760 / 1096
S744
ESTRO 36
_______________________________________________________________________________________________
G2 thereafter. The mean follow-up was 12 months (range
1-50 months). The Local control rate was: 87%, 72%, 65%
and 53%, 63% and 75% at 1 , 3 , 6 , 12, 24, 36 months
respectively. The time to local progression was ranged
between 1 and 12 months (mean: 6 months). The detailed
results are reported in Table 1. Five patients are dead (4
for disease and one for vascular accident). Univariate
analysis showed that Tmean, Tmax, Tmin, T90 parameters
were not associated with local control rate
follow-up (months) CR (%) PR (%) SD (%) PD (%)
1
20
48
19
13
3
22
28
22
28
6
26
4
35
35
12
20
6
27
47
24
37.5 -
25
37.5
36
25
-
50
25
TABLE 1: response rate in the time (months)
Conclusion
RT-HT is useful combined treatment with a good local
control rate and patient compliance. The clinical outcome
and the time duration of the follow-up is affected by the
advanced stage of diseases. A larger pool and a more
detailed patient stratification are needed to evaluate the
outcome data in the time
Acknowledgments
This work was supported by “5 per Mille 2009 Ministero
della Salute-FPRC Onlus”.
EP-1390 Superior target delineation of renal cell
carcinoma bone metastases on MRI vs CT
F.M. Prins
1
, J.M. Van der Velden
1
, A.S. Gerlich
1
, A.N.T.J.
Kotte
1
, W.S.C. Eppinga
1
, N. Kasperts
1
, L.G.W. Kerkmeijer
1
1
UMC Utrecht, Radiation oncology, Utrecht, The
Netherlands
Purpose or Objective
In metastatic RCC (mRCC) there has been a treatment shift
towards targeted therapy, which has resulted in a 50%
increase in overall survival. Therefore, there is a need for
better local control of the tumor and its metastases.
Image-guided SBRT in bone metastases provides improved
symptom palliation and local control. After SBRT for
mRCC, local control rates have been improved from 50%
to 85% when compared to conventional fractionation
schemes. With the use of SBRT there is also a need for
accurate target delineation. The hypothesis is that MRI
allows for better visualization of the extend of bone
metastases in mRCC for contouring in the context of
stereotactic treatment planning.
Material and Methods
From 2013 to 2016, nine consecutive patients who
underwent SBRT for RCC bone metastases at our center
were included. A planning CT and MRI were performed in
radiotherapy position according to our clinical protocol.
CT images were performed at 1 mm slice thickness on a
large bore CT scanner (Philips, The Netherlands). In
addition, all patients underwent a 1.5 Tesla MRI scan
(Philips Ingenia, The Netherlands) at 1.1 – 4 mm slice
thickness. For every patient, T1-weighted images were
acquired in transversal and sagittal direction, including a
transversal mDIXON scan, as well as T2-weighted images
in transversal and sagittal direction, and diffusion
weighted images (DWI) according to our clinical MRI
protocol. Gross tumor volumes (GTV) in both CT and MRI
were delineated. Contouring was performed by a
specialized radiation oncologist, based on local consensus
contouring guidelines (T1 images were used for target
delineation aided by the information derived from the T2
and
DWI
sequences).
In both CT and MRI the GTV volumes, conformity index (CI)
and distance between the centers of mass (dCOM) were
compared. Statistical differences in volumes between CT
and MRI were tested with Wilcoxon rank sum test.
Results
Nine patients with 11 RCC bone metastases were
evaluated. The volumes of the lesions on MRI were larger
compared to the CT, for all but one lesion (Table 1). This
lesion was comparable in size on MRI and CT. Two visual
examples of the difference in delineation are shown in
Figure 1. The median GTV volume on MRI was 33.39mL
(range 0.2mL – 247.6mL), compared to 14.87mL on CT
(range 0.2mL – 179.4mL). The difference in volume as
delineated on CT and MRI was statistically significant
(p=0.005). The CI in the different lesions varied between
0.08 and 0.75. The dCOM varied between 0.78 and 13.34
mm.
Conclusion
Contouring of RCC bone metastases on MRI resulted in both
clinically and statistically significant larger lesions
compared with CT. MRI seems to represent the extend of
the GTV in RCC bone metastases more accurately, possibly
due to improved visualization of bone marrow infiltration.
Contouring based on CT-only could result in an
underestimation of the actual tumor volume, which may
cause an under dosage of the GTV in SBRT treatment
plans.