ESTRO 2024 - Abstract Book

S1484

Clinical - Lower GI

ESTRO 2024

technique and delivery (3D-CRT or IMRT techniques were allowed) were left at the discretion of each institution. Baseline and preoperative CTCAE v.4 adverse events were prospectively scored during the trial.

Patients were excluded from the current analyses if no acute toxicity data during preoperative treatment were available. Evaluated adverse events were hematological (combined endpoint of anemia, thrombocytopenia, neutropenia, and leukocytopenia), gastro-intestinal (abdominal pain, diarrhea, fecal incontinence, proctitis, rectal pain and nausea/vomiting), general (fatigue/lethargy and weight loss), non-infective cystitis and radiation dermatitis. The highest graded adverse events per patient were included. In the EXP arm, the outcome chemotherapy compliance was defined as the number of patients that completed >75% of preoperative chemotherapy cycles. Grade > 3 and grade > 1 adverse events and chemotherapy compliance were compared between 3D-CRT and IMRT/VMAT, stratified by treatment arm, using univariable and multivariable logistic regression corrected for baseline toxicity (if not integrated in the grading definition), ECOG performance status and chemotherapy compliance in the EXP. Of 920 randomized patients in the RAPIDO trial, 901 were included in the current analyses (460 in EXP arm and 441 in STD arm). In the EXP arm, 122/460 (27%) were treated with IMRT/VMAT compared with 139/441 (32%) in the STD arm. In both treatment arms, the distribution of patient and tumour characteristics was similar between the 3D-CRT and IMRT/VMAT group, except for ECOG performance status in the EXP arm (ECOG 1: 24% (3D-CRT) versus 15% (IMRT); p = 0.037). Most relevant toxicities are displayed in Figure 1 (EXP) and Figure 2 (STD). No significant differences were seen in grade > 3 adverse events between 3D-CRT and IMRT/VMAT in either treatment arm. In the EXP arm, multivariable analyses revealed significantly more grade > 1 nausea/ vomiting (OR = 1.86 [95% CI 1.20 – 2.89]; p = 0.005) and fatigue (OR 2.80 [95% CI 1.65 – 4.70]; p = <0.001) after IMRT/VMAT compared with 3D-CRT. In the STD arm, no significant differences were found. Chemotherapy compliance in the EXP arm was comparable (88% in the 3D-CRT group versus 88% in the IMRT/VMAT group). Results:

Figure

1.

Frequencies

of

the

most

relevant

adverse

events

in

the

EXP

arm.