ESTRO 36 Abstract Book

530 / 1096

S515 ESTRO 36
_______________________________________________________________________________________________
PO-0929 Needle Migration in HDR Brachytherapy for
Prostate Cancer evaluated by Serial MRI a nd Photos
S. Buus1 , M. Lizondo2, S. Hokland 3, S. Rylander3, E.
Pedersen 4, L. Bentzen1 , K. T anderup3
1 Aarhus University Hospital, Department o f Oncology,
Aarhus C, Denmark
2 Hospital de la Santa Creu i Sant Pau, Servei de
Radiofísica i Radioprotecció, Barcelona, Spain
3 Aarhus University Hospital, Department of Medical
physics, Aarhus C, Denmark
4 Aarhus University Hospital, Department of Radiology,
Aarhus C, Denmark
Purpose or Objective
Needle migration in high dose rate brachytherapy (HDR-
BT) for prostate cancer may lead to insufficient target
coverage and increased dose to organs at risk. The aim of
this study was to assess the magnitude of needle migration
in HDR-BT with serial MRI and photos.
Material and Methods
12 patients with high risk prostate cancer treated with
EBRT and two separate boosts of HDR-BT were included in
the study. In order to fixate the needles, a thin silicone
pad was placed within the template, which was fixated to
perineum with 4 sutures. Following US guided needle
implant, patients were placed in supine positi on on an MRI
couch on trolley for the rest of the procedure. Three MRIs
were performed; one for planning (MRI1), one
immediately before HDR-BT (MRI2), and one after HDR-BT
(MRI3). All MRIs were a transversal T2-weighted turbo
spin-echo with 2 mm slice thickness and 1.2 x 1.49 mm
resolution. The position of the template was marked with
indian ink on the thighs of patients, and photos of the
perineum were taken after each MRI. MRI2 and MRI3 were
co-registered to MRI1 to match the prostate. Coordinates
of each needle tip defined on all three MRIs were used to
calculate the migration for each needle. An average
needle migration of ≤3 mm was considered "acceptable".
On photos, movement of the template relative to the ink
markings was regarded as needle migration, which was
scored as either "acceptable" or "considerable" from MRI1
to MRI2 and from MRI1 to MRI3. Scoring of needle
migration with MRI and photos was compared. An analysis
was performed to examine whether posterior needles
were more prone to migrate compared with anterior
needles.
Results
A median of 16 needles (14 - 21) were used for each HDR-
BT procedure. Serial photos were taken in 19/24
procedures. MRI2 was performed in 24/24 procedures and
MRI3 in 22/24 procedures. MRI evaluated needle migration
was median 2.2 mm per needle (-0.8 - 4.4) from MRI1 to
MRI2, median 2.6 mm per needle (0 - 10) from MRI2 to
MRI3, and median 3.9 mm per needle (0.3 - 9.8) from MRI1
to MRI3. Needle migration evaluated by MRI was found
"acceptable" in 23/24 procedures from MRI1 to MRI2, and
in 7/22 procedures measured from MRI1to MRI3. Needle
migration evaluated by photo was found "acceptable" in
17/19 procedures from MRI1 to MRI2 and in 13/18
procedures from MRI1 to MRI3. Concordance between
scoring by photo and MRI was found in 24/37procedures.
Average needle migration was 2.9 ± 1.6 mm for anterior
needles and 3.6 ± 1.5 mm for posterior needles (students
t-test, p=0.08)
Conclusion
Needle migration was of acceptable magnitude measured
from MRI1 to MRI2, but of considerable magnitude from
MRI1 to MRI3. Insufficient concordance between scoring by
photo and MRI indicates that visual inspection is
inadequate for evaluating implant stability. A likely
explanation for the lack of concordance between for
photos and MRI is the developing oedema following needle
insertion.
PO-0930 CT to TRUS based Prostate HDR: what is the
optimal dosimetric margin to use?
F. Lacroix1, M. Lavallée1, E. Vigneault1, W. Foster1, A.G.
Martin 1
1Centre Hospitalier Universitaire de Québec- L'Hôtel-
Dieu de Québec, Department of radio-oncology, Quebec,
Canada
Purpose or Objective
The contouring volume variability resulting from
delineating the target with Computed Tomography (CT) or
Transrectal Ultrasound (TRUS) results in a 30 to 50%
increase in volume when contouring a prostate on CT
versus TRUS due to the poor soft tissue contrast of CT. This
may have a significant dosimetric impact when moving
from a CT to a TRUS based prostate high-dose rate (HDR)
brachytherapy planning as the treated volumes are
susceptible to differ significantly. This study aims at
determining the proper dosimetric margin to apply when
going from CT to TRUS based planning in order to
compensate for this volume difference. By doing so, we
aim to treat the same volume of prostatic tissue in CT or
TRUS and insure a constancy in quality of care for prostate
cancer patients treated with HDR.
Material and Methods
Twenty-seven prostate cancer patients were given a 15Gy
HDR boost using a TRUS-based catheter insertion and
planning approach. A 2 mm isotropic dosimetric margin
was used for the TRUS planning. An average of 17
catheters were implanted. Without moving patients still
under general anesthesia, a CT on rails located inside the
operating room was used to image the pelvis. Three
experienced radiation oncologists specialized in
brachytherapy delineated the prostate on the resulting CT
images and an offline, independent CT based planning was
performed. A 1 mm isotropic dosimetric margin was used
in CT planning. The prostate volume, 15Gy volume and
V100 of the prostate were then collected and compared
for the US and CT based plans.
Results
The average prostate, 15Gy volumes and V100 are
presented in table 1.
Table 1: Average prostate volume, 15Gy volume and
V100 for TRUS and CT based planning
Modality Average prostate
volume (CC)
Average 15 Gy
volume (CC)
V100
(100%)
TRUS 38.0 50.2 96.3
CT 44.3 54.2 96.0
The average TRUS volume is 16.5% smaller than the
average CT volume. When using a 2 mm dosimetric
margin, the volume receiving 15Gy is smaller by 8% in
TRUS compared to CT based planning. The V100 are almost
identical with both modalities. The standard deviation on
the TRUS prostate volume is slightly lower (10.6) than on
CT (11.2).