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Brachytherapy:
Clinical implementation
LDR/HDR
Kent A. Gifford, Ph.D.
Prostate seed LDR (PPI)
• Advantages
– Dose conformity, normal tissue sparing
– Continuous LDR delivery
– Monotherapy can ablate prostate cancer
cells
– “One and done” procedure
– No concerns about EBRT motion, setup
uncertainties
Prostate seed LDR (PPI)
• Disadvantages
– Rapid falloff of ~25keV photon sources
– Edema of implant
– Variability of manufacture and activity of
sources
– Interseed and Intraseed attenuation
– Subject to skill/experience of
brachytherapist (art??)
Prostate seed LDR (PPI)
Seed properties
Radionuclide
Cs-131
I-125
Pd-103
Half-life (days)
9.65
59.4
16.97
Average Energy (keV)
29
27
21
Λ (cGy hr-1 U-1)
1.05
0.96-1.04
0.69
Half-value layer (mm)
0.035
0.025
0.008
Monotherapy and boost doses
Isotope
Cs-131
I-125
Pd-103
Monotherapy dose (cGy)
100-115
140-160
115-130
Boost (cGy)
70-80
100-110
80-110
Treatment Guidelines
• Seeds
– I-125: Nycomed-Amersham Model 6711 (NIST 99)
– Pd-103: Theraseed Model 200 (NIST 99)
• Activities used at MD Anderson
– I-125: .391 mCi = .497 U (used in planning software)
– Pd-103: 1.4 mCi= 1.810 U
– Will use 1 week decayed sources with a 7.77%
decay; .361 mCi= .457 U
Treatment Guidelines Cont.
• Doses are given as the total dose given over the life
of the radioactive seed (decayed to 0 mCi)
• Planned dose - TG 43
• Full Dose: Brachytherapy only
– I-125: 145 Gy
– Pd-103: 115 Gy
• External Beam + Brachytherapy
– XRT 45 Gy + I-125 110 Gy
– XRT 45 Gy + Pd-103: 100 Gy
Advantages and Disadvantages of
Seed Types
• I-125
• Advantages
– NIST Traceable
Calibration
– Well Characterized
dosimetry
– Rapid Strands available
• Disadvantages
– Relatively long half life
– Rounded seed ends
makes them mobile
– Very anisotropic dose
distribution
• Pd-103
• Advantages
– Short Half Life
– Cupped seed ends tend to
anchor seeds
– Seed activities within +/5%
• Disadvantages
– No calibration standard
– Dosimetry based on only
two studies
– Activity decays 4% a day
Which to use? I-125 or Pd-103
• Generally use Pd-103 for higher grade
tumors
• The disadvantage is Pd-103 short half
life – may miss the slower growing
tumor cells.
Pd-103 Seed in comparison with I-125
Seed
Prostate Implants at MD Anderson
• Modified Peripheral Loading based on
Seattle technique
• Pre-Plan/ Pre-loaded technique
• Use I-125 seeds, Pd-103, Cs-131
• Pre-Implant Ultrasound Volume Study
performed 2 weeks to a month before
actual implant by the Radiation Oncologist
and Resident
• Plan based on ultrasound images
acquired during volume study
Implants at MD Anderson Cont.
• Varian Variseed computer software used for
planning
• Implant performed under anesthesia as an
outpatient procedure
• Post Implant CTs performed on Day 1 and
Day 30 (2 wks potentially for Pd-103, Cs-131)
Pre-Implant US Volume Study
• 2 weeks to a month before actual implant
– scheduling
– ordering of seeds
• Done in Urology with the patient awake
• Procedure time: 20-30 min.
