Determination of tumour regression rates during radiotherapy for cervical carcinoma by serial MRI: comparison of two measurement techniques and examination of intraobserver and interobserver variability

Tumour regression rates of 11 patients with cervical carcinoma were estimated during external beam radiotherapy (EBRT) using serial MRI (average time interval 7 days; range 3-15 days). An average of five investigations (range 4-8) was performed per subject, Tumour volume was measured by two observers using the Cavalieri method of modern design stereology in combination with (a) planimetry and (b) point counting. The mean precision of all the volume estimates obtained by manually tracing the outline of the tumour was 6.6%. The mean precision obtained by counting an average of 176 points per investigation on the same transects was 6.7%. The intraobserver repeatability of planimetry, interobserver reproducibility of planimetry and point counting were excellent with no significant difference between the volume estimates obtained using either technique. Based on the planimetry measurements, initial tumour volumes ranged from 6.5 to 222 cm(3) (mean 63 cm(3), median 44 cm(3)). Based on the point counting measurements, initial tumour volumes ranged from 7.2 to 235 cm(3) (mean 68 cm(3), median 46 cm(3)). Tumour regression began within a few days of commencing EBRT and showed an exponential relationship with time (p