Transcript Gold Fiducial Markers for EBRT

Gold Fiducial Markers
Are used for soft tissue target volume localization and verification in
external beam radiation treatment procedures like
- IMRT
-3D-confomal irradiation
- CyberKnife or GammaKnive procedures
- or even Brachytherapy
It might be used in organs like
- Prostate
- Liver
- Pancreas
- Brain
e.g. Prostate
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EBRT nowadays is seen as one standard treatment for localized and advanced prostate cancer
patients.
Prostate cancer is a multifocal tumor which causes the whole organ to be treated. The organ
will be irradiated with homogeneous fields in 3D conformal technique or with IMRT.
Toxicity to bladder and rectum are limiting the dose to the organ to 72 Gray with regular
irradiation procedures.
5 year survival rate w/o PSA rise depending on applied dose
5 year survival rate (%) w/o PSA rise
Dose
64.8 – 70.2 Gy
75.6 Gy
81 – 86.4 Gy
p
Low risk
65
86
96
< 0.01
Intermediate. risk
44
61
87
< 0.01
High risk
22
43
69
< 0.01
Risk Group
Risk factors: ≥ T2, Gleason Score ≥ 7, PSA ≥ 10ng/ml. Low Risk = no risk factor; intermediate. Risk = 1 risk factor;
high risk = ≥ 2 risk factors.
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This table shows that higher doses are giving more local control.
Source: Zelefski, Sloane
Kettering CC, NY, NY
Intention
Goal:
High dose to the target volume, low
toxicity to the organs at risk.
But:
The organs at risk are adjecent to the
target volume.
1. Approach to a solution
The irradiated volume should be similar to the shape of the
organ to be treated (conformal).
 3D – conformal irradiation should be the standard.
 Better but more complex: IMRT Intensity Modulated Radiation Therapy
Conventional 3D conformal
IMRT with organ tracking
Fast moving leafs made from lead
and controlled by a computer and
shaping the beam from a LINAC.
The so called Multi Leaf
Collimator.
Whit this system the contour of
the beam can be shaped
according to the shape of the
organ at the respective angle of
the radiation field.
Source: Prof. D. Aebersold, Bern
But the main question is:
Where is the Prostate ?
Motion of the prostate during a 17 days cycle
Where is the Prostate ?
 Organ motion and therefore geographic miss is a
major problem when irradiating the prostate.
Hence a bigger target volume has to be irradiated.
But larger sections of the organs at risk will be
irradiated as well.
This might lead to increasing toxicity rates.
Field edge variability during
several treatment sessions
Setup error of
treatment sessions
Motion of the prostate
 Motion of the prostate might be induced by
- Tension of the pelvis muscles,
- Bowel and bladder filling
- Breathing
A cranial-caudal und ventral-dorsal misplacement of up to 2cm was observed.
 Therefore conventional treatment scemes aks for a 1 – 2 cm
margin around the organ.
 Aside from that the prostate is shrinking during the treatment.
Low margin  low toxicity but at the risk not hitting the whole organ during each
fraction  local control ??
Big margin  organ will be hit easily, but to save bladder and rectum the overall
dose has to be reduced
 local control ??
Approach to a solution: IGRT
 IGRT Image Guided Radiation
Therapy
Radiation Therapy with image guidance in intended to
localize and adjust the target volume. The image is
obtained by an on board imaging system (OBI). Today
this can be a flat panel sensor with MV or kV imaging,
extra portal imaging or cone beam CT.
 BUT:
 The prostate itself is hardly seen on x-ray
images.
 And bony structures might not be a
reliable aid.
Motion of the prostate versus
bony structures
Approach to a Solution: Navigation aid
= Marker
 The marker should provide a reliable and
reproducible localization of the prostate.
 The marker should be easily seen with the OBI of
the LINAC.
 The marker has to be of a radio opaque material.
E.g. gold, tungsten, silver etc., sometimes carbon.
 It has to be biocompatible.
Flouro refrence
LINAC OBI
Why Gold
 Gold does not react with the body.
 Gold is not causing any allergies.