• Patient positioned in stirrups similar to those in
the operating room
• Transrectal Ultrasound (TRUS) used to acquire
images
TRUS Imaging Diagram
Pre-Implant US Volume Study
• Without a good volume study a good plan can not be
designed
• Oncologist draws target volume, tissue that is
identified to be treated on each 5 mm slice
• Prostate Volume is determined from the prostatic
margin
• The target volume includes the prostate volume and
some of the surrounding tissue
Pre-Implant US Volume Study
Pre-Implant US Volume Study
– KY Jelly or Ultrasonic Gel used as medium for
ultrasound transmission
– Condom placed over the probe
– Standoff cap used for prostates that lie
posteriorly
– Requirements for adequate ultrasound images
• complete contact between transducer and the
medium
• absence of air in the medium
• good contact with the rectal wall
• absence of gas or stool in the rectum
Pre-Plan
Variseed Software: Template
Registration 3 Point Method
1.) Lower Left
Location: A 1.0
2.) Lower Right
Location: G 1.0
3.) Designated Row: Any Hole (usually row
5)
Template (in red)
Contours
Source Placement
•Set Reference
Plane to Base
Slice (0.00 cm)
•Right Click on
image when
highlighted in
big window
Planning Guidelines
• Pre-Implant US Volume Study ultrasound images used
• Modified Peripheral Loading Technique
• Base Pattern- basic pattern of needles that begin at the base of
the prostate
– Implant small letters (a,b,c,d…) and whole integers (1.0, 2.0,
3.0…) starting with the base slice
– Place needles and seeds in the template locations in the
prostate or within 1/2 cm from prostatic capsule delineated
by the contour
– Continue pattern every 1 cm
Base Pattern
Base
Slice
0.5cm
Slice
1.0cm Slice
1.5 cm Slice
2.0cm Slice
2.5 cm Slice
3.0cm Slice
3.5 cm Slice
0.0 cm Slice (base)
1.0 cm Slice
2.0 cm Slice
3.0 cm Slice
Planning Guidelines Cont.
•
Patching Pattern- On the slices with a retraction of a 1/2 cm from the previous
pattern– Implant at the big letters (A,B,C,D…) and the half-integers (1.5, 2.5, 3.5,…)
– Place needles and seeds in the template locations in the prostate or within a
1/2 cm from the prostatic capsule delineated by the contour
– Avoid the “Big D” column due to the position of the urethra
– Continue pattern every 1 cm
•
Modify central needles for urethral sparing
– remove complete needles if 100% isodose line sufficiently covers the
prostate
– Remove central seeds in the needles- leave seeds at base and apex
Patching Pattern
Base
Slice
0.5cm
Slice
1.0cm Slice
1.5 cm Slice
2.0cm Slice
2.5 cm Slice
3.0cm Slice
3.5 cm Slice
0.5 cm Slice
1.5 cm Slice
2.5 cm Slice
3.5 cm Slice (apex)
0.0 cm slice
2.0 cm slice
Urethral Sparing
Remove
seeds from
“c,d” between
rows 2 and 3
1.0 cm slice
3.0 cm slice
0.5 cm slice
1.5 cm slice
Urethral Sparing
Remove
seeds from
“C & D”
between rows
2.5 and 3.5
2.5 cm slice
3.5 cm slice
Considerations when Planning
•
Dipping of the 150% isodose line down the center of the gland - urethral
sparing
•
Don’t compromise the 100% isodose line for urethral sparing
Dipping of 150% Isodose Line
Urethral
Area
150% Line
150% Line
Considerations when Planning
• Dipping of the 150% isodose line down the center of the gland urethral sparing
• Don’t compromise the 100% isodose line for urethral sparing
• No needles can have less than 2 seeds
• Try to keep the needle count < 30
• Optimal prostate sizes to implant: 20-50 cc
• The length of the urethra that receives more than 400 Gy for I-125
should be kept as low as possible
Considerations when Planning
•
Plan with sufficient dose at the base
– loose periprostatic tissue has a high probability of causing seed migration
– a more extended lithotomy position during implant causes the base slice to be
larger
– decreases total number of slices
– area with most cold spots, due to anatomical position
•
Load posteriolateral aspects of the prostate light
– location of neurovascular bundles
– seed migration very likely
•
Symmetry is important for uniform dose
Considerations when Planning
• Solutions for prostates that lie posteriorly
– drop the needles in the “big letter (A,B,..)” columns from the halfintegers (1.5,2.5,…) to the whole integer (1.0,2.0,…) rows below them
– follow loading guidelines despite modifications
• Avoid the rectum as much as possible by loading the central
template locations cooler (“big” C-E)
