radiation protection in radiotherapy part 6 brachytherapy lecture 2: brachytherapy techniques iaea...
TRANSCRIPT
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Radiation Protection inRadiotherapy
Part 6
Brachytherapy
Lecture 2: Brachytherapy Techniques
IAEA Training Material on Radiation Protection in Radiotherapy
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Part 6, lecture 2: Brachytherapy techniques 2Radiation Protection in Radiotherapy
Brachytherapy
• Very flexible radiotherapy delivery
• Source position determines treatment success
• Depends on operator skill and experience
• In principle the ultimate ‘conformal’ radiotherapy
• Highly individualized for each patient
• Typically an inpatient procedure as opposed to external beam radiotherapy which is usually administered in an outpatient setting
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Part 6, lecture 2: Brachytherapy techniques 3Radiation Protection in Radiotherapy
Objectives
• To be familiar with different implant techniques
• To be aware of differences between permanent implants, low (LDR) and high dose rate (HDR) applications
• To appreciate the potential for optimization in high dose rate brachytherapy
• To be familiar with some special techniques used in modern brachytherapy (seed implants, endovascular brachytherapy)
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Part 6, lecture 2: Brachytherapy techniques 4Radiation Protection in Radiotherapy
Contents
1. Clinical brachytherapy applications
2. Implant techniques and applicators
3. Delivery modes and equipment
4. Special techniques• A. Prostate seed implants
• B. Endovascular brachytherapy
• C. Ophthalmic applicators
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Part 6, lecture 2: Brachytherapy techniques 5Radiation Protection in Radiotherapy
Clinical brachytherapy
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Part 6, lecture 2: Brachytherapy techniques 6Radiation Protection in Radiotherapy
History
• Brachytherapy has been one of the earliest forms of radiotherapy
• After discovery of radium by M Curie, radium was used for brachytherapy already late 19th century
• There is a wide range of applications - this versatility has been one of the most important features of brachytherapy
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Part 6, lecture 2: Brachytherapy techniques 7Radiation Protection in Radiotherapy
Today
• Many different techniques and a large variety of equipment
• Less than 10% of radiotherapy patients receive brachytherapy
• Use depends very much on training and skill of clinicians and access to operating theatre
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Part 6, lecture 2: Brachytherapy techniques 8Radiation Protection in Radiotherapy
A brachytherapy patient
• Typically localized cancer• Often relatively small tumour• Often good performance status (must
tolerate the operation)• Sometimes pre-irradiated with external
beam radiotherapy (EBT)• Often treated with combination
brachytherapy and EBT
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Part 6, lecture 2: Brachytherapy techniques 9Radiation Protection in Radiotherapy
Patient flow in brachytherapy
Treatment decision
Ideal plan - determines source number and location
Implant of sources or applicators in theatre
Treatment plan
Localization of sources or applicators (typically using X Rays)
Commence treatment
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Part 6, lecture 2: Brachytherapy techniques 10Radiation Protection in Radiotherapy
1. Clinical brachytherapy applications
A. Surface moulds B. Intracavitary (gynaecological, bronchus,..)C. Interstitial (Breast, Tongue, Sarcomas, …)not covered here: unsealed source
radiotherapy (Thyroid, Bone metastasis, …) - this is dealt with in the IAEA training material on radiation protection in Nuclear Medicine
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Part 6, lecture 2: Brachytherapy techniques 11Radiation Protection in Radiotherapy
A. Surface moulds
• Treatment of superficial lesions with radioactive sources in close contact with the skin
A mould for the back of a hand including
shielding designed to protect the patient
during treatment
Hand
Catheters for source transfer
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Part 6, lecture 2: Brachytherapy techniques 12Radiation Protection in Radiotherapy
Historical example
Surface applicator with irregular distribution of radium on the applicator surface(Murdoch, Brussels 1933)
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Part 6, lecture 2: Brachytherapy techniques 13Radiation Protection in Radiotherapy
Other example
Treatment of squamous cell carcinoma of the forehead
Catheters for source placement
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Part 6, lecture 2: Brachytherapy techniques 14Radiation Protection in Radiotherapy
Source distance from the skin
• Determines incident dose
• Determines dose fall off in skin - the further the sources are from the skin the less influence has dose fall off due to inverse square law
• Dose homogeneity - the further away the sources are the more homogenous the dose distribution is at the skin
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Simulator films of forehead mould
Dummy wires as markers for location
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Part 6, lecture 2: Brachytherapy techniques 17Radiation Protection in Radiotherapy
Surface mould advantages
• Fast dose fall off in tissues
• Can conform the activity to any surface
• Flaps available
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Part 6, lecture 2: Brachytherapy techniques 18Radiation Protection in Radiotherapy
B. Intracavitary implants
• Introduction of radioactivity using an applicator placed in a body cavity• Gynaecological implants
• Bronchus
• Oesophagus
• Rectum
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Part 6, lecture 2: Brachytherapy techniques 19Radiation Protection in Radiotherapy
