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S509
ESTRO 36 2017
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Poster: Brachytherapy: Prostate
PO-0926 Interstitial HDR prostate brachytherapy:
comparison of pre- and post-implant dose distribution.
S. Novikov
1
, S. Kanaev
1
, N. Ilin
1
, R. Novikov
1
, M.
Girshovich
1
1
Prof. N.N. Petrov Research Institute of Oncology,
Radiation Oncology, St. Petersburg, Russian Federation
Purpose or Objective
Prospective planning of interstitial high dose rate
brachytherapy (HDRBT) for prostate cancer permit high
accuracy of dose delivery to the tumour and\or prostate
with excellent sparing of normal organs. On line correction
of post-implant changes of prostate and normal tissues
volumes is the key factor of precious dose delivery.
The aim of the study was to evaluate possible
uncertainties in dose distribution in cases when
brachytherapy procedure is based only on pre-implant
planning with dose distribution after HDRB with post-
implant correction of dose distributiion.
Material and Methods
in 70 primary patients with prostate cancer we
analyzed
dosimetric plans that were obtained during the first
session of HDRBT. Pretreatment planning was performed
according to standard procedure with calculation of the
following dosimetric parameters: V100, D90 – for prostate,
D2cc – for rectum and D10 – for urethra. According to
standard HDRBT procedure after the end of needle
insertion we performed final US 3D-scanning with post
implant correction of prostate, urethra, bladder and
rectal volumes and subsequent post-implant optimization
of treatment plan.
During the study we also performed fusion of pre-implant
and post-implant images. Fusion was based on needle and
base-plan topography. After that we calculated dose
distribution according to the model when pre-implant plan
was used in patients with post-implant prostate and
normal organs volumes.
Results
Analysis of treatment plans with post-I mplantation
correction of the contours demonstrated h igh precision
and excellent dosimetric parameters: mean V100 - 94.1%
(V100 more than 90% in 97.2% cases), mean D90 – 104.3%
(D90 more than 100% in 95.7% observations). On the
contrary, after fusion of non-corrected plans and post-
implant volumes we mentioned high discrepancies
between preplanned and real dose distribution: V100 was
below 80% in 38.6% observations; D90 was below 80% in
24.3% cases. Only in 24.3% observations D90 was above
100% (table 1). In addition, in 18% of these cases D10 for
urethra was between 116% and 189%.
Conclusion
post-implantation correction of prostate, urethra, bladder
and rectum volumes with subsequent postimplantation
planning of dose distribution must be considered as
obligatory part of safe and accurate prostate
brachytherapy.
PO-0927 Plug-free needles provide dosimetric
advantages over plugged needles in I-125 prostate
brachytherapy
A.B. Mohamed Yoosuf
1
, L. Sarri
1
, M. Byrne
1
, G.
Workman
1
, D. Mitchell
2
, S. Jain
2
1
Northern Ireland Cancer Centre, Radiotherapy Medical
Physics Service, Belfast, United Kingdom
2
Northern Ireland Cancer Centre, Department of Clinical
Oncology, Belfast, United Kingdom
Purpose or Objective
To compare the dosimetric outcome of plugged and plug-
free implant needles in permanent prostate
brachytherapy (PPB) using global and multi-sector post
implant dosimetric analysis.
Material and Methods
70 consecutive men treated with I-125 PPB using either
plugged (group 1, n=35) or plug-free (Group 2, n=35) had
their post implant (CT) dosimetry compared. For global
analysis, dosimetric quality indicators evaluated between
two groups included: prostate volume (CT), number of
needles per unit volume, the minimum dose delivered to
90% of prostate volume (D
90
) and dose to 0.1 cm
3
of the
rectum (D
0.1cc
). Twelve sectors of the post-implant CT was
analysed for each case by dividing the prostate base, mid
gland and apex into four sectors each and D
90
was
compared for both groups.
Results
The mean prostate volume for Group 2 (40.38 cc ± 8.0 cc)
was significantly larger (p < 0.05) than Group 1 (36.45 cc
± 8.5 cc) but fewer needles were required per unit volume
(Group 2 - 0.59 ± 0.12 cm
-3
vs Group 1 - 0.72 ± 0.18 cm
-3
;
p < 0.001). Global dosimetry was similar for both groups
however seed loss was significantly reduced in Group 2 (p
< 0.05). Sector analysis, for Group 2, indicated increased
D
90
in the posterior mid-gland and apex regions (p < 0.05)
and a trend towards increased dose in the base sector as
shown in Figure 1. The mean rectal D
0.1cc
was higher in
Group 2 than Group 1 (124.73% ± 12.2% vs 122.54% ± 10.3%;
p = 0.4) which reflected the increased dose in the
posterior mid-gland. However, these remained within
recommended tolerances.