Gyne brachy Flashcards
why not use TRUS with gyne?
-can’t see where you are going with US
-gyne organs move a lot- need large “PTV”
typical gyne treatment
45/25 EBRT and 28/4 brachy (whole treatment within 55 days)
how do you usually image standard gyne treatments?
CBCT on unit (this is why gyne is on side of bed where you can remove the bars so you can get good image)
size of needles
18 cm- 24 cm
Dr.Patil- tend to “push” longer needles in more
gyne images
fuse MRI with CT
-ideally would be on same couch
can you make a smaller Miami?
No, sources would be too close together
-can get hyperdose sleeve (200% isodose lines join together to make a sleeve)- can get necrosis
issue with patients who smoke
less oxygenation- healing is not as good
describe vaginal vault treatment
-patient awake
-no imaging
-Only the length to be treated and cylinder diameter need to be known. Depth to treat is 5 mm beyond the outermost edge of the cylinder.
when do you radiation survey the patient?
before and after treatment
tagert coverage
• Generally want target (or representative points) to receive doses between 95-105%, although 100% of volume receiving at least 90% is typical objective for volume based planning in brachytherapy.
o Representative points may include point A for cervix/uterus treatment, or points at 5 mm depth for vaginal vault.
o Point B, rectum point and bladder point are used to evaluate the dose distribution.
Manchester system points
This point is 2cm superior to the phlange (cervical os) and 2cm lateral to the tandem midline
Point A is a common prescription point corresponding, approximately, to the point where the uterine vessels cross the ureter. Radiation tolerance is of these structures are thought to be the main limiting factor in irradiating the uterine cervix.
Point B is another dose reporting point located 5cm lateral from the patient’s midline.
Point B is intended to be representative of the pelvic lymph node dose, hence its definition relative to the patient’s midline rather than the tandem’s midline.
Bladder Point is the point of highest dose in the bladder.
Bladder dose should be less than 80% of dose to point A.
Rectal Point is the point of highest dose in the rectum.
Rectum dose should be less than 80% of dose to point A.
In machester system, why is Point A relative to tandem whereas point B is relative to patient body?
point A (which represents the crossing of the uterine artery and the ureter) is best approximated relative to the uterus while point B (which represents the pelvic lymph nodes) is best approximated relative to the patient’s body. This difference can be significant when the uterus is tilted relative to the pelvis.
3 important points for brachy planning
time, path, position
cervical cancer: what is american brachy society reocmmendation for dose to point A (D90)
EQD2 85-90 Gy total (including EBRT)
for advanced stage
65-75 Gy for earlier stages
vault dose in this clinic
monotherapy: 21/3
11/2 brachy with 45/25 EBRT
ring and tandem: 28/4 HDR with 45/25 EBRT
OAR doses for gyne brachy
point B: 45-50 Gy for early stage, 54-60 Gy for advanced
HDR bladder and rectal points < 70 % of point A dose
dose to lower vagina vs upper vagina
lower vagina doses are lower as upper vagina has lower tolerance to radiation
LDR constraints for rectal and bladder point
rectal point < 70 Gy; bladder point < 75 Gy (rectum more radiosensitive than bladder; LDR constraints are less restrictive than HDR)
what vaginal doses cause fibrosis and stenosis
> 50-60 Gy
at what dose does ovarian failure occur?
5-10 Gy
with what dose does sterilization occur?
