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R E S E A R C H A R T I C L E Open Access
CT texture analysis: a potential tool for
prediction of survival in patients with
metastatic clear cell carcinoma treated with
sunitinib
Masoom A. Haider
1*
, Alireza Vosough
2
, Farzad Khalvati
1
, Alexander Kiss
3
, Balaji Ganeshan
4
and Georg A. Bjarnason
5
Abstract
Background: To assess CT texture based quantitative imaging biomarkers in the prediction of progression free survival
(PFS) and overall survival (OS) in patients with clear cell renal cell carcinoma undergoing treatment with Sunitinib.
Methods: In this retrospective study, measurable lesions of 40 patients were selected based on RECIST criteria on
standard contrast enhanced CT before and 2 months after treatment with Sunitinib. CT Texture analysis was performed
using TexRAD research software (TexRAD Ltd, Cambridge, UK). Using a Cox regression model, correlation of texture
parameters with measured time to progression and overall survival were assessed. Evaluation of combined International
Metastatic Renal-Cell Carcinoma Database Consortium Model (IMDC) score with texture parameters was also performed.
Results: Size normalized standard deviation (nSD) alone at baseline and follow-up after treatment was a predictor of OS
(Hazard ratio (HR) = 0.01 and 0.02; 95% confidence intervals (CI): 0.00 –0.29 and 0.00 –0.39; p= 0.01 and 0.01). Entropy
following treatment and entropy change before and after treatment were both significant predictors of OS (HR = 2.68
and 87.77; 95% CI = 1.14 –6.29 and 1.26 –6115.69; p=0.02 and p= 0.04). nSD was also a predictor of PFS at baseline and
follow-up (HR = 0.01 and 0.01: 95% CI: 0.00 –0.31 and 0.001 –0.22; p=0.01and p= 0.003). When nSD at baseline or at
follow-up was combined with IMDC, it improved the association with OS and PFS compared to IMDC alone.
Conclusion: Size normalized standard deviation from CT at baseline and follow-up scans is correlated with OS and PFS in
clear cell renal cell carcinoma treated with Sunitinib.
Keywords: Prediction of outcome, Metastatic clear cell carcinoma, Quantitative imaging biomarkers, CT image features,
CT texture analysis
Background
Multi-targeted tyrosine kinase inhibitor (TKI) therapy
with Sunitinib is a standard treatment of metastatic clear
cell renal cell carcinoma (RCC). Non-imaging related
clinical prognostic factors have been identified for patients
receiving targeted therapy and introduced into treatment
guidelines and used to stratify patients on clinical trials
[1]. This clinical prognostic model and the associated
factors are described in the International Metastatic Renal-
Cell Carcinoma Database Consortium Model (IMDC),
which is used most commonly [2].
It is well known that enhancement features of RCC can
change on contrast enhanced CT in patients receiving
TKI’s such as Sunitinib and this is not always reflected in
an early change in the size of tumors thus limiting the
application of RECIST criteria [3]. Multiple alternative
response criteria which combine size and enhancement
change such as Choi, modified Choi and Morphology
Attenuation, Size and Structure (MASS) criteria have
demonstratedapredictiveabilitybycombiningsizeand
enhancement criteria to predict progression free survival
(PFS) in patients with metastatic RCC [4–8].
* Correspondence: masoom.haider@sunnybrook.ca
1
Department of Medical Imaging, Sunnybrook Health Sciences Center,
University of Toronto, Rm AG-46, 2075 Bayview Ave, Toronto, Onatrio M4N
3M5, Canada
Full list of author information is available at the end of the article
© The Author(s). 2017 Open Access This article is distributed under the terms of the Creative Commons Attribution 4.0
International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and
reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to
the Creative Commons license, and indicate if changes were made. The Creative Commons Public Domain Dedication waiver
(http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated.
