837 / 1096
S821
ESTRO 36
_______________________________________________________________________________________________
Italy
2
University of Perugia, Radiation Oncology, Perugia, Italy
3
Perugia General Hospital, Medical Physics Unit, Perugia,
Italy
4
University of Perugia and Perugia General Hospital,
Radiation Oncology, Perugia, Italy
5
University of Perugia, Internal Medicine- Endocrin and
Metabolic Sciences, Perugia, Italy
Purpose or Objective
Pelvic radiation is linked to high rate of toxicity, mainly
gastrointestinal. In 3D-conformal radiotherapy (3D-CRT),
prone position (PP) and a belly-board device are used to
reduce the incidence and severity of symptoms. Although
Intensity Modulated Radiotherapy (IMRT), over 3D-CRT,
allows a better conformal treatment of the targets and to
spare the organs at risk (OARs), only a few studies have
assessed the role of patient positioning in IMRT planning
for OARs sparing.
We evaluated the effect of a PP or
supine position (SP) with full bladder to spare OARs in
pelvic IMRT in gynaecologic malignancies.
Material and Methods
A PP and a SP Computed Tomography scan, slice thickness
of 3 mm, full bladder and empty rectum, were performed
in 13 patients with endometrial or cervical cancer, 8 of
whom submitted surgery. Target volumes, nodes and
uterus or vaginal cuff, and OARs were delineated by one
young in training radiation oncologist and review by a
senior radiation oncologist. Step and shoot technique IMRT
plans were elaborated for each position. A dose of 50.4 Gy
in
28
fractions
was
prescribed.
Dosimetric parameters were compared by non-parametric
Wilcoxon exact signed rank test for paired data and for
unpaired data with Mann Whitney test and Kruskal-Wallis
test (SPSS 22.0, Inc., Chicago, IL). Statistical significance
was assumed for p ≤ 0.05.
Results
In prone and supine plans the mean PTV volumes were
1374.93 cc for PP and 1413.47 cc for SP, median Dmean
were 50.27 Gy in PP and 50.18 Gy in SP, and PTV D50%
were 50.4 Gy for PP and 50.3 Gy for SP. Data regarding
conformity and homogeneity of IMRT plans for PP and SP
gave similar results. All parameters were calculated
according ICRU 83. We found that PP permits to spare
irradiated rectal volume from 10 to 45 Gy compared with
SP, but the difference was not significant. The dose-
volume histogram for the bladder was significant better in
SP at V45 (p = 0.03), V40 (p = 0,011), V30 (p = 0.033), V20
(p = 0.039), V10 (p = 0.039). The analysis of tabular dose-
volume histograms showed a significant decrease of the
small bowel volume at V20 (p = 0.005), V30 (p = 0.019),
V40 (p = 0.046), V45 (p = 0.028) and V50.4 (p = 0.019) in
favour of the PP. For V10 the reduction of irradiated bowel
was not significant (p = 0.055). Dmax and NTCP were
significantly lower in PP. In the operated group, a
significant difference was observed in small bowel NTCP
reduction for both PP and SP (p= 0.003 and 0.006,
respectively) compared with non operated group, but not
for rectum and bladder.
Conclusion
PP with a full bladder in pelvic IMRT for gynaecologic
malignancies permits a significant bowel sparing for doses
> 20 Gy providing similar target coverage and target
conformity. This is very useful when higher dose lymph-
node boost is planned. SP allows a larger bladder sparing.
Small bowel NTCP reduction in both position in operated
patients could be linked to the smaller target volume.
EP-1528 RapidPlan Head and Neck model: the
objectives and possible clinical benefits
L. Cozzi
1
, G. Reggiori
2
, C. Franzese
2
, F. Lobefalo
2
, M.
Scorsetti
1
, A. Fogliata
2
1
Humanitas Cancer Center and Humanitas University,
Radiation Oncology, Milan-Rozzano, Italy
2
Humanitas Cancer Center, Radiation Oncology, Milan-
Rozzano, Ital
y
Purpose or Objective
RapidPlan
TM
is the knowledge based planning process
recently implemented in the Varian Eclipse treatment
planning system. It estimates, according to the model
data, the organ at risk (OAR) DVHs to generate the
optimization objectives, tailored on any new patient, for
the plan optimization process. Advanced head and neck
cancer (AHNC) planning presents complexities due to the
anatomy and the low tolerance dose levels for the
surroundings OARs. In the present work a RapidPlan (RP)
model is configured and subsequently validated to
evaluate the RP quality relative to the clinical plans (CP).
Secondary, through normal tissue complication probability
(NTCP) estimations, the possible effective clinical benefit
in planning with RP is evaluated.
Material and Methods
83 patients presenting AHNC were selected from the
department database. The patients were chosen as their
plans were considered as dosimetrically optimal. All plans
were optimized for VMAT technique (RapidArc), with 2-4
arcs, 6 MV beam quality, treated on a department linac
equipped with Millennium 120-MLC or HD-MLC. Inverse
planning used the PRO optimizer, and final calculations
were with AAA. Dose prescription was to 69.96 Gy and
54.45 Gy to PTV2 and PTV1, respectively, in 33 fractions.
A RP model was generated for the OARs: spinal cord, brain
stem, oral cavity, parotids, submanidbular glands, larynx,
constrictor muscles, thyroid, eyes. To constrain the
uninvolved healthy tissue, the ‘body’ with all the targets
subtracted was included in the model. The optimization
objectives in the model included the line objective for all
OARs with generated priority. For serial organs, an upper
objective was added with generated dose at 0% volume
with a fixed priority of 90. For parotids and oral cavity, a
mean objective was added with generated dose and fixed
priority of 60. Targets upper and lower objectives were
placed in a very narrow interval, with priority 110 and 120.
The automatic Normal Tissue Objective NTO was added
with priority 280. The model was validated on a set of 20
similar patients selected from the clinical database. The
possible clinical benefit was evaluated through NTCP
estimation for some of the OARs, using the biological
evaluation availabile in Eclipse, based on LQ-Poisson
model.
Results
Regarding target dose homogeneity, the standard
deviation was reduced by 0.3 Gy with RP (p<0.05). The
mean doses to parotids, oral cavity, and larynx were
reduced with RP of 2.1, 5.2, and 7.0 Gy, respectively.
Maximum doses to spinal cord and brain stem were
reduced of 7.0, and 6.9 Gy, respectively (p<0.02). NTCP
reductions of 11%, 16%, and 13% were estimated for
parotids, oral cavity, and larynx, respectively, with RP
planning.
Conclusion
Model validation confirmed the better plan quality with RP
plans. NTCP estimation suggests that this dosimetric
effect could positively affect also the toxicity profiles for
patients receiving RP planning with an adequate model.
EP-1529 Reducing total Monitor Units in RapidArc™
plans for prostate cancer
K. Armoogum
1
, M. Hadjicosti
1
1
Derby Hospitals NHS Trust, Department of
Radiotherapy, Derby, United Kingdom
Purpose or Objective
A retrospective planning study was performed on prostate
cancer RapidArc (RA) plans to evaluate the use of the ‘MU