFECTS OF HDR

RADIOACTIVE SOURCES
Naturally occurring
Artificial
Induced by neutron bombardment
Induced by bombardment of protons
Fission product
CHARACTERISTICS
HALF LIFE
GAMMA ENERGY
BETA ENERGY
HALF VALUE LAYER
EXPOSURE RATE CONSTANT
BETA FILTRATION
DECAY SCHEME

IDEAL RADIONUCLIDE
Photon energy :low to medium- 0.03 to 0.5 MeV
Monoenergetic beam preferred
Moderate Gamma ray constant
Long half life
High specific activity
Isotropic
No gaseous disintegration/daughter product
Nuclei should not disperse if source damaged
Low beta energy
Low or no self attenuation
Insoluble and nontoxic
Flexible
Easily available and cost effective
Withstand sterilization process
Disposable without radiation hazards to environment

RADIUM 226
Sixth member of the radio active series which starts with uranium and ends with lead
Half life 1620 years
Gamma energy 0.83 MeV
Half value 12mm Pb
Exposure rate constant 8.25 Rcm 2 /mCi-h
Filtration 0.5 – 1 mm Pt

RADIUM SUBSTITUTES NAME ORIGIN T 1/2 γ ENERGY-MeV β ENERGY β FILTRATION HVL (Pb -mm) ERC SPECI. ACTI. DECAY PRODUCT Rn 222 NATURAL 3.83 days 0.83 Stainless steel 12 10.27 Pb 206 Cs 137 FISSION 30.17 yrs 0.662 0.512 1.17 - do - 6.5 3.26 87 Ba 137 Co 60 NEUTRON ACTIVAT. 5.26 yrs 1.17, 1.33 0.38 - do- 11 13.07 1020 Ni 60 Ir 192 - do - 73.8 yrs 0.136- 1.06 0.079-0.068 Platinum 4 4.69 7760 Pt 192 Tn 182 - do - 115 yrs 0.67 - Platinum 12 6.87 - - Au 198 - do - 2.7 days 1.088- 0.412 0.96 St. steel 3.3 2.376 - Hg 198 I 125 - do - 59.4 days 0.274, 0.314 No Titanium 0.01 10th 1.403 - Te 125 Pd 103 - do - 16.97 days 0.21 No Platinum 0.03 6.87 - Ru 103

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Brachytherapy Final

by PGIMER, AIIMS on Nov 08, 2008

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