ESTRO 36 Abstract Book

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S511 ESTRO 36 2017
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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.
Martin1
1 Centre 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).
Conclusion
Our study shows an average systematic 16% smaller
prostate volume on TRUS compared to CT. This differs
from the 30 to 50% smaller volumes on TRUS reported in
the literature. This discrepancy is probably due to the
presence of catheters implanted under TRUS guidance in
CT based planning which means that catheters are
inserted under TRUS guidance in both planning modalities.
These catheters act as fiducial markers to delimit the
prostate capsule transversely on CT. The residual 16%
volume variation is largely due to the uncertainty in
identifying the prostate apex. A 2.8 mm isotropic
dosimetric margin should be used in order to treat
comparable volumes in TRUS compared to CT based
planning.
PO-0931 Clinical outcome and quality of life after MRI-
guided HDR boost for prostate cancer.
F. Lakosi1, A. Miovecz1, G. Antal1, J. Pall 2, D. Nagy3, M.
Csima4, J. Hadjiev1, I. Rep a1, G. Toller1
1Kaposvar University, Radiotherapy, Kaposva r, Hungary
2Csolnoky Ferenc Hospital, Radiotherapy, Veszprem,
Hungary
3Kaposi Mor Teaching Hospital, Urology, Kaposvar,
Hungary
4Kaposvar University, Faculty of Pedagogy, Kaposvar,
Hungary
Purpose or Objective
To analyze 5-year clinical outcome and quality of life
(QoL) after MR-guided high-dose-rate brachytherapy
(HDR-BT) combined with 3D conformal external beam
radiotherapy (3D-EBRT).
Material and Methods
Fifty-two patients with intermediate (IR) (n=22) to high-
risk (HR) (n=30, 18 T3 diseases) localized prostate cancer
were treated with 46-60 Gy of 3D EBRT preceded and/or
followed by a single dose of 8-10 Gy MR-guided HDR-BT.
Template reconstruction, trajectory planning, image
guidance, contouring and treatment planning were
exclusively based on MR images. Ninety-six percent of the
patients received androgen deprivation. Biochemical
relapse–free survival (bRFS, Phoenix definition), local
relapse-free survival (LRFS), distant metastasis-free
survival (DMFS), cancer-specific survival (CCS) and overall
survival (OS) were analyzed actuarially. Morbidity were
scored using CTCAEv4.0, while patients self-reported
urinary and bowel QoL was measured with the Expanded
Prostate Cancer Index Composite (EPIC) instrument and
International Prostate Symptom Score (IPSS) at baseline
and at regular intervals up to 6 years.
Results
Median follow-up time was 73 (range:13-103) months. The
crude/5-year actuarial rates of bRFS, LRFS, DMFS, CSS and
OS were 94/97.4 %, 98/100 %, 96/97 %, 100/100 % and
92/91 %, respectively. Two distant failures occurred in HR
group, while one local recurrence in IR group. The main
urinary toxicity was dysuria, which were Gr. 2 in 24/52
cases, including 9 patients with alfa blocker use at
baseline. There were 3 urinary strictures including one Gr.
3 event. Late GI morbidity was mild, representing Gr. 1
diarrhea (10/51), Gr. 1 urgency (9/51), Gr. 2 proctitis
(1/52) and Gr. 2 fecal incontinence (1/52), respectively.
A significant decline in urinary domain was observed
within the first 3 months, which mostly recovered by 6
months, thereafter declined progressively (p>0.05) and
remained stable from 4th years follow up (p>0.05)
(Figure). A similar trend was seen for bowel QoL, where a
significant decline occured within the first 3 months that
subsequently returned to nearly baseline level within 6
months, however, in contrast to urinary functions
remained stable over time (p>0.05). The evolution of IPPS
scores showed the same pattern as EPIC urinary scores.