ESTRO 2021 Abstract Book

S202

ESTRO 2021

guided brachytherapy in LACC), that enrolled 1416 patients treated from 2008 to 2015, was analyzed. Severe grade (G≥3) physician-assessed (CTCAE v.3) gastrointestinal (GI) events were evaluated according the GI tract location: anus/rectum, sigmoid and colon/small bowel. Since diarrhea cannot be directly allocated to a single region of the GI tract, this symptom was analyzed individually in a previous study. Patient, disease and treatment related parameters were tested as risk factors with Cox proportional hazard regression in patients with at least one follow-up. Univariate (UVA) and multivariable (MVA) analyses were carried out. As the minimal dose to the most exposed 2 cm 3 of the rectum (D 2cm3 ) and the ICRU recto-vaginal reference point (RV- RP) are intercorrelated, parallel MVAs were carried out if both significant (p-value≤0.05) in UVA. Similarly, parallel MVAs were carried out for the volume irradiated to 57Gy with EBRT (V57Gy) and para-aortic (PAN) irradiation when both significant in UVA. Results A total of 1199 patients with a median follow-up of 48 [range:3-120] months were analyzed. Crude incidence rates were 2.8% (n=33), 1.8% (n=21) 2.3% (n=27) for G≥3 anus/rectum, sigmoid and colon/small bowel events, respectively. Table 1 shows the allocation of G≥3 events. Table 2 shows the Hazard Ratios for factors tested in MVA. Results for physician-assessed G≥3 diarrhea are also shown for comparison. Smoking status was a risk factor for colon/small bowel, diarrhea and showed a trend for sigmoid events. Patients with stages IIIA-IVA were at higher risk for anus/rectum events. MRI-assessed rectal invasion was associated with a trend of increased risk of anus/rectum and sigmoid events. EBRT prescription dose was a risk factor for anus/rectum and diarrhea events. Patients with large V57Gy and PAN irradiation were at higher risk for sigmoid and diarrhea events, but showed less impact for colon/small bowel events. Impact of rectum D 2cm3 was confirmed for anus/rectum and diarrhea events. Bowel D 2cm3 was a risk factor for sigmoid and colon/small bowel events. ICRU RV-RP had impact on anus/rectum, colon/small bowel and diarrhea events.

Conclusion Risk factors for severe GI morbidity were identified in a large multi-centric study. Smoking status has impact on colon/small bowel, sigmoid and diarrhea events. Patients with advanced disease are at higher risk of anus/rectum severe morbidity. Among treatment-related parameters, rectum and bowel D 2cm3 , as well as ICRU RV-RP have impact on severe morbidity. Large V57Gy and PAN irradiation are also risk factors and the impact of EBRT on GI morbidity in LACC should be further investigated.