Usefulness of double dose contrast-enhanced magnetic resonance imaging for clear delineation of gross tumor volume in stereotactic radiotherapy treatment planning of metastatic brain tumors: A dose comparison study

The purpose of this study was to compare the size and clearness of gross tumor volumes (gtvs) of metastatic brain tumors on t1-weighted magnetic resonance images between a single dose contrast administration protocol and a double dose contrast administration protocol to determine the optimum dose of contrast-enhancement for clear delineation of gtv in stereotactic radiotherapy (srt). a total of 28 small metastatic brain tumors were evaluated in 13 patients by intra-individual comparison of gtv measurements using single dose and double dose contrast-enhanced thin-slice (1-mm) magnetic resonance imaging (mri). all patients had confirmed histological types of primary tumors and had undergone hypo-fractionated srt for metastatic brain tumors. the mean tumor diameter with single dose and double dose contrast-enhancement was 12.0 ± 1.1 mm and 13.2 ± 1.1 mm respectively (p < 0.001). the mean incremental ratio (mir) obtained by comparing mean tumor diameters was 11.2 ± 0.02 %. the mean volume of gtv-1 (single dose contrast-enhancement) and gtv-2 (double dose contrast-enhancement) was 1.38 ± 0.41 ml and 1.59 ± 0.45 ml respectively (p < 0.01). the mir by comparing mean tumor volumes was 32.3 ± 0.4 %. the mir of gtv-1 with < 1ml volume and gtv-1 with > 1ml volume was 41.8 ± 0.05 % and 12.4 ± 0.03 % respectively (p < 0.001). we conclude that double dose contrast-enhanced thin-slice mri is a more useful technique than single dose contrast-enhanced thin-slice mri,especially for clear delineation of gtvs of small metastatic brain tumors in treatment planning of highly precise srt. © the author 2012. published by oxford university press on behalf of the japan radiation research society and japanese society for therapeutic radiology and oncology.