Coverage of lateral lymph nodes in rectal cancer patients with routine radiotherapy practice and associated locoregional recurrence rates

Abstract

Background & purpose: Involved internal iliac and obturator lateral lymph nodes (LLNs) are a known risk factor for ipsi-lateral local recurrences (LLR) in rectal cancer. This study examined coverage of LLNs with routine radiotherapy practice in the Netherlands and associated LLR rates.

Materials & methods: Patients with a primary tumor ≤8cm of the anorectal junction, cT3-4 stage and at least one internal iliac or obturator LLN with short-axis ≥5mm who received neoadjuvant (chemo)radiotherapy, were selected from a national, cross-sectional study of rectal cancer patients treated in the Netherlands in 2016. MR-images and radiotherapy treatment plans were reviewed regarding segmented LLNs as gross-tumor volume (GTV), location of LLNs within clinical target volume (CTV), and received proportion of the planned radiotherapy dose.

Results: A total of 223 out of 3057 patients with at least one LLN ≥5mm were selected. Of those, 180 (80.7%) LLNs were inside the CTV, of which 60 (33.3%) were segmented as GTV. Overall, 202 LLNs (90.6%) received >95% of the planned dose. Four-year LLR rates were not significantly higher for LLNs situated outside the CTV compared to inside (4.0% vs. 12.5%, p=.092) or when receiving <95% versus >95% of the planned radiotherapy dose (7.1% vs. 11.3%, p=.843), respectively. Two of seven patients who received a dose-escalation of 60Gy developed a LLR (4-year LLR rate 28.6%). Conclusion: This evaluation of routine radiotherapy practice showed that adequate coverage of LLNs was still associated with considerable 4-year LLR rates. Techniques resulting in better local control for patients with involved LLNs need to be explored further.