ESTRO 36 Abstract Book

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S965 ESTRO 36 2017
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Purpose or Objective
To evaluate if EQD2(α/β=3)at 0.1cc, 1cc and 2cc of vagina in
cylinder vaginal-cuff brachytherapy (VBT) ±external beam
irradiation (EBI) is associated with G2 toxicity in
postoperative endometrial carcinoma (P-EC).
Material and Methods
From June 2014-November 2015, 67 consecutive P-EC
patients received VBT±EBI: 54 EBI (median 45Gy, range 44-
50.4)) +VBT (7Gy) and 13 exclusive BT (6Gy x 3 fractions).
2.5cm of vagina was delineated after CT for 3D treatment
planning. The active source length was 2.5cm. The BT
dose was prescribed at 5mm from the applicator surface.
Patients were treated with HDR 192Ir source using a
MicroHDR source projector (Nucletron®). D90, V100 and
EQD2(α/β=3) at 0.1cc, 1cc and 2cc were calculated.
The mean follow-up was: 23.2 months (range 7.6-46.8).
D90 (cc): median 7.8 (range 4.6-8.9); V100 (Gy): median
7.9 ( range 4.4-10.8).
Vaginal toxicity was prospectively assessed using objective
LENT-SOMA scores. Late vaginal toxicity: 17/67 (25%) 8
with G1 and 9 G2. For this analysis G0 and G1 patients
were considered as no late toxicity (58/67, Group-1) and
9 patients with G2 (9/67,Group-2) were considered as
having late toxicity. Statistics: t-Student test and Chi
squared, alpha=5%.Results
The median EQD2(α/β=3)doses were 88.6Gy (62.8-177.6) for
0.1cc, 72.4Gy (57.1-130.4) for 1cc and 69Gy (53-113.4) for
2cc. There were no differences in toxicity and
EQD2(α/β=3) between exclusive VBT vs. EBI+VBT. EQD2(α/β=3):
The mean EQD2(α/β=3) : at 0.1cc was 92.9Gy (SD 17.7) for
Group-1 and 96.3Gy (SD 31.6) for Group-2 (p=0.62); being
72.3Gy (SD 6) at 1cc for Group-1 and 73.5Gy (SD 5.3) for
Group-2 (p= 0.58); and 67.6Gy (SD 6.2) at 2cc for Group-1
and 73.1Gy (SD 10.8) for Group-2 (p=0.03). 20.5% of
patients receiving doses ≥68Gy EQD2(α/β=3) at 2cc of vagina
developed G2 toxicity. All patients with G2 toxicity had
received doses ≥68Gy EQD2 (α/β=3) at 2cc (p=0.04).
Conclusion
68Gy EQD2(α/β=3)doses at 2cc were related to G2 toxicity
in P-EC VBT. In view of these results patients receiving
these doses should be informed of their risk and individual
characteristics should be considered in treatment planning
and follow-up to reduce G2 toxicity. Grant: Spanish
Association Against Cancer (AECC) Foundation
.
EP-1781 statistical and dosimetric analysis of air gaps
in vaginal cuff brachytherapy
S. Abdollahi1, L. Rafat-Motavalli2, H. Miri-Hakimabad2, M.
Mohammadi1, E. Hoseinian-Azghadi2, N. Mohammadi2, N.
Rafat-Motavalli 2, L. Sobhkhiz-Sabet1
1 Reza Radiation Oncology Center RROC, medical physics,
Mashad, Iran Islamic Republic of
2 Ferdowsi University of Mashhad, Physics, Mashhad, Iran
Islamic Republic of
Purpose or Objective
To retrospectively evaluate the incidence, magnitude,
and dosimetric impact of any air pockets between the
vaginal cylinders and the vaginal mucosa using CT-scan
images.
Material and Methods
120 postoperative vaginal cuff brachytherapy cases were
analyzed for receiving the prescribed dose to 5 mm depth
from the cylinder wall. CT-Based treatment planning was
performed in each fraction. The incidence, vaginal
mucosa displacement and air volume were assessed in
each treatment. A Monte Carlo study has also been done
to evaluate the dosimetric effect of air pockets around the
vaginal cylinder.