Haider et al. Cancer Imaging (2017) 17:4
DOI 10.1186/s40644-017-0106-8
Intratumoral heterogeneity is a recognized feature of
cancer behavior and in particular, therapeutic resistance
[9]. Analysis of tumor heterogeneity using CT texture
analysis has shown promise as a prognostic and predict-
ive measure in RCC. A previous study by Goh et al.
showed that CT texture analysis reflecting tumor hetero-
geneity is an independent factor associated with PFS and
has the potential to be used as a predictive imaging bio-
marker of response of metastatic RCC of various histo-
logic types [10]. A more recent study has also included a
variety of RCC histologies and confirmed potential prog-
nostic value of CT texture features in assessment of the
primary tumor site and outcome [11]. There have been
other studies on the prognostic value of CT texture
features for different types of cancer including breast
[12] lung [13], hepatic metastatic colorectal cancer [14],
pancreatic cancer [15] as well as reproducibility of CT
texture parameters [16]. To our knowledge, a study
specifically reviewing the potential prognostic and
predictive value of texture features in a pure clear cell
RCC cohort and evaluating this in the light of the IMDC
prognostic score has not been performed.
The purpose of this study was to assess CT texture ana-
lysis based Quantitative Imaging Biomarkers (QIB’s) in the
prediction of PFS and Overall Survival (OS) in patients
with clear cell RCC undergoing treatment with Sunitinib.
Methods
Patients
The institutional research ethics board approved this
retrospective single institution study and waived the
requirement for informed consent.
Patients with metastatic clear cell carcinoma who
received the TKI Sunitinib as first or second line therapy
at our institution between December 2005 and March
2010 were identified from institutional renal cancer
database. An attempt was made to optimize the activity
of Sunitinib by treating each patient to toxicity using
individualized dose and schedule [17]. An IMDC prog-
nostic score was assigned to each patient at baseline.
Patients were included if they were TKI naïve and had
received Sunitinib as the first or second line treatment
for metastatic clear cell carcinoma. Patients were ex-
cluded if: their baseline contrast enhanced CT was not
performed within 6 weeks before the start of treatment;
both their baseline and followup CT were not performed
with contrast enhancement; they did not have measur-
able disease at baseline as defined by RECIST 1.1.
From a total of 172 patients who were identified in the
institution database, 132 patients were excluded with 40
patients left for analysis. The most common reasons for
exclusion was lack of availability for the pre-treatment
or first follow-up scan, typically due to imaging being
performed at another institution.
CT examination
All patients underwent contrast enhanced CT examin-
ation of their chest, abdomen and pelvis (GE Lightspeed
Plus or GE Lightspeed VCT) following injection of
100 ml of an iodinated contrast agent (Omnipaque 300,
Iohexol, GE Healthcare, Princeton, NJ, USA) at a rate of
3 ml/s via an automated injector.
Images of the thorax were analyzed in arterial phase
(25-s delay) and images of the abdomen and pelvis were
analyzed in portal venous phase (70-s delay) with the
following acquisition parameters: 120 kV; auto mA and
Smart mA (angular and z-axis modulation); pitch 0.75:1
and 0.9:1; 20 mm collimation, 5 mm slice thickness and
40 mm collimation reconstructed; scan field of view
(FOV) 50 cm and display FOV adjusted to patient size;
matrix: 512x512 (pixel spacing: 0.933 mm). Region of
interest (ROI) was drawn by a radiologist with 6 years of
experience of reporting abdominal CT who was blinded
to the clinical outcome. Each ROI was drawn on the
slice through the largest diameter of the tumor site.
