ESTRO 2024 - Abstract Book

S1486

Clinical - Lower GI

ESTRO 2024

complications (2,3) and may considered overtreatment if employed in LPLN-negative patients. (4) The study objective was to assess the role of LPLN boost in LARC patients on the improvement of outcomes.

Material/Methods:

Histologically proven LARC who received long course NACTRT from 2013-2022 were retrospectively retrieved from our institutional database. Those patients who received SIB-IMRT to LPLN, who went on to either surgery, or were kept on observation as part of the wait and watch protocol were included. Patients who did not complete the scheduled course of NACTRT or progressed before treatment completion were excluded. Data about patient demographics, treatment details, and follow-up outcomes was obtained. Propensity score matching with variables T stage, Grade, and EMVI. Criteria of LPLN positivity was considered short axis diameter (SAD) of ≥ 7 mm alone, or SAD of ≥ 5mm along with either rounded shape, irregular border, or heterogeneous signal intensity, and nodal response was considered as SAD < 5 mm. (1,2,5,6)

Results:

A total of 188 patients were included; Boost =57, No Boost = 131. In the univariate and multivariate analysis grade and LPLN boost were shown to have a significant effect on LC (p <0.001 and 0.006) and OS (p <0.001 and 0.002). Similarly, grade and EMVI were shown to have a significant effect on DMFS (p=0.021, 0.006) and DFS (0.004, 0.02). After the 1:1 matching cohort was divided into a boost and no boost group with 51 patients in each. At the median follow-up of 36 months, outcomes were analyzed. Local recurrence was seen in 9 patients (17.6%) of no boost group compared to 0% in the boost group (p=0.003). Death was observed in 1 vs 11 patients from the boost and no boost group at 3 years (p=0.013), most of them had non-salvageable recurrences at the time of death. DFS amongst two groups was 82.4% vs 62.7% (p=0.078). There was no significant difference observed with DMFS, 82.4% vs 72.5 % in boost and no boost group(p=0.391). No significant difference was observed in radiotherapy related toxicity or surgical morbidity. Grade 3 or more radiation toxicity in the boost and no boost group was 2 % vs 12 %; p=0.118, while related grade 3 or more surgical morbidity was observed in 7% vs 4 % cases in the boost and no boost group respectively (p=0.654). The boost group had more patients with initial LPLN of > 7mm SAD (88% vs 67 %). All patients received NACTRT. Persistent LN of > 5 mm SAD was seen in 41% of cases in the boost