Fig. 2: Prostate tumor, tumor mask, andvasculature at week three•Growth in the prostate model was measurable (Fig. 1,2)•Tumor volume increased from 940 ± 50 mm3 to 4000 ± 200 mm3
over the span of three weeks•Vascular volume increased from 20 ± 5 mm3 to 320 ± 70 mm3•Ratio of vascular volume to tumor volume increased from
1.5% to 6%

Matthew Nyflot, Joseph Grudzinski, Robert Jeraj
Department of Medical Physics, UW Madison•Volume decreases in treated xenograft mice were
measurable (Fig. 3,5) and showed a linear relationship (Fig.
6)•Ratios of post-treatment tumor volume to pre-treatment volume:
66% ± 8% in expert group, 72% ± 8% in entire group,
76% ± 5% in untrained group.
•Ratios of post-treatment vascular volume to pre-treatment

Abstract

Entirestd dev

Expertmean

Expertstd dev

Untrained
mean

Untrained
std dev

Tumor volume 2-21-07 (mm3)

162.9

51.8

125.6

29.7

190.9

48.3

Tumor volume 3-01-07 (mm3)

118.3

41.6

82.7

18.5

145.0

32.1

Post-treatment volumePre-treatment volume0.72

0.08

0.66

0.08

0.76

0.05

Vascular volume 2-21-07 (mm3)16.45.0

16.9

2.7

16.0

6.8

Vascular volume 3-01-07 (mm3)

13.6

7.1

11.1

1.3

15.6

9.5

Post-treatment volumePre-treatment volume0.79

0.32

0.66

0.03

0.88

0.42

•Fractional changes in volumes were highly correlated in allgroups (less than 10% standard deviation)

Fig 5: Tumor and vascular segmentation volumes

Fig. 3: Visualization of author’s pre- and post-treatment segmentationof tumor and vasculature in mouse X1

250

ExpertUntrained
25200
20150

15100

1050

5

Vascular Volume (mm3)

Entiremean

Vasc3-01-07

Table 1: Interobserver segmentation results for xenograft mice. Absolute and relative volume
changes are shown for the expert, untrained, and entire groups.

•Observer training had a measurable impact on statisticalsignificance and standard deviation•Paired t-test for tumor volumes:
p=.04 in expert group, p=0.0003 for entire group, p=.74 foruntrained group•Paired t-test for vascular volumes:
p=.02 in expert group, p=.13 for entire group, p=.18 foruntrained group

Vasc2-21-07

Contemporary methods of evaluating cancer therapy (CT tumor size,clinical outcome) may be inadequate to understand treatment
response to new molecular therapies1. In particular, understanding
the vascular response to antivascular therapies may prove key to thepreclinical development of such agents and in the clinical evaluationof effectiveness. Unfortunately, current methods of evaluating
vascular dynamics in tumors are inadequate for longitudinal studies.
Histological staining can provide highly resolved images of vasculardensity and angiogenesis2,3 but is a destructive technique. CT or MR
perfusion techniques provide in vivo measurements of vascularcharacteristics4 but may have poor resolution and are unavailable on
many preclinical scanners. In vivo measurement of vascular volume
through contrast µCT may prove a useful tool to preclinicaldevelopment of such agents and in the clinical evaluation ofeffectiveness.

66% ± 3% in expert group, 79% ± 32% in entire group,
88% ± 42% in the untrained group.

Tumor
2-21-07

Introduction

volume:Tumor Volume (mm3)Growing interest in anti-angiogenic therapies has created a need formore sophisticated means to evaluate treatment response. This
novel method of minimally-invasive quantification of vascular volume
in murine tumor lines utilizes CT imaging of a blood pool contrast
agent. Transgenic and xenograft mouse lines were imaged tomonitor growth of tumor and vascular volumes and response toangiogenic treatments. Image sets of treatment response wereanalyzed by three expert and four untrained observers to determine
reliability of the vascular segmentation process. In conclusion,
observer training had a measurable impact on the statisticalsignificance of volume measurements.
Despite a fairly large
variation in absolute volume measurements, fractional changes involume were highly correlated in the expert group and shows aconsistent ratio of tumor to vasculature volume. Ultimately, contrastµCT imaging can be an effective technique monitor tumor growth
and response to anti-angiogenic therapy.

ResultsTumor
3-01-07

Novel microCT Imaging Techniques for in vivo
Quantification of Vascular Volume in Murine
Tumor Models

Fig. 1: Initial prostate tumor (yellow), tumor
mask (green), and vasculature (red)A transgenic adenocarcinoma mouse prostate tumor model (TRAMP)
was imaged with a blood pool contrast agent (Fenestra VC) over a
period of three weeks to test the quantification method and toevaluate the relative growth in tumor volume and vascular volume.
In addition, two xenograft mice (X1 and X2, line SCC-1483) wereimaged several times while receiving antivascular treatment withpanitumumab (Vectabix) and bevacizumab (Avastin).
Scans were performed using a Siemens Inveon µPET/CT scanner andanalyzed in Amira, a 3D visualization and segmentation package.
Images were manually segmented into tumor and vascular volumes
using a threshold-based region-growing tool. In the prostate model,
vasculature surrounded the outer surface of the tumor, so a vascularmask was created by expanding the tumor volume (Fig 1,2). Error
analysis in the segmentation of the prostate model was performedby using Amira’s grow function to expand the region for an upperbound, using the shrink function to contract the region for a lower
bound, and taking the average.
In the xenograft models, only vasculature within the tumor boundary
was considered. Pre- and post-treatment scans were segmented byseven observers into tumor and vascular volume. Three of theseven observers were considered experts (had experience withmouse µCT and Amira) and four were considered untrained.
Statistical analysis was performed to determine interobserver
reliability of the Fenestra segmentations and to estimate the error ofvascular segmentation for treatment response.

1: Miller 2005 J Natl Canc Inst

3: Hlatky 2002 J Natl Canc Inst

2: Eberhard 2000 Canc Research
4: Provenzale 2007 Am J RoentFig. 4: Comparison of expert observer segmentations (pretreatment scan of mouse X1)

200

ExpertUntrained
Expert Fit
Total Fit

150

100

50
100

150

200

Pre-treatment tumor volume (mm3)250

Post treatment vascular volume (mm3)Materials and Methods

Post-treatment tumor volume (mm3)

Fig 6: Linear response of treatment volumes in tumor and vasculature
ExpertUntrained
Expert Fit
Total Fit

25201510500510152025

Pre-treatment vascular volume (mm3)Conclusions
Contrast µCT imaging was shown to effectively monitor tumor
growth and response to anti-angiogenic therapy. While individualinterpretation of the tumor and vascular volumes can vary
dramatically, comparisons show that trained observers can measureconsistent response. A single observer might expect a 25% error inabsolute segmentation volume and a 10% error in relative
segmentation volumes. Preliminary results suggest that the ratio oftumor to vascular volume remains constant during angiogenic
therapy. Ultimately, when care is taken in the segmentation process,contrast µCT imaging can be an effective way to measure statisticallysignificant changes in tumor and vascular volume over time.

The authors wish to thank the UW cyclotron staff and Eric Armstrong
for technical support.
This work was supported by the UW
Department of Medical Physics and NIH grant 5 T32 GM08349