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Keio University School of Medicine Tokyo, Japan
WEB—This is a Web exclusive article.
Wang et al. [1] showed that heterogeneous distribution of contrast enhancement was seen among and within individual tumors, and tumor microvessel density significantly correlated with enhancement parameters. They stated that, to their knowledge, evaluating tumor microvascular heterogeneity with dynamic CT has not been previously reported. However, we previously reported that the enhancement pattern of RCC in dual-phase helical CT was heterogeneous among individual tumors and correlated with microvessel density [2].
There was a major difference in the methods between the Wang et al. [1] study and our study. They evaluated images of tumor obtained in multiphase scanning of every 4.9 seconds in a single level, whereas we evaluated the images of the whole tumor obtained in single-phase 35-second delayed phase scanning (early corticomedullary phase) after the administration of contrast material. In our method, tumors are scanned with a 40- to 45-second delay on average [1, 2].
For evaluation of the effect of antiangiogenetic therapy, the whole tumor,
not just tumor in a single level, should be scanned because the effect of
antiangiogenetic therapy may be different according to the location of the
tumor. Multiphase scanning of the whole tumor will result in a higher
radiation dose. Furthermore, as Wang et al.
[1] commented, antiangiogenic
therapy usually requires lifelong treatment; thus, clinical monitoring will
require numerous scanning procedures over a period of years, which will
further increase the radiation dose. All enhancement parameters they evaluated
(peak 
H, the tissue-density curve, areas under the time–density
curve, peak tissue–blood ratio, and slope) require multiphase
scanning.
If use of the enhancement parameters on multiphase scanning is really
necessary to evaluate tumor angiogenesis, the use of CT for evaluation of the
effect of antiangiogenesis therapy should be carefully considered. This reason
is the high radiation dose, even though Wang et al.
[1] concluded that the
enhancement parameters of dynamic CT may be suited to evaluate tumor
vascularity in vivo. On the other hand, with single-phase scanning, CT will be
a useful method in evaluating the degree of angiogenesis. Analyzing and
pinpointing the timing of how well the density difference before and after
tissue enhancement (H) or tissue–blood ratio correlates with
microvessel density of tumor will be a useful tool in clarifying how timing of
single-phase scanning should be obtained for evaluation of the effect of
antiangiogenesis therapy.
In addition, the H was different among individual tumors in the Wang
et al. [1] data. According to
our study, one important factor that affects the degree of tumor enhancement
and degree of angiogenesis of RCC is the subtype
[2]. In the Wang et al. study,
there was no description of the subtype of each RCC. It would be interesting
to know whether there was a correlation between the H of homogeneously
enhancing lesions of the tumor and the subtype.
In summary, before concluding whether dynamic contrast-enhanced CT images are suited for evaluating tumor angiogenesis, it would be necessary to clarify whether multiphase scanning is necessary or if single-phase scanning is enough in evaluating the degree of angiogenesis.
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