ESTRO 2024 - Abstract Book

S1476

Clinical - Lower GI

ESTRO 2024

trial are treated with two posterior oblique fields, acute radiation-induced lumbosacral plexopathy is included as a safety endpoint. Here we present a pre-planned preliminary safety analysis of the trial.

Material/Methods:

Study design and procedures have been reported previously (1). According to study protocol (prorect), spinal canal at the level of S1-S2 was prospectively delineated as OAR and used for plan optimization. Clinical outcomes regarding acute radiation-induced lumbosacral plexopathy during neoadjuvant radiotherapy are included in protocol CRF.

Results:

From June 2021 to June 2023, forty consecutive patients with LARC have been treated in the PRORECT trial. Baseline patient characteristics are summarized in Table 1. All patients received radiotherapy treatment 5 x 5 Gy (RBE) according to study protocol (prorect). Comparative dose plans are illustrated in Figure 3 (1). Both Dmax (23,2±1,7 vs 17,6±4,6 Gy, RBE) and Dmean (14.6±4.5 vs 8.6±2,8 Gy, RBE) to spinal canal were significantly higher in PBT arm. None of the patients in the cohort developed acute radiotherapy-induced serious adverse event (SAE). Specifically, we report no cases of acute lumbosacral plexopathy during neoadjuvant radiotherapy in patients treated with PBT.

Conclusion:

To the best of our knowledge, this is the first safety report concerning hypofractionated proton beam therapy in neoadjuvant treatment of locally advanced rectal cancer. This early analysis indicates that hypofractionated proton beam therapy is well tolerated with regard to safety endpoint acute lumbosacral plexopathy. These results are reassuring, supporting further investigation in the ongoing PRORECT trial.