Gynaecological implants
• Most common brachytherapy application - cervix cancer
• Many different applicators
• Either as monotherapy or in addition to external beam therapy as a boost
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Part 6, lecture 2: Brachytherapy techniques 20Radiation Protection in Radiotherapy
Gynecological applicators
Different design - all Nucletron
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Part 6, lecture 2: Brachytherapy techniques 21Radiation Protection in Radiotherapy
Vaginal applicators
• Single source line
• Different diameters and length
Nucletron
Gammamed - on the right with shielding
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Part 6, lecture 2: Brachytherapy techniques 22Radiation Protection in Radiotherapy
Bronchus implants
• Often palliative to open air ways
• Usually HDR brachytherapy
• Most often single catheter, however also dual catheter possible
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Part 6, lecture 2: Brachytherapy techniques 23Radiation Protection in Radiotherapy
Dual catheter bronchus implant
• Catheter placement via bronchoscope
• Bifurcation may create complex dosimetry
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Part 6, lecture 2: Brachytherapy techniques 24Radiation Protection in Radiotherapy
C. Interstitial implants
• Implant of needles or flexible catheters directly in the target area• Breast
• Head and Neck
• Sarcomas
• Requires surgery - often major
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Part 6, lecture 2: Brachytherapy techniques 25Radiation Protection in Radiotherapy
Interstitial implants - tongue implant
tongue
tongue
Catheter loop
Button
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Part 6, lecture 2: Brachytherapy techniques 26Radiation Protection in Radiotherapy
Breast implants
• Typically a boost
• Often utilizes templates to improve source positioning
• Catheters or needles
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Part 6, lecture 2: Brachytherapy techniques 27Radiation Protection in Radiotherapy
2. Implant techniques and applicators
• Permanent implants• patient discharged with implant in place
• Temporary implants• implant removed before patient is discharged
from hospital
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Part 6, lecture 2: Brachytherapy techniques 28Radiation Protection in Radiotherapy
Permanent implants
• Implantation of sealed sources (typically seeds) into the target organ of the patient
• Sources are NOT removed and patient is discharged with activity in situ (compare part 16 of the course)
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Part 6, lecture 2: Brachytherapy techniques 29Radiation Protection in Radiotherapy
Radiation protection issues
• Patients are discharged with radioactive sources in place:• lost sources
• exposure of others
• issues with accidents to the patient, other medical procedures, death, autopsies and cremation
Discussed in more detail in parts 9 (Medical Exposure),16 (Discharge of patients) and 17 (Public exposure)
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Part 6, lecture 2: Brachytherapy techniques 30Radiation Protection in Radiotherapy
Source requirement for permanent implants
• Low energy gammas or betas to minimize radiation levels outside of the patient (125-I is a good isotope)
• May be short-lived to reduce dose with time (198-Au is a good isotope)
• More details on most common 125-I prostate implants in section 4A of the lecture
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Part 6, lecture 2: Brachytherapy techniques 31Radiation Protection in Radiotherapy
Temporary implants
• Implant of activity in theatre
• Manual afterloading
• Remote afterloading
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Part 6, lecture 2: Brachytherapy techniques 32Radiation Protection in Radiotherapy
Implant of activity in theatre
• (Common for permanent implants)
• For temporary implants common practice 40 years ago when radium was commonly used• for example gynecological implants of radium or
137-Cs needles
• Today only very rarely used for temporary implants - one of few examples are 192Ir hairpins for tongue implants
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Part 6, lecture 2: Brachytherapy techniques 33Radiation Protection in Radiotherapy
Problems with handling activity in the operating theatre
• Potential of lost sources
• The time to place the sources in the best possible locations is typically limited
• Radiation protection of staff may require awkward operation
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Part 6, lecture 2: Brachytherapy techniques 34Radiation Protection in Radiotherapy
Afterloading
• Implant only empty applicator or needles/catheters in theatre
• Once patient has recovered, dummy sources are introduced to verify the location of the applicators (typically using diagnostic X Rays)
• The treatment is planned
• The sources are introduced into the applicator or needle/catheter
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Part 6, lecture 2: Brachytherapy techniques 36Radiation Protection in Radiotherapy
Afterloading
• Manual• The sources are placed
manually usually by a physicist
• The sources are removed only at the end of treatment
• Remote• The sources are driven
from an intermediate safe into the implant using a machine (“afterloader”)
• The sources are withdrawn every time someone enters the room
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Part 6, lecture 2: Brachytherapy techniques 37Radiation Protection in Radiotherapy
Afterloading advantages
• No rush to place the sources in theatre - more time to optimize the implant
• Treatment is verified and planned prior to delivery
• Significant advantage in terms of radiation safety (in particular if a remote afterloader is used)
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Quick question:
Why is afterloading the method of choice from a radiation safety perspective?