CT Texture Analysis
Target lesions were selected according to RECIST, version
1.1 (maximum of five target lesions, maximum of two le-
sions per organ). If the patient had not had resection of
primary tumor, it was included as a measurable tumor
and used for analysis. RECIST 1.1 criteria were used to
identify disease progression, which was confirmed using
subsequent imaging. Using RECIST 1.1, initial response
after two cycles of treatment was evaluated. CT texture
analysis of the lesions was performed using TexRAD com-
mercial research software (TexRAD Ltd, www.texrad.com,
part of Feedback Plc, Cambridge, UK) by drawing a ROI
around the peripheral margin of the selected lesions used
for RECIST. Metastases/primary lesions less than 1 cm in
maximal diameter were not included in the analysis. Air,
streak artifacts and dense calcifications were excluded
from the regions of interest. CT texture analysis com-
prised a filtration-histogram technique where the filtration
step extracted and enhanced (amplified) features using a
band-pass Laplacian of Gaussian spatial scale filter [18].
Quantification was done using different histogram based
statistical parameters in the selected region of interest in
CT images after the application of the band-pass filter at
intermediate scale which was chosen to mimic the scale
used by Goh et al. [10].
Histogram based statistical parameters comprised of
mean positive pixel intensity (the average value of the
positive pixels within the ROI), standard deviation (SD),
skewness (symmetry of the pixel intensity distribution),
kurtosis (pointiness of the pixel intensity distribution),
and entropy which represents irregularity or complexity
of pixel intensity in space. These are all first-order statis-
tical features except for entropy which is a second-order
Haider et al. Cancer Imaging (2017) 17:4 Page 2 of 9
statistical feature. A newer secondary histogram param-
eter derived from the above parameters, size normalized
standard deviation (nSD), was also evaluated. This was
done as it is known that SD estimate can be affected by
the size (meaning the number of pixels) specifically in
case of small tumors which may need correction or
normalization [18] (Eq. 1).
nSD of a given ROI is calculated as follows:
nSD ¼Ln SDðÞ
Ln NðÞ ð1Þ
where SD is the standard deviation of ROI (i.e., tumor)
and Nis the total number of pixels in the ROI.
These parameters were recorded for each lesion in
baseline CT images and the first follow-up CT images
after treatment with Sunitinib. Percentage change (PerC)
of the CT texture parameters before and after treatment
were calculated (Eq. 2).
PerC ¼Parameter post treatmentðÞ–Parameter pre−treatmentðÞ
Parameter pre−treatment
ðÞ
100
ð2Þ
As the value of Kurtosis can vary from −3to+3,to
negate division by 0 when calculating the percentage
change, we added 3, i.e. [((Kurtosis post treatment +3) -
(Kurtosis pre-treatment +3))/(Kurtosis pre-treatment +3)]
× 100. In case of Skewness, in order to avoid dividing by
0, only change (not the percentage change) was used, i.e.
Skewness post treatment –Skewness pre-treatment.
Statistical Analysis
For statistical analysis, average texture measurements of
all measured lesions in each patient at baseline CT and
the first follow-up CT performed about 2 months after
the start of treatment, the percentage change from
baseline value as well as the percentage change in lesion
size based on RECIST 1.1 criteria, which measures the
amount of lesion size reduction, were used. PFS was
defined as the time from the date of baseline CT to the
date of disease progression based on RECIST response
criteria. A Cox proportional hazards survival model was
performed to determine if any parameter was predictors
of OS or PFS. No adjustments for multiple testing were
carried out as these analyses are considered exploratory
and their results will serve to enhance future larger
studies. All statistical analysis was performed using SAS
Version 9.3 (SAS Institute, Cary, NC, USA).
The International Metastatic Renal-Cell Carcinoma
Database Consortium Model (IMDC) allocates patient
to three prognostic groups (good, intermediate and
poor) based on the degree of anemia, thrombocytosis,
neutrophilia, and hypercalcemia, as well as the Karnofski
performance status <80%, and <1 year from diagnosis to
treatment. To assess whether any of the CT texture
parameters adds to IMDC in prediction of PFS and OS,
we ran 2 variable Cox proportional hazards regression
models and assessed model fit using −2 log likelihood
(−2LL) statistics. For addition of one variable to IMDC,
a change of greater than 3.84 (the critical value associ-
ated with one degree of freedom for a chi-square statis-
tic) would indicate a significant model improvement.