Results
In 50 patients, a total of 90 air pockets were observed in
150 procedures. Four patients had pocket free insertion
during the whole treatment sessions. The volume of air
pockets ranged between 0.01 cm3 and 4.5 cm3 with
average value of 2.5cm3, and the maximum displacement
of vaginal mucosa from cylinder surface was between 0.2
and 2 cm with average value of 0.8cm. Thirty patients had
no air pockets on their first fraction but in subsequent
fractions. Twenty patients had incorrect applicator
insertion as they have an air gap between applicator tip
and cylinder dome ranged between 0.3 cm and 1.1 cm with
average value of 0.8 cm. The Monte Carlo dosimetry also
shows that the average dose reduction to the vaginal
surface and 5mm-depth, at the air pocket, is respectively
about 9.2% and 7.3% per 1 mm of the air thickness.
Conclusion
Air pockets between vaginal cylinder and the vaginal
mucosa are observed in the majority of treatment
fractions, and the probability of occurrence varies from
patient to patient and procedure to procedure. The dose
reduction effect of air pockets needs to be considered
especially around the vaginal cuff using imaged based
treatment planning in each fraction and the effect on the
clinical outcome should be put under more investigation.
EP-1782 Effect of the amount of bladder filling on
normal tissue doses in 3D-HDR vaginal vault
brachytherapy
I. Er 1, S. Kınay1, R. Kandemir1, F. Obuz2, A.N. Demiral1
1Dokuz Eylul Univ. Health Sciences Institute, Radiation
Oncology, IZMIR, Turkey
2Dokuz Eylul Univ. Health Sciences Institute, Radiology,
IZMIR, Turkey
Purpose or Objective
In this retrospective study, it was aimed to compare the
dose volume parameters of organs at risk for the bladder
filling of 50 cc versus 150 cc in high dose rate (HDR) three-
dimensional (3-D) vaginal cuff (VC) brachytherapy (BRT).
Material and Methods
The dosimetric data of the 8 hysterectomized patients
with gynecological malignancy who received
postoperative pelvic external radiotherapy (RT) + 3-D HDR
VC-BRT between March 2015 and August 2015 were
analyzed. Computerized tomography (CT) sectional
images obtained for VC BRT treatment planning were used
for the study. The proximal 1/3 portion of vagina, drawn
as a layer of 0.5 cm thickness from the vaginal mucosa
(cylinder surface), had been delineated as clinical target
volume (CTV). A total dose of 18 Gy (3x6Gy) had been
prescribed to the CTV. For the study, bladder, rectum,
sigmoid, bowel and CTV were recontoured in a 3-D manner
by the same radiation oncology resident. Then the
contours were controlled and corrected first by a staff
radiation oncologist and then a staff radiologist.
Afterwards, treatment planning was performed by the
medical physicist using BRT treatment planning system.
Mean CTV dose-volume parameters (D90%, D100%,
D50%/D90%, V100%, V150%) for all patients were similar in
the treatment plans for two different bladder fillings.
Bladder V50%, D50% and D2cc, rectum D2cc, sigmoid D2cc,
bowel D50% and D2cc were recorded from the dose-
volume histograms obtained in the treatment planning
system. Paired comparisons were made for the parameters
above for the bladder filling of 50 cc versus 150 cc.
Different bladder fillings were compared using Wilcoxon
Signed-Rank Test in the SPSS 15.0 statistics program.
Results
It was observed that as the amount of bladder filling
increases, bowel is displaced cranially from the
applicator. Bladder D50% decreases (p=0.012) while
bladder D2cc increases (p=0.025) in case of 150 cc bladder
filling instead of 50 cc. Rectum D2cc shows a statistical
trend for increase (p=0.05), however bowel D50%
decreases (p=0.012) in 150 cc bladder filling compared to
50cc.
Conclusion
The statistically significant decrease in bladder and
especially bowel D50% parameters supports filling bladder
with 150 cc instead of 50 cc in 3D VC-BRT.