CT assessment of tumour response to treatment: comparison of linear, cross-sectional and volumetric measures of tumour size

Changes in cross-sectional area are currently used to assess tumour respons e to treatment. The aims of this study were to validate a helical CT techni que for volume determination using a series of phantoms and to compare tumo ur responses indicated by one-, two- and three-dimensional measures of tumo ur size change in patients treated for germ cell cancer or lymphoma. All st udies were performed on an IGE HiSpeed Advantage helical CT scanner with an Advantage Windows workstation. Phantom volumes were calculated using volum e reconstruction software and compared with reference volumes determined by water displacement. 20 lymph node masses were studied on serial CT scans i n 16 patients treated with chemotherapy for germ cell cancer or lymphoma. F or each lesion the maximum diameter, maximum cross-sectional area and volum e were determined before and after treatment. Tumour response was assessed using the standard World Health Organisation criteria tie. changes in cross -sectional area) and the newly proposed unidimensional response evaluation criteria in solid tumour (RECIST). The CT volume measurement error was 1.0- 5.1% for regularly shaped phantoms larger than 35 cm(3). In the assessment of treatment response there was 90% agreement between one-dimensional (1D) and two-dimensional (2D) measurements and 100% agreement between 2D and thr ee-dimensional (3D) measurements. CT volume measurements are accurate and r eproducible, particularly for larger structures. Assessment of tumour respo nse using 1D, 2D and 3D measures had limited influence on the classificatio n of treatment response. However, the impact of CT assessment of tumour res ponse using 1D, 2D and 3D measurements on clinical decisions and patient ou tcome remains to be determined.