We could not explore models with 3 or more variables
due to limitations in sample size. A P value of less than
0.05 was considered to indicate statistical significance.
Results
The cohort consisted of 35 men and 5 women with a
mean age of 60 years (range of 34–76 years). All the
patients had clear cell carcinoma. 34 patients received
Sunitinib as first line therapy and 6 patients received
Sunitinib as the second line treatment after being treated
with a non-TKI drug (e.g. interferon). A total of 87
target lesions were analyzed. These lesions were scat-
tered across different locations as listed in Table 1.
The baseline contrast enhanced CT of the patients in-
cluded in the analysis was performed within 6 weeks before
the start of treatment (mean was 12.8 day pre-treatment)
and their followup CT was performed with contrast
enhancement (mean followup time was 67.5 days). Six of
40 patients had progressed during the study period with a
PFS of 60 days (range: 64–171 days). The length of follow-
up was up to 22.8 months following baseline CT or until
death whichever sooner. The significance of each texture
Table 1 Tumor Sites
Tumor Site Number of lesions
Lymph node 15
Lung 14
Primary 10
Bone 10
Liver 8
Peritoneum 6
Adrenal 4
Mediastinal Lymph Nodes 4
Nephrectomy bed 4
Other kidney 3
Hilar Lymph Nodes 3
Pleura 1
IVC Thrombus 1
Muscle 1
Spleen 1
Omentum 1
Psoas major muscle 1
Total 87
Haider et al. Cancer Imaging (2017) 17:4 Page 3 of 9
parameter in prediction of OS and PFS is summarized in
Tables 2 and 3, respectively.
Overall survival
Size normalized standard deviation (nSD) prior to treat-
ment with Sunitinib was a significant predictor for OS
(p= 0.01) such that higher nSD before treatment pre-
dicted for increased survival (positive correlation) (HR
= 0.01, 95% CI = 0.00 –0.29).Inaddition,nSDfollow-
ing treatment with Sunitinib was found to be significant
in predicting OS (p= 0.01) such that higher nSD after
treatment was associated with a lower hazard of death
or higher survival (positive correlation) (HR = 0.02, 95%
CI = 0.001 –0.39). Entropy following treatment and en-
tropy change both were significant predictors of OS
such that higher entropy following treatment or en-
tropy change predicted decreased survival (negative
correlation) (p=0.02, HR=2.68, 95% CI=1.14 –6.29
and p= 0.04, HR = 87.77, 95% CI = 1.26 –6115.69,
respectively) (Table 2).
Progression free survival
With regards to PFS, nSD prior to treatment with Sunitinib
was a significant predictor (p= 0.01) such that higher nSD
before treatment was related to increased PFS (positive
correlation) (HR = 0.01, 95% CI = 0.00 –0.31). Moreover,
nSD following treatment with Sunitinib was found to be
significant in predicting PFS (p= 0.003) such that higher
nSD after treatment leads to lower hazard of death or in-
creased PFS (positive correlation) (HR = 0.01, 95% CI = 0.00
–0.22). Neither entropy following treatment nor entropy
change was significant predictor of PFS (Table 3).
The lesion’s size change (percentage change, in terms
of reduction, in sum of the lesions’size in each patient
prior to and following treatment with Sunitinib) demon-
strated a significant relation to OS (positive correlation)
(p= 0.02), (HR = 0.97, 95% CI = 0.94 –1.00), while size
change was not a significant predictor of PFS.