2-3 Gy
dose contraints for uterus
<100 Gy
dose constraint for ureter
< 75 Gy
dose constraint for femoral heads
<50 Gy
vaginal cancer dose
HDR boost of 4-6 Gy X 2 after 45/25 EBRT
7 Gy x 3 if only brachy
describe the vault treatment
single channel
series of disks about a tandem. Disks are 2-4 cm diameter. Typical is 3 cm.
treat 5 mm beyond the disk surface
should be snug within vagina so the mucosa is treated
why can’t you use vault to treat beyond 5 mm?
plan would be too hot
how does the disk size for the vault affect the plan?
large disk- difficult to get homogeneous dose at upper part because side has 2 cm diameter whereas top is only 12 mm (for 4 cm cylinder); top tends to be hot. Dr. Bowes likes to not include the first dwell position to improve homogeneity.
small disk- hard to get homogeneous dose
-larger disk = impact of IS differences along vault less significant since IS is less significant at larger distances
length treated with vault
usually 4-5 cm top of vagina
how to set up vault in Oncentra
-create empty image series since no imaging is used for vault
-set dome of cylinder as origiom
-7 mm below origin is dwell position 1, then sources are every 5 mm (could also make them every 2.5 mm)
-each disk is 2.5 cm long
-for example, if treating 4 cm, activate 8-9 dwell positions 0.5 mm apart
-set up points- one at 5 mm from top of dome and others at 5 mm lateral from each dwell position
-want dose at each point within 90-100% (10% of each other)
-end dwell positions have longer dwell times since there isn’t contribution from neighboring sources
-want symmetric distribution of dwell times
why are 3 cm vault cylinders easy to plan?
about the same IS distance for top dwell position vs side ones
why are channels 1 and 2 used only for ovoids and channel 3 only for tandem? (won’t connect to other transfer tubes)
if 1 and 2 are switched by accident, does to both ovoids about similar
If 1 or 2 is switched with 3, error is significant
why is top dwell position point in Rad Calc off from Oncentra?
differences in how the anisotropy is modelled- will see this error when end to source
describe workflow
patient under anasthesia
dorsal lothotomy position, catheter
doctor may use abdo US to help see the bladder and uterus- make sure sound is in uterus fully
doctor uses sound to measure uterus length and dilates uterus, also checks response to EBRT
ring and tandem inserted, sutured to patient
patient straightened out on bed- kV CBCT image taken
patient woken up
patient plan done in Oncentra
patient then trated (2 fractions over 2 days)- applicator removed
a week later the process is repeated for 2 more fractions
- some doctors use a smit sleeve to keep the uterus dilated for all 4 fractions
why is ring and tandem used over ovoid and tandem?
position is more stable with ring
with ovoid and packing, things can move around more
also with ring there is space on the side to put needles
when do you need to implant vagina with needles?
if vaginal disease more than 5 mm thick
gyne fractionation
45/25 EBRT,
700 cGy X 4 brachy
what is a sound
long stick with measurements etched on it
measure how long the uterus is
describe ring and tandem
doctor chooses angle and length of applicator and ring size
ring goes around external os
tandem goes into ring and into uterus
how is applicator sutured on?
weaved around the ends of the applicator
what is packing used for?
fill space with packing to keep applicator still
what is done with bladder during ring and tandem
baldder is filled for the CBCT image and the treatments
what is dummy
string with radio-opaque beads is slid into ring and tandem applicator so we can see them on the CBCT image
-markers don’t correspond to dwell positions
dwell position steps in gyne
5 mm
not 2.5 mm like prostate
can use 2.5 mm but make sure to still cover the required region
what is contoured for ring and tandem?
bladder
rectum
sigmoid
how to find ring and tandem in oncentra images
find center of ring and align with tandem
put cross-hair in center of ring
turn on “fine” to scroll in smaller increments
reconstruct on slices with brightest markers
vienna ring and tandem
3 holes on each side of ring to put needles in (to get vaginal disease if needed)
new models have holes throughout ring
some have needles angled at 15 degrees (like MUPIT) to cover parametrium
need MRI guided so tou can contour the needles with MRI (don’t have dummies for needles- cannot see where you are putting them)
can put copper sulfate solution in cathater to see the line in MRI
what is moulage brachy
vaginal mold- design implant for the patient
ring and tandem desired dose distribution
pear shaped
If not enough dwell positions along tandem, will get crease at end of pear
if too many, will get dip
number of channels for ovoid and tandem, ring and tandem
3 for oivoid and tandem
2 for ring and tandem
where to put dwell positions in ring and tandem
3 on each side of ring (mimic oivoid)
along tandem to base of ring (want flat shape at base of pear shape)
why is there 4 mm offset between ring dwell position and actual position in Oncentra?