 Gold provides a good visibility under x-ray and
gamma-rays.
What is a gold marker and how
does it look like
 Generally gold markers are small cylinders or balls made of
gold.
 Most commonly used sizes vary from 0,8 to 1,2 mm in
diameter and 3 to 5 mm in lenght .
 Other dimensions might be used in special cases.
 Goldmarker also can be made of thin goldsprings or small
beads on a suture.
Marker Kit
The marker will be delivered
sterile preloaded in a 20 cm
needle blocked with bone wax or
a synthetic spacer at the front
end.
It comes in sterile pouch ready
for the implant.
Positioning of the Marker
 To prevent the marker from migration or dislocation
it has to be implanted in the organ.
 Skin marker or patient immobilisation are
unsufficient means.
How many markers are needed
 Usually three markers will be implanted
 In some special cases four markers might be
neccessary. This adds extra confidence and might
help in case of difficult bony conditions.
 Two markers are insufficient.
Where to place the markers
 Three markers will be place like
 One at the Base one at the Apex and one most lateral in the
middle of the gland.
 OR: One on the left side at the base, one on the right side of
the base and one under the urethra at the apex.
 The markers have to be placed inside the gland 3 to 5 mm
away from the capsule.
 The actual position of the markers is not as important as the
positioning at the maximum distance from each other.
Images
Base – Middle – Apex
Images
4 Markers; Base – Base – Middle – Middle
Images
Base – Base – Apex
How will the Markers
implanted.
 In many places the implant is performed by the Urologist
under Ultrasound conrol. Usually he uses the biopsy channel
of the rectal ultrasound probe to insert and visualize the
needle. The implant is done through the rectal wall.
 Some centers do have the equipment (stand, stepper,
template grid) to perform a perineal insertion. This is more
accurate but might cause a general anesthesia of the patient.
Procedure (one possible scenario)
 In collaboration with the Urologists there will be a ultrasound guided
implant of the Markers one or two weeks before the treatment planning
starts.
 With the localization of the Markers in the planning CT, the simulation and
the daily treatment sessions the actual prostate position can be detected
and the LINAC bed coordinates can be adjusted. This is the so called organ
tracking.
 Before each treatment session a control image is obtained and is matched
with the reference image.
 Prostate displacement will be compensated by moving the treatment bed
according to the calculated geographic miss.
Procedure
 Implant of the marker
by the Urologist in the urologists office or hospital.
 Reference image
for treatment planning and aquisition of the marker
position
 Postioning of the patient
on the bed of the LINAC on the first treatment day.
Procedure
 Aquisition of the images,
 Each day in two orthogonal
planes to detect the
geographical miss.
Modern LINACS offer a diagnsotic x-ray unit
in a 90° angle to the LINAC. This gives the
possibilty to create x-ray images or even CT
scans before the treatment starts.
Digitally reconstructed x-ray image as reference for the marker
position (A) calculation of the correction with a gold marker image
from the LINAC.
Procedure
 Calculation of the mismatch
 Modern systems offer the possibility match the actual
image with the reference image. The actual image will
be aligned with the reference image on the computer
monitor and the system generates the coordinates for
the movement of the patients bed.
 Correction of the bed
Mismatch
 Modern systems do have a remote controlled bed. So
compensation of the patient dislocation can be
performed in an easy and fast way. Extra dose for
imaging stays low.
 Irradiation
 Now the irradiation can start as usual. This localization
and compensation procedure will be performed each
day before each fraction.
Match
Conclusion
 The prostate will be hit safely and reproducible
during each treatment session.
 Therefore a preferably high dose can be applied to
the target volume.
 Increase in local tumor control rate.
 Decrease in toxicity.Die Nebenwirkungsrate wird
verringert.
 Or: With similar toxicity the local control can be
increased.
IGRT in pictures
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Increased conformity and better dose distribution by means of IMRT.
Excellent match of the 95% iso dose level (blue area) with the target volume (red line).
The black arrows show the implanted gold markers.
Gold marker
Quelle: PIRUS GHADJAR, DANIEL M.
AEBERSOLD
MRI and CT images with
gold markers