Imaging variables combined with IMDC
To analyze the added predictive value of imaging vari-
ables to IMDC, we started with a baseline Cox propor-
tion hazards model that only included the IMDC and
then added each of the imaging variables found to be
significant in the univariate survival analyses for OS or
PFS. The baseline model with IMDC alone was signifi-
cantly related to OS and had a −2 log likelihood statistic
of 181.3. Therefore, to see an improved fit in any of the
two-variable models tested, this statistic would have to
change by a minimum of 3.84 (a 1° of freedom change
Table 2 Imaging parameters as predictors of OS
Variable P-value Hazard ratio 95% CI
Mean positive pixel intensity prior
to treatment
0.34 1.01 0.98 –1.05
Mean positive pixel intensity
following treatment
0.77 1.00 0.99 –1.02
SD prior to treatment 0.24 0.98 0.96 –1.01
SD following treatment 0.46 0.99 0.98 –1.01
Entropy prior to treatment 0.27 1.74 0.65 –4.68
Entropy following treatment 0.02 2.68 1.14 –6.29
nSD prior to treatment 0.01 0.01 0.00 –0.29
nSD following treatment 0.01 0.02 0.001 –0.39
Kurtosis prior to treatment 0.26 1.24 0.85 –1.82
Kurtosis following treatment 0.78 1.03 0.81 –1.32
Skewness prior to treatment 0.15 2.02 0.77 –5.30
Skewness following treatment 0.30 1.47 0.70 –3.09
Percent change in size 0.02 0.97 0.94 –0.99
Mean pixel intensity Change 0.37 0.99 0.98 –1.01
SD Change 0.80 1.14 0.42 –3.09
Entropy Change 0.04 87.77 1.26 –6115.69
nSD Change 0.39 0.18 0.004 –8.56
Kurtosis Change 0.46 0.66 0.21 –2.02
Skewness Change 0.98 0.99 0.60 –1.65
Entries in bold were significant
Abbreviations: SD standard deviation, nSD size normalized standard deviation
OS overall survival
Table 3 Imaging parameters as predictors of PFS
Variable P-value Hazard ratio 95% CI
Mean positive pixel intensity
prior to treatment
0.61 1.01 0.98 –1.04
Mean positive pixel intensity
following treatment
0.72 1.00 0.99 –1.02
SD prior to treatment 0.71 0.99 0.97 –1.02
SD following treatment 0.33 0.99 0.97 –1.01
Entropy prior to treatment 0.25 1.84 0.64 –5.32
Entropy following treatment 0.08 2.23 0.91 –5.49
nSD prior to treatment 0.01 0.01 0.000 –0.31
nSD following treatment 0.003 0.01 0.001 –0.22
Kurtosis prior to treatment 0.21 1.28 0.87 –1.87
Kurtosis following treatment 0.34 1.12 0.89 –1.41
Skewness prior to treatment 0.32 1.66 0.62 –4.41
Skewness following treatment 0.65 1.20 0.55 –2.61
Percent change in size 0.14 0.98 0.96 –1.01
Mean pixel intensity change 0.36 0.99 0.98 –1.01
SD change 0.51 0.70 0.25 –2.02
Entropy change 0.21 15.12 0.21 –1096.9
nSD change 0.06 0.02 0.00 –1.21
Kurtosis change 0.92 1.06 0.37 –3.04
Skewness change 0.81 0.94 0.56 –1.58
Entries in bold were significant
Abbreviations: SD standard deviation, nSD size normalized standard deviation,
PFS progression free survival
Haider et al. Cancer Imaging (2017) 17:4 Page 4 of 9
for a chi-square statistic). This means that any value of
177.5 or less indicated a significant improvement in
model fit. This improvement was seen for all two-
variable models tested, however the ones that contained
nSD prior to treatment and nSD following treatment
showed the greatest improvement in fit. For both of
these models, IMDC was no longer significant. There-
fore, these variables (i.e., nSD prior to and following
treatment) were seen as stronger predictors of survival
in a model that included IMDC. The ability of each
texture parameter to add to IMDC model in the predic-
tion of OS is summarized in Table 4.