based on observed discrepancy between dummy source and where actual source went during QA
wheer to create A points in ring and tandem?
align to top of os and to tandem
create A points 2 cm up and away
also create to points 24 cm away- should be about 0.5 cm (gets pear shape)
normalize dose to A points
also use the created points for RadCalc
how to adjust local dose with ring and tandem?
graphical local
manually pull in or out at points
how is coverage evaluated for ring and tandem?
points A
3 items to print for ring and tandem plan
plam, DVH, screen capture of images including 3D capture
what is paracervix?
connective tissue of the pelvix floor, extending from the uterine cervix
available ovoid diameters and uterine lengths
3 cm, 2.5 cm, 2 cm
uterine tube: 6, 4 or 2 cm
how is ICRU system different than manchester system?
ICRU: relate the dose distribution to the target volume rather than to a specific point. (more like ext beam)
manchester system dose objective
achieve uniform dose (+/- 10%) throughout region to be treated
describe quimby system
-uniform distribution of source strength, accepting a non-uniform delivery of dose.
Usually, the dose in the centre of the treatment volume is higher than the dose near the periphery
Planar implants: the dose stated is the dose at the center of the plane (maximum dose)
Volume implants: the stated dose value is the minimum dose within the implanted volume.
rules for Paris system
Sources must be linear and their placement must be parallel.
Centers of all sources must be located in the same (central) plane.
Linear source strength (activity) must be uniform and identical for all sources in the implant.
Adjacent sources must be equidistant from one another.
paris vs manchester system
Paris System uses considerably fewer sources than Manchester System.
It results in a larger volume of high dose than Manchester System.
memorial system
Off-shoot of Quimby. Uses activity proportional to average of dimensions of implant
D2cc for rectum, sigmoid, and bladder in gyne brachy
rectum: 61 Gy
sigmoid: 66 Gy
bladder: 84 Gy
These are EQD2
are permanent LDR implants done for gyne?
rare
when is vaginal cuff (vault) treatment indidcated?
post hystorectormy
endometrial cancer
1) patients with grade 1 or 2 cancers with > 50 % myometrial invasion
2) patients with grade 3 cancers with < 50 % myometrial invasion
usually if invasion > 50 %, get EBRT plus brachy boost (in addition to operation)
if invasion < 50%, just get brachy boost (in addition to operation)
-studies showed that radiotherapy post hysterectomy prevented relapses, mostly in vaginal cuff
-brachy = less toxicity compared to EBRT
why are vaginal vaults planned without image?
clinical benefit of planning with an image is unclear
vault: dose to surface of vagina for larger vs smaller cylinder
dose at surfavce is smaller for larger cylinder because of IS fall-off
what fraction of the vagina do treatments with ovoids typically cover?
upper 1/3
vaults can do 1/3 to 2/3
type pof optimization for vaults
point-based
typical errors for vault plans
-cylinder slips from intended position
-uses wrong transfer tube
-source path length is measured wrong
-dose is specified at wrong distance from cylinder
-cylinder placed in wrong orifice
where is point B location correspond to?
obturator lymph nodes
why is MRI standard for gyne CTV definition?
CT tumor contours significantly overestimate the tumor width
GTVres, CTVhr, CTVir
GTVres is residual disease left after EBRT
CTVhr is cervix plus any residual tumor tissue
CTVir has additional margin
when is cervix brachy typically done?
boost treatment following EBRT
how to calculate EQD2 in brachy
TG89 includes procedures for LDR, PDR, and HDR
textbook EQD2 constraints for rectum, sigmoid, bladder in cervix treatment
75 Gy EQD2 for rectum and sigmoid
90 Gy EQD2 for bladder
2 most common indications of gyne brachy
post-operative endometrial
cervix
is cervical brachy therapy ever used as monotherapy?