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Part 6, lecture 2: Brachytherapy techniques 39Radiation Protection in Radiotherapy
Some radiation safety aspects of afterloading
• No exposure in theatre
• Optimization of medical exposure possible
• No transport of a radioactive patient necessary
‘Live’ implants should be avoided for temporary implants
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Part 6, lecture 2: Brachytherapy techniques 40Radiation Protection in Radiotherapy
Applicators for brachytherapy
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Part 6, lecture 2: Brachytherapy techniques 41Radiation Protection in Radiotherapy
Brachytherapy Applicators - lots to choose from, lots to learn
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Part 6, lecture 2: Brachytherapy techniques 42Radiation Protection in Radiotherapy
Some examples for applicators
• Gynaecological applicators
Fletcher Suit
Henschke typeRing type
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Part 6, lecture 2: Brachytherapy techniques 43Radiation Protection in Radiotherapy
Rotterdam Applicator
TandemLengths(in mm)
40506070
Ovoid Sizes
SmallMediumLarge
• A choice of sizes allows customized treatment of each patient
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Part 6, lecture 2: Brachytherapy techniques 44Radiation Protection in Radiotherapy
Close-up view
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Part 6, lecture 2: Brachytherapy techniques 45Radiation Protection in Radiotherapy
Other intracavitary applicators
• Vaginal • Bronchus
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Part 6, lecture 2: Brachytherapy techniques 46Radiation Protection in Radiotherapy
Interstitial applicators
• Needles• hollow and rigid
• may use templates for placement
• usually have pusher during implantation in tissue
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Part 6, lecture 2: Brachytherapy techniques 47Radiation Protection in Radiotherapy
Interstitial applicators
• Catheters• flexible
• open and closed end available
• often introduced into tissue via an open end needle
skin
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Part 6, lecture 2: Brachytherapy techniques 48Radiation Protection in Radiotherapy
3. Delivery modes and equipment
• Low Dose Rate (LDR)
• Medium Dose Rate (MDR)
• High Dose Rate (HDR)
• Pulsed Dose Rate (PDR)
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Part 6, lecture 2: Brachytherapy techniques 49Radiation Protection in Radiotherapy
Delivery modes - different classifications are in use
• Low Dose Rate
• Medium Dose Rate
• High Dose Rate
• Pulsed Dose Rate
• < 1Gy/hour
• around 0.5Gy/hour
• > 1Gy/hour
• not often used
• >10Gy/hour
• pulses of around 1Gy/hour
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Part 6, lecture 2: Brachytherapy techniques 50Radiation Protection in Radiotherapy
Low dose rate brachytherapy
• The only type of brachytherapy possible with manual afterloading
• Most clinical experience available for LDR brachytherapy
• Performed with remote afterloaders using 137-Cs or 192-Ir
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Part 6, lecture 2: Brachytherapy techniques 51Radiation Protection in Radiotherapy
Low dose rate brachytherapy
• Selectron for gynecological brachytherapy
• 137-Cs pellets pushed into the applicators using compressed air
• 6 channels for up to two parallel treatments
Nucletron
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Part 6, lecture 2: Brachytherapy techniques 52Radiation Protection in Radiotherapy
Simple design
• No computer required
• Two independent timers
• Optical indication of source locations
• Permanent record through printout
• Key to avoid unauthorized use
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Part 6, lecture 2: Brachytherapy techniques 53Radiation Protection in Radiotherapy
Treatment process
• Implant of applicator (typically in the operating theatre)
• Verification of applicator positioning using diagnostic X Rays (e.g. radiotherapy simulator)
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Part 6, lecture 2: Brachytherapy techniques 54Radiation Protection in Radiotherapy
Two orthogonal views allow to localize the applicator in three dimensions
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Part 6, lecture 2: Brachytherapy techniques 55Radiation Protection in Radiotherapy
Treatment planning
• Most commercial treatment planning systems have a module suitable for brachytherapy planning:• Choosing best source configuration
• Calculate dose distribution
• Determine time required to give desired dose at prescription points
• Record dose to critical structures
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Part 6, lecture 2: Brachytherapy techniques 56Radiation Protection in Radiotherapy
Treatment planning of different brachytherapy implants
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Part 6, lecture 2: Brachytherapy techniques 57Radiation Protection in Radiotherapy
High Dose Rate Brachytherapy
• Most modern brachytherapy is delivered using HDR
• Reasons?• Outpatient procedure
• Optimization possible
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Part 6, lecture 2: Brachytherapy techniques 58Radiation Protection in Radiotherapy
HDR brachytherapy
• In the past possible using 60-Co pellets
• Today, virtually all HDR brachytherapy is delivered using a 192-Ir stepping source
Source moves step by stepthrough the applicator - the
dwell times in different locationsdetermine the dose distribution
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Part 6, lecture 2: Brachytherapy techniques 59Radiation Protection in Radiotherapy
HDR 192-Ir source
From presentation by Pia et al.
