Preliminary results of simultaneous integrated boost intensity-modulated radiation therapy based neoadjuvant chemoradiotherapy on locally advanced rectal cancer with clinically suspected positive lateral pelvic lymph nodes.

BACKGROUND

Lateral pelvic lymph node (LPLN) is approximately 11-14% and always associated with poorer prognosis. This study investigated the efficacy and safety of simultaneous integrated boost intensity-modulated radiation therapy (SIB-IMRT) based on neoadjuvant chemoradiotherapy (NCRT) on locally advanced rectal cancer (LARC) patients with clinically suspected positive LPLNs.

METHODS

We retrospectively screened distal LARC patients with NCRT in our center from May 2016 and June 2019. The diagnostic criteria of positive LPLN were nodes of over 7 mm in short axis and irregular border or mixed-signal intensity. All patients with clinically suspected positive LPLN received 56-60 Gy SIB-IMRT in the LPLN area. Concurrent chemotherapy regimens were capecitabine as monotherapy treatment or in combination with oxaliplatin. The toxicities, local-regional recurrence (LRR), and disease-free survival (DFS) were investigated.

RESULTS

Fifty-two eligible patients with clinically suspected positive LPLN were screened and analyzed. The median distance from the distal tumor to the anal verge was 4 cm (range, 0-8 cm), while magnetic resonance imaging (MRI) analysis revealed the median short diameter of the pelvic LPLN to be 8 mm (range, 7-20 mm). There were 28 (53.8%) mesorectal fascia (MRF) positive and 22 (42.3%) extramural venous invasion (EMVI) positive patients. A radiotherapy dose of 41.8 Gy was administered to the pelvic area, while the LPLN received a median SIB dose of 60.0 Gy (range, 56-60 Gy) across 22 fractions. Synchronous capecitabine with or without oxaliplatin was administered during radiotherapy. In summary, 15 (28.8%) patients displayed grade 2-3 radiation-related toxicity, 8 (15.4%) patients underwent additional LPLN dissection, and positive nodes (26 nodes in total) were not observed. One patient suffered a LLR in the presacral region. The median follow-up duration was 21.2 months (range, 4.7-45.0 months), while the duration of 1- and 2-year DFS were 89.9% and 74.6%, respectively. Patients did not display LPLN recurrence.

CONCLUSIONS

The safety and efficacy of SIB-IMRT on clinically suspected positive LPLN of LARC patients were deemed acceptable. Patients did not exhibit in-field LPLN recurrence after NCRT combined with single total mesorectal excision (TME).