rarely, if early-stage cancer
LDR vs HDR gyne
LDR- radioactivity stays in patient whole time
HDR- put in for a few minutes, then patient doesn’t have to be isolated
LDR dose for gyne
40 Gy in 2 insertions (2 fractions of 20 Gy)
-0.2-4 Gy/h dose rate
roentgen to rad conversion factor in air
0.876 rad/R = 0.876 cGy/R
1 mg-Ra wquivalent
8.25 *10^-4 R/h
tolerances for doses to bladder, sigmoid colon, and rectum for combined EBRT and HDR treatment of endometrial or cervical cancer?
EQD2 of D2cc sigmoid < 75 Gy
EQD2 D2cc rectum < 75Gy
EQD2 D2cc bladder < 95 Gy
what HRD brachy option is available for inoperable endometrial cancer?
double tandem
-treatment isodose distribution should cover outer surface of the uterus
what does pt A represent?
crossing of ureter and uterine artery, forming the paracervical triangle
usual dose at pt B
25% of point A dose
(5 cm lateral to midline at same level as pt A)
pt B shows lateral spread of radiation dose
when do you do brachy for cervical cancer?
strongly indicated for stages I-II
if can be surgically resected, may not do brachy
guidlines for dose to OARs for gyne brachy
American brachy association calculates EQD2 for patient-specific plans
-typically, for 7 Gy fraction, 4Gy to hottest 2 cc of OARs is resonable
what could a doctor use for vaginal vault if concerned about rectal dose?
shielded applicator
when would you use Miami?
Miami is like a cylinder with 7 channels
-can use to get more heterogeneous dose
-patient with visible disease or recurrence (may have moer disease on one side than the other)
where is the os?
adjacent to the ring
why do we use 5 mm point from ring?
to get dose around ring
optimize with this
current consensus for medically inoperable endometrial cancer
Magnetic resonance (MR) imaging can be used to define the gross tumor volume (GTV), clinical target volume
(CTV), and the organs at risk (OARs). Brachytherapy alone can be used for medically inoperable
endometrial cancer patients with clinical Stage I cancer with no lymph node involvement and no
evidence of deep invasion of the myometrium on MR imaging. In the absence of MR imaging, a
combined approach using external beam and brachytherapy may be considered
clinical staging system for endometrial cancer
stage I - confied to uterus
stage II - involves corpus and cervix
stage III - parametrium, adnexa, or vagina, but confined to true pelvis
stage IV- involving local structures (rectum, bladder) or metastatic
what is target volume for inoperable endometrial cancer?
ueterus, cervix, and upper 3-5 cm of vagina
use MRI to determine uterine wall thickness, CT if MR not available
OARs can be contoured on MRI or CT (sigmoid, bladder, rectum, bowel)
advtange of using MRI in gyne cancer
MRI more sensitive to detection of parametrial involvement and estimation of tumor size
MRI more detailed view of uterine and cervical anatomy
recommended total dose to enlarged lympoh nodes
60-70 Gy
useful MRI sequences for delineating cervical cancers
fat-suppressed T2 weighted images
rectl pt
0.5 cm posterior to p[osterior vaginal wall, directly post to center of ring
-may not be max dose to rectum but should be close
bladder point
-likely not max dose to bladder..
on surface of foley balloon at trigone of bladder
dose to pt B from American brachy society
10-30 % of total brachy dose
when is chemo administered for gyne patients?
on EBRT day, not brachy day
-potential for increased complications because of normal tissue sensitization
usual number of sources used in LDR tandem and ovoids
3 in tandem and one in each ovoid
-hard to shape dose compared to with HDR
different brachy boost prescriptions for tandem and ring/ovoid with 45 Gy/25 EBRT
4 x 7 Gy
5 X 6 Gy
6 X 5 Gy
5 X 5.5 Gy
EQD2 at point A (a/beta of 10 Gy) goes from 83.9 to 79.8 from top to bottom
typically want EQD2 > 80 Gy to point A, although if patient not responding or tumor > 4 cm at time of brachy, want EQD2 to be 85-90Gy at point A
also have
9X 3.5 Gy
7X 4.25 Gy
5X 5Gy
(EQD2 from 79.7 to 75.5 top to bottom)
for 5 fractions brachy boost for cervical cancer, what is max dose at ICRU rectum and bladder point
3.7 Gy
what if machester plan gives hot doses to OARs?
