Tumor R2* is a prognostic indicator of acute radiotherapeutic response in rodent tumors.

Abstract

PURPOSE:

To test the prognostic potential of tumor R2* with respect to radiotherapeutic outcome. Blood oxygenation level dependent (BOLD) MRI images are sensitive to changes in deoxyhemoglobin concentration through the transverse MRI relaxation rate R2* of tissue water, hence the quantitative measurement of tumor R2* may be related to tissue oxygenation.

METHODS AND MATERIALS:

Tumor growth inhibition in response to radiation was established for both GH3 prolactinomas and RIF-1 fibrosarcomas with animals breathing either air or carbogen during radiation. In a separate cohort, the baseline R2* and carbogen (95% O2, 5% CO2)-induced DeltaR2* of rat GH3 prolactinomas and murine RIF-1 fibrosarcomas were quantified using multigradient echo (MGRE) MRI prior to radiotherapy, and correlated with subsequent tumor growth inhibition in response to ionizing radiation, while the animals breathed air.

RESULTS:

A radiation dose of 15 Gy caused pronounced growth delay in both tumor models and transient regression of the GH3 prolactinomas. When the animals breathed carbogen during radiation, the growth delay/regression was enhanced only in the GH3 prolactinomas. The GH3 prolactinomas, which exhibit a relatively fast baseline R2* and large DeltaR2* in response to carbogen breathing prior to radiotherapy, showed a substantial reduction in normalized tumor volume to 66 +/- 3% with air breathing and 36 +/- 5% with carbogen seven days after 15 Gy irradiation. In contrast, the effect of 15 Gy on the RIF-1 fibrosarcomas, which give a relatively slow baseline R2* and negligible DeltaR2* response to carbogen prior to treatment, showed a much smaller growth inhibition (143 +/- 3% with air, 133 +/- 12% with carbogen).

CONCLUSION:

Quantitation of tumor R2* and carbogen-induced DeltaR2* by MGRE MRI provides completely noninvasive prognostic indicators of a potential acute radiotherapeutic response.

• Authors: Loreta M Rodrigues, Franklyn A Howe, John R Griffiths, Simon P Robinson
• Journal: Journal of magnetic resonance imaging : JMRI (J Magn Reson Imaging) Vol. 19 Issue 4 Pg. 482-8 (Apr 2004) ISSN: 1053-1807 [Print] United States
• PMID: 15065173 (Publication Type: Journal Article, Research Support, Non-U.S. Gov't)
• Copyright: Copyright 2004 Wiley-Liss, Inc.

Chemical References

• Radiation-Sensitizing Agents
• Carbon Dioxide
• carbogen
• Oxygen

Topics

• Animals
• Carbon Dioxide (administration & dosage)
• Female
• Fibrosarcoma (metabolism, pathology, radiotherapy)
• Image Processing, Computer-Assisted
• Magnetic Resonance Imaging (methods)
• Mice
• Mice, Inbred C3H
• Neoplasm Transplantation
• Oxygen (administration & dosage, metabolism)
• Prognosis
• Prolactinoma (metabolism, pathology, radiotherapy)
• Radiation-Sensitizing Agents (administration & dosage)
• Radiotherapy Dosage
• Rats
• Rats, Inbred WF