• Rectal dose should not exceed 100 Gy
• Do not implant or include the seminal vesicles due to unreliable
source placement
Considerations when Planning
• Mid-gland- generous coverage laterally and anteriorly, no margin
posteriorly because of the rectum
• Recommended to load 70% on the periphery and 30% on the
interior
• Hot spots in the interior of 200-250 Gy can be expected
• 145 Gy line should extend 3-5 mm beyond the margin drawn
Final Plan
Images 1 - 4
Images 9 - 10
Images 5 - 8
Seed Assay and Loading
•
10% of seeds assayed and then sterilized
•
Loaded under a sterile environment
•
Seeds loaded according to VariSeed computer printouts
– seed positions with correct orientation
– most needles loaded with a seed to begin with and then a seed at
every cm with a spacer in between each seed
– each needle ends with a seed due to doctor preference
•
Once all the needles are finished then a verification film must be taken
to assure that the needles are loaded correctly
Prostate Seed Implant Needle QA Films
Needle Loading Box
Based on the
plan and
template
location, the
needles are
placed in the
needle box
after
verification and
taken up to the
Operating
Room the
following day
Operating Room Procedures
• In the Operating Room the patient will be returned to
the same position as they were in for the pre-plan (a
catheter will be placed with contrast in the Foley
balloon)
• Fluoroscopy used
• The Physician will need the pre-planning US to check
for patient position for the implant
• Need patient plan, loading diagram, small lead pig,
calculator, NaI detector, Geiger-Mueller detector and
any radiation safety forms you may need should the
patient require a stay in the hospital over night
Operating Room Setup
OR Procedures
• Coordinates of the needle and retraction of
the needle are read from the treatment plan
• When all the needles have been loaded, the
extra needles will be used to fill in at the apex
and any “cold” spots
– This is done using fluoroscopy as well as
ultrasound
• The urologist will do a cystoscopy to ensure there
are no seeds in the bladder, if there are seeds they
will be retrieved and put in the little lead pig
OR Procedures
• Make a note in the patient chart with total seeds and
needles, total activity, and survey meter reading of the
patient with the Geiger detector
• You must remain in the OR until every seed has been
accounted for!!!
• Once the patient has left the room, use the NaI detector
to survey EVERYTHING.
• X-ray taken of last fluoroscopic image to verify the
number of seeds implanted (verification)
Verification Fluoroscopy Image
Post-Implant Dosimetry
• Seed Identification- 5 mm CT scan example
Post-Implant Dosimetry
• 3-D Dose Reconstruction with Dose 100% isodose
cloud (2 different cases)
Post-Implant Dosimetry
• Timing of CT Scans
– Edema
• Average swelling- 20%-50% post implant (Range: 0-96%)
– calculated by interseed spacing
– prostate border delineation not as accurate of a measurement
•
•
•
•
T 1/2 = 10 days
D90 increases 30 % from day 1 to day 21
Anderson’s experience- prostate back to normal by day 30
Volume increase results in average of 10% underestimate
of dose
– Suggested Timing between 2 post-implant scans:
Pd-103- 2 weeks, I-125- 4 weeks
Post-Implant Dosimetry
• Dose Evaluations
– Isodose Distributions
• 2-D distributions on sequential slices of target
• Recommended isodose lines: 200%, 150, 100, 90, 80, and
50.
– Dose Volume Histograms (DVH)
• Cumulative DVH recommended
• Percent volume of prostate that receives greater than or
equal to dose delivered
– Report following:
• D100, D90, D80 (dose that 100% of the prostate receives)
Implementation, QA, physicist
responsibilities- TG-56
Nath et al., Med. Phys. 24(10) 1557-98 1997.
Implementation, QA, physicist
responsibilities
Nath et al., Med. Phys. 24(10) 1557-98 1997.
Implementation, QA, physicist
responsibilities
Nath et al., Med. Phys. 24(10) 1557-98 1997.
Implementation, QA, physicist
responsibilities
Nath et al., Med. Phys. 24(10) 1557-98 1997.
Implementation, QA, physicist
responsibilities
Nath et al., Med. Phys. 24(10) 1557-98 1997.
Implementation, QA, physicist
responsibilities
Nath et al., Med. Phys. 24(10) 1557-98 1997.
Implementation, QA, physicist
responsibilities
Nath et al., Med. Phys. 24(10) 1557-98 1997.
Implementation, QA, physicist
responsibilities
Nath et al., Med. Phys. 24(10) 1557-98 1997.