consider using 3D planning with targets instead of point based
consider using interstitial
does ABS recommend still using a tandem if doing interstitial?
yes, to prevent a cold spot
different brachy boost prescriptions for tandem and ring/ovoid with 50.4/28 EBRT
9X 3Gy
5X 4.5 Gy
EQD2 of 78.8 and 76.7
what does PDR do?
delivers radiation dose every hour that approximates the LDR dose rate of 0.4-0.6 Gy/h using Ir-192 with source strength < 1 Ci
pros and cons of PDR
-improved taret coverage and normal tissue sparing
-low dose rates of LDR and PDR allow for sublethal demage repair
-reduced exposure of personel, lets nurses and visitors see the patient inbetween exposures
-compared to HDR, applicator may move during treatment
what kind of loading are LDR gyne applicators?
manual afterloading
when does american brachy association recommened LDR or PDR boost?
2 applicatiors to allow for reduction in tumor volume and improved tumor coverage wth 2nd application
-first should be within 4-6 weeks of start of EBRT
-2nd should be 1-2 weeks later
LDR loading for gyne
-tandem is loaded with 36-43 U of Cs per cm of tandem length
-small ovoids usually 70-108 U each
LDR/PDR dose rate
0.4- 0.6 Gy/h
why use both EBRT and vaginal brachy for endometrial cancer?
-associated with better control
-if patient has low risk, may do brachy alone (with surgery of course)
how long after surgery do you do the vaginal vault?
at least 4 weeks
what if the vaginal vault cylinder is too small?
-can be air gaps or folds leading to underdosage of target
why do some centers CT sim the vaginal vault?
ensure no air gaps, cylinder is snug
vaginal vault LDR dose for brachy alone (no EBRT)
60 Gy to vaginal surface
brachy alone (no EBRT)
common vaginal vault fractionations for brachy alone (no EBRT)
7 Gy X 3 to 0.5 cm depth (most common)
5.5Gy X 4 to 0.5 cm depth
5 Gy X 5 to 0.5 cm depth
2,5Gy X 6 to 0.5 cm
6Gy X 5 to surface (2nd most common)
4 Gy X 6 to surface
8.5 Gy X 4 to surface
doesn’t recommend one over the other
EQD2 for tumour is about 50 Gy at surface and 30Gy at 5 mm depth for 3 cm cylinder (surface would be different for other cylinder sizes if prescribing at depth)
vaginal vault LDR dose for brachy with EBRT
70 Gy combined EQD2 to vaginal surface
70-80 Gy to vaginal lesion if recurrent disease
vaginal vault brachy doses if boost to EBRT
45 Gy EBRT + 5-6 Gy X 3 (to surface)
50.4 Gy EBRT + 6 Gy X2 (to surface)
45 Gy EBRT + 7 Gy X 3 (0.5 cm)
45 Gy EBRT + 6 Gy X 4 (0.5 CM)
45Gy EBRT + 6 Gy X 5 (surface)
45 Gy EBRT + 7 Gy X4 (surface)
LDR dose rate desired for vaginal vault
100 cGy/h
other than make the dose hetereogeneous, how else can miami applicators help distribution?
