Title:
Tumor volume reduction assessed by planning computed tomography in patients with rectal cancer during preoperative chemoradiation: impact of residual tumor volume on the prediction of pathologic tumor regression.

Abstract:
To determine whether the residual tumor volume measured using the Eclipse treatment planning system correlates with pathologic tumor regression grade after preoperative chemoradiotherpy for rectal cancer.
The study included 30 patients with rectal cancer who had undergone preoperative chemoradiotherpy followed by surgery from June 2008 to April 2011 at the Korea University Guro Hospital. The tumor volume was measured using the Eclipse treatment planning system in the initial simulation computed tomography and boost planning computed tomography. The correlation between the residual tumor volume in boost planning computed tomography and the pathologic tumor regression grade was analyzed. Tumor regression grade defined in the American Joint Committee on Cancer 7th edition was used.
The mean and median residual tumor volume was 57.34% ± 20.37% and 52.35% (range, 18.42%-95.79%), respectively. After surgery, pathologic complete response (tumor regression grade 0) occurred in 4 patients (13.33%), moderate response (tumor regression grade 1) in 18 patients (60%), minimal response (tumor regression grade 2) in 4 patients (13.33%), and poor response (tumor regression grade 3) in 4 patients (13.33%). When residual tumor volume was categorized into two groups (<50% and ≥50%), complete or moderate regression (tumor regression grade 0 or 1) was significantly greater for patients with a residual tumor volume <50% ( P <0.05). The mean residual tumor volume of tumor regression grade 0 or 1 was 49.07% ± 18.39% and that of tumor regression grade 2 or 3 was 76.31% ± 16.94% (P <0.05).
Residual tumor volume measured using routine boost planning computed tomography during preoperative chemoradiotherpy correlated significantly with pathologic tumor regression grade after surgery.