National Cancer Institute - NCI Division of Cancer Treatment and ...

Of the many successful programs within
the RRP grant and contract portfolio, three
scientific advances are presented, one
each for physics, tumor biology, and
drug-radiation interaction.
New Image Detector May
Enable Researchers to Determine
Tumor Volume
Acquiring high-quality megavoltage
images at extremely low radiation doses
will enable more frequent and useful
imaging. This is becoming a reality, thanks
to a new image detector being developed
through RRP-sponsored research at the
University of Michigan and the Palo Alto
Research Center. The new detection
technology may make megavoltage
computed tomography (MVCT) possible
at clinically practical doses, enabling
visualization of tumor volume with the
patient in the treatment position, thereby
minimizing errors due to patient or organ
motion. Moreover, MVCT is subject to less
X-ray scatter and is less sensitive to the
presence of metal objects (dental fillings
or hip implants) in the imaged volume
than diagnostic (kilovoltage) CT, where
such factors result in severe artifacts.
Such benefits will enable the radiotherapy
community to better achieve the central
goal of radiotherapy—delivering maximum
dose to the tumor while sparing
normal, healthy tissue and critical organs.
Sawant A, Antonuk LE, El-Mohri Y, Li Y, Su Z,
Wang Y, Yamamoto J, Zhao Q, Du H, Daniel J,
Street R. Segmented phosphors: MEMS-based
high quantum efficiency detectors for megavoltage
X-ray imaging. Med Phys 2005:32;553–65.
S C I E N T I F I C A D V A N C E S
Normalization of Tumor Vasculature
Because cancer cells in solid tumors
require access to blood vessels for growth
and metastasis, inhibiting vessel formation
through a process called antiangiogenesis
offers hope for reducing the mortality
and morbidity from these tumors. However,
when administered as single agents,
antiangiogenic drugs have produced only
modest objective responses in clinical
trials, and overall, they have not yielded
significant long-term survival benefits. In
contrast, when given in combination with
chemotherapy, bevacizumab, an antibody
targeted against the potent angiogenic
molecule vascular endothelial growth
factor (VEGF), has produced an unprecedented
five-month increase in survival
in colorectal cancer patients.
Work by Dr. Rakesh Jain of Massachusetts
General Hospital, supported with NCI
funding managed by RRP, has led to a
better understanding of the molecular and
cellular underpinnings of vascular normalization.
This research suggests that certain
antiangiogenic agents improve delivery of
drugs and oxygen to the targeted cancer
cells by transiently improving blood flow
to tumors. The increased drug penetration
to the tumor can enhance the outcome
of chemotherapy, and increased levels of
oxygen can enhance the efficacy of radiation
therapy and many chemotherapeutic
agents. This work may ultimately lead to
more effective therapies, not only for cancer
but also for other diseases with abnormal
vasculature, as well as regenerative
medicine, in which the goal is to create and
maintain a functionally normal vasculature.
Jain RK. Normalization of tumor vasculature: an
emerging concept in antiangiogenic therapy.
Science 2005:307;58–62.
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