Source length 5mm, diameter 0.6mmActivity: around 10Ci
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Part 6, lecture 2: Brachytherapy techniques 60Radiation Protection in Radiotherapy
Optimization of dose distribution adjusting the dwell times of the source in an applicator
Nucletron
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Part 6, lecture 2: Brachytherapy techniques 61Radiation Protection in Radiotherapy
HDR brachytherapy procedure
• Implant of applicators, catheters or needles in theatre
• For prostate implants as shown here use transrectal ultrasound guidance
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Part 6, lecture 2: Brachytherapy techniques 62Radiation Protection in Radiotherapy
HDR brachytherapy procedure
• Localization using diagnostic X Rays
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Part 6, lecture 2: Brachytherapy techniques 63Radiation Protection in Radiotherapy
Treatment planning
• Definition of the desired dose distribution (usually using many points)
• Computer optimization of the dwell positions and times for the treatment
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Part 6, lecture 2: Brachytherapy techniques 64Radiation Protection in Radiotherapy
Treatment
• Transfer of date to treatment unit
• Connecting patient
• Treat... Gammamed
Nucletron
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Part 6, lecture 2: Brachytherapy techniques 65Radiation Protection in Radiotherapy
HDR unit interface
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Part 6, lecture 2: Brachytherapy techniques 66Radiation Protection in Radiotherapy
HDR brachytherapy
• Usually fractionated (e.g. 6 fractions of 6Gy)
• Either patient has new implant each time or stays in hospital for bi-daily treatments
• Time between treatments should be >6hours to allow normal tissue to repair all damage
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Part 6, lecture 2: Brachytherapy techniques 67Radiation Protection in Radiotherapy
HDR units: different designs available
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Part 6, lecture 2: Brachytherapy techniques 68Radiation Protection in Radiotherapy
Catheters are indexed to avoid mixing them up
Transfer catheters are locked intoplace during treatment - green light
indicates the catheters in use
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Part 6, lecture 2: Brachytherapy techniques 69Radiation Protection in Radiotherapy
HDR systems
• Can be moved between different facilities or into theatre for intra-operative work
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Part 6, lecture 2: Brachytherapy techniques 70Radiation Protection in Radiotherapy
Pulsed dose rate
• Unit has a similar design as HDR, however the activity is smaller (around 1Ci instead of 10Ci)
• Stepping source operation - same optimization possible as in HDR
• Treatment over same time as LDR treatment to mimic favorable radiobiology
• In-patient treatment: hospitalization required
• Source steps out for about 10 minutes per hour and then retracts. Repeats this every hour to deliver minifractions (‘pulses’) of about 1Gy
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Part 6, lecture 2: Brachytherapy techniques 71Radiation Protection in Radiotherapy
Pulsed dose rate brachytherapy
• Different dose/time pattern possible
• Usually treatment about once per hour
• Illustration form ICRU report 58
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Part 6, lecture 2: Brachytherapy techniques 72Radiation Protection in Radiotherapy
Features of PDR:
• Advantages Emulates LDR Optimized dose
distribution Visitors and nursing
staff can use the time between pulses while the activity is in the safe
• Disadvantages- Potential radiation safety
hazard of a source stuck in the patient:
In LDR - low activity, no severe problem
In HDR - physicist is present during treatment
In PDR - will someone with sufficient training be there within 10 minutes? Even at midnight???
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Question:
Please list advantages and disadvantages of High Dose Rate Brachytherapy as compared to
Low Dose Rate brachytherapy. Assume both approaches are performed using remote
afterloading equipment.
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Part 6, lecture 2: Brachytherapy techniques 74Radiation Protection in Radiotherapy
The answer should include:
• Advantages Out patient procedure Optimization of dose
distribution using stepping source
Possibly better geometry as patient anesthetized
No exposure of nursing staff during procedure
No source preparation
• DisadvantagesPotential radiobiological
disadvantageFractionation requiredMore shielding requiredThere is no time to
intervene if machine failure occurs
More sophisticated (and expensive)