Comparison of conventional and three-dimensional conformal CT planning techniques for preoperative chemoradiotherapy for locally advanced rectal cancer

Relationship between anastomotic leakage and CT value of the mesorectum in laparoscopic anterior resection for rectal cancer

OBJECTIVE

This study aims to indicate whether the CT value of the mesorectum could be correlated with the incidence of anastomotic leakage (AL) in laparoscopic surgery for rectal cancer.

METHODS

The study subjects included 173 patients who underwent laparoscopic anterior resection (LAR) for rectal cancer from September 2005 to 2016 in our institution as well as reliable contrast-enhanced CT preoperatively. Univariate and multivariate analyses were performed to determine the correlation between surgical outcomes, including AL and CT value of the mesorectum.

RESULTS

AL was observed in 30 (17.3%) patients. Amongst short-term surgical outcomes, overall complication showed significant correlation with the CT value of the mesorectum (P = 0.003). In addition, AL was the only factor, which significantly correlated with the CT value of the mesorectum (P = 0.017). By plotting receiver operating characteristic curve, -75 HU was the threshold of the CT value of the mesorectum for predicting AL with an area under the curve of 0.772. Categorized into two groups as per the threshold, low group showed significantly higher incidence of AL (OR, 2.738; 95% CI, 1.105-6.788; P = 0.030) as well as whole complications (OR, 4.431; 95%CI, 1.912-10.266; P = 0.001).

CONCLUSION

The CT value of the mesorectum may be a helpful preoperative radiological biomarker to predict AL after LAR for rectal cancer.

Is Two-Dimensional Field Definition Sufficient for Pelvic Node Coverage in Rectal Cancer Compared to Technical Three-Dimensional Definition?

Background and aim

To assess the effectiveness of the potential advantages with 3-dimensional-based treatment planning versus 2-dimensional pelvic bone-based treatment planning in patients with rectal cancer, controlled for clinical stage.

Methods and materials

Areas at risk from computed tomography in 30 patients were delineated: mesorectum, presacral, internal iliac, obturator and external iliac nodes. Two planning target volumes per patient were created: PTV_T3 (M + PSN + ON + IIN) and PTV_T4 (M + PSN + ON + IIN + EIN). Two- and 3–dimensional treatment plans for each planning target volume were calculated. Three analyses were performed: 1) mean volume receiving doses >95% and >105%; according to the percentage of prescribed dose to cover at least 95% of the planning target volume, the treatment plan was defined as optimal dose >95%, acceptable dose between 95% and 90%, inferior dose <90%; 2) comparison of the percentage of volume covered by the dose for 2- vs 3-dimensional; 3) determination of the doses at which the lack of volume coverage started to decrease significantly.

Results

For PTV_T3, the following was seen: 1) 2D vs 3D comparison showed optimal PTV_T3 coverage in 76.7% and 96.7%, respectively; 2) 2D vs 3D TP coverage difference was significant between 29%-95% of the total dose; 3) the lack of volume coverage started at 30% for 2D and 89% for 3D. For PTV_T4, the following was seen: 1) 2D vs 3D comparison showed an optimal PTV_T4 coverage in 33.3% and 86.7%, respectively; 2) 2D vs 3D TP coverage difference was significant between 7%-97% of the total dose; 3) the lack of volume coverage started at 7% for 2D and 87% for 3D.

Conclusions

The 3D treatment planning was superior to 2D treatment planning in covering areas at risk for pelvic recurrence in patients treated for rectal cancer. The areas with suboptimal coverage may lead to an increased risk of recurrence and should be correlated with the patterns of recurrence.