For PFS models, the baseline model with IMDC
alone was not significantly related to PFS and had a
−2 log likelihood statistic of 174.4. Therefore to see an
improved fit in any of the two-variable models tested,
this statistic would have to change by a minimum of
3.84 (a 1° of freedom change for a chi-square statistic).
This means that any value of 170.6 or less indicated a
significant improvement in model fit. This improve-
ment was only seen for the 2 variable models that con-
tained nSD prior to treatment and nSD following
treatment. For both of these models, the nSD variables
significantly improved the model in predicting PFS
whereas in neither model IMDC was significant.
Therefore, these variables were seen as stronger pre-
dictors of survival in a model that included IMDC.
The ability of each texture parameter to improve
IMDC model in the prediction of PFS is summarized
in Table 5.
When added, the lesion size (percentage change in
sum of the largest diameter of the lesions’size prior to
and post treatment) did not make a significant
improvement to IMDC in prediction of OS. Finally,
separate univariate Cox proportional hazards models
wererun,oneforpercentchangeinsize,theotherfor
nSD prior to treatment, to compare the two variables.
nSD prior to treatment was found to be a better pre-
dictor of OS (p= 0.01 versus 0.02) with HR = 0.01, 95%
CI = 0.00 –0.29).
Examples of CT images demonstrating the appearance
of lesions in patients with varying outcomes (OS and PFS)
are presented in Fig. 1 and Table 6. The Kaplan-Meier
plots for significant parameters for OS and PFS are shown
in Figs. 2 and 3.
Discussion
In this study, we demonstrate that texture related CT
QIB’s are predictive of OS and PFS in metastatic RCC
treated with Sunitinib. This study is different from prior
studies including the ones done by Goh et al. [10] and
Lubner et al. [11] in that the population is limited to pa-
tients with clear cell RCC and that it assesses the im-
aging features in combination with the IMDC
prognostic model for RCC patients treated with targeted
therapy [1]. This is clinically relevant as one of the pro-
posed uses of QIB’s for personalized medicine is the se-
lection of optimal drug therapies. In the context of clear
cell RCC, there are more than one potential first line
TKI’s. Thus, it is important to know the baseline charac-
teristic in the context of single histologic tumor type
with the standard first line agent as a monotherapy. We
have shown that size normalized standard deviation at
baseline and follow-up, tumor size change, entropy at
initial follow-up, and entropy change before and after
treatment are potentially useful QIB’s.
In addition, the study in Goh et al. [10] only looks at
PFS while in this paper, both OS and PFS are studied.
Furthermore, we limited our cohort to clear cell carcin-
oma only and a single TKI drug while Goh et al. [10] in-
cludes multiple TKI’s and multiple tumor types. Thus,
the cohort used in this study would be more reflective to
be used as a benchmark of baseline Sunitinib activity to
compare new TKI’s in drug trials. The study by Lubner
et al. [11] includes a variety of RCC subtypes and does
Table 4 Imaging variables combined with IMDC to see if they
improve on the prediction of OS
Model IMDC IMDC Combined
Model
Fit statistic value
(−2LL)
Baseline model
with IMDC alone
Significant 181.3
IMDC + Entropy
following treatment
Not Significant Significant 176.4
IMDC + nSD prior
to treatment
Not significant Significant 176.1
IMDC + nSD
following treatment
Not significant Significant 175.3
IMDC + percent
change in lesion size
Not significant Not significant 177.8
IMDC + Entropy
change
Not significant Not significant 177.4
Entries in bold were significant
Abbreviations: nSD size normalized standard deviation, IMDC International
Metastatic Renal-Cell Carcinoma Database Consortium Model, OS
overall survival
Table 5 Imaging variables combined with IMDC to see if they
improve on prediction of the PFS
Model IMDC IMDC Combined
Model
Fit statistic
value (−2LL)
Baseline model with
IMDC alone
Not significant 174.4
IMDC + nSD
pre treatment
Not significant Significant 169.3
IMDC + nSD
post treatment
Not significant Significant 165.9
Entries in bold were significant
Abbreviations: nSD = size normalized standa rd deviation, IMDC International
Metastatic Renal-Cell Carcinoma Database Consortium Model, PFS progression
free survival
Haider et al. Cancer Imaging (2017) 17:4 Page 5 of 9
not specify what drugs used for patient treatment and
focuses more on prediction of histologic features.
