Tissue oxygen tension measurements in the Shionogi model of prostate cancer using 19F MRS and MRI

Abstract

To investigate changes in tumour tissue oxygenation throughout the tumour growth-regression-relapse cycle in an androgen-dependent animal tumour model. 19F T1 relaxometry of Perfluoro-15-Crown-5-Ether was used to measure in vivo partial oxygen pressure (pO2) of Shionogi tumours on a 2.35-T MR scanner. Perfluoro-15-Crown-5-Ether was administered as an emulsion injected intravenously or as a neat compound injected directly into the tumour. Non-localized, tumour 19F T1 measurements, made at multiple time points throughout the tumour cycle, were translated into pO2 levels. No correlation between tumour size and pO2 values was found. Values of pO2 for growing tumours (50 +/- 30 torr) were significantly lower than for regressing and relapsing tumours after 9 days post-castration (70 +/- 10 torr, p<0.05). Maximum pO2 values (90 +/- 30 torr) were reached between fifth and eighth day post-castration, when tumour pO2 was significantly higher than both pre-castration (p<0.001) and after 9 days post-castration (p<0.05). We demonstrate that longitudinal pO2 measurements in vivo are feasible. Values of pO2 for growing androgen-dependent tumours were significantly lower than for regressing and relapsing androgen-independent tumours. These results have potential clinical importance in optimizing the timing of chemotherapy and/or radiotherapy of hormone dependent tumours.