Response assessment in locally advanced head and neck cancer based on RECIST and volume measurements using cone beam CT images.

The purpose of this work was to find potential trends in RECIST measurements and volume regressions obtained from weekly cone-beam computed tomography images and to evaluate their relationship to clinical outcomes in locally advanced head and neck cancer. We examined thirty head and neck cancer patients who underwent a pre-treatment planning CT and weekly cone-beam computed tomography (CBCT) during the 5-7 week treatment period. The gross tumor volume (GTV) and lymph nodes were manually contoured on the treatment planning CT. The regions of interest enclosed by delineated contours were converted to binary masks and warped to weekly CBCT images using the 3D deformation field obtained by deformable image registration. The RECIST diameters and volumes were measured from these warped masks. Different predictor variables based on these measurements were calculated and correlated with clinical outcomes, based on a clinical exam and a PET imaging study. We found that there was substantial regression of the gross tumor volume over the treatment course (average gross tumor volume regression of 25%). Among the gross tumor volume predicators, it was found that the early regression of gross tumor volume showed a marginal statistical significance (p = 0.045) with complete response and non-complete response treatment outcomes. RECIST diameter measurements during treatment varied very little and did not correlate with clinical outcomes. We concluded that regression of the gross tumor volume obtained from weekly CBCT images is a promising predictor of clinical outcomes for head and neck patients. A larger sample is needed to confirm its statistical significance.