CT texture features and IMDS
Given that the IMDC prognostic model is well estab-
lished in RCC patients, we have demonstrated the
potential additional value of nSD to further improve pre-
diction of OS and PFS when added to IMDC. In our
study, nSD measured in CT images acquired before and
after treatment were added to IMDC model. The
entropy change prior to and following the treatment and
percentage change in the sum of the largest diameter of
Fig. 1 Baseline CT in patients with metastatic clear cell renal cell carcinoma and intermediate IMDC score (Left: prior to treatment, Right: following the
treatment). a72-year-old man: OS and PFS in this patient was 1074 and 1063 days, respectively with a baseline nSD = 0.66. Although the tumor remains
heterogeneous in appearance there is response by RECIST criteria. b40-year-old man: OS and PFS in this patient were poor at 159 and 113 days, respectively
with a lower baseline nSD of 0.54. The tumor is slightly larger but stable by RECIST criteria. The list of significant parameters for 2 cases is shown in Table 6
below. As it can be seen from the table, higher nSD prior to and following treatment and higher percent change in lesion size (i.e., higher size reduction)
were associated with higher survival; and higher entropy following treatment and entropy change predicted decreased survival. It should be noted that for
PFS, only nSD prior to and following treatment were statistically significant parameters
Table 6 The list of significant parameters (with median values) for 2 cases shown in Fig. 1
OS PFS Entropy following treatment nSD prior to treatment nSD following treatment Percent change in size Entropy Change
Median 729 358 4.76 0.58 0.56 7.65 −0.036
A 1074 1063 4.57 0.66 0.88 33 −0.119
B 159 113 4.79 0.54 0.55 −1−0.002
Haider et al. Cancer Imaging (2017) 17:4 Page 6 of 9
the lesions size prior to and post treatment did not make
a significant improvement to IMDC in the prediction of
OS. In a model comparing size and nSD prior to treat-
ment, the latter was a better predictor of OS.
CT texture features and RECIST criteria
The fact that early size change measured by RECIST is
correlated with OS but not PFS is interesting. This dis-
crepancy might be explained by the fact that PFS is re-
flective of the time course of a single drug as patients
would not switch to a second line TKI unless they pro-
gressed while OS includes a course of therapy which
may include second line and third line TKI’s. Thus, the
early size change on Sunitinib could be reflective of
overall responsiveness to the TKI’s family including sec-
ond and third line therapies. RECIST is a very intuitive
QIB. In contrast, the visual correlate of nSD may not be
intuitive and this may be a barrier to adoption. There-
fore, further study is required to investigate the visual
patterns of QIBs such as nSD and their histologic corre-
lates to make them more meaningful to the clinicians so
that they are not considered as the output of a black
box. A preliminary study has been done in this regard
by Miles et al. [18] however, further work is required.
Fig. 2 Kaplan-Meier plot of cumulative overall survival (OS) (a) Entropy following treatment (median: 4.76), (b) nSD prior to treatment (median: 0.58),
(c) nSD following treatment (median: 0.56), (d) Percent change in size (median: 7.65), and E) Entropy Change (median: −0.036)
Fig. 3 Kaplan-Meier plot of cumulative progression free survival (PFS) (a) nSD prior to treatment (median: 0.58) and (b) nSD following treatment
(median: 0.56)
Haider et al. Cancer Imaging (2017) 17:4 Page 7 of 9
For example, it is possible that nSD, by combining the
number of voxels in a ROI and standard deviation, is
combining both size and variation into a single bio-
marker and thus, providing value by not wholly
dispensing with size as a QIB.
