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