996 / 1096
S980
ESTRO 36
_______________________________________________________________________________________________
192, with a good coverage of the PTV and excellent results
as for acute toxicity. The greater toxicity was observed
immediately after the treatment was finished reducing in
an important way at the third month after treatment.
EP-1784 Needle use in cervical cancer brachytherapy
using the Utrecht applicator: a single center experience
M. Smolic
1
, C. Sombroek
1
, M. Bloemers
1
, B. Van Triest
1
,
M.E. Nowee
1
, A. Mans
1
1
Netherlands Cancer Institute Antoni van Leeuwenhoek
Hospital, Radiation Oncology, Amsterdam, The
Netherlands
Purpose or Objective
The Utrecht applicator (Elekta, Veenendaal, the
Netherlands) used in brachytherapy (BT) for cervical
cancer can include up to 10 interstitial needles along with
the intra-uterine and ovoid channels. The aim of this study
is to examine the clinical use of needles at our institute,
and to investigate whether the two needles with largest
discrepancy between application and use are essential to
treatment planning.
Material and Methods
The study included 22 cervical cancer patients treated
with 3 fractions of BT. The application of needles per
fraction was based on consensus amongst radiation
oncologists, medical physicists and RTTs, using the
available pre-treatment imaging, physical examination
and MRI scan made in the week before BT. We examined
how often each of the 10 possible needles (Figure 1) was
applied and the frequency of its subsequent use in
treatment planning, as well as the average intensity of
each needle’s use, given by the average ratio of needle
channel dwell time to total treatment time. We
investigated whether the two needles with lowest
frequency and intensity are essential for achieving the
planning aims while respecting OAR constraints and
yielding an acceptable conformal dose distribution. We
did this by removing these needles from the optimized
clinical plans (CP) and re-optimizing using the other
available needles, intra-uterine and ovoid channels (RP).
We aimed to obtain identical HR-CTV D90 values while still
trying to achieve similar OAR planning aims and dose
distribution conformality as achieved in the CP. We
compared RP and CP for DVH parameters (HR-CTV D90 and
OAR D2cc’s, as well as the ratio D2cc OAR to D90 HR-CTV
as a measure of DVH parameter favorability) and dose
distributions, characterized by high dose volumes HR-CTV
V200% and V300%, the dose homogeneity index (DHI = 1 –
HR-CTV V150%/HR-CTV V100%) and conformal index (COIN
= HR-CTV V100 (cc)/HR-CTV Volume (cc) x HR-CTV V100
(cc)/Implant V100 (cc)).
Results
Needles C, H, J and A are applied most often (in 89%, 89%,
71% and 67% of the cases, respectively) while the needles
with the lowest frequency of subsequent use are A (64%),
J (68%), F (68%), E (77%). Needles contributing the least to
the total treatment time are J (2.9%), E (2.9%), A (3.0%)
and F (3.5%). Needles A and J are thus applied often but
have the lowest frequency and intensity of subsequent
use. Of the 66 clinical treatment plans in this study, 25
made use of both needles A and J. Re-optimizing these
clinical plans without using needles A and J leads to
minimal differences in DVH parameters and dose
distributions between CP and RP (Table 1)
.
Conclusion
Needles C and H are applied and used most frequently and
intensely in our clinic. Needles A and J are applied often
but have the lowest frequency and intensity of subsequent
use. We managed to obtain equally clinically acceptable
plans without these needles, indicating that they are not
essential to treatment planning and may be discarded in
future.
EP-1785 use of rectal tube in vaginal cuff HDR-
brachytherapy: an unexpected advantage
A. Cerrotta
1
, C. Tenconi
2
, B. Pappalardi
1
, T. Giandini
2
, S.
Naimo
1
, D. Mazzeo
2
, E. Mazzarella
2
, S. Grisotto
2
, M.
Borroni
2
, C. Fallai
1
, M. Carrara
2
1
Fondazione IRCCS Istituto Nazionale dei Tumori,
Department of diagnostic imaging and radiotherapy-
Radiotherapy 2, Milan, Italy
2
Fondazione IRCCS Istituto Nazionale dei Tumori,
Department of diagnostic imaging and radiotherapy-
Medical Physics Unit, Milan, Italy
Purpose or Objective
Rectal toxicity, both early and late, is a substantial
problem in gynecological brachytherapy (BT) , occurring
in the majority of patients within the first 2 years after
the end of treatment. Specific strategies and efforts are
needed to limit high doses to the rectal mucosa without
reducing the overall target coverage. The aim of our
study, following an occasional observation, is to evaluate
if the rectal tube we use in our Institute for in vivo
dosimetry allows also a reduction of the rectal dose.
Material and Methods
In our Institute, adjuvant vaginal BT is always Image
Guided (CT/MRI) with a multichannel endovaginal
applicator, chosen taking into account both the comfort
of the patient and the best contact of the applicator
surface with the vaginal mucosa. For all patients, rectal
wall in vivo dosimetry is performed with a dedicated rectal
tube integrated with dosimeters and rigidly fixed to the
endovaginal applicator. Over the time, for technical/
clinical problems, two CT scans (acquired within a time
interval of 10 minutes) were obtained in 6 patients : one
without and one with rectal tube. Each treatment plan
was generated and delivered using CT-scan with rectal
tube in order to calculate dose to target and OARs (TPS:
Oncentra Brachytherapy System). Vaginal cuff, bladder,