Incorporation of new imaging response criteria such
as changes in attenuation, morphology and structure
into new classifications (Choi, modified Choi and
Morphology, Attenuation, Size, and Structure (MASS)
criteria) [4, 8] to assess response to antiangiogenic ther-
apies provides more accurate assessment of tumor
response to the targeted therapies, but has some limita-
tions. These criteria require follow-up imaging and are
not in themselves QIB’s, however, they are intuitive and
pragmatic. Further research into the optimal approach
and use of these measures in personalized medicine is
required.
Study limitations
Our study has limitations. In particular, we note that the
small sample size did not allow for multiple testing cor-
rection for the large number of QIB’s tested. This means
that the results for this study remain hypothesis generat-
ing and further prospective validation will be required as
with other similar studies published to date. In addition,
this study was retrospective, raising potential selection
biases. For example, patients who had a decline in renal
function and did not have contrast on their follow-up
were excluded from this analysis.
Clinical value
Of clinical interest is the value of baseline nSD both as a
predictive and prognostic parameter and its potential
additive value to the IMDC score at baseline. This opens
the door to prospective validation with the aim to define
a predictive biomarker for optimal drug selection ini-
tially without having to wait for a follow-up scan using a
practical and low cost standard of care test, a simple
contrast enhanced CT.
Conclusion
In conclusion, size normalized standard deviation is a
quantitative imaging biomarker texture feature that in
patients with metastatic clear cell carcinoma may add to
the IMDC score in prediction of therapy response and
overall survival. Further validation of this biomarker in
prospective trials is required.
Abbreviations
CI: Confidence interval; HR: Hazard ratio; IMDC: International Metastatic
Renal-Cell Carcinoma Database Consortium Model; nSD: normalized standard
deviation; OS: Overall survival; PerC: Percentage change; PFS: Progression free
survival; QIB: Quantitative imaging biomarker; RCC: Renal cell carcinoma;
ROI: Region of interest; SD: Standard deviation; TKI: Multi-targeted tyrosine
kinase inhibitor
Acknowledgements
Not applicable.
Funding
This research has been supported by Ontario Institute for Cancer Research
(OICR).
Availability of data and material
The datasets during and/or analyzed during the current study available from
the corresponding author on reasonable request pending the approval of
the institution and trial/study investigators who contributed to the dataset.
Authors’contributions
MAH, AV, FK, AK, BG, and GAB contributed to the design and
implementation of the concept. MAH, AV, and GAB contributed in collecting
and reviewing the data. MAH, FK, and AK contributed to the design and
implementation of quantitative feature extraction modules. AK contributed
to the statistical analysis of the data. All authors contributed to the writing
and reviewing of the paper. All authors read and approved the final
manuscript.
Competing interests
B. Ganeshan is a director, part-time employee and shareholder of Feedback
Plc (Cambridge, UK), a company that develops and commercializes the TexRAD
texture analysis research software analysis described in this manuscript.
The remaining authors declare that they have no competing interests.
Consent for publication
Not applicable.
Ethics approval and consent to participate
The institutional research ethics board approved this retrospective single
institution study and waived the requirement for informed consent.
Author details
1
Department of Medical Imaging, Sunnybrook Health Sciences Center,
University of Toronto, Rm AG-46, 2075 Bayview Ave, Toronto, Onatrio M4N
3M5, Canada.
2
Department of Radiology, North Bristol NHS Trust, Southmead
Hospital, Bristol, UK.
3
Sunnybrook Health Sciences Center, Toronto, Canada.
4
Institute of Nuclear Medicine, University College London, London, UK.
5
Sunnybrook Odette Cancer Centre, Division of medical Oncology, University
of Toronto, Toronto, ON, Canada.
Received: 16 September 2016 Accepted: 10 January 2017
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