-minimize effect of anisotropy at top of cylinder (hot or cold point at top)
diagnostic workup for vaginal disease
PET with CT or MRI
MRI good for defining tumour dimensions
PET/CT provides assessment of lymph nodes
who is candidate for interstitial brachy?
patients with stage I-IVA vaginal cancers or recurrent cervical, endometrial, or vulvar carcinoma in vagina with vaginal lesions > 0.5 cm thick
vaginal cancer EBRT dose
45-50.4 Gy in 25-28 fractions
MRI vs CT in gyne
MRI is better than CT for defining the tumor volume whereas it is equivalent for critical organ definition
desired dose for vaginal CTV
EQD2 of 70-85 Gy for the CTV
rectum and sigmoid < 2 cc to get EQD2 of 75 Gy and bladder 90 Gy
recommended dose for vagina LDR
25-40 Gy with brachy for total of 75-80 Gy with brachy+ EBRT
-prefered dose rate for LDR is 35-70 cGy/h
typical vaginal HDR doses
all over map..
4 Gy X 5
4.5 Gy X 5
5 Gy X 5
7 Gy X 3
5Gy X 6
5.5 Gy X 6
EBRT is typically 36/18, 39.6/22, 45/25, 50.4/28
EQD2 is 70-80 %
D2cc to limit rectum dose to < 70 Gy EQD2 for several fractionations
For 45/25 EBRT and 7x3 HDR - 5 Gy
For 45/25 and 5X5 HDR- 4 Gy
For 50.4/28 and 5x5 HDR, - 3Gy
repair half time in gyne
1.5-2 hours
What is FIGO?
French system of gyne cancer staging per ICRU 89
Includes clinical exam, chest x-ray, and IVP (intravenous pyelogram)
gold standard for diagnosis
-MRI for tumor assessment
-PET/CT for lymph node involvement
EQD2 doses for pt A or CTV high risk from external beam and brachy
total > 75-85 Gy
44 Gy to 65 Gy with EBRT
20-50 Gy with brachy
what is a brachy system
set of rules involving specific applicator type and radioactive isotope
-Stockholm
-Paris
-Manchester
-combination of Paris and Manchester system became Fletcher (MD Anderson system)
why did manchester system select points A and B?
assumption that the absorbed dose in the
para-cervical triangle, and not the actual absorbed
dose to the bladder, rectum, or vagina, determined
normal tissue tolerance
-Fletcher added in bladder and rectum?
why use tandem and cylinder?
narrow vagina
treat varying lengths of vagina if there is spread of disease
issues with Point A?
The Point A
absorbed dose overestimates the target absorbed
dose in large tumors and underestimates the target
absorbed dose in small tumors
issue with Pt B
it does not always represent the absorbed dose to the
obturator nodes
A strong correlation between absorbed dose to
Point B and nodal absorbed doses estimated from
CT-assisted analysis does not exist
what is included in the low risk CTV in cervical cancer? Intermediate risk? High risk?
CTV-TLR comprises the whole
parametria, the whole uterus, the upper part of the
vagina, and the anterior/posterior spaces toward the
bladder and rectum
CTV-THR = CTV-Tadapt that includes the GTV-Tres, the
whole cervix, and adjacent residual pathologic tissue,
if present
CTV-TIR = The CTV-TIR represents the GTV-Tinit as superimposed on the topography at the time of brachytherapy, together with a margin surrounding the
anatomical cervix border (CTV-THR) in areas
without an initial GTV-Tinit
What is GTV-T
CTV-T
GTV-Tres
CTV-Tadapt
GTV-T = macroscopic demonstratable disease
CTV-T = The CTV-T includes the GTV-T and a
volume of surrounding tissue in which the risk of
microscopic disease is deemed so high that this region
should be treated with a dose sufficient to control
microscopic disease
GTV-Tres = residual tumor at the time
of brachytherapy application after treatment assumed
sufficient to control microscopic disease. (i.e. received EBRT before brachy)
-may not be the same biologically as the GTVinit- studies have shown the disease may be gone
CTV-Tadapt = CTV-Tadapt can be defined after any treatment phase
and includes the GTV-Tres and the residual pathologic
tissue that might surround the residual GTV-T
dose fall-off from vault plan
1 cm to go from 200% to 100 %, 1 cm to go from 100% to 50 %
